A Hybrid Electric Vehicle (HEV) is a modern combination of an internal combustion engine (ICE) and an electric propulsion system (hybrid drivetrain). The electric powertrain is used in an HEV to achieve better fuel economy than a conventional vehicle for better performance. HEVs can be classified according to powertrain, hybridization, and Energy Management Systems (EMS). Modern HEVs use energy- efficiency technologies such as regenerative braking that converts the vehicles kinetic energy into electric energy that is stored in battery or supercapacitors. The battery is connected to an ECU (Electronic Control Unit) and a BMS (Battery Management System). To maintain the cooling of the engine and BMS it is connected to a coolant. In this case study we are going to study about the following things in an HEV :- 1. Hybrid Electric Vehicle (HEV) subsystems 2. Toyota Prius Powertrain 3. Transmission system in HEV 4. Use of Brushless DC Motor (BLDC) and Permanent Magnet Synchronous Motor (PMSM) 5. The steering system 6. Braking system in HEV with regeneration 7. Suspension system with construction, working, type and necessity

1. A Case Study on Hybrid Electric Vehicles
Executive Summary
Project Name Case study on Hybrid Electric Vehicles
Name Bibidh Baguli
Institute of Engineering and Management (IEM), Kolkata
Department of Mechanical Engineering
Materials 1. IC Engine (Internal Combustion Engine)
2. Lithium-ion battery (Auxiliary)
3. Electric Traction Motor
4. Electric generator
5. Exhaust System
6. Battery Management System (BMS)
7. Electronic Control Unit (ECU)
8. Transmission (Reduction Gear and Planetary Gear)
9. Thermal Management (Coolant)
10. AC/DC Converter
Social Impact 1. Effects on mobility and travel
2. Higher efficiency rate than normal fossil fuel vehicles.
3. Relatively less environmental impact.
4. Charging an electric vehicle is cheaper than filling fuels.
Project Execution 1. Data is collected and scheduled.
2. Literature review is done.
3. Study on the design and working of the vehicles are done.
4. Knowledge of Power calculation and Simulink system is gained.
5. Case study is made and draft is formed.
Future Scope 1. It will stay ahead of global developments in accordance to inflation.
2. With more battery technology there will be more efficiency in
driving cars.
3. Efficiency of IC engine will increase.
4. In 2025 there will be 20% HEV in sale and by 2030 it will be 40%.

2. Introduction
An Hybrid Electric Vehicle (HEV) is a modern combination of an internal combustion
engine (ICE) and an electric propulsion system (hybrid drivetrain). The electric
powertrain is used in an HEV to achieve better fuel economy than a conventional
vehicle for better performance. HEVs can be classified according to powertrain,
hybridization, and Energy Management Systems (EMS). Modern HEVs use energy-
efficiency technologies such as regenerative braking that converts the vehicles kinetic
energy into electric energy that is stored in battery or supercapacitors. The battery is
connected to an ECU (Electronic Control Unit) and a BMS (Battery Management
System). To maintain the cooling of the engine and BMS it is connected to a coolant.
In this case study we are going to study about the following things in an HEV :-
1. Hybrid Electric Vehicle (HEV) subsystems
2. Toyota Prius Powertrain
3. Transmission system in HEV
4. Use of Brushless DC Motor (BLDC) and Permanent Magnet Synchronous Motor
(PMSM)
5. The steering system
6. Braking system in HEV with regeneration
7. Suspension system with construction, working, type and necessity

3. Literature review
U.S. Department of Energy:[1] Today's hybrid electric vehicles (HEVs) are powered
by an internal combustion engine in combination with one or more electric motors that use
energy stored in batteries.
Clay Jordan:[2] Hybrid electric vehicles are growing in popularity because of the
ability to achieve similar performance to a standard automobile while greatly improving fuel
efficiency and tailpipe emissions.
Bernard Tardieu:[3] In classic hybrids 4 components work together, the IC engine,
the control unit, an electric motor and a battery system.
W.F Hamilton:[4] The social and environmental impacts of electric and hybrid
vehicles include effects on mobility and travel, electricity supply system operation, petroleum
and other fuel consumption, air pollution and traffic noise.
D.S Automobiles:[5] It is predicted that in 2025, 20% of all new global car sales
will be electric, in 2030 this will jump to 40% by 2040.
Alex Valler: [6] The Toyota Prius uses a series parallel components making it a
series-parallel hybrid.
O I Petrov:[7] A sequential hybrid vehicle transmission is a transmission in which
two power supplies power one electrical power unit (electric motor) that drives the vehicle.
D Torres:[8] Regenerative braking stored energy back into the battery thus
increasing life of friction pads on brake shoe.
Dmitry Levkin:[9] A permanent magnet synchronous motor, like any rotating
electric motor, consists of a rotor and a stator. The stator is the fixed part. The rotor is the
rotating part.
D K Warinner:[10] Electrically powered hydraulic steering pumps along with column
drive electric assist unit.
Peter Els:[11] While regenerative braking is well established, the relatively new
regenerative active suspension systems have the potential to bring about further energy
conservation and range extension improvements.

4. Methodology
In this study certain approach is taken to learn and study about the HEV subsystems, Toyota
Prius powertrain, transmission, BMDC and PMSM motors used, regenerative braking etc.
1. First the overall components and their connection with each other are studied in details.
2. Data on Toyota Prius model and its powertrain are collected and studied.
3. The working of the transmission system and use of planetary gears in an HEV is studied
and applied for design.
3. Design of subsystems are learnt in Simulink using MATLAB.
4. How BMDC and PMSM motors work in an HEV are studied.
5. Connection between IC engine, Battery, Coolant, ECU and motor is studied.
6. Classification of HEV according to hybridization, use of powertrain etc. are studied.
7. Steering system is studied.
8. Regenerative braking system which is used to convert kinetic energy into electric energy
has been learnt.
9. Working, types and construction of regenerative suspension is studied.
10. How to code and make a subsystem are performed.
11. Power calculation of motor is done using excel sheet and by application of required
formula.

5. Study
1. Hybrid Electric Vehicles subsystems
Regardless of any type of hybrid electric vehicle every one of them consists of the following
components and subsystems. These are an electric motor, energy storage system (battery), a
fuel supplying system i.e. a fuel cell, gasoline tank, a thermal management system i.e. a coolant,
a battery management system (cell balancing circuit), transmission system, a voltage current
temperature measurement module (VITM). An electric motor is the main driving force of the
vehicle which is connected to the battery. It can be a PMSM or a BLDC motor. The battery is
used to store energy on which the engine later functions to save fuel by a start-stop system. The
fuel tank is used to store fuel/gasoline. Regenerative braking is used to make powerful brakes
by making friction pads preventive to wear and tear.
2. Toyota Prius powertrain
The Toyota Prius uses a series parallel combination of best components of engine making it
a series parallel hybrid. The Prius has a power split device consisting of a gearbox connecting
the generator, an electric motor, and a gas engine. In a series hybrid, the gasoline engine charges
the car’s battery which powers the electric motor. The gas does not power the wheels directly.
In parallel hybrid engines, the vehicle can receive power from the electric motor, gasoline
engine, or both. A ring gear attaches to the electric motor and transfers the motor’s power to a
reduction gear on the final drive. The power split device has a planetary gear set with sun and
planet gears. About 70% of the lost energy can be regenerated into usable energy for
acceleration. The engine and motor switch off at a complete stop. The car uses the battery
power to maintain the radio, lighting, air conditioning, and display screens until you start the
car again. At steady speeds over 15 MPH, some of the gasoline powers the generator to produce
electricity for the batteries. Power split devices can reduce fuel consumption, depending on the
planetary gear configuration.
3. Transmission system in HEV
A sequential hybrid vehicle transmission is a transmission in which two power supplies
power one electrical power unit (electric motor) that drives the vehicle. Most often, for hybrid
vehicles, a series circuit is used. The first energy source is the fuel tank , the energy converter
(power plant) is an internal combustion engine connected to an electric generator . The
generator output is connected to the DC power bus through a controlled electronic converter
(rectifier). The second energy source is a high-voltage storage battery connected to the DC
power bus using a controlled bidirectional power electronic converter (DC / DC converter).
The traction motor receives energy from the power bus through a controlled electronic
frequency converter The traction motor is connected to the main gear, it can be used both as a
motor and as a generator. This transmission may require a battery charger to charge the batteries
using a wall outlet. The disadvantage of the typical scheme is that the power of the internal
combustion engine is converted several times. First, with the help of a generator into alternating
current, then with the help of a rectifier into direct current, and then with the help of an inverter
again into alternating current required to control the power of the traction motor by changing
the frequency and magnitude of the current. Each transformation increases the cost of the
electrical transmission scheme and is accompanied by energy losses.

6. The planetary gear hybrid powertrain (PGHP) is known as
one of the most efficient configurations for hybrid electric vehicles. The system controls the
speed and torque of each component so that it can produce adequate input and output speeds
for the optimal operation of the total system. The performances of the electric motor and
generator were decisive factors owing to the loss in the energy conversion. In a simulation on
an urban driving schedule, the optimal operation of the engine was able to be obtained, and the
system showed an improvement of 2.2 per cent in fuel economy.
4. BLDC and PMSM motor work
Brushless DC motors do not use brushes. With brushed motors, the brushes deliver current
through the commutator into the coils on the rotor. So how does a brushless motor pass current
to the rotor coils? It doesn’t—because the coils are not located on the rotor. Instead, the rotor
is a permanent magnet; the coils do not rotate, but are instead fixed in place on the stator.
Because the coils do not move, there is no need for brushes and a commutator. With the brushed
motor, rotation is achieved by controlling the magnetic fields generated by the coils on the
rotor, while the magnetic field generated by the stationary magnets remains fixed. To change
the rotation speed, you change the voltage for the coils. With a BLDC motor, it is the permanent
magnet that rotates; rotation is achieved by changing the direction of the magnetic fields
generated by the surrounding stationary coils. To control the rotation, you adjust the magnitude
and direction of the current into these coils.
Permanent Magnet Synchronous Motors (PMSMs)
are brushless and have very high reliability and efficiency. Due to their permanent magnet
rotor, they also have higher torque with smaller frame size and no rotor current, all of which
are advantages over AC Induction Motors (AICMs). With their high power-to-size ratio,
PMSMs can help make your design smaller without the loss of torque. The Permanent Magnet
Synchronous Motor (PMSM) is an AC synchronous motor whose field excitation is provided
by permanent magnets and that has a sinusoidal back EMF waveform. The permanent magnets
enable the PMSM to generate torque at zero speed. PMSMs offer higher torque density as
compared to AC Induction Motors (ACIMs), providing a smaller frame size for the same
power. They also deliver high-efficiency operation but require a digitally controlled inverter.
5. The Steering system in HEV
A steering system generally includes a steering gear for controlling a steer axle of a hybrid
vehicle in response to rotation of a steering wheel. The steering system also includes a power
steering pump functionally connected to an internal combustion engine for supplying
pressurized fluid to the steering gear. The steering system further includes an accumulator, a
power steering controller, and a pressure sensor for monitoring the pressure of the
accumulator.
In use, the steering system continuously monitors the pressure of the accumulator via the
pressure sensor. In several instances, the steering system keeps track of whether the
accumulator pressure exceeds an engine shut-down prohibition level and/or an engine restart
level. From these signals, the internal combustion engine can be instructed to restart from its
engine-off condition and/or the internal combustion engine can be prohibited operating in its
engine-on condition to transition to its engine-off condition.

7. 6. Braking system in HEV with Regeneration
Regenerative braking is a mechanism found on most hybrid and full-electric vehicles. It
captures the kinetic energy from braking and converts it into the electrical power that charges
the vehicle’s high voltage battery. Regenerative braking also slows the car down, which
assists the use of traditional brakes.
Nearly all of the kinetic energy propelling your car forward is lost as heat when you apply
the brakes. Regenerative braking solves this problem by recapturing upwards of 70% of the
kinetic energy that would otherwise be lost during braking. The amount of energy recovered
depends on your car model and driving behaviour.
Regenerative braking turns kinetic energy into electricity by reversing the process that drives
the car forward. In electric cars, the drivetrain is powered by a battery pack that powers a
motor (or motors), creating torque–rotational force–on the wheels. In other words, electrical
energy from the battery becomes mechanical energy that spins the wheels.
With regenerative braking, the energy from your spinning wheels is used to reverse the
direction of electricity - from the electric motor(s) to the battery. All you have to do is
remove your foot from the accelerator or, in some cases, press the brake pedal to activate
regenerative braking. The electric motor not only acts as an electric generator, but it also
helps slow your car down because energy is consumed by the wheels as they rotate the shaft
in the electric motor.
7. Suspension system, construction, types, and it’s working in HEV
Suspension system consists of shock absorbers and linkages used to reduce the vibrations
and increasing comforts. Air bag also called air bladders are fitted into coil springs in vehicle,
for better stability of ride and better comfort for passenger. This work deals with basic
designing of a hybrid suspension system that is used on pick-ups. The hybrid suspension
system is better as the air spring part is easily to install and cheap but it makes system more
complex.

8. Analysis
In this study we have found the different methods of designing, application and uses of different
components and parts of a Hybrid Electric Vehicle. Although in many cases it has been found
that some methods and technique that are used in modern hybrid technology are contradictory
and maybe changed in the future for the betterment of the automobile industry. For example,
in case of motor work in an HEV, BLDC can be completely replaced by PMSM motors because
of its efficiency and high reliability. Again, it can generate higher torque in comparison and
can generate torque from zero speed. Again, there should be transformation in the transmission
system because each transmission generates major electric energy loss and also increases the
cost of the scheme. Power of the internal combustion engine is also changed several times.
Regenerative braking is potentially a perfect technology still it has some drawbacks. First
drivers feel indifferent in this system as they are not used to such system. Braking is not so
smooth at low speed of the vehicle. Potentially these brakes have less stopping power than
conventional brakes and drivers have to push harder to stop the vehicle. But this problem has
been solved with the new improved regenerative brakes.
Conclusion
In the end hybrid is the future for sure. The growing technology on automobile industry made
a major change by creating this machine which is economical, technically improved, automatic
and environment friendly. Each and every system has its own advantages and disadvantages
but this is going to improve and technology further rolls out new engineering solutions.
Regarding the usage of hybrid cars in countries like India will certainly grow by 2040 by nearly
60% as companies like TATA and others have already started to make such cars. From the
above study we have got to know a hands-on grip over the technology and assembly of a hybrid
electric vehicle and how it can be designed and used in future technology. Also, we have
understood the social impact of these cars and how we can improve the technology to make it
more environment and socio-friendly for better and more usage.

9. References
(1) Bernard Tardieu: [2016] In classic hybrids 4 components work together, the IC engine, the
control unit, an electric motor and a battery system.
Hybrid Electric Vehicles (HEV) - Definition, Benefits, Types (ackodrive.com)
(2) W.F Hamilton: [2005] The social and environmental impacts of electric and hybrid
vehicles include effects on mobility and travel, electricity supply system operation, petroleum
and other fuel consumption, air pollution and traffic noise.
(3) D.S Automobiles: [2011] It is predicted that in 2025, 20% of all new global car
sales will be electric, in 2030 this will jump to 40% by 2040.
(4) Alex Valler: [2010] The Toyota Prius uses a series parallel components making
it a series-parallel hybrid.
Hybrid Technology: How Does a Prius Work? - Exclusively Hybrid
(5) O I Petrov: [2015] A sequential hybrid vehicle transmission is a transmission in
which two power supplies power one electrical power unit (electric motor) that drives the
vehicle.
pdf (iop.org)
(6) D Torres: [2017] Regenerative braking stored energy back into the battery thus
increasing life of friction pads on brake shoe.
(7) Dmitry Levkin: [2020] A permanent magnet synchronous motor, like any rotating
electric motor, consists of a rotor and a stator. The stator is the fixed part. The rotor is the
rotating part.
Permanent Magnet Synchronous Motor (PMSM) Control | Microchip Technology
(8) D K Warinner: [2018] Electrically powered hydraulic steering pumps along with
column drive electric assist unit.
https://www.google.com/url?sa=i&url=https%3A%2F%2Fmechanicalboost.com%2Fsteering
-
system%2F&psig=AOvVaw1chPw2NsnAZINbyoCAILBM&ust=1672479911360000&sourc
e=images&cd=vfe&ved=0CBEQjhxqFwoTCPDspKqHofwCFQAAAAAdAAAAABAD
(9) L Narrain: [2019] Regenerative braking is potentially a perfect technology still it has
some drawbacks. First drivers feel indifferent in this system as they are not used to such system.
Regenerative Braking: Advantages, Disadvantages, & How It Works | Tires Plus
(10) Peter Els : [2020] While regenerative braking is well established, the relatively new
regenerative active suspension systems have the potential to bring about further energy
conservation and range extension improvements.
Regenerative Braking: Advantages, Disadvantages, & How It Works | Tires Plus

10. (11) Lee Wanghoo : [2019] Today's hybrid electric vehicles (HEVs) are powered by an
internal combustion engine in combination with one or more electric motors that use energy
stored in batteries.
(12) William C. [2010] A steering system generally includes a steering gear for
controlling a steer axle of a hybrid vehicle in response to rotation of a steering wheel.
STEERING SYSTEMS AND METHODS FOR HYBRID VEHICLES - PACCAR INC (freepatentsonline.com)