A COMPARATIVE STUDY AND ANALYSIS OF THE PERFORMANCE OF VARIOUS REGENERATIVE BRAKING SYSTEMS

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 8, Issue 3, March 2017, pp. 66–76 Article ID: IJMET_08_03_008
Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
A COMPARATIVE STUDY AND ANALYSIS OF
THE PERFORMANCE OF VARIOUS
REGENERATIVE BRAKING SYSTEMS
Dattatraya K Chavan
PhD, Professor, Department of Mechanical Engineering, MIT, Pune, India
Anish S Gorantiwar
UG Scholar, Department of Mechanical Engineering, MIT, Pune, India
Kunal R Nalamwar
Ritesh G Deokar
ABSTRACT
Regenerative Braking System (RBS) converts a part of the vehicle’s kinetic energy
into a useful form of energy. Thus the fuel requirements and the level of pollutants
exhausted by the vehicle are reduced, and can be controlled. Various Regenerative
Braking Systems include Mechanical Flywheel RBS, Elastomeric Flywheel RBS,
Hydraulic Power-Assist RBS, Ultra capacitor RBS, etc. In this paper, a typical
mathematical analysis of the performance of Mechanical flywheel RBS, Elastomeric
Flywheel RBS, and Hydraulic Power-Assist RBS has been studied on different car
models based on current research, and a comparison of the efficiencies and fuel
savings by these systems has been done taking into consideration, a basic Volvo car
model. Analysis shows the efficiencies of Elastomeric Flywheel RBS, Hydraulic
Power-Assist RBS, and Mechanical Flywheel RBS will be in a descending order.
Key words: Efficiency, Elastomeric Flywheel RBS, Hydraulic Power Assist RBS,
Mechanical Flywheel RBS, Regenerative Braking System.
Cite this Article: Dattatraya K Chavan, Anish S Gorantiwar, Kunal R Nalamwar and
Ritesh G Deokar, A Comparative Study and Analysis of the Performance of Various
Regenerative Braking Systems. International Journal of Mechanical Engineering and
Technology, 8(3), 2017, pp. 66–76.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=3
THRUST AND MOTIVATION FOR THIS STUDY
The initial stimulus for undertaking study in regenerative braking system was personal
interest. Rising pollution and environment concerns has also brought this novel energy saving

Dattatraya K Chavan, Anish S Gorantiwar, Kunal R Nalamwar and Ritesh G Deokar
concept in the spotlight. This paper encompasses the majorly used regenerative system
installed on hybrid vehicles.
PROBLEM STATEMENT
To analyse the parameters affecting the performance of RBS and compare their efficiencies to
select the best RBS system for a given Light Motor Vehicle (LMV).
1. INTRODUCTION
Today as we are on the path of technological advancement, various countries are on the verge
of exploiting the natural reserves to harness energy, and sustain in the competition. Hence, the
world reserves of petroleum products, oil and natural gas are drastically reducing. There are
1.3 trillion barrels of proven oil reserves left in the world’s major fields, which at present rates
of consumption will last around 40 years. Burning fossil fuels produces around 21.3 billion
tonnes of carbon dioxide per year, and only half of that is absorbed by natural processes. The
result is catastrophic, increasing global warming and causing the average surface temperature
of the planet to rise.
The highest share of energy consumption in the world is of the Automobile Sector. Thus,
wide research is being going on to make automobiles consume lesser amount of fuel, and
reduce the resulting harmful effects on the environment.
Figure 1 Graph of Carbon Emissions from Fossil Fuel burning
2. REGENERATIVE BRAKING
Contrary to conventional friction braking, in regenerative braking, a part of the kinetic energy
(KE) of the vehicle is converted into useful form of energy.
This stored energy is then used in future as per requirement and the dynamic conditions
prevailing. Without Regenerative braking the whole of KE is converted into friction and heat,
which is a total loss.
The regenerative systems considered for comparison in this paper are:
 Mechanical Flywheel Regenerative Braking System
 Elastomeric Flywheel Regenerative Braking System
 Hydraulic Power-Assisted Regenerative Braking System

A Comparative Study and Analysis of the Performance of Various Regenerative Braking Systems
2.1. Mechanical Flywheel RBS System
This regenerative braking system is a type of a conventional system. During light and gradual
braking, the kinetic energy of the system is stored in the form of rotational kinetic energy of
the flywheel. This energy is then given back to the system when it is required for the vehicle
to accelerate. The basic parts of this system are flywheel, gearbox and a clutch system. The
flywheel is enclosed in an evacuated chamber to avoid friction losses and also for safety
issues. The flywheel weighs around 8-10 kg depending on the weight of the vehicle. The
flywheel rotates at high RPMs and when power is required, the clutch is engaged and the
power is transmitted to the wheels through the gearbox [1].
The wheel of the vehicle is connected to the secondary pulley of Continuously Variable
Transmission (CVT) through a clutch arrangement. The primary pulley of the CVT is further
connected to the flywheel fixed gearing through another clutch. This fixed gearing is
permanently connected to the flywheel of the vehicle. Thus a two-step gear transmission is
present in this system. Thus, the overall gear ratio Goverallis-
Goverall= Gfixed flywheel gearing * GCVT
Figure 2 Mechanical flywheel RBS
2.2. Elastomeric Flywheel RBS System
This system is an improvement over the existing conventional flywheel system [6]. The
flywheel is made up of composite material. As the speed of the flywheel increases, the
flywheel expands due to the elastic nature of the material used. Due to this, the Moment of
inertia of the flywheel increases and compared to the conventional rigid flywheel system,
more energy can be stored. The system of the elastic flywheel has the same components as the
conventional flywheel system [7].
Wheel
Wheel
Transmission
System
EngineMechanical
Flywheel

R 0.11m 0.05m
Initial Condition of Elastomeric Flywheel
R 0.134m
Figure 3 Increased radius of Flywheel at maximum angular velocity
2.3. Hydraulic Power-Assisted RBS System
Hydraulic power assist is a type of regenerative braking system which stores the kinetic
energy of the vehicle in the form of pressurized hydraulic fluid. This pressurized energy
which is stored in the high pressure accumulator is released when required for extra boost.
When the vehicle starts regenerative braking, the pump uses rotational energy of the
driveshaft and pumps oil from low pressure accumulator to high pressure accumulator. The
high pressure accumulator has a pre-charge of nitrogen gas. This pre-charge is further
pressurized when oil is pumped form the low pressure accumulator. As and when the vehicle
will require boost, pressurized fluid is released through a poppet valve. The pump then acts as
a motor where this stored energy is given to the driveshaft through a gearbox.
Figure 4 Hydraulic Power-Assisted Regenerative Braking System Configuration Diagram
Elastic
Flywheel
Elastic
Flywheel

3. NOMENCLATURE
m = mass of the vehicle
= ℎ
= ℎ ℎ
= ℎ ℎ
= ℎ
= ℎ
= ℎ ℎ ( − )
= ℎ ( / )
= ℎ ( / )
= ℎ ℎ ( )
= ℎ ( )
= ℎ ( )
= ℎ ( − )
= ℎ ( )
L1 = × = ℎ −
= × = ℎ
= × = ℎ
= × = ℎ
= ℎ
=
= ℎ
=
= ℎ
=
, = − ℎ
, = − ℎ
, = − ℎ ℎ
4. ANALYSIS OF RBS SYSTEMS
4.1. Mechanical Flywheel RBS System
The following observations have been noted after system testing of Mechanical Flywheel
RBS System installed on a car as specified in [3]. Three cases of regenerative braking and
three cases of acceleration have been covered in the test. Further analysis of these
observations has been done as follows:

Case 1 2 3 4 5 6
Wheel Initial
Velocity(m/s)
16.9875 12.964 12.516 16.095 12.295 16.095
Wheel Final
Velocity(m/s)
13.411 13.858 15.647 12.964 15.2 12.7417
Flywheel Initial
Speed(rpm)
3500 7300 6600 3200 6670 3507
Flywheel Final
Speed(rpm)
7295.815 6319.89 2976.634 6677.187 3771.596 6945.954
Initial Gear Ratio 5.48 14.36 14.02 5.3 14.4 5.8
Final Gear Ratio 14.47 12.13 5.06 13.7 6.6 14.5
Time(sec) 1.214 0.27 0.99 1.015 0.953 1.08
Analysis of Table
Case 1- This is a case of regenerative braking.
Wheel Condition Initial Final
Speed (km/hr) 61.155 48.28
Speed (m/sec) 16.9875 13.411
Angular velocity of wheel (rad/sec) 66.88 52.8
Therefore,
Change in Kinetic Energy of wheel ΔK.E. = Δ mv2
+ Δ Iω2
= ( mv1
2
- mv2
2
) + ( Iω1
2
- Iω2
2
)
= [ (150)(16.98752
) – (150)(13.4112
)]
+[ (10.1)(66.882
) - (10.1)(52.82
)]
Change in Kinetic Energy of wheel = 16.6637 KJ (1)
Flywheel Condition Initial Final
Speed (rpm) 3500 7295.815
Angular velocity (rad/sec) 366.519 764.016
Therefore,
Change in Kinetic Energy of Flywheel = Δ Iω2
= Iω2
2
- Iω1
2
= [0.038] [(764.0162
) – (366.5192
)]
Change in Kinetic Energy of Flywheel = 8.5383 KJ (2)
Therefore, Fraction of energy absorbed by the flywheel, off the total energy lost by the
wheel
=
.
.
= 0.51239 or 51.239% (3)
Similarly, solving the cases 2 to 6, the result of these 6 cases has been shown below:

Case 1
(braking)
2
(acceleration)
3
(acceleration)
4
(braking)
5
(acceleration)
6
(braking)
% energy absorbed by
flywheel, off the total
energy lost by the wheel 51.239 % --- --- 51.326 % --- 50.547 %
% energy required by the
wheel to accelerate, that is
supplied by flywheel --- 75.64 % 53.5 % --- 51.488 % ---
Hence, from the above system, we can conclude that-
 Out of total energy loss of wheels in braking, about 51 % of the energy is absorbed by the
flywheel.
 During acceleration, the mechanical flywheel provides nearly 60 % of the energy requirement
of the wheel.
In the given mechanical system, two flywheel RBS systems have been installed on the
vehicle, and hence the effective weight on each system will be half the weight of the vehicle.
Due to similarities in the relative parameters of the vehicle mentioned in [3] and Volvo
S60, further analysis on Volvo S60 has been done.
For Volvo S60 model,
Moment of Inertia of Flywheel = If = r2
= (8)(0.12
) = 0.04 kg-m2
.
Moment of Inertia of wheel = 70.363 kg-m2
.
Considering regenerative braking from 22.22 m/sec to 0 m/sec ,
Change in Kinetic Energy of wheel = Δ mv2
+ Δ Iω2
= [ (1045)(22.222
) – (1045)(02
)] +
[ (70.363)(111.12
) - (70.363)(02
)]
Change in Kinetic Energy of wheel = 692.2256 KJ
Hence, according to conclusions of Case 1-6 , Energy absorbed by the flywheel of Volvo
S60 during regenerative braking from 22.22 m/s to 0 m/s = 51% of 692.2256 KJ
= 0.51*692.2256
Energy absorbed by the flywheel = 353.035 KJ
When the flywheel is used during acceleration , the velocity ‘v’ that can be attained by the
car using the energy stored by the flywheel is given by the equation which can be referred in
[4] & [5]–
mv2
+ Iω2
= 353035 J
(1045)v2
+ (70.363)(
.
)2
= 353035
Therefore, solving the quadratic equation and neglecting the negative root, we get,
v = 15.868 m/sec.
Thus, after braking from 22.22 m/sec to 0 m/sec using mechanical flywheel regenerative
braking system, we can accelerate the car back up to 15.868 m/sec.
Efficiency of the mechanical flywheel system is given by
=
× ×
× ×
=
( . )
( . )
, = 50.99%

4.2. Elastomeric Flywheel Calculations
Natural Rubber has been selected as the material for Elastomeric Flywheel. The following
parameters are required for analysis of Elastomeric Flywheel RBS System.
= 2090 = 22.22 / = 0.2 = 930 = 0.05 ( )
4.2.1. Calculations
ℎ = ℎ ÷
= × ×
= 930 × Π × 0.11 × 0.11 × 0.05 = 1.7676
=
1
2
× × =
1
2
× 1.7676 × 0.11 × 0.11
= 0.01069 −
=
1
2
× × = 70.363 −
= =
22.22
0.2
= 111.11 /
= 11925 /
By law of conservation of angular momentum
+ = +
7818.03 = 70.363 × + 1053.315 ×
351.815 × + 10539.315 × = 7818.03 (1)
By law of conservation of energy
1
2
× × ω =
1
2
× × + 1/2 × × ( )
1
2
× × × × 11925 = 2090 × +
70.363
0.2
×
100545065.1 × = 2090 × + 1759.075 ×
= 0.000038282 ×
= 0.006187 × (2)
Substituting equation (2) in equation (1), we get
351.815 × + 0.4025 × = 7818.05
= 21.684 /
Substituting the above value in equation (2)
= 0.134
Efficiency of the elastomeric flywheel system is given by
=
× ×
× ×
=
(21.684)
(22.22)
= 95.23%

5. HYDRAULIC POWER ASSIST
The three different systems of regenerative braking have been compared on the basis of the
final velocity attained by the car and the overall efficiency of the system.
5.1. Calculations
The HPA System used for the analysis has been derived from [8] .The following values have
been taken for calculating the efficiency of the Hydraulic Power Assist (HPA) system:
= 172 = 2090
= 344 = 1.4
Figure 5 Different positions of piston inside the accumulator
Three different positions of the piston inside the accumulator are shown. The first position
corresponds to the pre-charge pressure of the nitrogen gas inside the accumulator. The second
and the third positions correspond to the minimum and maximum working pressure inside the
accumulator.
= =
(75)(0.00545) .
= (172) .
= (344) .
= 0.0030125 m3
, and = 0.001836 m3
The energy stored inside the accumulator is given by the equation:
=
×
− 1
× [ − 1] ≥
1
2
× ×
172 × 10 × 30.125 × 10
1.4 − 1
×
172
344
.
.
− 1 =
1
2
× 2090 ×
= 16.476
Efficiency of the Hydraulic Power Assist system is given by:
=
1/2 × ×
1/2 × ×
= ℎ ℎ
= 54.981%
75 bar 172 bar 344 bar

6. CONCLUSION
As can be seen from the calculations above, after braking from a speed of 22.22 m/sec to 0
m/sec and accelerating using the stored energy by the system, the velocity that can be attained
using these systems has been evaluated for all the three RBS systems mentioned in this paper.
The velocity attained by these systems during acceleration, and the efficiency of the
respective RBS system have been tabulated below.
RBS System used
Velocity attained using the stored
energy by the RBS system during
acceleration
Efficiency of the RBS System
Mechanical Flywheel RBS 15.868 m/sec 50.99%
Elastomeric Flywheel RBS 21.684 m/sec 95.23%
Hydraulic Power Assist 16.476 m/sec 54.98%
 The results above have been obtained by installing these three RBS systems on a car model-
Volvo S60.
 Observing the results obtained, it can be concluded that the efficiency of Elastomeric
Flywheel RBS System is the highest for Volvo S60, followed by Hydraulic Power-assisted
and Mechanical Flywheel RBS Systems. So, Elastomeric Flywheel RBS System would be the
best choice of RBS System for Volvo S60 model.
 The above method of calculations can also be used as a reference to analytically evaluate the
best RBS System for any other automobile model, just by replacing the specifications of
Volvo S60 car model with the new automobile model to be considered.
REFERENCES
[1] Ricardo Chicurrel –Uziel, ‘Flywheel energy Storage with Mechanical Input- Output for
Regenerative Braking’, Modern Mechanical Engineering,2014,4,175-182,October 13,
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[3] Anirudh Pochiraju, ‘Design principles of a flywheel regenerative braking system (F-RBS)
for Formula SAE Type Racecar and system testing on a virtual Test rig modeled on MSC
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[4] William Ennis, ‘A report on Regenerative Braking Systems’, MENGR 407
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[8] S.Hui, Y. Lifu, Jing. J, ‘Hydraulic/electric synergy system (HESS) design for heavy
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[9] Jia-Shiun Chen, “Energy efficiency comparison between Hydraulic Hybrid and Hybrid
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A COMPARATIVE STUDY AND ANALYSIS OF THE PERFORMANCE OF VARIOUS REGENERATIVE BRAKING SYSTEMS

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