Electrical Vacuum Pump: Notes

During phases of driving in pure electric mode, the combustion engine is at a standstill and thus does not power the mechanical vacuum pump. To ensure the brake vacuum supply even during these phases, the E72 has an additional electrical vacuum pump. It is installed in the engine compartment, on the right as seen in the direction of travel, on the front end of the crankcase.

The pump element is a double diaphragm pump. The inner structure is almost symmetric, so that one intake valve and one discharge valve are installed on each of the two end faces. The two valves can be identified by the shape of the housing cover. The pump input is connected to the vacuum line. The pump draws in air at the input, thus generating a vacuum. The air that is drawn in is fed to the outside via discharge holes on one housing cover.

The electrical vacuum pump can be replaced during service only as a complete unit.

The motor of the electrical vacuum pump is supplied with current using the SBA control unit and two relays. The relays are:

• One electromechanical relay installed in the spare wheel well just to the right of the second 12 V battery.
• One semiconductor relay installed in the area of the right rear light.

The two relays for activating the electrical vacuum pump are switched in series. In normal operation, the SBA control unit switches on the electromechanical relay as soon as terminal 30g is switched on. However, the actual switching on and off of the electrical vacuum pump is carried out by the semiconductor relay. This provides the advantage of a gear shift that is free of wear and noise.