TRAILER CONTROL VALVE OF A TOWING VEHICLE

Abstract

A trailer control valve for controlling a hydraulic dual-line brake system of a trailer vehicle has an inlet for a hydraulic supply line of the towing vehicle, a tank outlet for an unpressurized return-flow line of the towing vehicle, a brake pressure outlet, and a supplemental pressure outlet. The brake pressure outlet can be connected in a stepped manner with an electronically controlled brake control valve to the supply pressure inlet or to the tank outlet. The supplemental pressure outlet can connect using a valve arrangement so that an outlet pressure of the supply pressure is reduced to a supplemental pressure at the supply pressure inlet or at the tank outlet. The valve arrangement has a pressure-limiting valve and a shut-off valve arranged in series. The shut-off valve can be a 3/2-way valve, which when not energized, the supplemental pressure outlet is connected to the tank outlet.

Claims

1. A trailer control valve (4) of a towing vehicle for controlling a hydraulic dual-line brake system of a trailer vehicle, the trailer control valve comprising: a supply pressure inlet (P) for the connection of a hydraulic supply line (12, 44) of the towing vehicle; a tank outlet (T) for the connection of an unpressurized return-flow line (46) of the towing vehicle; a brake pressure outlet (C) for the connection of a brake line (50) of the trailer vehicle; and a supplementary pressure outlet(S) for the connection of a supplementary line (54) of the trailer vehicle; wherein the brake pressure outlet (C) is configured to be connected in a stepped manner by means of an electronically controlled brake control valve (34) to the supply pressure inlet (P) or to the tank outlet (T); wherein the supplementary pressure outlet (S) is configured to be connected by way of a valve arrangement (39) with at least one electronically controlled valve (38) either to the supply pressure inlet (P), resulting in the reduction of an initial value of the supply pressure to a supplementary pressure, or connected to the tank outlet (T); wherein the valve arrangement (39) comprises a pressure-limiting valve (36) and a shut-off valve (38); wherein the pressure-limiting valve (36) and the shut-off valve (38) are arranged in series one after the other with the shut-off valve (38) arranged fluidically downstream from the pressure-limiting valve (36); wherein the initial pressure of the valve arrangement (39) can be reduced to the supplemental pressure by means of the pressure-limiting valve (36); and wherein the shut-off valve (38) is in the form of a 3/2-way solenoid switching valve by means of which, when it is not energized, the supplemental pressure outlet (S) is connected to the tank outlet (T) but, when it is energized, the supplemental pressure outlet(S) is connected to the working outlet of the pressure-limiting valve (36).

2. (canceled)

3. Trailer The trailer control valve according to claim 1, wherein to detect the supplemental pressure present at the supplemental pressure outlet(S), an electro-hydraulic pressure sensor (74) or an electro-hydraulic pressure switch (78) is connected to the supplemental line (54) inside or outside the trailer control valve (68, 68) and close to the supplemental pressure outlet(S).

4. The trailer control valve according to claim 1, wherein the brake control valve (34, 34) is in the form of a 3/3-way proportional solenoid valve or a 3/2-way proportional solenoid valve with a return flow of the brake pressure produced on the valve spring side to the valve piston, by means of which valve, when it is not energized, the brake pressure outlet (C) is connected unthrottled to the tank outlet (T), and when it is fully energized, the brake pressure outlet (C) is connected unthrottled to the supply pressure inlet (P).

5. The trailer control valve according to claim 1, wherein to detect the brake pressure at the brake pressure outlet (C), an electro-hydraulic pressure sensor (72) is connected to the brake line (50) inside or outside the trailer control valve (68, 68) and close to the brake pressure outlet (C).

6. The trailer control valve according to claim 1, wherein to detect the supply pressure at the supply pressure inlet (P), an electro-hydraulic pressure sensor (70) is connected to the supplemental line (12, 44) inside or outside the trailer control valve (68, 68) and close to the supply pressure inlet (P).

7. The trailer control valve according to claim 1, wherein to detect the coupling status of a trailer vehicle, an electric signal line (58) is connected to an associated electronic control unit (6) directly, or via the trailer control valve (4, 4, 68, 68).

8. The trailer control valve according to claim 1, comprising a brake pressure inlet (PB, PB) connected to a brake line (20, 20) of the towing vehicle and a redundant control branch (82, 82) with a pressure-controlled relay valve (86, 86) for the brake-pressure-dependent adjustment of a brake pressure, and a redundancy valve (88, 88) for activating and deactivating the redundant control branch (82, 82).

9. The trailer control valve according to claim 8, wherein: the relay valve (86, 86) is connected to the supply pressure inlet (P), the tank outlet (T) and, via a shuttle valve (90), to the brake pressure outlet (C), and is provided with a control inlet; and the redundancy valve (88, 88) is in the form of a 3/2-way solenoid switching valve by means of which, when it is not energized, the control inlet of the relay valve (86, 86) is connected to the brake pressure inlet (PB, PB) and, when it is energized, the relay valve (86, 86) is connected to a venting outlet or to the tank outlet (T).

10-13. (canceled)

14. The trailer control valve according to claim 1, wherein at least the brake control valve (34, 34), the pressure-limiting valve (36), the shut-off valve (38, 38), the relay valve (86, 86), the redundancy valve (88, 88) and the shuttle valve (90) are connected to one another by plug and/or screw connections.

15. The trailer control valve according to claim 1, wherein at least the brake control valve (34, 34), the pressure-limiting valve (36), the shut-off valve (38, 8), the relay valve (86, 86), the redundancy valve (88, 88) and the shuttle valve (90) are arranged in a common valve housing (62, 62, 76, 76, 92, 100, 100, 100).

16. A trailer control valve (4) of a towing vehicle for controlling a hydraulic dual-line brake system of a trailer vehicle, the trailer control valve comprising: a supply pressure inlet (P) for the connection of a hydraulic supply line (12, 44) of the towing vehicle; a tank outlet (T) for the connection of an unpressurized return-flow line (46) of the towing vehicle; a brake pressure outlet (C) for the connection of a brake line (50) of the trailer vehicle; a supplementary pressure outlet(S) for the connection of a supplementary line (54) of the trailer vehicle; wherein the brake pressure outlet (C) is configured to be connected in a stepped manner by means of an electronically controlled brake control valve (34) to the supply pressure inlet (P) or to the tank outlet (T); wherein the supplementary pressure outlet(S) is configured to be connected by way of a valve arrangement (39) with at least one electronically controlled valve (38, 38) either to the supply pressure inlet (P), resulting in the reduction of an initial value of the supply pressure to a supplementary pressure, or to the tank outlet (T); wherein the valve arrangement (39) comprises a pressure-limiting valve (36) and a shut-off valve (38); wherein the pressure-limiting valve (36) and the shut-off valve (38) are arranged in series one after the other with the shut-off valve (38) arranged fluidically upstream from the pressure-limiting valve (36); wherein the initial pressure of the valve arrangement (39) can be reduced to the supplemental pressure by means of the pressure-limiting valve (36); and wherein the shut-off valve (38) is in the form of a 3/2-way solenoid switching valve by means of which, when it is not energized, the supplemental pressure outlet(S) is connected to the tank outlet (T) but, when it is energized, the supplemental pressure outlet(S) is connected to the supply pressure inlet (P).

17. The trailer control valve according to claim 16, wherein, to detect the supplemental pressure present at the supplemental pressure outlet(S), an electro-hydraulic pressure sensor (74) or an electro-hydraulic pressure switch (78) is connected to the supplemental line (54) inside or outside the trailer control valve (68, 68) and close to the supplemental pressure outlet(S)

18. The trailer control valve according to claim 16, wherein the brake control valve (34, 34) is in the form of a 3/3-way proportional solenoid valve or a 3/2-way proportional solenoid valve with a return flow of the brake pressure produced on the valve spring side to the valve piston, by means of which valve, when it is not energized, the brake pressure outlet (C) is connected unthrottled to the tank outlet (T), and when it is fully energized, the brake pressure outlet (C) is connected unthrottled to the supply pressure inlet (P).

19. The trailer control valve according to claim 16, wherein to detect the brake pressure at the brake pressure outlet (C), an electro-hydraulic pressure sensor (72) is connected to the brake line (50) inside or outside the trailer control valve (68, 68) and close to the brake pressure outlet (C).

20. The trailer control valve according to claim 16, wherein to detect the supply pressure at the supply pressure inlet (P), an electro-hydraulic pressure sensor (70) is connected to the supplemental line (12, 44) inside or outside the trailer control valve (68, 68) and close to the supply pressure inlet (P).

21. The trailer control valve according to claim 16, wherein to detect the coupling status of a trailer vehicle, an electric signal line (58) is connected to an associated electronic control unit (6) directly, or via the trailer control valve (4, 4, 68, 68).

22. The trailer control valve according to claim 16, comprising a brake pressure inlet (PB, PB) connected to a brake line (20, 20) of the towing vehicle and a redundant control branch (82, 82) with a pressure-controlled relay valve (86, 86) for the brake-pressure-dependent adjustment of a brake pressure, and a redundancy valve (88, 88) for activating and deactivating the redundant control branch (82, 82).

23. The trailer control valve according to claim 22, wherein: the relay valve (86, 86) is connected to the supply pressure inlet (P), the tank outlet (T) and, via a shuttle valve (90), to the brake pressure outlet (C), and is provided with a control inlet; and the redundancy valve (88, 88) is in the form of a 3/2-way solenoid switching valve by means of which, when it is not energized, the control inlet of the relay valve (86, 86) is connected to the brake pressure inlet (PB, PB) and, when it is energized, the relay valve (86, 86) is connected to a venting outlet or to the tank outlet (T).

24. The trailer control valve according to claim 16, wherein the supply inlet of the relay valve (86) is connected by way of a connecting line (98) to the connecting line (96) between the shut-off valve (38) and the pressure-limiting valve (36).

25. The trailer control valve according to claim 24, wherein by virtue of control means within the associated electronic control unit (6) that maintain a most recent switching state of the shut-off valve (38), the shut-off valve (38) is secured against a defect-related failure.

26. The trailer control valve according to claim 24, comprising a second shut-off valve (38) connected in parallel with the shut-off valve (38), wherein the second shut-off valve (38) has a structure identical to that of the first shut-off valve (38), and the working outlets of the two shut-off valves (38, 38) are connected by a shuttle valve (102) to the connecting line (96) that leads to the pressure-limiting valve (36).

27. The trailer control valve according to claim 25, wherein in the connecting line (96) between the shut-off valve (38) and the connection to the connecting line (98) that leads to the relay valve (86), a one-way valve (102) that blocks in the direction toward the shut-off valve (38) and that can be unblocked by means of an applied control pressure, the valve (102) having a control inlet is arranged, to which control inlet an electronically controlled pilot valve (104) is connected, and wherein the pilot valve (104) is in the form of a 3/2-way solenoid switching valve by means of which, when the valve (104) is not energized the control inlet of the one-way valve (102) is connected to the tank outlet (T) and when the valve (104) is energized the control inlet of the one-way valve (102) is connected to the supply pressure inlet (P).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The trailer control valve with the features of the invention is explained in greater detail with reference to the example embodiments illustrated in the attached drawing, which shows, represented schematically in each case:

[0030] FIG. 1: A basic embodiment of the trailer control valve according to the invention in a brake system of a towing vehicle,

[0031] FIG. 2: An alternative basic embodiment of the trailer control valve,

[0032] FIG. 3: An extension of the trailer control valve shown in FIG. 1,

[0033] FIG. 4: An alternative extension of the trailer control valve shown in FIG. 1,

[0034] FIG. 5: An extension of the trailer control valve shown in FIG. 3,

[0035] FIG. 6: An extension of the trailer control valve shown in FIG. 2,

[0036] FIG. 7: A first further development of the trailer control valve shown in FIG. 6, and

[0037] FIG. 8: An alternative, second further development of the trailer control valve shown in FIG. 6.

DETAILED DESCRIPTION

[0038] FIG. 1 shows a brake system 2 of a towing vehicle, a trailer control valve 4 arranged in the towing vehicle and an electronic control unit 6 associated therewith. The trailer control valve 4 serves to control a hydraulic dual-line brake system of a coupled trailer vehicle. The brake system 2 of the towing vehicle, only partially shown in FIG. 1, is in this case for example a compressed-air brake system which comprises a compressor 8 and a preparation unit 10. From the preparation unit 10 a first pneumatic supply line 12 for a first service brake circuit and a second pneumatic supply line 14 for a second brake circuit lead to a foot-brake valve 16. By means of the foot-brake valve 16 a brake pressure can be produced in a brake line 18 of the first service brake circuit and in a brake line 20 of the second brake circuit To measure the brake pressure produced therein, in each respective case an electro-pneumatic pressure sensor 22, 24 acting as a brake value emitter is connected to the brake lines 18, 20 and connected to the control unit 6 by sensor lines indicated by broken lines. In addition, from the preparation unit 10 a further pneumatic supply line 26 leads to a parking brake valve 28, by means of which a parking release pressure can be produced in a connected parking brake line 30. To measure the parking release pressure an electro-pneumatic pressure sensor 32 acting as a parking brake sensor is connected to the parking brake line 30 and also connected to the control unit 6 by a sensor line.

[0039] The trailer control valve 4 bas a supply pressure inlet P, a tank outlet T, a brake pressure outlet C and a supplemental pressure outlet S, and comprises a brake control valve 34, a pressure-limiting valve 36 and a shut-off valve 38. A hydraulic supply line 44 is connected to the supply pressure inlet P, which line is fed by an oil pump 40 and a preparation unit 42 arranged downstream therefrom. To the tank outlet T is connected a return-flow line 46, which leads to a collecting container 48. To the brake pressure outlet C is connected a brake line 50, which leads to a brake coupling 52 for connecting a brake line on the trailer side. To the supplemental pressure outlet S is connected a supplemental line 54 which leads to a supplemental coupling 56 for connecting a supplemental line on the trailer side. In addition, a signal line 58 runs from the control unit 6 via the trailer control valve 4 to a plug socket 60 for connecting a signal line on the trailer side. The trailer control valve 4 can be made by connecting the valves 34, 36, 38 mentioned, by way of plug connections and/or screw connections, mechanically and hydraulically to one another, or they can be arranged in a shared valve housing 62.

[0040] The brake control valve 34 is in the form of a 3/3-way proportional solenoid valve with a return-flow on the valve spring side of the brake pressure produced by the valve piston and is connected to the control unit 6 by an electric control line. It should be mentioned here that all the electric control lines are represented by broken lines. The brake control valve 34 serves to control a brake pressure at the brake pressure outlet C, of between 0 Pa and 150 10.sup.5 Pa, as a function of a brake value measured by at least one of the pressure sensors 22, 24. By way of the brake control valve 34, when the latter is not energized the brake pressure outlet C is connected unthrottled to the tank outlet T (0 Pa) and when it is fully energized the brake pressure outlet C is connected unthrottled to the supply pressure inlet P under a pressure there, for example, of 15010.sup.5 Pa.

[0041] When the towing vehicle is started up, the brake pressure outlet C can be acted upon by the maximum brake pressure (15010.sup.5 Pa) for a few seconds by maximum energisation of the brake control valve 34, in order to fill a pressure accumulator of the trailer vehicle with hydraulic oil under high pressure, provided that previously it has been recognized via the signal line 58 (with the plug of the trailer vehicle connected) that a trailer vehicle is in fact coupled.

[0042] By means of the pressure-limiting valve 36 the supply pressure applied on the input side is reduced on the output side to a constant supplemental pressure between 1510.sup.5 Pa and 3510.sup.5 Pa. The shut-off valve 38, which in the present case is connected pneumatically downstream from the pressure-limiting valve 36, is in the form of a 3/2-way solenoid switching valve and is connected to the control unit 6 by an electric control line. By means of this shut-off valve 38, when it is not energized the supplemental pressure outlet S is connected to the tank outlet (0 Pa) and when it is energized the supplemental pressure outlet S is connected to the working outlet of the pressure-limiting valve 36, which can be at a hydraulic pressure between 1510.sup.5 Pa and 3510.sup.5 Pa.

[0043] Once the towing vehicle concerned has been started up, the supplemental pressure outlet S with the release of the parking brake, which is detected by the parking brake sensor 32, is acted upon by energizing the shut-off valve 38 with the intended supplemental pressure (1510.sup.5 Pa to 3510.sup.5 Pa), provided that a coupled trailed vehicle has previously been recognized via the signal line 58. If thereafter a defect in the brake system of the trailer vehicle 4 is established or an emergency off-switch is actuated in the towing vehicle or a parking brake of the towing vehicle is engaged by actuating the parking brake valve 28, then the supplemental pressure outlet S is depressurized by switching off the shut-off valve 38 and thereby an emergency braking or secondary braking of the trailer vehicle is triggered. The basic embodiment of the trailer control valve 4 described is advantageously effective without a pressure sensor connected to the brake line 50 and/or to the supplemental line 54.

[0044] The trailer control valve 4 illustrated in FIG. 2 differs from the trailer control valve 4 in FIG. 1, though having the same functionality, essentially in that in its valve arrangement 39 the shut-off valve 38 is now connected downstream from the pressure-limiting valve 36. Thereby, the inlet of the pressure-limiting valve 36 is connected by the shut-off valve 38, when not energized to the tank outlet T (0 Pa) and when energized to the supply pressure inlet P (15010.sup.5 Pa).

[0045] In this example embodiment the brake control valve 34 is in the form of a 3/2-way proportional solenoid valve with a return flow, on the valve spring side, of the controlled brake pressure to the valve piston, which is controlled by the control unit 6. In this case the brake pressure outlet C of the trailer control valve 4 in the non-energized state of the brake control valve 34 is unthrottled, and in the fully energized state the brake control valve 34 is connected to the tank outlet T and unthrottled to the hydraulic supply pressure inlet P.

[0046] Furthermore, in the example embodiment shown in FIG. 2 the brake system 2 of the towing vehicle is in the form of a hydraulic brake system. Consequently, the supply lines 12, 14, 26 concerned are now connected to the preparation unit 42 downstream from the oil pump 40, and the supply line inlet P of the trailer control valve 4 is connected to the supply line 12 of the first service brake circuit. In this case, as the brake value emitter for example an adjustment path sensor 64 is provided, which is arranged on the foot-brake valve 16 and is connected to the control unit 6 by way of a sensor line. The switching state of the parking brake valve 28 is now detected by a switching sensor 66 that acts as a parking brake sensor, which is connected to the control unit 6 by a sensor line.

[0047] FIG. 3 illustrates a trailer control valve 68 which has the features of the invention, which compared with the trailer control valve 4 shown in FIG. 1 is extended by three electro-hydraulic pressure sensors 70, 72, 74. The first pressure sensor 70 is connected to the already-mentioned hydraulic supply line 44 and is connected by way of a sensor line to the control unit 6. Measurement of the supply pressure existing at the supply pressure inlet P enables a more accurate adjustment of the brake pressure at the brake pressure outlet C by means of the brake control valve 34, since depending on the supply pressure on the inlet side, there may be slight changes of the control characteristics stored in the control unit 6 for the brake control valve 34. Thus, depending on the current supply pressure the respective optimum characteristic for controlling the brake control valve 34 can be selected and used.

[0048] The second pressure sensor 72 is connected to the brake line 50 and is also connected to the control unit 6 by a sensor line. Measurement of the brake pressure at the brake pressure outlet C can detect a deviation from the brake pressure to be set by the brake control valve 34, which deviation indicates a defect in the brake system on the trailer side or a leak in the brake line 50. Consequently, a visual or acoustic warning signal can be emitted in the driver's cabin of the towing vehicle and/or, by switching off the brake control valve 34 and the shut-off valve 38, an emergency braking of the trailer vehicle can be triggered and the escape of pressure oil into the surroundings can be prevented.

[0049] The third pressure sensor 74 is connected to the supplemental line 54 and again to the control unit 6 by way of a sensor line. Measurement of the supplemental pressure at the supplemental pressure outlet S can detect a deviation from the supplemental pressure to be set by the pressure-limiting valve 36, which deviation indicates a defect in the brake system on the trailer side or a leak in the supplemental line 58. As a result, a visual or acoustic warning signal can be emitted in the driver's cabin of the towing vehicle and/or, by switching off at least the shut-off valve 38 an emergency braking of the trailer vehicle can be triggered and the escape of pressure oil into the surroundings can be prevented.

[0050] In the representation shown in FIG. 3 the three pressure sensors 70, 72, 74 are arranged inside the trailer control valve 68. This should make it clear that the pressure sensors 70, 72, 74 can be connected to their respective lines or valves 34, 36, 38 by means of plug connections and/or screw connections, and can therefore form the trailer control valve 68. Moreover, it is made clear that those pressure sensors 70, 72, 74 together with the valves 34, 36, 38 and the lines concerned can be accommodated in a shared valve housing 76. However, it is also possible for the pressure sensors 70, 72, 74 to be connected outside the trailer control valve 68 to their respective pressure lines 44, 50, 54.

[0051] The further embodiment of a trailer control valve 68 shown in FIG. 4 differs from the trailer control valve 68 in FIG. 3, in that instead of the pressure sensor 74 between the shut-off valve 38 and the supplemental pressure outlet S, there is now an electro-hydraulic pressure switch 78 connected to the supplemental line 54 and also connected to the control unit 6 by a signal line. With reference to the switching signal of the pressure switch 78, which is actuated by a supplemental pressure slightly below the intended supplemental pressure, the control unit 6 can recognize whether, when the shut-off valve 38 is energized, the intended supplemental pressure exists at the supplemental pressure outlet S or has not been reached. If the pressure at the supplemental pressure outlet S is too low, a defect in the brake system of the trailer vehicle or a leak in the supplemental line 58 can be assumed, which results in switching off at least of the shut-off valve 38 and hence to an emergency braking of the trailer vehicle. Moreover, FIG. 4 makes it clear that with a brake system 2 of the towing vehicle in the form of a compressed-air brake system as well, instead of the pressure sensors 22, 24, 26 provided as in FIGS. 1 and 3, an adjustment path sensor 64 as the brake value emitter and a switching sensor 66 on the parking brake valve 28 can be used.

[0052] FIG. 5 shows a trailer control valve 80, which compared with the trailer control valve shown in FIG. 3, is extended by means of a pneumatic brake pressure inlet PB and a redundant control branch 82. The pneumatic brake pressure inlet PB is connected by a connecting line 84 to the brake line 20 of the second brake circuit of the towing vehicle. The redundant control branch 82 comprises a pneumatic pressure-controlled relay valve 86, a redundancy valve 88 and a shuttle valve 90. The relay valve 86 is connected to the supply pressure inlet P and the tank outlet T by way of the shuttle valve 90. To the shuttle valve 90 are also connected the working outlet of the brake control valve 34 and the brake pressure outlet C. The control inlet of the relay valve 86 can be connected to the brake pressure inlet PB by way of the redundancy valve 88. The redundancy valve 88 is in the form of a 3/2-way solenoid switching valve and is connected to the control unit 6 via an electric control line.

[0053] By way of the redundancy valve 88, the control inlet of the relay valve 86 is connected to the brake pressure inlet PB when the valve 88 is not energized and to a venting outlet when it is energized. Thus, in the non-energized state of the redundancy valve 88 the relay valve 86 and therefore the redundant control branch 82 are activated, and in the energized state of the redundancy valve 88 they are deactivated. Thus, in the event of a failure of the control unit 6, the brake control valve 34 is automatically deactivated and the redundant control branch 82 is activated, whereby during driving operation the production of a brake pressure at the brake pressure outlet C is ensured in all circumstances.

[0054] The trailer control valve 80 can be formed by connecting the valves 34, 36, 38, 86, 88, 90 to one another by plug and/or screw connections, or they can be arranged in a common valve housing 92. In the present case the three pressure sensors 70, 72, 74 mentioned are also arranged inside the trailer control valve 80. This makes it clear that the pressure sensors 70, 72, 74 are connected by plug and/or screw connections to the valves 34, 36, 38, 86, 88, 90 concerned and can therefore form the trailer control valve 80, or that the pressure sensors 70, 72, 74 can be arranged with the valves 34. 36, 38, 86, 88, 90 concerned in a common valve housing 92. However, it is also possible for the pressure sensors 70, 72, 74 to be connected to the pressure lines respectively associated with them outside the trailer control valve 80.

[0055] FIG. 6 shows a trailer control valve 94 according to the invention, which for example is based largely on the trailer control valve 4 according to FIG. 2 but, like the embodiments shown in FIGS. 3, 4 and 5, is provided with pressure sensors 70, 72, 74 and also comprises a hydraulic brake pressure inlet PB and a redundant control branch 82. Furthermore, the hydraulic brake system 2 of the towing vehicle is for example equipped with pressure sensors 22, 24, 32 for measuring the brake pressures in the associated brake lines 18, 29 and the brake releasing pressure in the parking brake line 30.

[0056] The brake pressure inlet PB is connected by a connecting line 84 to the brake line 20 of the second hydraulic brake circuit of the towing vehicle. The redundant control branch 82 is made similarly to that shown in FIG. 5 and comprises a hydraulic pressure-controlled relay valve 86, a redundancy valve 88, and a shuttle valve 90. The supply inlet of the relay valve 86, however, instead of being connected to the supply pressure inlet P, is now connected by a connecting line 98 to a connecting line 96 between the shut-off valve 38 and the pressure-limiting valve 36. Furthermore, the relay valve 86 is connected to the tank outlet T and by the shuttle valve 90 to the brake pressure outlet C. The control inlet of the relay valve 86 can be connected by the redundancy valve 88 to the brake pressure inlet PB. The redundancy valve 88 is in the form of a 3/2-way solenoid switching valve and is connected to the control unit 6 by an electric control line. By way of the redundancy valve 88 the control inlet of the relay valve 86 is connected to the brake pressure inlet PB when the valve 88 is not energized and to the tank outlet T when it is energized.

[0057] Since the supply inlet of the relay valve 86 is only connected to the supply pressure inlet P via the connecting line 96 and the connecting line 98 when the shut-off valve 38 is energized, and is then at the supply pressure, particular measures are provided in order to avoid an unintentional switching-off of the shut-off valve 38 and a consequent deactivation of the redundant control branch 82. Thus, in the present case it is provided that the shut-off valve 38 is secured against a defect-related failure by control means within the electronic control unit 6 which maintain its most recent switched state.

[0058] For that purpose, in the trailer control valve 94 shown in FIG. 7, while its design is in other respects the same, alternatively or in addition a second shut-off valve 38 is provided. which is connected in parallel with the first shut-off valve 38 and preferably has an identical structure. The working outlets of the two shut-off valves 38, 38 are connected by a shuttle valve 102 to the connecting line 96 that leads to the pressure-limiting valve 36. If there is a defect in one of the two shut-off valves 38, 38, pressure oil can still be delivered at the supply pressure into the connecting line 96 by way of the respective other shut-off valve (38 or 38).

[0059] In the trailer control valve 94 shown in FIG. 8, while its design is in other respects the same as that of the trailer control valve 94 in FIG. 6, a further possibility for avoiding an unintentional switching-off of the shut-off valve 38 is shown. In this case, in the connecting line 96 between the shut-off valve 38 and the connection point of the connecting line 96 that leads to the relay valve 86 there is connected a one-way valve 104 with a control inlet, which blocks in the direction toward the shut-off valve 38 but can be unblocked by an applied control pressure, to which valve an electronically controlled pilot valve 106 is connected. The pilot valve 106 is in the form of a 3/2-way solenoid switching valve, by means of which the control inlet of the one-way valve 104, when the valve 106 is not energized, is connected to the tank outlet T, and when the valve 106 is energized, is connected to the supply pressure inlet P. By virtue of the one-way valve 104 in the connecting line 96 that can be unblocked, when the shut-off valve 38 is not energized the inlet of the pressure-limiting valve 36 and the supply inlet of the relay valve 96 can only be vented by positive actuation, i.e., by energizing the pilot valve 106, and can thereby be depressurized.

[0060] The trailer control valves 94, 94, 94 illustrated can respectively be formed by connecting the valves 34, 36, 38, 86 88 90 and in addition the valves 38 or 102, 104 to one another by means of plug and/or screw connections, or arranging them in a common valve housing 100, 100, 100. In the present case the three pressure sensors 70, 72, 74 are also arranged inside the respective trailer control valve 94, 94, 94. This makes it clear that the pressure sensors 70, 72, 74 can be connected by plug and/or screw connections to the associated valves 34, 36, 38, 86, 90 and can thus form the trailer control valve 94, 94, 94 concerned, or that the pressure sensors 70, 72, 74 together with the associated valves 34, 36, 38, 86, 88, 90, and in addition with the valves 38 or 102, 104, can be arranged in a respective common valve housing 100, 100, 100. However, it is also possible for the pressure sensors 70, 72, 74 to be connected outside the respective trailer control valve 100, 100, 100 to the respectively associated pressure line 12, 50, 54.

LIST OF INDEXES

[0061] 2 Brake system, compressed-air brake system [0062] 2 Brake system (hydraulic) [0063] 4, 4 Trailer control valve (first or second embodiment) [0064] 6 Electronic control unit [0065] 8 Compressor [0066] 10 Preparation unit [0067] 12, 12 First planetary supply line [0068] 14, 14 Second pneumatic supply line [0069] 16, 16 Foot-brake valve (first or second embodiment) [0070] 18, 18 Brake line of the first service brake circuit [0071] 20, 20 Brake line of the second service brake circuit [0072] 22, 22 Pressure sensor on the brake line 18, 18, brake value emitter [0073] 24, 24 Pressure sensor on the brake line 20, 20, brake value emitter [0074] 26, 26 Further pneumatic supply line [0075] 28, 28 Parking brake valve (first or second embodiment) [0076] 30, 30 Parking brake line [0077] 32, 32 Pressure sensor on the parking brake line 30, 30, parking brake sensor [0078] 34 Brake control valve (in the form of a 3/3-way proportional solenoid valve) [0079] 34 Brake control valve (in the form of a 3/2-way proportional solenoid valve) [0080] 36 Pressure-limiting valve [0081] 38 First shut-off valve, 3/2-way solenoid switching valve [0082] 38 Second shut-off valve, 3/2-way solenoid switching valve [0083] 39 Valve arrangement (first embodiment) [0084] 39 Valve arrangement (second embodiment) [0085] 40 Oil pump [0086] 42, 42 Preparation unit [0087] 44 Preparation unit (first or second embodiment) [0088] 46 Retum flow line [0089] 48 Collecting container [0090] 50 Brake line [0091] 52 Brake coupling [0092] 54 Supplemental line [0093] 56 Supplemental coupling [0094] 58 Signal line [0095] 60 Plug socket [0096] 62, 62 Valve housing (first or second embodiment) [0097] 64, 64 Adjustment path sensor (first or second embodiment) [0098] 66, 66 Switching sensor, parking brake sensor (first or second embodiment) [0099] 68 Trailer control valve (third embodiment) [0100] 68 Trailer control valve (fourth embodiment) [0101] 70 Pressure sensor [0102] 72 Pressure sensor [0103] 74 Pressure sensor [0104] 76, 76 Valve housing (third or fourth embodiment) [0105] 78 Pressure switch [0106] 80 Trailer control valve (fifth embodiment) [0107] 82, 82 Redundant control branch (first or second embodiment) [0108] 84, 84 Connecting line (first or second embodiment) [0109] 86, 86 Relay valve (first or second embodiment) [0110] 88, 88 Redundancy valve, 3/2-way solenoid switching valve (first or second embodiment) [0111] 90 First shuttle valve [0112] 92 Valve housing (fifth embodiment) [0113] 94 Trailer control valve (sixth embodiment) [0114] 94 Trailer control valve (seventh embodiment) [0115] 94 Trailer control valve (eighth embodiment) [0116] 96 Connecting line [0117] 98 Connecting line [0118] 100 Valve housing (fourth embodiment) [0119] 100 Valve housing (fifth embodiment) [0120] 100 Valve housing (fifth embodiment) [0121] 102 Second shuttle valve [0122] 104 One-way valve [0123] 106 Pilot valve, 3/2-way solenoid switching valve [0124] C Brake pressure outlet [0125] P Supply pressure inlet