Brake system

A brake system of the ‘brake-by-wire’ type for actuating a motor vehicle brake system comprising:

• a brake booster operable in response to an input of a driver by a brake pedal and by an electronic regulating and control unit;
• a device provided to decouple a force-transmitting connection between the brake pedal and the brake booster in a ‘brake-by-wire’ operating mode;
• a master brake cylinder connected downstream of the brake booster in terms of effect, to one or more pressure chambers of which wheel brakes of the motor vehicle are connected;
• a pedal travel simulator which interacts with the brake pedal in order for a resetting force acting on the brake pedal can be simulated in the ‘brake-by-wire’ operating mode independently of an actuation of the brake booster, and which can be enabled in the ‘brake-by-wire’ operating mode when the force-transmitting connection between the brake pedal and the brake booster is decoupled and can be disabled outside the ‘brake-by-wire’ operating mode;
• a first sensor (6) sensing a brake pedal actuating travel (SBp);
• a second sensor (18) for sensing a travel (SDs) of an output member (20) of the brake booster;
• a third sensor for sensing a brake pressure prevailing in the system, wherein output signals of the sensors are sent to the electronic regulating and control unit (7);
• a control circuit for controlling the travel (SDs) covered by the output member (20) of the brake booster (3), a nominal value (SDsnominal) of the travel (SDs) covered by the output member (20) of the brake booster (3) being calculated corresponding to the actuating travel (SBp) of the brake pedal (1);
• a monitoring module (24) which, in the case of a fault such as inclusion of air or brake circuit failure, performs a partial compensation of the extension of the travel (SDs) covered by the output member (20) of the brake booster (3), which extension is caused by the fault;
• and
• wherein a pressure fluid volume/pressure characteristic curve is stored in the monitoring module (24), so that the dependency of the pressure fluid volume absorption (Q) of the brakes or of the travel (SDs) covered by the output member (20) of the brake booster (3) and corresponding to the pressure fluid volume absorption (Q) on the hydraulic pressure (p) Q or SDs=f(p), and in that the monitoring module (24) is furnished with the actual values (SDsactual,pactual)of the travel (SDs)covered by the output member 20 of the brake booster (3) and of the hydraulic pressure (p) prevailing in the system, and a travel value (Smodel ) corresponding to the nominal value (Qnominal)of the pressure fluid volume is calculated from the actual pressure value (pactual)and compared with the actual value (SDsactual) of the travel (SDs)covered by the output member 20 of the brake booster (3), and a correction value (Scorr) is produced in the monitoring module (24) from which a fault in the system is inferred, when the comparison result (ΔSdiff=Smodel−SDsactual) exceeds a threshold value (Sthreshold).