5 Electric and Hybrid Vehicles the vehicle. The energy source within the vehicle could be the diesel or gasoline for the IC engines or the stored energy in batteries for electric motors. The flow of power and energy in the powertrain is controlled by a set of electronic controllers. In addition to the electronic controller units ( ECUs ) for each of the energy conversion and power transmission devices in the powertrain, there is a master controller for coordinating the system-level functions of the vehicle. This controller is termed as the vehicle supervisory controller ( VSC ).
The supervisory controller is a key component in hybrid vehicles since it has to coordinate the energy conversion of multiple devices and power transmission through both the electrical and mechanical paths. The supervisory controller is like the brain of the vehicle designed to generate the control commands for the individual powertrain component ECUs. The supervisory controller interacts with the components of the vehicle through a communication network, which is based on a control- ler area network ( CAN ) protocol. The CAN protocols are presented in Chapter 11, while the hybrid vehicle control strategies are discussed in Chapter 15.
The primary powertrain components in a conventional ICEV are the engine and the transmis- sion. These components deliver power to the wheels through the driveshaft and other coupling devices. The coupling devices include the differential and final drive in most cases. This mechanical power transmission path (MPTP) is shown in Figure 1.2. The power transmission path in an electric vehicle is mostly electrical except for the coupling devices between the electric propulsion motor and the wheels. This power transfer path will be referred to as the electrical power transmission path (EPTP). This transmission path is shown in Figure 1.3.
The coupling device can simply be a gear to match electric machine speeds to vehicle speeds. The coupling can even be direct without any gear- ing in wheel-mounted motors, which are known as hub motors . The striking difference in this path from that in an ICEV is that power and energy flow can be bidirectional. In EVs, kinetic energy of the vehicle can be processed back to the energy storage device through the electric machine when the vehicle brakes to slow down or stop. Both the electrical and mechanical transmission paths exist in the powertrain of a hybrid vehicle. The architecture and components of the powertrain of an HEV is varied depending on the type of hybrid vehicle.
A generic configuration for a charge sustaining hybrid is shown in Figure 1.4. The charge sustaining hybrids are those that never need to be plugged in for recharging the energy stor- age system. The only energy source within the vehicle is the stored fuel for the IC engine. All of the propulsion energy gets processed through the engine regardless of whether the power transmission path is electrical or mechanical. The propulsion power comes from one or more electric motors and the IC engine.
The propulsion power is transmitted to the wheels through either the MPTP or Fu el Internal Combustion Engine Transmission Wheels Coupling Devices MPTP FIGURE 1.2 Power transmission path in a conventional ICE vehicle. Wheels EPTP FIGURE 1.3 Power transmission path in an EV. Energy Storage Electric Machine and Drive Coupling Devices