GA8P70HZ automatic gearbox with electric gearbox oil pump

The automatic gearbox is equipped with a separating clutch. The separating clutch and the electrical machine are fitted in one joint housing. The separating clutch is designed as a wet multi-plate clutch.

The separating clutch is used in certain operating states to disconnect the combustion engine from the electrical machine and the remaining power train. This takes place for example with purely electrical driving as well as in the coasting driving mode. So that the connection and disconnection of the combustion engine is not noticeable, the separating clutch has high actuating precision.

In the same way as all clutches and multi-plate brakes of the automatic gearbox, the separating clutch is operated by the mechatronics module. At static pressure, the separating clutch is opened. This means that gearbox oil pressure is required to close the clutch. This is provided either by the electric gearbox oil pump or the mechanical oil pump.

With the separating clutch opened, the mechanical oil pump is driven by the electrical machine. This means that if the electrical machine fails and the gearbox oil temperature is below 0 °C, the separating clutch cannot be closed and the vehicle cannot be driven off.

The electric gearbox oil pump is a vane-type pump in the same way as the mechanical oil pump. The electric gearbox oil pump is driven by a brushless DC motor. The control electronics is integrated in the housing of the electric transmission oil pump and is activated by the electronic transmission control (EGS). The electric gearbox oil pump can be operated as of a gearbox oil temperature of 0 °C.

Fig 1: Identifying Torsional Vibration Damper And Decoupler

Courtesy of BMW OF NORTH AMERICA, INC.

To insulate the torsional vibrations, a torsional-vibration damper is used in the automatic gearbox. The torsional-vibration damper sets up the mechanical connection between the flywheel of the combustion engine and the separating clutch.