Brake system for motor vehicles

A brake system for a motor vehicle which, in a brake-by-wire operating mode, can be activated both by the vehicle driver and also independently of the vehicle driver, and is normally operated in the brake-by-wire operating mode and can be operated in at least one fall-back operating mode in which only operation by the vehicle driver is possible, comprising:

• a brake pedal for actuating a hydraulic piston-cylinder arrangement having a hydraulic piston on which an actuating force is exerted when the brake system is actuated by the vehicle driver and which is guided directly and displaceably in a housing along an actuation axis,
• a hydraulically actuable pedal travel simulator which is releasable and blockable by means of a simulator release valve,
• a travel detection device which detects the actuation travel of the hydraulic piston,
• a pressure medium reservoir,
• an electrically controllable pressure source which delivers a brake system pressure,
• a pressure modulation unit having electrically controllable pressure regulating valves for adjusting wheel-individual brake pressures which are derived from the brake system pressure of the electrically controllable pressure source, the brake system pressure of the electrically controllable pressure source being supplied via a brake system pressure line to inlet connections of the pressure regulating valves which deliver or transmit the brake system pressure of the electrically controllable pressure source through the pressure regulating valves when the pressure regulating valves are in an unenergized state, wherein the pressure regulating valves are open in the unenergized state to allow fluid to flow from the brake system pressure line toward the corresponding wheel brake and closed in an energized state to prevent fluid from flowing from the brake system pressure line toward the corresponding wheel brake;
• dividing piston devices which are associated with each of the motor vehicle wheel brakes of the vehicle and are subjected on a first dividing piston surface to the wheel-individual brake pressure set or transmitted by the pressure regulating valves and which transmit the wheel-individual brake pressure exerted by a second dividing piston surface to the motor vehicle wheel brakes,
• activating elements for exerting the actuating force or for mechanically activating the dividing piston devices, which activating elements can be brought into force-transmitting connection with the piston, and
• an electronic control and regulation unit.