GB2057078A

GB2057078A - Hydraulic brake system for a traction vehicle

Info

Publication number: GB2057078A
Application number: GB8022631A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1979-07-13
Filing date: 1980-07-10
Publication date: 1981-03-25
Also published as: DE2928312A1; FR2460820A1; GB2057078B; BE884294A; NL8003676A; FR2460820B1

Abstract

A hydraulic brake system for a traction vehicle enables a trailer connected (through hydraulic coupling 23) to the traction vehicle to be braked through application of the vehicle handbrake 1 as well as through application of the vehicle service brake 5, thereby enabling the driver safely to leave his vehicle to uncouple the trailer. To this end, the traction vehicle brake system includes a trailer brake valve 11 through which a trailer brake line 13 which supplies the trailer brake unit can be pressurized, and it is arranged that the trailer brake valve 11 is operated either by service brake pressure from the vehicle main brake cylinder 6 or by the vehicle handbrake 1. The coupling between the vehicle handbrake and the brake valve can be mechanical (Fig. 1) or hydraulic (Fig. 2). <IMAGE>

Description

SPECIFICATION Hydraulic brake unit for a traction vehicle The invention relates to a hydraulic brake unit for a traction vehicle.

Conventicnally, a brake unit for a vehicle for use with a trailer includes a trailer brake valve, which is controlled by brake pressure from the main brake cylinder and which operates to connect a trailer brake line to a pressure medium source. The trailer brake line has an hydraulic coupling by which the line can be connected to a trailer brake unit.

The purpose of hydraulic brake units of this kind is to provide, as a function of the operation of the main brake cylinder, both an appropriate brake pressure for the operation of the service brake of the traction vehicle and an adequate trailer brake pressure for the operation. of the service brake of the trailer. The traction vehicle and trailer each have a respective mechanical handbrake which usually serves, inter alia, to secure the vehicle when stationary.

A hydraulic brake unit of this kind is described, for example, in DE-AS 22 54 089. With this brake unit when the trailer is to be uncoupled at the place of destination, the driver must first maintain the service brake position of the traction vehicle and of the trailer (by operating the brake pedal associated with the main brake cylinder) until the trailer is secured by the handbrake associated with it and the traction vehicle is secured by its handbrake. The driver then releases the service brake position so that the trailer brake liine is depressurised following which the hydro-coupling can be disengaged.

If, with such a brake unit, the traction vehicle is secured only by the handbrake (the service brake being disengaged) ramming accidents can occur, especially in the case of agricultural vehicle. This happens chiefly when a light traction vehicle and a loaded trailer stop on a slope and the driver leaves the traction vehicle to secure the trailer -- inter alia by means of the trailer's handbrake -- and uncouple it: during the time between the driver releasing the service brake (so that he can leave the cab) and the trailer handbrake being applied, the trailer is, in fact, left unsecured.

The problem with which the invention is concerned is that of providing a hydraulic brake unit which renders possible simplified coupling and uncoupling of a trailer whilst avoiding problems of overruning or ramming.

The present invention provides a hydraulic brake unit for a traction vehicle, including a trailer brake valve which is operable to-connect a trailer brake line to a pressure medium source, the trailer brake line being connectible to a hydraulic brake unit of a trailer, in which the trailer brake valve is controllable both by brake pressure from a main brake cylinder and as a function of the operation ol the handbrake of the traction vehicle.

Two embodiments of the invention are described in more detail, by way of example, with reference to the drawings, in which Figure 1 is a diagrammatic representation of a hydraulic brake unit for a traction vehicle, with mechanical control of the trailer brake valve from the traction vehicle handbrake, Figure 2 is a diagrammatic representation of another hydraulic brake unit for a traction vehicle, with hydraulic control of the trailer brake valve from the traction vehicle handbrake.

The traction vehicle handbrake of the arrangement shown in Figure 1 has a hand lever 1 pivotable about a fixed point, and brake-rod linkage 4 hinged to the hand lever 1 and cooperating with wheel brakes 2 and 3 of the traction vehicle.

The hydraulic brake unit of the arrangement shown in Figure 1 has a main brake cylinder 6 operable mechanically by way of a pedal 5.

The main brake cylinder 6 is connected by a brake line 7 to brake cylinders 8 and 9 which are associated with the wheel brakes 2 and 3.

The brake line 7 is connected by a control line 10 to a trailer brake valve 11.

The trailer brake valve 11 has a control member 12 by means of which a trailer brake line 13 can be connected either to a return 14 or to a pressure medium source 1 5.

The pressure medium source 15, in the present example, is a hydraulic accumulator which is connected to be supplied by a plump 18 via a cutoff valve 1 6 having a further outlet which is connected to a load-supplying line 1 7 (not relevant to the present invention).

Associated with the trailer brake valve 11 is a control means 1 9 which cooperates with the hand lever 1 of the handbrake and by means of which the control member 12, in the absence of brake pressure, can be mechanically controlled on operation of the handbrake.

The control means 19 is formed by a lever 20 secured to the hand lever 1 of the handbrake, and a push rod 21 cooperating with this lever 20 and associated with the trailer brake valve 11 at the control chamber side thereof. The push rod 21 is sealed, in known manner, in a housing bore of the trailer brake valve 11, being guided for sliding movement therein, and is arranged to cooperate, with its end face, with the control member 12 which is spring-loaded against it.

The trailer brake line 13 is connected by a valve 22 to a hydraulic coupling 23 by means of which a hydraulic brake unit, not shown, of a trailer can be connected.

The valve 22 which, in the position shown in the drawing, connects the hydraulic coupling 23 to the trailer brake valve, is mechanically-operable against the force of a spring into a release position in which the trailer coupling 23 is connected to the return 14.

The operation of the hydraulic brake unit described so far is as follows.

In the driving position shown (that is, when the brakes are not applied), the brake line 7 is without pressure. The trailer brake valve 11 is held, by the spring action on the control member 12, in its starting position in which the trailer brake line 13 is connected to the return 14. Since the handbrake is released, the push rod 21 associated with the trailer brake valve 11 is unoperated and lies adjacent to the control member 12. The pressure medium source 1 5 is connected by the cut-off valve 1 6 to the pump 18 and is thus permanently held at a predetermined maximum load.

On operation of the pedal 5, the main brake cylinder 6 introduces a corresponding brake pressure into the brake line 7 and further into the brake cylinders 8 and 9 associated with the wheel brakes 2 and 3, and service braking of the traction vehicle is thus initiated.

The brake pressure built up in this manner in the brake line 7 is simultaneously, by way of the control line 10, applied to the control memeber 1 2 of the trailer brake valve 11, causing the control member 12 to assume a braking position against the action of the spring. In this braking position of the trailer vavle 11, the trailer brake line 1 3 is connected to the pressure source 1 5 so that a trailer brake pressure is introduced via the valve 22 and the hydraulic coupling 23 into the hydraulic brake unit (not shown) of the trailer, coupled thereto, After operation of the pedal 5, the main brake cylinder 6 reassumes its starting position, and the brake line 7 and also the control line 10 are again without pressure.The control member 12 of the trailer brake valve 11 then assumes its starting position under the action of the associated spring, and the driving position described at the beginning is thus reassumed.

On operation of the traction vehicle handbrake by means of the hand lever 1, mechanical control of the trailer brake valve 11 is also effected simultaneously by way of the lever 20 and the push rod 21. Thus, when the traction vehicle handbrake is pulled on, the control member 12 of valve 11 is held in the above-described braking position independently of brake pressure controlled by the main brake cylinder 6, in which braking position (as already described) the trailer brake line 1 3 is connected to the pressure medium source 1 5 and a brake pressure for operating the service brake of the trailer is applied by way of the trailer brake line 1 3 to the hydraulic coupling 22.

In this manner, the trailer coupled to the traction vehicle is automatically secured by its service brake when the handbrake of the traction vehicle is applied. The driver therefore no longer has to operate the pedal 5 to prevent the trailer from overruning during temporary stationary periods. Instead, with the traction vehicle handbrake applied and thereby, simultaneously, the service brake of the trailer, he can leave the traction vehicle to operate, for example, the handbrake of the trailer and to make possible uncoupling of the trailer.

The hydraulic coupling 23 is operable usually when there is no pressure in the trailer brake line 1-3. When the trailer is being uncoupled it must, therefore first of ali be secured, for example by the mentioned trailer handbrake, whereafter the valve 22 is moved into the release position to separate the trailer brake line 13 at the coupling side from the pressure medium source 1 5 and join it with the return 14. The hydraulic coupling 23 is then operable, to uncouple the trailer, and at the same time the service bral < e of the trailer is released.

Figure 2 shows a further example of a hydraulic brake unit according to the invention in which those components having the same function as corresponding components in Figure 1 have the same reference numbers as in Figure 1.

The hydraulic brake unit according to Figure 2 has, in contrast to that of Figure 1, a purely hydraulically controlled trailer brake valve 11 a which, by way of control means 1 spa, can be controlled both by the main brake cylinder 6 and by operation of the hand lever 1 of the traction vehicle handbrake.

The control means 1 9a, in this case, comprises a lever 20a secured to the hand lever 1, a hydraulic transmitter 24 operable by the lever 20a, and a two-way nonreturn valve 25 connected to the transmitter 24 and into the brake line 7.

The transmitter 24 is of known construction and includes a piston (not shown) which is hinged on the one hand, by way of a piston rod, to the lever 20a and on the other hand, by a rod, to the brake-rod linkage 4.

The transmitter 24 can also be arranged to be operable, parallel to the brake-rod linkage 4 by the hand lever 1.

The operation of the hydraulic brake unit according to Figure 2 differs from that according to Figure 1 in the following respects: On operation of the pedal 5, the main brake cylinder. 6 introduces a corresponding brake pressure into the brake line 7, under the action of which the two-way nonreturn valve 25 opens the connection to the brake cylinders 8 and 9 and to the control line 10 and closes the connection to the transmitter 24, thus initiating service-braking of the traction vehicle.

Under the action of the brake pressure applied simultaneously by way of the control line 10 in the control chamber of the trailer brake valve 11 a, the control member 12 is held (against the action of the associated spring) in a braking position in which the trailer brake line 1 3 is connected to the pressure medium source 1 5 so that, by way of the..

valve 22 and. the hydraulic coupling 23, a trailer brake pressure for the operation of the trailer service brake is applied to the hydraulic brake unit of the trailer.

On operation of the traction vehicle hand brake by means of the hand lever 1 , the hydraulic transmitter 24, which is operated at the same time by way of the lever 20a, applies an appropriate pressure under the action of which the two-way nonreturn valve 25 (if the brake pressure controlled by the main brake cylinder 6 has subsided or is absent) opens the connection between the transmitter 24 and the brake cylinders 2 and 3 and the control line 10, and closes the connection to the main brake cylinder 6. Then, with the braking position of the traction vehicle being held hydraulically and mechanically, the trailer brake valve 11 a is hydraulically controlled in the manner already described for the purpose of applying a trailer brake pressure.

It is possible so to arrange the two-way nonreturn valve 25 in the brake line 7 that the main brake cylinder 6 is connected, by way of a line branching off between the main brake cylinder 6 and the two-way nonreturn valve 25, directly to the brake cylinders associated with the wheel brakes of one axle of the traction vehicle, and can be connected to the brake cylinders associated with the wheel brakes of another (for example, the rear) axle only by way of the two-way nonreturn valve 25. In this case, when the handbrake is operated only the brake cylinders associated with the wheel brakes of the latter (rear) axle and the trailer brake valve 11 a, are controlled by the pressure applied by the transmitter 24.

It is also possible to arrange the two-way nonreturn valve 25 in the control line 10 so that, when the traction vehicle hand brake is operated, the traction vehicle is mechanically secured and only the trailer brake valve 11 a is controlled by the pressure applied by the transmitter 24 for the purpose of applying the trailer brake pressure.

As already indicated, an advantage that can be achieved by the use of the arrangements just described is that, as a result of the service brake of the trailer being operable additionally as a function of the operation of the handbrake of the traction vehicle, when it is desired to secure the trailer by means of its handbrake and wheel chocks the driver is excused from operation the brake pedal 5 associated with the main brake cylinder 6 and is able to secure the trailer in the manner of single operator control.

A further advantage is that the traction vehicle and the trailer can temporarily be locked in position when there are incalculable periods of standing still in heavy street traffic merely by operating the traction vehicle's handbrake.

The valve 22 associated with the trailer brake line 13 on the traction vehicle side of the hydraulic coupling 23 provides the advantage that the service brake setting of the trailer effected by the traction vehicle handbrake, can be released in a simple manner, for example for the purpose of operating the hydraulic coupling 23 when there is no pressure in the trailer brake iine. The arrangement of the valve 22 so that it is mechanically operable from the operating position of the hydraulic coupling 23 also facilitates singleoperator control for coupling.

The construction of valve 22 with a release setting held against the action of a spring under the action of a mechanical operating force ensures that the valve, after operation, automatically returns to the starting position in which the trailer brake line 13 at the hydraulic coupling 23 can be connected by the trailer brake valve 11 to the pressure medium source 15, thereby enabling the service brake of the trailer to be operated without any problem.

In the arrangement of Fig. 2, the control means 1 9a formed on the basis of a hydraulic transmitter 24 operable by the hand lever 1 of the traction vehicle's handbrake and of a two-way nonreturn valve 25 provides primarily the advantage of purely hydraulic control of the trailer brake valve 11 a. There are furthermore supplementary advantages for on the one hand, the trailer brake valve 11 a is usable without alteration and, on the other hand, the transmitter 24 can be arranged in a simple manner in the operative connection of the hand lever 1 with the brake-rod linkage 4 (or brake cables) of the traction vehicle handbrake.

In the arrangement of Fig. 1, the control means 1 9 formed by a lever 20 secured to the hand lever 1 of the traction vehicle's handbrake, and a push rod 21 cooperating with this lever 20 and associated with the trailer brake valve 11, provides the advantage of a simple-to-construct, robust, mechanical control means for the trailer brake valve which from an economic view-point is of special interest for agricultural vehicles.

Claims

1. A hydraulic brake unit for a traction vehicle, including a trailer brake valve which is operable to connect a trailer brake line to a pressure medium source, the trailer brake line being connectible to a hydraulic brake unit of a trailer in which the trailer brake valve is controllable both by brake pressure from a main brake cylinder and as a function of the operation of the handbrake of the traction vehicle.

2. A hydraulic brake unit according to claim 1, in which the trailer brake valve is connected to the traction vehicle hand brake to be controlled mechanically as a function of the operation of the handbrake.

3. A hydraulic brake unit according to claim 1 or claim 2, in which the trailer brake valve is controllable via control means comprising a lever connected to the traction vehicle handbrake and coupled to a push rod co-operating with a control member of the trailer brake valve.

4. A hydraulic brake unit according to claim 3, in which the push rod is movably guided and sealed in the trailer brake valve.

5. A hydraulic brake unit according to claim 1, in which the trailer brake valve is coupled to the traction vehicle hand brake to be controlled hydraulically as a function of the operation of the handbrake.

6. A hydraulic brake unit according to claim 1 or claim 5, in which the trailer brake valve is controllable via control means comprising a) a hydraulic transmitter operable by the traction vehicle handbrake, and b) a two-way nonreturn valve connecting either the hydraulic transmitter or the main brake cylinder with a control inlet of the trailer brake valve.

7. A hydraulic brake unit according to claim 6, in which the hydraulic transmitter is arranged to be operable by means of a lever connected to the traction vehicle hand brake.

8. Hydraulic brake unit according to claim 6 or claim 7, in which the hydraulic transmitter includes a piston which is connected at one end to the traction vehicle handbrake and at the other end to the handbrake-rod linkage.

9. A hydraulic brake unit according to any one of the claims 6 to 8, in which the two-way nonreturn valve is associated with a control line connecting the control inlet of the trailer brake valve via a brake line to the main brake cylinder.

10. A hydraulic brake unit according to any one of the claims 6 to 8, in which the two-way nonreturn valve is associated with a brake line connecting the main brake cylinder to the brake cylinders of wheel brakes and, by way of a control line to the control inlet of the trailer brake valve, the two-way nonreturn valve connecting the brake cylinders of the said wheel brakes and the control inlet of the trailer brake valve either to the main brake cylinder or to the hydraulic transmitter.

11. A hydraulic brake unit according to any one of the preceding claims, in which the trailer brake line terminates in a hydraulic coupling by which the trailer brake line is connectible to the trailer brake unit, and in which there is arranged, in the trailer brake line, a release valve by means of which the hydraulic coupling can be discharged of pressure.

12. A hydraulic brake unit according to claim 11, in which the release valve has a release position into which the valve is movable, against a resilient bias, under the action of an operating force, in which position the trailer brake line at the coupling side of the valve is blocked off from the pressure medium source and connected to a pressure medium return.

13. A hydraulic brake unit according to claim 12, in which the release valve is arranged to be mechanically operable from the operating position of the hydraulic coupling.

14. A hydraulic brake unit for a traction vehicle substantially as described herein with reference ot, and as illustrated by Fig. 1 or Fig. 2 of the accompanying drawings.

1 5. A traction vehicle including a hydraulic brake unit according to any one of the preceding claims.

16. A traction vehicle according to claim 15 with a trailer, in which the trailer brake line is connected to the hydraulic brake unit of the trailer.