Automotive Power Transmission Systems

10 Hybrid Powertrains

A hybrid electric vehicle (HEV) is the combination of a conventional internal combustion engine (ICE) powered vehicle and an electric vehicle. It uses both an ICE and one or more electric machines for the propulsion of a vehicle. The two power devices, the ICE and the electric motor, can be connected in series or in parallel from the power flow point of view. When the ICE and motor are connected in series, the HEV is a series hybrid in which only the electric motor is providing mechanical power to the wheels. When the ICE and the electric motor are connected in parallel, the HEV is a parallel hybrid in which both the electric motor and the ICE can deliver mechanical power to the wheels, separately or together.

In an HEV, the ICE is the main power converter that provides all the energy for the vehicle. The electric motor increases the system efficiency and reduces fuel consumption by recovering kinetic energy during regenerating braking; and optimizes the operation of the ICE during normal driving by adjusting the engine torque and speed. The ICE provides the vehicle with an extended driving range, thereby overcoming the disadvantages of a pure EV.

In a plug‐in HEV (PHEV), in addition to the liquid fuel available on the vehicle, there is also electricity stored in the battery which can be recharged from the electric grid. Therefore, fuel usage can be further reduced.

In a series HEV or PHEV, the ICE drives a generator (referred to as the I/G set). The ...