1.2 Operating modes
Hybrid vehicles allocate drive power between the internal combustion engine (ICE) and the electric motor based on operating conditions and required torque. The hybrid control system defines two driving approaches that determine how torque is distributed (see 2.2 Hybrid vehicle operating strategies). The coordination among the ICE, electric motor, and battery defines different operating modes: hybrid driving, pure electric driving, boost mode, generator mode, and regenerative braking.
1.2.1 Hybrid driving
Hybrid driving refers to all states where both the ICE and the electric motor produce driving torque. When deciding how to split driving torque, the hybrid control system considers optimization objectives such as fuel consumption and emissions, and also the battery state of charge.
1.2.2 Pure electric driving mode
Only full-hybrid systems can propel the vehicle solely by the electric motor over extended distances. In this case, the ICE is decoupled from the electric motor, and the vehicle runs nearly silently with zero local emissions.
1.2.3 Boost mode
In boost mode, both the ICE and the electric motor output positive driving torque. Their combined maximum torques are used to deliver the highest possible tractive torque.
1.2.4 Generator operation mode
In generator mode the ICE is operated to produce more power than required for vehicle traction. The surplus power is transferred to the generator and converted to electrical energy for storage in the battery. During coasting mode, and provided the battery charge state allows it, the generator can be used to charge the energy storage.
1.2.5 Regenerative braking
During regenerative braking the vehicle is braked by the electric motor's regenerative braking torque rather than, or in addition to, the friction torque from the service brakes. The motor operates as a generator, converting the vehicle's kinetic energy into electrical energy stored in the battery. Regenerative braking is also called energy-storage braking or feedback braking.
