A brake system for motor vehicles, including:
- an actuation device in the form of a brake pedal,
- a travel simulator arranged to generate a feedback force on the actuation device,
- a first piston-cylinder device, wherein the piston-cylinder device has at least one piston and at least one working chamber and is connected via one or more hydraulic connecting lines to one or more wheel brakes of one or more brake circuits,
- a control device,
- at least one pressure supply unit driven by an electric motor and having a double-stroke piston, a first working chamber, and a second working chamber, wherein, by means of the pressure supply unit, brake pressure is enabled to be built up or reduced in one or more of the wheel brakes simultaneously, wherein the first working chamber is connectable via a first controllable switching valve with a storage container and the second working chamber is connectable via a second controllable switching valve with the storage container, and
- one or more outlet valves, wherein either a respective outlet valve of the one or more outlet valves is associated with only a respective one of the one or more wheel brakes or a respective outlet valve of the one or more outlet valves is associated with only one wheel brake of a respective one of the one or more brake circuits, wherein the one or more outlet valves are arranged in respective hydraulic connection(s) between the wheel brake(s) with which it/they are associated and the storage container, there being no further valve(s) arranged between the one or more outlet valves and the storage container,
- wherein the brake system is adapted to determine a required pressure change in one or more wheel brakes, wherein the brake system is further adapted to utilize a pressure-volume mapping to determine a defined stroke distance for the required pressure change, wherein a pressure volume control is implemented by displacing the double-stroke piston by the defined stroke distance,
- wherein at least one of the one or more wheel brakes is assigned to a respective one of the brake circuits and each of the one or more wheel brakes is enabled to be connected to an associated one of the one or more connecting lines via a respective third controllable switching valve, wherein the respective controllable switching valve is open in an unpowered state, and
- wherein the wheel brake pressure is reducible via establishing a hydraulic connection of one of the first or second working chambers of the pressure supply unit with the storage container by opening the respective one of the first or second controllable switching valve as follows:
- a) in at least one or more of the wheel brakes, controlled pressure reduction is arranged to occur via the respective third controllable switching valve associated with the respective wheel brake(s) via the pressure volume control by means of a return stroke of the double-stroke piston into the storage container, and/or
- b) in at least one or more of the wheel brakes, controlled pressure reduction takes place via the respective third controllable switching valve associated with the respective wheel brake(s) via the pressure volume control by means of a forward stroke of the double-stroke piston into the storage container,
- wherein the wheel brake pressure of the at least one or more of the wheel brakes is further reducible by opening the respective one of the one or more outlet valves associated with the at least one of the one or more wheel brakes or the wheel brake of the respective one of the one or more brake circuits by, in parallel with a) and/or b), in at least one wheel brake, using a time control of the respective one of the one or more outlet valves to allow pressure medium to thereby flow into the storage container,
- wherein the control device includes a memory that stores actual wheel brake pressures set in the respective wheel brakes and/or continuously calculates in a control model probable brake pressures of the respective wheel brakes and updates these with measured values, wherein for simultaneous pressure reduction in at least two of the one or more wheel brakes of one of the brake circuits, to different nominal pressures, the control unit evaluates a respective pressure-volume curve of respective wheel brakes of the at least two wheel brakes and uses a lowest nominal pressure to be generated to calculate a piston travel of the double-stroke piston required for this and moves the piston by the piston travel of the double-stroke piston by means of a drive of the pressure supply unit, wherein a respective third controllable switching valve associated with a wheel brake of the one or more wheel brakes associated with the lowest nominal pressure remains open until the lowest nominal pressure has been set in that wheel brake;
- and wherein for the third controllable switching valves associated with the other wheel brakes not associated with the lowest nominal pressure, the control device calculates individually temporal duration(s) for which the respective third controllable switching valves must remain open so that the pressure(s) in the respective other wheel brakes is/are reduced to the respective nominal pressure(s), and opens the respective third controllable switching valve(s) only for the respective calculated duration(s), wherein a respective third controllable switching valve is opened first at a time at which pressure in an associated brake circuit is equal to or higher than an actual pressure in the wheel brake associated with the lowest nominal pressure, and wherein at the same time as or temporally overlapping pressure reduction in the various ones of the one or more wheel brakes over the brake circuit(s), pressure is reduced in at least one further wheel brake of the one or more wheel brakes by opening an associated outlet valve of the one or more outlet valves.