Analysis and discussion of hybrid vehicle drive system working mode

1.2 Working Mode

In a hybrid vehicle, the internal combustion engine and the electric motor are each responsible for different degrees of driving power, depending on the operating state and the required torque. The hybrid control system has two driving modes that specify how to distribute the torque (see "2.2 Hybrid Vehicle Working Strategy"). The way the internal combustion engine, electric motor and battery work together specifies different operating modes: hybrid driving and electric driving, supercharging, generator mode and regenerative braking.

1.2.1 Hybrid driving

Hybrid driving refers to all states where both the internal combustion engine and the electric motor generate drive torque (Figure 1-3). When considering how to distribute the drive torque, the hybrid control system must also consider the battery charge state in addition to the optimization target (fuel consumption and emissions).

1.2.2 Pure Electric Driving Mode

Only a full hybrid system can drive the vehicle purely electrically over longer driving distances using the electric motor alone. In this case, the internal combustion engine is disconnected from the electric motor (Figure 1-4) and the vehicle runs almost silently and without emissions.

1.2.3 Boost mode

In boost mode, the internal combustion engine and the electric motor output positive drive torque, and their maximum torque output is used to output maximum traction torque (Figure 1-5).

1.2.4 Generator operation mode

Because the battery is charged in generator mode, the internal combustion engine will output more power than the traction required by the vehicle. The excess power is transmitted to the generator and converted into electrical energy and stored in the battery (Figure 1-6).

In coasting mode, the energy storage device is charged via the generator, provided the battery charge state permits.

1.2.5 Regenerative Braking

During regenerative braking, the vehicle is braked by the regenerative braking torque of the electric motor instead of (or not only) the friction torque of the foot brake. In addition, the electric motor is also in generator mode and converts the vehicle's kinetic energy into electrical energy and stores it in the accumulator (Figure 1-7). Regenerative braking is also called energy storage braking or feedback braking.

Source: BOSCH traditional power system and hybrid power system