Dynamically-Self-Inflating Tire System Michael Alexander, Anthony Brieschke, Jonathan Quijano, and Lau Yip

Instructor: Professor Panos Papalambros

Analytical Product Design - Fall 2006, Team #7 (APD 2006-07) Department of Mechanical Engineering

University of Michigan Ann Arbor, MI 48109-2125

Final Report

December 12, 2006

ABSTRACT Driven by studies that show that a drop in tire pressure by just a few PSI can result in the reduction of gas mileage, tire life, safety, and vehicle performance, we have developed an automatic, self-inflating tire system that ensures that tires are properly inflated at all times. Our design proposes and successfully implements the use of a centralized compressor that will supply air to all four tires via hoses and a rotary joint fixed between the wheel spindle and wheel hub at each wheel. The rotary joints effectively allow air to be channeled to the tires without the tangling of hoses. With the recent oil price hikes and growing concern of environmental issues, this system addresses a potential improvement in gas mileage; tire wear reduction; and an increase in handling and tire performance in diverse conditions.

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TABLE OF CONTENTS 1. PROJECT MOTIVATION 5 1.1 Tire Wear, Fuel Economy, Performance, and Safety 5 1.2 Product Market 6 1.3 Beneficiaries 6 2. SURVEY ANALYSIS 7 3. DESIGN OBJECTIVES 8 3.1 Ability to Provide Proper Tire Pressure 8 3.2 Minimize Negative Visual Aesthetics 8 3.3 Ability to Provide Automatic System 8 3.4 Low Cost Device 9 4. BENCHMARKING 10 4.1 Benchmarking Existing Solutions from Commercial Market and Patented Concepts 10

4.1.1 CTIS System (Patent 4924926) 10 4.1.2 Electromagnetic pump driven system (Patent 6691754) 10 4.1.3 Micromechanical pump driven system (Patent 5846354) 10 4.1.4 Centrifugal pump system (Patent 5558730) 10 4.1.5 High pressure reservoir (Patent 5355924) 11 4.1.6 Heating element to inflate bladder within tire (Patent 5119856) 11 4.1.7 Compression of routed hoses to inflate/deflate tire (Patent 4922984) 11

4.2 Comparison of Patented Ideas and Existing Products 11 5. CONCEPT GENERATION 12 5.1 Heating/Cooling Device to Control Pressures 12 5.2 Magnetically Actuated Tire Profile 13 5.3 Dynamically Adjustable Toe-In Alignment 14 5.4 Self-Actuated Air Pumps on Wheels 14 5.5 Expandable Wheel to Increase Pressure 15 5.6 High Pressure Reservoir on Wheel 16 6.1 Best Design Solution: Centralized Compressor System 17 7. PRODUCT OVERVIEW 18 8. ROTARY JOINT DESIGN 18 8.1 Design Details 19 9. ELECTRONICALLY-AUTOMATED SYSTEM 20 9.1 OOPic 20 9.2 Electronic Control Program Description 20 9.3 Required Hardware Interface 21 10. ALPHA PROTOTYPE DESCRIPTION 22 11. BETA+ PROTOTYPE DESCRIPTION 22 11.1 Machining the Rotary Joint 23 11.2 Reducing Rotary Joint Leakage 23 11.3 Compressor and Air Tubing 24 11.4 Hose Fittings for Inlet and Outlet 24 11.5 Construction of Testing Apparatus 24 11.6 Attaching/Packaging the Inflation System to the Vehicle Suspension 24 11.7 Beta+ Prototype Functionality 24 11.8 Beta Prototype Reflection 25 12. ENGINEERING ANALYSIS AND OPTIMIZATION 26 12.1 Compressor 26 12.2 Air Valve Sizing 26 12.3 Vibration Analysis: Deflections due to Resonance 27 12 30 .4 Vibration Analysis: Deflections due to Mass Eccentricity 30 12.5 Rotary Joint Design Optimization 32

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13. MICROECONOMIC MODEL 33 13.1 Estimate Market Size for Our Product 33 14. REFINED PROFIT OPTIMIZATION 35 14.1 Net-Present Value/Breakeven Analysis 37 16. DESIGN PROCESS 38 16.1 Develop Design Prototypes 38 16.2 Develop Engineering Model 38 16.3 Optimize Engineering Model 39 16.4 Select Optimal Design Solution 39 16.5 Estimate Product Volume 39 16.6 Estimate Product Cost 39 16.7 Optimize Microeconomic Model 39 16.9 Develop Refined Design Prototype 40 16.10 Develop Marketing Demand Model 40 16.11 Review Product Design 40 16.12 Submit Final Product Design 40 17. DESIGN FOR ENVIRONMENT 41 17.1 Material cycle/ Energy use/ Toxic emissions consideration 41 18. REFLECTION OF PERSONAL VALUES IN THE FINAL DESIGN 42 20. REFERENCES 44 20. REFERENCES 44 APPENDIX A: 48 QFD 48 APPENDIX B: PUGH CHART 49 APPENDIX C: BENCHMARKING OF EXISTING SOLUTIONS (COMMERCIAL AND PATENTS) 50 APPENDIX D: DESIGN PROCESS 50 APPENDIX D: DESIGN PROCESS 51 APPENDIX E: ROTARY JOINT VIBRATION ANALYSIS – RESONANCE ANALYSIS 52 APPENDIX F: ROTARY JOINT VIBRATION ANALYSIS – MASS ECCENTRICITY ANALYSIS 53 APPENDIX G: FLOW RATE ANALYSIS 54 APPENDIX H: AIR VALVE ANALYSIS 55 APPENDIX I: ROTARY JOINT DESIGN OPTIMIZATION 56 APPENDIX J: PROGRAMMING SCRIPT FOR OOPIC AUTOMATED ELECTRONIC CONTROL 57 APPENDIX K: VARIABLE COST ESTIMATION 58 APPENDIX L: FIXED COST ESTIMATION 59 APPENDIX M: VOLUME ESTIMATION 60 APPENDIX N: PROFIT OPTIMIZATION 61 APPENDIX O: REFINED PROFIT OPTIMIZATION 62 APPENDIX P: NPV/BREAKEVEN ANALYSIS 63

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NOMENCLATURE V Volume [in3] ρ Density of the rotary joint [lbf/in3] T Temperature [°F] G Gravity [ft/s2] P Pressure [psi] Cv Coefficient of Flow Avisible Visible area of the rotary joint [in2] Q Flow rate [ft3/hr] Adisk Visible area of the brake disk [in2] N Moles Cp Constant heat capacity [kJ/kg-k] Vdisk Initial volume of the disk [in3] T1 Inlet temperature of compressor [°F] k Stiffness of the shaft [lbf/in] T2 Outlet temperature of compressor [°F] m Mass of the disk [lbf·s2/ft] h2 Outlet enthalpies of valve [kJ/kJ-k] lshaft Length of the shaft [in] h1 Inlet enthalpies of valve [kJ/kJ-k] P1 Inlet pressure of valve [psi] W Work done on the compressor [kJ] P2 Outlet pressure of valve [psi] V2 Outlet velocity of valve [ft/s] Vtire Velocity of the tire [ft/s] ωtire Angular velocity of the rotary joint-shaft

system [rpm] Cf Total fixed cost [$]

ΔP Pressure drop through the valve [psi] Cv Variable cost [$] Ashaft Cross-sectional area of the shaft [in2] Δα Design change vector E Elastic modulus of the shaft [kpsi] λd Design elasticity vector Ve Volume of the eccentricity [in3] λp Price elasticity me Mass of the eccentricity [lbf·s2/ft] θ Maximum demand rtire Radius of the tire [in] P Profit [$] drim Diameter of the rim [in] ζ Damping coefficient ωcrit Critical speed of the rotary joint shaft-

system [rpm] Xdisk Deflection amplitude of the rotary

joint-shaft system [in] G Specific gravity relative to air at

atmospheric condition [ft/s2-kg] ωn Natural frequency of the rotary joint-

shaft system [rpm]

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Figure 1: Difficult to Notice Under-Inflated Tire [6] In this case, the tire on the left is 31% under-inflated from

the tire that is at nominal pressure on the right.

INTRODUCTION 1. PROJECT MOTIVATION Improperly inflated tires are fairly common problems on passenger vehicles. In fact, 80% of passenger vehicles on the road have at least one under-inflated tire [1] and 36% of passenger cars have at least one tire that is 20% or more under-inflated [2]. Often pressure loss in tires is a result of natural permeation of the gas through the elastic rubber, road conditions (such as potholes), and seasonal changes in temperature (According to Weissler of Popular Mechanics, for every drop of 10 ºF, tire pressure drops by 1 psi [7]). Most vehicle owners are unaware of the fact that their tires are not at the correct pressures because it is difficult to determine the tire pressure visually; a tire that is properly inflated to the correct pressure looks very similar to one that is either over-inflated or under-inflated (Fig 1). According to the Rubber Manufacturing Association (RMA) survey, 80% of people are unsure of how to check their tire pressures. Thus, from the viewpoint of passenger vehicle owners, they are losing money due to increased tire wear and decreased fuel efficiency, and a solution needs to be found to correct this issue. From the viewpoint of the designers, however, the root cause of improperly-inflated tires is due to vehicle owners not knowing proper tire pressures for certain conditions, difficulty finding an air pump, lack of pressure measuring device, and a general lack of concern. Thus, the combination of the user and expert viewpoints will be used to make decisions in our design process of this product. 1.1 Tire Wear, Fuel Economy, Performance, and Safety An under-inflated tire can have dramatic effects on tire wear. Since the contact patch of the tire has a larger wave pattern, friction and heat increase cause the contact patch to wear out more quickly than if the tire was inflated properly. “Goodyear estimated that a tire’s average tread life would drop to 68 percent of the expected tread life if tire pressure dropped from 35 psi to 17 psi and remained there” [2]. According to an unpublished study by Goodyear, the average cost for a tire $61.00, and the average tread life is 45,000 miles [2]. Thus, at an average cost of $61.00/tire, and given as a circumstance that the owner keeps a vehicle for 100,000 miles, the owner will have to change the tires three times instead of twice. The owner would then be paying $244 more for tires, and in both situations, the most-recently installed tires will only have approximately 10,000 miles of use. Doran Manufacturing offers more statistics regarding the effects of under-inflated tires:

• 20% under-inflation can reduce tire life by 30% • 20% under-inflation can increase tires wear by 25%

Fuel economy is also greatly affected by under-inflated tires. According to fueleconomy.gov, an under-inflation of 1 psi in all four tires on a passenger vehicle reduces efficiency by 0.4%. Based on average gas prices, there is a potential of 3.3% in savings, which translates to $0.09 per gallon. As vehicle speeds increase, the tire pressures should also increase accordingly to reduce rolling resistance

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(which improves fuel economy) and to limit damage due to the increased frequency of tire profile deflections. Since highways are typically smoother than local roads, increasing the tire pressure will not negatively impact ride quality in terms of noise and vibrations. Properly inflated tires also have a significant effect on safety; the reduction in tire wear and increase in vehicle safety are strongly correlated. 660 deaths and approximately 33,000 injuries per year are associated with under-inflated tires according to National Highway Traffic Safety Administration (NHTSA) [4]. Worn out tires have a significant negative impact on traction in all weather conditions. Under-inflated tires also increases the stopping distance of vehicles on both dry and wet roads [4]. At the same time, drivers would also “find a noteworthy loss of steering precision and cornering stability” [6]. Additionally, heat buildup and the wear of the tire structure can cause a sudden unexpected blowout on the highways, which is a common cause of many accidents. 1.2 Product Market The target customer for this product would be an automotive Original Equipment Manufacturer (OEM) that would find this improvement to be a worthy device to add to their vehicles. These companies will be marketing it towards the end user. The OEMs will be most interested in the implementation of the design and how it can be integrated into certain vehicles. They will also be interested in the installation and maintenance aspects of this design. However, the consumers/users of the product will be the vehicle owners themselves. They will be the ones willing to pay extra when purchasing a new vehicle to have this option installed. The targeted user is one who is knowledgeable and aware of the ways that they can improve fuel economy, tire wear, performance, and safety in the vehicle that they own and drive. Not only are they concerned with obtaining a return on their investment through reduced fuel and tire consumption, but they also find satisfaction in reducing the depletion of natural resources and filling of landfills. Since this will be optional equipment for most vehicles, the user should be willing to purchase the type of vehicle that would have this option available – specifically mid to luxury grade vehicles. Both the customer and end user will be expecting a low-cost product with significant future cost savings. In addition, the US Dept of Transportation recently passed a legislation to require all passenger cars under 10,000 pounds to be equipped with a tire pressure monitoring system (FMVSS No. 138) [8]. This system will further implement the safety envisioned by the legislation by automatically maintaining tire pressures. 1.3 Beneficiaries As previously mentioned, the main beneficiaries of this advancement in technology that will allow for tire pressure to be adjusted for driving conditions will be the vehicle owners. Despite an initial investment in the technology, they will experience a reduction in tire wear and an increase in fuel economy; both of which will result in saving money in the long run. It is plausible to say that society as a whole will benefit from the resulting design. The reduction in tire disposal in landfills and decrease the rate of consumption of natural resources will truly benefit society. Also, the improvement in vehicle safety will benefit all people who drive a vehicle on the roadways. However, not everyone will benefit from this technology. Both tire manufacturers and the petroleum industry will be negatively affected by this resulting design. Tire manufacturers will be negatively affected since this product is being designed with the reduction of tire wear in mind. The demand for their products will decrease as tires last longer and fewer replacements are needed. This is similarly true for the petroleum industry since this product results in an increase in fuel economy for passenger vehicles, and the demand for oil will go down.

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2. SURVEY ANALYSIS We administered a 27 question survey to potential users for this dynamically self-inflating tire system to gain an understanding of their knowledge regarding the topic as well as to observe their preferences for certain aspects that we can incorporate with our system. Below is a list of the main points discovered from our results:

• Only 4.3% of those surveyed check their tire pressures on a weekly basis. • Only 5.3% of survey participants check their tire pressures for fuel economy. • Most participants check their tire pressures for safety reasons instead of tire wear. • Those that do not check their tire pressures either do not care or do not know the correct pressures. • Roughly half of those surveyed have had their tires replaced in the 3-4 year timeframe. • Almost half of those surveyed never check their tire tread depth. • Those that do check their tread depths mostly check it for safety concerns. • Those that never check their tread depths either do not know the correct depth or do not care. • 70% of those surveyed drive on the highway a moderate amount (50% of all driving done on

highways). • 48% of survey participants drive over the legal speed limit. • 52% of those surveyed drive compact cars and the rest sports cars, trucks/SUVs, and mid size cars. • 66% care about vehicle appearance. • 86% of survey participants listen to music/radio at a moderate to loud volume level. • Almost half of those surveyed get their vehicle service every 6 months and are mostly willing to

wait either 1 hour or 1 day depending on the type of service required. • 70% of survey participants would look to purchase a middle grade vehicle. • With regards to system override, people are most interested in being able to control the pressures in

each tire. • Of all options presented to them, people mostly want a light to show them that the system is turned

on as well as a numeric display of the pressures in each tire. • 52% of those surveyed expect to see a return on investment for this device in 1 year.

Thus, these survey results were used to narrow down the scope of our project and help to define key targets. The following is a list of conclusion and changes to our design scope based on our survey results:

• We need to include a light to show the user that the system is turned on. • We should provide the users with a numeric display of the pressures in each tire. • Noise from the system is not huge issue since most potential users have moderate-loud music to

mask the sounds. • When developing our speed-pressure gradient, we should take into account that people drive over

the speed limit quite often, especially on the highway. • Our system should be developed with compact car components in mind (size is an issue) • This system is now targeted towards those willing to buy as optional equipment (middle grade

vehicles) • Our system must be aesthetically appealing or at the very least, minimally affect exterior

appearance. • Our system must properly function for at least 6 month intervals without repairs or maintenance • We project to have a non-complex system design based on the users’ maintenance time patience. • Our design must give the user the option to control the pressures in each tire. • The price of the system should allow for a return on investment (tire and gas savings) in one year.

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3. DESIGN OBJECTIVES The overall goal of our design project is to develop a product that will decrease tire wear while improving fuel economy, performance and safety of a passenger vehicle through dynamically-adjustable tire pressures. However, there are several key objectives that the team has targeted our design to meet, and these objectives include both design characteristics and business objectives. 3.1 Ability to Provide Proper Tire Pressure The ideal functional objective of our design is its capability to adjust the pressures in all four tires of a passenger vehicle to obtain the proper pressure for varying road/driving conditions. Specifically, it is desired that:

• Cold tire pressure is maintained during vehicle use to account for slow leaks and fluctuating tire temperatures

• As vehicle speed increases, tire pressures increases • As vehicle speed decreases, tire pressures decreases • As vehicle load increases, tire pressures increase • As vehicle load decreases, tire pressures decrease

Based on more detailed research on the components necessary for the system, it was discovered that a specialized rotary joint must be designed to support this process. This design consideration required additional product development time that was not originally anticipated. Therefore, the ideal functional objectives have been modified to account for this design requirement. Specifically, the new objectives require that:

• Cold tire pressure (35 psi) is maintained by ensuring that the rotary joint-shaft system does not fail structurally

• Cold tire pressure (35 psi) is maintained by ensuring that the rotary-joint shaft system does not leak excessively

• Cold tire pressure (35 psi) is maintained by ensuring that the entire system (compressor, air tubes, rotary joint, etc.) can provided sufficient flowrate

Because of the detailed level of explanation required for these items, these objectives are described numerically in the Engineering Analysis and Optimization section of this document. 3.2 Minimize Negative Visual Aesthetics Another design objective is to ensure that the product will not have a negative effect on current vehicle aesthetics. All components should be located as inconspicuously as possible and should only be seen when servicing the unit. However, in the case of the rotary joints, which may still be visible through the wheel rims, an attempt must be made to minimize its visibility around the brake disks. Specifically, it is desired that

where Avisible is the visible area of the rotary joint and Adisk is the visible area of the brake disk. 3.3 Ability to Provide Automatic System A third objective is to provide all of the said benefits to the user through an automatic system, thus minimizing user intervention. Specifically, it is desired that the system automatically increase or decrease the tire pressures for the given road conditions. However, since this objective is closely linked with the ideal objectives in maintaining the proper tire pressure, and thus unattainable due to time constraints, this objective will not be pursued.

diskvisible AA 05.0≤

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3.4 Low Cost Device For both the customer (OEM) and end user (vehicle owner), it is imperative to keep the price of the device as low as possible. Considering the potential benefits and cost savings that this design has to offer and the prices of optional equipment for passenger vehicles with similar complexity, the target price range for this device has been identified as $800-$1000. This is the price for both the OEM and vehicle owner, assuming that the OEM does not mark up the price. In addition, this price range should be able to support the costs of components of the system, manufacturing, and any necessary installation.

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PRODUCT DESIGN EVOLUTION 4. BENCHMARKING 4.1 Benchmarking Existing Solutions from Commercial Market and Patented Concepts 4.1.1 CTIS System (Patent 4924926) CTIS system is jointly developed by Dana Corp and Eaton Corp, primarily used in Semi Trucks and military vehicles; the primary purpose is to increase fuel efficiency/decrease tire wear, and improve traction control across a variety of terrain and load, respectively. The sophisticated system is electronically-controlled, warns driver when speed exceeds tire pressure settings, adjusts pressure according to terrain and load condition, allows manual override by driver, and enables a flat tire to be driven for up to 45 minutes by continuously pumping air into the tire. 4.1.2 Electromagnetic pump driven system (Patent 6691754) This design is owned by Chrysler corp.; it integrates a tire pump with the wheel rim of a vehicle. The pump is activated electromagnetically to automatically inflate the tire when tire pressure is below a required value. This invention draws air from the atmosphere, and pumps it into the tire via a plunger operation. An electromagnet forces the plunger into an open or close position upon receiving a signal of low tire pressure. 4.1.3 Micromechanical pump driven system (Patent 5846354) This design incorporates a chamber that can be heated and sealed. The gas is introduced to the chamber, the chamber is sealed and then heated to cause the pressure of the gas to increase, and the pressurized gas is released directly into the plenum. An alternative choice is to have an air transfer chamber and a pumping chamber separated by a flexible membrane, wherein compression of the plenum provides a pumping force. Valves are provided in the micromechanical pumps to regulate movement of the gas through the pumps. 4.1.4 Centrifugal pump system (Patent 5558730) This design is developed by Hughes Aircraft, and it proposes the integration of a pump to a wheel. The pump includes a piston which moves radially outward in a cylinder by centrifugal force to draw air from the atmosphere into a compression chamber, and is capable of moving radially-inward by a biasing element to compress the air in the compression chamber and pumping it into the inflation region. The biasing element prevents the piston from moving outward until the wheel rotates above a certain speed, thereby preventing contaminants such as water and dirt from entering the compression chamber during low speed operation of the vehicle in adverse terrain. A stopper mechanism prevents the piston from moving when the tire pressure is above a normal value. This prevents the pump from operating when it is not actually needed, reducing frictional wear and increasing the service life of the pump.

Figure 2: CTIS System

Figure 3: Electromagnetic pump driven system

Figure 4: Micromechanical pump driven system

Figure 5: Pump fixed to wheel

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4.1.5 High pressure reservoir (Patent 5355924) This idea is proposed by Hughes Aircraft, the system contain a high pressure reservoir that releases air into the tire via a regulating valve. It also proposes integrating a radially extending bore within the wheel, where a movable piston may compress atmospheric air and replenish air into the reservoir. 4.1.6 Heating element to inflate bladder within tire (Patent 5119856) This patent states that a two-phase system is contained within at least one sealed, elastically deformable toric bladder mounted to the rim of said tire wheel. A volatile liquid is distributed throughout a sponge within the bladder, when heated by a thermoelectric element can expand the bladder and increase tire pressure, or contract the bladder and decrease tire pressure. 4.1.7 Compression of routed hoses to inflate/deflate tire (Patent 4922984) Inflation of the tire is provided by a deformable hose mounted for rotation with the tire and arranged coaxially with the tire. The hose has one open end in communication with atmospheric pressure and another open end in communication with a gas pressure inside the tire. Rotation of the tire causes a local reduction in the sectional area of the hose to move air along the length of the hose and compress air therein, reaching into the inside of tire. 4.2 Comparison of Patented Ideas and Existing Products In spite of the existence of these designs, no single design meets all of our design objectives (See Section 5: Design Objectives). While the CTIS system is a highly effective application for military vehicles and semi-trucks, it would not work on passenger cars because most passenger cars lack air brakes or the specific suspension/steering configuration found on military vehicles and semi-trucks required for implementation. Air brakes conveniently supply air to the tires on semi-trucks, while military vehicles allow for a simple rotary joint to connect tire to air pump. The electromagnetic pump and micromechanical pump systems are effective in replenishing tire pressure, but since the system is decentralized, the need for four individual pumps increases cost significantly. The centrifugal pump is driven by centripetal force at high speed, therefore only works at high speeds and its efficiency depends upon speed. In addition, the needs for multiple chambers may require a new tire design, which in turn increases implementation cost. The high-pressure reservoir system is cost-efficient and effective in refilling tire pressure, however requires routine maintenance whenever the pressure in reservoir is depleted. Also, it does not allow manual override or adjustment according to load and terrain. The heating element system requires a complex thermal design and alternate tire design, thus a more expensive system. The hose inflation system is a low-power but very complex pure-mechanical system, which provides no electronic control and requires high maintenance effort. Therefore, since no single design meets all of our design objectives, we have decided to use the knowledge that we have obtained from our patent searches to develop our own unique design. See Appendix C for our full evaluation of existing designs.

Figure 6: High pressure reservoir

Figure 7: Heating element to inflate bladder within tire

Figure 8: Route hoses compression to inflate/deflate tire

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5. CONCEPT GENERATION Based on the design objectives, seven conceptual design solutions were proposed. The first six designs are described in this section, while the seventh (best concept) is discussed in the following section. It should be noted, however, that all of the models described have significant similarities to designs that have already been patented. Therefore, these concepts should not be considered as completely original; rather, they should be viewed as modified designs based on the aforementioned design objectives. 5.1 Heating/Cooling Device to Control Pressures The first concept generated consists of a tire containing a thermoelectric heating device. In this arrangement, an automatic, speed-based sensor would alert the tire inflation system of a necessary pressure increase due to a significant increase in vehicle speed (such as in highway driving). This would then permit the DC-operated heat pump to increase the temperature of the wheel rim along the perimeter, which would in turn increase the temperature of the air in the tires due to convection. The tire pressure would then be increased in accordance to the ideal gas law

VnRTp = (Equation 1)

where the pressure p is proportional to the temperature T (assuming constant volume V and constant number of moles n). Because the thermoelectric device that has been researched is only capable of functioning within a temperature range of 67°C, it has been proposed that a more temperature-sensitive gas be used in the tire. This would enable the tire pressure to be increased more significantly for a given change in temperature. Similarly, the tire inflation system would be capable of being adjusted manually for severe weather conditions (such as snow) or rough road conditions, where lower tire pressure may be desired. In this case, the thermoelectric device would act as a heat sink, pulling heat from the gas in the tire through convection. The tire pressure would then be decreased in accordance to the ideal gas law. It should be noted that this device would be located on the rear of the wheel rim (nearest the inside of the vehicle) to make it as inconspicuous as possible (Figure 9).

Figure 9: Tire Pressure Adjustment through a Thermoelectric Heating/Cooling Device

There are a number of positive traits in this concept that are related to the design objectives. The maximum tire pressure would be able to be effectively controlled because of thermocouples present within the heating apparatus. The system would also be fully-automatic while the tire pressure is being adjusted based on speed conditions. Because the system would have no moving components, there would

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also be limited vibration or noise generated. In addition, the presence of a speed sensor in the system would ensure proper activation of tire inflation at higher speeds. However, there are several, more critical items in this concept that were deemed unacceptable by the design objectives set. First, the system has no effective way of setting the cold tire pressure in the event of under-inflation; the tire pressure would only increase based on speed conditions. Additionally, the presence of such a thermoelectric heating device would potentially consume a great deal of the vehicle’s energy. Finally, the act of tire inflation itself would not necessarily be efficient as many heat-driven systems take a significant amount of time before reaching steady-state conditions. 5.2 Magnetically Actuated Tire Profile The second concept generated consists of a magnetically-actuated tire profile. For this setup, an electromagnet would be situated in the wheel hub while a metal strip would be embedded inside the circumference of the tire. A sensor would then detect excessive vehicle rolling resistance and direct the system to send a current to the electromagnet. This would create a magnetic field within the tire, which would in turn create a repulsion force on the metal strip in the tire. This would change the tire shape by expanding the profile along the circumference of the tire. Additionally, this would provide the tire with greater stiffness. Ultimately, these two factors would reduce rolling resistance in the tire and hence improve vehicle fuel economy, tire wear, and safety (Figure 10).

Figure 10: Magnetically-Actuated Tire Profile

As with the first concept, there are a number of positive traits in this concept that are related to the design objectives. Because the system would be driven by a sensor, the tire profile adjustment would be fully-automatic. In addition, because of the lack of mechanical components in the system, there would be minimal space and weight requirements for the operation of this product. Nevertheless, there are some considerable drawbacks with this concept. The cold tire pressure would be almost impossible to adjust for this model because no air would be added or removed from the tire during operation. Another disadvantage is that the “improved, rounded” tire profile would be difficult to maintain through magnetism. A more powerful force would be necessary to sustain this tire profile for an extended period of time. Additionally, the maintenance effort involved in keeping the system functional would be extensive because of the complexity of the magnetic forces in the operation. Finally, the presence of a magnetic field inside the tire could adversely affect the environment.

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5.3 Dynamically Adjustable Toe-In Alignment The third concept generated consists of a dynamically adjustable toe-in alignment system for the tire-wheel assembly. The toe-in angle is the amount by which the front tires of a vehicle are angled inward for vehicle driving stability. This angle, although necessary, could become misaligned such that the degree to which the front tires “toe-in” would be much greater than the nominal condition. Such a situation could potentially lead to excessive lateral tire wear. Therefore, the proposed design includes a tie rod that would dynamically adjust the toe-in angle based on the vehicle’s speed or road conditions. The adjustment would improve both tire wear and fuel economy. Note that the system would be directed by sensors monitoring the vehicle’s speed and road conditions through vibration. The sensors would then send this information to an electronic control unit in the vehicle that would directly adjust the toe-in angle (Figure 11).

Figure 11: Dynamically Adjustable Toe-In Alignment

There are a few positive aspects for this concept that relate to the design objectives. The presence of the sensors and the electronic control unit in the system enables the toe-in operation to be performed automatically. In addition, the lack of moving mechanisms in the system would minimize the amount of potential vibration and noise. Because few additional components would be added to the vehicle, the overall space and weight requirements would also be minimal. However, there are some major shortcomings with this model as well. The cold tire pressure for this system would not be able to be directly controlled to improve fuel economy. Additionally, the system may drastically minimize the toe-in angle such that the front tires are exactly parallel to one another. This would then result in driving instability in the vehicle. 5.4 Self-Actuated Air Pumps on Wheels The fourth concept generated consists of a self-actuated air pump for each tire on a passenger vehicle. In this arrangement, four air pumps (one for each tire) would be situated at the center of the wheel hubs. The system would then be activated as the vehicle was in motion through the rotation of the wheels. This rotation would generate a suction force proportional to the speed (revolutions per minute) of the vehicle, pulling fresh air into the air pump. From here, a single air passageway connecting the pump to the tire would enable the tire to be filled with air as necessary. It should be observed, therefore, that this tire inflation system would be primarily dependent on vehicle speed (Figure 12).

Figure 12: Tire Pressure Adjustment through Self-Actuated Air Pumps

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There are a few notable positive attributes of this concept that relate to the design objectives. Because the system would function based on the motion of the vehicle, the tire inflation process would be completely automatic. For the same reason, this method of tire inflation would minimize the amount of power required for the system to be operational. Additionally, this concept would be able to provide a sufficient flowrate into the tire due to the constant suction force of the air pumps. Nevertheless, there are other aspects of this model that made it less than desirable. First, there is no effective way to set or adjust the cold tire pressure. This is primarily because the pressure adjustment would be based solely on vehicle speed. In addition, the system as a whole would be difficult to control. No distinction is made, for example, between forward or backward motion of the vehicle when describing the tire inflation process. Also, the constant flow of fresh air into the system could possibly result in greater vehicle drag, thus placing unnecessary strain on the drivetrain. The presence of the air pumps behind the wheel rims would also create an unattractive appearance to the consumer. 5.5 Expandable Wheel to Increase Pressure The fifth concept generated involves an expandable wheel rim. For this design, a wheel rim with hollowed-out spokes containing ejector pins would be used. Surrounding this rim would be a durable, elastic band covering the perimeter of the wheel. This band would be the only barrier between the wheel rim and the inside of the tire. A pressure sensor would then detect insufficient pressure within the tires and direct the system to adjust the tire pressures accordingly. When activated, a DC-current would power motors in the wheel hubs that would radially extend the ejector pins and the surrounding elastic band on the wheel rims. This would result in a volume reduction of air in the tires. The tire pressures would then be increased as given in the ideal gas law

p = nRT/V (Equation 2) where the pressure p is inversely proportional to the volume V of the tire (assuming constant number of moles n and constant temperature T). It should be mentioned that the ejector pins would only extend the necessary amount to provide sufficient tire pressure (Figure 13).

Figure 13: Tire Pressure Adjustment By Way of an Expandable Wheel Rim

One of the positive attributes of this model is the automatic system. Because the tire inflation process is based on a pressure sensor directing the system, it would enable complete operation with no user input. Additionally, the wheel rim design for this system would result in minimal space and weight requirements. Also, because the ejector pins would be housed inside the wheel rim, the overall appearance would not be adversely affected by this concept. However, the negative aspects of this model significantly outweigh these latter attributes. The cold tire pressure, for example, could not be sufficiently

16

controlled in this arrangement because the pressure increase would be solely based on the compression of the air in the tire. In addition, the width of the ejector pins would be limited to the width of the spokes of the wheel rim. This would, in turn, affect the stability of the surrounding elastic band. The presence of the ejector pins could also potentially lead to excessive noise and vibration while driving. Furthermore, these ejector pins could result in vehicle instability through rotating unbalance. Finally, this concept would require a complete redesign of the wheel rim, which may be costly to both manufacturers and consumers. 5.6 High Pressure Reservoir on Wheel The final concept documented in this section involves a high-pressure reservoir system. In this setup, a high pressure reservoir would be placed directly on each wheel rim with air passageways linking the reservoirs with the tires. Actuator-controlled valves would then maintain the tire pressures as specified by the consumer. It should be noted that the actuator-controlled valve would be nominally set to the cold tire pressure and that a pressure relief valve would be placed on each tire to reduce pressure as necessary (Figure 14).

Figure 14: Tire Pressure Adjustment through High Pressure Reservoir

Among the positive aspects of this concept is that the cold tire pressure could be adequately set by sending air from the reservoirs to the tires. The presence of the actuator also ensures that the system would be automatic. Also, because this system only involves small actuator-controlled valves, power requirements for this process would be minimal. Nevertheless, several items have ultimately led this concept to be considered deficient. Because of the limited volume of the reservoir, several refills may be necessary over the life of the system. In addition, the presence of the reservoir would introduce extra mass in the system and a potential rotating unbalance. This rotating balance could lead to a potential hazardous condition due to vehicle instability. Maintenance effort for this system would also be high as the reservoir would have to be removed before servicing any other components in the system. Moreover, the appearance of a reservoir on such a conspicuous surface such as the wheel rim would result in unsatisfactory visual aesthetics.

17

Figure 15: Hummer’s visible exterior valve and air supply

tube [1].

Figure 16: Geared hub on Hummer H1 allows direct routing of air supply tube

6. CONCEPT SELECTION In order to determine the best design solution, a Pugh Chart (see Appendix B) was created to compare the seven most-promising design concepts to figure out which one addressed the design criteria the best. Once that design was chosen, the remaining designs were evaluated to determine which ones were the best alternatives in the case the “best design” failed to meet the design criteria. 6.1 Best Design Solution: Centralized Compressor System Having scored the highest in the Pugh Chart used for weighing the design concepts, the centralized compressor system was selected as the design that satisfies customer needs/wants the best. In addition, the compressor concept shows the most promise for successfully fulfilling its design intent, which is to maintain proper air pressure in the tires for increased fuel economy, provide maximum tire life, and eliminate the risk of tire blowouts from over- or under-inflated tires. This is because it can continuously supply air to the tires, while most of the other concepts can not compensate for air that that is lost over time (normal tires leak 0.5 to 1.0 psi per month [7]) or lower ambient temperatures that reduce tire pressure. Unlike the other concepts that do provide air to the tires, the centralized compressor system will not require consumers to change out/fill tanks or provide regular maintenance. Unless the system fails, the air compressor will be able to vary pressure/compensate for lost air automatically and without user effort. Though there are similar systems already being used, like Dana/Eaton Corporation’s CTIS, which is used on semi-trucks, military vehicles, and Hummer H1, such a system has not been adapted to passenger vehicles. On semis, the air is supplied to the tires from the air brakes, and no additional compressor is involved. On the Hummer H1, a centralized compressor provides the air supply, but the setup is quite different from what needs to be achieved. Their system is not fully automatic and requires that the driver set the pressure on the front and rear tires; the user does not have control over the individual tires however. On the H1, a visible air tube is fed through the center of the wheel to the exterior and then to the air inlet/release valve on the outside perimeter of the wheel rim. One of our design goals involves a setup that would not use a visible air tube on the exterior of the wheel. In addition, we would like to incorporate a visual display that informs the driver of tire pressure settings and provide a simple manual-overriding interactive display that would easily adjust tire pressure for diverse driving conditions/driver preferences. The major design difference would be in how we get the air to the spinning tire. The Hummer has a unique feature with its hub design that allows the air hose to be connected to the rotating tire. It has a geared hub where the axle shaft enters the hub above the center of the wheel; since there is no solid axle shaft at the center of the wheel, the hose can be routed through the center of the spindle. In most passenger vehicles however, the axle shaft runs straight into the center of the wheel forcing us to find an alternative route. We propose using a sealed rotary joint along the backside of the brake discs that will allow us to input air on the stationary end, and obtain this air on end that is spinning with the brakes/wheel.

18

PRODUCT DESCRIPTION 7. PRODUCT OVERVIEW We have developed a system that is capable of automatically maintaining tire pressure in a passenger vehicle. This has been achieved through use of a centralized air compressor that is placed in the engine compartment of a vehicle. This compressor is attached to a distribution block which houses (4) solenoid valves used to control which tires receive inflation pressure. From this distribution block, the air travels via ¼” dia. hoses to a rotary joint located at each wheel. This rotary joint allows our system to pass air from the vehicle chassis to the rotating tire. The system that we have developed is to be integrated with the tire pressure monitoring systems currently found on vehicles to provide our microprocessor with tire pressure data. To reduce tire pressures, our system also incorporates solenoid valves at each tire valve which plan to be operated either through wireless technology or electrical contacts in each rotary joint. Figure 17 displays the configuration of our system relative to a passenger vehicle package.

8. ROTARY JOINT DESIGN As previously mentioned, the major design difference between the current Hummer CTIS and our design is how we get air to the spinning tire. We are designing this device for common passenger vehicles, and the main challenge is the presence of the axle shaft that runs straight into the center of the wheel forcing us to find an alternative method of routing the air. Our proposed solution to this challenge is to place a rotary joint that has one half spinning with the drive axle hub and the other half stationary with the spindle. Within this rotary joint will be an air chamber that will allow air to pass from the stationary half of the joint into the half that is rotating. There are numerous types of air tight rotary joints available on the market; however, we were unable to find one that had a large bore in the center to run a car axle through or one that had air inlets/outlets located on the far outside radius. Most of the joints that we were able to find were for air entering and exiting directly in the axis of rotation and did not allow for any object to be placed in the center of them. Since we could not find a rotary joint that met our criteria, we chose to design our own.

Compressor

Distribution Block

Solenoid Valves

Rotary Joint

Solenoid Valves

Figure 17: Tire Inflation System Configuration

19

8.1 Design Details The main criteria for our rotary joint design were the following:

• Must have a 40mm hole in the center to allow for the axle to either pass through or support the joint.

• Air inlets and outlets must be located at the outer radius to allow the hoses on the outside of the joint to clear the vehicle spindle and hub.

• Overall thickness of the joint must be no greater than 25mm to so as not to interfere with the vehicle driveline or suspension components.

• Ball bearing system must be used to reduce contact friction between the two rotating halves both axial and planar.

We were able to develop a joint to meet the above criteria as shown in Figure 18. This design incorporates a 40mm bore in the center that allows the rotating half to completely rest on the drive axle while the stationary side rests above it and does not contact the rotating axle at all. The loose ball bearing system with “diagonally oriented” contact races allow the two halves to rotate relative to each other with minimal radial and planar friction. It is also exactly 25mm in thickness and 125mm in diameter. This allows it to fit within the driveline constraints and brake components. It is important to note that the air chamber is not designed to be completely air tight. Pressure losses across the rotary joint are expected and we will size the rest of our system (compressor, hoses, valves, etc.) to take this into account. However, we have designed the air chamber to reduce as much pressure loss as possible without sacrificing friction when the joint rotates. This has been obtained by use of stepped features on one half that insert into the slots on the other half of the joint. These walls create a more complex passage for the air to escape, hence increasing the resistance. We are also using Rulon, which is a low friction material to help reduce the size of this gap while having a minimal impact on rotational friction.

Figure 18: Rotary Joint CAD Model

Stationary Spindle-Side Rotating Hub-Side

Air Channel

Seal

Seal

20

9. ELECTRONICALLY-AUTOMATED SYSTEM Our final product possesses the ability to automatically maintain the cold tire pressure in all four individual tires of the vehicle that it is installed on. The main functions of these electronics is to take the pressure sensor reading from each of the tires, and then decide whether or not to inflate them or deflate them to ensure proper cold tire pressure. 9.1 OOPic The OOPic is the main component of our electronics system. Essentially, an OOPic is an Object Oriented Peripheral Interface Micro Controller. This allows us to make virtual circuits in a small chip so we can link logic between our different objects (compressor, pressure sensors, and solenoid valves). Figure 19 shows the different components of an OOPic board.

9.2 Electronic Control Program Description The logic that our OOPic needs to control is quite basic. We have 13 components which we are interfacing with: air compressor, (4) in-tire pressure sensors, (4) distribution block solenoid valves, (4) pressure release solenoid valves. Figure 20 is a flowchart of the logic steps that we will be taking in our program. When the program starts up, the first thing that it does is check all of the tire pressures. If at least one of the tire pressures is low, it will turn on the compressor. For the given low pressure tire, the corresponding distribution block solenoid valve will open allowing the tire to inflate. This inflation process will continue until the pressure sensor detects that the tire has reached the optimal pressure; the solenoid valve will then close. However, if a tire pressure is too high, the pressure release valve at the appropriate tire will open and stay open until

Figure 19: Components of an OOPic Board

21

the optimal tire pressure is achieved. The actual program code can be seen in Appendix J. We decided to just model the code for one tire since the code would be very similar for the other three tires.

9.3 Required Hardware Interface We cannot control the air compressor directly through the OOPic. The compressor motor requires at least 12VDC and 3A to operate and the OOPic supplies a maximum of 5VDC and 0.25A. We can deal with this issue by using a two channel amplifier that amplifies the power from the OOPic in order to operate the motor. We can then use a pulse width modulation output from the OOPic as the positive reference input on the amplifier. Pulse width modulation is a method predefined within the OOPic that allows us to specify the voltage (between 0Vand 5VDC) we output from the OOPic. When we output a 5V signal from the OOPic the amplifier will amplify a +12V signal and turn the compressor on. Similarly, all of our solenoid valves will require 12VDC to open, and due to the current draw, we cannot control the compressor directly through the OOPic. However having an amplifier for all (8) solenoid valves in our system would be too complex and costly. The better route to take would be to use relays for each valve. A relay works like an electronically triggered switch. When it is powered, it completes the circuit and 12VDC from the power supply (car battery) is sent straight to the solenoid valve to open it. When the 12 volts is removed from the solenoid valve, it automatically closes The tire pressure sensor will be interfaced directly with the OOPic. The component can be powered by the 5VDC provided by the OOPic. There is a special Input/Output area of the OOPic where the pins are arranged such that one row of pins will power a device and take an input from the device. However, we do not have the specifics on the particular output readings of the tire pressure monitoring device. Optimally, we would have a linear relationship between the tire pressure reading and the devices’ output voltage.

Perform Test

Check Pressure

in FL

Check Pressure

in FR

Check Pressure

in RL

Check Pressure

in RR

Is Tire Pressure Low?

Is Tire Pressure Low?

Is Tire Pressure Low?

Is Tire Pressure Low?

Open Solenoid

Is Tire Pressure High?

Open Solenoid

Turn on Compressor

Keep Open if Pressure Low,

Else Close

Keep Open if Pressure High,

Else Close

Yes

No

Open Solenoid

Is Tire Pressure High?

Open Solenoid

Turn on Compressor

Keep Open if Pressure Low,

Else Close

Keep Open if Pressure High,

Else Close

Yes

No

Open Solenoid

Is Tire Pressure High?

Open Solenoid

Turn on Compressor

Keep Open if Pressure Low,

Else Close

Keep Open if Pressure High,

Else Close

Yes

No

Open Solenoid

Is Tire Pressure High?

Open Solenoid

Turn on Compressor

Keep Open if Pressure Low,

Else Close

Keep Open if Pressure High,

Else Close

Yes

No

Figure 20: Flowchart of The Logic Steps That Will Be Taken By Our Automatic System

22

10. Alpha Prototype Description To demonstrate our concept and how we expect things to work, we created an alpha prototype. The components that are represented in our prototype are included in Figure 21 below. The main focus of our prototype is to show how we plan on getting the air to the tire. By running the tube from the compressor into the end of the rotary joint that is stationary and then from the end of the rotary joint that is spinning out to the tire valve, we are able to avoid tangling the hose. We also want to show how we plan on using an air distribution block controlled by solenoid valves to manage the flow of air into the tires. Thus, our prototype shows that our design will “work” in a sense that we will be able to control the tire pressures in each individual tire and route the air from the centralized compressor to the rotating tire without tangles and without negatively affecting vehicle aesthetics. 11. BETA+ PROTOTYPE DESCRIPTION Having demonstrated the general idea of our design in the alpha prototype, we created a refined (Beta+) prototype to display functionality, packaging, and design manufacturing feasibility. Figure 22 shows our rotary joint, suspension components, testing apparatus, air compressor, and vehicle tire.

Figure 22: Beta+ Prototype and Major Components

Rotary Joint

Figure 21: Alpha Prototype

CV Joint

Air Distribution Block

Compressor Rotary Joint

Solenoid Valves

Wheel

Air Hoses

Hub

Spindle

CV Joint

Suspension

Air Compressor

Vehicle Tire

23

11.1 Machining the Rotary Joint The rotary joint, which is one of the key components of our design, consists of two cylindrical pieces with a hollow channel for air flow to the tire. Fifteen hours of labor were spent machining (using a CNC mill with dimensions from our SolidWorks CAD file) these parts out of cylindrical slabs of an aluminum alloy (6160 T6 Aluminum). This material was chosen due to its material properties and machinability. We discovered that it is possible to machine the parts to the tolerance we need by using the CNC mill instead of the lathe. By creating these joints in such a precise fashion, we were able to inspect and conclude that our rotary joint will be able to channel air through the “stationary” half of the rotary joint and out of the half that revolves with the wheel hub. There is very little friction in the axial and planar directions from the use of ¼” spherical, stainless steel balls placed on diagonally situated races located near the axis of the joint between the “revolving” and “stationary” halves. 11.2 Reducing Rotary Joint Leakage We decided to use a low friction fluoropolymer known as Rulon to minimize the gap in our seal design between the two halves of the rotary joint. This material is commonly used in ball bearing races and linear slide bearings. The material however requires a bit of “break-in” because the surface comes quite rough from the manufacturer. During the “break-in” process, the rough surface of the Rulon polishes the surface of the metal that it is rubbing against. The surface of the Rulon itself starts to become polished. After the “break-in”, you are left with a very low friction contact between the two, and since the Rulon is slightly compressible, it can be used as a seal. This 0.047” thick sheet was cut into rings using a laser cutter. The static coefficient of friction for this material is 0.12, and dynamic coefficient is 0.20.

Figure 23: Machined 6061 T6 Aluminum Rotary Joint

Figure 24: Rulon Rings Used as Low Friction Seals

Rulon

24

11.3 Compressor and Air Tubing The beta prototype also uses a Campbell Hausfield CC2300 12V compressor, which is similar in functionality to the one that we plan to incorporate under the hood of production vehicles for the tire inflation system. According to the manufacturer, it can produce pressures up to 230psi. Its cordless capabilities will allow greater ease of use when performing tests on our system. The tubing we are using is ¼” flexible PVC hose. 11.4 Hose Fittings for Inlet and Outlet We decided to use a ¼” brass barbed hose fitting with a 1/8” NPT tap. We chose this fitting because it had the best transition for our ¼” hose from the base to tip. Also, the 1/8” NPT was significantly smaller in diameter compared to other fittings and allowed us to use a smaller hole to connect it to the rotary joint. To install the fitting, we had to drill a hole with an “R-size” drill bit and use a 1/8” NPT tap. We then sealed this connection by using Teflon tape (see Figure 25). 11.5 Construction of Testing Apparatus To support the suspension (and eventually the wheel/tire on the Beta plus prototype), we constructed a testing apparatus from two 4’ x 2’ sheets of medium density fiber board. This structure (seen above) will support the suspension system, rotary joint, CV joint, and wheel, which will allow us to effectively demonstrate and test our system’s design with an actual passenger vehicle’s suspension/wheel system: the vehicle in this case is a 2006 Daewoo Lanos. This apparatus was built in the Art and Architecture woodshop and required 6 hours of labor. Additional hours were put into the surface preparation and painting. 11.6 Attaching/Packaging the Inflation System to the Vehicle Suspension The “revolving” half of the rotary joint attaches to the wheel hub, while the “stationary” half attaches to the spindle. In order to achieve appropriate dimensioning of our rotary joint for our prototype (from the Daewoo Lanos suspension/wheel system), we had to remove the wheel hub from the spindle. As a result of this, the two halves of the rotary joint seal together and collaboratively become a “spacer” that fits tightly between the spindle and wheel hub, while allowing the CV joint to pass through the center of the rotary joint. With this design, the rotary joint is obscured, and it provides an effective air transport system that eliminates all risk of the air tubing from tangling when the vehicles is moving. 11.7 Beta+ Prototype Functionality To test the functionality of our Beta+ prototype, we decided to inflate a balloon. Since inflating the tire would be too difficult to see, using a balloon allowed us to visually verify the system’s performance (see Figure 26). We were able to prove functionality because our prototype allowed us to rotate the tire while still inflating the balloon. The friction felt during rotation of the wheel felt similar to that of a typical powertrain that is caused primarily by inertia and resistance in the wheel bearings

Figure 25: View of Brass Barb Fitting on Rotary Joint

25

11.8 Beta Prototype Reflection From the manufacturing of our entire beta prototype we have learned the following:

• The 1/8” groove on the rotating hub-side of the rotary joint takes a long time to create because the very small diameter end mill requires a slow federate to prevent tool damage.

• Our design should utilize prefabricated sealed ball bearings that press into the spacer • We should incorporate a shield or boot around the device to seal it from dirt and liquids. • The general shape of the rotary joint should be first die cast with the surfaces requiring a specific

tolerance/finish machined afterwards. This is because machining the aluminum cylinders resulted in a lot of waste due to the number of channels and grooves.

• The thicknesses of the outer walls are very thin and look like they can be made thicker without compromising the design.

• According to the Material Safety Data Sheet for Rulon, one must be cautious of the dust created from the cutting process.

In our Beta+ prototype, we differed from our final design in the following ways:

• Aluminum rotary joint housing instead of steel allow • Did not have a pressure sensor in the tire • Lacked check valve to prevent backflow of air into system • No solenoid valve or distribution block after compressor • No release solenoid valve

Figure 26: Demonstration of System Inflation Capabilities

Inflating Balloon

26

ENGINEERING ANALYSIS 12. ENGINEERING ANALYSIS AND OPTIMIZATION To analyze the inputs and outputs of the compressor for our use, as well as selecting the proper compressor, we analyzed all necessary components involved in our design. Due to limited resources and the large tolerance in inputs/outputs allowed, we resorted to analytical solutions rather than computer simulated models. In some of our analysis, due to the complexity, we used worst case scenario for best safety practice. Several factors have been considered upon performing the engineering analysis for the centralized compressor tire inflation system. These included items such as stress, vibration, and fluid analyses of the rotary joint as well as a system-wide fluid analysis. Each of the aforementioned items directly addressed the design objectives relative to the functionality of the system. However, only items that have been thought to cause critical failure modes based on the assumed design applications and parameters were investigated. One such parameter ensures that the pressure within the rotary joint is sufficiently low at all times, or more specifically,

psip 60≤ which was based on the maximum allowable pressure of the tire (60 psi). Using this information, it was been assumed that the stresses generated in the rotary joint due to the pressure would be negligible, thus eliminating the need for a stress analysis. This ultimately has led the team to only consider vibration and fluid analyses of the rotary joint and a system-wide fluid analysis. It should be noted that the rotary joint also underwent design optimization in MS Excel. Brief sample calculations are illustrated in the sections below; however, the entire calculations for each analysis can be found in Appendix E and F. 12.1 Compressor Assuming an adiabatic compressor, air as an ideal gas, stagnant inlet velocity of air, inlet air temperature and pressure at atmospheric conditions, negligible pressure losses through joints and tubing, and a rough estimate of outlet air temperature; the first law of thermodynamic (see equation 4) is employed to determine outlet velocity of air. By rearranging parameters in the first law of thermodynamics, the outlet velocity (V2) can be found by equation 3, where w represents the work done on the compressor, h1 and h2 represent inlet and outlet enthalpies respectively, T1 and T2 represent inlet and outlet temperatures respectively, and Cp represents constant heat capacity.

( )122 2 hhwV −××= (Equation 3) ( )1212 TTChh p −=− (Equation 4)

Using "

83

air hose, the flow rate (Q) of air is dictated by the cross section area of the air hose, and the

velocity of the flow, as stated in equation 5,

2

2

2 163 VQ ×⎟

⎠⎞

⎜⎝⎛×= π (Equation 5)

12.2 Air Valve Sizing Assuming pressure drop and negligible pressure leaks, industry technical bulletin [11] proposed equation 6 and 7, depending on pressure drop, to determine coefficient of flow (Cv), where G is the specific gravity relative to air at atmospheric condition, T is the temperature of gas through the valve in Fahrenheit, P1 and P2 are inlet and outlet pressure in PSI respectively, and ΔP is the pressure drop through the valve in PSI as

27

well. Equation 6 is used if pressure drop across the valve is less than half of the inlet pressure, and equation 7 is used if the pressure drop exceeds half the inlet pressure. In the case where pressure drop exceeds half the inlet pressure, the flow rate is limited by super-sonic flow and therefore only depends on the inlet pressure.

( )( )21360

460PP

TGQCv ×Δ×+××

= (Equation 6)

( )1660

460P

TGQCv ×+××

= (Equation 7)

12.3 Vibration Analysis: Deflections due to Resonance In performing the vibration analysis, one potential failure mode of the rotary joint system that was identified dealt with excessively large deflections of the CV joint shaft to which the rotary joint is attached. These large deflections would only occur if the angular velocity of the tire (and hence CV joint shaft) matched the natural frequency of the rotary joint and shaft system, or more specifically, if

tiren ωω = where ωn is the natural frequency of the rotary joint-shaft system and ωtire is the angular velocity at which the tire is operating. The condition that leads to large shaft deflections is known as resonance, and if this occurs, catastrophic failure due to shear is likely. In order to alleviate this problem, the natural frequency of the system (also known as the critical speed) should always be significantly above the angular velocity of the tire, or more specifically,

tirecrit ωω > where ωcrit is the critical speed of the rotary joint shaft-system and ωtire represents the same quantity previously mentioned. This design problem has been modeled based on the following assumptions:

1. The CV joint shaft can be considered as a solid steel cylinder with a diameter of 0.75 inches, a length of 18 inches, and a modulus of elasticity of 30,000 kpsi.

2. Only half of the rotary joint (the portion located on the CV joint shaft) rotates; the other half, which is attached to the spindle at the base of a vehicle strut is stationary.

3. The rotating portion of the rotary joint can be modeled as an aluminum “rotating disk” with initial dimensions as indicated in the CAD drawing in figure 19 and Appendix I. The mass eccentricity introduced by the presence of the air tube connection can be considered negligible for this specific problem.

4. The vehicle (and hence tire) speeds cannot exceed 150 mph, which corresponds to the “worst case” design scenario.

5. The tires can be modeled as P205/65/15 grade as used on the Toyota Camry. The procedure of this analysis can therefore be summarized as the following:

1. Determine the maximum angular velocity of the tire. 2. Determine the critical speed of the rotary joint shaft system. 3. Compare the critical speed with the maximum angular velocity. If the critical speed exceeds the

maximum angular velocity, then the design criterion is satisfied. If the critical speed is less than

28

the maximum angular velocity, then the dimensions of the rotary joint must be changed such that the critical speed exceeds the maximum angular velocity.

The first item needed to calculate the angular velocity of the tire is the radius of the tire. Knowing the grade of the tire for this application, the radius can simply be found by

rimtiretire dwr2165.0 += (Equation 8)

where wtire refers to the width of the tire in inches, drim refers to the diameter of the rim in inches, and rtire refers to the radius of the tire in inches. Note that the coefficient of the wtire term is merely the aspect ratio relating of the height and width of the tire, which is stated in the tire grade. With wtire=205 mm and drim=15 in, the radius of the tire is

( ) ( )inmm

inmmrtire 1521

4.25120565.0 +⎟

⎠⎞

⎜⎝⎛= (Equation 9)

inrtire 75.12=

The angular velocity of the tire is then expressed as the following:

tire

tiretire r

V=ω (Equation 10)

where Vtire is the velocity of the tire in mph, rtire is the radius of the tire in inches, and ωtire is the angular velocity of the tire in rpm. With Vtire=150 mph and rtire=12.75 in, the angular velocity of the tire is

( )⎟⎠⎞

⎜⎝⎛

⎟⎠⎞

⎜⎝⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛

=radrev

in

hrftin

mileftmph

tire πω

21

75.12min60

1125280150 (Equation 11)

rpmtire 88.1977=ω

In determining the critical speed of the rotary joint-shaft system, the first step is to determine the stiffness of the shaft. This quantity can be found by

shaft

shaft

lEA

k = (Equation 12)

where E is the elastic modulus of the shaft in kpsi, Ashaft is the cross-sectional area of the shaft in in2, lshaft is the length of the shaft in inches, and k is the stiffness of the shaft in lbf/in. With E=30,000 kpsi and lshaft=18 in, the stiffness of the shaft is

29

( ) ( )

in

inkpsi

psikpsik

18

75.041

100030000 2⎟⎠⎞

⎜⎝⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛

=

π

(Equation 13)

inlbfxk 51036.7=

The next phase is to calculate the mass of the rotating portion of the rotary joint according to the equation

gV

m diskρ= (Equation 14)

where ρ is the density of the disk in lbf/in3, Vdisk is the initial volume (given in CAD drawing) of the disk in in3, g is the gravitational acceleration in ft/s2, and m is the mass of the disk in lbf·s2/ft. With ρ =0.098 lbf/in3, the mass of the disk is

( )

2

33

2.32

9.6098.0

sft

ininlbf

m⎟⎠⎞

⎜⎝⎛

=

ftslbfm

2

02.0 ⋅=

(NOTE: Detailed volume calculation omitted due to excessive length) Finally, the critical speed of the rotary joint-shaft system can be determined by

mk

crit =ω (Equation 15)

where k and m are the same quantities calculated above and ωcrit is the critical speed of the system in rpm. With k=7.36 x 105 lbf/in and m=0.02 lbf·s2/ft, the critical speed of the system is

⎟⎠⎞

⎜⎝⎛

⎟⎠⎞

⎜⎝⎛

⋅

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛

=min60

21

02.0

121036.7

2

5

sradrev

ftslbf

ftin

inlbfx

crit πω

rpmcrit 70.195883=ω

Because the critical speed is on the order of 100 times greater than the maximum angular velocity of the shaft, it can be stated that the rotary joint-shaft system is more than sufficiently stable. An optimization on this to reduce the critical speed from an apparent “over-design” situation is made possible by increasing the mass via increasing the overall size of the rotary joint.

30

12.4 Vibration Analysis: Deflections due to Mass Eccentricity Another potential failure mode of the rotary joint system is the deflection interference of the rotating half of the rotary joint with the fixed half of the rotary joint. Since the outer walls in the rotating portion of the rotary joint have a small clearance between the outer walls in the fixed portion of the rotary joint (for assembly purposes), it is possible that only slight vibrations might cause the components to crash into one another, leading to undesired noise levels and potential failure. In order to alleviate this problem, the deflections of the rotating half of the rotary joint-shaft system must be smaller than the clearance between the components, or more specifically

inX disk 0394.0<

where Xdisk is the amplitude of deflection of the rotary joint-shaft system in inches. This design problem has been modeled based on the same assumptions stated in the resonance analysis, with the following exceptions:

1. The mass eccentricity introduced by the presence of the air tube connection must be considered, as it is the source of a harmonically forced vibration.

2. The damping coefficient of the system does not affect the accuracy of the solution as long as it reflects moderate under-damping and thus can be approximated as 0.8.

The procedure of this analysis can therefore be summarized as the following:

1. Determine the amplitude of the deflection of the rotary joint-shaft system due to the mass eccentricity.

2. Compare this value with the maximum allowable deflection above. If the deflection due to the mass eccentricity is less than this maximum deflection, than the design criterion is satisfied. If this is not the case, than the dimensions of the rotary joint must be changed such that the design criterion is satisfied.

The first item needed to calculate the deflection magnitude of the rotary joint-shaft system is the mass of the eccentricity. This is given by

gV

m ee

ρ= (Equation 16)

where ρ is the density of the eccentricity in lbf/in3, Ve is the volume of the eccentricity in in3, g is the gravitational acceleration in ft/s2, and me is the mass of the eccentricity in lbf·s2/ft. With ρ=0.098 lbf/in3, the mass of the disk is

( ) ( ){ }( )

2

223

2.32

394.0236.0354.0098.0

sft

ininininlbf

me

−⎟⎠⎞

⎜⎝⎛

=π

ftslbfxme

241036.2 ⋅

= −

31

From here, the ratio of the angular velocity of the system to its natural frequency (or critical speed) must be determined. This is given by

crit

tireRωω

= (Equation 17)

where ωtire is the angular velocity of the rotary joint-shaft system in rpm and ωcrit is the natural frequency of the system in rpm. Using ωtire=1977.88 rpm and ωcrit=195883.70 rpm from the calculations in the first vibration analysis, the ratio R is

rpmrpmR

70.19588388.1977

=

0101.0=R

Finally, the amplitude of the deflection of the rotary joint-shaft system can be found by

( ) ( )222

2

21 RR

Rm

emX e

disk

ζ−−⎟⎠⎞

⎜⎝⎛= (Equation 18)

where me, m, and R are the same quantities calculated above, e is the distance of the eccentricity from the mass center of the disk in inches, ζ is the damping coefficient, and Xdisk is the amplitude of the deflection in inches. With me=2.36x10-4 lbf·s2/ft, m=0.02 lbf·s2/ft, R=0.0101, and e=2.01 in, the amplitude is

( )( )

( )( ) ( )( )( )222

2

2

24

0101.08.020101.01

0101.0

02.0

01.21036.2

−−⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

⋅

⎟⎟⎠

⎞⎜⎜⎝

⎛ ⋅

=

−

ftslbf

inft

slbfxX disk

inxX disk

61056.2 −=

Because the amplitude is on the order of 10,000 times less than the maximum allowable deflection, it can be stated that the rotary joint-shaft system is more than sufficiently stable. An optimization on this to reduce the critical speed from an apparent “over-design” situation is made possible by increasing the mass via increasing the overall size of the rotary joint.

32

12.5 Rotary Joint Design Optimization Since the rotary joint is the key component of our design's success (it distinguishes our design from the CTIS, which does not have a wheel spindle to work around), we set out to optimize the tradeoff between minimizing area for air leakage from the perimeters of the rotary joint (both along the interior and exterior perimeters), minimizing rotary joint side-wall plate thickness, and maximizing the rotary joint mass (volume) to eliminate apparent over-design in shaft deflection (vibration). Specifically, Microsoft Excel Solver was used (See Appendix I) to optimize the design tradeoff that occurs when increasing mass increases wall thickness and increases the radius of the rotary joint. To optimize the radii within the “stationary” side of the rotary joint (R2, R3, and R4, with a fixed R1 determined by the dimensions of the wheel hub of the application vehicle— Figure 19), three equations that defined these tradeoffs were entered collectively as the “Objective” equation in Microsoft Excel. Specifically, our objective was to minimize Equation 19,

platesrotaryjoV intjoint wallrotary leakage

1 t A ++ (Equation 19)

Where

(Equation 20)

)]R[P(2)]R-(R[ )R2R(2

A3

23

24y31

leakage ππτππ +

= , (Equation 21)

and

)R2R(2)]RR[P(S

t23y

22

23f

joint wallrotary ππτππ

+−

= . (Equation 22)

These variables are geometrically defined in the CAD drawing. Once the equation and the variables were set in Excel, the design constraints determined from the actual parts that we are basing our prototype from were entered and the solver function was executed. The optimized values of the radii of the “stationary” half of the rotary joint were determined to be: R2 = 1.46 inches, R3 = 1.83 inches, and R4 = 5.55 inches.

R1

R2

R3

R4

)h}r-(r)]dr-(r

)R-(R)R-[(R-)tr-{(rV2

diski,2

coupledisk2

chamberi,2

chambero,

23

24

21

22

2diski,

2disko,platesjoint rotary

++

+= π

Figure 27: Definition of variables (R1, R2, R3, and R4) used in Microsoft Excel Solver Design Optimization

33

MICROECONOMIC ANALYSIS 13. MICROECONOMIC MODEL 13.1 Estimate Market Size for Our Product Because the centralized compressor tire inflation system will only be installed on new vehicles, it was necessary to identify the total number of new vehicles sold in the US annually. Based on an article from BusinessWeek Online, this number was approximately 17 million units in 2005. Using the fact that this product has been targeted for mid-grade vehicles and above, it was necessary to determine the number of likely consumers based on income level. The team assumed that those persons having annually salaries of $50,000 or greater would be the “likely consumers”; therefore, using data obtained from US Census 2000, it was found that nearly 50% of new vehicle owners would be capable of purchasing such a system. Therefore, the total market size was calculated as:

aserhiclePurchMidGradeVeleSalesTotalVehictSizeTotalMarke %×= ( )( )50.0000,000,17 unitstSizeTotalMarke =

unitstSizeTotalMarke 000,500,8= From here, it was assumed that 25% of the total market would be interested in a dynamically-self-inflating tire system and that our target market share as a new automotive supplier would be about 5%. Hence, the projected annual volume for our system was:

eMarketSharUsersInterestedtSizeTotalMarkeualVolumeojectedAnn %%Pr ××= ( )( ) )05(.25.0000,500,8Pr unitsualVolumeojectedAnn =

unitsualVolumeojectedAnn 250,106Pr = 13.2 Economic Analysis The primary aim of the profit optimization analysis was to identify the best price to sell the centralized compressor tire inflation system with respect to profitability. Specifically, it was desired to maximize equation 23

( )( ) fvT

dp CCPP −−Δ++=Π αλλθ (Equation 23)

where Π is the profit, θ is the maximum demand at “zero price” for a simple microeconomic model, λp is the price elasticity, P is the unit price, λd is the design elasticity vector, Δα is the design change vector, Cv is the unit variable cost, and Cf is the fixed operating cost. It should be noted that the variable cost is a function of the demand and selected design attributes, whereas the fixed cost remains constant. In order to optimize this problem, it was necessary to determine all of the parameters in the equation except for the price and the design change vector (which are variables of optimization). From the previous section, it is assumed that the maximum demand is approximately 106,250 units. However, the maximum price of the product at “zero demand” must also be known in order to determine the price elasticity. Assuming that the consumer would not be willing to pay more for the product than its total potential savings over five years, the team was able to estimate the maximum price. Using the data stated in the project background, the estimated tire savings over five years would be equivalent to one additional tire change during this period:

( )( ) 244$4/61$ == tirestireavingsTotalTireS Similarly, based on project background information stating that properly inflated tires results in 3.3% savings, the estimated fuel savings would be the following:

34

( )( ) 297$5033.000.3$251000,15

=⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛= years

gallonmilesgallon

yearmilesavingsTotalFuelS

Observe that in performing this latter calculation, it was assumed that an “average” vehicle travels 15,000 miles/year, has a gas mileage of 25 mpg, and that the cost of gas is about $3/gallon. Therefore, the total savings of this product (and hence the maximum price a consumer would pay for it) is:

541$297$244$ =+=gsTotalSavin From here, the maximum demand and the maximum price was interpreted as the “y-intercept” and the “x-intercept” of the demand-price “curve”, respectively. A straight line connecting the two points generated following plot.

Microeconomic Model: Demand vs. Price

y = -196.4x + 106250

0

20000

40000

60000

80000

100000

120000

0 100 200 300 400 500 600

Price ($)

Dem

and

(Qua

ntity

)

Figure 28: Demand vs. Price Curve

The design elasticity was finally determined by viewing the slope of this plot, which is λp=-196 units/$. The next phase was to determine the values within the design elasticity vector. The design factors that were chosen for this process included the system noise level and the compressor weight. This selection was based on information from a QFD analysis as well as the team’s engineering and marketing knowledge about such products. The values within the design elasticity vector were found by assuming that the noise level and compressor weight would have sensitivities of 5% and 10%, respectively, of the price elasticity. Hence, these computations resulted in values of λdb=-10 units/dB for the noise level and λlb=-20 units/lbf for the compressor weight. The negative signs indicate that both design attributes have the same effect on demand as price. The variable and fixed cost parameters were the final terms needed to determine the profit equation. Some liberty was taken in estimating the many components of these parameters; however, all assumptions have been based on trusted books, websites, and other relevant resources. Due to the magnitude of the assumptions made, all of these are appended in the appropriate sections of this document (See References, Appendix K, Appendix L). This process yielded a total variable cost function (to be adjusted during optimization) and a total fixed cost of about $15.6 million. With all of the necessary parameters determined, the profit optimization was able to be executed. Using the constraints equations described in Appendix N, it was discovered that the best price to maximize profit for this product is about $479. Nevertheless, this resulted in an annual profit loss of about $14.8 million. This profit loss was most likely due to the fact that the parameters in the demand function were incorrectly estimated. Therefore, a refined microeconomic model with a better demand function would be necessary to obtain valid results.

35

MARKETING ANALYSIS 14. REFINED PROFIT OPTIMIZATION In developing a refined, more “accurate” profit optimization, it was necessary to reformulate the “demand function”, which was originally assumed to be linear. We carried out this process by first determining the “value”, or demand, of particular attributes of the centralized compressor tire inflation system through the use of the Sawtooth® Survey program. Once these values, called “beta values”, were computed by the Sawtooth® program, we plotted the beta values for each of the attribute levels (see Table 1 below), and created a spline curve to interpolate the “optimal product” for maximum profit from products with traits (corresponding to different beta values) between the discrete product arrangements. The surveys used for this process enabled participants to select products on the basis of price, sound (noise) level, and compressor weight with the following levels:

Table 1: Definition of Attribute Levels Used Price Sound Level Compressor Weight $400 15 dB 5 lbf $650 60 dB 25 lbf $900 80 dB 55 lbf

Plots illustrating the beta values of each product attribute are listed below.

Spline Curve for Price

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0 200 400 600 800 1000

Price ($)

Bet

a Va

lue

Figure 29: Spline Curve of Price Beta Values

Spline Curve for Sound Level

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 20 40 60 80 100

Sound Level (dB)

Bet

a Va

lue

Figure 30: Spline Curve of Noise Beta Values

36

Spline Curve for Compressor Weight

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0 10 20 30 40 50 60

Weight (lb)

Bet

a Va

lue

Figure 31: Spline Curve of Compressor-Weight Beta Values

From this point, the refined profit optimization was performed with many of the same variables, constraints, and parameters that were used in the old model. One notable difference was that a more generalized objective function was used. This equation was given by

( )fv CQCQP +−=Π (Equation 24) where Q is the demand function in units sold and the remaining variables represent the same quantities mentioned in the old microeconomic model. Additionally, it should be observed that the price was constrained to the upper and lower limits used in the survey (Appendix O). This was necessary because prices selected outside this range during optimization could not be interpolated accurately and could yield faulty results. Another difference in this model is that the number of interested users was determined through the beta values. Specifically, these values assisted in finding the number of interested users with the equation

∑+

∑=

oductFinalNoChoice

oductFinal

ee

eUsersInterestedPr

Pr25.0%ββ

β

(Equation 25)

where βFinalProduct is the beta value for each product attribute after optimization and βNoChoice is the beta value for not choosing the product at all. The factor of 25% was used to account for the fact that the majority of survey participants (APD classmates) were not the most likely users and therefore might not truly represent the “interested users” described in the project background. Since the beta values are varied during the optimization, the sample calculations for this quantity are omitted. The results from the new optimization yielded an annual profit of about $ 2.1 million with a projected annual volume of just over 57,780 units. The design associated with this optimization was priced at $900/unit, produced 32 dB of noise, and weighed 5 lbf (Appendix O).

37

14.1 Net-Present Value/Breakeven Analysis Using the results of the refined profit optimization, a net-present value and breakeven analysis was performed. The net-present value was given by

∑=

⎟⎠⎞

⎜⎝⎛ −

Π=

5

1

1001

nn

netrNPV (Equation 26)

where NPV is the net-present value, � is the annual profit, rnet is the net interest rate (including inflation), and n is the number of years. Observe that in performing this analysis, the team assumed an annual market growth of about 12%/year (based on research). Therefore, the annual profit term in the above equation is not constant, but varies with the increase in demand. Additionally, an interest rate of 3.50% and an inflation rate of -1.31% was assumed based on research and general knowledge of the market. Because this calculation was rather lengthy, it is omitted here but included in Appendix X. The result of this analysis yielded a net-present value of approximately $31.9 million over five years, which is significantly greater than the capital investment of about $10.2 million. Given this information, the development of our centralized compressor tire inflation system would be a sound business opportunity (Appendix P). For the breakeven analysis, the team developed a plot illustrating the amount of the initial investment remaining after each profit period (Figure 32).

Breakeven Analysis Cash Flow

$(15,000,000)

$(10,000,000)

$(5,000,000)

$-

$5,000,000

$10,000,000

$15,000,000

$20,000,000

$25,000,000

0 1 2 3 4 5

Time (Years)

Cas

h Fl

ow

Figure 32: Breakeven Analysis Shows Breakeven By 3 Year Mark

With this model, the breakeven point could be interpreted as the time at which the balance of the initial investment was completely paid. Based on the above figure, this breakeven time was just under three years.

38

PRODUCT DEVELOPMENT PROCESS 16. DESIGN PROCESS The design process for this model has been developed based on observations made of existing processes described in coursework literature (Germany’s VDI 2221 standard) as well as some industrial experiences of the team members. Therefore, the team’s design process is an amalgamation of these ideas into the current best process for the product. It should be noted that only the processes involving the refinement of the centralized air supply routing design are included in this section. This corresponds to the portion of the design process diagram beginning with the “Develop Design Models/Prototypes” block (Appendix D). The steps prior to this portion of the diagram have already been performed in compiling information for this project proposal. 16.1 Develop Design Prototypes This initial phase of concept refinement would involve the creation of both a physical and virtual model of the centralized air supply routing system. The physical model would consist of the beta prototype, which primarily focuses on the design of the rotary joint but necessarily includes the other system components. This model would be used to test the general concept only (i.e. no formal experimentation with real numbers). The virtual model, however, would consist of a CAD drawing of the rotary joint with actual initial dimensions and would also include data regarding other components of the system. This information would then be used to analyze the overall system design in a more rigorous manner. 16.2 Develop Engineering Model The virtual model from the prior phase would then be used to analyze and test the functionality of the product. In preparing for this stage of development, quantifiable design characteristics based on the design objectives have been generated. The characteristics that the team has selected to examine are the critical speed of the rotary joint-shaft system (ωcrit), the deflection amplitude of the rotary joint-shaft system (Xdisk), the leakage area of the rotary joint, and the overall flowrate of the system. Each characteristic has been related to several design variables and parameters in the following functional format:

),,,,,,,,,,,,,,( 4321,,,, hdtrrrrrrrrrkgf diskcouplechamberichamberodiskidiskocrit ρω = where g is the gravitational acceleration ft/s2, k is the CV joint shaft stiffness in lbf/in, ρ is the density of the rotary joint in lbf/in3, and the remaining terms are dimensions of the rotary joint in inches (see Appendix E for details).

),,,,,,,,,,,,,,,,,,,( 4321,,,,,,, ehhdtrrrrrrrrrrrkgfX ediskeoeicouplechamberichamberodiskidiskotirecritdisk ωωρ= where ωtire is the angular velocity of the rotary joint-shaft system in rpm and the remaining variables and parameters represent the same quantities as mentioned previously.

Using these relations and making certain assumptions about the system, governing engineering equations describing the system can be developed. This would then be used to analyze the design concept in terms of:

• Vibration analysis • Fluid Analysis

The results from these analyses would then be used for the next stage in the design process.

39

16.3 Optimize Engineering Model In this phase, the engineering model would be optimized to accommodate customer requirements. The methods used would only consist of those that would be presented throughout the course; therefore, rigorous application of optimization techniques would not be used. Note that this would require at least a partial iteration of all phases leading up to the optimization including prices. If the model is determined to be functional, the concept would then proceed to the next stage. 16.4 Select Optimal Design Solution This phase would involve further refinement of the concept through prioritizing customer needs. Since some of the engineering objectives consists of conflicting engineering parameters, such as minimizing vibrations and stress on the rotary joint and maximizing air flow to the tire. It should be observed that the purpose in performing this would be to obtain the best possible model based on predetermined vital product attributes. 16.5 Estimate Product Volume The product volume estimation phase would require the team to approximate the number of units that might be sold over the product life based on consumer demand. Therefore, additional research about the target market, such as demographics, income, or other items would have to be investigated in order to arrive at the best volume estimate. Surveys, as well as general understanding of supply-demand curves as studied in class, would also have to be employed for this process. as well. In successfully determining the product volume, it would be possible to identify the best manufacturing processes to be executed for the concept. 16.6 Estimate Product Cost During this stage, the team would have to approximate the unit cost of the product based on material cost, design cost, manufacturing cost, and a host of other related items. The number of items considered in this cost estimation would primarily emerge from requirements set in the course curriculum. Based on the scope of the project, other items may have to be considered as well based on the scope of this project. It should be observed that all of the components of the cost estimate would have to be based on research performed by the design team. Calculations would then be performed to scale the researched costs of various items to the appropriate values. Information such as the product volume would be instrumental in this phase in aiding the team to arrive at a unit cost for the concept. The results of these calculations would then be compared to the target cost set in the design objectives. If the calculations result in a cost that exceeds the target, then the design team would have to reexamine the design for manufacturing items in order to produce a more cost- effective concept. In the event that the calculations result in a cost that is no more than the target, then the concept would be able to proceed to the optimization stage. 16.7 Optimize Microeconomic Model With estimated product cost, demand, price and design parameters, we assemble them into an integrated model to predict profit based on various design parameters and price. By varying different price and design parameters, we alter the demand curve and attain maximum possible profit. This integrated model allows us to maximize profit, not only based on price and demand, but also designs parameters. 16.8 Select Optimal Design Solution This phase would involve further refinement of the engineering parameters that conflict between profits and engineering attributes. It should be observed that the purpose in performing this would be to obtain the best possible model based on predetermined vital product attributes. With a new set of optimized design parameters, a refined prototype is built for testing by the design team. The prototype is then handed to marketing group for reexamining and determines if it should be finalized or readjusted. If the design is approved by both design and marketing group, it will proceed to the final product design stage.

40

16.9 Develop Refined Design Prototype In this phase, a physical prototype would be created to test the functionality, reliability, ease of assembly to analyze the overall system design in a more rigorous manner. The new prototype with altered parameters would be compared with the earlier prototype to see if significant quality has been compromised due to profit optimization. Also, the physical prototype would allow us to determine if there are any important parameters unaccounted for. 16.10 Develop Marketing Demand Model The marketing demand model would then be developed to determine the best way to advertise our product, through direct sales force, or to Tier 1 or Tier 2 suppliers. 16.11 Review Product Design The refined product design from the previous stage would then be critically reviewed by the team. The emphasis of this review would be placed intensely on product functionality and cost; however, because this would be the last design review, greater emphasis would also be placed on addressing issues of value to the consumer. A revised QFD may be a valuable tool in enabling the team to quantitatively assess the overall design. If the results from the QFD are deemed unsatisfactory due to design for manufacturing items (i.e. design for assembly, design for disassembly, and design for maintenance), then the design team would have to revisit those phases as necessary. However, if the results from the QFD indicate that the concept is unsatisfactory due to consumer-valued issues, then the design team would have to consider an alternative design concept (see Section 7.2 “Alternative Design Concepts” section) or develop new concepts for analysis. Once again, this would require at least a partial iteration of all design phases leading up to the refined product design review (Appendix D). Nevertheless, if the QFD indicates that the model is satisfactory, then the concept would then proceed to the marketing phase. 16.12 Submit Final Product Design The final phase of the design process would be the actual delivery of the final design. This would involve the submission of a formal, detailed written report as well as other appropriate documents such as worksheets, plots, charts, and images. A final prototype of the refined concept would also be developed to illustrate the functionality of the product. Lastly, a formal slide presentation would accompany the written report for a high-level understanding of the product functionality

41

PRODUCT BROADER IMPACT 17. DESIGN FOR ENVIRONMENT To account for the environmental impact of our design, the following analysis is done with accordance with the United Nations Environmental Program’s PROMISE Manual http://www.unep.org. One of the major intentions of our design is to reduce tire use and improve fuel efficiency, environmental impact analysis is an essential part of justifying its use. 17.1 Material cycle/ Energy use/ Toxic emissions consideration Considering production and supply of all materials and components used in our design, it consists of two types of materials: Aluminum and Steel for the compressor, rotary joint, distribution block, air valves and steel reinforced air hoses; Rubber for the compressor and air hoses. Consider the beginning life cycle of metal usage, it depletes natural resources through mining, water acidification for metal processing, requiring power and chemicals to heat-treat metals; at the end of its life cycle, metal can be recycled for other uses. Toxic emission only occurs during metal processing and during recycling when metal is melted for reshaping. At the beginning of rubber’s lifecycle, latex is extracted from rubber trees and turned into rubber via chemical processing; alternatively, we may also use recovered or recycled rubber as well to minimize rubber extraction [9]. The environmental comes from power and heat required for chemical processing, as well as toxic waste emission during manufacturing process. At the end of its lifecycle, rubber is recycled and therefore causes minimal environmental impact [10]. As for the assembly process of our system, it only requires simple assembly of components via joints and air hoses, without additional metal processing or chemical treatments. The distribution of our products requires shipment of components to automobile OEM, thus requiring use of semi-trucks and depletion of petroleum. Due to the small volume of our components, shipments of components are highly efficient and require minimal number of shipments. During operation of our system, it utilizes electric power to drive compressor and solenoid valves. Since the system is designed to function fully automatically, the usage of such system impacts the environment positively. Since the tire is always properly inflated, it improves fuel efficiency and reduce tire use; thus reducing depletion of natural resources. Servicing the system may require special tools to replace or repair components such as compressor, air hose, or solenoid valves. Thus depletes additional natural resources to make those tools, and uses power used in the repairing process. At the end of the system’s life cycle, it will most likely be taken apart along with other components of the vehicle in a junk yard. The metal and rubber pieces will likely be recycled or reused, thus creating minimal environmental impact. To help improve the new concept development, we will also consider additional services that can be provided by our system, and thus increase the shared use of our system. To improve physical optimization, we attempt to increase reliability and durability, thus reducing servicing needs. Alternatively, we may also design for easy maintenance and repair to achieve the same goal of reducing servicing effort. To improve material selection, we chose recyclable materials and uses recycled materials (both metal and rubber); or reducing its use by narrowing hose diameter or relocating the position of the compressor such that the length of the hose can be shortened. To optimize production pollution problems, we may reduce production steps and reduce production waste. Due to the fact that the major production step is on simple assembly, the production of the rotary

42

joint will likely bring the most environmental impact. The rotary joint required may be produced by a casting process that requires high temperature sources, and other materials to assist in the casting process. To optimize distribution, we can lessen or use recyclable/reusable packing materials. We may pack the components in returnable buckets such that no packing material is wasted. However, such investment will require a larger initial investment to build a sturdy returning bucket for packing purposes. To improve end of life cycle, we can look into re-manufacturing/refurbishment of our product for new vehicles use. The compressor may be reused, and only new air hoses might be required for refurbishment. We may also look into safer incineration and design for disassembly. 18. REFLECTION OF PERSONAL VALUES IN THE FINAL DESIGN The members of our team have a strong passion to design with sound ethics and artistic expression. From concept generation through final design selection, we were determined to design a unique, dynamically-self-inflating tire system for passenger vehicles that successfully incorporated these aspects without infringing on previous ideas. The concept we chose not only showed the most promise in ensuring that our system would improve safety for vehicle passengers and decrease the impact on the environment by optimizing tire life and increasing fuel economy, but it minimized the impact of our design on the vehicle’s overall aesthetic appearance more than the other concepts. Since our system is largely obscured in the engine compartment and behind the wheels, there is not really a way to make our design artistic. However, since our system is incorporated on new vehicles, the artistic value of the vehicles aesthetics could have been affected by our design had we chosen a different concept/tube routing. Looking at Hummer H1 with an old version of Central Tire Inflation System (Figure 15), it is seen that the air tubing is visible from the wheel center to the air intake valve on the outer perimeter of the wheel. Though this degradation in the H1’s appearance is arguably acceptable when you consider that an H1 is intended to be mostly all utilitarian and not so much for show, this would likely not be the case on passenger vehicles, especially those sold with premium “rims.” In addition, when looking at the successful vehicles on the market today, it is seen that many of those are appear flashy with state-of-art design, like the Chrysler 300C. Thus, even though our system itself can not be meaningfully artistic and appealing (since it is not visible), the overall impact of our design favors the artistic value of the vehicle’s aesthetics since the air tubing and the compressor will be obscured. From an ethics standpoint, we designed our system with the intent to improve safety for vehicle passengers; reduce waste by preserving tires and optimizing tire life suggested by the tire manufacturers by keeping tires properly inflated and improving fuel economy. We also wanted to design an original air-channeling system that did not infringe on any patents, which we accomplished with the rotary joint. Thus, since our design is original; obscured from the vehicle’s exterior appearance; reduces vehicles’ impact on the environment; and improves the safety of it’s user; it fits well in the context of a “designed world,” with particular emphasis on artistic value and good ethics, which are the most important aspects of design to our team.

43

CONCLUSION 19. SUMMARY The dynamically-self-inflating tire system would be capable of succeeding as a new product in the automotive supplier industry. It specifically addresses the needs of the consumers by maintaining appropriate tire pressure conditions for:

• Reduced tire wear • Increased fuel economy • Increased overall vehicle safety

Because such a product does not currently exist for the majority of passenger vehicles, the market conditions would be favorable for the introduction of a self-inflating tire system. Through extensive engineering analysis, it has also been determined that the self-inflating tire system would actually function as desired. In particular, the product would be capable of:

• Providing sufficient airflow to the tire with minimal leakage • Withstanding the static and dynamic loading exerted on the rotary joints

Note that likewise, this system would not produce any negative dynamic effects (such as CV joint failure due to resonance) on surrounding systems. Most significantly, the self-inflating tire system would be a successful product because of its economic benefits to investors. Specifically, the final product would:

• Sell at about $900/unit, with total first year profit and sales of nearly $2.1 million and 58,000 units, respectively

• Experience 12% annual market growth each year for the first five years of the product, bringing total sales up to 370,000 units

• Break-even on the capital investment in just under three years For further development of this product, we recommend increasing the capability of the system by adding the following features:

• Pressure adjustment based on increasing vehicle speed • Pressure adjustment based on increasing vehicle load • Adaptability for recreational use (inflating rafts, sports balls, etc.) • Implementation of interactive display • Creation of universal design for aftermarket use

44

20. REFERENCES [1] Obringer, Lee Ann. “How Self-Inflating Tires Work.” Howstuffworks.com. Retrieved

September 30, 2006, from http://auto.howstuffworks.com/self-inflating-tire.htm [2] “Keep Your Tires at Proper Inflation.” Doran MFG LLC. Retrieved September 30,

2006, from http://www.doranmfg.com/industry_studies.htm. [3] “Tips for Tire Safety.” DentalPlans.com. 22 September 2006. Retrieved September

30, 2006, from http://www.dentalplans.com/articles/Tips%2520For%2520Tire%2520Safety.

[4] “Tire Pressure & Survey Results.” N.D. Retrieved September 30, 2006, from

http://www.nhtsa.dot.gov/cars/rules/rulings/TirePresFinal/FEA/TPMS3.html. [5] “Tires & Fuel Economy.” E-RoadStar.com: Driving the Information Highway. July

2005. Retrieved September 30, 2006, from http://www.roadstaronline.com. [6] “Tire Tech/General Tire Info” The Tire Rack: Online Performance Source. N.D.

Retrieved September 30, 2006, from http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1.

[7] Weissler, Paul. “Tire Maintenance.” Popular Mechanics. 2006. Retrieved September

30, 2006, from http://men.msn.com/articlepm.aspx?cp-documentid=850928. [8] “NPRM on TIRE PRESSURE MONITORING SYSTEM FMVSS No. 138.” US Dept.

of Transportation. Retrieved September 30, 2006, from http://www.nhtsa.dot.gov/cars/rules/rulings/TPMS_FMVSS_No138/.

[9] “Recycling Rubber” Retrieved September 30, 2006, from http://www.itdg.org/docs/technical_information_service/recycling_rubber.pdf [10] “Advantages of reclaiming and recovering rubber” Retrieved October 15, 2006,

from http://www.tve.org/ho/doc.cfm?aid=636 [11] “Siemens Building Technologies HVAC Products” Retrieved October 15, 2006, from

http://www.sbt.siemens.com/HVP/Components/Documentation/15370186.pdf

45

19. References (Continued) [12] Vella, Matt. "Best Small Cars for Fall." BusinessWeek Online. September 18, 2006.

Retrieved October 15, 2006, from http://www.businessweek.com/autos/content/sep2006/bw20060918_324180.htm?chan=autos_autos+index+page_news

[13] "United States Census 2000: Demographic Profiles: 1990 and 2000 Comparison

Tables." U.S. Census Bureau. June 17, 2002. Retrieved October 15, 2006, from http://www.census.gov/Press-Release/www/2002/dptables/2k00.xls [14] Inman, Daniel J. Engineering Vibration, 2nd. Ed. Upper Saddle River, NJ: Prentice Hall, 2001. [15] “Tire Ratings” Retrieved October 15, 2006, from http://autorepair.about.com/cs/generalinfo/l/bldef_760a.htm [16] “Tire Tech/General Tire Info” Retrieved October 15, 2006, from http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=7 [17] “Camry Tires” Retrieved October 15, 2006, from http://www.dragtimes.com/Toyota-Camry-Tires-m44-n191.html [18] Vella, Matt. "Best Small Cars for Fall." BusinessWeek Online. September 18, 2006.

Retrieved October 15, 2006, from http://www.businessweek.com/autos/content/sep2006/bw20060918_324180.htm?chan=autos_autos+index+page_news)

[19] "United States Census 2000: Demographic Profiles: 1990 and 2000 Comparison

Tables." U.S. Census Bureau. June 17, 2002. Retrieved October 15, 2006, from http://www.census.gov/Press-Release/www/2002/dptables/2k00.xls [20] “Calculating Gross Profit Margin” Retrieved October 22, 2006, from http://beginnersinvest.about.com/cs/investinglessons/l/blgrossmargin.htm [21] “Coast Distribution System Reports Operating Results for the 2006 Third Quarter”

Retrieved October 22, 2006, from http://www.theautochannel.com/news/2006/11/13/028410.html [22] “Steel vs. Aluminum: Cost Benefit Analysis” Retrieved October 22, 2006, from

http://www.ussautomotive.com/auto/steelvsal/hood.htm

46

19. References (Continued) [23] “200 Series “Hardmount” VIAIR Air Compressor” Retrieved October 22, 2006, from http://www.central4wd.com/inventorydetail.aspx?page=id%7C6802;folder%7C17

222 [24] “Portable Onboard Air Installation” Retrieved October 22, 2006, from http://www.4x4wire.com/tech/portable_oba/ [25] “Camry Overview” Retrieved October 27, 2006, from http://www.cars.com/carsapp/national?szc=02114&srv=parser&act=display&mkn

m=Toyota&mdnm=Camry&tf=/features/2002overview/toyota/camry.tmpl [26] “Buyer wants high-quality copper but high prices remain a burden” Retrieved

October 27, 2006, from http://www.purchasing.com/article/CA6376871.html?ref=nbcs [27] “American and British Wire Gauges” Retrieved October 27, 2006, from http://www.unc.edu/~rowlett/units/scales/wiregauge.html [28] ”Tire Sensors to Be Mandatory?” Retrieved October 27, 2006, from http://money.cnn.com/2005/04/06/Autos/tires.dj/ [29] “Why are my power bills so high? Which appliances use the most power?”

Retrieved October 27, 2006, from http://home.howstuffworks.com/question272.htm [30] “Kawasaki C-Controller” Retrieved November 4, 2006, from http://www.eterix.se/index.php?doc=6 [31] “MSL Steering Committee Meeting” Retrieved November 4, 2006, from http://msl1.mit.edu/msl/meeting_04161999/urbance.pdf [32] “The Official Dynamat Website” Retrieved November 4, 2006, from http://www.dynamat.com/index.html [33] Bureau of Labor Statistics. Retrieved November 4, 2006, from http://www.bls.gov/ [34] Kalpakjian, Serope and Steven R. Schmid. Manufacturing Engineering and

Technology, 4th Ed. Upper Saddle, NJ: Prentice Hall, 2001.

47

19. References (Continued) [35] “Industry Lease Rates Drop as Rent Concession Made – Real Estate Quarterly”

Retrieved November 4, 2006, from http://www.findarticles.com/p/articles/mi_m5072/is_3_24/ai_82323397 [36] “Current Inflation” Retrieved November 4, 2006, from http://inflationdata.com/Inflation/Inflation_Rate/CurrentInflation.asp

48

APPENDIX A: QFD

Customer Requirements Impo

rtan

ce

Impr

oved

Fue

l Effi

cien

cy

Set

Col

d Ti

re P

ress

ure

Max

imum

Pre

ssur

e

Hig

h Sp

eed

Pres

sure

Set

Con

ditio

n

Max

imum

Spe

ed

Min

imal

Mai

nten

ance

Req

s.

Aut

omat

ic S

yste

m

Man

ual O

verri

de

Min

imal

Vib

ratio

n

Min

imal

Noi

se

Low

Pro

duct

Cos

t

Inte

ract

ive

Dis

play

Min

imal

Vol

ume

Min

imal

Wei

ght

Min

imal

Pow

er C

onsu

mpt

ion

Acc

urat

e P

ress

ure

Sen

sing

Acc

urat

e Sp

eed

Sens

ing

Suf

ficie

nt H

igh

Spee

d Pr

ess.

Gra

dien

t

Suf

ficie

nt F

low

rate

Min

imal

Mai

nten

ance

Effo

rt

Cur

rent

Rat

ing

(1-5

)

Com

petit

or A

Rat

ing

(Wor

ld C

lass

)

Com

petit

or B

Rat

ing

(1-5

)

Targ

et R

atin

g (1

-5)

Rat

io o

f Im

prov

emen

t

Sale

s Po

int

Abs

olut

e W

eigh

t

Rel

ativ

e W

eigh

t, %

Save Money on Gas 10 9 1 1 9 1 1 1 3 3 3 3 1 9 2 5 3 5 2.5 1.5 38 0.224

Improve Tire Wear 9 9 9 1 1 1 3 9 1 1 3 4 4.0 1.5 54 0.323

Tires Don't Blow Out 7 9 9 1 9 3 1 3 9 3 3 3 1 1 3 4 4.0 1.5 42 0.251

Auto-Deployment @ High Speeds 9 9 3 3 9 3 1 9 1 3 1 3 3 3 9 3 1 2 3 3 5 2.5 1.5 34 0.202

Works at Extreme Speeds 5 9 9 9 3 9 3 1 3 3 3 3 3 1 1 3 3

Reliable 8 3 1 1 1 9 9 9 1 3 9 3 3 3 9

Easy to Use 8 3 9 9 9 9

Control Over System 4 3 9 9 9 1

Smooth Ride 5 9 1 3 3 9 3 3 3

Quiet 5 1 3 9 9

Environmentally-Friendly 4 9 3 1 3 3

Inexpensive 9 9 9 9 1 9 3 1 3 1 3 3 3

Knows System Works 7 9 3 1 1 9

Visual Aesthetics 7 9 9

Easy to Repair 6 9 3 1 1 1 9

% psi psi mph mph #/yr. n/a n/a Hz dB $ n/a in3lbf A psi mph psi/mphin3/min min

Absolute Weight 396 312 224 166 152 351 394 265 120 82 159 361 120 105 93 197 135 316 63 2340.093 0.073 0.053 0.039 0.036 0.083 0.093 0.062 0.028 0.019 0.037 0.085 0.028 0.025 0.022 0.046 0.032 0.074 0.015 0.055

Importance Ranking 1 6 9 11 13 4 2 7 15 18 12 3 15 16 17 10 14 5 19 8

Competitor A Value (World Class)Target Value 8 30 44 65 149 2 40 750 5 2.5 .01P .01V 0.17 12 15

Measurement Unit

Current Value

Relative Weight

Engineering Characteristics

RelationshipsStrong Positive Medium Positive Medium Negative Strong Negative

Relationships9 Strongly Related3 Somewhat Related1 Weakly Related_ Unrelated

49

APPENDIX B: Pugh Chart

Design Criteria Wei

ght

Cen

tral

ized

Com

pres

sor S

yste

m

Self

Act

uate

d A

ir Pu

mps

on

Whe

els

Mag

netic

ally

Act

uate

d Ti

re P

rofil

e

Expa

ndab

le W

heel

Spo

kes

Hig

h Pr

essu

re R

eser

voirs

Dyn

amic

ally

Adj

usta

ble

Toe-

In A

lignm

ent

Ther

moe

lect

ric H

eatin

g/C

oolin

g D

evic

es

Improved Fuel Efficiency 10 +1 +1 0 +1 +1 +1 +1Set Cold Tire Pressure 9 +2 +2 +2 +2 +2 +2 +2Limit Maximum Pressure 9 +1 0 0 (N/A) +2 +1 0 (N/A) +2High Speed Pressure Set Condition 9 +1 0 0 (N/A) 0 0 0 (N/A) 0High Speed Functionality 5 +1 +1 +1 +1 +1 +1 +1Minimal Maintenance Req. 8 0 +1 +1 +1 -1 +1 +1Automatic System 8 +2 +2 +2 +2 +2 +2 +2Manual Override 4 +1 -1 +1 +1 0 +1 +1Minimal Vibration 5 +1 +1 -1 -1 +1 +2 +2Minimal Noise 5 +1 +1 -1 -1 +1 +1 +2Low Product Cost 9 -1 -1 0 0 +1 -1 -1Interactive Display 7 +1 -1 +1 +1 -1 -1 0Minimal Volume 7 +1 0 +2 +2 +1 +2 0Minimal Weight 6 +2 0 +2 +1 +1 +2 0Minimal Power Consumption 7 0 +2 0 0 +2 0 0Accurate Pressure Sensing 9 +1 0 0 (N/A) 0 0 0 (N/A) -1Accurate Speed Sensing 8 +1 +2 0 0 +2 0 0Sufficent High Speed Press. Gradient 8 +1 +1 0 (N/A) +1 +1 0 (N/A) +1Sufficient Flowrate 7 +1 +2 0 (N/A) +1 +1 0 (N/A) 0Minimal Maintenance Effort 8 0 0 +2 0 -1 +1 0Good Visual Aesthetics 8 +1 0 +1 +1 +1 +2 +1

+ 155 119 108 129 143 126 1150 3 7 9 6 3 7 8- 9 20 10 10 23 16 18

Total Score 146 99 98 119 120 110 97

50

APPENDIX C: Benchmarking of Existing Solutions (Commercial and Patents)

Patent 4924926 CTIS system

Patent 6691754 Electromagnetic pump

Patent 5846354 Micromechanical

pump

Patent 5558730 Centrifugal Pump

Patent 5355924 High Pressure Reservoir

Patent 5119856 Heating Element

inside Tire

Patent 49922984 Route Hoses inflation

Commercial Production Yes No No No No No NoCost Low High High High Low High High

Indication Light Yes Possible Possible Unlikely Unlikely Possibly UnlikelyManual Override of system Yes Possible Possible Unlikely Unlikely Unlikely Unlikely

Allow tire to run flat Yes Possible Possible Unlikely Unlikely Unlikely Unlikely

Tire pressure selection for various conditions Yes Possible Possible Unlikely Unlikely Possibly Unlikely

Power source Electromagnet Mechanical Centrifugal force High Pressure Thermal Electric Compression

Air pressure source Air-Brakes/ Air Pump Air pump on rim Air Pump on rim Air pump on rim High Pressure

Reservoir Expansion of gas Compression of route hose

Centralized/Decentralized system

Decentralized/ Centralized Decentralized Decnetralized Decentralized Decentralized Decentralized Decentralized

Route Hoses Yes No No No No No Yes

Refill gas into tire Yes Yes Yes Yes Yes No No

Routine Maintenance No No No No Yes Yes No

Modification to current tire design No No No Yes No Yes Yes

Special Features Programmable, Tire leak detection

Electromagnetic driven pump Mechanical air pump

Utilize centrifugal pump to pump air into tire via springs

Utilize high pressure reservoir to fill up tire

Utilize heat to increase tire pressure

Compresses hoses to pump pressure

into tire

g g

51

APPENDIX D: Design Process

52

APPENDIX E: Rotary Joint Vibration Analysis – Resonance Analysis Assumptions: 1. Shaft (CV joint shaft) can be modeled as a solid steel cylinder with the approximate dimensions above. 2. Rotating portion of spacer can be modeled as a "rotating disk" with the approximate dimensions shown above. 3. Vehicle (and hence tire) speeds cannot exceed 150 mph. 4. The tires can be modeled as P205/65/15 tires for the Toyota Camry. System Constants System Variables

E (kpsi) 3.00E+04 r1 (in) 1.23 g (ft/s2) 32.2 r2 (in) 1.58

r3 (in) 2.27 System Parameters r4 (in) 2.40

dshaft (in) 0.75 Vdisk (in3) 6.9 Ashaft (in2) 0.44 m (lbf*s2/ft) 0.02 lshaft (in) 18

ρ (lbf/in3) 0.098 System Outputs k (lbf/in) 7.36E+05 ωcrit (rpm) 195883.70 ro,disk (in) 2.46 ri,disk (in) 0.77 System Output Constraints

ro,chamber (in) 2.20 Vtire (mph) 150 ri,chamber (in) 1.81 wtire (mm) 205 rcouple (in) 1.07 drim (in) 15

t (in) 0.591 rtire (in) 12.75 ddisk (in) 0.394 ωtire (rpm) 1977.88

h (in) 0.394 System Output Constraint Equation ωtire<ωcrit or equivalently 0<(gk)/(ρπ{(ro,disk

2-ri,disk2)t-[(r2

2-r12)+(r4

2-r32)+(ro,chamber

2-ri,chamber2)]ddisk+(rcouple

2-ri,disk2)h})-ωtire

Equations Used to Calculate System Parameters Ashaft=(π/4)dshaft

2 k=EAshaft/lshaft

Vdisk=π{(ro,disk2-ri,disk

2)t-[(r22-r1

2)+(r42-r3

2)+(ro,chamber2-ri,chamber

2)]ddisk+(rcouple2-ri,disk

2)h} m=(ρVdisk)/g ωcrit = (k/m)1/2

rtire=0.65wtire+(1/2)drim ωtire=Vtire/rtire

53

APPENDIX F: Rotary Joint Vibration Analysis – Mass Eccentricity Analysis Assumptions: 1. Shaft (CV joint shaft) can be modeled as a solid steel cylinder with the approximate dimensions above. 2. Rotating portion of spacer can be modeled as a "rotating disk" with the approximate dimensions shown above.3. Vehicle (and hence tire) speeds cannot exceed 150 mph. 4. The tires can be modeled as P205/65/15 tires for the Toyota Camry.

System Output Constraints System Parameters Vtire (mph) 150 ζ 0.8 ro,e (in) 0.354 wtire (mm) 205 dshaft (in) 0.75 ri,e (in) 0.236 drim (in) 15 Ashaft (in2) 0.44 t (in) 0.591 rtire (in) 12.75 lshaft (in) 18 ddisk (in) 0.394

ωtire (rpm) 1977.88 ρ (lbf/in3) 0.098 h (in) 0.394 R 0.0101 k (lbf/in) 7.36E+05 he (in) 0.394

X (in) 0.0394 ro,disk (in) 2.46 e (in) 2.01 ri,disk (in) 0.77 Ve (in3) 0.086

System Variables ro,chamber (in) 2.20 me (lbf*s2/ft) 2.63E-04 r1 (in) 1.23 ri,chamber (in) 1.81 r2 (in) 1.58 rcouple (in) 1.07 r3 (in) 2.27 r4 (in) 2.40 System Outputs System Constants

Vdisk (in3) 6.9 ωcrit (rpm) 195883.70 Eshaft (kpsi) 3.00E+04 m (lbf*s2/ft) 0.02 Xdisk (in) 2.56E-06 g (ft/s2) 32.2

System Output Constraint Equation 0<[(mee/m)(R2/((1-R2)2+(2ζR)2)1/2))]-X Equations Used to Calculate System Parameters Ashaft=(π/4)dshaft

2 k=EAshaft/lshaft

Vdisk=π{(ro,disk2-ri,disk

2)t-[(r22-r1

2)+(r42-r3

2)+(ro,chamber2-ri,chamber

2)]ddisk+(rcouple2-ri,disk

2)h}Ve=π(ro,e

2-ri,e2)he

m=(ρVdisk)/g me=(ρVe)/g ωcrit = (k/m)1/2

Xdisk=(mee/m)(R2/((1-R2)2+(2ζR)2)1/2)) rtire=0.65wtire+(1/2)drim ωtire=Vtire/rtire

R=ωtire/ωcrit

54

APPENDIX G: Flow Rate Analysis Through the compressor Assumptions: Adiabatic Compressor, Ideal gas Outlet temperature Zero inlet velocity Pipe (Air hose) size 3/8" 0.00953m C_p 1.004 kJ/kg-K w 10 kJ/kg Air State 1 State 2 T1 298 k T2 320 k P1 14.69594 psi P2 35 psi 1 atm h1-h2= C_p (T1 - T2) -22.088 kJ/kg Thermodynamic First Law V2= sqrt [ 2 * -w * (h1-h2) ] V2 21.018 m/s Flow Rate (Q) = Area x Velocity Q 0.00599 m3/s 761.6065 ft3/hr

55

APPENDIX H: Air Valve Analysis Pressure Drop For Steam No air leaks (Oversize by 25% to cover leakage) Initial P Pressure Drop Pipe (Air hose) size = 3/8" 15 psi 5 psi G 1 50 psi 7.5 psi T 116.33 F 100 psi 10 psi 320 k Over 100 psi 10% of line pressure P1 35 psi P2 40 psi C_v Liquids Q sqrt (S/P) C_v Gas Q sqrt(G(T+460)) P2>1/2 P1 Low P C_v 0.150308 1360 sqrt(ΔP*P2) Q sqrt(G(T+460)) P2< 1/2P1 High P C_v 0.791506 660 P1 T in Farhenheit, Q in scfh (cubic feet per hour at 14.7 psig and 60 degrees farhenheit) Change in pressure - psi at maximum flow P1, P2 Pressure at maximum flow, psia (abs) G specific gravity of gas relative to air at 14.7 psig and 60 degrees farenheit

56

APPENDIX I: Rotary Joint Design Optimization

57

APPENDIX J: Programming Script for OOPic Automated Electronic Control ' Declarations Dim Volts As New oA2D 'Pressure Sensor Voltage Dim Motor As New oPWM 'Compressor Control (DC Motor control) Dim IntitialAir As New oByte 'Variable for initial voltage before adding air Dim FinalAir As New oByte 'Variable for final voltage after air is added Dim InValve As New oDIO1 'Inlet Solenoid valve Dim OutValve As New oDIO1 'Outlet Solenoid valve Dim Screen As New oSerial 'Output to monitor ' Main Program Sub Main () ' Activate DC Compressor Motor, Pressure Sensor, and Solenoid Valve Motor.IOLine = 17 'DC Compressor Motor on pin 17 Motor.Operate = 1 'DC Compressor Motor power on Volts.IOLine = 1 'Pressure Sensor on pin 1 Volts.Operate = 1 'Pressure Sensor active InValve.IOLine = 8 'Inlet Solenoid Valve on pin 8 InValve.Direction = cvOutput OutValve.IOLine = 9 'Outlet Solenoid Valve on pin 9 OutValve.Direction = cvOutput Initial = Volts 'Store top pressure value Screen.Baud = cv9600 Screen.Operate = cvTrue ' Step 1: Take Initial Tire Pressure Sensor Reading Do While Volts < 105 Motor = 255 'Motor runs when pressure sensor is low InValve = 1 'Inlet Valve is opened during inflation OutValve = 0 'Outlet Valve is closed during process Loop Motor = 125 'Motor turns off when voltage > 125 FinalAir = Volts.Value 'Final voltage from pressure sensor 'Display Final Pressure Value onto monitor Screen.String = "Initial Volume: " + Str$(FinalAir) Screen.Value = 13 Screen.Value = 10 ' Step 2: Release excess pressure Do While Volts > 205 InValve = 0 'Inlet Valve is opened during inflation OutValve = 1 'Outlet Valve is closed during process 'Display final pressure of tire onto monitor Screen.String = "Final Volume: " + Str$(FinalAir) Screen.Value = 13 Screen.Value = 10 Do Loop Until Volts = Initial Motor = 125 End Sub

58

APPENDIX K: Variable Cost Estimation

59

APPENDIX L: Fixed Cost Estimation

Initial Development

Product Design Personnel Rate ($/hr) Labor (hrs) Cost

Engineering 10 $ 35.00 320 $ 112,000.00 Industrial Design 5 $ 35.00 120 $ 21,000.00 Marketing 5 $ 35.00 240 $ 42,000.00

Mfg. Process Development Cost Equipment (10 Mach Ctr @ $500K) $ 5,000,000.00

(10 Die-Cast Machines @ $55K) $ 550,000.00 (10 Transfer Mach.@ $150K) $ 1,500,000.00

(10 Robots @ $45K) $ 450,000.00 Setup (4 tech., 80 hrs @ $30/hr) $ 9,600.00 Factory Furnishing $ 2,000,000.00 Backup Components $ 375,000.00

Initial Tooling Cost

Design (10 Tool Dies @ $15K) $ 150,000.00 Parts (Miscell.) $ 4,000.00

Testing Personnel Rate ($/hr) Labor (hrs) Cost

Safety 2 $ 25.00 32 $ 1,600.00 Durability 4 $ 35.00 80 $ 11,200.00 Operating Costs

Employees Personnel Rate ($/hr) Labor (hrs) Cost

Line Workers 100 $ 15.00 3840 $ 5,760,000.00 Marketing/Sales 20 $ 35.00 1920 $ 1,344,000.00 Cleaning/Maintenance 60 $ 15.00 1920 $ 1,728,000.00 Plant/Operation/Facility Managers 3 $ 65.00 1920 $ 374,400.00 Quality/Process/Maint. ng/Mat'ls/Supervisors 15 $ 35.00 1920 $ 1,008,000.00

Administrative Costs

Rent (100,000 sq ft. @ $0.50/sq ft.) $ 600,000.00 Utilities $ 72,000.00 Employee Insurance/Benefits Health) $ 2,042,880.00 (Pension Plan) $ 510,720.00 (401K Matching) $ 817,152.00 (Life) $ 306,432.00 Business Insurance (Property Insurance) $ 531,930.00 (Power Outage/Downtime) $ 468,070.00 TOTAL FIXED COST ($/yr) $ 15,563,584.00

60

APPENDIX M: Volume Estimation Total US Vehicle Sales 1.7.E+07 Potential Users (%) 50 No. of Potential Users 8.5.E+06 Interested Users (%) 10 Projected Annual Volume (units) 8.5.E+05 Assumptions: In 2005, 17,000,000 new vehicles were sold in the US (Vella). Using Results from the 2000 Census (United States Census 2000): We assume that households that have an annual income of $15,000 or more will potentially buy these new vehicles (United States Census 2000). Therefore, of the 100% of households, 84.2% of them will potentially buy a new vehicle: However, with our assumption that only mid-level or above cars will potentially be sold have this system, the households that would potentially purchase such a vehicle will have an annual income of $50,000 or more: Thus, based on the 2000 Census, 42% of households have an income of $50,000 or more.

Therefore, the fraction of households in the United States that would potentially purchase a new mid-level or greater passenger vehicle is 42/84.2 = .49 Thus, 0.49881235*17,000,000 = 8,479,810 new vehicles that are sold in a year are mid-level or greater. Assuming that 10% of the this population would be interested in a dynamically-self-inflating tire system, the potential annual market for our system is 847,981 units/vehicles.

61

APPENDIX N: Profit Optimization

Profit Optimization Objective: Value Units Maximize Profit: Π -14811426 $ Where: Π=R-C Parameters: Value Units θ 106250 units λp -196 units/$ λdB -10 units/dB λlb -20 units/lb Cv 417 $/unit Cf 15563584 $ ΔαdB 20 dB Δαlb -7 lb

Q 12154 units Q=θ-λpP+λdBΔαdB +λlbΔαlb

R 5819526 $ R=QP C 20630953 $ C=CvQ+Cf Variables Value Units P 479 $ Sound 80 dB Weight 5 lb Constraints:

80 Sound-80 dB <0 15 15 db-Sound <0 55 Weight-55 lb <0 5 5 lb -Weight<0

Assumptions: 1. Design elasticity for sound is 5% of price elasticity 2. Design elasticity for compressor weight is 10% of price elasticity 3. "Base" model of inflation system produces 60 dB noise and has compressor weight of 12 lbs (Used to find Δα)

62

APPENDIX O: Refined Profit Optimization

Refined Profit Optimization Attribute Information Final Product Weight Specification Part Worth Splines Level 5 25 55 Weight 5 0.47238Est. Beta 0.47238 0.24341 -0.71579 Sound 32.25789737 1.104521597 Price 900 -0.82537Sound Level 15 60 90 Utility "v" % Market Selection Est. Beta 1.46136 0.10511 -1.56647 Final Product 0.751531597 0.543879726 No Choice 0.57556 0.456120274Price Level 400 650 900 Market Size Est. Beta 0.66659 0.15878 -0.82537

Total Consumers 8500000

Qm 57787 Variable and Fixed Costs

Cv $ 594 Profitability

Cf $ 15,563,584 Revenue $ 52,008,499 Costs $ 49,886,696 Constraints Profit $ 2,121,803 Min Max Weight 5 55 Sound 15 80 Price 400 900 Variables Weight 5 lbf Sound 32 dB ΔSound* -28 dB *Not TRUE variable; only used for Cv, which is cost for CHANGE in sound

63

APPENDIX P: NPV/Breakeven Analysis

NPV/Breakeven Analysis Annual Demand Annual Revenue Q1 (units) 57787 R1 ($/yr) $52,008,498.79 Q2 (units) 64722 R2 ($/yr) $58,249,518.65 Q3 (units) 72488 R3 ($/yr) $65,239,460.88 Q4 (units) 81187 R4 ($/yr) $73,068,196.19 Q5 (units) 90929 R5 ($/yr) $81,836,379.73 Annual Variable Cost Annual Profit Cv1 ($/yr) $ 34,323,112.22 Π1 ($/yr) $ 2,121,803 Cv2 ($/yr) $ 38,441,885.68 Π2 ($/yr) $ 4,244,049 Cv3 ($/yr) $ 43,054,911.96 Π3 ($/yr) $ 6,620,965 Cv4 ($/yr) $ 48,221,501.40 Π4 ($/yr) $ 9,283,111 Cv5 ($/yr) $ 54,008,081.57 Π5($/yr) $ 12,264,714 NPV Ccap ($) $ 10,226,400 rint (%) 3.50 rinf (%) 1.31 rnet (%) 2.19 NPV ($) $ 31,862,969 Σ(Π/(1+rnet/100)n) 1<n<5 Assumptions: 1. Interest rate estimated based on inflation data/research 2. Inflation rate based on data for October 2006 3. Market growth of 12% each year