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1. A brake system for motor vehicles which in a brake-by-wire operating mode is configured to be activatable both by the vehicle driver and independently of the vehicle driver, and is normally operated in the brake-by-wire operating mode and which is configured to be operated in at least one fallback operating mode, comprising
a brake master cylinder having a housing and two pistons which define in the housing a first pressure chamber and a second pressure chamber, the first pressure chamber having a first brake circuit associated therewith and being selectively connectable thereto, the first brake circuit having one or more wheel brakes associated therewith, and the second pressure chamber having a second brake circuit associated therewith and selectively connectable thereto, the second brake circuit having one or more wheel brakes is associated therewith, a brake pedal coupled to the brake master cylinder for actuating the brake master cylinder, a first electrically operable, normally open isolation valve for the first brake circuit and a second electrically operable, normally open isolation valve for the second brake circuit, the first and second isolation valves for isolating the first and second pressure chambers from the respective first and second brake circuits, the first isolation valve associated with the first pressure chamber and first brake circuit, the second isolation valve associated with the second pressure chamber and the second brake circuit, a respective electrically operable, normally open inlet valve and a respective electrically operable, normally closed outlet valve for each individual wheel brake for setting wheel-individual brake pressures of a pressure medium, the respective inlet valve and outlet valve for each individual wheel brake defining a respective valve pair such that there a number of respective valve pairs corresponding to the number of wheel brakes, each individual valve pair of the multiple valve pairs being associated with the first brake circuit or the second brake circuit, wherein the first brake circuit has one or more associated wheel brakes and a corresponding number of one or more valve pairs, and the second brake circuit has one or more associated wheel brakes a corresponding number of one or more valve pairs, a first electrically controllable pressure supply unit having a cylinder-piston arrangement with a piston which is operable by an electro mechanical actuator, a first electrically operable normally closed sequence valve for the first brake circuit and a second electrically operable normally closed sequence valve for the second brake circuit, the first sequence valve being for hydraulically connecting the first pressure supply unit to the first brake circuit, the second sequence valve being for hydraulically connecting the first pressure supply unit to the second brake circuit, the first sequence valve associated with the first brake circuit, the second sequence valve associated with the second brake circuit, a simulation device which is hydraulically connectable by means of an electrically or mechanically operable simulator release valve to at least one of the first and second pressure chambers of the brake master cylinder and which communicates to the vehicle driver a predetermined brake pedal feel in the brake-by-wire operating mode, a first electronic control and regulation unit for activating the first pressure supply unit, the first and second isolation valves, the first and second sequence valves, and the simulator release valve, and a second electrically controllable pressure supply unit having at least one intake port selectively connectable to one of the first and second pressure chambers and at least one pressure port, the at least one intake port including a first intake port and the at least one pressure port including a first pressure port, wherein the first intake port is selectively connectable to a selected one of the first and second pressure chambers and the first pressure port is connected to the first or second brake circuit associated with the selected one of the first and second pressure chambers, the pressure supply unit being configured to draw pressure medium from the selected one of the first and second pressure chambers in an unenergized state of the first and second isolation valves and of the inlet valves and the outlet valves. |
