(Electric Machine, Basic Function - GF08.10-P-2000A)

Electric vehicles and hybrid vehicles 

Overview 

This document contains information on:

• General 
• Function 

General 

The electric machine converts the electrical energy in engine mode into mechanical energy, and thus provides a drive torque. In generator mode, the electric machine converts mechanical energy into electrical energy (regenerative braking).

Function 

The following applies for electric vehicles:

A vehicle can contain one or two electric machines. Each of these can be designed as an asynchronous motor with a squirrel cage or as a permanently magnet-energized three-phase current synchronous machine. The rotor is connected to the output shaft via a permanently transmitted transmission without a mechanical connecting point. The electrical connection is made via the power electronics control unit.

The changeover between the operating modes engine/alternator operation is controlled by the power electronics control unit. To do this, the three phase currents of the electric machine are regulated depending on the operating mode and the rotor position. These phase currents generate a magnetic rotary field that generates a mechanical torque together with the rotor field. In engine mode, this leads to a torque that acts directly on the drive and thus powers the vehicle. In generator mode, the electric machine generates a braking torque.

The following applies for hybrid vehicles:

The electric machine is designed as a permanently magnet-energized three-phase current synchronous machine. The electrical connection is made via the power electronics control unit. Depending on the model, the electric machine may be located in the drivetrain as follows:

• In automatic transmissions, in the transmission bell housing.

  There is a positive connection between the rotor and the engine separator clutch via the rotor carrier.

• Together with the engine separator clutch and the dual clutch in the coupling unit.

  The design of the electric machine as a wet runner allows for optimum dissipation of rotor and stator heat loss.

  The changeover between the operating modes engine/alternator operation is controlled by the power electronics control unit. To do this, the three phase currents of the electric machine are regulated depending on the operating mode and the rotor position. These phase currents generate a magnetic rotary field that generates a mechanical torque together with the rotor field. In engine mode, this leads to a torque that acts directly on the drive and thus powers the vehicle or that drives the combustion engine. In generator mode, the electric machine generates braking torque that decelerates the vehicle or places a load on the combustion engine. Depending on the model, the transmission of the torque from the electric machine depends on the position of the engine separator clutch.