BRAKE SYSTEM WITH NOVEL MUX REGULATION (MUX 2.0) WITH AN OUTLET VALVE/BRAKE SYSTEM OR AN OUTLET VALVE PER BRAKE CIRCUIT, AND METHOD FOR PRESSURE CONTROL

Abstract

A brake system for motor vehicles may include an actuation device (e.g., brake pedal), a first piston-cylinder unit having at least one piston that separates two working chambers, a control device and a pressure supply unit driven by an electric motor and having a double-stroke piston delimiting working chambers. At least one brake circuit may have associated therewith at least one wheel brake, and each wheel brake may be connected to an associated hydraulic connecting line via a controllable switching valve. An outlet valve may be assigned to a single wheel brake or to a single wheel brake of each brake circuit in a hydraulic connection between the wheel brake and a pressure medium storage container.

Claims

1. A method of controlled pressure reduction via at least one pressure supply unit of a brake system, wherein a brake pressure of the brake system is reduced using a pressure supply unit with a double-stroke piston which divides a working chamber into a first working chamber and a second working chamber, wherein a controlled pressure reduction takes place in at least one wheel brake via a pressure volume control, a) wherein the method includes: establishing a fluid connection between the first working chamber and the at least one wheel brake via an open switching valve, which is assigned to the respective at least one wheel brake, and employing a return stroke of the double-stroke piston to increase a volume of the first working chamber; and/or b) wherein the method includes: establishing a fluid connection between the second working chamber and the at least one wheel brake via the opened switching valve, which is assigned to the respective at least one wheel brake, and; opening a first switchable valve to establish a fluid connection between a reservoir and the first working chamber, and employing a forward stroke of the double-stroke piston to increase a volume of the second working chamber.

2. The method according to claim 1, wherein the pressure supply unit is a pressure supply unit driven by an electric motor.

3. The method according to claim 1, the method further including establishing a fluid connection between the reservoir and the at least one wheel brake via an opened time controllable outlet valve by means of a time control, which is assigned to the respective at least one wheel brake.

4. The method according to claim 3, wherein the time control controls the time controllable outlet valve simultaneously with the switching valve or with a time offset relative to the switching valve.

5. The method according to claim 1, wherein, with normal brake force boosting in all wheel brakes, pressure is built up and reduced simultaneously or sequentially via a travel control of the double-stroke piston of the pressure supply unit, taking into account a pressure-volume characteristic curve.

6. The method according to claim 1, wherein during recuperation in all wheel brakes, pressure is built up and reduced simultaneously or sequentially via a travel control of the double-stroke piston of the pressure supply unit, taking into account a pressure-volume characteristic curve.

7. The method according to claim 1, wherein in ABS operation with a low road friction value (low ?), the pressure in all wheel brakes is increased and reduced simultaneously or sequentially via a travel control of the double-stroke piston of the pressure supply unit, taking into account a pressure-volume characteristic curve.

8. The method according to claim 1, wherein in ABS operation with high dynamic requirements for high road friction coefficient (high-?), pressure in the wheel brakes is reduced simultaneously or with a time offset, whereby the pressure is reduced via the double-stroke piston of the pressure supply unit, taking into account one or more pressure-volume characteristic curve and by means of time control via at least one outlet valve.

9. The method according to claim 1, wherein in ABS operation with high dynamic requirements for high road friction coefficient (high-?), pressure in the wheel brakes is reduced simultaneously or with a time offset, whereby the pressure is reduced via the double-stroke piston of the pressure supply unit, taking into account one or more pressure-volume characteristic curve and by means of time control via at least one outlet valve.

10. The method according to claim 1, wherein an outlet valve of a particular wheel brake of the wheel brakes is opened so that the pressure in the particular wheel brake is reduced.

11. The method according to claim 10, wherein the pressure is released simultaneously or with a time offset via at least one outlet valve and at least one switching valve, wherein the at least one outlet valve is time-controlled and the at least one switching valve is pressure volume-controlled via the pressure supply unit.

12. The method according to claim 11, wherein the at least one switching valve comprises first, second, third, and fourth switching valves, wherein the first switching valve and/or the second switching valve and/or the third switching valve, and/or the fourth switching valve is/are switched with a time offset.

13. The method according to claim 1, wherein after a first pressure reduction in the brake system, a second switchable valve is opened for a further pressure reduction.

14. The method according to claim 10, wherein a control device controls the at least one switching valve and/or at least one separating valve and/or the at least one outlet valve.

15. The method according to claim 1, wherein to perform further pressure reduction, pressure is released in a first wheel brake of the wheel brakes via the first working chamber by movement of the double-stroke piston, and pressure is simultaneously built up in another of the wheel brakes using the second working chamber.

16. A brake system for motor vehicles, the brake system including: at least one pressure supply unit driven by an electric motor, which has a piston, a first working chamber and a second working chamber, wherein the brake pressure is able to be reduced simultaneously in one or more wheel brakes as desired by means of the pressure supply unit, brake circuits, wherein at least one wheel brake of the one or more wheel brakes is assigned to each brake circuit, and wherein each respective one of the one or more wheel brakes is able to be connected to a connecting line assigned to the respective wheel brake via a respective controllable switching valve, wherein the controllable switching valve is open in an unpowered state, and wherein pressure is maintained in the respective wheel brake by closing the respective controllable switching valve and the pressure is reduced in the respective wheel brake by opening the respective controllable switching valve, a control device, and a reservoir, wherein the first working chamber is connectable via a first controllable switching valve with the reservoir and/or wherein the second working chamber is connectable via a second controllable switching valve with the reservoir, wherein wheel brake pressure is reducible via establishing a hydraulic connection of one of the working chambers of the pressure supply unit with the reservoir by opening the respective controllable switching valves as follows: a) in one or more respective ones of the wheel brakes reducing pressure via one or more of the respective controllable switching valves assigned to the one or more of the respective ones of the wheel brakes via a pressure volume control by means of a return stroke of the piston into the reservoir, and/or b) in one or more respective ones of the wheel brakes reducing pressure via one or more of the respective controllable switching valve assigned to the one or more respective ones of the wheel brakes via a pressure volume control by means of a forward stroke of the piston into the reservoir.

17. The brake system according to claim 16, further including: an actuation device in the form of a brake pedal, and a travel simulator configured to generate a feedback force on the actuation device.

18. The brake system according to claim 16, further including one or more outlet valves, wherein a respective one of the one or more outlet valves is assigned to only one wheel brake or wherein respective ones of the one or more outlet valves are respectively assigned to only one wheel brake of each brake circuit, the/a respective outlet valve being arranged in a hydraulic connection between the assigned wheel brake and the reservoir, no further valve being arranged between the/a respective outlet valve and the pressure medium reservoir.

19. The brake system according to claim 18, wherein an outlet valve of the one or more outlet valves is assigned to a front wheel brake of the one or more wheel brakes, and/or wherein at least one pressure sensor serves to determine a pressure in at least one of the brake circuits, and/or wherein the controllable switching valves are digital valves that are open in an unpowered state.

20. The brake system according to claim 18, wherein wheel brake pressure is further reducible by opening the respective one of the one or more outlet valves assigned to at least one wheel brake, wherein the respective one of the one or more outlet valves is a time controllable outlet valve and the pressure reduction takes place via the time controllable outlet valve, by means of a time control, into the storage container.

21. The brake system according to claim 20, wherein the time control is configured to control the time controllable outlet valve simultaneously with the respective controllable switching valve assigned to the at least one wheel brake or with a time offset with respect to the respective controllable switching valve assigned to the at least one wheel brake.

22. The brake system according to claim 16, wherein the control device has a memory which stores actual wheel brake pressures set in each wheel brake, wherein by means of the stored actual wheel brake pressures and nominal wheel brake pressures, the control unit determines, taking into account one or more pressure-volume curves of the wheel brake(s), a time for which one or more outlet valves are to be opened in order to reach the nominal wheel brake pressure(s) in one or more of the wheel brakes, and wherein the control device closes the one or more outlet valves after expiry of the time.

23. The brake system according to claim 22, wherein the control device is configured to reduce the brake pressure: a) in a first one of the wheel brakes, to which an outlet valve of the one or more outlet valves is assigned, via the assigned outlet valve, which is opened for a precalculated time, into the reservoir, and b) simultaneously in a second one of the wheel brakes by opening a respective assigned switching valve and by actuating the pressure supply unit.

24. The brake system according to claim 16, further including: a piston cylinder system including a piston; and one or more outlet valves, wherein at least one of the one or more outlet valves is assigned to a wheel brake of a respective one of the brake circuits, wherein the outlet valve assigned to the wheel brake of the respective one of the brake circuits serves for pressure reduction in all wheel brakes of the respective one of the brake circuits, wherein for common pressure reduction, the control device opens all switching valves of all brakes of the respective one of the brake circuits and the assigned outlet valve, and wherein during opening of the switching valves of the wheel brakes of the respective one of the brake circuit, the control device separates the respective one of the brake circuits from the pressure supply unit by closing an associated isolating valve or by locking the piston of the piston cylinder system.

25. The brake system according to claim 16, wherein the control device has a memory which stores a respective actual wheel brake pressure set in each wheel brake and/or continuously calculates in a control model a respective probable brake pressure of each wheel brake and updates these with measured values, wherein for simultaneous pressure reduction in at least two wheel brakes of one of the brake circuits to different nominal pressures in the wheel brakes, the control unit evaluates a pressure-volume curve of each of the wheel brakes concerned and using the lowest nominal pressure to be generated calculates a piston travel of the piston required for this and moves the piston by the piston travel by means of the electric motor, wherein a switching valve of a wheel brake with a lowest nominal pressure out of the wheel brakes of the one of the brake circuits remains open until the nominal pressure has been set in the wheel brake with the lowest nominal pressure; and wherein, for the switching valves of the other wheel brakes of the one of the brake circuits, the control device calculates individually respective temporal durations for which the respective switching valves must remain open so that the pressures in the respective wheel brakes are reduced to the respective nominal pressures, and opens the respective switching valves only for the respective calculated durations.

26. The brake system according to claim 16, wherein the control device has a memory which stores a respective actual wheel brake pressure set in each wheel brake and/or continuously calculates in a control model a respective probable brake pressure of each wheel brake and updates these with measured values, wherein for simultaneous pressure build-up in at least two wheel brakes of one brake circuit to different nominal pressures, the control unit evaluates a pressure-volume curve of each of the wheel brakes concerned and using the highest nominal pressure to be generated calculates a piston travel of the piston required and moves the piston by the piston travel by means of the electric motor, wherein the switching valve of the wheel brake of the brake circuit with the highest nominal pressure remains open until the nominal pressure has been set in the wheel brake of with the highest nominal pressure; and wherein for the switching valves of the other wheel brakes of the brake circuit, the control device calculates individually respective temporal durations for which the respective switching valves must remain open so that the pressures in the respective wheel brakes are built up to the respective nominal pressures, and opens the respective switching valves only for the respective calculated durations.

27. The brake system according to claim 16, wherein the pressure supply unit is a piston-cylinder system with one piston, the one piston of which is driven by the electric motor and delimits the first and the second working chambers from each other, wherein both the first and the second working chambers, by corresponding actuation of isolating valves, are enabled to be used for simultaneous and/or temporally offset pressure build-up and pressure reduction in the wheel brakes of the two brake circuits.

28. The brake system according to claim 16, wherein for pressure build-up and/or pressure reduction in at least one of the wheel brakes, the control device evaluates a pressure-volume curve of each respective wheel brake of the at least one wheel brake and, from a pressure rise or fall to be generated, calculates a piston travel of the piston required for the pressure rise or fall to be generated and, by corresponding actuation of required valves, moves the piston by the piston travel (ds) by means of the electric motor.

29. The brake system according to claim 16, wherein the control device is arranged to determine a first pressure in a first one of the brake circuits by means of a pressure sensor and to determine a second pressure in a second one of the brake circuits via a phase current of the electric motor, and wherein the control device takes account of at least the first pressure in the control of pressure build-up or pressure reduction in the wheel brakes.

30. The brake system according to claim 16, wherein inlet valves are used instead of the switching valves, each inlet valve having an interior or armature housing connected via a hydraulic line to an associated brake circuit and a valve seat outlet connected via a hydraulic line to the associated wheel brake.

31. The brake system according to claim 16, wherein the second working chamber of the pressure supply unit is connected via a hydraulic connection to the reservoir, wherein a switchable valve serves to shut off the hydraulic connection such that a pressure reduction in at least one wheel brake is enabled to take place in a time-controlled fashion by opening the associated switching valve of the at least one wheel brake and by opening the switchable valve, wherein a predefined opening time determines a wheel brake pressure to be set via the first pressure chamber by means of the pressure supply unit.

32. The brake system according to claim 16, wherein: the first pressure chamber of the pressure supply unit is connected via a hydraulic connection to a working chamber of a first piston-cylinder unit, wherein the hydraulic connection is enabled to be shut off by movement of the piston of the first piston-cylinder unit into a shut-off position which is assumed automatically in a fall-back level of the piston, and/or on pressure build-up and/or on pressure reduction, the control device takes into account an absolute position of the piston of the pressure supply unit and determines a necessary movement travel of the piston of the pressure supply unit depending on actual pressures, nominal pressures and pressure-volume curve of the respective wheel brakes involved in the pressure build-up or reduction, and/or in normal operation with normal brake force amplification, recuperation, and/or ABS at low ?, pressures are built up and reduced simultaneously or sequentially in all wheel brakes via travel control of the piston of the pressure supply unit, taking into account respective pressure-volume curves, and wherein in operating situations with ABS at high ?, ? split, ESP and/or anti-slip regulation (ASR), a pressure in at least one wheel brake is reduced via the assigned outlet valve for the at least one wheel brake and/or via outlet valves of the pressure supply unit.

33. A brake system for motor vehicles, the brake system including: at least one pressure supply unit having at least one working chamber, wherein the at least one pressure supply unit is configured to build up and/or reduce brake pressure in at least one wheel brake simultaneously or successively, wherein the pressure supply unit is driven by an electric motor and the at least one wheel brake is connected to the pressure supply unit via at least one connection line; at least one control device; and at least one switching valve controlled by the control device, wherein the at least one switching valve is assigned to the at least one wheel brake, wherein the controllable switching valve is in an open state when unpowered, wherein the brake system is configured such that: a) pressure is maintained in at least one the wheel brake if the at least one switching valve is closed; and b) the pressure in the at least one wheel brake is only reducible if the at least one switching valve is open, wherein wheel brake pressure is sequentially or simultaneously reducible via pressure-volume control.

34. The brake system according to claim 33, wherein the at least one switching valve has a respective valve seat, the at least one switching valve being arranged on the at least one wheel brake by means of the respective valve seat, so that the at least one switching valve for the pressure build-up and the pressure volume control is opened by pressure in the respective wheel brake.

Description

DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1a: shows a first possible embodiment of the brake system according to the invention with master brake cylinder, pressure supply with outlet valve(s) in one or two brake circuits;

[0062] FIG. 1b: shows an example of a simplified pressure-volume curve;

[0063] FIG. 1c: shows pressure regulation options in the basic system of FIG. 1a;

[0064] FIG. 1d: shows valve circuit with AV/EV in the regulation systems of the prior art;

[0065] FIG. 1e: shows advantageous valve circuit for new regulation system with switching valves and an outlet valve in one brake circuit;

[0066] FIG. 1f: shows inlet valve according to the invention in the brake circuit;

[0067] FIG. 2a: shows pressure-volume control in a closed brake circuit (AV, ZAV closed);

[0068] FIG. 2b: shows pressure-volume curve for wheel brake 1 and wheel brake 2 with offset shift by opening of brake circuit;

[0069] FIG. 3: shows conventional multiplex regulation in sequential order;

[0070] FIG. 3a: shows cycle shortening of multiplex regulation with AV valve in pressure reduction;

[0071] FIG. 3b: shows time control on pressure reduction via outlet valve;

[0072] FIG. 4: shows temporal development of an exemplary regulation with 4 wheel brakes;

[0073] FIG. 4a shows temporal development of an exemplary regulation with 4 wheel brakes;

[0074] FIG. 4b: shows temporal development of an exemplary regulation with 4 wheel brakes;

[0075] FIG. 5: shows advantageous brake system structure with double-stroke piston (DHK);

[0076] FIG. 5a shows pressure build-up regulation in multiplex mode according to the invention with DHK and outlet valve;

[0077] FIG. 5b shows simultaneous pressure build-up and pressure reduction in multiplex mode in DHK return stroke and outlet valve;

[0078] FIG. 5c shows simultaneous pressure build-up and pressure reduction in multiplex mode in DHK advance stroke and outlet valve;

[0079] FIG. 5d shows regulated or controlled pressure reduction in both brake circuits in closed circuit via pressure-generating unit and PD3 valve;

[0080] FIG. 6: shows double-stroke piston system in advantageous dual circuit design.

DESCRIPTION OF THE FIGURES

[0081] FIG. 1a describes the basic embodiment of the brake system according to the invention with master brake cylinder HZE, pressure supply unit DE with single-stroke piston (3) and outlet valve(s) AV1, AV3 in one or optionally two brake circuits. Brake circuit II is advantageously assigned to the front axle. The outlet valve AV1 is optional, i.e. need not necessarily be provided.

[0082] The brake system consists of a master brake cylinder according to the prior art, comprising a master brake cylinder unit HZE, floating piston SK with return spring 1, a pressure piston DK or ram or an auxiliary piston HiKo, a hydraulically actuated travel simulator WS and corresponding control valves HZV for the function of the piston-cylinder unit, as described for example in the prior art.

[0083] The following embodiments amongst others are possible: [0084] a) master brake cylinder with two pistons in the form of a pressure piston DK and a floating piston SK with connected travel simulator which can be shut off via a valve, [0085] b) 3-piston system with auxiliary piston HS for travel simulator actuation and infeed valve and/or mechanical intervention in the event of a fault, [0086] c) 2-piston system with floating piston SK and auxiliary piston HiKo with infeed.

[0087] In all embodiments, the master brake cylinder unit HZE can be isolated from the pressure supply unit DE. According to variant Var2, this can be achieved via isolating valves TV1 and TV2, or in the second variant Van shown, via blocking of the supply of the floating piston. The valve circuit of the HZE ensures that no undesirable feedback occurs to the pedal BP when the pressure supply unit DE is active, and in fall-back level (system failure) the volume of the master brake cylinder unit HZE is guided to the wheel brakes RB1-4. Also, a switching valve SV1-4 is arranged for each wheel brake in the hydraulic connection to the respective associated working chamber A1 or A2 of the brake master cylinder HZE. The concrete embodiment of the master brake cylinder HZE is not however relevant for the brake system according to the invention.

[0088] The brake system has four switching valves SV1, SV2, SV3 and SV4, via which the pressure supply DE and the master brake cylinder HZE are connected to the wheel brakes RB1-4. The switching valves SV1-4 preferably have a low flow resistance and are suitable for MUX operation. In addition, an outlet valve AV3 is provided in a brake circuit for pressure reduction in the wheel brake in RB3 independently of the MUX, and is arranged in the hydraulic connection between the wheel brake RB3 and the storage container 10. Preferably, the outlet valve AV3 is positioned on the front wheel brake RB3 of a brake circuit since, in extreme cases, the pressure in this wheel brake must be reduced quickly and without great time delay because the significant braking effect originates from the front axle.

[0089] The pressure supply unit DE consists of an electric motor M, which via a spindle 2 drives a piston 3 which compresses or shifts the volume in the pressure chamber 4. The motor M of the pressure supply unit may comprise two or three sensors: a) angle sensor 6, b) current measurement sensor for measuring the phase currents of the electric motor 7, and c) if necessary, a temperature sensor 8 for determining the coil temperature of the electric motor M.

[0090] The pressure-generating unit DE is preferably arranged in the valve block or HZE. The pressure chamber 4 of the pressure-generating unit DE is connected to a storage container 10 via a check valve 5. A pressure sensor 9 is arranged at the outlet of the pressure-generating unit DE. The brake circuit II is connected via the isolating valve TV2, and brake circuit I via the isolating valve TV1, to the pressure supply unit DE. The isolating valve TV1 may be omitted if one chamber is separated by the pressure supply unit DE in fall-back level. This can be achieved by a pressure infeed from the pressure-generating unit DE via the blow hole SL of the floating piston SK.

[0091] For pressure modulation in ABS and recuperation, the control device and its regulator determine the necessary pressure change for pressure build-up (referred to below as P.sub.auf) and pressure reduction (referred to below as P.sub.ab). The pressure is regulated by the pressure-generating unit DE, in that simultaneously or with a temporal offset, the individual wheels/wheel cylinders are supplied with pressure. For this, the electric motor M shifts the corresponding volume for pressure change in both directions via e.g. the piston 3.

[0092] Here, the pressure change according to the prior art can be modified by corresponding time control with PMW of the switching valves and pressure control of the pressure of the DE. This however requires a very precise PWM process with complex pressure model. Preferably, therefore, the volume control is used as already described above. For this, the data of the pressure-volume curve (p-V curvesee FIGS. 1a and 2a) of the respective wheel brake RB1-4 involved in the pressure build-up or reduction are stored in the memory of the regulator unit. If now the regulator requests a pressure change ?p, for pressure regulation at the wheel the differential volume ?V is adjusted accordingly by the piston in both directions ??S. For this, one or more switching valves are opened which are closed again after completion of the volume shift. The position of the piston 3, e.g. at the start, middle or end of the stroke, is irrelevant for ?P volume control for the regulation. Here, during the pressure change, a temporal control may be used in order to implement transition functions towards the end of the pressure change, e.g. to reduce the pressure fluctuations and the associated noise.

[0093] A high dynamic is important if two or more wheels require a pressure change simultaneously. For this, the invention proposes that to relieve the load on the motor dynamics, one or two additional outlet valves AV are used. For volume control, in particular also the pressure level in the pressure-generating unit DE and in the wheels is important. It is favourable here that the pressure level on pressure change corresponds to the starting pressure of the wheel to be regulated. This achieves a rapid and low-noise pressure regulation. The temporal developments are illustrated in FIGS. 3, 3a, 3b and 4, 4a, 4b.

[0094] Suitable pressure-generating units DE are all pumps with single piston, stepped piston, double-stroke piston and also e.g. gear pumps which allow precise volume control.

[0095] In FIG. 1a, for the above-mentioned functions, the pressure generation takes place in one circuit directly via an isolating valve TV1 in BK1 (Var2) or alternatively via a blow hole SL on the front of the SK piston (Var1). The pressure is supplied to brake circuit BK2 via an isolating valve TV2. For infeed via the blow hole SL on the front of the floating piston SK, optionally the isolating valve TV1 may be omitted since, on system failure, the pressure-generating unit DE is isolated from the master brake cylinder effect because piston SK moves and shuts off the pressure supply DE. Alternatively, as drawn in dotted lines, the pressure-generating unit DE may be connected directly to BK1 via TV1 (Var2). Since the SK piston in Var1 is only moved in fall-back level, a special diagnosis circuit is required in which the floating piston SK is moved and checked for tightness.

[0096] FIG. 1b describes the known pressure control based on a simplified pressure-volume curve which forms the basis of the MUX regulation. Depending on the required pressure difference Op, from the curve a volume change ?V is read which is implemented as a travel change ?s of the piston 3 by shifting the plunger of the pressure-generating unit DE. This applies for both pressure build-up and pressure reduction.

[0097] FIG. 1c shows a fundamental possibility for pressure regulation in the basic embodiment of FIG. 1. The system itself has the following degrees of freedom in pressure regulation: [0098] pressure build-up and pressure reduction in all brake circuits BKI and BKII mainly with multiplex regulation (pressure regulation with pressure-volume control) in all wheel brake cylinders simultaneously or sequentially; [0099] multiplex regulation in pressure build-up and pressure reduction in brake circuit I via the opened isolating valve TV1 and simultaneous pressure reduction in brake circuit II via the outlet valve AV3; [0100] multiplex regulation via SV1, SV2, SV4 in pressure build-up and pressure reduction in brake circuit I and II for wheel brakes RB1, RB2 and RB4, and simultaneous pressure reduction in wheel brake RB3 via opened outlet valve AV3 with closed switching valve SV3.

[0101] The pressure reduction p.sub.ab via switching valves SV1 and SV2 in BK I takes place mainly via pressure-volume control, sequentially or simultaneously. For this, the respective switching valve SVi is always opened. For simultaneous pressure reduction p.sub.ab at different starting pressures, optionally by deviation from the MUX regulation, switching valves SV1 and SV2 may be opened with a time offset, and pressure reduction p.sub.ab controlled via a switching valve SV2.

[0102] The isolating valve TV1 is always opened on pressure reduction. In this exemplary embodiment, the wheel brake RB1 has a higher pressure, therefore the associated switching valve SV1 is opened before the switching valve SV2. On the basis of knowledge of the pressure differencethe pressures in wheel brakes RB1 and RB2 and the pressure in the pressure-generating unit DE are knownthe time control may be dimensioned precisely. SV2 is opened when the pressure in the pressure-generating unit DE is approximately reached. Further pressure reduction then takes place simultaneously in both wheel brake cylinders RB1 and RB2 by control via piston 3 when switching valves SV1, SV2 and TV1 are open. When the target pressure of a wheel is reached, the corresponding switching valve SV1 or SV2 is closed. If further pressure reduction is desired in one wheel, the further pressure reduction can take place in the respective wheel brake.

[0103] As already described, to simplify the system, preferably the PWM control is omitted, in particular also for noise reduction.

[0104] Exemplary temporal curves of the pressure reduction are described in FIGS. 4a to 4c.

[0105] FIG. 1d shows a conventional valve circuit for ABS with four inlet valves EV and four outlet valves AV. If this is also used with fewer AV for MUX, e.g. with differential pressure in MUX, as well as this pressure the fault case must be taken into account in which, on an asymmetric road surface, the pressure-generating unit and also the valve actuation fail suddenly e.g. due to the ECU, and at the same time the pressure-generating unit has a low pressure level. In this case for example, EV1 has 130 bar and EV2 0 bar. On failure of the pressure-generating unit, this means that for EV1 the return spring of the valve armature must open around 130 bar. To enable this, the magnet circuit of the valve must be sufficiently large, whereby the valve becomes costly. Alternatively, a pressure-relieved valve may be used, but its costs are also high.

[0106] In dimensioning of the valve seat, it must also be taken into account that this should be as large as possible in order to generate a small backup pressure if the brake pressure is to be built up rapidly by the pressure-generating unit.

[0107] The backup pressure is introduced directly into the motor torque or power.

[0108] FIG. 1e shows a modified throughflow of the switching valves SV. The hydraulic medium flows from the brake circuit or pressure-generating unit through the armature chamber to the valve seat and onto the wheel cylinder. If the above fault case occurs, the wheel pressure opens the switching valve. The magnetic force must however also close around 130 bar, which takes place however with a small armature air gap in the valve end position. The return spring of the switching valve SV need therefore only be slightly strengthened so that the switching valve does not snatch at correspondingly high volume flow. Since conventional inlet valves must close at around 220 barin FIG. 1e, 130 bar, with the same magnet dimensioning the valve seat area may be increased which means a smaller backup pressure or flow resistance and is advantageous for MUX mode. The valve circuit depicted in FIG. 1e is therefore advantageous for the brake system according to the invention.

[0109] FIG. 1f shows a possible embodiment of the inlet valve EV according to the invention and the connection to the brake circuit BK and the pressure supply DV and wheel brakes RBi.

[0110] The inlet valve EV has a magnet armature MA, a magnetic base body MGK and an exciter coil ES. When the magnetic valve EV is powered, the magnet force MK shifts the armature MA from position S.sub.A0 to position S.sub.A2 by the differential travel S.sub.A. The magnet armature MA moves a ram MSt? by the same travel, so that the ram MSt? comes to rest on the valve seat VS and closes the outlet Ea of the magnetic valve. The armature MA at this point still has a residual air gap S.sub.0 from the magnetic base body MKG, which is provided so that the armature MA does not stick to the magnetic housing MGK when the power to the exciter coil ES of the valve EV is switched off, due to re-magnetisation losses of the iron circuit. When the valve current is switched off, the return spring RF moves the armature MA back to the starting position. The magnet force F.sub.M rises nonlinearly with a smaller air gap, e.g. with increasing travel. The return spring F.sub.RF is dimensioned such that the magnetic force F.sub.M in the starting position S.sub.A0 is greater than the spring force, so that a secure closure of the valve is guaranteed. The spring force increases with the increasing travel S.sub.A and in the end position S.sub.A2 is however smaller than the magnet force F.sub.M. Preferably, a linear spring is used, so that the magnet force F M in the end position for a given current is significantly higher than the return force, so that the valve can be retained with low current, or secure closure is guaranteed even at high differential pressures between the wheel brake and the pressure supply. This retention is also ensured at high differential pressures since the magnet force increases strongly nonlinearly at the closed valve position. The return spring must however also be dimensioned such that the function as an unpowered open valve can be ensured and the valve always opens safely.

[0111] The outlet Ea of the valve is connected to the wheel brakes RBi (RB1-RB4), the inlet E, to one brake circuit BKi or to the pressure supply unit DV (20). With such connections, the inlet valve EV can be opened both by the return spring RF and by the pressure in the wheel brake, which is very important in particular in the event of a fault or malfunction in the brake system (e.g. loss of voltage to the valve). Also, even at high pressures in the brake circuit and small pressures in the wheel brake, only the pressure difference between inlet Ei and outlet Ea acts on the ram MSt?. This differential pressure at the valve is relatively low in pressure build-up, but must however be taken into account in the spring design RF so that the pressure difference does not lead to the valve being pushed back on pressure build-up when the volume of the pressure supply DV is delivered to the wheel brake. Valves with large opening cross-section ?Q or low flow losses reduce this effect.

[0112] In particular on pressure build-up with pressure-volume control or time control with low differential pressure between the pre-pressure and actual pressure in the wheel brake, the valves described above with large opening cross-section may be used since the regulation accuracy is very high. This in turn has advantages in that only low flow losses occur, in particular with rapid pressure build-up (TTL), and the drive motor requires only a low power for rapid pressure build-up in a very short time (TTL=150 ms).

[0113] Also, because of the low flow losses of the advantageously configured inlet valves, a pressure reduction can take place quickly via the inlet valves. Precise pressure reduction via the inlet valves EV can take place with corresponding control of the piston movement of the pressure supply unit 20. Optionally, it is also possible to implement the known MUX process with the valve circuit described above, or with pressure reduction control via outlet valves AV in one brake circuit, in particular for consumers with low volume balance, e.g. the wheel brakes on the rear axle. In other words, a combination is also possible which uses the MUX process in connection with the new valve circuit only in two wheel brakes (e.g. front axle), and the pressure reduction takes place conventionally on two further wheel brakes. This would mean that two wheel brakes/actuators are provided with inlet and outlet valves (EV+AV) and two wheel brakes/actuators only with inlet or switching valves EV. In this case, only the wheel brakes of the front axle are equipped with the new valve circuit according to the invention as shown in FIGS. 1a and 1b, and a standard circuit/standard valves are used on the rear axle.

[0114] FIG. 2a shows the pressure-volume curve of the wheel/wheel cylinder with connecting lines as far as the switching valve SV and pressure sensor. Two curves are shown. Curve P.sub.aufa corresponds to a so-called stiff curve, the other curve P.sub.auf requires substantially more volume. This may in extreme cases cause vapour bubbles due to e.g. play or poor purging.

[0115] This means that the values for V.sub.a e.g. for ?P=P.sub.1?P.sub.2 are equal to V.sub.1?V.sub.2=?V.sub.a=?S.sub.a and at V.sub.auf=?.sub.P equal to V.sub.1a?V.sub.2a=?V=?S. This curve for p.sub.auf and p.sub.ab is stored e.g. for the first time on line-end tests in the memory of the control device both for the individual wheel brakes and for the brake circuits for both p.sub.auf and p.sub.ab. On each braking, the curve is measured by comparison of pressure P with the volume V.sub.(?S). If a great deviation occurs, with a stationary vehicle, the curves can be recorded or adapted as in the above-mentioned test. It is also significant that the values can fluctuate between P.sub.auf and P.sub.ab. It is normal that due to play, V.sub.0 is greater on pressure build-up P.sub.auf but not on pressure reduction P.sub.ab. When the play has been eliminated, the curves are almost equal.

[0116] With poor purging or vapour bubbles, the curves behave similarly but with greater volume for the corresponding pressure value.

[0117] For regulation, the p-V curves are used for pressure build-up P.sub.auf and pressure reduction p.sub.ab.

[0118] FIG. 2b describes the simplified relevant pressure-volume curves for pressure regulation without hysteresis in a closed brake circuit or shifting after pressure reduction with opened outlet valve AV. Starting from a pressure p1, by defining a nominal differential pressure ?p, the necessary volume shift ?V or travel change ?s of the piston can be read from the curve. These differ and are dependent on whether the pressure is changed in one or more brake circuits. The piston is then moved accordingly. If the pressure is reduced via one or more outlet valves, there is a volume loss in the pressure-generating unit. For further pressure reduction or pressure build-up in the closed brake circuit, the travel allocation of the pressure-volume curve is determined by detecting the pressure. This is required in regulation for monitoring the volume balance, since the working chamber of the pressure-generating unit only has a limited volume and thus towards the end of the piston stroke, the piston would travel to the stop. If the piston of the pressure-generating unit travels close to the stop after a pressure change and a further pressure rise is impending, the piston is retracted briefly with closed switching valves SV in order to draw in volume from the storage container. In the design with double-stroke piston (FIG. 5-6), this is retracted or switched to return stroke mode.

[0119] FIG. 3 shows a time development of the MUX regulation as known from WO 2006/111393 A1 or WO 2010/091883 A1. This system is known as the 4-channel MUX in which, except in the critical case of simultaneous pressure reduction (simultaneous p.sub.ab), the pressure reduction p.sub.ab is processed serially per wheel channel (cylinder). In the worst case scenario, this leads to a great delay time which causes large speed differences or even slip because of the individual response times of the valve, motor and the time for the respective pressure reduction p.sub.ab. This both reduces the stability of the braking and disadvantageously extends the braking distance. Optimisation is performed on the response time of the switching valves, motor and pressure reduction gradients. Costs however limit optimisation. The case of simultaneous pressure reduction p.sub.ab for all channels however occurs rarely in practice.

[0120] A further restriction exists in the regulation concept known from WO 2006/111393 A1 or WO 2010/091883 A1 in the necessary priority for the pressure reduction p.sub.ab. If a pressure reduction is required, no pressure build-up p.sub.auf can take place. Since usually the time for pressure build-up P.sub.auf in the regulation cycle is around 200 ms, and two or three small p.sub.auf take place per control cycle each with approximately 10 ms delay time, this was not considered critical but is noted as a minor defect of the 4-channel MUX.

[0121] The brake system according to the invention with its regulation concept offers the following improvements: [0122] introduction of an additional outlet valve on the front axle; [0123] various control methods and strategies for control and regulation of the wheel brakes, e.g. VA, corner braking; [0124] possibility of pressure build-up P.sub.auf with simultaneous pressure reduction p.sub.ab (described in FIG. 5b and FIG. 5c).

[0125] FIG. 3 shows the pressure curve in the individual wheel brakes over time for conventional MUX mode in which the pressure in the wheel brakes is reduced temporally successively. V1 and V2 are the front wheel brakes, H1 and H2 the rear wheel brakes. At X, the signal is given for simultaneous pressure reduction p.sub.ab. The response time t.sub.vSV of the switching valve SV is around 5 ms. The response time t.sub.vM of the motor is around 10 ms. It is taken into account here that the pistons of the pressure-generating unit must first be positioned at (1) for the different pressure levels of the individual wheels before the pressure change. Then the pressure reduction p.sub.ab takes place, assuming t.sub.ab of around 10 ms, wherein during this time the pressure is reduced by ?p equal to around 20 bar.

[0126] The response times for the switching valves and motor assumed in FIG. 3 are also assumed, for an objective comparison, for the depiction of the temporal pressure development in FIG. 3a which corresponds to the pressure development according to the invention.

[0127] With conventional ABS systems with 4 inlet and 4 outlet valves, the ABS regulator always determines a ?p and then determines the time for which the outlet valve must be opened in order for the required pressure reduction to take place in the wheel brake. This time control is known to be subject to tolerances, which limits the precision of the pressure regulation. Also, on closure of the outlet valve AV, pressure fluctuations always occur which cause disadvantageous noise.

[0128] The ABS regulator here determines the necessary pressure difference ?p substantially from the wheel angular acceleration and partially from the wheel slip, with correction factors for a) wheel inertia moment, b) gear stage and c) fading detection.

[0129] In contrast to time control, in conventional MUX as shown in FIGS. 1 and 1a, a volume control of the pressure supply is used in which ?v=?p, wherein this takes place with evaluation of the pressure-volume curve of the wheel. Thus the precision of the pressure regulation is much greater, and the temporal pressure development can be influenced towards the end of the pressure reduction so that only slight pressure fluctuations occur.

[0130] At V1 in FIG. 3, after (X), the response time of t.sub.vM and t.sub.v of SV1 acts. After opening of the switching valve SV1, the motor M is able to reduce the pressure over the time t.sub.ab. Then SV1 is closed again at (2). First however, the motor has already reached the required pressure level via the described volume control of the pressure supply.

[0131] Then the motor already begins the pressure reduction p.sub.ab of the front wheel V2, which takes place after opening of SV2 of V2. Thus the sequence V1-H2 has a total delay time of 60 ms with the above assumptions. This corresponds approximately to a regulation deviation Av of around 15 km/h.

[0132] FIG. 3a shows the temporal pressure curve for the regulation concept according to the invention. The pressure reduction p.sub.ab at the front wheel brake V1 at time (1) corresponds to (1) in FIG. 3. At the front wheel brake V2, the additional outlet valve ?V is used for pressure reduction p.sub.ab. The pressure reduction p.sub.ab takes place almost without delay at (11) via a time control ?t described above, at which at (12) after closure of SV2 the pressure fluctuation occurs. Thus regulation of the front wheels V1 and V2which at high ? make a considerably greater contribution to the brake force effect than the rear wheelsis almost not delayed. During pressure reduction p.sub.ab of V.sub.1, the motor at (13) is already prepared for pressure change at the rear wheel H1. This take place at (14) to (15) by volume control by means of the pressure-generating unit DE. Since the rear wheels H1, H2 often have the same higher pressure level than V1 or V2, a simultaneous pressure reduction p.sub.ab can take place by volume control. Alternatively, at H2 at (16) a time-controlled pressure reduction p.sub.ab into the brake circuit can take place. One condition for this is that the MUX pressure level in the wheel brake of the rear wheel H2 is lower than at the rear wheel H1, at which the pressure reduction takes place by means of volume control. It is also possible that the pressure reduction in the rear wheel brake H2 takes place by time-controlled opening of the associated outlet valve.

[0133] Variants of the front axle and rear axle regulation are shown in detail and described in FIGS. 4, 4a, 4b. A comparison of the delay times tv in relation to the conventional MUX methods in FIG. 3 show a significant improvement at (10) with 60 ms and (17) with 25 ms. This is possible by the use of the time-controlled pressure reduction p.sub.ab at V2 and H2 by means of outlet valve or into the brake circuit, partially simultaneous p.sub.ab at H1 and H2, and priority control at H1 and (13).

[0134] FIGS. 4-4b show the pressure development with different actual pressure levels and variants of the front and rear wheels H1, H2, V1 and V2 with the regulation concept according to the invention.

[0135] FIG. 4 shows the temporal pressure development V1 to H2 in different phases. Phase 0-X shows a pressure development in which, because of the different pressure levels in the wheel brakes, no simultaneous pressure build-up p.sub.auf and pressure reduction p.sub.ab can take place, which is most often the case. Consequently, here also full multiplex mode is active i.e. precise Op regulation via volume control both for pressure build-up p.sub.auf and for pressure reduction p.sub.ab. At pressure build-up P.sub.auf, sometimes e.g. at 20 with simultaneous pressure build-up requirement, a temporally offset pressure build-up P.sub.auf takes place at H1 and H2. However also a partially simultaneous pressure build-up p.sub.auf may take place. Also, a partially simultaneous pressure reduction is possible as shown in FIG. 4b.

[0136] At X in FIG. 4, the signal p.sub.ab for simultaneous pressure reduction in all wheel brakes is given, which is implemented without time delay. These two variants A and B are shown in more detail in FIG. 4a and FIG. 4b.

[0137] FIG. 4a shows the variant A, again starting at point X, with p.sub.ab at V1 and V2 as described in FIG. 3a. At the front wheel V1, the pressure reduction p.sub.ab takes place by means of volume control by the pressure-generating unit DE. For the rear wheel H2, at 21 a controlled p.sub.ab takes place over time dt=f(dp). This pressure reduction takes place when a sufficient differential pressure ?p between H2-V1 is present. The pressure levels of all wheels are known in the regulation concept according to the invention or MUX method, so that a relatively precise pressure reduction p.sub.ab in the rear wheel H2 is achieved by the time control or opening of the switching valve SVH2. The necessary opening time ?t may, because of the change in pressure level, be adapted flexibly by M1 (MUX). The pressure reduction p.sub.ab of the rear wheel H1 also takes place via volume control, starting from the preparation at 13, and then by opening of the associated switching valve at 22.

[0138] As a result, there is a relatively small tvmax as described in FIG. 3a. At 11, the time-controlled pressure reduction p.sub.ab for the front wheel V2 takes place. Here again, the pressure difference from the storage container is known and hence a precise pressure control is possible by the time-controlled opening of the outlet valve.

[0139] FIG. 4b shows variant B for partially simultaneous pressure reduction at the rear wheels H1 and H2, starting from a relatively small pressure difference between the rear wheels H1 and H2. Here, after preparation at 13, at 23 the pressure reduction p.sub.ab takes place with MUX, i.e. volume control by means of the pressure-generating unit. At 24, the rear wheel H2 is switched to pressure reduction p.sub.ab by opening of the switching valve SVH2 assigned to the rear wheel H2. At 25, the controlled pressure reduction p.sub.ab for H2 is achieved, so the switching valve SVH2 is closed. At 26, via the volume control, the ?p for the rear wheel H1 is reached, so at 26 the switching valve SVH1 is closed.

[0140] Both methods allow a short delay time. In some cases, the controlled pressure reduction p.sub.ab causes the pressure fluctuations, which however only occur in extreme cases with simultaneous pressure reduction p.sub.ab.

[0141] To summarise and in addition, the following features apply: [0142] the pressure of each wheel at the start and end of the pressure reduction p.sub.ab (FIG. 4, 4a) is stored in the memory; the two values are used as reference for the subsequent pressure changes of the wheel or following wheels; [0143] the pressure of the last pressure build-up p.sub.auf (FIG. 4) is stored in the memory and thus forms the basis for setting the pressure of the pressure-generating unit DE in preparation for the following pressure reduction p.sub.ab; [0144] the outlet valves AV are time-controlled, wherein for this the pressure difference from the storage container is taken into account; one wheel of the front axle is connected to the brake circuit only via switching valve SV, wherein a switching valve SV towards the brake circuit and an outlet valve AV towards the storage container are assigned to the second wheel of the front axle, so that switching valves SV of the rear axle are time-controlled to p.sub.ab, while MUX controls the wheels of the front axle with low pressure level, in which the time control t.sub.ab of the switching valves SV of the rear axle HA evaluates the differential pressure ?p; [0145] as well as the differential pressure, for the time control (valves are opened for a predefined time), the ?p of the corresponding outlet valve AV is evaluated from the pressure-volume curve. Priority control of the MUX with orientation towards driving stability with braking distance, e.g. wheel of the front axle VA has priority and also, at positive ? jump with highest negative p.sub.ab or positive acceleration p.sub.auf, since here the ?p to be regulated is greatest; [0146] the pressure change by volume control by means of the pressure-generating unit, and the time-controlled opening of outlet valve or switching valve used in parallel, forms the combined MUX regulator; [0147] in time control, the corresponding volume must be taken into account in the volume delivery, corresponding to the pressure change ?p determined by the regulator.

[0148] FIG. 5 describes a further embodiment of the pressure supply unit DE according to the invention with pressure regulation with master brake cylinder, master brake cylinder valves HZV, pressure supply with double-stroke piston, switching and outlet valves.

[0149] The master brake cylinder HZE is connected to brake circuits BKI and BKII. For the separation logic, the same applies as in FIG. 1a. The advance stroke chamber 4 of the double-stroke piston 3 is connected to brake circuit BI via the isolating valve TV1, and to BK II via the isolating valve TV2. The return stroke chamber 4a is connected via the isolating valve TV2b to BK II and via HZE to BK I. The transmission preferably takes place by the floating piston SK. The advance stroke chamber 4 and return stroke chamber 4a can be connected together hydraulically via a switching valve ShV. This switching valve SvH allows a short-circuit between the two chambers, and is used in particular on advance stroke (towards the left) to reduce the hydraulically active area of the piston 3. The return stroke chamber 4a of DHK 3 is connected via the switching valve PD1 to the storage container 10. The two chambers 4 and 4a are also each connected via a check valve to the storage container 10. This system configuration offers the following degrees of freedom: [0150] pressure build-up and pressure reduction in all brake circuits with multiplex regulation (pressure regulation with pressure-volume control) in all wheel brake cylinders simultaneously or sequentially via isolating valves TV1, TV2 and PD1, and the switching valves SV1-SV4 of the wheel brakes RB1-RB4; [0151] multiplex regulation in pressure build-up and pressure reduction in brake circuit I and pressure reduction in brake circuit II via outlet valves AV3, ZAV; [0152] multiplex regulation with simultaneous pressure reduction in brake circuit BK I and pressure build-up in BK II via double-stroke piston control; [0153] multiplex regulation with simultaneous pressure reduction in brake circuit BK II and pressure build-up in BK I via double-stroke piston control; [0154] pressure reduction RB3 at any time via AV3 in multiplex regulation.

[0155] FIG. 5a shows as an example some of the pressure regulation possibilities which may take place temporally in parallel with each other: [0156] controlled pressure reduction in RB1 via SV1, TV1 by pressure-volume control by means of return stroke of the double-stroke piston 3 with open PD3 valve, or alternatively pressure control of pressure reduction via pressure estimation based on phase current measurement in brake circuit I; [0157] controlled pressure reduction in RB2 via SV2, TV1 via pressure-volume control by means of return stroke of double-stroke piston 3 with open PD3 valve, or alternatively pressure control of pressure reduction via pressure estimation based on phase current measurement in brake circuit I; [0158] pressure reduction in RB3 via AV3 with time control of outlet valve AV3; [0159] pressure reduction in RB4 by means of double-stroke piston 3 with time control of one of the switching valves SV4 or PD1, wherein the other valve must also be opened at this time, or alternatively pressure control of pressure reduction via pressure estimation based on pressure measurement in brake circuit II.

[0160] For simultaneous pressure reduction p.sub.ab at different starting pressures, optionally a deviation may occur from the MUX regulation in that the switching valves SV1 and SV2 are opened with time offset. The isolating valve TV1 is here opened continuously on pressure reduction. Since a higher pressure prevails in RB1, the switching valve SV1 is opened before switching valve SV2. On the basis of knowledge of the pressure difference (wheel pressure RB1 and RB2 and pressure in the advance stroke chamber of the pressure supply unit), the time control can be dimensioned precisely. If the pressure in the advance stroke chamber of the pressure supply unit DE is not determined precisely, because at the same time a pressure reduction via ZAV is taking place in wheel brake RB4, and TV2 is closed, the pressure in the advance stroke chamber may be used via pressure estimation p/i from the torque of the electric motor. The switching valve SV2 is open when the pressure of the pressure-generating unit DE is approximately reached. The further pressure reduction then takes place simultaneously in both wheel brake cylinders by control via piston 3 with open SV1, SV2 and TV1. When the target pressure of a respective wheel is reached, the corresponding valve SV1 or SV2 is closed. If further pressure reduction is required in a wheel, further pressure reduction can take place only in one wheel brake.

[0161] In parallel to the pressure reduction control in MUX mode, in BK II the pressure can be reduced by time control of AV3. This can be determined temporally freely because closure of SV3 does not influence the other wheel brake cylinders. Also, the temporal activation of the pressure reduction in wheel brake RB4 can be selected freely on pressure reduction of BK 1 in MUX mode.

[0162] FIG. 5b shows as an example some of the pressure regulation possibilities which may take place temporally in parallel with each other: [0163] controlled pressure reduction in RB1 via switching valves SV1 and TV1 via pressure-volume control by means of return stroke of double-stroke piston 3 with closed PD1 valve; [0164] controlled pressure reduction in RB2 via switching valves SV2 and TV1 via pressure-volume control by means of return stroke of double-stroke piston 3 with closed PD1 valve; [0165] pressure reduction in RB3 via outlet valve AV3 with time control ?t (opening of AV3 valve for period at); [0166] pressure build-up in RB4 via isolating valve TV2b (ZAV) with pressure-volume control by means of return stroke of double-stroke piston with closed PD1 valve.

[0167] For simultaneous pressure reduction and pressure build-up in wheel brake RB4, the pressure build-up dynamic is determined by the pressure reduction dynamic and the effective piston area and hydraulic differential pressures. This must be taken into account in the regulation. When the target pressure is reached in wheel brake RB4, the switching valve SV4 is closed. If the pressure in BKI is to be reduced further, PD1 is opened for further pressure reduction in brake circuit I.

[0168] FIG. 5c shows as an example some of the pressure regulation possibilities which may take place temporally in parallel with each other: [0169] controlled pressure reduction in RB1 via switching valves SV1 and TV1 via pressure-volume control by means of advance stroke of double-stroke piston 3 with open PD1 valve; [0170] controlled pressure reduction in RB2 via switching valves SV2 and TV1 via pressure-volume control by means of advance stroke of double-stroke piston 3 with open PD1 valve; [0171] pressure reduction in RB3 via outlet valve AV3 with time control of outlet valve AV3; [0172] pressure reduction in RB4 via double-stroke piston 3 with time control of switching valve SV4 or PD1 valve.

[0173] For the many functions of pressure reduction p.sub.ab in one brake circuit and pressure build-up P.sub.auf in the other brake circuit, it is possible for the floating piston SK of the master brake cylinder HZE to move. To prevent this, a blocking element SE may be arranged in BK1 or BK2 which acts directly on the SK as mechanical blocking. The blocking element may also be part of the HZV.

[0174] With this pressure regulation system, the functions described in 5b and 5c of p.sub.auf in one brake circuit and p.sub.ab in the other can be implemented independently of the pressure level of the brake circuits.

[0175] FIG. 5d shows as an example the pressure reduction in brake circuit I and brake circuit II which is implemented on pressure reduction from high pressures. With isolating valves TV1 and TV2 open, the following is carried out: [0176] controlled pressure build-up in RB1 by time control of valves SV1 and PD3 via pressure control of the pressure reduction by pressure estimation based on phase current measurement in brake circuit I; [0177] controlled pressure build-up in RB2 by time control of valves SV2 and PD3 via pressure control of the pressure reduction by pressure estimation based on phase current measurement in brake circuit I; [0178] controlled pressure build-up in RB3 by time control of valves SV3 and PD3 via pressure control of the pressure reduction by pressure measurement based on the pressure sensor in brake circuit II; [0179] controlled pressure build-up in RB4 by time control of valves SV4 and PD3 via pressure control of the pressure reduction by pressure measurement based on the pressure sensor in brake circuit II.

[0180] For pressure reduction for individual wheels, in the same way as shown in in FIG. 5a, the switching valves SV1-SV4 may be switched with a temporal offset.

[0181] One possibility (not shown) is that of pressure reduction via PD1 valve which is similar to the process for PD3 valve. The pressure reduction may take place for all brake circuits via the PD1 valve. The pressure reduction may also take place via PD3 and PD1 valve. This is similar to FIG. 5a with the difference that the pressure of all wheel brakes is reduced via the pressure supply unit, and hence the advantages of pressure reduction in the closed brake circuit are obtained, which has safety advantages in particular after completion of a braking process (e.g. after ABS operation).

[0182] FIG. 6 describes a system with double-stroke piston in advantageous dual circuit design. The structure of THZ, DE and the valve circuits for pressure control ABS with MUX and AV is identical to FIG. 5c.

[0183] in contrast to FIG. 5c, the pressure supply in the advance stroke acts on brake circuit II and the back of the floating piston SK. This transmits the volume and pressure to brake circuit I. If the double-stroke piston has travelled close to the end position, it is reversed and operated in return stroke and acts on BK I. Then via the return stroke, pressure acts on the front side of the floating piston SK. This transmits the pressure again to brake circuit BK II. The SK piston is always active with its seals, as in the current THZ.

[0184] The double-stroke piston 3 also has a bypass valve ShV, which is switched substantially under three conditions: [0185] a) at high pressure, to reduce the piston force, the volume of the advance stroke is also conducted to the back of the double-stroke piston 3 to balance the pressure; [0186] b) in ABS regulation and also MUX regulation, the double-stroke piston 3 is switched in a single circuit via the ShV valve; [0187] c) pressure reduction p.sub.ab from high pressure level takes place simultaneously in both brake circuits BK I and BK II.

[0188] This valve circuit has the consequence for the floating piston position that the return spring 1 moves the floating piston SK to the right stop or locks it in the middle position. The pressure sensor 9 measures the pressure in BK II and, with a single circuit arrangement for the regulation and control functions, can evaluate the pressure in both brake circuits.

[0189] For special functions with pressure build-up p.sub.auf in BK I and pressure reduction p.sub.ab in BK II and vice versa, it is advantageous to place in the connection to THZ in BK II, or a blocking element SE in brake circuit BK 1 which prevents the movement of the floating piston SK. The blocking valve SE may also be part of the HVZ.

[0190] This system contains the additional potential for reducing the pressure in BK II via the DHK piston 3, and separately from BK I via the valves TV2b and PD1.

[0191] This solution has advantages in use for different pressure level activation on the two axles in recuperation. For this, the blocking element SE must then be used at SK or in BK I.

[0192] The functions described in FIGS. 5-6 and the additional overlaid time control via outlet valve(s) give the MUX system according to the invention a very good performance with high regulation dynamic and precision, with significantly lower cost than individual wheel regulation with inlet and outlet valves.