Introduction

The topics covered in this chapter are as follows:

• •  Hybrid Electric Vehicles (HEV)

•  Energy use in conventional vehicles

•  Energy saving potential of hybrid drive trains

•  Various HEV configurations and their operation modes

 

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.