Vacuum Supply, Function - GF42.22-P-1004RFH

Model 205.012/013/047/053/054/147/212/213/247/253, 

Model 253.353/354/953/954/99 

Function requirements, general 

• Circuit 15 ON and drivetrain operational (hybrid mode)
• Engine running (supply via mechanical vacuum pump)

The electronic ignition lock control unit (N73) sends the status of circuit 15 over the suspension FlexRay (Flex E) to the Electronic Stability Program control unit (N30/4).

The CDI control unit (N3/9) (for diesel engine) or the ME-SFI [ME] control unit (N3/10) (for gasoline engine) sends the "Drivetrain operational" signal or the "Engine running" signal over the drive CAN (CAN C1), powertrain control unit (N127) and the suspension FlexRay to the Electronic Stability Program control unit.

Vacuum supply 

The vacuum supply ensures that there is always sufficient vacuum in the BAS brake booster (A7/7). When the combustion engine is running, this vacuum is generated by a mechanical vacuum pump which is driven by the engine.

When the combustion engine is switched off, in hybrid mode, the required vacuum is generated by the electric vacuum pump (M56). The Electronic Stability Program control unit actuates the electric vacuum pump via the Q relay (K40/8kQ) and the vacuum pump relay (+) (K40/8kI). When the ignition is switched on, the Electronic Stability Program control unit actuates the Q relay. The vacuum pump relay (+) is not actuated until the vacuum drops in the BAS brake booster hybrid mode. The vacuum in the BAS brake booster is detected by the brake vacuum sensor (B64/1) (except model 253.353/953) or the dual brake vacuum sensor (B150/2) (model 253.353/953). The Electronic Stability Program control unit reads in the signals from the brake vacuum sensor directly (except model 253.353/953) or the dual brake vacuum sensor (model 253.353/953) and evaluates them.

Both vacuum pumps may operate for a brief transitional period of 1 s. This is the case if the combustion engine is started where the electrical vacuum pump is already running.

The electrical vacuum pump is not actuated in a stationary vehicle. If the vehicle with switched on ignition is, however, rolling, the electrical vacuum pump is actuated. In the case of a defect in the electric vacuum pump, switched off combustion engine and falling vacuum, the Electronic Stability Program control unit requests a forced engine start.

The vacuum pump relay (+) is designed as a semiconductor relay in order to realize a quick response time and a high switching frequency. Semiconductor relays have no mechanical components. The Electronic Stability Program control unit monitors the function of the vacuum pump relay (+) via a feedback line.