Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof.

Abhishek H A

Unit-1
Transportation System: Comparison with conventional vehicle technologies, History of vehicle
hybridization, Origin and Fall of EV’s, components of EV’s, challenges and Key aspects of EV,
social and environmental importance of hybrid and electric vehicles.
Vehicle Hybridization: EV’s, Basics of EV, Basics of HEV, Basics of Plug-In Hybrid Electric
vehicle (PHEV), Basics of Fuel Cell Vehicle (FCV). Hybrid Electric Vehicles: Classification, Micro,
Mild, Full, Plug in, EV. Layout and Architecture-Series, Parallel, Series-Parallel Hybrid, Propulsion
systems and components, Hybrid Electric Vehicles System, Types and controls.

Introduction:
Conventional vehicles with internal combustion engines (ICE) provide good performance and long
operating range by utilizing the high energy-density advantages of petroleum fuels. However,
conventional ICE vehicles bear the disadvantages of poor fuel economy and environmental pollution.
The main reasons for their poor fuel economy are (1) engine fuel efficiency characteristics are
mismatched with the real operation requirements, (2) dissipation of vehicle kinetic energy during
braking, especially while operating in urban
areas, and (3) low efficiency of hydraulic transmission in current automobiles in stop-and-go driving
patterns Battery-powered electric vehicles (EV), on the other hand, possess some advantages over
conventional ICE vehicles, such as high energy efficiency and zero environmental pollution.
However, the performance, especially the operation range per battery charge, is far less competitive
than ICE vehicles, due to the lower energy content of the batteries vs. the energy content of gasoline.
Hybrid electric vehicles (HEV), which use two power sources — a primary power source and a
secondary power source — have the advantages of both ICE vehicles and EV and overcome their
disadvantages.

CONVENTIONAL VEHICLES:
A conventional engine-driven vehicle uses its engine to translate fuel energy into shaft power,
directing most of this power through the drive train to turn the wheels. Much of the heat generated
by combustion cannot be used for work and is wasted, both because heat engines have theoretical
efficiency limit.
Moreover, it is impossible to reach the theoretical efficiency limit because:
• Some heat is lost through cylinder walls before it can do work
• Some fuel is burned at less than the highest possible pressure
• Fuel is also burned while the engine is experiencing negative load (during braking) or when the
vehicle is coasting or at a stop, with the engine idling.

What is a hybrid?
A hybrid vehicle combines any two power (energy) sources. Possible combinations include
diesel/electric, gasoline/fly wheel, and fuel cell (FC)/battery. Typically, one energy source is
storage, and the other is conversion of a fuel to energy. The combination of two power sources
may support two separate propulsion systems. Thus to be a True hybrid, the vehicle must have at
least two modes of propulsion.
For example, a truck that uses a diesel to drive a generator, which in turn drives several electrical
motors for all-wheel drive, is not a hybrid. But if the truck has electrical energy storage to provide
a second mode, which is electrical assists, then it is a hybrid Vehicle. These two power sources
may be paired in series, meaning that the gas engine charges the batteries of an electric motor
that powers the car, or in parallel, with both mechanisms driving the car directly.

Hybrid electric vehicle (HEV)

Consistent with the definition of hybrid above, the hybrid electric vehicle combines a gasoline
engine with an electric motor. An alternate arrangement is a diesel engine and an electric motor
(figure 1).

Page 1 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Figure 1: Components of a hybrid Vehicle that combines a pure gasoline with a

pure EV.
As shown in Figure 1, a HEV is formed by merging components from a pure electrical vehicle and
a pure gasoline vehicle. The Electric Vehicle (EV) has an M/G which allows regenerative braking
for an EV; the M/G installed in the HEV enables regenerative braking. For the HEV, the M/G
is tucked directly behind the engine. In Honda hybrids, the M/G is connected directly to the engine.
The transmission appears next in line. This arrangement has two torque producers; the M/G in
motor mode, M-mode, and the gasoline engine. The battery and M/G are connected electrically.
HEVs are a combination of electrical and mechanical components. Three main sources of electricity
for hybrids are batteries, FCs, and capacitors. Each device has a low cell voltage, and, hence,
requires many cells in series to obtain the voltage demanded by an HEV. Difference in the source
of Energy can be explained as:
a. The FC provides high energy but low power.
b. The battery supplies both modest power and energy.
c. The capacitor supplies very large power but low energy.
The components of an electrochemical cell include anode, cathode, and electrolyte
(shown in fig2). The current flow both internal and external to the cell is used to describe the
current loop.

Figure 2: An electrode, a circuit for a cell which is converting chemical energy to

electrical energy. The motion of negative charges is clockwise and forms a closed
loop through external wires and load and the electrolyte in the cell.
Page 2 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

A critical issue for both battery life and safety is the precision control of the
Charge/Discharge cycle. Overcharging can be traced as a cause of fire and failure. Applications
impose two boundaries or limitations on batteries. The first limit, which is dictated by battery
life, is the minimum allowed State of Charge. As a result, not all the installed battery energy can
be used. The battery feeds energy to other electrical equipment, which is usually the inverter. This
equipment can use a broad range of input voltage, but cannot accept a low voltage. The second
limit is the minimum voltage allowed from the battery.

Historical development (root) of Automobiles

In 1900, steam technology was advanced. The advantages of steam-powered cars included high
performance in terms of power and speed. However, the disadvantages of steam-powered cars
included poor fuel economy and the need to “fire up the boiler” before driving. Feed water
was a necessary input for steam engine, therefore could not tolerate the loss of fresh water. Later,
Steam condensers were applied to the steam car to solve the feed water problem. However, by
that time Gasoline cars had won the marketing battle.
Gasoline cars of 1900 were noisy, dirty, smelly, cantankerous, and unreliable. In comparison,
electric cars were comfortable, quiet, clean, and fashionable. Ease of control was also a desirable
feature. Lead acid batteries were used in 1900 and are still used in modern cars. Hence lead acid
atteries have a long history (since 1881) of use as a viable energy storage device. Golden age of
Electrical vehicle marked from 1890 to 1924 with peak production of electric vehicles in 1912.
However, the range was limited by energy storage in the battery. After every trip, the battery
required recharging. At the 1924 automobile show, no electric cars were on display. This
announced the end of the Golden Age of electric-powered cars.
The range of a gasoline car was far superior to that of either a steam or an electric car and
dominated the automobile market from 1924 to 1960. The gasoline car had one dominant feature;
it used gasoline as a fuel. The modern period starts with the oil embargoes and the gasoline
shortages during the 1970s which created long lines at gas stations. Engineers recognized that the
good features of the gasoline engine could be combined with those of the electric motor to
produce a superior car. A marriage of the two yields the hybrid automobile.

Figure 3: Historical development of automobile and development of interest and

activity in the EV from 1890 to present day.
Electric Vehicle merged into hybrid
electric vehicle.

Page 3 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

1769
The first steam-powered vehicle was designed by Nicolas-Joseph Cugnot and constructed by
M. Brezin that could attain speeds of up to 6 km/hour. These early steam-powered vehicles
were so heavy that they were only practical on a perfectly flat surface as strong as iron.
1807
The next step towards the development of the car was the invention of the internal combustion
engine. Francois Isaac de Rivaz designed the first internal combustion engine in, using
a mixture of hydrogen and oxygen to generate energy.
1825
British inventor Goldsworthy Gurney built a steam car that successfully completed an 85 mile
round-trip journey in ten hours time.
1839
Robert Anderson of Aberdeen, Scotland built the first electric
vehicle1860
In, Jean Joseph Etienne Lenoir, a Frenchman, built the first successful two-stroke gas driven
engine.
1886
Historical records indicate that an electric-powered taxicab, using a battery with 28 cells and a
small electric motor, was introduced in England.
1888
Immisch & Company built a four-passenger carriage, powered by a one-horsepower motor
and 24-cell battery, for the Sultan of the Ottoman Empire. In the same year, Magnus Volk
in Brighton, England made a three-wheeled electric car. 1890 – 1910 (Period of significant
improvements in battery technology)

Invention Of hybrid vehicle

1890
Jacob Lohner, a coach builder in Vienna, Austria, foresaw the need for an electric vehicle that
would be less noisy than the new gas-powered cars. He commissioned a design for an electric
vehicle from Austro-Hungarian engineer Ferdinand Porsche, who had recently graduated from the
Vienna Technical College. Porsche's first version of the electric car used a pair of electric motors
mounted in the front wheel hubs of a conventional car. The car could travel up to 38 miles. To
extend the vehicle's range, Porsche added a gasoline engine that could recharge the batteries, thus
giving birth to the first hybrid, the Lohner- Porsche Elektromobil.

Early Hybrid Vehicles

1900
Porsche showed his hybrid car at the Paris Exposition of 1900. A gasoline engine was used to
power a generator which, in turn, drove a small series of motors. The electric engine was used to
give the car a little bit of extra power. This method of series hybrid engine is still in use today,
although obviously with further scope of performance improvement and greater fuel savings
1915
Woods Motor Vehicle manufacturers created the Dual Power hybrid vehicle, second hybrid car in
market. Rather than combining the two power sources to give a single output of power, the
Dual Power used an electric battery motor to power the engine at low speeds (below 25km/h)
and used the gasoline engine to carry the vehicle from these low speeds up to its 55km/h maximum
speed. While Porsche had invented the series hybrid, Woods invented the parallel hybrid.
1918
The Woods Dual Power was the first hybrid to go into mass production. In all, some 600 models
were built by. However, the evolution of the internal combustion engine left electric power a
marginal technology

Page 4 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

1960
Victor Wouk worked in helping create numerous hybrid designs earned him the nickname
of the “Godfather of the Hybrid”. In 1976 he even converted a Buick Skylark from gasoline to
hybrid.
1978
Modern hybrid cars rely on the regenerative braking system. When a standard combustion engine
car brakes, a lot of power is lost because it dissipates into the atmosphere as heat. Regenerative
braking means that the electric motor is used for slowing the car and it essentially collects this
power and uses it to help recharge the electric batteries within the car. This development alone is
believed to have progressed hybrid vehicle manufacture significantly. The Regenerative Braking
System, was first designed and developed in 1978 by David Arthurs. Using standard car
components he converted an Opel GT to offer 75 miles to the gallon and many home
conversions are done using the plans for this system that are still widely available on the Internet

Modern Period of Hybrid History

The history of hybrid cars is much longer and more involved than many first imagine. It is,
however, in the last ten years or so that we, as consumers, have begun to pay more attention to the
hybrid vehicle as a viable alternative to ICE driven cars. Whether looking for a way to save
money on spiraling gas costs or in an attempt to help reduce the negative effects on the
environment we are buying hybrid cars much more frequently.
1990s
Automakers took a renewed interest in the hybrid, seeking a solution to dwindling energy supplies
and environmental concerns and created modern history of hybrid car
1993
In USA, Bill Clinton's administration recognized the urgency for the mass production of cars
powered by means other than gasoline. Numerous government agencies, as well as Chrysler, Ford,
GM, and USCAR combined forces in the PNGV (Partnership for a New Generation of Vehicles),
to create cars using alternative power sources, including the development and improvement of
hybrid electric vehicles.
1997
The Audi Duo was the first European hybrid car put into mass production and hybrid production
and consumer take up has continued to go from strength to strength over the decades.
2000
Toyota Prius and Honda Insight became the first mass market hybrids to go on sale in the United
States, with dozens of models following in the next decade. The Honda Insight and Toyota
Prius were two of the first mainstream Hybrid Electric Vehicles and both models remain a popular
line.
2005
A hybrid Ford Escape, the SUV, was released in 2005. Toyota and Ford essentially swapped patents
with one another, Ford gaining a number of Toyota patents relating to hybrid technology and
Toyota, in return, gaining access to Diesel engine patents from Ford.

Present of Hybrid Electric vehicle

Toyota is the most prominent of all manufacturers when it comes to hybrid cars. As well as the
specialist hybrid range they have produced hybrid versions of many of their existing model
lines, including several Lexus (now owned and manufactured by Toyota) vehicles. They have
also stated that it is their intention to release a hybrid version of every single model they
release in the coming decade. As well as cars and SUVs, there are a select number of hybrid
motorcycles, pickups, vans, and other road going vehicles available to the consumer and the list is
continually increasing.

Future of Hybrid electrical vehicle

Since petroleum is limited and will someday run out of supply. In the arbitrary year 2037, an
estimated one billion petroleum-fueled vehicles will be on the world’s roads. gasoline will become
Page 5 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

prohibitively expensive. The world need to have solutions for the “400 million otherwise useless
cars”. So year 2037 “gasoline runs out year” means, petroleum will no longer be used for personal
mobility. A market may develop for solar-powered EVs of the size of a scooter or golf cart. Since
hybrid technology applies to heavy vehicles, hybrid buses and hybrid trains will be more
significant.

Economic and Environmental Impact of Electric Hybrid Vehicle:

As modern culture and technology continue to develop, the growing presence of global warming
and irreversible climate change draws increasing amounts of concern from the world’s
population. It has only been recently, when modern society has actually taken notice of these
changes and decided that something needs to change if the global warming process is to be stopped.
Countries around the world are working to drastically reduce CO2 emissions as well as other
harmful environmental pollutants. Amongst the most notable producers of these pollutants are
automobiles, which are almost exclusively powered by internal combustion engines and spew out
unhealthy emissions.
According to various reports, cars and trucks are responsible for almost 25% of CO2 emission and
other major transportation methods account for another 12%. With immense quantities of cars on
the road today, pure combustion engines are quickly becoming a target of global warming blame.
One potential alternative to the world’s dependence on standard combustion engine vehicles are
hybrid cars. Cost-effectiveness is also an important factor contributing to the development of an
environment friendly transportation sector.

Hybrid Vehicle
A hybrid vehicle combines any type of two power (energy) sources. Possible combinations
include diesel/electric, gasoline/fly wheel, and fuel cell (FC)/battery. Typically, one energy source
is storage, and the other is conversion of a fuel to energy. In the majority of modern hybrids, cars
are powered by a combination of traditional gasoline power and the addition of an electric motor.
However, hybrid still use the petroleum based engine while driving so they are not completely
clean, just cleaner than petroleum only cars. This enables hybrid cars to have the potential to
segue into new technologies that rely strictly on alternate fuel sources.
The design of such vehicles requires, among other developments, improvements in power train
systems, fuel processing, and power conversion technologies. Opportunities for utilizing various
fuels for vehicle propulsion, with an emphasis on synthetic fuels (e.g., hydrogen, biodiesel,
bioethanol, dimethylether, ammonia, etc.) as well as electricity via electrical batteries, have been
analyzed over the last decade.
In order to analyze environment impact of vehicle propulsion and fueling system; we are presenting
a case study which has been reported in literature (Chapter: Ibrahim Dincer, Marc A. Rosen and
Calin Zamfirescu,” Economic and Environmental Comparison of Conventional and Alternative
Vehicle Options”, Book: Electric and Hybrid Vehicles: Power Sources, Models, Sustainability,
Infrastructure and the Market by Gianfranco Pistoia (2010))

A Case study
This case treated the following aspects: economic criteria, environmental criteria, and a combined
impact criterion. The latter is a normalized indicator that takes into account the effects on both
environmental and economic performance of the options considered.
Case compared four kinds of fuel-propulsion vehicle alternatives. Two additional kinds of vehicles,
both of which are zero polluting at fuel utilization stage (during vehicle operation) were also
included in analysis. The vehicles analyzed were as follows:
1. Conventional gasoline vehicle (gasoline fuel and ICE),
2. Hybrid vehicle (gasoline fuel, electrical drive, and large rechargeable battery),
3. Electric vehicle (high-capacity electrical battery and electrical drive/generator),
4. Hydrogen fuel cell vehicle (high-pressure hydrogen fuel tank, fuel cell, electrical drive),
5. Hydrogen internal combustion vehicle (high-pressure hydrogen fuel tank and ICE),

Page 6 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

6. Ammonia-fueled vehicle (liquid ammonia fuel tank, ammonia thermo-catalytic

decomposition and separation unit to generate pure hydrogen, hydrogen-fueled ICE).

For environmental impact analysis, all stages of the life cycle were considered, starting from
a) The extraction of natural resources to produce materials and
b) Ending with conversion of the energy stored onboard the vehicle into mechanical energy for
vehicle displacement and
c) Other purposes (heating, cooling, lighting, etc.).
In addition, vehicle production stages and end-of-life disposal contribute substantially when
quantifying the life cycle environmental impact of fuel-propulsion alternatives.
The analysis were conducted on six vehicles, each was representative of one of the above
discussed categories. The specific vehicles were:
1) Toyota Corolla (conventional vehicle),
2) Toyota Prius (hybrid vehicle),
3) Toyota RAV4EV (electric vehicle),
4) Honda FCX (hydrogen fuel cell vehicle),
5) Ford Focus H2-ICE (hydrogen ICE vehicle),
6) Ford Focus H2-ICE adapted to use ammonia as source of hydrogen (ammonia-fueled ICE
vehicle).

Economical Analysis
A number of key economic parameters that characterize vehicles were:
A. Vehicle price, B. Fuel cost, and C. Driving range.
This case neglected maintenance costs; however, for the hybrid and electric vehicles, the cost of
battery replacement during the lifetime was accounted for. The driving range determines the
frequency (number and separation distance) of fueling stations for each vehicle type. The total
fuel cost and the total number of kilometers driven were related to the vehicle life (see Table 1).
Table1: Technical and economical values for selected vehicle types
Vehicle type Fuel Type Initial Specific fuel Driving Price of battery
Price Price Range Changes During
(USk$) (US$/100 km) (Km) Vehicle Life cycle
(USk$)

Conventional Gasoline 15.3 2.94 540 1 x 0.1

(Toyota Corolla)
Hybrid Gasoline 20 1.71 930 1 x 1.02
(Toyota Prius)
Electric Electricity 42 0.901 164 2 x 15.4
(Toyota RAV4EV)
Fuel cell Hydrogen 100 1.69 355 1 x 0.1
(Honda FCX)
H2-ICE (Ford Hydrogen 60 8.4 300 1 x 0.1
Focus H2-ICE)
NH3–H2-ICE Ammonia 40 6.4 430 1 x 0.1
(Ford Focus H2-
ICE and ammonia
Adaptive)

For the Honda FCX the listed initial price for a prototype leased in 2002 was USk$2,000, which
is estimated to drop below USk$100 in regular production. Currently, a Honda FCX can be leased
for 3 years with a total price of USk$21.6. In order to render the comparative study reasonable,
the initial price of the hydrogen fuel cell vehicle is assumed here to be USk$100. For electric
Page 7 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

vehicle, the specific cost was estimated to be US$569/kWh with nickel metal hydride (NiMeH)
batteries which are typically used in hybrid and electric cars.
Historical prices of typical fuels were used to calculate annual average price.

Environmental Analysis
Analysis for the first five options was based on published data from manufacturers. The results
for the sixth case, i.e. the ammonia-fueled vehicle, were calculated from data published by Ford
on the performance of its hydrogen-fueled Ford Focus vehicle. Two environmental impact
elements were accounted for in the:
a) Air pollution (AP) and
b) Greenhouse gas (GHG) emissions.
The main GHGs were CO2, CH4, N2O, and SF6 (sulfur hexafluoride), which have GHG impact
weighting coefficients relative to CO2 of 1, 21, 310, and 24,900, respectively.
For AP, the airborne pollutants CO, NOx, SOx, and VOCs are assigned the following weighting
coefficients: 0.017, 1, 1.3, and 0.64, respectively.
The vehicle production stage contributes to the total life cycle environmental impact through the
pollution associated with
a) The extraction and processing of material resources,
b) Manufacturing and
c) The vehicle disposal stage.

Additional sources of GHG and AP emissions were associated with the fuel production and
utilization stages. The environmental impacts of these stages have been evaluated in numerous
life cycle assessments of fuel cycles.
Regarding electricity production for the electric car case, three case scenarios were considered
here:
1. when electricity is produced from renewable energy sources and nuclear energy;
2. when 50% of the electricity is produced from renewable energy sources and 50% from
natural gas at an efficiency of 40%;
3. when electricity is produced from natural gas at an efficiency of 40%.

AP emissions were calculated assuming that GHG emissions for plant manufacturing correspond
entirely to natural gas combustion. GHG and AP emissions embedded in manufacturing a natural
gas power generation plant were negligible compared to the direct emissions during its utilization.
Taking those factors into account, GHG and AP emissions for the three scenarios of electricity
generation were presented in Table 2.

Table2: GHG and air pollution emissions per MJ of electricity produced

Electricity- Description of Electricity generation GHG emission (g) AP emission
generation Scenario (g)
scenario

1 Electricity produced = 100% (Renewable 5.11 0.195

Energy + Nuclear Energy)
2 Electricity produced = (50% Renewable 77.5 0.296
Energy + 50% Natural gas)
3 Electricity produced = 100% Natural Gas 149.9 0.573

Hydrogen charging of fuel tanks on vehicles requires compression. Therefore, presented case
considered the energy for hydrogen compression to be provided by electricity.

Page 8 of 30
Dept. Mech. Engg. DSCE
 Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Table 3: GHG and air pollution emissions per MJ fuel of Hydrogen from natural gas
produced
Fuel GHG emissions, g AP emissions, g
Hydrogen from natural gas
Scenario 1 78.5 0.0994
Scenario 2 82.1 0.113
Scenario 3 85.7 0.127

GHG and AP emissions were reported for hydrogen vehicles for the three electricity-generation
scenarios considered (see table 3), accounting for the environmental effects of hydrogen
compression.
Table 4. Environmental impact associated with vehicle Overall Life cycle and Fuel
Utilization State
Fuel utilization stage Overall life cycle
Vehicle type GHG emissions AP emissions GHG emissions AP emissions
(kg/100 km) (kg/100 km) (kg/100 km) (kg/100 km)
Conventional 19.9 0.0564 21.4 0.06
Hybrid 11.6 0.0328 13.3 0.037
Electric-S1 0.343 0.00131 2.31 0.00756
Electric-S2 5.21 0.0199 7.18 0.0262
Electric-S3 10.1 0.0385 12 0.0448
Fuel Cell -S1 10.2 0.0129 14.2 0.0306
Fuel Cell -S2 10.6 0.0147 14.7 0.0324
Fuel Cell -S3 11.1 0.0165 15.2 0.0342
H2-ICE 10 0.014 11.5 0.018
NH3–H2-ICE 0 0.014 1.4 0.017
The environmental impact of the fuel utilization stage, as well as the overall life cycle is
presented in Table 4. The H2-ICE vehicle results were based on the assumption that the only
GHG emissions during the utilization stage were associated with the compression work, needed to
fill the fuel tank of the vehicle. The GHG effect of water vapor emissions was neglected in this
analysis due its little value, for the ammonia fuel vehicle, a very small amount of pump work was
needed therefore, ammonia fuel was considered to emit no GHGs during fuel utilization.

Results of technical–economical–environmental Analysis:

In present situation this case study provides a general approach for assessing the combined
technical–economical–environmental benefits of transportation options.
This analysis showed that the hybrid and electric cars have advantages over the others. The
economics and environmental impact associated with use of an electric car depends
significantly on the source of the electricity:
a. If electricity is generated from renewable energy sources, the electric car is
advantageous to the hybrid vehicle.
b. If the electricity is generated from fossil fuels, the electric car remains
competitive only if the electricity is generated onboard.

Page 9 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

c. If the electricity is generated with an efficiency of 50–60% by a gas

turbine engine connected to a high-capacity battery and electric motor, the
electric car is superior in many respects.
d. For electricity-generation scenarios 2 and 3, using ammonia as a means to
store hydrogen onboard a vehicle is the best option among those analyzed (as
shown in figure 5).

Figure4: Environmental indicators for six vehicle types

Figure5: Normalized economic and environmental indicators for six vehicle

types

Page 10 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

The electric car with capability for onboard electricity generation represents a beneficial option
and is worthy of further investigation, as part of efforts to develop energy efficient and ecologically
benign vehicles.

The main limitations of this study were as follows:

(i)the use of data which may be of limited accuracy in some instances; (ii) the subjectivity of
the indicators chosen; and
(iii)the simplicity of the procedure used for developing the general indicator without using
unique weighting coefficients.
Despite these limitations, the study reflects relatively accurately and realistically the present situation
and provides a general approach for assessing the combined technical–economical– environmental
benefits of transportation options.

Basic Architecture of Hybrid Drive Trains and Analysis of Series Drive Train The Hybrid
Electric Vehicle (HEV)

What exactly is an HEV? The definition available is so general that it anticipates future
technologies of energy sources. The term hybrid vehicle refers to a vehicle with at least two sources
of power. A hybrid-electric vehicle indicates that one source of power is provided by an electric
motor. The other source of motive power can come from a number of different technologies, but is
typically provided by an internal combustion engine designed to run on either gasoline or diesel
fuel. As proposed by Technical Committee (Electric Road Vehicles) of the International
Electrotechnical Commission, an HEV is a vehicle in which propulsion energy is available from
two or more types of energy sources and at least one of them can deliver electrical energy. Based
on this general definition, there are many types of HEVs, such as: the gasoline ICE and battery, diesel
ICE and battery, battery and FC, battery and capacitor, battery and flywheel, battery and battery
hybrids.
Most commonly, the propulsion force in HEV is provided by a combination of electric motor
and an ICE. The electric motor is used to improve the energy efficiency (improves fuel consumption)
and vehicular emissions while the ICE provides extended range capability.

Energy Use in Conventional Vehicles

In order to understand how a HEV may save energy, it is necessary first to examine how conventional
vehicles use energy. The breakdown of energy use in a vehicle is as follows:
In order to maintain movement, vehicles must produce power at the wheels to overcome:
a. aerodynamic drag (air friction on the body surfaces of the vehicle, coupled with pressure forces
caused by the air flow)
b. rolling resistance (the resistive forces between tires and the road surface)
c. resistive gravity forces associated with climbing a grade

Further, to accelerate, the vehicle must its inertia. Most of the energy expended in acceleration is then
lost as heat in the brakes when the vehicle is brought to a stop.
The vehicle must provide power for accessories such as heating fan, lights, power steering, and
air conditioning.
Finally, a vehicle will need to be capable of delivering power for acceleration with very little delay
when the driver depresses the accelerator, which may necessitate keeping the power source in a
standby (energy-using) mode.
A conventional engine-driven vehicle uses its engine to translate fuel energy into shaft power,
directing most of this power through the drivetrain to turn the wheels. Much of the heat generated
by combustion cannot be used for work and is wasted, both because heat engines have theoretical
efficiency limit. Moreover, it is impossible to reach the theoretical efficiency limit because:
- some heat is lost through cylinder walls before it can do work
- some fuel is burned at less than the highest possible pressure

Page 11 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

fuel is also burned while the engine is experiencing negative load (during braking) or when the
vehicle is coasting or at a stop, with the engine idling.
Although part of engine losses would occur under any circumstances, part occurs because in
conventional drivetrains, engines are sized to provide very high levels of peak power for the
acceleration capability expected by consumers, about 10 times the power required to cruise at
100Km/h. However, the engines are operated at most times at a small fraction of peak power and
at these operating points they are quite inefficient.
Having such a large engine also increases the amount of fuel needed to keep the engine operating
when the vehicle is stopped or during braking or coasting, and increases losses due to the added
weight of the engine, which increases rolling resistance and inertial losses. Even gradeability
requirements (example: 55 mph up a 6.5% grade) require only about 60 or 70% of the power needed
to accelerate from 0 to 100Km/h in under 12 seconds.

The Figure 6 shows the translation of fuel energy into work at the wheels for a typical midsize vehicle
in urban and highway driving. From Figure 6 it can be observed that:
At best, only 20% of the fuel energy reaches the wheels and is available to overcome the tractive
forces, and this is on the highway when idling losses are at a minimum, braking loss is infrequent,
and shifting is far less frequent.
Braking and idling losses are extremely high in urban driving and even higher in more congested
driving, e.g., within urban cores during rush hour. Braking loss represents 46% of all tractive losses
in urban driving. Idling losses represent about one sixth of the fuel energy on this cycle.
Losses to aerodynamic drag, a fifth or less of tractive losses in urban driving, are more than half of
the tractive losses during highway driving.

Figure 6:Translation of fuel energy into

work in a vehicle

Energy Savings Potential of Hybrid Drivetrains

In terms of overall energy efficiency, the conceptual advantages of a hybrid over a
conventional vehicle are:
Regenerative braking. A hybrid can capture some of the energy normally lost as heat to
the mechanical brakes by using its electric drive motor(s) in generator mode to brake
the vehicle
More efficient operation of the ICE, including reduction of idle. A hybrid can avoid
some of the energy losses associated with engine operation at speed and load combinations
where the engine is inefficient by using the energy storage device to either absorb part of
the ICE’s output or augment it or even substitute for it. This allows the ICE to operate
only at speeds and loads where it is most efficient. When an HEV is stopped, rather than
running the engine at idle, where it is extremely inefficient, the control system may

Page 12 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

either shut off the engine, with the storage device providing auxiliary power (for heating
or cooling the vehicle interior, powering headlights, etc.), or run the engine at a higher-
than-idle (more efficient) power setting and use the excess power (over auxiliary loads)
to recharge the storage device. When the vehicle control system can shut the engine
off at idle, the drivetrain can be designed so that the drive motor also serves as the
starter motor, allowing extremely rapid restart due to the motor’s high starting torque.
Smaller ICE: Since the storage device can take up a part of the load, the HEV’s
ICE can be down sized. The ICE may be sized for the continuous load and not for the
very high short term acceleration load. This enables the ICE to operate at a higher fraction
of its rated power, generally at higher fuel efficiency, during most of the driving.

There are counterbalancing factors reducing hybrids’ energy advantage, including:

Potential for higher weight. Although the fuel-driven energy source on a hybrid
generally will be of lower power and weight than the engine in a conventional vehicle of
similar performance, total hybrid weight is likely to be higher than the conventional
vehicle it replaces because of the added weight of the storage device, electric motor(s), and
other components. This depends, of course, on the storage mechanism chosen, the vehicle
performance requirements, and so forth.
Electrical losses. Although individual electric drivetrain components tend to be quite
efficient for one-way energy flows, in many hybrid configurations, electricity flows back
and forth through components in a way that leads to cascading losses. Further, some of
the components may be forced to operate under conditions where they have reduced
efficiency. For example, like ICEs, most electric motors have lower efficiency at the low-
speed, low-load conditions often encountered in city driving. Without careful component
selection and a control strategy that minimizes electric losses, much of the theoretical
efficiency advantage often associated with an electric drivetrain can be lost.

HEV Configurations
Concept of a hybrid drivetrain
In Figure 7 the generic concept of a hybrid drivetrain and possible energy flow route is shown.
The various possible ways of combining the power flow to meet the driving requirements are:
1. powertrain 1 alone delivers power
2. powertrain 2 alone delivers power
3. both powertrain 1 and 2 deliver power to load at the same time
4. powertrain 2 obtains power from load (regenerative braking)
5. powertrain 2 obtains power from powertrain 1
6. powertrain 2 obtains power from powertrain 1 and load at the same time
7. powertrain 1 delivers power simultaneously to load and to powertrain 2
8. powertrain 1 delivers power to powertrain 2 and powertrain 2 delivers power ton load
9. powertrain 1 delivers power to load and load delivers power to powertrain 2.

The load power of a vehicle varies randomly in actual operation due to frequent acceleration,
deceleration and climbing up and down the grades. The power requirement for a typical driving
scenario is shown in Figure 8. The load power can be decomposed into two parts:
i. steady power, i.e. the power with a constant value
ii. dynamic power, i.e. the power whose average value is zero

Page 13 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Figure 7:Generic Hybrid Drivetrain

Figure 8: Load power decomposition

In HEV one powertrain favours steady state operation, such as an ICE or fuel cell. The other
powertrain in the HEV is used to supply the dynamic power. The total energy output from the
dynamic powertrain will be zero in the whole driving cycle. Generally, electric motors are used to
meet the dynamic power demand.

Architectures of Hybrid Electric Drive Trains: (Classification of HEVs Based on Architecture)

The architecture of a hybrid vehicle is loosely defined as the connection between the components
that define the energy flow routes and control ports. Traditionally, HEVs were classified into two
basic types: series andparallel. It is interesting to note that, in 2000, some newly introduced HEVs
could not be classified into these kinds.
Therefore, HEVs are now classified into four kinds: series hybrid, parallel hybrid, series–parallel
hybrid, and complex hybrid, which are functionally shown in Figure 9.
In Figure 9, a fuel tank-IC engine and a battery-electric motor are taken, respectively, as
examples of the primary power source (steady power source) and secondary power source (dynamic
power source). Of course, the IC engine can be replaced by other types of power sources, such as
fuel cells. Similarly, the batteries can be replaced by ultracapacitors or by flywheels and their
combinations, which will be discussed in detail in the following chapters.

Page 14 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

FIGURE 9 Classification of hybrid electric vehicles

Series Hybrid Electric Drive Trains

A series hybrid drive train is a drive train where two power sources feed a single powerplant (electric
motor) that propels the vehicle. The most commonly found series hybrid drive train is the series
hybrid electric drive train shown in Figure 10. The unidirectional energy source is a fuel tank and the
unidirectional energy converter is an engine coupled to an electric generator. The output of the
electric generator is connected to an electric power bus through an electronic converter (rectifier).
The bidirectional energy source is an electrochemical battery pack, connected to the bus by means of
a power electronics converter (DC/DC converter). The electric power bus is also connected to the
controller of the electric traction motor. The traction motor can be controlled either as a motor or a
generator, and in forward or reverse motion. This drive train may need a battery charger to charge
the batteries by a wall plug-in from the power network.

Series hybrid electric drive trains potentially have the following operation modes:
1. Pure electric mode: The engine is turned off and the vehicle is propelled only by the batteries.
2. Pure engine mode: The vehicle traction power only comes from the engine-generator, while the
batteries neither supply nor draw any power from the drive train. The electric machines serve as an
electric transmission from the engine to the driven wheels.
3. Hybrid mode: The traction power is drawn from both the engine generator and the batteries.
4. Engine traction and battery charging mode: The engine-generator supplies power to charge the
batteries and to propel the vehicle.
5. Regenerative braking mode: The engine-generator is turned off and the traction motor is operated
as a generator. The power generated is used to charge the batteries.
6. Battery charging mode: The traction motor receives no power and the engine-generator charges
the batteries.
7. Hybrid battery charging mode: Both the engine-generator and the traction motor operate as
generators to charge the batteries.

Page 15 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

FIGURE 10 Configuration of a series hybrid electric drive train

Series hybrid drive trains offer several advantages:

1. The engine is fully mechanical when decoupled from the driven wheels. Therefore, it can be
operated at any point on its speed–torque characteristic map, and can potentially be operated solely
within its maximum efficiency region as shown in Figure 10. The efficiency and emissions of the
engine can be further improved by optimal design and control in this narrow region. A narrow region
allows greater improvements than an optimization across
the entire range. Furthermore, the mechanical decoupling of the engine from the driven wheels allows
the use of a high-speed engine. This makes it difficult to power the wheels directly through a
mechanical link, such as gas turbines or powerplants, with slow dynamics like the Stirling engine.
2. Because electric motors have near-ideal torque–speed characteristics, they do not need multigear
transmissions. Therefore, their construction is greatly simplified and the cost is
reduced. Furthermore, instead of using one motor and a differential gear, two motors may be used,
each powering a single wheel. This provides speed decoupling between the two wheels
like a differential but also acts as a limited slip -differential for traction control purposes. The ultimate
refinement would use four motors, thus making the vehicle an all-wheel-drive without the expense
and complexity of differentials and drive shafts running through the frame.
3. Simple control strategies may be used as a result of the mechanical decoupling provided by the
electrical transmission.
However, series hybrid electric drive trains have some disadvantages:
1. The energy from the engine is converted twice (mechanical to electrical in the generator and
electrical to mechanical in the traction motor). The inefficiencies of the generator and traction motor
add up and the losses may be significant.
2. The generator adds additional weight and cost.
3. The traction motor must be sized to meet maximum requirements since it is the only powerplant
propelling the vehicle.

5.2.2 Parallel Hybrid Electric Drive Trains

A parallel hybrid drive train is a drive train in which the engine supplies its power mechanically to
the wheels like in a conventional ICE-powered vehicle. It is assisted by an electric motor that is
mechanically coupled to the transmission. The powers of the engine and electric motor are coupled

Page 16 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

together by mechanical coupling, as shown in Figure 11. The Mechanical combination of the engine
and electric motor power leaves room for several
different configurations.

FIGURE 11 Configuration of a parallel hybrid electric drive train

The parallel HEV (Figure 9) allows both ICE and electric motor (EM) to deliver power to drive
the wheels. Since both the ICE and EM are coupled to the drive shaft of the wheels via two
clutches, the propulsion power may be supplied by ICE alone, by EM only or by both ICE and
EM. The EM can be used as a generator to charge the battery by regenerative braking or absorbing
power from the ICE when its output is greater than that required to drive the wheels.

The advantages of the parallel hybrid drivetrain are:

Both engine and electric motor directly supply torques to the driven wheels and no energy form
conversion occurs, hence energy loss is less compactness due to no need of the generator and smaller
traction motor.

The drawbacks of parallel hybrid drivetrains are:

- Mechanical coupling between the engines and the driven wheels, thus the engine operating
points cannot be fixed in a narrow speed region.
- The mechanical configuration and the control strategy are complex compared to series hybrid
drivetrain.
- Due to its compact characteristics, small vehicles use parallel configuration. Most passenger
cars employ this configuration.

Series-Parallel System
In the series-parallel hybrid (Figure 9), the configuration incorporates the features of both the
series and parallel HEVs. However, this configuration needs an additional electric machine and a
planetary gear unit making the control complex.

Complex Hybrid System

The complex hybrid system (Figure 9) involves a complex configuration which cannot be
classified into the above three kinds. The complex hybrid is similar to the series-parallel hybrid
since the generator and electric motor is both electric machines. However, the key difference is
due to the bi-directional power flow of the electric motor in complex hybrid and the unidirectional
power flow of the generator in the series-parallel hybrid. The major disadvantage of complex
hybrid is higher complexity.
Page 17 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Classification of HEVs Based on Degree of Hybridization:

Parallel and combined hybrids can be categorized according to degree of hybridization. Degree of
hybridization depends upon the power supplied by IC engine and electric motor. In some vehicles, IC engine
is dominant; electric motor turns on only when boost is needed. In many vehicles, both IC engine and electric
motor share equal loads. Others can run only with electric motor system operating. The ratio of power
developed by an electric motor in a hybrid vehicle to the total power consumed by the vehicle is known as
degree of hybridization.

Degree of hybridization
Type Of hybrid
Micro <5%
Mild Up to 10%
Full Hybrid:
Parallel 10% to 50%
Series 50% to 75%
Electric vehicle 100%

Figure 12. Overview of Hybrid-powertrain concepts

Page 18 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Strong hybrid ( = full hybrid)

A full hybrid EV can run on just the engine, just the batteries, or a combination of both. A large,
high- capacity battery pack is needed for battery-only operation.
Examples:
The Toyota Prius, Auris and Lexus are full hybrids, as these cars can be moved forward on battery
power alone. The Toyota brand name for this technology is Hybrid Synergy Drive. A computer
oversees operation of the entire system, determining if engine or motor, or both should be running.
The ICE will be shut off when the electric motor is sufficient to provide the power.

Medium hybrid ( = motor assist hybrid)

Motor assist hybrids use the engine for primary power, with a torque-boosting electric motor
connected in parallel to a largely conventional powertrain. EV mode is only possible for a very
limited period of time, and this is not a standard mode. Compared to full hybrids, the amount of
electrical power needed is smaller, thus the size of the battery system can be reduced. The electric
motor, mounted between the engine and transmission, is essentially a very large starter motor, which
operates not only when the engine needs to be turned over, but also when the driver "steps on the
gas" and requires extra power. The electric motor may also be used to re-start the combustion engine,
deriving the same benefits from shutting down the main engine at idle, while the enhanced battery
system is used to power accessories. The electric motor is a generator during regenerative breaking.
Examples:
Honda's hybrids including the Civic and the Insight use this design, leveraging their reputation for
design of small, efficient gasoline engines; their system is dubbed Integrated Motor Assist (IMA).
Starting with the 2006 Civic Hybrid, the IMA system now can propel the vehicle solely on electric
power during medium speed cruising.
A variation on this type of hybrid is the Saturn VUE Green Line hybrid system that uses a smaller
electric motor (mounted to the side of the engine), and battery pack than the Honda IMA, but
functions similarly.
Another variation on this type is Mazda's e-4WD system, offered on the Mazda Demio sold in Japan.
This front-wheel drive vehicle has an electric motor which can drive the rear wheels when extra
traction is needed. The system is entirely disengaged in all other driving conditions, so it does not
enhance performance or economy.

Mild hybrid / micro hybrid (= start/stop systems with energy recuperation)

Mild hybrids are essentially conventional vehicles with oversized starter motors, allowing the engine
to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly and cleanly.
During restart, the larger motor is used to spin up the engine to operating rpm speeds before injecting
any fuel. That concept is not unique to hybrids; Subaru pioneered this feature in the early 1980s, and
the Volkswagen Lupo 3L is one example of a conventional vehicle that shuts off its engine when at
a stop.
As in other hybrid designs, the motor is used for regenerative braking to recapture energy. But there
is no motor-assist, and no EV mode at all. Therefore, many people do not consider these to be
hybrids, since there is no electric motor to drive the vehicle, and these vehicles do not achieve the
fuel economy of real hybrid models.
Some provision must be made for accessories such as air conditioning which are normally driven by
the engine. Those accessories can continue to run on electrical power while the engine is off.
Furthermore, the lubrication systems of internal combustion engines are inherently least effective
immediately after the engine starts; since it is upon startup that the majority of engine wear occurs,
the frequent starting and stopping of such systems reduce the lifespan of the engine considerably.
Also, start and stop cycles may reduce the engine's ability to operate at its optimum temperature, thus
reducing the engine's efficiency.

Page 19 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Figure 13. Powertrain of a mild HEV

Examples:
BMW succeeded in combining regenerative braking with the mild hybrid "start-stop" system in
their current 1-series model.
Citroën proposes a start-stop system on its C2 and C3 models. The concept-car C5 Airscape
has an improved version of that, adding regenerative breaking and traction assistance
functionalities, and supercapacitors for energy buffering.

Plug-in hybrid (= grid connected hybrid = vehicle to grid V2G)

All the previous hybrid architectures could be grouped within a classification of charge sustaining:
the energy storage system in these vehicles is designed to remain within a fairly confined region of
state of charge (SOC). The hybrid propulsion algorithm is designed so that on average, the SOC of
energy storage system will more or less return to its initial condition after a drive cycle.
A plug-in hybrid electric vehicle (PHEV) is a full hybrid, able to run in electric-only mode, with
larger batteries and the ability to recharge from the electric power grid. Their main benefit is that
they can be gasoline-independent for daily commuting, but also have the extended range of a hybrid
for long trips.
Grid connected hybrids can be designed as charge depleting: part of the “fuel” consumed during a
drive is delivered by the utility, by preference at night. Fuel efficiency is then calculated based on
actual fuel consumed by the ICE and its gasoline equivalent of the kWh of energy delivered by the
utility during recharge. The "well-to-wheel" efficiency and emissions of PHEVs compared to
gasoline hybrids depends on the energy sources used for the grid utility (coal, oil, natural gas,
hydroelectric power, solar power, wind power, nuclear power).
In a serial Plug-In hybrid, the ICE only serves for supplying the electrical power via a coupled
generator in case of longer driving distances. Plug in hybrids can be made multi-fuel, with the
electric power supplemented by diesel, biodiesel, or hydrogen.
The Electric Power Research Institute's research indicates a lower total cost of ownership for PHEVs
due to reduced service costs and gradually improving batteries.
Some scientists believe that PHEVs will soon become standard in the automobile industry. Plug-in
vehicles which use batteries to store electric energy outperform cars which use hydrogen as carrier
for the energy taken from the grid. The following figures indicate the efficiencies of a hydrogen fuel
cell HEV and a battery powered EV.

For typical driving cycles, the achieved efficiencies are lower. The battery powered EV achieves
efficiencies in the range of 50 to 60%. The hydrogen powered EV has a total efficiency of about
13% only at those drive cycles.
Examples:
Mercedes BlueZERO E-CELL PLUS (concept car): series
HEV. Opel Ampera: series HEV.

Page 20 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Figure 14. Traction power efficiency of a plugged EV.

Left a battery powered plug in EV (Mitsubishi Lancer Evolution MIEV))
Right a Fuel Cell EV (Mercedes NECAR 3)

Figure 15. Plug-in-Hybrid Opel Ampera

The Plug-in-Hybrid Volvo C30 (concept car) is a series HEV. It has a 1,6 liter gasoline/bio-
ethanol ICE. A synchronous generator charges the Li-polymer battery (ca. 100 km autonomy)
when the battery SoC is lower than 30%. There are four electric wheel-motors.

Figure 16. Plug-in-Hybrid Volvo C30

Page 21 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

3. Types by nature of the power source

Electric-internal combustion engine hybrid

There are many ways to create an electric-internal combustion hybrid. The variety of electric-ICE
designs can be differentiated by how the electric and combustion portions of the powertrain
connect (series, parallel or combined), at what times each portion is in operation, and what percent
of the power is provided by each hybrid component. Many designs shut off the internal combustion
engine when it is not needed in order to save energy, see 2.3.

Fuel cell hybrid

Fuel cell vehicles have a series hybrid configuration. They are often fitted with a battery or
supercapacitor to deliver peak acceleration power and to reduce the size and power constraints on
the fuel cell (and thus its cost). See 1.1.

Human power and environmental power hybrids

Many land and water vehicles use human power combined with a further power source. Common
are parallel hybrids, e.g. a boat being rowed and also having a sail set, or motorized bicycles. Also
some series hybrids exist. Such vehicles can be tribrid vehicles, combining at the same time three
power sources e.g. from on-board solar cells, from grid-charged batteries, and from pedals.
The following examples don’t use electrical power, but can be considered as hybrids as well:

Pneumatic hybrid
Compressed air can also power a hybrid car with a gasoline compressor to provide the power.
Moteur Developpement International in France produces such air cars. A team led by Tsu-Chin
Tsao, a UCLA mechanical and aerospace engineering professor, is collaborating with engineers
from Ford to get Pneumatic hybrid technology up and running. The system is similar to that of a
hybrid-electric vehicle in that braking energy is harnessed and stored to assist the engine as needed
during acceleration.

Hydraulic hybrid
A hydraulic hybrid vehicle uses hydraulic and mechanical components instead of electrical ones.
A variable displacement pump replaces the motor/generator, and a hydraulic accumulator (which
stores energy as highly compressed nitrogen gas) replaces the batteries. The hydraulic
accumulator, which is essentially a pressure tank, is potentially cheaper and more durable than
batteries. Hydraulic hybrid technology was originally developed by Volvo Flygmotor and was used
experimentally in buses from the early 1980s and is still an active area.
Initial concept involved a giant flywheel (see Gyrobus) for storage connected to a hydrostatic
transmission, but it was later changed to a simpler system using a hydraulic accumulator connected
to a hydraulic pump/motor. It is also being actively developed by Eaton and several other
companies, primarily in heavy vehicles like buses, trucks and military vehicles. An example is the
Ford F-350
Mighty Tonka concept truck shown in 2002. It features an Eaton system that can accelerate the
truck up to highway speeds.

Propulsion systems and components

The electric propulsion subsystem comprises of:
 The electronic controller
 Power converter
 Electric Motor (EM)
 Mechanical transmission
 Driving wheels
 mechanical coupling is of two types:

Page 22 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

The Mechanical propulsion subsystem comprises of

Torque coupling: In this case the coupler adds the torques of the ICE and EM together and delivers
the total torque to the driven wheels. The ICE and EM torque can be independently controlled. The
speeds of the ICE, EM and the vehicle are linked together with a fixed relationship and cannot be
independently controlled because of the power conservation constraint.
Speed coupling: In this case the speeds of the ICE and EM can be added together and all
torques are linked together and cannot be independently controlled.

Torque Coupling
In Figure 17, a conceptual diagram of mechanical torque coupling is shown. The torque
coupling, shown in Figure 17, is a two-degree-of-freedom mechanical device. Port 1 is a
unidirectional input and Port 2 and 3 are bi-directional input or output, but both are not input at the
same time. Here input means the energy flows into the device and output means the energy flows
out of the device. In case of HEV
port 1 is connected to the shaft of an ICE directly or through a mechanical
transmission.
port 2 is connected to the shaft of an electric motor directly or through a
mechanical transmission
port 3 is connected to the driven wheels through a mechanical linkage

Figure 17: Mechanical torque coupler

For a losses torque coupler in steady state, the power input is always equal to the power
output from it. For the torque coupler shown in Figure 17, the power balance is

A gearbox used in the vehicles is a typical example of torque couple. Some torque coupler are
shown in Figure 18

Page 23 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

FIGURE 18 Commonly used mechanical torque coupling devices

Speed Coupling
The power produced by two power plants may be coupled together by adding their speed. This is
done with the help of speed coupling devices (Figure 19). The Speed Coupler is a three port two-
degree-of-freedom device. Port 1 is a unidirectional input and Port 2 and 3 are bi-directional input
or output, but both are not input at the same time. Here input means the energy flows into the
device and output means the energy flows out of the device. In case of HEV
port 1 is connected to the shaft of an ICE directly or through a mechanical
transmission.
port 2 is connected to the shaft of an electric motor directly or through a
mechanical transmission
port 3 is connected to the driven wheels through a mechanical linkage

Figure 19:Mechanical speed coupler

For a losses speed coupler in steady state, the power input is always equal to the power
output from it. For the speed coupler shown in Figure 19, the speed relation is

Page 24 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

A typical speed coupler is the planetary gear (Figure 20). The planetary gear unit is a three
port device consisting of
Sun gear, marked 1 in Figure 20
Ring gear, marked 2 in Figure 20
Carrier or Yoke, marked 3 in Figure 20

FIGURE 20 Typical speed-coupling devices

Challenges and Key aspects of EV:

EV cost and battery cost:

The cost is the most concerning point for an individual when it comes to buying an electric vehicle.
However, there are many incentives given off by central and state governments. But the common
condition in all policies is that the incentives are only applicable for up to a certain number of vehicles
only and after removing the discount and incentives the same EV which was looking lucrative to buy
suddenly becomes unaffordable. This tells that buying EV’s no more be cheaper after a certain
saturation point.

BatteryCost:
It’s no more hidden from anyone that the Li-ion battery in electric vehicles is built to last till 6-7
years or hardly 8 years and after the battery decay period of an electric vehicle battery its user remains
with no other choice than to buy a newer battery which costs nearly 3/4 th of the whole vehicle cost.
Battery cost is going to be a pressing issue for the EV buyers because electric vehicles are new to
both market and customers the battery issue requires at least 5 years to surface this will going to be
impacted in a long run.

Page 25 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Beta version of vehicles:

Right now, both the technology and companies are new to the market and the products they are
manufacturing are possibly facing real costumers for the first time. And it’s nearly impossible to
make such a complex product like an automobile perfect for the customers in the first go, and as
expected the buyers faced many issues. Vehicles like RV400, EPluto 7G, Nexon all them has to
update their vehicle up to a very high extent after customer feedback and reviews.
Recently Pure EV has made a lot of changes in their policies, software, hardware, and not even Tata
motors has to upgrade their BMS and regen software after a lot of complaints from the customers
regarding extremely low range. So, buying the vehicle from the first batch of the company’s
production would be a bad idea and can even give you an extremely bad experience.

Poor Infrastructure and range anxiety:

Poor infrastructure is among the most pressing issue among people thinking to opt for electric
vehicles. Poor infra doesn’t only include a lack of charging stations but also the lack of proper
charging set up in their home. Charging a heavier electric car could be a major problem for any
electric car owner if he/she lacks proper setup (Powerful MCB, wire, and earthing) near their place.

Range anxiety: This problem of mental pressure comes due to lack of charging infrastructure which
is improving day by day but still required to improve a lot in this area.
Many companies are offering mad range for their EVs in ideal conditions like 200, 180, 150 but in
real conditions, 150 km is like a dream and if you are from the category of an average Indian male
with some luggage and riding in a city like a condition then you should be satisfied with a 100 km
driving range. In electric cars, the loading capacity may not have much impact, but for small vehicles
like electric scooters or electric bikes, even a small difference in driving conditions can impact your
EV range a lot.

No Universal charger and Ecosystem (Lack of standardization):

Every second electric vehicle-making company has its own different charging port which is becoming
a hurdle to setting up a proper charging ecosystem.
Also, many EV users complained about facing moral trouble for charging their vehicle in different
EV-making company’s charging stations which can impact the growth of the EV industry.
Lack of standardization is a curse to the Indian electric vehicle industry; it’s damaging the present
and future of the EV market. Every second electric scooter has its own different charging port, which
affects the charging station infrastructure because no specific charging station can be built that can
charge all types of electric vehicles. Also, the lack of standardization reduces the EV adoption rate
in society-based communities.
Just like electric cars get a specific charging port (CCS-2), electric two and three-wheelers should
maintain a similar standard to achieve the mass adoption of electric vehicles.

Temperature Issues:
Temperature can affect the performance of an EV battery at a large extent which makes EV’s
inappropriate for too cold (Uttarakhand, Meghalaya) or too hot regions like (Rajasthan, Kerala). The
battery can give its ideal performance when it’s in use under the temperature range of 15-40 degrees.

Very few academic and local skill awareness:

EV push is necessary along with the academic awareness and importance to the students of coming
generations. Because the EV spare part and servicing industry is another essential part of the growth
of EV’s. When one is stuck with their broke ICE vehicle, he/she can easily find a help or costumer
support near them but when it’s about electric vehicles it’s surely a tedious task to find someone who
can fix their issue or help them.

Page 26 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Less performance for ideal economy:

IC engine-driven vehicles are still way ahead of electric vehicles when it comes to performance. In
order to make sure that an EV is giving the promised range it becomes highly important to drive the
vehicle at lower performance and be aware of maximum usage of ‘regen‘.
Will increase the electricity demand at a national level:
It’s just a matter of assuming the increment in electricity demand when everyone in the city is using
solely electricity to charge their vehicle. It’ll be a horrific increment in the demand for electricity and
as of now, we are majorly dependent on burning fossils for generating electricity.
Until we use renewable sources of energy for generating electricity the EV revolution will be of no
use.

Environmental concerns:
The EV revolution is necessary for the most populated and polluted parts of India like Delhi, Mumbai,
etc. but in such cities the major chunk of electricity is generated through burning fossil fuels which
are equivalent to spreading the pollution through the ICE vehicle smoke, even most of the charging
stations are reportedly operating upon diesel-driven electricity generator.
So, the only solution to the emission problem is to use renewable energy sources. (Like Solar power,
wind energy, tidal power, etc).
Shifting to renewable energy sources is equally important as shifting to electric mobility.

Servicing is in danger:
Servicing and spare parts are some of the most important parts for any vehicle, especially for vehicles
facing Indian roads. Also, the quality of material offered in new-age electric vehicles are of very low
quality and upon which the companies are adding some very high-tech functionalities like onboard
GPS, touch screen panels, extremely delicate sensors. In some unfortunate period if even a light or
indicators damages, you won’t have any other choice than replacing from the company itself (Which
will be extremely costly). Because almost every company is using their costume made part in a highly
vulnerable product like the vehicle it’ll cost a lot in a long term for the vehicle owners if even a very
small defect like breaking of light takes place.

Vehicle Control in HEV:

The control system of the HEV is very complex. For large-scale and complex systems, multilevel
hierarchical control is an important control technique. Hierarchical regulation is thus commonly
adapted to HEV control, as seen in Figure 21. (series HEV). The HEV controller consists of an
interpreter for driver control, a vehicle system controller and an electronic controller. The Vehicle
System Controller is the level of decision to assess the torque requirements of the engine, generator,
ICE, and mechanical brake according to the torque demand of the driver, vehicle speed, and state of
charge of the battery (SOC), where the SOC is estimated by the battery management system (BMS),
the sensor feeds the vehicle speed (Serrao, Onori and Rizzoni, 2009) (Pisu and Rizzoni, 2007) The
electronic controller is the execution stage at which the vehicle system controller carries out the
order to make the corresponding parts operate.
(1) Command Interpreter for Drivers. The driver command interpreter's job is to measure the torque
demand of the driver according to the desired vehicle speed and actual vehicle speed. Vehicle
speed is controlled by the direction of the accelerator pedal and brake pedal. By changing the
accelerator pedal and brake pedal position, this is a feed control device to make the vehicle obey the
desired vehicle (Wenzhong and Porandla, 2005). (Yan, Wang and Huang, 2012
(2) Vehicle System Controller. HEV is a multiple energy source compared to traditional vehicles,
so how to divide the required power between energy sources is referred to as EM. By using EM
strategies according to command signals obtained from the driver command interpreter and
parameter information input from the electronic controller, the vehicle system controller performs
powertrain control. As shown in Figure 5, the vehicle system controller can be categorized into three
feature blocks.(Johnson, Wipke and Rausen, 2000) (Lee and Sul, 1998) (Enang and Bannister,
2017) I) Required vehicle interpreter capacity. (ii) Methods for handling electricity. (iii)
Page 27 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Translator of torque. The vehicle interpreter's necessary power is a function block for translating
the torque demand of the driver to power demand. HEV is a multiple energy device, distinct from
traditional vehicles that can only produce power, not only can battery output power, but also
consume energy. The hot topic among technology developers is how to divide the necessary power
between two energy sources and mechanical brakes in order to reduce fuel consumption or emissions.
(Plett, 2004).
Electronic Controller (3). The electronic controller is an embedded device that carries out commands
from the controller of
the vehicle system to operate the corresponding components. In Figure 21, the electronic controller
comprises the engine control unit (ECU), the engine control unit (MCU), the generator control unit
(GCU), the mechanical brake control unit and the battery management system (BMS). The engine
control unit is an electronic control unit (ECU) for ICE control; by injecting fuel into the ICE
combustion chambers, it generates the desired ICE output torque coming from the vehicle system
controller control signal. The ICE operating point can be defined by torque and velocity. There
is no mechanical link between ICE and the transmission in the HEV series, so how can ICE speed
be controlled? There is a mechanical link between the ICE and the generator, so the speed of the ICE
is regulated by the torque demand of the generator. Motor is the final drive system and is connected to
the transmission by mechanical connection, and thus the speed of the motor depends on the driving
cycle, similarly,
the operating point of the motor can typically be represented by torque and speed; due to mechanical
connection to transmission, the torque demand of the motor is determined by the torque demand of
the driver. Using FOC technology, the MCU normally makes the engine run at the desired torque.
During braking or down slope, engines, commonly used for traction, may also become a generator.
Therefore, the kinetic energy of the engine, otherwise burned in the form of heat in the brake drums,
can be transformed into electrical energy and sent back to the battery. If the battery is non-receptive,
it will operate with the electronic braking system control unit.

Figure 21. Vehicle Control in HEV

Notation Explanation
sd Desired speed of vehicle
s Speed of vehicle
Δs: Difference of desired speed and speed of vehicle
Tdrv dmd: Driver demand
SOC: State of charge
Tice dmd Torque demand of ICE
Tgc dmd: Torque demand of generator
Tmc dmd: Torque demand of motor
Tbh dmd: Torque demand of braking

Page 28 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

Basics of Fuel Cell Vehicle (FCV):

- Fuel cells and batteries convert chemical energy into electrical energy and are very useful
forms of galvanic cell.
- A galvanic or voltaic cell is an electrochemical cell that converts chemical energy into
electrical energy through the redox reactions that occur within the cell.
- Galvanic cells that are designed to convert the energy of combustion of fuels like hydrogen,
methane, methanol, etc. directly into electrical energy are called fuel cells. One of the most
successful fuel cells uses the reaction of hydrogen with oxygen to form water.

Mechanism:
The Fuel Cell Electric Vehicle (FCEV) combines hydrogen and oxygen to generate an electric
current and water is the only byproduct.
Hydrogen + Oxygen = Electricity + Water Vapour
2H2 (g) + O2 (g) → 2 H2O (l)

 Fuel Cell Electric Vehicle (FCEV) engines are similar to the conventional internal
combustion engines because they also rely on a constant supply of fuel (hydrogen) and
oxygen.

o However, there are no moving parts in the fuel cell, so they are more efficient and
reliable.
 Stationary fuel cells are the largest and most powerful fuel cells. These are being designed
to provide a cleaner, reliable source of on-site power to hospitals, banks, airports and homes.
 The successful development of the technology would provide energy for transportation and
electric power.
 Hydrogen fuel tanks are made from highly durable carbon fibre. Some FCEVs have a triple-
layer hydrogen tank made of woven carbon fibre.

Advantages:
 FCEVs produce much smaller quantities of greenhouse gases and none of the air pollutants
that cause health problems.
 Fuel cells emit only heat and water as a byproduct and are far more energy-efficient than
traditional combustion technologies.
 FCEVs do not need to be plugged in for charging, like battery-powered EVs.
 There is a wide availability of resources for producing hydrogen.

Disadvantages:
 The process of making hydrogen needs energy, often from fossil fuel sources, which raises
questions over hydrogen’s green credentials.
 Handling of hydrogen is a safety concern because it is more explosive than petrol.
 These vehicles are expensive and fuel dispensing pumps are scarce.

Status in India
 In India, so far, the definition of Electric Vehicles only covers Battery Electric Vehicles
(BEVs).

o BEVs have no internal combustion engine or fuel tank and run on a fully electric
drivetrain powered by rechargeable batteries.
 The Government of India has launched FAME India Scheme with the objective to support
hybrid/electric vehicles market development and manufacturing ecosystem. It also covers
Hybrid & Electric technologies like Mild Hybrid, Strong Hybrid, Plug in Hybrid & BEVs.
 The Ministry of New and Renewable Energy, under its Research, Development and
Demonstration (RD&D) Programme, has been supporting various projects on hydrogen and
fuel cells.
Page 29 of 30
Dept. Mech. Engg. DSCE
Hybrid & Electric Vehicle Technology Prepared by: Dr. Mohan Das A N & Prof. Abhishek H A

 The Ministry of Science and Technology has supported two networked centres on hydrogen
storage led by IIT Bombay and Nonferrous Materials Technology Development Centre,
Hyderabad.

Fuel economy:
The following table compares EPA's fuel economy expressed in miles per gallon gasoline equivalent
(MPGe) for the two models of hydrogen fuel cell vehicles rated by the EPA as of September 2021,
and available in California.

Comparison of fuel economy expressed in MPGe for hydrogen fuel cell vehicles
available for sale or lease in California and rated by the U.S. Environmental Protection
Agency as of September 2021
Combined City Highway
Model Annual
Vehicle fuel fuel fuel Range
year fuel cost
economy economy economy
Hyundai 2019– 380 mi
61 mpg-e 65 mpg-e 58 mpg-e
Nexo 2021 (610 km)
Toyota 2016– 312 mi
66 mpg-e 66 mpg-e 66 mpg-e
Mirai 2020 (502 km)
Toyota 402 mi
2021 74 mpg-e 76 mpg-e 71 mpg-e
Mirai (647 km)
Notes: One kg of hydrogen has roughly the same energy content as one U.S. gallon of gasoline.[38]

Page 30 of 30
Dept. Mech. Engg. DSCE