ELECTROPNEUMATIC ASSEMBLY INCLUDING INTEGRATED FAILURE SAFETY-VALVE ARRANGEMENT FOR MULTIPLE FAULT, ELECTRONICALLY CONTROLLABLE PNEUMATIC BRAKING SYSTEM, AND METHOD FOR OPERATING A BRAKING SYSTEM

Abstract

An electropneumatic assembly is for an electronically controllable pneumatic braking system for a commercial vehicle. The electropneumatic assembly includes a reservoir port for receiving a reservoir pressure, at least one redundancy brake-pressure port for providing a redundancy brake pressure for a first axle and/or a trailer of the vehicle, a failure supply port for providing a failure supply pressure that is limited with respect to and lower than the reservoir pressure, and a failure safety-valve arrangement, which is connected to the failure supply port and the redundancy brake-pressure port, and which has a failure brake valve that is realized as a monostable valve and can be switched in the event of a fault in order, based on the failure supply pressure, to deliver the redundancy brake pressure at the redundancy brake-pressure port.

Claims

1. An electropneumatic assembly for an electronically controllable pneumatic braking system for a vehicle, including a commercial vehicle; the electropneumatic assembly comprising: a first compressed-air reservoir; a reservoir port for receiving a reservoir pressure from said first compressed-air reservoir; a first redundancy brake-pressure port for providing a first redundancy brake pressure for at least one of the following: a first axle of the vehicle and a first axle of a trailer of the vehicle; a failure supply port for providing a failure supply pressure limited with respect to and lower than the reservoir pressure; and, a failure safety-valve arrangement connected to the failure supply port and the redundancy brake-pressure port, or at least to a first redundancy control port, and having a first failure brake valve realized as a monostable valve and being switchable in an event of a fault in order, based on the failure supply pressure, to deliver the first redundancy brake pressure at the first redundancy brake-pressure port or at least a first redundancy control pressure at the first redundancy control port.

2. The electropneumatic assembly of claim 1, further comprising a second compressed-air reservoir; and, a spring-brake cylinder; and, wherein the failure supply pressure originates from said first compressed-air reservoir, said second compressed-air reservoir or said spring-brake cylinder.

3. The electropneumatic assembly of claim 1, wherein said first failure brake valve is a 3/2-way valve having a first failure brake-valve port receiving said failure supply pressure, a second failure brake-valve port delivering said first redundancy brake pressure or said first redundancy control pressure, and a third failure brake-valve port connected to a vent; and, in a non-activated switch position, the first failure brake-valve port is connected to said second failure brake-valve port and, in an activated switch position, said second failure brake-valve port is connected to said third failure brake-valve port.

4. The electropneumatic assembly of claim 1, further comprising a pressure limiter upstream of said failure supply port or said electropneumatic assembly having a pressure limiter for limiting the pressure received at the failure supply port.

5. The electropneumatic assembly of claim 1, wherein said failure safety-valve arrangement has an electromagnetic bistable valve pneumatically connected in series with said first failure brake valve.

6. The electropneumatic assembly of claim 5, wherein said electromagnetic bistable valve has a first bistable valve port receiving said failure supply pressure, a second bistable valve port connected to said first failure brake valve, and a third bistable valve port connected to a vent.

7. The electropneumatic assembly of claim 6, further comprising: a working valve arrangement being connected to said reservoir port and receiving reservoir pressure therefrom and being switchable to deliver said first redundancy brake pressure at said first redundancy brake-pressure port or to deliver a working pressure at a working port of said electropneumatic assembly; and, an electronic control unit for operating said working valve arrangement.

8. The electropneumatic assembly of claim 7, wherein said electronic control unit operates said first failure brake valve.

9. The electropneumatic assembly of claim 7, wherein said electronic control unit operates said bistable valve.

10. The electropneumatic assembly of claim 1, wherein the failure safety-valve arrangement has a second failure brake valve realized as a monostable valve pneumatically connected in series to said first failure brake valve.

11. The electropneumatic assembly of claim 10, wherein said second failure brake valve is operated by a further electronic control unit.

12. The electropneumatic assembly of claim 7, wherein said working valve arrangement has a first electromagnetic pilot unit and a first main valve unit; said first electromagnetic pilot unit is connected to said reservoir port and delivers a first working control pressure at said first main valve unit in dependence on first pilot-control switching signals of said electronic control unit; and, said first main valve unit is connected to said reservoir port and delivers a first working brake pressure in dependence on said first working control pressure received.

13. The electropneumatic assembly of claim 12, wherein said working valve arrangement has a second electromagnetic pilot unit and a second main valve unit; said second pilot unit is connected to said reservoir port and delivers a second working control pressure at said second main valve unit in dependence on second pilot-control switching signals of said electronic control unit; and, said second main valve unit is connected to said reservoir port and delivers a second working brake pressure in dependence on said second working control pressure received.

14. An electronically controllable pneumatic braking system for a vehicle including a commercial vehicle; the electronically controllable pneumatic brake system comprising: a front axle modulator for providing a front-axle service-brake pressure at a first front-axle service-brake actuator and at a second front-axle service-brake actuator on a front axle of the vehicle; a rear-axle modulator for providing a rear-axle service-brake pressure at least at a first rear-axle service-brake actuator and at a second rear-axle service-brake actuator on a rear axle of the vehicle; and, an electropneumatic assembly including: a first compressed-air reservoir; a reservoir port for receiving a reservoir pressure from said first compressed-air reservoir; a first redundancy brake-pressure port for providing a first redundancy brake pressure for at least one of the following: a first axle of the vehicle and a first axle of a trailer of the vehicle; a failure supply port for providing a failure supply pressure limited with respect to and lower than the reservoir pressure; and, a failure safety-valve arrangement connected to the failure supply port and the redundancy brake-pressure port, or at least to a first redundancy control port, and having a first failure brake valve realized as a monostable valve and being switchable in an event of a fault in order, based on the failure supply pressure, to deliver the first redundancy brake pressure at the first redundancy brake-pressure port or at least a first redundancy control pressure at the first redundancy control port; wherein said first redundancy brake-pressure port is connected to at least one of the following: i) a front-axle redundancy port of the front-axle modulator; and, ii) to a rear-axle redundancy port of said rear-axle modulator to cause redundant delivery of the front-axle service-brake pressure and rear-axle service-brake pressure, respectively.

15. The electronically controllable pneumatic braking system of claim 14, further comprising a central control unit providing front-axle brake signals at said front axle modulator to cause electronic delivery of said front-axle service-brake pressure and providing rear-axle brake signals at said rear-axle modulator to cause electronic delivery of said rear-axle service-brake pressure, wherein said central control unit operates said first failure brake valve.

16. The electronically controllable pneumatic braking system of claim 15, wherein the electropneumatic assembly is a secondary brake module of said electronically controllable pneumatic braking system and is configured to cause redundant delivery of said front-axle service-brake pressure and/or rear-axle service-brake pressure in an event of said central control unit being prevented from electronically delivering the front-axle service-brake pressure and/or rear-axle service-brake pressure.

17. The electronically controllable pneumatic braking system of claim 16, further comprising: a parking brake unit for providing a parking brake pressure at a first spring-brake cylinder and a second spring-brake cylinder on said rear axle of said vehicle, wherein said failure supply port is connected to said first spring-brake cylinder and/or said second spring-brake cylinder to receive the parking brake pressure or a pressure derived therefrom as failure supply pressure.

18. The electronically controllable pneumatic braking system of claim 17, wherein the electropneumatic assembly is integrated with the parking brake unit to form an assembly.

19. The electronically controllable pneumatic braking system of claim 14, further comprising: a trailer control unit for providing a trailer brake pressure at a trailer brake pressure port, wherein the first redundancy brake pressure port or a further redundancy brake pressure port of the electropneumatic assembly is connected to a trailer redundancy port of the trailer control valve to cause redundant delivery of the trailer brake pressure.

20. A method for controlling an electronically controllable pneumatic braking system which includes a front axle modulator for providing a front-axle service-brake pressure at a first front-axle service-brake actuator and at a second front-axle service-brake actuator on a front axle of the vehicle; a rear-axle modulator for providing a rear-axle service-brake pressure at least at a first rear-axle service-brake actuator and at a second rear-axle service-brake actuator on a rear axle of the vehicle; and, an electropneumatic assembly including: a first compressed-air reservoir; a reservoir port for receiving a reservoir pressure from said first compressed-air reservoir; a first redundancy brake-pressure port for providing a first redundancy brake pressure for at least one of the following: a first axle of the vehicle and a first axle of a trailer of the vehicle; a failure supply port for providing a failure supply pressure limited with respect to and lower than the reservoir pressure; and, a failure safety-valve arrangement connected to the failure supply port and the redundancy brake-pressure port, or at least to a first redundancy control port, and having a first failure brake valve realized as a monostable valve and being switchable in an event of a fault in order, based on the failure supply pressure, to deliver the first redundancy brake pressure at the first redundancy brake-pressure port or at least a first redundancy control pressure at the first redundancy control port; wherein said first redundancy brake-pressure port is connected to at least one of the following: i) a front-axle redundancy port of the front-axle modulator; and, ii) to a rear-axle redundancy port of said rear-axle modulator to cause redundant delivery of the front-axle service-brake pressure and rear-axle service-brake pressure, respectively; the method comprising: providing a reservoir pressure at a reservoir port of an electropneumatic assembly; providing, at a failure supply port of the electropneumatic assembly, at least while the vehicle is moving, a failure supply pressure limited with respect to and lower than the reservoir pressure; and, locking out the failure supply pressure when the electronically controllable pneumatic braking system is in a fault-free state.

21. The method of claim 20, further comprising: in the event of a fault of the electronically controllable braking system, the method includes the steps of: de-energizing a first failure brake valve of the electropneumatic assembly; and, passing the failure supply pressure through the first failure brake valve to activate redundant braking of the vehicle via front-axle service-brake actuators and/or rear-axle service-brake actuators.

22. A vehicle including a commercial vehicle, the vehicle comprising: a front axle; a first rear axle and an electronically controllable pneumatic braking system; the electronically controllable pneumatic braking system including: a front axle modulator for providing a front-axle service-brake pressure at a first front-axle service-brake actuator and at a second front-axle service-brake actuator on a front axle of the vehicle; a rear-axle modulator for providing a rear-axle service-brake pressure at least at a first rear-axle service-brake actuator and at a second rear-axle service-brake actuator on a rear axle of the vehicle; and, an electropneumatic assembly including: a first compressed-air reservoir; a reservoir port for receiving a reservoir pressure from said first compressed-air reservoir; a first redundancy brake-pressure port for providing a first redundancy brake pressure for at least one of the following: a first axle of the vehicle and a first axle of a trailer of the vehicle; a failure supply port for providing a failure supply pressure limited with respect to and lower than the reservoir pressure; and, a failure safety-valve arrangement connected to the failure supply port and the redundancy brake-pressure port, or at least to a first redundancy control port, and having a first failure brake valve realized as a monostable valve and being switchable in an event of a fault in order, based on the failure supply pressure, to deliver the first redundancy brake pressure at the first redundancy brake-pressure port or at least a first redundancy control pressure at the first redundancy control port; wherein said first redundancy brake-pressure port is connected to at least one of the following: i) a front-axle redundancy port of the front-axle modulator; and, ii) to a rear-axle redundancy port of said rear-axle modulator to cause redundant delivery of the front-axle service-brake pressure and rear-axle service-brake pressure, respectively; said electronically controllable pneumatic braking system being configured to execute a method for controlling said electronically controllable pneumatic braking system with the method steps of: providing a reservoir pressure at a reservoir port of an electropneumatic assembly; providing, at a failure supply port of the electropneumatic assembly, at least while the vehicle is moving, a failure supply pressure limited with respect to and lower than the reservoir pressure; and, locking out the failure supply pressure when the electronically controllable pneumatic braking system is in a fault-free state.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] The invention will now be described with reference to the drawings wherein:

[0042] FIG. 1 shows a first embodiment of an electropneumatic assembly;

[0043] FIG. 2 shows a commercial vehicle having an electronically controllable pneumatic braking system and an electropneumatic assembly;

[0044] FIG. 3 shows a second embodiment of an electropneumatic assembly;

[0045] FIG. 4 shows a third embodiment of the electropneumatic assembly;

[0046] FIG. 5 shows a fourth embodiment of the electropneumatic assembly; and,

[0047] FIG. 6 shows a fifth embodiment of the electropneumatic assembly.

DETAILED DESCRIPTION

[0048] FIG. 1 shows an electropneumatic assembly 1 according to the disclosure. The electropneumatic assembly 1 has a housing 2 in which a plurality of valves are integrated, as will be described below. On the housing, the electropneumatic assembly 1 has a reservoir port 4 via which the electropneumatic assembly 1 receives reservoir pressure pV from at least a first compressed-air reservoir 6. In addition, the electropneumatic assembly 1 has a first redundancy brake-pressure port 8 for providing a first redundancy brake pressure pR1 for a first axle A1, for example a front axle VA (cf. FIG. 2) of a vehicle 200, in particular a commercial vehicle 202. In addition, the electropneumatic assembly 1 has a failure supply port 10 for receiving a failure supply pressure pAV, which is limited with respect to and lower than the reservoir pressure pV. In the embodiment shown in FIG. 1, the failure supply port 10, via which the electropneumatic assembly 1 can be provided with a failure supply pressure pAV that is limited with respect to and lower than the reservoir pressure pV, is provided inside the electropneumatic assembly 1. However, it is not absolutely necessary for the pressure already received at the failure supply port 10 to be limited, but rather pressure limitation may also be effected inside the electropneumatic assembly 1, as shown in FIG. 1. There, a pressure limiter 12 is connected immediately downstream of the failure supply port 10, such that the pressure delivered by the pressure limiter 12 is the limited failure supply pressure pAV. According to the embodiment shown in FIG. 1, the reservoir port 4 is connected, inside the electropneumatic assembly 1, to a working valve arrangement 15 that receives the reservoir pressure pV and delivers a working pressure pA at a first working port 16. The working pressure pA may be, for example, a brake pressure for one or more axles of the vehicle 200, a trailer brake pressure or a parking brake pressure. The working valve arrangement 15 may have one or more electrically switchable electromagnetic valves, as will be described in more detail below. In addition to the working valve arrangement 15, the electropneumatic assembly 1 may also include an electronic control unit, not shown in FIG. 1, which controls at least the working valve arrangement 15.

[0049] The electropneumatic assembly 1 has a failure safety-valve arrangement 14, which is connected to both the failure supply port 10 and the redundancy brake-pressure port 8. The failure safety-valve arrangement 14 serves to deliver the first redundant brake pressure pR1 in the event of a failure of the electronically controllable pneumatic braking system 204 (cf. FIG. 2) of the vehicle 200, in order thereby to enable safe deceleration of the vehicle 100, preferably to a standstill. The purpose of this is to implement a fail-safe feedback control. For this purpose, the failure supply pressure pAV is passed through or, if necessary, volume-boosted by the failure safety-valve arrangement 14, and delivered as a first redundancy brake pressure pR1 at the first redundancy brake-pressure port 8. The latter is then in turn connected or connectable to one or more corresponding redundancy ports of the electronically controllable pneumatic braking system 204, as will be described in more detail below.

[0050] In the embodiment shown in FIG. 1, the failure safety-valve arrangement 14 includes a first monostable failure brake valve 16 and an optional second monostable failure brake valve 18.

[0051] The first failure brake valve 16 is connected to a first electronic control unit 300 via a first control line 20 to carry signals and energy. The first control unit 300 in this case is assigned to a first redundancy level B2 (cf. FIG. 2) of the electronically controllable pneumatic braking system 204. The second failure brake valve 18 is connected to a second electronic control unit 302 via a second control line 22 to carry signals and energy. The second electronic control unit 302 in this case is assigned to a first operating level B1 of the electronically controllable pneumatic braking system 204 not represented in greater detail in FIG. 1.

[0052] The first failure brake valve 16 and the second failure brake valve 18 are pneumatically connected in series in a valve main line 24 of the failure safety-valve arrangement 14. The valve main line 24 in this case extends from the failure supply port 10 to the first redundancy brake-pressure port 8.

[0053] The first failure brake valve 16 and the second failure brake valve 18 are represented here in a non-activated and de-energized state, in which they are each in an open position. In the open position, a pneumatic connection is established between a first failure brake-valve port 16.1 and a second failure brake-valve port 16.2 of the first failure brake valve 16. In the activated switch position, not shown in FIG. 1, the second failure brake-valve port 16.2 is connected to a third failure brake-valve port 16.3, which in turn is connected to a vent 3. In the open position of the second failure brake valve 18, a pneumatic connection is established between a fourth failure brake-valve port 18.1 and a fifth failure brake-valve port 18.2 of the second failure brake valve 18. A sixth failure brake-valve port 18.3 of the second failure brake valve 18 is again connected to a vent 3. In the de-energized stable switch position, the fifth failure brake-valve port 18.2 is connected to the sixth failure brake-valve port 18.3, such that the first redundancy brake-pressure port 8 is vented.

[0054] By provision of a first switching signal S1 via the first control line 20, the first failure brake valve 16 can be switched, against the resistance of a first return spring 17, from the open position to a venting position. In the vent position, a pneumatic connection is established between the first failure brake-valve port 16.1 and the third failure brake-valve port 16.3. By provision of a second switching signal S2 via the second control line 22, the second failure brake valve 18 can be switched, against the resistance of a second return spring 19, from the open position to a venting position. In the vent position, a pneumatic connection is established between the fourth failure brake-valve port 60.1 and the sixth failure brake-valve port 18.3.

[0055] When the vehicle 200 is in normal operating mode, it is provided, in particular, that the two failure brake valves 16, 18 are in their respective vent position, such that the first redundancy brake-pressure port 8 is vented. In this state, there is thus no pneumatic connection between the failure supply port 10 and the first redundancy brake-pressure port 8, since the pneumatic connection is interrupted at least at two sites, namely at the first failure brake valve 16 and at the second failure brake valve 18.

[0056] In the embodiment shown in FIG. 1, additionally arranged in the valve main line 24 there is a bistable valve 26 that is pneumatically connected in series to the first failure brake valve 16 and also to the second failure brake valve 18. Specifically, in the embodiment shown here, the bistable valve 26 is connected between the first failure brake valve 16 and the pressure limiter 12. Thus, as viewed from the failure supply port 10, the bistable valve 26 is connected upstream of the first and second failure brake valves 16, 18. The bistable valve 26 has a first bistable valve port 26.1, a second bistable valve port 26.2 and a third bistable valve port 26.3. The bistable valve 26 has a first and a second stable switch position, and in FIG. 1 it is shown in the second stable switch position in FIG. 1. In the first stable switch position, the first bistable valve port 26.1 is connected to the second bistable valve port 26.2, and pneumatic connection between the failure supply port 10 and the first redundancy pressure port 8 is possible when the first and the second failure brake valve 16, 18 are also in the switch position shown in FIG. 1. However, if the bistable valve 26 is in the second switch position, as shown in FIG. 1, the second bistable valve port 26.2 is connected to the third bistable valve port 26.3, which in turn is connected to a vent 3. In this way, the main valve line 24 is vented and a first redundancy brake pressure pR1 cannot be delivered. The bistable valve 26 is connected to the first electronic control unit 300 via a bistable-valve signal line 28, but could equally be connected to the second electronic control unit 302 or another electronic control unit, not shown in FIG. 1. In response to a third switching signal S3, the bistable valve 26 can be switched back and forth between the two stable switch positions. In particular, the bistable valve 26 is switched in dependence on an autonomous operating mode of the vehicle 200. If the vehicle 200 is in a manual operating mode, delivery of the first redundancy brake pressure pR1 is usually not necessary, as it can be braked pneumatically by actuation of a foot brake pedal 262, as described in more detail later with reference to FIG. 2. The delivery of the first redundant brake pressure pR1 serves, in particular, to prevent uncontrolled coasting of the vehicle 200 when the vehicle 200 is in an autonomous operating mode. In this respect, in the manual operating mode, the bistable valve 26 can be moved to the second switch position shown in FIG. 1, while in the automated operating mode of the vehicle 200 it is preferably in the first switch position, not shown in FIG. 1, in order then, in the event of a fault, to enable the failure supply pressure pAV to be passed through and to enable the main line 24 to be released.

[0057] In manual driving mode, the switch position of the first and second failure brake valves 16, 18 is irrelevant, as the valve main line 24 is vented by the bistable valve 26in any case. In this way, the first and second failure brake valves 16, 18 can remain in their stable switch position, thus saving electrical energy. However, if the bistable valve 26 is in the first switch position, not shown in FIG. 1, such that it can in principle release the valve main line 24, the first and second failure brake valves 16, 18, or at least one of the two, must be brought into the activated switch position, not shown in FIG. 1, in order to leave the valve main line 24 still vented and thus prevent the first redundancy brake pressure pR1 from being delivered. In automated operating mode, the first electronic control unit 300 and the second electronic control unit 302 thus provide the first and second switching signals S1, S2 such that the first and second failure brake valves 16, 18 are energized.

[0058] In the event of a multiple fault FM, in particular a dual fault FD, that is, if both the first switching signal S1 and simultaneously the second switching signal S2 are absent, and both the first failure brake valve 16 and the second failure brake valve 18 are thus de-energized, both the first failure brake valve 16 and the second failure brake valve 18 automatically return to their open position shown in FIG. 1 due to the restoring force generated by the respective return spring 17, 19.

[0059] Such a dual fault FD may be caused, for example, by a simultaneous power failure FS in both the operating level B1 and the first redundancy level B2, when both the first electronic control unit 300 and the second electronic control unit 302 are without energy supply. Accordingly, in such a simultaneous power failure FS, no switching signal S1, S2 can be directed to the first and second failure brake valves 16, 18.

[0060] Furthermore, a dual fault FD may also manifest itself in the occurrence of an exception error FA both in the first electronic control unit 300 and in the second electronic control unit 300, and in a zero signal being switched by the respective electronic control unit 300, 302 as a fault measure (in particular in the absence of other program alternatives), and thus the first and second switching signals S1, S2 being set to 0 for the purpose of switching the first and second failure brake valves 16, 18 to the open position. In this regard, for the presence of a multiple fault FM, various types of faults may be present in the individual electronic control units 300, 302; for example, in the case of a dual fault FD, there may be a power failure FA in the first electronic control unit 300 and there may be an exception error FA in the second electronic control unit 302, or vice versa.

[0061] Illustrated now in FIG. 2 is a vehicle 200, namely in particular a commercial vehicle 202, having a first axle A1, which here is a front axle VA, a second axle A2, which here is a first rear axle HAL and a third axle A3, which here is a second rear axle HA2. The vehicle 200 includes an electronically controllable pneumatic braking system 204, which has an operating level B1 and a first redundancy level B2. It additionally includes a second redundancy level B3, as described below, and an electropneumatic assembly 1 that is configured to brake the vehicle 200 in the event of a dual fault FD or a major single fault occurring in the operating level B1 and in the first and/or the second redundancy level B2, B3.

[0062] In the operating level B1, the electronically controllable pneumatic braking system 204 includes a central control unit 400, also referred to as a central module, which, via a vehicle BUS 206, is connected to an autonomous driving unit 208 and receives braking demand signals SBA from it. The central control unit 400 is supplied with electrical energy from a first voltage source 210.

[0063] On the front axle VA, the electronically controllable pneumatic braking system 204 includes a front-axle modulator 220, which is realized here as a single-channel modulator and receives reservoir pressure pV from a first compressed-air reservoir 6. For this purpose, the front-axle modulator 220 includes, in a known manner, a front-axle reservoir port 222, which is pipe-connected to the first compressed-air reservoir 6. The front-axle modulator 220 is connected, via a front-axle signal line 22, to the central control unit 400, and from it receives front-axle brake signals SBV that cause one or more electromagnetic valves (not shown) of the front-axle modulator 220 to switch, as a result of which the front-axle modulator 220 delivers a front-axle brake pressure pBVA, which is delivered via first and second ABS valves 226, 227 at a first front-axle service-brake actuator 228a and a second front-axle service-brake actuator 228b in a wheel-specific manner. On the one hand, the front-axle signal line 224 may be implemented as direct wiring of the electromagnetic valves of the front-axle modulator 220 to the central control unit 400, such that final stages for electromagnetic valves of the front-axle modulator 220 are preferably integrated into the central control unit 400. Alternatively, the front-axle signal line 224 may also be realized as a BUS connection (CAN-BUS), in particular if the front-axle modulator 220 has its own intelligence.

[0064] The electronically controllable pneumatic braking system 204 also includes a rear-axle modulator 230, which here is integrated in the central control unit 400, together with the first electronic control unit 300. The rear-axle modulator 230 receives reservoir pressure pV from a second compressed-air reservoir 7. The first electronic control unit 300 converts the brake demand signals SBA, received via the vehicle BUS 206, into a rear-axle brake signal SBH and switches one or more electromagnetic valves of the rear-axle modulator 230, which are not shown in detail here, such that a rear-axle service-brake pressure pBHA is generated, which is delivered at first and second rear-axle service-brake actuators 232a, 232b at the first rear axle HA1 and to third and fourth rear-axle service-brake actuators 232c, 232d at the second rear axle HA2. The rear-axle service-brake pressure pBHA is delivered in a side-specific manner, and in this respect the rear-axle modulator 230 is a dual-channel modulator.

[0065] In addition, the electronically controllable pneumatic braking system 204 shown here includes a parking brake unit 240, which is likewise connected to the vehicle BUS 206 and to the first voltage source 210 and receives electrical energy from the latter. Here, the parking brake unit 240 is connected to both the first and the second compressed-air reservoir 6, 7 and receives reservoir pressure pV from both. The layout shown in FIG. 2 relates to a configuration found primarily in North America, in which no separate parking brake reservoir is provided. It is to be understood that, instead of the first and second compressed-air reservoirs 6, 7 being connected to the parking brake unit 240, there may also be a third compressed-air reservoir, which separately supplies reservoir pressure to the parking brake unit 240.

[0066] The parking brake unit is configured to deliver a parking brake pressure pBP, via a spring accumulator port 264, at first and second spring-brake cylinders 242a, 242b at the first rear axle HAL and to third and fourth spring-brake cylinders 242c, 242d at the second rear axle HA2.

[0067] The electronically controllable pneumatic braking system 204 is also configured to supply a trailer, and for this purpose has a trailer control unit 250, which likewise receives reservoir pressure pV from both the first compressed-air reservoir 6 and the second compressed-air reservoir 7. The trailer control unit 250 is connected to the central control unit 400 and receives trailer brake signals SBT from it via a trailer signal line 252. In this respect, the trailer control unit 250 is also supplied by the first voltage source 210. In dependence on the received trailer brake signal SBT, the trailer control unit 250 delivers a trailer brake pressure pBT at a trailer brake pressure port 251. For example, a normal service brake signal, an anti-jackknife braking function signal for implementing an anti-jackknife braking function, or a trailer parking signal for parking the trailer may be transferred via the trailer brake signal SBT.

[0068] In order to realize a first redundancy level B2, which in this case is electrical, the electronically controllable pneumatic braking system 204 includes a secondary brake module 402, into which the second electronic control unit 302 is also integrated. The secondary brake module may be realized as or include an electropneumatic assembly 1. Accordingly, the secondary brake module 402 is also connected to the first compressed-air reservoir 6 and receives reservoir pressure pV from it. The secondary brake module 402 is likewise interfaced to the vehicle BUS 206, via which it receives brake demand signals SBA. It is supplied by a second voltage source 212, which is independent of the first voltage source 210. The second electronic control unit 302 is able to process the brake demand signals SBA and to operate a working valve arrangement 15 in order to deliver a first working pressure pA1, possibly as a first redundancy brake pressure pR1, at a first redundancy brake-pressure port 8, and to deliver a second working pressure pA2, possibly as a second redundancy brake pressure pR2, at a second redundancy brake-pressure port 9. The first redundancy brake pressure pR1 is here provided to the front axle VA and the second redundancy brake pressure pR2 is here provided to the rear axle HAL HA2. More precisely, the first redundancy brake pressure pR1 is delivered in a fundamentally known manner, via a first shuttle valve 254, at a front-axle redundancy port 256 of the front-axle modulator 220. The front-axle modulator 220 then converts the first redundancy brake pressure received at this port and, based on this, delivers the front-axle brake pressure pBVA in redundant manner. For this purpose, the front-axle modulator 220 may, in a fundamentally known manner, have a monostable redundancy valve, as well as a relay piston or a pneumatically switchable main valve, in order to deliver in a volume-boosted manner the first redundancy brake pressure pR1 provided at the front-axle redundancy port 256. The first redundancy brake pressure pR1 is also delivered at a trailer redundancy port 253, in order thus to enable redundant braking of a trailer.

[0069] In a corresponding manner, the rear-axle modulator 230 or the central control unit 400, into which the rear-axle modulator 230 is integrated, has a rear-axle redundancy port 258 at which the second redundancy brake pressure pR2 can be provided via a second shuttle valve 260. The secondary brake module 402 thus delivers the first and second redundancy brake pressures pR1, pR2 in an axle-specific manner, and can thus again be described as a dual-channel modulator. The central control unit 400 is then in turn configured to deliver the rear-axle brake pressure pBHA based on the received second redundancy brake pressure pR2. For this purpose, the central control unit 400 may in turn, in a fundamentally known manner, have a redundancy valve, as well as a relay piston or a pneumatically switchable main valve, in order to deliver the second redundancy brake pressure pR2 in a volume-boosted manner, as rear-axle brake pressure pBHA. In this way, an electronically controllable fallback level, in this case the first redundancy level B2, can be provided.

[0070] Moreover, the electronically switchable pneumatic braking system 204 shown in FIG. 2 has a fallback level B3 that can be actuated manually and that, in the embodiment shown here, includes a foot brake pedal 262. The foot brake pedal 262 can be used to deliver a foot brake pressure pBF to both the first shuttle valve 254 and the second shuttle valve 260. The first and second shuttle valves 254, 260 are each configured to deliver the higher of the applied foot brake pressure pBF and of the first and second redundancy pressures pR1, pR2 at the front-axle modulator 220 and rear-axle modulator 230, respectively. In this way, for example, the delivered first and the second redundancy brake pressure pR1, pR2 can be overridden by actuation of the foot brake pedal 262. Conversely, the secondary brake module 402 can also override the foot brake pressure pBF delivered by a driver.

[0071] A third redundancy level, which here according to the disclosure, however, is realized here only as a fail-safe level, is constituted by the electropneumatic assembly 1. The parking brake pressure pBP is connected to the secondary brake module 402, more precisely to the failure supply port 10. The parking brake pressure pBP is a pressure that is limited with respect to the reservoir pressure pV, and that is also reduced. Typical values of reservoir pressures pV are in a range of from 8-12 bar, while the level of the parking brake pressure pBP is typically limited to 8 bar. In the embodiment shown here, the level of the reservoir pressure pV is approximately 12 bar, while the parking brake pressure pBP is approximately 8 bar.

[0072] If the electropneumatic assembly 1 is now implemented as shown in FIG. 1, if the vehicle 200 is in autonomous operating mode, the bistable valve 26 is first switched to the first switch position, not shown in FIG. 1. Both the first and the second failure brake valve 16, 18 are energized, while the first electronic control unit 300 and the second electronic control unit 302 function normally.

[0073] If the first electronic control unit 300 fails, the first failure brake valve 16 is de-energized first. The second electronic control unit 302 can then, as part of the secondary brake module 402, take over the controlling of the electronically controllable pneumatic braking system 204, as described above, by delivering the first and second redundancy brake pressures pR1, pR2. In the event that this also fails, for example due to the dual fault FD, the second failure brake valve 18 is de-energized and brought by the second spring 19 into the switch position shown in FIG. 1. The parking brake pressure pBP provided at the failure supply port 10 is subsequently further limited by the pressure limiter 12, passed through by the bistable valve 26, the first failure brake valve 16, the second failure brake valve 18 and provided at the first redundancy brake port 8 and delivered as a first redundancy brake pressure pR1, reaches the front-axle redundancy port 256 via the first shuttle valve 254, whereupon the front-axle modulator 220 delivers the front-axle brake pressure pBVA and brakes the front axle VA. Since the parking brake pressure pBP is a static pressure, that is, is not further adapted in dependence on speed, the vehicle 200 is thereby braked to a standstill. Since the parking brake pressure pBP is a limited and reduced pressure, locking of the front axle VA is prevented.

[0074] FIG. 3 now shows the electropneumatic assembly 1 realized as a secondary brake module 402. The secondary brake module 402 has a reservoir port 4 at which the electropneumatic assembly 1 receives reservoir pressure pV, the failure supply port 10, which here is preceded by the pressure limiter 12 and is not integrated as in the embodiment example described with reference to FIG. 1, the failure supply pressure pAV being provided at the failure supply port 10, a first redundancy brake-pressure port 8, at which a first redundancy brake pressure pR1 can be delivered, and a second redundancy brake-pressure port 9, at which a second redundancy brake pressure pR2 can be delivered.

[0075] The electropneumatic assembly 1 has the first failure brake valve 16 and the bistable valve 26. A second failure brake valve 18, as described with reference to FIG. 1, is not provided in the embodiment according to FIG. 3. The bistable valve 26 is in turn pneumatically connected upstream of the first failure brake valve 16, as viewed from the failure supply port 10. The bistable valve 26 and the first failure brake valve 16 are pneumatically connected in series in the valve main line 24. In addition to the failure safety-valve arrangement 14, the electropneumatic assembly 1 in this embodiment also has a working valve arrangement 15, which has a structure like that of a fundamentally known dual-channel axis modulator. In the embodiment shown in FIG. 3, the working valve arrangement 15 includes a first electromagnetic pilot unit 32 and a first main valve unit 34. The first electromagnetic pilot unit 32 includes a first inlet valve 36, which is realized as a 2/2-way valve and connected to the reservoir port 4 for the purpose of receiving reservoir pressure pV. The first inlet valve 36 includes a first inlet-valve port 36.1 and a second inlet-valve port 36.2, the first inlet-valve port 36.1 being connected to the reservoir port 4. In a first stable switch position, shown in FIG. 3, the first inlet valve 36 is closed and the first and the second inlet-valve port 36.1, 36.2 are disconnected. On the other hand, in a second, activated switch position, not shown in FIG. 3, the first and the second inlet-valve port 36.1, 36.2 are connected, such that the first inlet valve 36 delivers a first working control pressure pS1 into a first control line 38. Here, the first main valve unit 34 includes a first relay valve 40. The first relay valve 40 has a first relay-valve reservoir port 40.1, a first relay-valve working port 40.2, a relay-valve vent port, not shown here, and a first relay-valve control port 40.3. The first working control pressure pS1 is received at the first relay-valve control terminal 40.3. The first relay valve 40 boosts the volume of this first working control pressure pS1 and correspondingly delivers a first working brake pressure pA1 at the first relay-valve working port 40.2.

[0076] In the embodiment shown here, the first relay-valve working port 40.2 is connected to the first redundancy brake-pressure port 8, such that the first working brake pressure pA1 is provided at the first redundancy brake-pressure port 8 and thus also functions as a first redundancy brake pressure pR1. The first redundancy brake-pressure port 8 is connected, as shown in FIG. 2, to the front-axle modulator 22, such that the first redundancy level B2 can be implemented by the actuation of the first pilot unit 32 and the first main valve unit 34.

[0077] For this purpose, the second electronic control unit 302 is also integrated into the electropneumatic assembly 1, to form the secondary brake module 402. In the embodiment shown here, the second electronic control unit 302 may provide first pilot-control switching signals S4, S5 at the first pilot unit 32 in order, in particular, to cause the first inlet valve 36 to switch into the second switch position, not shown in FIG. 3. In order to vent the first working control pressure pS1, the first pilot unit 32 also includes a first outlet valve 42. The first outlet valve 42 is again realized as a monostable 2/2-way valve and includes a first outlet valve port 42.1 and a second outlet valve port 42.2. In a first stable switch position, shown in FIG. 3, the first and the second outlet valve port 42.1, 42.2 are pneumatically connected, whereas when the first outlet valve 42 is in the activated state they are pneumatically disconnected. The first outlet valve port 42.1 is connected to the first control line 38, and the second outlet valve port 42.2 is connected to the valve main line 24, in the case shown in FIG. 3 more specifically to the first failure brake valve 16, more specifically, the second failure brake-valve port 16.2. Since the valve main line 24 is typically intended to be vented during normal operation of the vehicle 200, either as shown in FIG. 3, via the bistable valve 26, which connects the second bistable valve port 26.2 to the third bistable valve port 26.3 and thus to the vent 3, or via the first failure brake valve 16 when it is activated, the first control line 38 may also be vented via the first outlet valve 42.

[0078] At this point, the difference between the electropneumatic assembly 1 according to the present disclosure and a conventional dual-channel axle modulator also becomes apparent. In a conventional dual-channel axle modulator, the second outlet valve port 42.2 is typically connected either directly to a vent or, via an interposed backup valve or redundancy valve, which may be similar in configuration to the first failure brake valve 16, to a redundancy port via which, for example, a pneumatic redundancy pressure or an anti-compound pressure can be injected and which also functions as a vent during normal operation. In the embodiment of the electropneumatic assembly 1 shown in FIG. 3, however, the bistable valve 26 is additionally provided, as well as the pressure limiter 12, via which the failure supply pressure pAV is permanently applied to the failure supply port 10. The venting of the first control line 38 therefore is not effected via the failure supply port 10, but via the vent 3 of the first failure brake valve 16 and/or of the bistable valve 26. The first relay valve 40 may have its own vent, or may also be connected to one of the vents 3 of the first failure brake valve 16 and of the bistable valve 26.

[0079] The working valve arrangement 15 further includes a second electromagnetic pilot unit 44 and a second main valve unit 45, which are similar to the first pilot unit 32 and the first main valve unit 34. In this respect, the second pilot unit 44 also includes a second inlet valve 46, as well as a second outlet valve 52 and a second relay valve 50. Again, the second inlet valve 44 is connected to a third and a fourth inlet-valve port 46.1, 46.2, the third inlet-valve port 46.1 being connected to the reservoir port 4, and the fourth inlet-valve port 46.2 being connected to a second control line 48 into which the second inlet valve 46 delivers a second working control pressure pS2. The second relay valve receives the second working control pressure pS2 in a second relay-valve control port 50.3, receives reservoir pressure pV in a second relay-valve reservoir port 50.1, and delivers a second working brake pressure pA2 at a second relay-valve working port 50.2, which is also connected here to the second redundancy brake-pressure port 9, such that the second working brake pressure pA2 can also function as a second redundancy brake pressure pR2. The second redundancy brake-pressure port 9 is connected (cf. FIG. 2) to the rear-axle modulator 230, such that, via the second pilot unit 44 and the second main valve unit 45, the first redundancy level B2 can be implemented in the electronic delivery. The second outlet valve 52 is again connected to the second control line 48 via the third outlet-valve port 52.1, and to the main valve line 24 via the fourth outlet-valve port 52.2, such that the second control line 48 can also be vented via the failure safety-valve arrangement 14. The second electronic control unit 302 may provide second pilot switch signals S6, S7 in order to bring the second inlet valve 46 and the second outlet valve 52 into the activated switch positions, which are not shown.

[0080] In automated operating mode, in particular, when there is no driver present, the bistable valve 26 should be in the first switch position, not shown in FIG. 3, in which the first bistable valve port 26.1 is connected to the second bistable valve port 26.2, such that in principle the failure supply pressure pAV is passed through the bistable valve 26 and is then preferably applied at the second failure brake-valve port 16.2. The first failure brake valve 16 is then in the activated switch position, not shown in FIG. 3, such that the main valve line 24 is connected to the vent 3. If a dual fault FD then occurs and the second electronic control unit 302 also fails, the latter can no longer provide the first and second pilot-control switching signals S4, S5, S6, S7, such that the first inlet valve 36, the first outlet valve 42, the second inlet valve 46 and the second outlet valve 52 each fall back into their monostable switch positions shown in FIG. 3. The first failure brake valve 16 also falls to the stable switch position, shown in FIG. 3, in which the first failure brake-valve port 16.1 is connected to the second failure brake-valve port 16.2. Since the first and second outlet valves 42, 52 are also in their open switch positions, the failure supply pressure pAV delivered by the first failure brake valve 16 can be passed through the valve main line 24 and injected into the first and second control lines 38, 48 via the first and second vent valves 42, 52 and is then applied at the first and second relay-valve control ports 40.3, 50.3. The first and second relay valves 40, 50 then effect volume-boosting of this pressure, namely in this case a first and a second redundancy brake-pressure pRS1, pRS2, respectively, and deliver this, as a first and a second redundancy brake-pressure pR1, pR2, respectively, at the first and second redundancy brake-pressure ports 8, 9. In this way, the vehicle 200 can then be braked safely.

[0081] This means that, in contrast to the first embodiment (FIG. 1), the failure safety-valve arrangement 14 in the embodiment shown here (FIG. 3) is not connected directly to the first or second redundancy brake-pressure port 8, 9, but to the first relay-valve control port 40.3, which functions as a first redundancy control port 40.4, and to the second relay valve control port 50.3, which functions as a second redundancy control port 50.4.

[0082] It may also be provided, however, that the first relay valve 40 and/or the second relay valve 50 are part of the failure safety-valve arrangement 40.

[0083] A third embodiment of the electropneumatic assembly 1 is shown in FIG. 4. Same and similar elements are denoted by the same reference designations as in the previous embodiments, such that reference is made to the entirety of the description above. The third embodiment (FIG. 4) is based on the second embodiment (FIG. 3), and in particular the differences are highlighted below.

[0084] In contrast to the second embodiment (FIG. 3), in the third embodiment (FIG. 4) the second failure brake valve 18, as already described with reference to FIG. 1, is provided. It is pneumatically connected in series to the first failure brake valve 16 and the bistable valve 26. It is arranged between the first failure brake valve 16 and the bistable valve 26, although these valves may also be arranged in a different sequence, in particular in order to realize the smallest possible installation space.

[0085] The second failure brake valve 18 is controlled, as already described with reference to FIG. 1, by the electronic control unit 300 of the central control unit 400. In this respect, safety is increased in the third embodiment in comparison with the second embodiment, since both the electronic control unit 300 and the electronic control unit 302 must fail in order to effect the delivery of the first redundancy brake pressure pR1 based on the failure supply pressure pAV.

[0086] Represented in the fourth embodiment (FIG. 5) is a variant of the electropneumatic assembly that is based substantially on the embodiment of FIG. 1. Same and similar elements are denoted by the same reference designations as in the previous embodiments, such that reference is made to the entirety of the description above. In particular, the differences are highlighted below.

[0087] In the fourth embodiment (FIG. 5), the electropneumatic assembly 1 is integrated with a parking brake unit 240. The reservoir port 4 thus also serves to supply reservoir pressure pV to the working valve unit 15, which here is used in a fundamentally known manner to deliver the parking brake pressure pBP. For this purpose, both the first compressed-air reservoir 6 and the second compressed-air reservoir 7 are connected to the reservoir port 4, as also shown in FIG. 2.

[0088] The parking brake unit has a spring accumulator port 264 to which one or more spring-brake cylinders can be connected. In the embodiment of the electronically controllable pneumatic braking system 204 shown in FIG. 2, all four spring-brake cylinders 242a, 242b, 242c, 242d are connected to it. The failure supply port 10 is also connected to the spring-brake cylinders 242a, 242b, 242c, 242d and receives the parking brake pressure pBP. Here, the pressure limiter 12 is still connected downstream of the failure supply port 10, although this is not absolutely necessary if the parking brake pressure pBP is already sufficiently limited with respect to the reservoir pressure pV. Here, the failure supply port 10 is outside of the housing 2, together with the spring-brake cylinders 242a, 242b, 242c, 242d. In the case of an integrated arrangement as shown in FIG. 5, it is also useful to transfer the parking brake pressure pBP internally. In this case, the failure supply port 10 could be arranged immediately downstream of the working valve unit 15.

[0089] Despite the integration with the parking brake unit 240, the first failure brake valve 16 and the bistable valve 26 are operated by the electronic control unit 300, and the second failure brake valve 18 is operated by the electronic control unit 302. Id the parking brake unit 240 has its own intelligence, it is preferred that at least the bistable valve 26 and/or the first failure brake valve 16 and/or the second failure brake valve 18 is/are operated by the intelligence (electronic control unit) of the parking brake unit 240.

[0090] In a fifth embodiment (FIG. 6), embodiments 2 and 4 as shown in FIGS. 3 and 5 are substantially combined. Here, the electropneumatic assembly 1 includes both the parking brake unit 240 as illustrated in FIG. 5 and the secondary brake module 402 as illustrated in FIG. 3. The reservoir port 4 may again be connected to the first compressed-air reservoir 6 and the second compressed-air reservoir 7, although this is not shown in FIG. 6. The reservoir pressure pV is then transferred within the electropneumatic assembly 1 and provided to the first pilot valve unit 32, the second pilot valve unit 44, the first main valve unit 34 and the second main valve unit 45. The parking brake pressure pBP may also preferably be transferred internally within the housing 2, as already described with reference to FIG. 5. In this way, a fully integrated module is created, in which a saving can advantageously be made on parts, in particular valves.

[0091] It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

LIST REFERENCE DESIGNATIONS ART OF THE DESCRIPTION

[0092] 1 electropneumatic assembly [0093] 2 housing [0094] 4 reservoir port [0095] 6 first compressed-air reservoir [0096] 8 first redundancy brake-pressure port [0097] 9 second redundancy brake-pressure port [0098] 10 failure supply port [0099] 12 pressure limiter [0100] 14 failure safety-valve arrangement [0101] 15 working valve arrangement [0102] 16 first monostable failure brake valve [0103] 16.1 first failure brake-valve port [0104] 16.2 second failure brake-valve port [0105] 16.3 third failure brake-valve port [0106] 17 first return spring [0107] 18 second monostable failure brake valve [0108] 18.1 fourth failure brake-valve-port [0109] 18.2 fifth failure brake-valve port [0110] 18.3 sixth failure brake-valve port [0111] 19 second return spring [0112] 20 first control line [0113] 22 second control line [0114] 24 valve main line [0115] 26 bistable valve [0116] 26.1 first bistable valve port [0117] 26.2 second bistable valve port [0118] 26.3 third bistable valve port [0119] 28 bistable valve signal line [0120] 32 first electromagnetic pilot unit [0121] 34 first main valve unit [0122] 36 first inlet valve [0123] 36.1 first inlet-valve port [0124] 36.2 second inlet-valve port [0125] 38 first control line [0126] 40 first relay valve [0127] 40.1 first relay-valve reservoir port [0128] 40.2 first relay-valve working port [0129] 40.3 first relay-valve control port [0130] 40.4 first redundancy control port [0131] 42 first outlet valve [0132] 42.1 first outlet-valve port [0133] 42.2 second outlet-valve port [0134] 44 second electromagnetic pilot unit [0135] 45 second main valve unit [0136] 46 second inlet valve [0137] 46.1 third inlet-valve port [0138] 46.2 fourth inlet-valve port [0139] 48 second control line [0140] 50 second relay valve [0141] 50.1 second relay-valve reservoir port [0142] 50.2 second relay-valve working port [0143] 50.3 second relay-valve control port [0144] 50.4 second redundancy control port [0145] 52 second outlet valve [0146] 52.1 third outlet-valve port [0147] 52.2 fourth outlet-valve port [0148] 200 vehicle [0149] 202 commercial vehicle [0150] 204 electronically controllable pneumatic braking system [0151] 206 vehicle BUS [0152] 208 autonomous driving unit [0153] 210 first voltage source [0154] 212 second voltage source [0155] 220 front-axle modulator [0156] 222 front-axle reservoir port [0157] 224 front axle signal line [0158] 226 first ABS valve [0159] 227 second ABS valve [0160] 228a first front-axle service-brake actuator [0161] 228b second front-axle service-brake actuator [0162] 230 rear-axle modulator [0163] 232a first rear-axle service-brake actuator [0164] 232b second rear-axle service-brake actuator [0165] 232c third rear-axle service-brake actuator [0166] 232d fourth rear-axle service-brake actuator [0167] 240 parking brake unit [0168] 242a first spring-brake cylinder [0169] 242b second spring-brake cylinder [0170] 242c third spring-brake cylinder [0171] 242d fourth spring-brake cylinder [0172] 250 trailer control unit [0173] 251 trailer brake-pressure port [0174] 252 trailer signal line [0175] 253 trailer redundancy port [0176] 254 first shuttle valve [0177] 256 front-axle redundancy port [0178] 258 rear-axle redundancy port [0179] 260 second shuttle valve [0180] 262 foot brake pedal [0181] 264 spring accumulator port [0182] 300 first electronic control unit [0183] 302 second electronic control unit [0184] 400 central control unit [0185] 402 secondary brake module [0186] A1 first axle [0187] A2 second axle [0188] B1 operating level [0189] B2 first redundancy level [0190] B3 second redundancy level [0191] FD dual fault [0192] FM multiple fault [0193] FS power failure [0194] FA exception error [0195] pA working pressure [0196] pBF foot brake pressure [0197] pBHA rear-axle service-brake pressure [0198] pBP parking brake pressure [0199] pBT trailer brake pressure [0200] pBVA front-axle service-brake pressure [0201] pR1 first redundancy brake pressure [0202] pR2 second redundancy brake pressure [0203] pRS1 first redundancy control pressure [0204] pRS2 second redundancy control pressure [0205] pS1 first working control pressure [0206] pS2 second working control pressure [0207] pV reservoir pressure [0208] pAV failure supply pressure [0209] HA1 first rear axle [0210] HA2 second rear axle [0211] S1 first switching signal [0212] S2 second switching signal [0213] S3 third switching signal [0214] S4 first pilot-control switching signal [0215] S5 second pilot-control switching signal [0216] S6 third pilot-control switching signal [0217] S7 fourth pilot-control switching signal [0218] SBA brake demand signal [0219] SBT trailer brake signal [0220] SBV front-axle brake signals [0221] VA front axle