BACKGROUND OF THE INVENTION Fundamental considerations of road safety require that, when a road going vehicle such as a trailer is towed behind another vehicle, the towed trailer should itself have a braking system; otherwise there is a danger of the towed vehicle overrunning the towing vehicle when brakes are applied on the latter, thereby resulting in serious loss of control and possible jack-knifing.

While such combinations of towing and towed vehicles may take various forms, for example, a car towing a trailer or caravan, for simplicity in the following description the towing vehicle will be referred to as the prime mover'and the towed vehicle as the trailer'.

Disregarding the pneumatic braking system fitted to heavy commercial vehicles and trailers, current braking systems of trailers fall into the simple mechanical cable/rod brakes, wholly independent of the prime mover's braking system. The over-run inertia-type brake which reacts to forward pressure of the trailer upon the prime mover to operate it, due to the fact that the inertia-type

brake at present operates a cable or a rod or a combination of both, is not as efficient as would be preferred. For this reason an alternative trailer braking system has been developed, in which a hydraulic circuit replaces the cable/rod system.

SUMMARY OF THE INVENTION According to one aspect of the invention there is provided an over-run, auto-reverse hydraulic braking system on a trailer comprising a rotatable brake disc on the trailer, and a movable calliper mounted on the trailer carrying a pair of brake pads one to each side of the disc and a hydraulically-actuated piston, the arrangement being such that, on the application of hydraulic fluid under pressure to the piston, the first brake pad is urged by the piston into engagement with the disc, the movable mounting of the calliper ensuring that an even braking pressure is subsequently applied to the disc by both brake pads, the first and second brake pads each being guided for axial movement towards and away from the disc, and at least the second brake pad being guided for limited angular movement in the direction of reverse rotation of the disc, the braking system further including an hydraulic master cylinder for supplying fluid under pressure to said piston, . flow of fluid to said piston resulting from relative movement between the trailer and a towing vehicle towards

one another, characterised in that, on the rear face of the second brake pad remote from the disc, there are formed at least two raised parallel sections each having an end face substantially parallel with the plane of the disc, the leading edge of each section being inclined to the plane of the disc and tapering from the end face at an angle towards and into the rear face of the brake pad, the braking system further comprising, to the side of the second brake pad remote from the disc, a plate guided for axial movement towards and away from the disc but angularly fixed relative to the disc, the face of the plate adjacent the second brake pad having at least two raised parallel sections each having an end face substantially parallel with the plane of the disc which, under normal braking'conditions, abuts an associated one of the sections on the second brake pad, the arrangement being such that, on reverse rotation of the disc with the brake actuated, the disc moves the second brake pad angularly under friction whereby the end faces of the sections of the second brake pad are displaced from the end faces of the sections on the plate to bring the tapering leading edges of the sections on the second brake pad into alignment with the end faces of the sections on the plate whereby pressurised engagement between the second brake pad and the plate is released and the braking pressure on the disc is reduced.

The braking system of the invention reduces friction between the brake pads and the brake disc during reverse manoeuvring, thereby allowing a reverse manoeuvre to take place without the necessity for the driver to leave the prime mover. As soon as forward motion is resumed, the braking system returns to a fully operational state automatically.

The first brake pad may be a guided for limited angular movement in the direction of reverse rotation of the disc, the braking system further comprising, to the side of the first brake pad remote from the disc, a further plate guided for axial movement towards and away from the disc but angularly fixed relative to the disc, the face of the further plate adjacent the first brake pad having one or more raised sections thereon adapted to engage the face of the first brake pad remote from the disc.

The braking system may include a mechanical parking brake comprising a mechanical piston secured to, to move with, the hydraulically-actuated piston and a lever pivotally mounted on the calliper, one end of the lever engaging the mechanical piston such that, on pivoting movement of the lever, the mechanical piston is displaced whereby the hydraulically-actuated piston is displaced and the braking system is mechanically actuated.

According to a further aspect of the invention there is provided an over-run, auto-reverse hydraulic braking system on a trailer comprising a rotatable brake disc on the trailer, and a movable calliper mounted on the trailer carrying a pair of brake pads one to each side of the disc and a hydraulically-actuated piston, the arrangement being such that, on the application of hydraulic fluid under pressure to the piston resulting from relative movement between the trailer and a towing vehicle towards one another, the first brake pad is urged by the piston into engagement with the disc, the movable mounting of the calliper ensuring that an even braking pressure is subsequently applied to the disc by both brake pads, characterised by a mechanical parking brake comprising a mechanical piston secured to, to move with, the hydraulically-actuated piston and a lever pivotally mounted on the calliper, one end of the lever engaging the mechanical piston such that, on pivoting movement of the lever, the mechanical piston is displaced whereby the hydraulically-actuated piston is displaced and the braking system is mechanically actuated.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a view in section of the hydraulic brake calliper complete with parking brake mechanism, brake disc and brake pads.

Fig. 2 shows an aerial view of the hydraulic brake calliper (the rear in section), carrier and associated components.

Fig. 3 shows a front view of the calliper and carrier.

Fig. 4 shows a rear view of the calliper, parking brake mechanism, and the calliper carrier.

Fig. 5 shows a view, in section, of the calliper guide-pin before securing to the calliper.

Fig. 6 shows a view, in section, of the calliper guide-pin when the pin is secured to the calliper.

Fig. 7 shows an aerial view of the layout of the brake disc, pad and support plate in a rearward mode.

Fig. 8 shows a view of the brake disc with the brake pad in a rearward mode.

Fig. 9 shows an aerial view of the layout of the brake disc, pad and support plate in a forward mode.

Fig. 10 shows a view of the brake disc with the brake pad in a forward mode.

KEY TO DRAWINGS 1. Calliper

2. Carrier 3. Hydraulic Piston 4. Mechanical Piston 5. Hydraulic Piston Seal 6. Mechanical Piston Hydraulic Seal 7. Hydraulic Feed Connection 8. Hydraulic Bleed Connection 9. Mechanical Piston Bush 10. Hydraulic Piston Weather Cover 11. Static Plate Inner 12. Brake Pad Support Plate Inner 13. Brake Pad Inner 14. Brake Disc 15. Brake Pad Outer 16. Brake Pad Support Plate Outer 17. Static Plate Outer 18. Parking Brake Lever Pivot Bolt

19. Parking Brake Lever Nut 20. Spring Washer 21. Spacer 22. Parking Brake Lever 23. Parking Brake Lever Roller 24. Parking Brake Weather Cover 25. Calliper Guide Pin 26. Calliper Guide Pin Bush 27. Guide Pin Retaining Bolt 28. Guide Pin Weather Cover 29. Brake Pad Support Plate Return Spring DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, the brake disc 14 is secured to a road wheel hub (not shown) in the usual manner, the carrier 2 for the calliper, brake pads, brake pad support plates and the static plates is correctly positioned over the brake disc 14 and is secured to the axle or suspension by nuts and bolts or similar means.

Brake pads 13 and 15, brake pad support plates 12 and 16,

and static plates 11 and 17 are correctly positioned within the carrier 2. The brake calliper 1 is correctly positioned and secured to the carrier 2 by guide pins 25 and guide pin retaining bolts 27, thereby enabling only axial movement of the calliper 1 relative to the carrier 2.

Thus should hydraulic pressure be created within the trailer's hydraulic braking circuit (not shown), the guide pins 25 ensure an even pressure is applied to the brake disc 14 by both brake pads 13 and 15 during a reverse manoeuvre. Hydraulic pressure would also be created within the trailer's hydraulic braking circuit (not shown).

Forward or rearward movement will have the same effect on the trailer's hydraulic braking circuit.

In order to reduce the braking effect during a reverse manoeuvre, both brake pads 13 and 15 and brake pad support plates 12 and 16 slide rearwards within their captive channels in the carrier 2. When the inclined face sections of the two parallel raised sections on the brake pad support plate 16 come into line with the right angled edge of the raised parallel sections on the static plate 17 and slide further rearward, both brake pads 13 and 15 are released from pressurised engagement with the brake disc 14. As soon as forward motion is resumed, both brake pads 13 and 15 and the support plates 12 and 16 slide forwards

assisted by the relative friction from the brake pads 13 and 15 against the brake disc 14 and by return springs 29, thus enabling the braking system to return to a fully operational mode automatically.

The trailer's parking brake is mechanically actuated.

The brake calliper 1 houses two pistons in tandem, the hydraulic piston 3 and a mechanical piston 4 attached in tandem to the piston 3 by the rodded end of the piston 4.

Hydraulic seals 5 and 6 ensure that hydraulic brake fluid remains captive within the cylinder of the hydraulic piston 3. At the rear end of the brake calliper is a pivoted parking brake lever 22 pivoting on a bolt 18 and a nut 19, spacers 21 and spring washers 20 being provided one to each side of the parking brake lever 22. At the end of the parking brake lever 22 remote from the mechanical piston 4 provision is made for a parking brake cable (not shown) to be secured. At the other end of the lever 22 is secured a roller 23 which abuts the mechanical piston 4 such that, when force is applied to the parking brake cable (not shown), the pivoted parking brake lever 22 applies a force through the roller 23 to the mechanical piston 4. In turn, said force is applied to the hydraulic piston 3 and to the brake pads 13 and 15, thereby providing a mechanical

parking brake operated by way of a cable operating lever (not shown).

By way of summary, there has been described a hydraulic trailer brake designed for trailers which are permitted to use an over-run, inertia-type auto-reverse braking system.

The hydraulic brake master cylinder (not shown) would be capable of building up hydraulic pressure and relaying said pressure to one or more of the trailer's braking circuits (not shown).

The hydraulic brake calliper piston 3 would be capable of moving the brake-pads 13 and 15 beyond the minimum requirements.

The brake pad support plates 12 and 16 would enable the trailer to be reversed without permitting a force beyond the permitted levels to be applied to the brake disc 14.

The brake pad support plates 12 and 16 would, after a reverse manoeuvre, enable the brake pads 13 and 15 to return automatically to their position for forward motion.

The design of brake pads 13 and 15 and brake pad support plates 12 and 16 would enable trailers travelling

in a forward direction to exceed the minimum requirements with regard to braking efficiency.

The calliper design would accommodate the necessary components required for a mechanical parking brake.

The hydraulically damped tow coupling (not shown) activating the trailer's brake master cylinder (not shown) and any mechanical components linking both together would be set in such a manner as to displace the precise maximum of brake fluid within the trailer's hydraulic braking circuit (not shown). Should any or the maximum amount of brake fluid displacement take place during a reverse manoeuvre, then the brake pad support plates 12 and 16 would alleviate any excessive force from being applied to the brake disc 14 by the brake pads 13 and 15.

The above would provide a balanced braking system for trailers when being applied in a forward, rearward and stationary mode.