fsae engine modifications team #17 - dalhousie...
TRANSCRIPT
1
MECH 4010 & 4015
Design Project II
Requirement Verification Report
FSAE Engine Modifications
Team #17
Whitney Hurlbut
Kirk Fraser
Emerson Hawkins
Saad Mohamed
Greg Fitzpatrick
Submitted April 8th, 2014
to
Dr. Clifton Johnston
Table of Contents 1 Design Requirements ................................................................................................................................................... 3 2 Testing and Verification .............................................................................................................................................. 3
2.1 Static Testing .......................................................................................................................................................... 3 2.1.1 Weight ............................................................................................................................................................. 4 2.1.2 Crankshaft Vibration Analysis ............................................................................................................... 5
2.2 Dynamic Testing ................................................................................................................................................... 7 2.2.1 Horsepower & Torque .............................................................................................................................. 7 2.2.2 Throttle Response .................................................................................................................................... 10 2.2.3 Acceleration ................................................................................................................................................ 10 2.2.4 Completed .................................................................................................................................................... 11 2.2.5 Incomplete ................................................................................................................................................... 11
Appendix A ............................................................................................................................................................................... 13
List of Figures Figure 1: Crankshaft being weighed on lab scale ....................................................................................................... 4 Figure 2: Summary of weight testing results ............................................................................................................... 5 Figure 3: Crankshaft torsional vibration diagram (Huneycutt, 2013) .............................................................. 6 Figure 4: Design team engine Dyno testing .................................................................................................................. 8 Figure 5: Engine #1 Dyno horsepower curve .............................................................................................................. 9 Figure 6: Engine #1 Dyno torque curve ......................................................................................................................... 9 Figure 7: Dalhousie FSAE car during fall term acceleration testing ................................................................. 10
3
1 Introduction
This report serves to provide a brief background to the testing and overall results of the 2014
Dalhousie Formula SAE Engine Internals Group (EIG) project. For complete details, discussion and
results please see the 2014 Winter Design Report.
2 Design Requirements
The modified engine design shall meet all rules as outlined by the 2014 Formula SAE® Rulebook;
the following are the main outcome requirements of the project:
1. Shall increase the throttle response of the engine by 10% from a baseline number of 0.427s seconds.
2. Should increase the output torque of the engine by 5% from a baseline number of 53.7 Nm.
3. Should increase the overall horsepower output of the engine by 5% from a baseline number
of 70.5 hp.
4. Shall decrease a 75 m acceleration time by 5% from a baseline of 4.797 seconds.
5. Shall decrease the overall combined mass of the crankshaft, flywheel and gearbox by 5% from a baseline number of 10.87 kg
6. The crankshaft and flywheel shall be balanced to ±0.5 g to minimize vibration.
For complete team requirements and specifications please see Appendix A.
3 Testing and Verification
In order to verify the modifications to the engine components would satisfy the EIG requirements,
they were subject to two types of testing plans – static and dynamic. Sections 3.1 and 3.2 detail the
static and dynamic testing performed.
3.1 Static Testing
For static testing, the engine internals were weighed and the effects on rotational mass before and
after modifications were analyzed. In addition, a vibration analysis was performed on the
4
crankshaft as it is the heaviest and fastest rotating component in the engine. The EIG wanted to
ensure no additional vibration effects were introduced with the modifications.
3.1.1 Weight
The weight component of static testing encompasses much more than just the measured weight in
kilograms of each modified component. All the modified components in the engine are designed to
rotate at high speeds, specifically the crankshaft and flywheel, for this reason their moment of
inertia is crucial. The larger an object’s moment of inertia, the more resistance it will have to
changes in angular velocity. Decreasing the moment of inertia by strategically removing mass in
these high-speed components will yield a larger increase in engine output power than simply
removing static mass. For the purpose of this project, the moment of inertia is theoretically
calculated.
Figure 1: Crankshaft being weighed on lab scale
The modifications can also be compared by their equivalent mass, this is a term used often in
industry to equate the difference between a static objects weight on a piece of machinery and a
dynamic object’s weight on a piece of machinery. The equivalent mass is directly proportional to
the mass of the object and is theoretically calculated.
5
Lastly, the power requirement directly relates to the amount power required to drive an object of a
certain mass and geometry. Reducing this power increases the power available to go to the wheels.
This value is theoretically calculated and is directly proportional to the moment of inertia.
Figure 2: Summary of weight testing results
3.1.2 Crankshaft Vibration Analysis
The crankshaft torsional and resonant vibration tests are described in the following sections.
3.1.2.1 Torsional Vibration
There are two forms of vibration that can manifest within the crankshaft. The first being torsional
vibration. Torsional vibration is an expected response when operating a crankshaft at high RPMs.
The vibration creates a positive and negative deflection in the crankshaft; positive deflection
matching the primary direction of rotation for the crankshaft. The negative deflection is between 6-
8% of the positive deflection. The oscillation between the negative and positive deflection is the
vibration from the crankshaft that can be detected by the driver. See Figure 3 for a detailed diagram
of the expected deflection on the crankshaft.
6
Figure 3: Crankshaft torsional vibration diagram (Huneycutt, 2013)
The negative deflection is too small in magnitude to ever cause failure within the system as it is
directly correlated to the positive deflection, hence any failure in the part will be from an excessive
moment on the crankshaft. The planned modifications to the crankshaft will not directly affect the
strength of the member, since the mass being removed is only coming from the lobes of the
crankshaft. It is also important to note that the crankshaft was designed to withstand torque from a
stock street motorcycle, which operates at 1.3 times the horsepower that the Formula SAE
restricted engine is capable of producing.
Lastly this research concluded that as the engine is optimized, the increased torque acting on the
crankshaft (which will have a reduced over all weight) will produce a proportional increase in
vibration. This will only effect how smooth the low-end (low RPM) drive is, which is not a primary
concern when designing a car for a high-speed racing environment.
Collecting data for torsional vibration also presents some complications, primarily is the safety
concern that the engine must be running while collecting data. Secondly, it is the hardware
complications, most sensors are magnetic, but the engine block is made of aluminum. The sensors
could be attached with wax, but it would melt as soon as the engine warmed up. Lastly, the sensors
have a limited safe temperature range that they can operate within; therefore special sensors
would be required. For this reason, the team decided not to collect experimental data for torsional
vibration, but rely firmly after extensive research that it will not be the source of any malfunction
within the engine.
7
3.1.2.2 Resonant Vibration
The resonant frequencies of high-speed parts are always an area of concern. There are several
published reports on the vibration of crankshafts within gasoline internal combustion engines; all
agree that the lobes are the primary location that vibration will occur. The measured deflection
from vibration increases when approaching the furthest edges of the lobes. As the lobes are the
locations where the design team plans to remove mass, it will in-fact reduce vibration.
It is important to evaluate the primary resonant frequency of the modified and unmodified
crankshaft with respect to the operating frequency of the car. This can be done theoretically using
SolidWorks and also experimentally following the procedure for an industry standard bump test.
These results (Table 1) are compared to ensure validity and then compared against the operating
frequency of the car, which can be calculated using the max engine rpm.
Table 1: Results of crankshaft vibration testing
Frequency: Unmodified Crankshaft:
Modified Crankshaft:
Unit: Percent
Increase:
Experimental Resonant Frequency Trial 1: 2126 2494 Hz 15%
Experimental Resonant Frequency Trial 2: 2124 2333 Hz 9%
Experimental Resonant Frequency Trial 3: 2121 2484 Hz 15%
Experimental Resonant Frequency Trial 4: 2131 2491 Hz 14%
Theoretical Resonant Frequency: 4412 4678 Hz 6%
3.2 Dynamic Testing
In order to measure the performance gains of the engine, many different dynamic tests were
performed. These tests included dynamometer testing and road testing of the car.
3.2.1 Horsepower & Torque
To test and verify the requirements of increased torque and horsepower, the engine was tested
using an engine dynamometer (hereafter referred to as a ‘dyno’). The Dalhousie Mechanical
Engineering Department has a PowerDyne Engine Dynamometer that was used to execute these
tests and relay engine performance data. Using this eddy current dyno, the data acquisition (DAQ)
system returns engine torque and horsepower at a given engine speed. The majority of the engine
8
tuning and testing was done in second gear because with this gear ratio the dyno is the most
accurate for the given engine speeds. Testing using the dyno was supervised by a faculty member
at all times. The design team is shown in Figure 4 during engine dyno testing.
Figure 4: Design team engine Dyno testing
The results for testing from Engine #1 for horsepower and torque are shown in Figure 5 and Figure
6 on the next page.
9
Figure 5: Engine #1 Dyno horsepower curve
Figure 6: Engine #1 Dyno torque curve
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
2000 4000 6000 8000 10000 12000 14000
Pow
er (
HP
)
Engine Speed (RPM)
Design Project Horsepower
#1 Baseline Nov24/13
30.0
35.0
40.0
45.0
50.0
55.0
2000 4000 6000 8000 10000 12000 14000
Torq
ue
(Nm
)
Engine Speed (RPM)
Design Project Torque
#1 Baseline Nov24/13
10
3.2.2 Throttle Response
The throttle response was measured using the vehicle’s onboard engine control unit (ECU), a
MoTeC m400, to trace engine speed (in RPM) versus the throttle position (% open). This data
acquisition was done by performing a step input on throttle position, and comparing the delay-time
until the RPM peaked. The data collected from the ECU was analyzed using MoTeC i2 software
where graphs can be easily made and interpreted. This test was done in first gear because the gear
ratios were the same for first on both gear sets causing the same inertia from the output sprocket.
3.2.3 Acceleration
The only method that the acceleration of the Formula SAE car can be accurately tested is by
physically test-driving the car. Test-driving will verify the requirement of improving the vehicle’s
acceleration, which will improve the team’s standings during the SAE competition’s Acceleration,
Autocross and Endurance events. Test-driving involves towing the vehicle to a pre-approved
parking lot (Figure 7), setting up a coned-off course and running the events as accurately as
possible to replicate the competition. Just as for the dyno tests, faculty supervision is required. In
addition, team members with fire extinguishers are placed accordingly around the event area.
The test relies completely on the time of the event and comparing to the baseline time. The time
difference between the stock engine and the modified engine determines the improvement in
acceleration. During these tests, the ECU data is also recording engine RPM and throttle position.
This can be used to analyse the test farther and verify throttle response in a different situation.
Figure 7: Dalhousie FSAE car during fall term acceleration testing
11
3.2.4 Completed Requirements
While not all requirements were met, the design team was still able to meet the requirements set
out that did not require extended run-time of a rebuilt engine.
Of the main requirements, the EIG completed the following:
Shall decrease the overall combined mass of the crankshaft, flywheel and gearbox by 5% from a baseline number of 10.886 kilograms.
The crankshaft and flywheel shall be balanced to ±0.5 g to minimize vibration.
For the first requirement, the combined mass of the crankshaft, flywheel and gearbox was
successfully reduced by 5%. The final weight reduction achieved was 11.99%, bringing the total
weight of the system to 9.580 kilograms.
The second requirement to have the crankshaft and flywheel balanced to ±0.5 g was also
accomplished. After removing the specified amount of material from each piece, they were then
brought to Nova Automotive in Dartmouth to be balanced. Nova successfully balanced both the
crankshaft and flywheel to within 0.1 g.
3.2.5 Incomplete Requirements
The incomplete requirements for this project were ones that required a fully functioning engine to
be running for an extended period of time in order to obtain the appropriate data. After performing
three engine rebuilds, the design team was unable to produce a functioning engine that could be
tested to meet the performance requirements sought out for the engine. After extensive
investigation the reason for the engine failures was not due to the engineered modifications of the
engine components, but rather the inexperience of the team to successfully rebuild an engine.
The list of incomplete requirements is:
Shall increase the throttle response of the engine by 10% from a baseline number of 0.427s seconds. (Incomplete)
Should increase the peak output torque of the engine by 5% from a baseline number of 53.7
Nm. (Incomplete)
Should increase the peak horsepower of the engine by 5% from a baseline number of 70.5 hp. (Incomplete)
12
Shall decrease a 75 m acceleration time by 5% from a baseline of 4.797 seconds.
(Incomplete)
As stated, the reason the team could not claim to have met these requirements is because two
rebuilt engines with the modified components were unable to be tested due to other component
failures. In the testing plan, the throttle response and acceleration were intended to be tested on
the engine after engine tuning was completed. Since the project was never able to complete the
tuning stage before the engine failure, throttle response and vehicle acceleration were never tested.
13
Appendix A
Done Component Type Requirement
x Torque Performance 5% increase from baseline
Horsepower Performance 5% increase from baseline
x Throttle response Performance 10% increase from baseline
x Acceleration time Performance 5% increase from baseline
Internal rotating mass Weight 5% decrease overall from baseline
Crankshaft Balancing Shall be balanced within ±0.5 g for
vibration
Flywheel Balancing Shall be balanced within ±0.5 g for
vibration
Crankshaft Dimensions Shall fit inside the stock crankcase
Crankshaft/Clutch Dimensions 0 tolerance on gear misalignment
Transmission shafts Dimensions Maintain OEM dimensions for installation
Transmission shafts Dimensions 0 tolerance on gear misalignment
Top Speed Performance Choose desired top speed for gear ratios
Shift Drum Functionality Should not allow shift into removed gears
Torque Measurement Obtain baseline and final values
Horsepower Measurement Obtain baseline and final values
x Throttle response Measurement Obtain baseline and final values
x Acceleration time Measurement Obtain baseline and final values
Crankshaft Modeling A detailed CAD model should be made
Flywheel Modeling A detailed CAD model should be made
Transmission shafts Modeling A detailed CAD model should be made