Automotive Power Transmission Systems

9Electric Powertrains

An electric vehicle (EV) is similar to an engine‐powered vehicle except that the engine‐powertrain is now replaced by an electric machine, and the onboard fuel (gasoline or diesel) is replaced by an electric energy storage device, such as a battery pack.

9.1 Basics of Electric Vehicles

Figure 9.1 shows the basic structure of an EV. In this configuration, the battery stores energy in a chemical form. The most popular is a lithium‐ion battery at the present time. The battery is charged from an electric outlet with an electric charger either carried on board or installed at the charging station. Typically, a low power charger is carried on board (3.3 kW, 6.6 kW) and fast chargers are installed at charge stations. The inverter converts the battery’s DC voltage to a multi‐phase AC to drive the electric machine. The inverter can change the amplitude and frequency of the power flow into the motor so that the torque, speed, and direction of the motor are controlled to drive the vehicle in the desired operation mode. During braking of the vehicle, the battery is charged by regenerative energy recovered from the kinetic energy of the vehicle which is converted from mechanical energy to electric energy by the electric motor, acting as a generator. Due to the characteristics of the electric machines, the mechanical transmission is usually simpler for an EV than in a conventional vehicle. Many EVs use a single speed gear reduction to satisfy all the driving needs, ...