Hybrid electric vehicles are mainly divided into series type (Shev) and parallel type (PHEV) in the form of energy synthesis.
The series power consists of three parts of engine, generator and motor, which form a Shev power unit system in series. The load hour is driven by the battery-driven motor to drive the wheel, and when the load is large, the engine drives the generator to power the motor. When the electric vehicle is in the start-up, acceleration, climbing conditions, the engine-motor group and the battery pack together to provide electric power to the motor, when the electric vehicle at low speed, glide, idle operating conditions, the battery-driven motor, from the engine-generator unit to the battery pack charge. This series-type electric car, regardless of the operating conditions, ultimately by the motor to drive the wheels. For example, the Ford "new energy level -2010" Shev, its batteries using fuel cells, in urban urban driving all by the fuel cell-driven motor, motor through the reducer (transmission) and drive axle drive wheels, reached the "zero emissions" requirements. When high speed and climbing, the engine-motor unit and fuel cell unit are used to power the motor and drive the wheels.
The engine and the motor of the parallel device drive the automobile by the mechanical energy superposition, the engine and the motor belong to two systems, can provide the torque independently to the automobile transmission system respectively, can drive on different road and can drive separately. The motor can be used as an electric motor and as a generator. Because there is no single generator, the engine can drive the wheel directly through the drive mechanism, so the device is closer to the traditional vehicle drive system and is widely used. For example Volkswagen's golf PHEV, the engine passes the clutch 1 to drive the electric-generator, and the output torque is then driven through the other side of the Clutch 2 drive vehicle. When stationary, the battery is powered by an electric-generator, which is the starter of the engine. After the engine starts, the engine, on the one hand, drives the wheels as a separate power source for the vehicle, and on the other hand drives the electric-generator to charge the battery, just like the traditional car. When driving in the urban area, the engine shuts down, the clutch is 1 off, the clutch is 2 jointed, the battery is used as the only energy supply to the motor, and the motor is replaced by an engine-driven wheel. When the electric vehicle needs high-speed or high load, the engine starter clutch 1 is closed, and the engine and the electric-generator system are composed of compound drive forms to the maximum power drive vehicles.
Hybrid cars have matured in developed countries and some have entered a practical phase. Because of its complex structure and high cost, hybrid cars are only a transitional product before the advent of electric vehicles.