GB2088982A

GB2088982A - Failsafe Hydraulic Trailer Brake System

Info

Publication number: GB2088982A
Application number: GB8135691A
Authority: GB
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1980-12-02
Filing date: 1981-11-26
Publication date: 1982-06-16
Also published as: ATA488881A; AT387194B; FR2495080A1; DE3045455A1; FR2495080B1; DE3045455C2

Abstract

A hydraulic trailer brake system for towing vehicles, the trailer brake cylinders (11) of which are actuatable by means of a brake valve (1) provided on the tractor, is characterised in that the brake lines (7, 9) downstream and upstream of the brake line coupling (8) each contain a shut-off valve (12, 13) held in the open position, against spring biasing, by the line pressure on the side adjacent the brake line coupling (8), and the brake line pressure is always kept at a level which overcomes the spring basing of the shut-off valve (12, 13). When the coupling (8) is intact the valve (13) may also connect the line (9) with an accumulator (fig. 2, not shown). When the coupling is broken, the shut-off valve connects the accumulator to the trailer brake cylinders (11). <IMAGE>

Description

SPECIFICATION Hydraulic Trailer Brake System for Towing Vehicles The invention relates to a hydraulic trailer brake system according to the preamble to claim 1.

Trailer brake systems must be so designed that the trailer brakes can be reliably actuated at all times. In normal operation of the towed and towing vehicles this requirement is satisfied by the towing vehicle brake line being coupled to the trailer brake line via a brake line coupling. In the event of breakaway of the trailer from the towing vehicle, the trailer brakes are immediately actuated independently of the towing vehicle operating pressure. This is usually achieved by activation of a mechanical or hydraulic accumulator in the trailer brake system. If the trailer breaks away from the towing vehicle in such a way that the brake lines are separated at the coupling, there are no complications, but breakaway of the trailer from the towing vehicle is an unpredictable danger.Nor can it be assumed that the brake lines will always tear apart at the coupling and if they do break away outside the coupling then one side of either the trailer brake system or of the towing vehicle brake system is exposed with the consequent considerable danger that larger quantities of hydraulic fluid will escape from the open brake line and a hydraulic supply system connected to the leaking line will be rendered inoperative. On the one hand this results in dangerous road fouling while on the other hand important working units (e.g. of the steering brake system) of the train may break down, thus greatly impairing operational reliability.

The object of this invention, therefore, is to provide a hydraulic trailer brake system for towing vehicles of a construction such that even in the event of breakaway of the brake lines next to the brake line coupling operational reliability of the towed and towing vehicles is unimpaired and the danger of road fouling is reduced.

This objective is achieved by the features indicated in the characterising part of claim 1.

According to the invention, each shut-off valve movable into the open position against spring biasing is incorporated in its respective brake line section and according to the invention the valves are subjected to the brake line pressure between the valve and the brake line coupling, with the result that in the event of breakaway of the brake lines next to the coupling the pressure holding the shut-off valve in the open position abruptly drops and the shut-off valve is automatically brought into the shut-off position so that the broken brake line is reliably sealed and the escape of hydraulic fluid is effectively prevented.

According to one preferred embodiment of the invention, the shut-off valve is a 2/2-way valve constructed in the form of a spool valve, one side of which is subject to the action of a pressureadjusting means while the other side is subject to the action of another control spring. The specific advantage of this embodiment is that it greatly simplifies balancing of the counteracting valve adjusting forces.

To keep the brake line pressure constantly at a level which overcomes the control spring biasing force, the brake valve on the towing vehicle, i.e. in the return line leading to the hydraulic fluid tank, contains a spring-biased and preferably adjustable non-return valve.

The embodiment of the trailer brake system according to the invention as disclosed in claim 5 is particularly advantageous. In this case the shutoff valve in the trailer brake system exercises another important function: in the event of the trailer or brake line on the trailer side breaking away, the shut-off valve closes the broken brake line section in the manner indicated hereinbefore while on the other hand the trailer brakes are simultaneously subjected to the pressure of a hydraulic accumulator. This is an additional means of increasing operational reliability of the trailer brake system and of the vehicle train.

The features of claim 6 give a very simple structural solution to the problem of controlling the trailer brakes.

Other advantageous aspects of the invention will be apparent from the other sub-claims.

A number of exemplified embodiments of the invention will be explained in detail hereinbelow with reference to diagrammatic drawings wherein: Fig. 1 is a schematic diagram showing a first embodiment of the hydraulic trailer brake system and Fig. 2 is a schematic diagram of another embodiment of the hydraulic trailer brake system.

The hydraulic trailer brake system shown in Fig. 1 comprises a reservoir S for pressure fluid and a constant-pressure pump P, which is driven in any desired manner and which delivers pressure fluid from a hydraulic fluid tank HFT to the reservoir S via a non-return valve R. A brake supply line 2 is connected to the reservoir S and feeds the pressure fluid at constant pressure to a brake valve 1. The latter is, for example, constructed as a 3/3-way valve which in Fig. 1 is biased by a return spring 3 to a position in which a brake line branch 4 is connected to the hydraulic fluid tank via a return line 5. Return line 5 incorporates an adjustable spring-biased nonreturn valve 6 so that the pressure in the return line can always be kept at a given level.

Brake line branch 4 merges into a tractor or towing vehicle brake line 7 connected to a trailer brake line 9 via a coupling 8. Trailer brake line 9 extends to a trailer brake cylinder 11 via a load matching valve 10. Sections 7 and 9 of the brake line each contain a shut-off valve 12, 13, both of which are constructed as 2/2-way valves in the form of spool valves. Valves 12 and 13 are biased into the closing position at one end by adjustable spring means 14, 1 5 and subjected at the other end to the action of pressure-adjusting means 16, 1 7 connected respectively via pressure control lines 18, 1 9 to the brake line sections situated between the shut-off valves 12, 13 and the brake line coupling 8.The pressure to which the brake lines 7 and 9 are set by the adjustable non-return vaive- 6 is such as to overcome the adjustable spring means 14, 1 5 so that the shut-off valves 12, 13 assume operating position A in the position illustrated for brake valve 1. When the brake valve is subjected to a brake force F,, the brake lines 7 and 9 are increasingly subjected to the pressure of the reservoir S and actuation of the trailer brake cylinder 11 is started.

In the event of breakaway of the trailer or of the brake lines 7 or 9, the pressure in the broken away or opened section of the brake line, and hence the pressure in the associated control pressure line 18, falls abruptly so that the pressure adjusting means 16, 17 can no longer overcome the force of the adjustable spring means 14, 15 and the shut-off valves 12, 13 are moved into their shut-off position B. This prevents pressure fluid from escaping from a pressurized brake line. If the brake line of the towing vehicle or of the trailer brake system are respectively in communication with a pressure source or a working unit, a breakage in the brake line will no longer jeopardize the operational reliability or serviceability of the working unit.On the other hand, the hydraulic trailer brake system shown in Fig. 1 can prevent the road from being fouled by escaping hydraulic fluid, thus extensively reducing danger to road traffic.

Fig. 2 shows another embodiment of a hydraulic trailer brake system very similar to the system shown in Fig. 1. In Fig. 2, like references denote like parts and parts having a like action.

The difference between this embodiment and the embodiment shown in Fig. 1 lies in the construction of the trailer system and, more particularly, the modified construction of the trailershut-offvalve 13'. In this embodiment valve 13' is in the form of a 3/2-way valve which in the operating position A' illustrated feeds a trailer hydraulic accumulator 20 via a non-return valve 21 and a charging line 22. Otherwise this other embodiment of the hydraulic trailer brake system operates in the same way as that shown in Fig. 1. The special nature of this embodiment becomes apparent in the event of the trailer breaking away from the towing vehicle. If the trailer brake line 9 ruptures, the pressure in the control pressure line 19 rapidly drops to atmospheric pressure so that the adjustable spring means 1 5 moves the shut-off valve 13' into position B'.In this position the trailer brake line is decoupled from the trailer brake system and a fluid connection is simultaneously established between the hydraulic accumulator 20 and the brake cylinders As a result, the trailer automatically performs immediate braking while at the same time no leakage of hydraulic fluid can escape from the broken brake line 9.

Shut-off valve 13' is preferably connected to a breakaway cord which, in the event of the towing vehicle or tractor breaking away from the trailer causes the shut-off valve 13' to be brought automatically into its position B'. In this way, the use of the shut-off valve does away with the need for a special breakaway safeguard since the shutoff valve takes over that function. Consequently, the shut-off valves 12, 13 and 13' also act as hose rupture and breakaway safeguards.

The level of the pressure in the brake line can be adjusted by means of the non-return valve 6 to a value of, for example, about 5 bar.

Claims

1. A hydraulic trailer brake system for towing vehicles, the brake cylinders of which are actuatable by means of a brake valve provided on the towing vehicle, by means of which valve the brake lines leading to the brake cylinders via a brake line coupling can be alternatively fed with brake pressure or be connected to a return to a hydraulic fluid tank, characterised in that the brake lines (7, 9) downstream and upstream of the brake line coupling (8) each contain a shut-off valve (12, 13; 13') held in the open position, against spring biasing, by the line pressure on the side adjacent the brake line coupling (8), and the brake line pressure is always kept at a level which overcomes the spring biasing of the shut-off valve (12,13; 13').

2. A hydraulic brake system according to claim 1, characterised in that the shut-off valve (12, 13) is constructed as a 2/2-way valve in the form of a spool valve subjected at one end to the action of a spring means (14, 15) and at the other end of the action of a pressure-adjusting means (16, 17) connected via a control pressure line (18, 19) to the associated brake line section (7 and 8).

3. A hydraulic brake system according to claim 1 or 2, characterised in that the return line (5) contains a spring-biased non-return valve (6).

4. A hydraulic brake system according to claims 1 to 3, characterised in that the spring means (14, 1 5), the pressure-adjusting means (1 6, 17) and the limit pressure of the non-return valve (6) are adjustable to one another.

5. A hydraulic brake system according to claims 1 to 4, characterised in that the shut-off valve (13') in the trailer brake line (9) is connected, when in its shut-off position (B'), to a hydraulic accumulator (20) chargeable via the brake line (9) and a non-return valve (21).

6. A hydraulic brake system according to claim 5, characterised in that the shut-off valve (13') is a 3/2-way valve which, in its operating position (A') in which it opens the trailer brake line (9), feeds the hydraulic accumulator (20) via a nonreturn valve (21) incorporated in the shut-off valve (13') and which, in its operating position (B') closing the-brake line (9), establishes an unthrottled connection between the trailer brake cylinder (11) and the hydraulic accumulator (20).

7. A hydraulic brake system according to claim 5 or 6, characterised in that the shut-off valve (1 3') incorporated in the trailer brake system is coupled to a trailer breakaway device whereby it is automatically movable into its shut-off position (B') in the event of breakaway of the trailer.

8. A hydraulic brake system according to claims 1 to 7, characterised in that the shut-off valves (12, 1313') and the non-return valve (6) incorporated in the return line (5) are combined in one housing.

9. A hydraulic trailer brake system substantially as described herein with reference to the accompanying drawings.