4 Electric and Hybrid Vehicles more devices can be achieved through an electrical or a mechanical device. The power flow control and blending of the mechanical and electrical transmission paths are internal and transparent to the user; the driver in a hybrid vehicle interfaces with the vehicle in the same way as he does with a present-day conventional ICEV. The vehicle design complexity increases significantly with hybrid vehicles, since controls and support systems are needed for both the IC engine and the electric machine in addition to the components needed for controlled blending of power coming from the two sources.
The power transmission paths of the HEV consist of different mechanical and electrical subsystems. The high performance and high efficiency of the electric power transmission path reduce the run time of the IC engine, thereby reducing emissions and increasing fuel efficiency. The components and the power transmission paths for the electric and hybrid vehicles are dis- cussed in the following section. The hybrid vehicle architectures will be addressed in Chapter 3 after vehicle kinetics are presented in Chapter 2.
1.3 ELECTRIC AND HYBRID VEHICLE COMPONENTS The automobile is a complex system made of numerous hardware components and software algo- rithms interconnected through mechanical links and electrical communications network. The design of the automobile extends from systems-level design to intricate details of a subsystem or component design. The system design fundamentals are in the physics of motion, energy and power, and in the principles of energy conversion from one form to another, the forms being chemical, electrical and mechanical.
The primary hardware components in the automobile are the energy conversion and power transmission devices; many secondary components are necessary for the functioning of the primary components. This book addresses the system-level design fundamentals, the primary hardware components and the connectivity among these components. The secondary components will be discussed as and when appropriate. A chapter is dedicated to discuss the various cooling systems required in a modern automobile. The primary energy conversion devices in an electric or hybrid vehicle are the IC engine , the electric machine and the energy storage device.
The IC engine is a heat engine that converts chemi- cal energy to mechanical energy. The electric machine can be used either as a motor or as a genera- tor to convert mechanical power to electrical power or vice versa, respectively. In FCEVs, the fuel cell is the engine that converts chemical energy to electrical form. The transmission in the vehicle is a key component for power transfer from the IC engine to the wheels. With the introduction of electric machines for power and energy transfer in electric and hybrid vehicles, 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 ultracapacitor-bank can also be used for energy storage in hybrid vehicles. Flywheels have also been used in prototype research hybrid vehicles for energy storage in mechani- cal 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 electric drives are made of power electronic devices and electronic controllers . The drives are electrical-to-electrical energy conver- sion device that converts steady voltages with fixed frequency into a variable voltage supply for the electric machine.
The drives can also process electrical power in the other direction assisting the electric machine to convert mechanical power into electrical power when the electric machine operates as a generator. The DC/DC converter is another electrical power management device used for DC power conversion from high to low voltage levels or vice versa. The converter is made of power electronic devices and energy storage inductors; this device can be bidirectional as well. The DC/DC converter is a key component for the fuel cell interface with the electric motor drive.
The energy flow in a vehicle starts from the source of energy and ends at the wheels with the delivery of propulsion power; the path for this power and energy flow is known as the powertrain of