hydraulic regenerative barking system

Chapter 1

Introduction

1.1 Background

A group of students senior to us worked on a system that can generate power using

weight force. Their work served as an inspiration, initially it was decided to

improve their work. Due to the some shortcomings the project turned out to be

very difficult to pursue, hence we had to look for something else in the same

bracket of energy recovery. This quest finally led us to the idea of “Hydraulic

Regenerative Braking” or “Hydraulic Hybrid” (as compared to Electric Hybrid).

Discussion of motion is incomplete without considering Friction. Friction if

unintentional can cause big loss of energy like in case of contacting surfaces where

it is highly undesirable, but if put to use intentionally it can be very handy like in

case of automobile brake mechanism. Conventional braking mechanism of

automobiles utilizes friction to overcome the momentum of vehicle. In case of

“Friction Disk brakes” brake caliper comes in contact with the rotating disk,

momentum possessed by the disk is consumed by the friction between the two

contacting surfaces. Almost all of the energy consumed by friction is lost to

atmosphere in form of heat. Conventional friction brake mechanism though

effective but is wasteful in terms of energy. Immense amount of precious work

produced by automobile engine is lost to friction and eventually heat. HRB

(Hydraulic Regenerative Braking) is an approach towards recovering that energy

and reusing it to gain the lost momentum back.

Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 1

1.2 Energy situation in Pakistan

According to “Pakistan Energy Yearbook 2009” issued by Hydrocarbon Development Institute of Pakistan, Pakistan produced 62.6 MTOE energy in the year 2008-09. Figure # 1.1 shows the supply of energy by source in year 2008-09 and 2003-04.

SourcesOil: 32.1 % of the 62.6 MTOE energy consumed in Pakistan during year 2008-09 was produced using Oil as fuel, which includes Petrol, Diesel, Furnace oil and all other variants. In year 2008-09 net indigenous production of Oil was 3.22 MTOE and the imports were 18.226MTOE.

Gas: 48.3 % of 62.6 MTOE consumed in Pakistan was produced using Gas during year 2008-09. Gas is an indigenous product hence no imports were made.

LPG: 0.6 % of 62.6 MTOE produced using LPG as fuel.

Coal: 4.75 MTOE energy was produced using coal in year 2008-09, out of which 1.67 MTOE was imported.

Hydro and Nuclear: 7.074 MTOE energy was produced using Nuclear and Hydro energy.


15.219120.1

25.3

30.26

3.31

4.76

6.82

7.07

0

10

20

30

40

50

60

70

2003-04 2008-09

Hydro & Nuclear

Coal

Gas

LPG

Oil

Fig #1.1 Primary energy supplies by source (Pakistan) Source: Pakistan Energy Yearbook 2009

Mil

lion

TO

E

1.3 Energy consumption in transportation (Pakistan)

Transport sector is a major consumer of liquid fuel or Oil. It includes all road

transport such as trucks, trawlers, cars, motor cycles and buses, trains, Airplanes

etc.

In

year 2008-09 net indigenous production of Oil was 3.22 MTOE and the imports

were 18.226MTOE hence only around 15 % of the total requirement was met

domestically while the rest was imported, summing up to be staggering USD

9440.71 million. From figure # 1.2 nearly 50% of the oil is consumed in

transportation sector alone which corresponds to a worth of USD ½ billion. In a

country like Pakistan where per capita income is less than 1100 USD, ½ billion is

really a burden on economy.


Fig #1.2 Petroleum products consumption by sector (Pakistan)Source: Pakistan Energy Yearbook 2009

1.4 Energy consumption in transportation (international perspective)

Energy use in the transportation sector includes the energy consumed in moving

people and goods by road, rail, air, water, and pipeline. The road transport

component includes light-duty vehicles, such as automobiles, sport utility vehicles,

minivans, small trucks, and motorbikes, as well as heavy-duty vehicles, such as

large trucks used for moving freight and buses used for passenger travel.

Consequently, transportation sector energy demand hinges on growth rates for both

economic activity and driving the population. Economic growth spurs increases in

industrial output, which requires the movement of raw materials to manufacturing

sites, as well as the movement of manufactured goods to end users.

Almost 20 percent of the world's total delivered energy is used in the transportation

sector, where liquid fuels are the dominant source. Transportation alone accounts

for more than 50 percent of world consumption of liquid fuels, and its share

increases over the projection period. The transportation share of total liquid fuels

consumption rises to 61 percent in 2035, as their share declines in the other end-

use sectors. Because liquids play a key role in the world transportation sector,

understanding how the sector is likely to evolve could be the most important factor

in assessing the future of liquid fuel markets. From 2007 to 2035, growth in

transportation energy use accounts for 87 percent of the total increase in world

liquids consumption.

(Source: International Energy Outlook 2010 (Transportation) http://www.eia.doe.gov)


http://www.eia.doe.gov/

1990 1991 1992 1993 1994 1995(R)

19961997 1998 1999

(R) 2000

(R) 2001

2002(R)

20032004 2005

(R) 2006

(R) 2007

(R) 2008

(P) 2009

Domestic production, totala

8.91 9.08 8.87 8.58 8.39 8.32 8.29 8.27 8.01 7.73 7.73 7.67 7.63 7.40 7.23 6.90 6.84 6.85 6.73 7.27

Crude oilb 7.36 7.42 7.17 6.85 6.66 6.56 6.46 6.45(R)

6.25(R)

5.885.82 5.80 5.75 5.68 5.42 5.18 5.10 5.06 4.95 5.36

Natural gas plant liquids

1.56 1.66 1.70 1.74 1.73 1.76 1.83 1.82 1.76 1.85 1.91 1.87 1.88 1.72 1.81 1.72 1.74 1.78 1.78 1.91

Gross imports, total

8.02 7.63 7.89 8.62 9.00 8.83 9.4810.1

610.7

110.8

511.4

611.8

711.5

312.2

613.1

513.7

113.7

113.4

712.9

211.69

Crude oilb,c 5.89 5.78 6.08 6.79 7.06 7.23 7.51 8.23 8.71 8.73 9.07 9.33 9.14 9.6610.0

910.1

310.1

210.0

39.78 9.01

Petroleum productsd 2.12

(R) 1.84

1.80 1.83 1.93(R)

1.611.97 1.94

(R) 2.00

2.12 2.39 2.54 2.39 2.60 3.06 3.59 3.59 3.44 3.13 2.68

Exports 0.86 1.00 0.95 1.00 0.94 0.95 0.98 1.00 0.94(R)

0.941.04 0.97

(R) 0.98

1.03 1.05 1.16 1.32 1.43 1.80 2.02

U.S. net importse

(R) 7.16

(R) 6.63

(R) 6.94

(R) 7.62

(R) 8.05

(R) 7.89

8.50 9.16(R)

9.769.91

10.42

10.90

(R) 10.5

5

11.24

(R) 12.1

0

(R) 12.5

5

12.39

12.04

11.11

9.67

U.S. petroleum consumption

16.99

16.71

17.03

17.24

17.72

17.72

18.31

(R) 18.6

2

18.92

19.52

19.70

19.65

19.76

20.03

20.73

20.80

20.69

20.68

19.50

18.77

By the transportation sector

(R) 10.8

9

(R) 10.7

6

(R) 10.8

8

11.12

(R) 11.4

2

(R) 11.6

7

11.92

(R) 12.1

0

12.42

(R) 12.7

6

13.01

12.94

(R) 13.2

1

13.32

(R) 13.7

2

(R) 13.9

6

14.18

14.29

13.71

13.27

Transportation petroleum use as a percent of domestic petroleum production

(R) 122.

1

(R) 118.

6

(R) 122.

7

(R) 129.

6

(R) 136.

1

(R) 140.

2

143.7

(R) 146.

3

155.0

(R) 165.

1

168.3

168.7

(R) 173.

2

180.0

(R) 189.

8

(R) 202.

4

207.3

208.6

203.6

182.6

Transportation petroleum use as a percent of domestic petroleum consumption

(R) 64.1

(R) 64.4

(R) 63.9

(R) 64.5

(R) 64.4

(R) 65.8

65.1(R)

65.065.7

(R) 65.4

66.0 65.8(R)

66.866.5

(R) 66.2

(R) 67.1

68.5 69.1 70.3 70.7

World petroleum consumption

66.69

(R) 67.2

9

(R) 67.4

8

(R) 67.6

0

(R) 68.9

2

70.13

71.67

73.43

(R) 74.0

7

(R) 75.7

6

76.74

77.47

(R) 78.1

2

79.68

(R) 82.4

6

(R) 84.0

4

85.20

86.14

85.75

U


Table#1.1 Overview of U.S. Petroleum Production, Imports, Exports, and Consumption.Source: http://www.bts.gov (Bureau of Transportation Statistics)

http://www.bts.gov/

According to some researchers the world is left with 40 years of oil and 65 years of

gas if we keep consuming on the same rate as we are right now. In this regard it is

our moral and humanitarian obligation to try and find out ways of reducing the

consumption of the precious fuels.

1.3Energy use in transportation and environmental impact


Fig # 1.3 Future liquid fuel consumption predictionSource: International Energy Outlook 2010 (Transportation) http://www.eia.doe.gov


Transportation sector in Pakistan is a major contributor towards greenhouse gas

emissions. Figure # 1.4 shows CO2 emission by sector in Pakistan for the year

1999, which suggests that 26% of the total emissions of CO2 were made by

transportation sector in year 1999. Global warming is a major concern these days,

which is caused by greenhouse gases in our atmosphere. Keeping in view the

impact it is having on our life as we know it, latest of which is 2010 Super Flood in

Pakistan which affected more than 20 million Pakistani’s, greenhouse gas

emissions (particularly CO2) if not curtailed may have serious implications.

Looking at the economic perspective Pakistan is not self sufficient in Oil and great

deal of foreign exchange is spent every year to fulfill oil requirement of the nation.

Therefore it is very important that Oil consumption in Pakistan be made more

efficient. In order to do so let’s have a look at the largest oil consumer which is


Fig #1.4 CO2 emissions by sector (Pakistan)Source: www.earthtrends.wri.org

http://www.earthtrends.wri.org/

transport sector. Fuel consumption in transport sector can be brought down in

following possible ways

1. By doing demand side management (DSM)

2. By coming up with new cleaner, cheaper and more environment friendly

resources of energy like Solar, Bio-fuel etc.

3. By improving energy efficiency of vehicles

The proposal made in this thesis deals with the third option which is to improve the

energy efficiency of vehicles. In order to do so first the areas where loses occur

have to be identified.


Steps towards improving automobile’s energy efficiency

Overall efficiency of an automotive may increase if the already existing parts of it

function more efficiently or some auxiliary efficiency improving systems like

turbo chargers are incorporated in to the vehicle.

First areas of an automobile where losses occur must be identified, which can be

mechanical losses of Engine, Aerodynamic losses, rolling friction, last but

definitely not the least automobile Brakes.

Figure # 1.5 produced by Eaton hydraulics USA suggests that on average

automobile brakes accounts for around 50% of the total losses that occur in an

urban vehicle. Hence making it the largest share holder of the total energy lost.

Energy lost due to brake can be recovered by using considerably new phenomenon

of Regenerative braking. As the name suggests in such brake mechanisms energy

lost in conventional brake due to friction is converted to some form that can be

reused again. Two types of regenerative braking systems for vehicles are known;

1. Electrical regenerative brake

2. Hydraulic regenerative brake

Electrical regenerative braking system uses excess energy to power a reversible

generator and charges a battery to for future use, while Hydraulic regenerative

braking system stores access energy in hydraulic form to reuse. Drawback of

electric regenerative braking is that it can only be used in Electric or Electric

Hybrid vehicles which are not very commonly used around Pakistan. On the

contrary Hydraulic regenerative braking system can be employed on any

conventional I.C engine powered vehicle hence can have wider impact on the

overall energy situation.

Hydraulic Regenerative Braking is an obvious choice between the two.


Table#2.1 energy loss due to brake in urban


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http://www.eaton.com/EatonCom/ProductsServices/Hybrid/SystemsOverview/HydraulicHLA/

1.4Maximum available potential

To appreciate potential available for Hydraulic Regenerative Braking system let’s

have a sample calculation that can give us an idea of how much energy is available

for regeneration.

Calculations below have been made neglecting the aerodynamic and rolling

friction losses. It is assumed that the vehicle’s engine runs at maximum efficiency.

Considerations: Fully loaded medium sized Diesel truck weighing 25 tons, running

at 30 km/hr. It is an urban service truck which is supposed to cover a distance of 10

km, with expected stop at every 200 m due to traffic and service compulsions. The

time duration between pressing the brake paddle and vehicle coming to halt is 4

sec.

Following example demonstrates the amount of energy lost in conventional

automobile brake. If recovered part of it can bring improvement in energy

efficiency in transportation.

Truck Mass (m) = 25 tons = 25000 kg

Initial speed (vi) = 30 km/hr = 8.333 m/sec

Final speed (vf) = 0 m/s

Average mileage = 5 km/L

Distance traveled = 10 km

Total fuel consumption = Distance traveled / Average mileage = 10/5 = 2 L

Density of diesel = 0.832 kg/L


This energy loss corresponds to diesel consumption of 2 L = 1.664 kg.

Average C.Vdiesel = 36 MJ/L = 43.27 MJ/kg

Distance / Stop = 200m

Number of stops = 50

Time taken to reach zero velocity (t) = 4 sec

Energy required to stop vehicle

W = F.d ------------ (i)

F = m.a ------------- (ii)

a = vf – vi ---------- (iii) t

d = distance traveled after pressing brake paddle

d = vi t + ½ a t2 --- (iv)

by putting the values of speed and time in eq: (iii) and (iv)

a = 2.0833 m/s2

d = 16.666 m

put a = 2.0833 m/s2 in eq: (ii)

∴ F = 52082.5 N = 52.08 kN

put value of ‘F’ and ‘d’ in eq: (i)

∴ W = 868041.3 J = 868.04 kJ = 0.868 MJ/stop

Hence energy lost in 50 stops

= 0.868 x 50


= 43.4 MJ

Comparison with total energy consumed

Fuel consumption = Distance traveled / Average mileage = 10 / 5 = 2 L

Total energy consumed = Fuel consumption x Average C.Vdiesel

= 2 x 36 = 72 MJ

% energy loss due to braking = Energy lost in braking x 100 Total energy consumed

= (43.4 / 72) x 100 = 60.3 %

In light of above calculation it is evident that automobile brake is a huge source of

energy loss and if recovered it can contribute a great deal towards improving

energy efficiency of automobile.


Chapter 2

Hydraulic Regenerative Braking system

2.1Components

HRB (Hydraulic Regenerative Braking) system consists of following main

components

1. Transfer case

2. Hydraulic machine (Pump/Motor)

3. Accumulator

4. Low pressure reservoir

5. Power transmission fluid

6. Controller


Transfer case

Transfer case is a gearbox which brings power from main propeller shaft to the

hydraulic machine. It is similar to the PTO (Power Take Off) used in agricultural

machinery.

Transfer case can be of two kinds

Constant mesh gear box

Variable transmission gear box

Constant mesh gearbox

Advantages Limitation

Easier to design, since only two gears

have to be designed.

Limited speed range.

Less complex manufacturing and repair. Bigger in size.

Easier design of controller Not good manipulator of available

power.

Such transfer case has only two gears that always remain meshed with each other.

It brings power from main shaft to the reversible pump and then back.


Variable transmission gearbox

A gearbox having more than single mesh arrangement, in which gear can be

changed as the speed of vehicle increases is called variable transmission gearbox.

There can be two or more than two pairs of gear mounted on each shaft, which will

each engage as the vehicle approaches their operating speed.

Such systems enable better distribution of the energy available and tend to increase

the speed range in which the apparatus can be used.

Advantages Limitation

Greater speed range. Complex design.

More energy efficient. Sophisticated controller required.

Smaller in size. Complex manufacture and repair.


Hydraulic Machine

Here the requirement from the Hydraulic machine is to work both as a pump and

hydraulic motor. In first stage of operation the machine has to act as a pump and in

later as a motor. This constraint leaves us with only a few options that are

Gear pump/motor

Swash plate pump/motor

Bent axis pump/motor

Gear pump/motor

A gear pump uses the meshing of gears to pump fluid by displacement. They are

one of the most common types of pumps for hydraulic fluid power applications.

Gear pumps are also widely used in chemical installations to pump fluid with a

certain viscosity. There are two main variations; external gear pumps which use

two external spur gears and internal gear pumps which use an external and an

internal spur gear. Gear pumps are positive displacement (or fixed displacement),

meaning they pump a constant amount of fluid for each revolution. Some gear

pumps are designed to function as either a motor or a pump.

Working

As the gears rotate they separate on the intake side of the pump, creating a void

and suction which is filled by fluid. The fluid is carried by the gears to the

discharge side of the pump, where the meshing of the gears displaces the fluid. The

mechanical clearances are small— in the order of 10 μm. The tight clearances,


http://en.wikipedia.org/wiki/Fluid

http://en.wikipedia.org/wiki/Hydraulic_motor

http://en.wikipedia.org/wiki/Positive_displacement_pump

http://en.wikipedia.org/wiki/Gear

http://en.wikipedia.org/wiki/Hydraulic_machinery

http://en.wikipedia.org/wiki/Pump

along with the speed of rotation, effectively prevent the fluid from leaking

backwards.

The rigid design of the gears and houses allow for very high pressures and the

ability to pump highly viscous fluids.


Fig#2.1 Exploded view of gear pumpSource: www.wikipedia.org

http://en.wikipedia.org/wiki/Viscosity

Swash plate pump/motor

An axial piston / swash plate pump is a positive displacement pump that has a

number of pistons in a circular array within a cylinder block (Chamber). It can be

used as a stand-alone pump, a hydraulic motor or an automotive air

conditioning compressor.

Components of swash plate pump/motor

Housing

Plungers

Chamber

Swash plate

Valve plate


Chamber

Plungers

Swash plate

Housing

Fig#2.2 Swash plate pumpSource: Author

http://en.wikipedia.org/wiki/Air_conditioning

http://en.wikipedia.org/wiki/Air_conditioning


http://en.wikipedia.org/wiki/Cylinder_block

http://en.wikipedia.org/wiki/Piston

Features

Swash plate serves as a cam for the plungers as the plungers move along the

plate they raise as the plate rises and go for suction as the plate goes down.

Angle of swash plate determines the compression ratio of the pump it can be

increased by increasing the angle of swash plate hence increasing the

displacement of the plungers. The angle of swash plate is controlled using

feedback from high pressure and low pressure reservoirs.

Normally there are odd number of pistons most common arrangement is 9

pistons.

These pumps are used where space is confined and the output has to be

given in the axial direction.

According to Eaton Hydraulics USA recommended viscosity range of fluids

for such pumps is 16 – 40 cSt.

Bent axis pump/motor

Working of bent axis motors is same as that of swash plate motors only because of

the bent casing the swash plate cannot change its inclination to compensate

variable pressure requirements.


Accumulator

A hydraulic accumulator is an industrial device basically used for storage of

energy. In this device, a non-compressible hydraulic fluid is held under pressure

for an outside source. This external or outside source can be compressed gas or

spring or raised height. Considered as pressure storage device, a hydraulic

accumulator is used to store hydraulic energy.

Compressed gas accumulators are by far the most common type. These are also

called hydro-pneumatic accumulators.

Types of accumulator

Raised weight accumulator

A raised weight accumulator consists of a vertical cylinder containing fluid

connected to the hydraulic line. The cylinder is closed by a piston on which a

series of weights are placed that exerts a downward force on the piston and thereby

energizes the fluid in the cylinder. In contrast to compressed gas and spring

accumulators, this type delivers a nearly constant pressure, regardless of the

volume of fluid in the cylinder, until it is empty. (The pressure will decline

somewhat as the cylinder is emptied due to the decline in weight of the remaining

fluid.)

Compressed gas (or gas-charged) accumulator

A compressed gas accumulator consists of a cylinder with two chambers that are

separated by an elastic diaphragm, a totally enclosed bladder, or a floating piston.


One chamber contains hydraulic fluid and is connected to the hydraulic line. The

other chamber contains an inert gas under pressure (typically nitrogen) that

provides the compressive force on the hydraulic fluid. Inert gas is used because

oxygen and oil can form an explosive mixture when combined under high pressure.

As the volume of the compressed gas changes the pressure of the gas, and the

pressure on the fluid, changes inversely.

The compressed gas accumulator was invented by Jean Mercier, for use in variable

pitch propellers.

Spring type

A spring type accumulator is similar in operation to the gas-charged accumulator

above, except that a heavy spring (or springs) is used to provide the compressive

force. According to Hooke's law the magnitude of the force exerted by a spring is

linearly proportional to its extension. Therefore as the spring compresses, the force

it exerts on the fluid is increased linearly.

Metal bellows type

The metal bellows accumulators function similarly to the compressed gas type,

except the elastic diaphragm or floating piston is replaced by a hermetically sealed

welded metal bellows. Fluid may be internal or external to the bellows. The

advantages to the metal bellows type include exceptionally low spring rate,

allowing the gas charge to do all the work with little change in pressure from full

to empty, and a long stroke relative to solid (empty) height, which gives maximum

storage volume for a given container size. The welded metal bellows accumulator

provides an exceptionally high level of accumulator performance, and can be

produced with a broad spectrum of alloys resulting in a broad range of fluid


http://en.wikipedia.org/wiki/Hooke's_law

http://en.wikipedia.org/wiki/Variable_pitch_propeller

http://en.wikipedia.org/wiki/Variable_pitch_propeller

http://en.wikipedia.org/wiki/Jean_Mercier

http://en.wikipedia.org/wiki/Explosive

http://en.wikipedia.org/wiki/Nitrogen

compatibility. Another advantage to this type is that it does not face issues with

high pressure operation, thus allowing more energy storage capacity.

Spring-loaded piston

A spring-loaded piston accumulator is identical to a gas-charged unit, except that a

spring forces the piston against the liquid. Its main advantage is that there is no gas

to leak. A main disadvantage is that this design is not good for high pressure and

large volume.


Fig#2.3 Working mechanism of different types of accumulatorsSource: www.google.com.pk

Low pressure reservoir

Low pressure reservoir is a storage tank that holds hydraulic fluid at low pressure.

It should be made of material that is chemically inert to the hydraulic fluid, so that

the power transmission fluid does not get contaminated.


Fig# 2.4. Oil tank with strainer on topSource: www.google.com.pk

Controller

An efficient controller can dramatically improve the performance of the system.

Controller can either be PLC (Programmable Logic Controller) based or micro

controller based.

Job of controller is mainly to engage or disengage clutch. Since speed range for the

system is limited therefore the controller must be able to decide whether to engage

the clutch or not. In case of variable transmission transfer case controller has to

perform an additional task of switching gears as the speed changes.

Following are the parameters that should be considered before choice or design of

controller.

Controller must be rigid enough to sustain environmental conditions.

Controller must be temperature resistant

Controller must be water proof

Controller must be shock resistant


Power transmission fluids

Hydraulic fluids, also called hydraulic liquids, are the medium by which power is

transferred in hydraulic machinery. Common hydraulic fluids are based on mineral

oil or water. Examples of equipment that might use hydraulic fluids

include excavators and backhoes, brakes, power.

Steering systems, transmissions, garbage trucks, aircraft flight control

systems, elevators, and industrial machinery.

Hydraulic systems like the ones mentioned above will work most efficiently if the

hydraulic fluid used has low compressibility.

Brake fluid is a type of hydraulic fluid used in hydraulic brake applications

in automobiles, motorcycles, light trucks, and some advanced bicycles. It is used to

transfer force into pressure. It works because liquids are not

appreciably compressible - in their natural state the component molecules do not

have internal voids and the molecules pack together well, so bulk forces are

directly transferred to trying to compress the fluid's chemical bonds. Brake fluids

must meet certain requirements as defined by various standards set by

organizations such as the SAE, or local government equivalents. For example,

most brake fluid sold in North America is classified by the US Department of

Transportation (DOT) under their own ratings such as "DOT 3" and "DOT 4".

Their classifications broadly reflect the concerns addressed by the SAE's

specifications, but with local details

Service and maintenance

Most automotive professionals agree that glycol-based brake fluid; (DOT 3, DOT

4 and DOT 5.1) should be flushed, or changed, every 1–2 years. Many


http://en.wikipedia.org/wiki/DOT_4

http://en.wikipedia.org/wiki/DOT_3

http://en.wikipedia.org/wiki/Department_of_Transportation

http://en.wikipedia.org/wiki/Department_of_Transportation

http://en.wikipedia.org/wiki/Society_of_Automotive_Engineers

http://en.wikipedia.org/wiki/Physical_compression

http://en.wikipedia.org/wiki/Liquid

http://en.wikipedia.org/wiki/Bicycle

http://en.wikipedia.org/wiki/Light_truck

http://en.wikipedia.org/wiki/Motorcycle

http://en.wikipedia.org/wiki/Automobile

http://en.wikipedia.org/wiki/Hydraulic_brake

http://en.wikipedia.org/wiki/Hydraulic_fluid

http://en.wikipedia.org/wiki/Compressibility

http://en.wikipedia.org/wiki/Elevator

http://en.wikipedia.org/wiki/Aircraft_flight_control_system

http://en.wikipedia.org/wiki/Aircraft_flight_control_system

http://en.wikipedia.org/wiki/Garbage_truck

http://en.wikipedia.org/wiki/Transmission_(mechanics)

http://en.wikipedia.org/wiki/Power_steering

http://en.wikipedia.org/wiki/Power_steering

http://en.wikipedia.org/wiki/Brake

http://en.wikipedia.org/wiki/Backhoe

http://en.wikipedia.org/wiki/Excavator

http://en.wikipedia.org/wiki/Mineral_oil

http://en.wikipedia.org/wiki/Mineral_oil


manufacturers also require periodic fluid changes to ensure reliability and safety.

Once installed, moisture diffuses into the fluid through brake hoses and rubber

seals and, eventually, the fluid will have to be replaced when the water content

becomes too high. Electronic testers and test strips are commercially available to

measure moisture content. The corrosion inhibitors also degrade over time. New

fluid should always be stored in a sealed container to avoid moisture intrusion.

Examples

DOT 3 Polyethylene glycol-based

DOT 4 Polyethylene glycol-based

DOT 5 Silicone based

Oil Dry boiling point Wet boiling point

DOT 3 205 °C (401 °F) 140 °C (284 °F)

DOT 4 230 °C (446 °F) 155 °C (311 °F)

DOT 5 260 °C (500 °F) 180 °C (356 °F)

DOT 5.1 270 °C (518 °F) 190 °C (374 °F)

2.2 Working mechanism


http://en.wikipedia.org/wiki/Polyethylene_glycol

http://en.wikipedia.org/wiki/Polyethylene_glycol

http://en.wikipedia.org/wiki/Test_strip

http://en.wikipedia.org/wiki/Molecular_diffusion

http://en.wikipedia.org/wiki/Moisture

The working of the proposed system may be broadly divided into two stages

1. Regeneration mode:When it is intended to stop the vehicle, driver applies brake. During application of

brake power produced by engine and inertia of vehicle are of no use anymore.

Pump is engaged and operates by this energy and pumps hydraulic fluid from low

pressure tank to the high pressure accumulator. The energy is stored in

accumulator which is also called mechanical charger and can be reused whenever

needed.

2. Launch assist mode:When vehicle needs to be accelerated, driver presses the accelerator. In such

situation rather than using engine power oil in accumulator is used to drive the

hydraulic machine that now will work as a motor, which in turn makes the vehicle

move.


Fig # 2.5 Hydraulic Regenerative Braking (Schematic View)Source: Author

2.3Areas of application


Fig#2.6 Schematic view Hydraulic Regenerative BrakingSource: www.eaton.com

Hydraulic regenerative braking can be highly effective for urban vehicles. It is best

suited for vehicles with short stop and go cycles examples are;

School buses

Public transport buses

Refuse trucks that collect garbage

Delivery vans etc

According to “The Nation” newspaper

“The number of registered vehicles in the Federal Capital has crossed the figure

of 0.3 million as the vehicles of embassies were not included in this figure.”

(Feb: 24, 2009)

Total area of Islamabad is 233 km2

∴ Vehicle density in Islamabad ≈ 1300 vehicles / km2

At such high vehicle density, traffic jams and unexpected stoppages are no

surprise. Such environments are ideal for systems like Hydraulic Regenerative

Braking.

2.4 Parallel developments

Hydraulic regenerative braking system is a fairly new idea in energy efficiency

improvement in transportation sector. Many mainstream companies both in


automobile and hydraulics are working on design and development of Hydraulic

Regenerative Braking systems, some designs as proposed by different international

companies are mentioned;

1 Hydrostatic Regenerative Braking (Bosch Rexroth)

2 Hydraulic Launch Assist (Eaton Hydraulics)

3 Runwise (Parker)


Fig # 2.7 Hydrostatic Regenerative BrakingSource: www.bosch Rexroth.com

Fig # 2.8 Hydraulic Launch AssistSource: www.eaton.com

Chapter 3


Fig # 2.9 Parker’s RunwiseSource: www.parker.com

Types of HRB

Hydraulic regenerative braking system can be classified on two grounds

1. On the basis of Hydraulic machine

HRB with reciprocating type hydraulic machine

HRB with Swash plate type hydraulic machine

2. On the basis of Transfer case

HRB with constant gear ratio transfer case

HRB with variable transmission transfer case

3.1Hydraulic regenerative Braking system with reciprocating type hydraulic machine


Fig# 3.1 Components of HRBSource: Author

Vehicle weight actuated generator gave rise to the idea of a similar mechanism

mounted on the vehicle chassis, which uses brake energy rather than vehicle

weight, hence makes it much lighter.

It is a mechanical charger unit that charges on the energy otherwise wasted due to

braking and allows the reuse of the stored energy.

A reciprocating type unit is used to serve as reversible pump.

1. Transfer case:

2. Clutch:

3. Pump/Motor unit:

4. Accumulator:

Drawbacks

Reciprocating unit not generally used as hydraulic motor

More fluid intake volume per revolution

Vibration

Bulky design


3.2 Hydraulic Regenerative Braking System with constant gear ratio Transfer case

This design is for low speed application because of the limitation of the gears.

Because only one gear arrangement is given and the pump has a maximum limit of

speed it can work on hence this system can only work in a given range of speed.

Both pinion and gear are of same size.


Fig# 4.5 helical gear

Fig# 3.2 Constant gear ratio transfer case with swash plate unit and clutchSource: Author

3.3 Hydraulic Regenerative Braking system with variable transmission transfer case

This system can work with a wider speed range because of the variable

transmission transfer case provided that can keep the pump under safe operating

speed. Only problem is the complex design of its transfer case.


Fig# 3.3 Variable transmission transfer case with swash plate unit and clutchSource: Author

Chapter 4

Modeling and Analysis

The design is proposed for a medium size truck (capacity 15 – 30 Ton) with

following specifications. All the 3d models and simulations have been done using

Solidedge V19 licensed to Mehran University of Engineering and Technology.

Empty weight 10 Ton

Loaded weight 15 Ton

Gross weight 25 Ton

Maximum rated power 220 hp = 160 kW

Maximum propeller shaft speed 3000 r.p.m


Hydraulic Regenerative Braking system with Variable Transmission Transfer case


Fig # 4.2 Hydraulic Regenerative Braking system with variable transmission transfer caseSource: Author

Transfer case

Accumulator

Pump / Motor Unit

Low Pressure Reservoir

Fig# 4.1 Volvo F10 Source: www.3dcontentcentral.com


Fig # 4.3 Hydraulic Regenerative Braking system (showing gear meshing)Source: Author

4.1 Transfer case


Fig # 4.4 Transfer case and axial piston unit (Exploded View)Source: Author

Gea

r #

1

Gea

r #

2

Gea

r #

3

Gea

r #

4

Table # 4.1 Design specifications of gear # 1 and 2

Gear # 1 and 2 < 2000 r.p.m

Material Carbon steel (CS 125)

Diameter (both gears) 150 mm

Gear ratio 1

Face width 32 mm

Helix angle 0o

Max: speed 3000 rpm

Max: power 160 kW

No: of teeth 28

Table # 4.2 Design specifications of gear # 3 and 4

Gear # 3 and 4 > 2000 r.p.m

Material Carbon steel (CS 125)

Diameter (gear # 3) 100 mm

Diameter (gear # 4) 200 mm

Gear ratio 2

Face width 40 mm

Helix angle 0o

Max: speed (gear #3) 3000 rpm

Max: power 160 kW

No: of teeth (gear # 3) 17

No: of teeth (gear #4) 34


The results shown above have been generated and verified using “Spur gear

designer” module of “Solid edge V19”, which uses NASTRAN solver to verify

results.

Gear #1 and 2 will remain engaged at propeller shaft speeds less than 2000r.p.m,

while gear # 3 and 4 will engage speed greater than 2000 r.p.m. Speed range for

each gear arrangement has been selected considering the fact that the assumed

pump/ motor unit has maximum working speed of 2000 r.p.m, therefore in no

circumstances the speed of pump shaft shall exceed 2000 r.p.m.


Fig # 4.5 Variable transmission transfer caseSource: Author

4.2 Accumulator


Fig # 4.6 Solid Edge V19 (Spur Gear designer module)Source: Author

Gas charged bellow type accumulator is used because of ease of availability and

maintenance. These accumulators almost never fail or need maintenance in their

standardized lifetime.

Usable volume 15 L = 15000 cm3

Maximum pressure 210 bar

4.3 Pump / Motor unit


Fig # 4.7 Hydraulic AccumulatorSource: Author

Swash plate pump / motor is best suited for the application because of its compact

size and precedence of application in hydraulic power transmission.

Specifications

No: of plungers 9

Plunger dia: 2 cm

Chamber dia: 10 cm

Swash plate angle 250

Maximum speed 2000

r.p.m

Volume flow / revolution = Cross section area of each plunger x total displacement

x No: of plungers

= (pie /4 x 22) x 3.73 x 9 = 105.4 cm3/ rev:

Time to fill the accumulator =

Volume of accumulator / (Volume flow rate / rev: x maximum allowable speed)

= 15000 / (105.4 x 2000/60)

= 4.3 sec



Fig # 4.8 Swash plate pump/motor assemblySource: Author

4.4 Sample calculation with HRB

Data considered here is from article # 1.4 (Maximum available potential).


Fig #4.9 Swash Plate pump / motor dimensions (mm)Source: Author

HRB specifications

Accumulator volume = 15 L

Accumulator pressure = 210 bar = 210 x105 N/m2

Time required to fill Accumulator = 4 sec

No: of pistons in Axial piston unit = 9

Volume flow rate of Axial piston unit = 105.4 cm3 / rev:

Maximum speed of Axial piston unit = 2000 r.p.m

Energy accumulated by HRB / stop

= Accumulator pressure x Accumulator volume

= 210 x 105 x 15/1000 = 315000 J

= 0.35 MJ

Total energy accumulated = Energy accumulated / stop x No: of stops

= 0.35 x 50 = 17.5 MJ

Total energy lost due to braking = 43.4 MJ (from article # 1.4)

% Energy recovered with HRB = Total energy accumulated x100 Total energy lost due to braking

= (17.5/43.4) x 100 = 40.3 %

% Increase in mileage

Total available energy = Fuel consumption x Average C.VDiesel


With HRB in place 40 % of the energy that previously was wasted can be recovered and put to positive use.

= 2 x 36 = 72 MJ/L

Total energy lost in braking = 43.4 MJ

Net energy available for accelerating (without HRB) = 72 – 43.4 = 28.6 MJ

Energy recovered with HRB = 17.5 MJ

Net energy available for accelerating (with HRB) = 28.6 + 17.5 = 46.1 MJ

Which is enough for the vehicle to travel 16 km as compared to 10 km without

HRB.

Result: 60% increase in mileage

∴ New mileage = 16/2 = 8 km/L% increase in mileage = (7-5 /5) x 100 = 40 %

% cost saving

Mileage with HRB = 8 km/L

Mileage without HRB = 5 km/L

% cost saving = (1 – mileage without HRB/mileage with HRB) x 100= (1 – 5/8) x 100 = 37.5 %

Money saved in fuel by installing HRB in given setup can be as high as 37.5 %.



Fig #4.10 Hydraulic Regenerative Braking System assembly in TruckSource: Author

4.5 Fabricated model


Fig # 4.11 Hydraulic Regenerative Braking system in Truck (orthogonal projection)Source: Author

To demonstrate the working of HRB a model has been fabricated with resources

generated locally. Following are the specifications

Axial piston unit

No: of pistons 9

Volume flow rate/rev 0.278 in3/rev

Maximum speed 2000 r.p.m

Maximum volume flow rate 556 in3/min = 9.26667 in3/sec

Maximum pressure 210 bar (3000 psi)

Direction of rotation Counter clockwise

Accumulator

Type Bladder type

Powered by Nitrogen gas

Volume 0.5 L

Maximum pressure 210 bar


Overall cost

Axial piston unit (Used) Rs. 8000

Accumulator (Used) Rs. 6000

Gears, Bearings, Shafts, Mounting

plate, Valve, Pipes and Service

charges.

Rs. 14000

Miscellaneous Rs.3000

Total cost Rs. 31000

Chapter 5Design and modeling of Hydraulic Regenerative Braking System for Vehicles | 53

Cost estimate of full scale prototype

Full scale prototype ready for testing for the proposed design can cost up to Rs.

200,000.

Swash Plate pump/ motor $ 400 to $ 1500 (www.ebay.com)

Accumulator $ 1090 (www.alibaba.com)

Transfer case $ 500 approx

Controller $ 200 approx

Mountings and accessories $ 200 approx

Minimum total cost $ 2400 ≈ Rs. 200,000


http://www.alibaba.com/

http://www.ebay.com/

5.1 Payback period

Payback period refers to the period of time required for the return on an investment

or to "repay" the sum of the original investment.

Considering today’s price of Diesel (Green XL of PSO) Rs. 78.33 per liter.

Total investment on HRB Rs. 200,000

Daily running of vehicle 50 km

Annual running of vehicle 50 x 300 = 15000 km

Payback period = Total investment/ Annual fuel cost saving

Annual fuel saving = Saving (L/km) x Annual running of vehicle

= (0.75/10) x 15000 = 1125 L

Annual fuel cost saving = 1125 x 78.33 = Rs. 88121.25

Payback period = 200,000 / 88121.25 = 2.3 years

= 2 years 4 months

Initial investment can be recovered in a period of 2years and 4 months. Service life

of vehicles is way longer then the payback period, therefore this figure is attractive.


Result discussion and conclusion

Energy lost due to conventional friction braking of automobile is very high.

HRB offers a great improvement in energy efficiency and reduction in

emission of greenhouse gases.

Payback period is as low as 2 years and 4 months for a vehicle doing only 50

km a day.

In specific case 60 % increase in mileage.

37.5 % less spending on fuel.

System is feasible for

Urban mass transit buses

Refuse trucks

Construction site vehicles

Cars

Considering Pakistan’s case 37.5 % saving in fuel consumption means as

high as

USD 0.1875 billion = USD 187.5 million ≈ Rs. 16 billion

In fiscal year 2010-11 money allocated for health sector in the province of

Sindh, Pakistan is Rs. 16.9 billion. Comparing to that Rs. 16 billion can almost

double the health budget in province of Sindh, Pakistan.


Systems like HRB are the need of the age where environmental problem is

ever increasing and fossil fuel reserves depleting at a rate faster than ever

before. Therefore such eco friendly systems should be promoted and

governments around the world should allocate funds for research and

development of such systems for the betterment of human life and its

survival on earth.


References

Books and literature

1 A textbook of Machine design by R.S Khurmi and J.K Gupta

2 The Nation Daily Feb 25th 2009

3 Pakistan energy year book 2009 Issued by Hydrocarbon Development Institute, Ministry of Petroleum and Natural Resources, Pakistan

Software

4. Solidedge V19

5. Microsoft Paint

6. Microsoft Office

Internet

7. www.google.com.pk

8. www.wikipedia.org

9. www.eaton.com Eaton Hydraulics

10.www.boschrexroth.com Bosch Rexroth

11.www.parker.com Parker Hannifin Corporation

12.www.eia.doe.gov Energy Information Administration (USA)

13.www.bts.gov Bureau of Transportation Statistics (USA)


http://www.bts.gov/


http://www.parker.com/

http://www.boschrexroth.com/

http://www.eaton.com/

http://www.wikipedia.org/

http://www.google.com.pk/

14.www.3dcontentcentral.com Solidworks community

15.www.aesti.com Alternate Energy Source Technology Inc.

16.www.ebay.com

17.www.alibaba.com

18.www.earthtrends.wri.org


http://www.earthtrends.wri.org/

http://www.alibaba.com/

http://www.ebay.com/

http://www.aesti.com/

http://www.3dcontentcentral.com/

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