Activation of the Electrical Vacuum Pump

Of course, the semiconductor relay used here is also designed to last the service life of the vehicle. If, despite this, there should be a component defect of the semiconductor relay, measures must be taken so that the hybrid brake system still functions reliably.

If, after the combustion engine is started, the brake vacuum supply from the mechanical vacuum pump is working properly, the hybrid brake system remains in by-wire mode even in the event of a fault of the electrical vacuum pump. Otherwise, the hybrid brake system switches to conventional mode.

The SBA control unit can identify any component defects using the monitoring line, which branches off between the output of the semiconductor relay and the switching contact of the electromechanical relay. The SBA control unit measures the current at this monitoring line and compares it to the expected value, which depends on the required switching modes (relay on or off).

The SBA control unit controls the demand-based switching on and off of the electrical vacuum pump based on the information regarding whether the combustion engine is running and the brake vacuum, measured at the brake servo. If the brake vacuum is too low, it activates the electrical vacuum pump.