Patent ID: 8424976

Claim:
A brake system for motor vehicles which is configured to be actuated in a brake-by-wire operating mode both by a vehicle driver and independently of the vehicle driver, said brake system comprising: a sensor device for sensing a driver deceleration request, an input force element which is coupled to a brake pedal via a pushrod, a master brake cylinder which has at least one master cylinder piston, and is connected to wheel brake circuits of a vehicle, a pressure medium reservoir vessel which is assigned to the master brake cylinder and to which pressure spaces of the master brake cylinder are connected, an electrically controllable pressure supply device, an electronic open-loop and closed-loop control unit for actuating the electrically controllable pressure supply device with the effect of performing closed-loop control of the hydraulic pressure which is output by it, a pedal decoupling unit which is connected upstream of the master brake cylinder and which has a restraining piston which accommodates, in a hydraulically sealed fashion, an axial protrusion of the master cylinder piston, which can be connected in a force-transmitting fashion to the master cylinder piston and having a first annular face that bounds, with the master cylinder piston, a first hydraulic chamber to which the pressure which is output by the electrically controllable pressure supply device is applied, wherein application of pressure to the chamber brings about a force effect on the master cylinder piston in the activation direction and on the restraining piston counter to the activation direction, and a simulation device with at least one elastic element, which simulation device provides a vehicle driver with a pedal sensation in the brake-by-wire operating mode and which is arranged between the input force element and the restraining piston, wherein the restraining piston is a stepped piston having a second annular face that bounds a second hydraulic chamber which is configured to be shut off, wherein a pressure effect in the second hydraulic chamber corresponds to a force which acts on the restraining piston counter to the activation direction.