Modularly designed pressure control device of a fluid pressure brake system of a vehicle

A pressure control device of a vehicle, including a pressure controller of a fluid pressure brake system for brake slip-dependent control, including a relay valve having a supply port supplied by a supply pressure, a venting port connected to a pressure sink, a control port and at least two working ports, in which a working port is assigned to at least one brake cylinder and the other working port is assigned to at least one brake cylinder of another wheel, in which each working port of the relay valve is connected to a 2/2-way valve controlled by a control unit and assigned to a respective vehicle side and establishes a connection between the relevant working port and the assigned brake cylinder or blocks the connection, depending on control unit actuation, and in which the control port of the relay valve is connectable to a brake control pressure formed in accordance with the braking input, to a supply pressure of a pressure reservoir or to a pressure sink by a valve system formed by one 3/2-way or two 2/2-way solenoid valves and controlled by the control unit.

FIELD OF THE INVENTION

The present invention relates to a pressure control device of a fluid pressure brake system of a vehicle for the at least brake slip-dependent control of brake pressures in brake cylinders of each individual wheel of an axle.

BACKGROUND INFORMATION

A pressure control device of this kind is discussed in DE 102 36 922 A1, for example, wherein the pressure control device is configured as a 2-channel pressure control module and contains a two-channel valve unit with one relay valve per channel, and each of the two relay valves is assigned just one solenoid control valve configured as a 3/2-way valve. Brake slip control can be carried out separately for the two channels. However, relay valves, in particular, of which the known 2-channel pressure control module has two, involve a certain complexity of construction.

SUMMARY OF THE INVENTION

It is therefore an object of the exemplary embodiments and/or exemplary methods of the present invention to refine a pressure control device of the type mentioned at the outset in such a way that, despite offering brake slip control of each individual wheel, it can be produced at lower cost. Moreover, the intention is that the pressure control device should be constructed in such a way that it can be expanded in a simple manner in terms of its control functions merely by adding individual components, e.g. as regards expansion by a drive slip control system (ASR), a vehicle dynamics control system (ESP) or by an electronic brake system (EBS).

According to the exemplary embodiments and/or exemplary methods of the present invention, this object may be achieved by the features described herein.

The exemplary embodiments and/or exemplary methods of the present invention are based on the aspect that the pressure control devicea) contains a single relay valve having a supply port that is supplied by a supply pressure, a venting port connected to a pressure sink, a control port and at least two working ports, wherein one working port is assigned to at least one brake cylinder of a wheel on one vehicle side of the axle and the other working port of the single relay valve is assigned to at least one brake cylinder of a wheel on the other vehicle side of the axle, whereinb) each working port of the relay valve is connected to a 2/2-way valve, which is controlled directly or indirectly by a control unit and assigned to a respective vehicle side and which either establishes a connection between the relevant working port of the relay valve and the assigned brake cylinder or blocks said connection, depending on actuation by the control unit,c) the control port of the relay valve can be connected either to a brake control pressure (p4) formed in accordance with the driver's braking input, to a supply pressure of a pressure reservoir or to a pressure sink by a valve system formed by one 3/2-way solenoid valve or by two 2/2-way solenoid valves and controlled by the control unit.

Thus, the pressure control device according to the exemplary embodiments and/or exemplary methods of the present invention comprises just four basic elements: the single relay valve, the valve system, which comprises just one 3/2-way solenoid valve or two 2/2-way solenoid valves, and the two 2/2-way valves. With these valves, which can be produced relatively easily and at relatively low cost, brake slip control of each individual wheel can be achieved within certain limits, that is to say, for example, a pressure buildup or pressure reduction at a wheel brake cylinder on one vehicle side while the pressure is simultaneously maintained in a wheel brake cylinder on the other vehicle side. However, an opposed pressure profile (pressure reduction, pressure buildup) at wheels on different vehicle sides is not possible.

In particular, just one single relay valve is used to achieve control of large pressure medium cross sections in the brake cylinders of each individual wheel, inter alia by a central, relatively small control pressure flow. As a result, the pressure control device can be produced at very low cost overall.

Advantageous developments and improvements of the present invention indicated herein are possible by the further measures presented herein.

According to a particular embodiment, the 2/2-way valves are diaphragm valves, which are pneumatically pilot-controlled by respective 3/2-way solenoid pilot control valves electrically controlled by the control unit and assigned to the same vehicle side. It is thereby possible to feed large pressure medium flows into the brake cylinders relatively quickly by small control pressure medium flows.

In this case, the 3/2-way solenoid pilot control valves may be configured in such a way that, on the one hand, they pass a supply pressure of a pressure reservoir or the control pressure formed in accordance with the driver's braking input to a control port of the assigned 2/2-way valve or, on the other hand, connect said control port to a pressure sink, depending on control by the control unit.

The case where the 3/2-way solenoid pilot control valves pass the control pressure formed in accordance with the driver's braking input to the control port of the assigned 2/2-way valve has the advantage that, if the ABS is in a pressure holding phase during a driver-initiated braking operation and the driver releases the brake pedal during this pressure holding phase, the control pressure formed in accordance with the driver's braking input falls and hence the assigned 2/2-way valve, which is closed during the pressure holding phase, can open in order to dissipate brake pressure (pressure lowering). As a result, the driver obtains greater influence and can “override” the ABS functions.

In the other case, where the 3/2-way solenoid pilot control valves pass the supply pressure of the pressure reservoir to the control port of the assigned 2/2-way valve, release of the brake pedal during a pressure holding phase of the ABS would not lead to a lowering of the brake pressure in the brake cylinder. This would only be possible as part of the next ABS cycle (pressure lowering), although without the possibility of intervention by the driver.

In this case, the control unit is configured in such a way that brake slip control of each individual wheel is implemented as part of the typical ABS functions of increasing the pressure, maintaining the pressure and reducing the pressure to achieve optimum wheel slip by control of at least the valve system and the 2/2-way valves, each assigned to one vehicle side.

Taking this ABS-compatible basic layout as a starting point, drive slip control (ASR) is achieved by the valve system interacting in such a way with just one single solenoid valve electrically controlled by the control unit that the control port of the single relay valve is connected to the control pressure formed in accordance with the driver's braking input, a supply pressure of a pressure reservoir or to a pressure sink in accordance with the drive slip of the wheels of the axle.

In an advantageous manner, the ABS-compatible basic layout of the pressure control device is therefore supplemented by just one single solenoid valve in order additionally to achieve drive slip control (ASR) of each individual wheel. It may be preferred here if the single additional solenoid valve is a 3/2-way solenoid valve if the valve system is likewise formed by just one 3/2-way solenoid valve.

In this case, the control unit is configured in such a way that, in addition to the ABS functions, drive slip control (ASR) of each individual wheel is also achieved by control at least of the single additional solenoid valve.

However, if the valve system comprises two 2/2-way solenoid valves, one 2/2-way solenoid valve may be an outlet valve which either connects the control port of the single relay valve to a pressure sink or blocks said connection, and the other 2/2-way solenoid valve is, in particular, a valve which can also be used as a backup valve of an EBS which either connects the control port of the single relay valve to the control pressure formed in accordance with the driver's braking input or blocks said connection. In this case, the single additional solenoid valve provided for achieving the drive slip control of the axle is an inlet valve configured as a 2/2-way solenoid valve.

By the inlet valve, the outlet valve and the backup valve, it is then possible to form not only a drive slip control system but also an electronic brake system (EBS) with a higher-priority electropneumatic brake circuit and a lower-priority pneumatic brake circuit, which furthermore contains at least one pressure sensor in pressure-transmitting connection with at least one working port of the single relay valve.

For this purpose, the ABS-compatible basic layout having a valve system consisting of two 2/2-way solenoid valves (outlet valve, backup valve) for controlling the single relay valve is supplemented by just one inlet valve configured as a 2/2-way solenoid valve in order, together with at least one pressure sensor and a suitably programmed control unit, to form a complete electronic brake system (EBS) including drive slip control for the relevant axle.

In this case, the control unit is configured in such a way that, in addition to performing the ABS and ASR functions, it adapts the actual brake pressure measured by the at least one pressure sensor to a desired brake pressure formed in accordance with the driver's braking input by controlling the inlet valve and the outlet valve in order to provide brake pressure control.

To form a vehicle dynamics control system ESP, just one further pressure sensor for measuring the control pressure formed in accordance with the driver's braking input is provided. At least one pressure control device of the type described is then assigned to each axle on the vehicle. The ESP expands the ABS/ASR control system by the variables which describe the movement of the vehicle, i.e. by the transverse dynamics, by forming a corrective yawing moment in the case of oversteer or understeer. This corrective yawing moment is then converted into a wheel slip by braking individual wheels or a number of wheels by the pressure control device according to the present invention.

For example, the control unit is configured in such a way that it controls at least the valve system and the single additional solenoid valve in such a way when there is a braking operation initiated by the vehicle dynamics control system ESP that the control port of the relay valve is supplied with the supply pressure of the pressure reservoir in accordance with the yaw rate of the vehicle, the 2/2-way valve assigned to one brake cylinder on one vehicle side is switched to the through flow position, and the 2/2-way valve assigned to the other brake cylinder on the other vehicle side is switched to the blocking position.

Overall, the various expansion stages based on the ABS-compatible basic layout differ by just one single valve for the purpose of additionally achieving an ASR function, an EBS or an EBS with vehicle dynamics control ESP. The result is a modular construction of the pressure control device without the need to modify the structure of each expansion stage with its simpler scope in order to be able to integrate the valve to be added into the structure.

Further measures that improve the exemplary embodiments and/or exemplary methods of the present invention are explained in greater detail below with reference to the drawing, together with the description of illustrative embodiments of the present invention.

DETAILED DESCRIPTION

InFIG. 1,1designates an exemplary embodiment of a pressure control device, which comprises a valve unit2and an electronic unit, connected directly thereto mechanically and electrically, as a control unit, which is not illustrated here owing to the scale of the drawing. According to the exemplary embodiment, the pressure control device1is integrated into an air brake system of a commercial vehicle.

The pressure control device1is configured for the at least brake slip-dependent control of brake pressures in brake cylinders3,4of each individual wheel of an axle, e.g. a driven axle. For this purpose, it comprises a single relay valve5having a supply port6that is supplied by a supply pressure p11, a venting port7connected to a pressure sink, a control port8and two working ports9,10.

In this arrangement, one working port9is assigned to one brake cylinder3of a wheel on one vehicle side of the axle and the other working port10of the single relay valve5is assigned to the brake cylinder4of the wheel on the other vehicle side of the axle to enable a brake pressure p21to be fed into brake cylinder4or a brake pressure p22to be fed into brake cylinder3. Each working port9,10of the relay valve5is furthermore connected to a 2/2-way valve11,12, which is controlled, which may be indirectly, by the control unit and assigned to a respective vehicle side.

The 2/2-way valves11,12either establish a connection between the relevant working port9,10of the relay valve5and the assigned brake cylinder3,4or block said connection, depending on control, which in this case may be indirect, by the control unit.

According to the embodiment inFIG. 1, the control port8of the relay valve can be connected either to a brake control pressure p4formed in accordance with the driver's braking input or to a pressure sink14by a valve system formed by, for example, one 3/2-way solenoid valve13and controlled by the control unit. The 3/2-way solenoid valve13may be spring loaded and, when deenergized, is therefore preloaded into the operating position in which it connects the control port8of the relay valve5to the brake control pressure p4formed in accordance with the driver's braking input. When energized, on the other hand, the control port8of the relay valve5is connected to the pressure sink14.

In this case, the brake control pressure p4formed in accordance with the driver's braking input is produced by a driver-actuated foot brake module, for example (not shown here).

In a particular embodiment, the 2/2-way valves11,12are pneumatically controlled diaphragm valves which may be pneumatically pilot-controlled by respective 3/2-way solenoid pilot control valves15,16electrically controlled by the control unit and assigned to the same vehicle side. In this case, the 3/2-way solenoid pilot control valves15,16may be configured in such a way that, on the one hand, they pass the supply pressure p11of the pressure reservoir to a control port17,18of the assigned 2/2-way valve11,12or, on the other hand, connect said control port17,18to a pressure sink19,20, depending on control by the control unit. The 3/2-way solenoid pilot control valves15,16may be spring loaded and, when deenergized, are therefore preloaded into the operating position in which they connect the control port17,18of the assigned 2/2-way valve11,12to the pressure sink.

When deenergized, on the other hand, the control ports17,18of the 2/2-way valves11,12are connected to the pressure sink19,20.

In this case, the control unit is configured in such a way that brake slip control of each individual wheel is implemented as part of the typical ABS functions of increasing the pressure, maintaining the pressure and reducing the pressure to achieve an optimum desired wheel slip by control of the 3/2-way solenoid valve13and of the two 3/2-way solenoid pilot control valves15,16for indirect control of the 2/2-way valves11,12. For calculation of the actual brake slip, the control unit receives information on the wheel speeds of the wheels of the axle in a known manner via wheel speed sensors (not shown here).

Given this background, the following mode of operation of the pressure control device1illustrated inFIG. 1is obtained:

During a normal service braking operation, the central 3/2-way solenoid valve13for pilot control of the relay valve15and the two 3/2-way solenoid pilot control valves15,16are in the spring-actuated deenergized normal position shown inFIG. 1, and therefore the 3/2-way solenoid valve13connects the control port8of the relay valve5to the brake control pressure p4formed in accordance with the driver's braking input. Consequently, the relay valve5modulates said brake control pressure p4to give brake pressures p21and p22, respectively, at the two working ports9,10thereof. Since the two 3/2-way solenoid pilot control valves15,16are likewise in the deenergized normal position thereof, the pneumatic control ports17,18of the two 2/2-way valves11,12are connected to the respective pressure sinks19,20, and are therefore in the through flow position shown inFIG. 1in order to feed the brake pressures p21and p22available at the working ports9,10of the relay valve5into the brake cylinders3,4respectively. Here, the brake pressures p21and p22for one vehicle side and the other vehicle side are of substantially the same magnitude.

During an ABS- or brake slip-controlled braking operation with a tendency to lock up on just one side, the 3/2-way solenoid valve13is initially energized and thereby switched to the venting position thereof, in which the control port8of the relay valve5is connected to the pressure sink14. As a result, both working ports9,10of the relay valve5are connected to the pressure sink7thereof. At the same time, the 3/2-way solenoid pilot control valve15on the vehicle side on which there is no wheel lockup is energized by the control unit and thereby switched to the position in which the control port17of the relevant 2/2-way valve is supplied with the supply pressure p11. As a result, the 2/2-way valve11switches to the blocking position thereof and thereby maintains the brake pressure p22in the brake cylinder3of the non-locking wheel (pressure holding). On the vehicle side on which wheel lockup has been detected, on the other hand, the 3/2-way solenoid pilot control valve16is not switched over by the control unit but remains in the deenergized normal position thereof, in which the control port18of the relevant 2/2-way valve12remains connected to the pressure sink20. As a result, the 2/2-way valve12remains in the through flow position thereof shown inFIG. 1, as a result of which the brake pressure p21in the brake cylinder4of the locking wheel can dissipate via the pressure sink7of the relay valve5(pressure lowering).

In the illustrative embodiments shown inFIG. 2toFIG. 6, those parts which remain the same and have the same action as in the illustrative embodiment are denoted by the same reference signs.

In the illustrative embodiment inFIG. 2, the valve system consists not of a single 3/2-way solenoid valve but of two 2/2-way solenoid valves21,22, wherein one 2/2-way solenoid valve21acts as an outlet valve, either connecting the control port8of the relay valve5to a pressure sink23or blocking said connection, as shown. On the other hand, the other 2/2-way solenoid valve22either connects the control port8of the relay valve5to the brake control pressure p4formed in accordance with the driver's braking input or blocks said connection. Both 2/2-way solenoid valves21,22are spring loaded into the normal position thereof shown inFIG. 2, in which one 2/2-way solenoid valve21is switched to the blocking position and the other 2/2-way solenoid valve22is switched to the through flow position.

Given this background, the following mode of operation of the pressure control device1illustrated inFIG. 2is obtained:

During a normal service braking operation, one 2/2-way solenoid valve21is in the deenergized blocking position, while the other 2/2-way solenoid valve22is in the through flow position. Moreover, the two 3/2-way solenoid pilot control valves15,16are also in the spring-actuated deenergized normal position shown inFIG. 2, with the result that the other 2/2-way solenoid valve22connects the control port8of the relay valve5to the brake control pressure p4formed in accordance with the driver's braking input, asFIG. 2shows. As described above, the relay valve5modulates said brake control pressure p4to give respective brake pressures p21and p22at the two working ports9,10thereof. Since the two 3/2-way solenoid pilot control valves15,16are likewise in the deenergized normal position thereof, the pneumatic control ports17,18of the two 2/2-way valves11,12are connected to the respective pressure sinks19,20, with the result that they are in the through flow position shown inFIG. 2in order to feed the brake pressures p21and p22available at the working ports9,10of the relay valve5into the brake cylinders3,4respectively. Here, the brake pressures p21and p22for one vehicle side and the other vehicle side are of substantially the same magnitude.

During an ABS- or brake slip-controlled braking operation with a tendency to lock up on just one side, one 2/2-way solenoid valve is energized as an outlet valve21and is thereby switched to the through flow position thereof, in which the control port8of the relay valve5is connected to the pressure sink23. The other 2/2-way solenoid valve22is also energized and is thereby switched to the blocking position thereof, thereby decoupling the control port8of the relay valve5from the brake control pressure p4. As a result, both working ports9,10of the relay valve5are connected to the pressure sink7thereof. The two 3/2-way solenoid pilot control valves15,16are switched in the manner described with respect to the previous illustrative embodiment, and therefore the 2/2-way valve11on the non-locking vehicle side is switched to the blocking position thereof, as a result of which the brake pressure p22in the brake cylinder3of the non-locking wheel is maintained (pressure holding). On the vehicle side on which wheel lockup has been detected, on the other hand, the 3/2-way solenoid pilot control valve16is not switched over by the control unit but remains in the deenergized normal position thereof, in which the control port18of the relevant 2/2-way valve12remains connected to the pressure sink20. As a result, the 2/2-way valve12remains in the through flow position thereof shown inFIG. 2, as a result of which the brake pressure p21in the brake cylinder4of the locking wheel can dissipate via the pressure sink7of the relay valve5(pressure lowering).

According to the embodiment inFIG. 3, in contrast to the embodiments shown inFIG. 1andFIG. 2, it is not a supply pressure p11of a pressure reservoir but the brake control pressure p4formed in accordance with the driver's braking input which is connected to the control ports17,18of the 2/2-way valves11,12via the two 3/2-way solenoid pilot control valves15,16. If the ABS is then in a pressure holding phase during a driver-initiated braking operation and the driver releases the brake pedal during this pressure holding phase, the control pressure p4formed in accordance with the driver's braking input falls and hence the assigned 2/2-way valves11and12, which are closed during the pressure holding phase, can open in order to reduce brake pressures p21and p22(pressure lowering).

To achieve drive slip control (ASR), the ABS-compatible basic layout shown inFIG. 1toFIG. 3is supplemented by just one solenoid valve24in accordance with the embodiment inFIG. 4, said valve being electrically controlled by the control unit. This solenoid valve24then interacts with the valve system13in such a way that the control port8of the single relay valve5is connected to the control pressure p4formed in accordance with the driver's braking input, the supply pressure p11of the pressure reservoir or to a pressure sink14in accordance with the drive slip of the wheels of the axle. As an option here, the single additional solenoid valve is a 3/2-way solenoid valve24, and the valve system is likewise formed by a 3/2-way solenoid valve13in a manner similar toFIG. 1.

In this case, the control unit is configured in such a way that, in addition to the ABS functions, drive slip control (ASR) of each individual wheel is also achieved by control at least of the additional 3/2-way solenoid valve. As regards the control of the relay valve5, this additional 3/2-way solenoid valve24is inserted ahead of the 3/2-way solenoid valve13forming the valve system. In the spring-loaded deenergized normal position thereof, it transmits the control pressure p4formed in accordance with the driver's braking input to the 3/2-way solenoid valve13and, in the energized operating position thereof, it transmits the supply pressure p11to said valve.

In the case where the drive slip at the two wheels of the axle is not excessive, the additional ASR valve24transmits the control pressure p4formed in accordance with the driver's braking input to the 3/2-way solenoid valve13, with the result that the control port8of the relay valve5is supplied with air or vented as described in relation to the illustrative embodiment inFIG. 1, depending on whether the control pressure p4formed in accordance with the driver's braking input represents a brake release control pressure or a brake application control pressure. In the case of a brake release control pressure p4, i.e. when the foot brake valve is not actuated, the relay valve5outputs only low brake release pressures p21and p22respectively to the working ports9,10thereof, thus releasing both wheel brake cylinders3,4.

In the case of an impermissible drive slip, on the other hand, the additional ASR valve24transmits the supply pressure p11to the 3/2-way solenoid valve13, which is switched to the through flow position in relation thereto, as a result of which the control port8of the relay valve5is supplied with a brake application control pressure and therefore outputs a brake application pressure to the working ports9,10thereof. The operating positions of the 3/2-way solenoid pilot control valves15,16and of the two 2/2-way valves11,12are then as shown inFIG. 4, with the result that the wheel brake cylinders3,4of the axle are applied temporarily to provide wheel slip control while the impermissible wheel slip is present.

According to an embodiment which is an alternative to the above and is shown inFIG. 5, it is, as in the embodiment inFIG. 3, not the supply pressure p11of the pressure reservoir but the brake control pressure p4formed in accordance with the driver's braking input which is connected to the control ports17,18of the two 2/2-way valves11,12via the two 3/2-way solenoid pilot control valves15,16. If the ASR is then in a pressure holding phase and the driver actuates the brake pedal during this pressure holding phase, the control pressure p4formed in accordance with the driver's braking input rises, allowing the assigned 2/2-way valves11and12, which are closed during the pressure holding phase, to open in order to build up brake pressures p21and p22(pressure increase).

If the valve system does not include a 3/2-way solenoid valve13but two 2/2-way solenoid valves21,22as shown inFIG. 3andFIG. 6, one 2/2-way solenoid valve21may be an outlet valve which either connects the control port8of the relay valve5to the pressure sink23thereof or blocks said connection. The other 2/2-way solenoid valve22is, in particular, a valve which can also be used as a backup valve of an EBS, which either connects the control port8of the relay valve5to the control pressure p4formed in accordance with the driver's braking input or blocks said connection. According to the embodiment inFIG. 6, the single additional solenoid valve provided for achieving the drive slip control of the axle may be an inlet valve26configured as a 2/2-way solenoid valve.

According toFIG. 6, the inlet valve26, the outlet valve21and the backup valve22then form not only a brake slip control system (ABS) and a drive slip control system (ASR) but also an electronic brake system (EBS) with a higher-priority electropneumatic brake circuit and a lower-priority pneumatic brake circuit if, in addition, one working port9,10of the single relay valve5is in pressure-transmitting connection with a pressure sensor27, for example.

In this case, the control unit is configured in such a way that, in addition to carrying out the ABS and ASR functions, it also adapts the actual brake pressure measured by the pressure sensor27to a desired brake pressure formed in accordance with the driver's braking input by controlling the inlet valve26and the outlet valve21in order to provide brake pressure control.

The mode of operation of the EBS is then as follows:

In the course of a normal braking operation, the outlet valve21remains in the spring-loaded blocking position thereof, while the inlet valve26is switched to the through flow position in order to supply the control port8of the relay valve5with supply pressure. This ensures a brake application pressure p21and p22at the two working ports9,10of the relay valve5, which is passed through to the wheel brake cylinders3,4via the two opened 2/2-way valves11,12. During this process, the backup valve22remains in the energized blocking position thereof, thus preventing the control pressure p4applied to it, which is formed in accordance with the driver's braking input, from being passed through to the control port8of the relay valve5.

However, if the electric brake circuit of the EBS fails, the solenoid valves15,16,21,22,26can no longer be energized. The inlet valve26thus switches back to the deenergized and spring-loaded blocking position thereof, thus ensuring that supply pressure no longer reaches the control port8of the relay valve5. The outlet valve21likewise remains in the blocking position. The control port8of the relay valve8is then supplied via the backup valve22, which is switched to the through flow position under spring load when deenergized, with the control pressure p4produced by the foot brake valve and formed in accordance with the driver's braking input in order to apply the wheel brake cylinders3,4.

The ABS and ASR functions then run as in the embodiments described above, i.e. the control port8of the relay valve5is, depending on the function involved, connected via the inlet valve26to the supply pressure p11, via the backup valve22to the control pressure p4formed in accordance with the driver's braking input or via the outlet valve21to the pressure sink23of the outlet valve21.

In another expansion stage, a further pressure sensor28for measuring the control pressure p4formed in accordance with the driver's braking input is provided in addition to the pressure sensor27for measuring the brake pressure p21or p22. If one pressure control device1in accordance withFIG. 6is then provided for each axle, e.g. for a front axle and for a rear axle, vehicle dynamics control (ESP) can be achieved.

In this case, the control unit is configured in such a way that it controls the outlet valve21, the backup valve22and the inlet valve26in such a way when there is a braking operation initiated by the vehicle dynamics control system (ESP) that the control port8of the relay valve5is supplied with the supply pressure p11of the pressure reservoir in accordance with the yaw rate of the vehicle. For this purpose, for example, the outlet valve21and the backup valve22are switched to the blocking position thereof, while the inlet valve26is switched to the through flow position in order to supply the control port8of the relay valve5with air.

At the same time, the 3/2-way solenoid pilot control valves15,16are controlled by the control unit in such a way that, for example, the 2/2-way valve11assigned to one brake cylinder3on one vehicle side is switched to the through flow position in order to supply said brake cylinder with air, and the 2/2-way valve12assigned to the other brake cylinder4of the other vehicle side is switched to the blocking position in order to isolate said brake cylinder4from the pressure buildup. It is self-evident that, when there is a yawing moment building up in the opposite direction, the 2/2-way valve11must be switched to the blocking position and the 2/2-way valve12must be switched to the through flow position by appropriate control of the 3/2-way solenoid pilot control valves15,16.