GB2138084A

GB2138084A - A hydraulic overrun brake system for a trailer

Info

Publication number: GB2138084A
Application number: GB08309835A
Authority: GB
Inventors: Walter Urbanke
Original assignee: IFA KAROSSERIEWERKE VEB
Current assignee: IFA KAROSSERIEWERKE VEB
Priority date: 1983-03-18
Filing date: 1983-04-12
Publication date: 1984-10-17
Also published as: FR2543899B1; GB2138084B; FR2543899A1; DE3309728A1; GB8309835D0

Abstract

A hydraulic brake system for a trailer whose brakes are hitch- actuated and wherein a brake master cylinder 1 on the trailer for the individual wheel brake cylinders 2 is actuable by a strut member of the hitch-actuation system is arranged to not operate automatically during reversal, by rendering the hitch-actuated brake system inoperative when the normal direction of travel of the towing vehicle is reversed. For this purpose at least one wheel brake is provided with floating brake shoes 4, a support 5 is arranged on a base plate to which the brake shoes are adapted to be contiguous, end relief means 13 are provided which are actuable by the relative movement of the secondary brake shoe, Fig. 4, or via a link, Fig. 3, to create a communication 9 between the pressure side of the brake master cylinder 1 and the brake fluid reservoir 11 during reversal of the normal direction of travel of the towing vehicle. The spring loaded piston 15 also acts as a brake pressure limiting valve during forward travel of the trailer. <IMAGE>

Description

SPECIFICATION A hydraulic brake system for a trailor This invention relates to a hydraulic brake system for a trailer whose brakes are hitchactuated and wherein a master brake cylinder on the trailer is actuable by a strut member of the hitch-actuation system.

From US patent specification 3007552 hitch-actuated brake systems of the aforesaid kind are known, in which a plurality of wheel brake cylinders are actuable by means of a master brake cylinder.

From patent specification 1 780222 of the Federal German Republic a double-acting master brake cylinder for trailer brake systems is known, having a pressure chamber associated with each of its operating directions.

This master cylinder is connected by its respective pressure chamber to the wheel brake cylinder supply conduit via a valve which is responsive to the direction of travel and controlled by the brake segments of a disc brake.

This brake system is actuated at the instant at which the speed of the trailer exceeds that of the towing vehicle, until the brake system becomes operative. This condition occurs when the brakes are applied to the towing vehicle travelling in its normal direction of travel and when reversing downhill.

That invention however does not solve the problem of providing a trailer with automatic braking during reversal of the normal direction of travel.

It is an aim of the present invention to provide a trailer with a hydraulic brake system which operates automatically during reversal, in order thereby to increase and improve the scope of application of hydraulic brake systems for trailers.

This involves solving the technical problem of rendering the hitch-actuated brake system inoperative when the normal direction of travel of the towing vehicle is reversed.

In accordance with the invention this problem is solved by providing at least one wheel brake with floating brake shoes, a support being so arranged on the base plate to which the brake shoes are adapted to be contiguous that relief means are provided which are controllable directly or via mechanical coupling members, fixedly arranged with respect to the base plate, actuable by the relative movement of the secondary brake shoe and the link member and the coupling rod, and, during reversal of the normal direction of travel of the towing vehicle, create a communication between the conduit connected to the pressure side of the master brake cylinder and the brake fluid reservoir from the reservoir return conduit.

Thereby it is possible to equip the trailer with a hydraulic brake system which operates automatically during reversal.

In a preferred embodiment of the invention the relief means are incorporated in the said support. A link member for coupling the brake shoes passes through the relief means, so that a tie rod and separate release means can be dispensed with. Such an arrangement provides a simplified design taking up less space, and during reversal the relief means open the brake pressurising system under the mechanical control of a slidably arranged secondary brake shoe, the brake fluid also returning to the reservoir and the pressure rising until a predetermined residual brake moment permitting satisfactory reversal, is reached.Whilst proceeding in the normal direction of travel, once a predetermined maximum permissible brake pressure has been reached, the relief means open in the manner of a known overpressure valve acting as a braking force limiter or braking pressure limiter, the brake fluid being returned to the reservoir. By means of the relief means, a known braking force limiter and means providing automatic operation during reversal are provided in a single component.

In order to ensure jolt-free operation of the automatic device during reversal, a check valve may be provided in the relief means controlled connection between the pressure side of the master cylinder and the reservoir.

Two forms of the brake system embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 shows a first form of the complete brake system with separate relief means; Figure 1 a shows a check valve; Figure 2 shows the relief means and coupling members when the brakes are applied during (forward) travel in the normal direction of travel; Figure 3 shows the relief means and coupling members when the brakes are applied during travel in the reverse direction; and Figure 4 shows a second form of the brake system, in which the relief means are incorporated in the support.

Referring to Figure 1, the brake system shown therein is that installed on the trailer. A master cylinder 1 having a reservoir 11 is connected in known manner to the hitch system, which actuates the plunger of the master cylinder 1. Via a conduit 8 the connection between the master cylinder 1 and the wheel cylinders 2, 2' is provided for the transmission of the braking pressure, the plungers of the wheel cylinders 2, 2' transmitting their strokes to the primary brake shoe 3 and the secondary brake shoe 4.

Since the invention essentially relates only to the special design of a wheel brake, the latter only will be described. The brake shoes 3, 4 are floatingly supported by the base plate and interconnected by a link 6, This link 6 is slidable in a support 5, which is secured to the base plate and arranged oppositely to the wheel cylinder 2 between the brake shoes 3, 4. Via a coupling rod 7, the link 6 is connected to relief means 13, from which a conduit 9 goes back to the reservoir 11 of the master cylinder 1, whilst a conduit 10 connects the relief means 1 3 to the conduit 8.

When braking in the normal (forward) direction of travel, the pressure produced in the master cylinder 1 is transmitted by the plungers of the wheel cylinder 2 to the brake shoes 3, 4, whereby the wheel is braked, the support surface A of the primary brake shoe 3 coming into abutment with the support 5. The braking moment substantially acts on the support surface A of the primary brake shoe 3, the secondary brake shoe 4 remaining spaced from the support surface B by a distance a, so that the hydraulic relief means 1 3 are not actuated in this mode of travel.

The relief means 1 3 alsc act as an overpressure valve, when the maximum pressure permissible for the brake system is exceeded.

If the braking pressure is increased beyond the permissible value, the pressure in the conduit 10 increases. Thereby the relief means 1 3 are actuated and communication is established with the conduit 9, so that the excessively high pressure is reduced and the hydraulic fluid is returned to the reservoir 11 of the master cylinder 1 via the conduit 9.For this purpose it is however necessary to provide in the support 5 a degree of freedom for the tie rod 7 in the form of an elongate slot 1 7. A check valve 14 (as shown in Figure 1 a) may be inserted in the conduit 9, which maintains, even after the relief means 1 3 have been actuated, a minimum braking pressure such that the secondary brake shoe is still just able to actuate the relief means 1 3 by its reaction force in the direction of the support 5.

When reversing, i.e. when the trailer is pushed by the towing vehicle, the pressure produced by the master cylinder 1 is also applied to the wheel cylinders 2, 2' and via its plungers to the brake shoes 3, 4. Furthermore the brake shoes 3 and 4 come into abutment with the brake drum 12, and the secondary brake shoe 4 is carried along by the brake drum 12, until it comes into abutment with the support surface B of the support 5. Thereby the link 6 is displaced in the support 5 with respect to the primary brake shoe 3 and carries the tie rod 7, which is rotatably attached to it, with it. The opposite end of the tie rod 7 is connected to the relief means 1 3 and actuates the relief means 1 3 in such a way that communication is established between the conduit 10 and the conduit 9.

Thereby the pressure is reduced by the relief means 1 3 to such an extent that reverse travel under the influence of a predetermined residual braking moment is possible.

Referring now to Figure 4, the brake system shown therein is also that installed on the trailer. A master cylinder 1 having a reservoir 11 is connected in known manner to the hitch system, which actuates the plunger of the master cylinder 1. Via a conduit 8 the connection between the master cylinder 1 and the wheel cylinders 2, 2' is provided for the transmission of the braking pressure, the plungers of the wheel cylinders 2, 2' transmitting their strokes to the primary brake shoe 3 and the secondary brake shoe 4.

Since the invention essentially relates only to the special design of a wheel brake, the latter only will be described. The brake shoes 3, 4 are floatingly supported by the base plate. The relief means 1 3 are incorporated in the support 5. The brake shoe 4 and the plunger 15 are connected by a link 6. The link 6 may alternatively be arranged to pass through the relief means 13, and hence the support 5, at both ends and interconnect the brake shoes 3, 4. The central portion of the link 6 is slidable in the relief means 1 3. A conduit 10 interconnects the conduit 8 and the relief means 13. From the relief means 1 3 a conduit 9 goes back to the reservoir 11 of the master cylinder 1.

When braking in the normal (forward) direction of travel, the pressure prcduced in the master cylinder 1 is transmitted by the plungers of the wheel cylinder 2 to the brake shoes 3, 4, whereby the wheel is braked, the support surface A of the primary brake shoe 3 coming into abutment with the support 5. The braking moment substantially acts on the support surface A of the primary brake shoe 3, the secondary brake shoe 4 remaining spaced from the support surface B by a distance a so that the hydraulic relief means 1 3 are not actuated in this mode of travel. The entire pressure is then applied to the primary brake shoe 3.

When reversing, i.e. when the trailer is pushed by the towing vehicle, the pressure produced by the master cylinder 1 is also applied to the wheel cylinder 2 and via its plungers to the brake shoes 3, 4.

Furthermore, the brake shoes 3 and 4 come into abutment with the brake drum 1 2 and the seccndary brake shoe 4 is carried along by the brake drum 12, until it comes into abutment with the support surface B of the support 5. Thereby the link 6 and the valve plunger 15 to which it is attached are displaced with respect to the primary brake shoe 3 against the force of a return spring 1 6 in the relief means 1 3 in the support 5. Thus communication is established in the relief means 13 between the conduit 10 and the conduit 9, so that the pressure is reduced.

Thereby reverse travel under the influence of a residual braking moment is provided CLAIMS

Claims

1. A hydraulic brake system for a trailer which is towable by a towing vehicle and whose brakes are hitch-actuable, wherein a master brake cylinder on the trailer for the individual wheel brake cylinders of the trailer is actuable by a strut member of the hitchactuation system, characterised in that at least one wheel brake is provided with a primary and a secondary floating brake shoe, a support being so arranged on a base plate to which the brake shoes are contiguous, that relief means which are controllable directly or via a mechanical linkage and which are fixedly arranged with respect to the base plate and are actuable by the relative movement of the secondary brake shoe and a link, create a communication for the brake fluid between the pressure side of the master brake cylinder and the brake fluid reservoir during reversal of the normal direction of travel of the towing vehicle.

2. A hydraulic brake system according to Claim 1, characterised in that the relief means are incorporated in the support, and in that the link connecting the secondary brake shoe or the primary and secondary brake shoes to a plunger of the relief means passes through the relief means, and hence the support, at one or both ends of said relief means.

3. A hydraulic brake system according to Claim 1 or Claim 2, characterised in that a check valve is included in conduit means controlled by said relief means and connecting the latter to the pressure side of the master brake cylinder and said reservoir.

4. A hydraulic brake system according to any one of the preceding claims, characterised in that the relief means are arranged to limit the braking force in the forward direction of travel of the trailer.

5. A hydraulic brake system according to Claim 1 and constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 to 3, or Figure 4, of the accompanying diagrammatic drawings.

6. A combination of a towing vehicle and a trailer according to Claim 6.

6. A trailer having a hydraulic brake system according to any one of the preceding claims.

7. A ccmbination of a towing vehicle and a trailer according to Claim 6.

CLAIMS 21 Dec 1983

1. A hydraulic brake system for a trailer which is towable by a towing vehicle, the system comprising a hitch-actuatable master cylinder having a reservoir and communicating with individual wheel brake cylinders, each of which actuates a wheel brake, and further comprising a conduit providing communication between the pressure side of the master cylinder and its reservoir, the conduit being controlled by relief means arranged to open the conduit on reversing, wherein at least one of said wheel brakes has a base plate, is provided with a primary and a secondary floating brake shoe and includes a support mounted on the base plate and engageable by the brake shoes, the support being so arranged that the relief means, which are firmly fixed on the base plate, are controllable by the secondary brake shoe via link means, and wherein the relief means are arranged to limit the braking force on braking during forward driving.

2. A system according to Claim 1, wherein the relief means are incorporated in the support, and the link means include a link member connecting the secondary brake shoe, or both the primary and secondary brake shoes, to a control element in the relief means and passing into or through the relief means and hence the support. 3. A system according to Claim 1 or 2, wherein the conduit includes a check valve for ensuring minimum pressure in the conduit and consequently minimum braking pressure in the braking system. 4. A hydraulic brake system according to Claim 1, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 to 3, or Figure 4, of the accompanying drawings.

5. A trailer having a hydraulic brake system according to any one of the preceding claims.