Electric and Hybrid vehicle

Electric Vehicles

An electric vehicle is a vehicle that has the following features: (1) The energy source is portable

and electrochemical or electromechanical in nature, and (2) Traction effort is supplied only by

an electric motor. The following figure shows the block diagram of an electric vehicle system

driven by a portable energy source. The electromechanical energy conversion linkage system

between the source and wheels is the power train of the vehicle.

An electric vehicle system

Hybrid Vehicles

The term hybrid vehicle or hybrid electric vehicle refers to vehicles that use an IC engine in

conjunction with one or more electric machines for propulsion. A hybrid road vehicle is one in

which the propulsion energy during specified operational missions is available from two or

more types of energy stores, sources, or converters, of which at least one store or converter must

be on board.

The definition of hybrid vehicles can be extended to vehicles that have engines different from

IC engines. The vehicle in which energy from fuel cells and battery packs are utilized to deliver

power through an electric motor is also a hybrid vehicle. The fuel cell is essentially an engine

where stored chemical energy in fuel is converted into electrical energy directly without any

combustion process.

Electric and Hybrid vehicle Components

The primary energy conversion devices in an electric or hybrid vehicle are the IC engine,

electric machine, and energy storage device. The IC engine is a heat engine that converts

chemical energy into mechanical energy. The electric machine can be used either as a motor or

as a generator to convert mechanical power to electrical power or vice versa.

With introduction of electric machines for power and energy transfer, energy storage devices

and electrical-to-electrical power/energy conversion devices become essential. A high energy

capacity battery pack is the most common energy storage device in these vehicles. An Ultra-

capacitor bank can also be used in hybrid vehicles. Flywheels have also been used for energy

storage in mechanical form. The electric machines require an electric drive to control the

machine and deliver the required power based on requested demands and feedback signals.

The energy flow in a vehicle starts from source of energy and ends at wheels with the delivery

of propulsion power; the path for this power and energy flow is known as the powertrain of

vehicle. The flow of power and energy in powertrain is controlled by a set of electronic

controllers.

Classification

1. Based on the path of energy flow

a. Mechanical power transmission path (MPTP)

b. Electrical power transmission path (EPTP)

c. Combination of MPTP and EPTP

2. Based on architecture

a. Series

b. Parallel

c. Series-Parallel

3. Based on degree of hybridization

a. Mild

b. Power

c. Energy

4. Charge depleting

5. Charge sustaining

Mechanical power transmission path (MPTP)

The primary powertrain components in a conventional ICE vehicle are engine and

transmission. The energy flow in a vehicle starts from source of energy and ends at wheels with

the delivery of propulsion power known as power transmission

Power transmission path in a conventional ICE vehicle

Electrical power transmission path (EPTP)

In electric vehicle power transmission is almost electrical except for coupling devices between

electric propulsion motor and wheels. The coupling device can

simply be a gear to match electric machine speeds to vehicle speeds.

Power transmission path in an electric vehicle

Combination of MPTP and EPTP

The propulsion power is transmitted to wheels through either MPTP or EPTP or combination

of both. The MPTP is associated with an IC engine and transmission, whereas EPTP consists of

energy storage system, a generator, propulsion motor and transmission.

A hybrid electric vehicle powertrain

Series HEV

A series hybrid is one in which only one energy converter can provide propulsion power. Only

electric motor provides all propulsion power to wheels. A downsized IC engine drives a

generator, which supplements batteries and can charge them when it fall below certain charge

level. The drawback is size of traction motor, which as to be rated for max. power requirement

of vehicle.

Series HEV powertrain

Parallel HEV

A parallel hybrid is one in which more than one energy conversion device can deliver

propulsion power to the wheels. The IC engine and electric motor are configured in parallel

with a mechanical coupling. The power requirements of electric motor is lower than that of

series HEV.

Parallel HEV powertrain

Series-Parallel HEV

It combines the benefits of series and parallel architecture with charge sustaining capability.

The power-split device divides the output from the engine into mechanical and electrical

transmission paths. Even IC engine is also used to charge the battery. They are capable of

providing continuous high output power compared to series or parallel powertrain.

Series –Parallel combination HEV

Torque characteristics

The torque characteristic of a motor is shown along with torque characteristics of IC engine. For

electric motor, a high torque is available at starting, which is the rated torque of motor. The peak

or rated power from a motor is obtained at base speed (w b) when motor characteristics enter the

constant power region from constant torque region once voltage limit of power supply is

reached. The motor rated speed (w rated) is at end of the constant power region. The IC engine

peak power and torque occur at the same speed.

Power(W) = Torque(Nm)*Speed(rad/sec)

Electric motor and IC engine torque characteristics

Commercial vehicles

Toyota Prius

Toyota Highlander

Ford Escape

Mercury Mariner

Honda Insight

Honda Civic HEV

Honda Accord HEV

Advantages of a Hybrid Car

Here are few of the top advantages of having a hybrid vehicle

1. Environment Friendly: One of the biggest advantage of hybrid car over gasoline powered

car is that it runs cleaner and has better gas mileage which makes it environmentally friendly. A

hybrid vehicle runs on twin powered engine (gasoline engine and electric motor) that cuts fuel

consumption and conserves energy.

2. Financial Benefits: Hybrid cars are supported by many credits and incentives that help to

make them affordable. Lower annual tax bills and exemption from congestion charges comes in

the form of less amount of money spent on the fuel.

3. Less Dependence on Fossil Fuels: A Hybrid car is much cleaner and requires less fuel to run

which means less emissions and less dependence on fossil fuels. This in turn also helps to

reduce the price of oil in domestic market.

4. Regenerative Braking System: Each time you apply brake while driving a hybrid vehicle

helps you to recharge your battery a little. An internal mechanism kicks in that captures the

energy released and uses it to charge the battery which in turn eliminates the amount of time and

need for stopping to recharge the battery periodically.

5. Built from Light Materials: Hybrid vehicles are made up of lighter materials which means

less energy is required to run. The engine is also smaller and lighter which also saves much

energy.

6. Higher Resale Value: With continuous increase in price of gasoline, more and more people

are turning towards hybrid cars. The result is that these green vehicles have started commanding

higher than average resale values. So, in case you are not satisfied with your vehicle, you can

always sell it at a premium price to buyers looking for it.

Disadvantages of a Hybrid vehicle

There disadvantages to owning a hybrid car, but they are probably not what you think. Contrary

to popular myth, hybrid cars have just as much power as regular cars and have no issue with

mountain driving or towing. The disadvantages will depend on the type of hybrid fuel that your

car uses.

Here are few of the disadvantages of a hybrid vehicle:

1. Less Power: Hybrid cars are twin powered engine. The gasoline engine which is primary

source of power is much smaller as compared to what you get in single engine powered car and

electric motor is low power. The combined power of both is often less than that of gas powered

engine. It is therefore suited for city driving and not for speed and acceleration.

2. Can be Expensive: The biggest drawback of having a hybrid car is that it can burn a hole in

your pocket. Hybrid cars are comparatively expensive than a regular petrol car and can cost

$5000 to $10000 more than a standard version. However, that extra amount can be offset with

lower running cost and tax exemptions.

3. Poorer Handling: A hybrid car houses an gasoline powered engine, a lighter electric engine

and a pack of powerful batteries. This adds weight and eats up the extra space in the car. Extra

weight results in fuel inefficiency and manufacturers cut down weight which has resulted in

motor and battery downsizing and less support in the suspension and body.

4. Higher Maintenance Costs: The presence of dual engine, continuous improvement in

technology, and higher maintenance cost can make it difficult for mechanics to repair the car. It

is also difficult to find a mechanic with such an expertise.

5. Presence of High Voltage in Batteries: In case of an accident, the high voltage present

inside the batteries can be hazardous. There is a high chance of you getting electrocuted in such

cases which can also make the task difficult for rescuers to get other passengers and driver out

of the car.

Conclusion

Using the concept of Hybridization of cars results in better efficiency and also saves a

lot of fuel in today’s fuel deficit world. A hybrid gives a solution to all the problems to

environment related issues. One can surely conclude that this concept will follow with even

better efficiency & conservation rate.