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.

70
Million TOE

60 7.07
4.76
50
6.82
Hydro & Nuclear
3.31
40
Coal
30.26
30 Gas
25.3
LPG
20
Oil

10 20.1
15.2191

0
2003-04 2008-09

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

Sources
Oil: 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.


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.

0.5
In
5.4 2.1
0.4
42.3
Agriculture
Transport
Power
Industrial
Domestic
49.3 Other Govt.

year 2008-09 net indigenous production of Oil was 3.22 MTOE and the imports sector (Pakistan)
Fig #1.2 Petroleum products consumption by
Source: Pakistan Energy Yearbook 2009
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.


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)


Table#1.1 Overview of U.S. Petroleum Production, Imports, Exports, and Consumption.
Source: http://www.bts.gov (Bureau of Transportation Statistics)
(R) (R) (R) (R) (R) (R) (R) (P)
1990 1991 1992 1993 1994 1995 1997 1998 1999 2002 2004 2005
1996 2000 2001 2003 2006 2007 2008 2009

Domestic
production, 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
totala

(R) (R)
Crude oilb 7.36 7.42 7.17 6.85 6.66 6.56 6.46 6.45 5.82 5.80 5.75 5.68 5.42 5.18 5.10 5.06 4.95 5.36
6.25 5.88

Natural gas
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
plant liquids

Gross
8.02 7.63 7.89 8.62 9.00 8.83 9.48 10.16 10.71 10.85 11.46 11.87 11.53 12.26 13.15 13.71 13.71 13.47 12.92 11.69
imports, total

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 9.66 10.09 10.13 10.12 10.03 9.78 9.01

Petroleum (R) (R) (R)
2.12 1.80 1.83 1.93 1.97 1.94 2.12 2.39 2.54 2.39 2.60 3.06 3.59 3.59 3.44 3.13 2.68
productsd 1.84 1.61 2.00

(R) (R)
Exports 0.86 1.00 0.95 1.00 0.94 0.95 0.98 1.00 0.94 1.04 0.97 1.03 1.05 1.16 1.32 1.43 1.80 2.02
0.94 0.98

U.S. net (R) (R) (R) (R) (R) (R) (R) (R) (R) (R)
8.50 9.16 9.91 10.42 10.90 11.24 12.39 12.04 11.11 9.67
importse 7.16 6.63 6.94 7.62 8.05 7.89 9.76 10.55 12.10 12.55

U.S.
(R)
petroleum 16.99 16.71 17.03 17.24 17.72 17.72 18.31 18.92 19.52 19.70 19.65 19.76 20.03 20.73 20.80 20.69 20.68 19.50 18.77
18.62
consumption

By the
(R) (R) (R) (R) (R) (R) (R) (R) (R) (R)
transportation 11.12 11.92 12.42 13.01 12.94 13.32 14.18 14.29 13.71 13.27
10.89 10.76 10.88 11.42 11.67 12.10 12.76 13.21 13.72 13.96
sector

Transportation
petroleum use
as a percent (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R)
143.7 155.0 168.3 168.7 180.0 207.3 208.6 203.6 182.6
of domestic 122.1 118.6 122.7 129.6 136.1 140.2 146.3 165.1 173.2 189.8 202.4
petroleum
production

Transportation
petroleum use
as a percent (R) (R) (R) (R) (R) (R) (R) (R) (R) (R) (R)
65.1 65.7 66.0 65.8 66.5 68.5 69.1 70.3 70.7
of domestic 64.1 64.4 63.9 64.5 64.4 65.8 65.0 65.4 66.8 66.2 67.1
petroleum
consumption

World
(R) (R) (R) (R) (R) (R) (R) (R) (R)
petroleum 66.69 70.13 71.67 73.43 76.74 77.47 79.68 85.20 86.14 85.75 U
67.29 67.48 67.60 68.92 74.07 75.76 78.12 82.46 84.04
consumption


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

1.3 Energy use in transportation and environmental
impact


CO2 emissions by sector, Pakistan, 1999

10% 5%

electricity & heat production
29%
26% Other energy industries
Manufacturing & construction
Transportation
Residences

29% Other sectors
1%

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

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


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

Table#2.1 Hybrid vehicles which in urban very commonly used around Pakistan. On the
energy loss due to brake are not
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.


Design and modeling of Hydraulic Regenerative Braking System for Vehicles |
Fig # 1.5 Urban Vehicle energy loss in Braking, Aerodynamic and Rolling friction
Source: http://www.eaton.com/EatonCom/ProductsServices/Hybrid/SystemsOverview/HydraulicHLA/

10

1.4 Maximum 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

 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
This energy loss corresponds to diesel
= 43.4 MJ consumption of 2 L = 1.664 kg.

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

2.1 Components

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

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.

Advantages Limitation
Easier to design, since only two gears Limited speed range.
have to be designed.
Less complex manufacturing and repair. Bigger in size.
Easier design of controller Not good manipulator of available
power.

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,
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 pump
Source: www.wikipedia.org

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 pump
Source: Author

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
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 accumulators
Source: 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 top
Source: 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
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


Fig # 2.5 Hydraulic Regenerative Braking (Schematic View)
Source: Author
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#2.6 Schematic view Hydraulic Regenerative Braking
Source: www.eaton.com

2.3 Areas of application


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)

Fig # 2.7 Hydrostatic Regenerative Braking
Source: www.bosch Rexroth.com

2 Hydraulic Launch Assist (Eaton Hydraulics)


Fig # 2.8 Hydraulic Launch Assist
Source: www.eaton.com

3 Runwise (Parker)

Fig # 2.9 Parker’s Runwise
Source: www.parker.com


Chapter 3
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


Hydraulic regenerative Braking system with
3.1 reciprocating type hydraulic machine

Fig# 3.1 Components of HRB
Source: 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


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

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.

3.3 Hydraulic Regenerative Braking system with
variable transmission transfer case

Fig# 4.5 helical gear


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

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.

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

Transfer Fig# 4.1 Volvo F10
Pump /
case Source: www.3dcontentcentral.com
Motor Unit

Accumulator

Low Pressure
Reservoir

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

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


4.1 Transfer case

Gear # 3

Gear # 4
Gear # 2
Gear # 1

Fig # 4.4 Transfer case and axial piston unit (Exploded View)
Table # 4.1 Source: specifications of gear # 1 and 2
Design Author


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 case
Source: 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

Fig # 4.7 Hydraulic Accumulator
Source: Author

4.3 Pump / Motor unit


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 assembly
Source: Author


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

4.4 Sample calculation with HRB
Data considered here is from article # 1.4 (Maximum available potential).


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) With HRB in place
40 % of the energy
% Energy recovered with HRB = Total energy accumulated x100 that previously was
Total energy lost due to braking wasted can be
recovered and put to
= (17.5/43.4) x 100 = 40.3 % positive use.

% Increase in mileage

Total available energy = Fuel consumption x Average C.VDiesel

= 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 Truck
Source: Author


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

4.5 Fabricated model


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 Rs. 14000
plate, Valve, Pipes and Service
charges.
Miscellaneous Rs.3000
Total cost Rs. 31000

Chapter 5
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

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)

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


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