GB2326205A

GB2326205A - A trailer overrun braking system

Info

Publication number: GB2326205A
Application number: GB9805346A
Authority: GB
Inventors: Reginald John Henry Strong
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-03-18
Filing date: 1998-03-12
Publication date: 1998-12-16
Anticipated expiration: 2018-03-12
Also published as: GB2326205B; GB9805346D0; GB9705607D0

Abstract

A trailer overrun braking system includes a hydraulically operated disc brake wherein the brake pads are actuated in response to a trailer over-run condition, and are de-activated on reverse motion of the trailer. In one arrangement, the calliper assembly 6 (62, Fig.7) has a lost motion connection 11 (63, 64) to a back plate 9 (61) and, on reverse motion, is moved rearwardly from its normal position thus actuating a pressure relief valve 7 through abutment 12 which bleeds hydraulic pressure from the brake circuit. When the brake is locked by a manual actuator or a valve in the hydraulic circuit the lost motion cannot be taken up and the valve 7 is not operated. A second, manually operable hydraulic circuit (99-101, Fig.9) may be provided. In an alternative embodiment, an electric pressure relief valve is operated by engaging reverse gear and the lost motion connection is not required.

Description

TITLE: Braking Systems for Trailers This invention relates to a braking system for trailers and is particularly concerned with an overrun braking system for road trailers up to 3500 kgs axle weight capacity.

It is known to provide overrun braking systems on trailers and in one form these comprise a mechanical construction utilising cables which operate on brake drums by mechanical means through the force exerted by the trailer on the towing vehicle when the towing vehicle slows down.

A disadvantage with many such constructions is that it is necessary to mechanically disconnect the overrun brake in order to reverse the vehicle and trailer combination. This often entails the driver leaving the vehicle to actuate the appropriate mechanism.

One of the objects of this invention is to provide a braking system for a trailer using hydraulically operated brakes. Another object of this invention is to provide an hydraulic braking system for a trailer which is operated on the overrun but which is automatically rendered inactive during reversing operations.

In accordance with this invention there is provided an overrun braking system for a trailer including a hydraulic master cylinder and ram assembly coupled with the towing mechanism whereby the ram is operated on trailer overrun relative to the towing vehicle with hydraulic trailer wheel brakes being operated through the hydraulic master cylinder, lost motion relative to an associated wheel being provided in at least one trailer wheel brake assembly whereby movement of the wheel brake assembly permitted by the lost motion is operative to actuate a hydraulic pressure relief valve in the wheel brake hydraulic circuit following reverse motion of the trailer which takes up the lost motion through brake drag occurring prior to the relevant wheel brake becoming locked.

In a preferred arrangement movement of the wheel brake assembly is permitted in a linear direction having a component towards or away from the wheel axis whereby locking the brakes throughfan actuating means prior to reverse motion of the trailer is effective to prevent movement of the wheel brake assembly through the lost motion causing actuation of the pressure relief valve.

In a preferred embodiment lost motion is provided between the wheel brake assembly (calliper) and the braking friction surfaces (disc or drum).

In one embodiment the brake callipers acting on the brake discs are mounted to have a limited degree of fore- aft movement with the plunger of a pressure relief valve located at one end of the calliper and arranged so that the valve plunger contacts a fixed abutment on movement of the calliper to thereby relieve hydraulic pressure on the brake pads, allowing the vehicle to reverse the trailer.

Preferably the wheel brake assembly is mounted through cooperating pegs and slots permitting limited linear movement forming the lost motion said slots allowing movement in both a radial and a tangential direction relative to the brake disc Although reference is made herein to fore-aft movement of the calliper, or the brake assembly if a drum system, it will be understood that this relates to the calliper when mounted vertically above the disc axis.

The calliper could be mounted in any convenient orientation whilst achieving the same mechanical effect on reversal of the wheel rotation taking up the lost motion the movement being in a tangential direction.

With a construction of this kind the brake master cylinder ram is actuated mechanically on overrun of the trailer to thereby provide appropriate hydraulic fluid pressure to the disc brake callipers to provide braking for the trailer. On reverse movement of the vehicle the lost motion in the brake calliper is initially arranged to move the calliper physically through drag of the brake pads whereby the pressure relief valve is actuated to bleed off any further pressure increase, thus preventing effective operation of the trailer brakes when reversing.

Although a preferred construction is described in relation to hydraulically operated disc brakes, it is possible to adapt a construction for use with hydraulically operated drum brakes where appropriate lost motion is provided in the brake shoes and hydraulic ram assembly.

Embodiments according to this invention are now described as examples only and with reference to the accompanying drawings showing an arrangement for a trailer using hydraulically operated disc brakes. In the drawings: Figure 1 shows schematically a typical hydraulic circuit, Figure 2 shows lost motion in the disc brake calliper, Figure 3 shows lateral free movement in the disc brake calliper, Figure 4 shows operation during normal overrun braking, Figure 5 shows operation during reversing, Figure 6 shows a modified construction for the calliper assembly during normal braking, Figure 7 shows the assembly of Fig. 6 during reversing, Figure 8 shows schematically an overall arrangement incorporating a hand brake assembly, and Figure 9 shows schematically a further arrangement incorporating a hand brake assembly.

Referring firstly to Figure 1 of the drawings, there is shown a schematic diagram of the hydraulic system which incorporates a brake master cylinder and ram assembly 1. The ram is operated by a coupling rod 2 connected so as to be moved by a conventional overrun mechanism in the tow bar connection between the towing vehicle and the trailer. Low pressure hydraulic fluid is supplied from a reservoir 3 to the master cylinder via a connection 4. High pressure hydraulic fluid is passed along line 5 to feed hydraulic slave cylinders in a disc brake calliper assembly 6.

A pressure switch means 7 is provided by which the fluid from the slave cylinders 6 may be released down line 8 to return to the reservoir 3. The operation of pressure switch 7 is described in conjunction with Figures 2 to 5 of the drawings.

As shown in Figures 2 to 5, the brake calliper slave cylinder assembly 6 is mounted to a back plate 9 by means of pegs or pins 10 which pass through elongated slots 11 in the back plate. As may be seen in Figure 2, the calliper assembly may move fore and aft in the direction of arrows A being parallel to a tangent of the disc, thus giving a degree of lost motion to the mounting of the calliper assembly on the back plate. As shown in Figure 3, there is also a movement laterally as indicated by arrows B. This provides the necessary lateral float of the callipers in relation to the plane of the discs.

Referring more particularly to Figures 4 and 5, as may be seen from Figure 4, during forward motion of the trailer the calliper assembly 6 is maintained in the forward position by virtue of incipient drag between the pads and the brake discs 6a. Overrun of the trailer relative to the vehicle will cause hydraulic pressure to be applied through line 5 and thus initiating braking action of the trailer in a conventional manner. When the vehicle is reversed the trailer initially moves backwards and as shown in Figure 5 the drag between the brake pads and brake discs cause the calliper assembly 6 to move backwards by virtue of the lost motion provided between pins 10 and slots 11. A pressure relief valve is provided having a plunger 7 and during this reverse motion plunger 7 is actuated by contact with a fixed abutment stop 12 which thus relieves the pressure in the brake calliper assembly preventing any substantial braking action occurring. It will be understood that this relief of pressure is automatic on reversing and does not require any action to be taken by the driver of the vehicle.

The pressure relief valve 7 may be situated in any position on the calliper which will enable actuation to be effected as a result of the lost motion. The plunger and stop shown in Figures 2, 4 and 5 illustrate one position for explanatory purposes. A different position which produces the same effect may be preferred.

A separate mechanical or manual hydraulic actuated hand brake assembly may also be included whereby the trailer can be braked against both forward and reverse motion when necessary. To achieve this a valve may be included in the hydraulic circuit to lock-in pressure or a lever provided to apply pressure. In this arrangement the calliper is prevented from moving due to lack of freedom of movement in a radial direction, thus the release of pressure via valve 7 cannot occur. The arrangement provides for a totally sealed hydraulic disc braking system to be used which may function even when the trailer is fully submerged in water.

This was hitherto not possible. A safety wire or chain connection may be provided between the towing vehicle and the trailer which will initiate application of a manual hand brake in the event of separation.

The embodiment of this invention shown in Figures 6 and 7 includes the brake disc 60, brake back plate 61 and calliper 62 which carries the brake actuating piston and cylinder assemblies as well as the brake pads. The assembly includes the pressure relief valve 7 as already described with actuating abutment stop 12. In the normal forward motion direction shown in Fig. 6 the braking system operates in response to overrun and the valve 7 is not operative. In Fig. 7 the reversing direction is shown wherein the drag of the brake pads on the disc 60 displaces the calliper assembly 62 thus operating the pressure relief valve 7 via stop 12. The feature of this construction is the inclined linear axis of the lost motion slots 63 which engage the locating pins 64 on the back plate 6.

This feature, and in accordance with an aspect of this invention, permits the calliper assembly to move in a radial direction which is outward of the disc axis. With this arrangement one of the advantages is that the effect of any play in the assembly is reduced when the brake is applied thus reducing the possibility of the valve 7 being actuated, The arrangement also permits a degree of vertical motion as well as the horizontal motion required for actuation of the valve 7. This is effective because of the immediate application of pressure to the brake pads which locks-up the calliper assembly preventing movement in contrast to the trailer reversing action where pressure is more gradual allowing the calliper to move and thus the pads to slide in a radial direction relative to the disc to activate valve 7.

Figure 8 shows a trailer construction in accordance with this invention and having a chassis 80 vehicle coupling 81 incorporating an over-run mechanism 83 which applies pressure to the piston of a hydraulic master cylinder assembly 82. The master cylinder 82 is supplied from a reservoir 84 and braking pressure is fed through the lines 85 to the calliper slave cylinder assemblies on each of the wheels 86.

Each calliper unit has a reverse motion pressure relief valve 7 not shown here which returns brake fluid via the relief lines 87 to the reservoir 84. In this arrangement one pressure relief valve is needed on any one calliper assembly. A hand brake lever 88 is included on the chassis to apply manual force to the master cylinder piston by means of a cam thus locking up the brakes against both forward and reverse motion. This is a characteristic feature of the invention achieved by the special arrangement of achieving the lost motion which then becomes inoperative to relieve the pressure in this situation. It is a particular advantage that this method avoids separate linkages or independent braking means to function as a.

In the arrangement described there is provided for the incorporation of a normal hydraulic braking system which will provide braking on a stationary trailer by locking the hydraulic pressure in the brake callipers. This then preventing the radial movement of the pads and callipers relative to the disc and as a consequence operation of the pressure relief valve is prevented. However in practical applications there are occasions where it is preferable to use the hand brake to control the motion of the trailer on an incline after it has been disconnected from the towing vehicle. For example when easing a boat trailer down a slipway for launching into water. In the arrangement described any attempt to apply the to the trailer whilst in reverse motion will cause the pressure relief valve to operate and braking action will be lost.

The embodiment shown in Figure 9 overcomes this problem and is designed to retain the benefits of the system described for trailers attached to towing vehicles and, in addition, provides a facility for controlling the motion of an uncoupled trailer on an incline by proportional control manual application of a hand brake.

A normal automotive brake calliper assembly includes two sets of slave cylinders to provide adequate braking with the considerable dynamic forces involved in deceleration of a heavy vehicle. These including so-called "double-pot" callipers. With a towed trailer having an axle weight up to the maximum of 3,500 kgs adequate and effective overrun braking is achieved through a single slave cylinder. This then leaves the second cylinder available for alternative uses.

As shown in Figure 9 this embodiment provides two separate and independent braking systems within the one hydraulic system, the one being the overrun brake as previously described, and the other being a manually operable hand brake operating the trailing cylinder brake pad.

In Figure 9 a trailer chassis 90 has two wheels 91 each with a two slave cylinder brake calliper assembly 92. The chassis has a tow bar 93 with vehicle coupling 94 incorporating the usual over run brake actuating mechanism operating on the hydraulic master cylinder 95 being similar to that already described. The master cylinder 93 has two independent hydraulic cylinders both of which are supplied from a common reservoir 96 via line 97. One of the cylinders 98 is coupled with the telescopic over run brake mechanism incorporated into the tow bar 93 and this provides dynamic over run braking to the leading brake pad of each calliper 92 and as previously described. On reversal of the trailer the pressure relief valve (7) not shown is actuated to bleed fluid back to the reservoir 96 via lines 102. The pressure relief valve is operative on the leading pad cylinder only.

The second cylinder 99 is mechanically connected to a hand brake lever 100 and the manual operation of this causes the cylinder 99 to apply pressure through a separate hydraulic line 101 to the trailing brake pad of each calliper assembly 92.

Thus when the trailer has been disconnected from the towing vehicle manual control is available through the hand brake lever 100 in both the forward and reverse directions as the pressure relief valve is not operative on circuit 101.

An advantage of the all hydraulic system described is that the hydraulic lines can be run within the trailer chassis tubes thus affording protection against damage and deterioration.

This invention provides a construction which enables an hydraulic braking system using disc brakes to be incorporated into a trailer where such arrangements were not previously possible due to the requirement for inhibiting operation of the overrun brake during reversal.

The mechanical lost motion method of pressure relief for reversing is most applicable to trailers on which electrical supply from the towing vehicle will be removed prior to manoeuvring such as boat-carrying trailers at time of launch. However, there are other applications in which the electrical supply to the trailer will remain connected at all times until the towing vehicle is removed, such as caravans. In such cases, an alternative electrical method of pressure relief may be employed whereby the engagement of reverse gear on the towing vehicle will actuate an electric pressure relief valve, such as a solenoid-operated valve, to prevent application of the trailer brakes when reversing. In this embodiment of the application, the lost motion action of the calliper will not be required.

Essentially disc brakes require hydraulic activation which is a reason why they have not previously been employed on trailers using overrun braking. This invention now provides for the use of disc brakes on such trailers being totally independent of the towing vehicle brake system.

Claims

1. An overrun braking system for a trailer including a hydraulic master cylinder and ram assembly coupled with the towing mechanism whereby the ram is operated on trailer overrun relative to the towing vehicle with hydraulic trailer wheel brakes being operated through the hydraulic master cylinder, lost motion relative to an associated wheel being provided in at least one trailer wheel brake assembly whereby movement of the wheel brake assembly permitted by the lost motion is operative to actuate a hydraulic pressure relief valve in the wheel brake hydraulic circuit following reverse motion of the trailer which takes up the lost motion through brake drag occurring prior to the relevant wheel brake becoming locked.

2. An overrun braking system in accordance with Claim 1, wherein movement of the wheel brake assembly is permitted in a linear direction having a component towards or away from the wheel axis whereby locking the brakes through an actuating means prior to reverse motion of the trailer is effective to prevent movement of the wheel brake assembly through the lost motion causing actuation of the pressure relief valve.

3. An overrun braking system according to Claim 1 or 2, wherein the said wheel brakes comprise disc brakes.

4. An overrun braking system according to Claim 1 or 2 or 3, wherein the lost motion is provided in the wheel brake assembly attachment means, the pressure relief valve being located on the brake assembly and arranged so that reverse motion of the trailer takes up the lost motion through brake drag to actuate the valve whereby hydraulic pressure is bypassed or relieved so that the brakes do not effectively operate.

5. An hydraulic braking system for a trailer including a master cylinder and ram assembly, a hydraulic disc brake assembly for each trailer wheel and including a brake calliper unit mounted so as to allow limited movement providing lost motion permitting a degree of radial movement of the calliper relative to the brake disc, and a pressure relief valve or switch means operative to bleed pressure from the brake circuit when the trailer is put into reverse motion the drag of the brake pads taking up the said lost motion.

6. An hydraulic braking system according to Claim 5, wherein the brake callipers acting on the brake discs are mounted to have a limited degree of movement with the plunger of a pressure relief valve located at one end of the calliper and arranged so that the valve plunger contacts a fixed abutment on movement of the calliper to thereby relieve hydraulic pressure on the brake pads, allowing the vehicle to reverse the trailer.

7. A system according to any preceding ciaim, wherein a separate mechanical or manual hydraulic actuated hand brake assembly is included whereby on operation when the trailer is stationary the brakes are locked preventing lost motion movement and thus pressure relief, the trailer being braked against both forward and reverse motion when required.

8. A system according to Claim 7, wherein a valve is included in the hydraulic circuit to lock-in pressure or a lever provided to apply pressure.

9. A system according to Claim 7 or 8, wherein each brake assembly includes two braking means the one being coupled with the over run braking system and the other being operatively coupled with an independently operable brake, preferably a manually actuated hand brake effective on both forward and reverse movement of the trailer.

10. A system according to any preceding claim, including a safety wire or chain connection provided between the towing vehicle and the trailer which will initiate application of a manual hand brake in the event of separation.

11. A system according to any preceding claim, modified whereby an electrically actuated pressure relief valve is provided to by-pass or relieve hydraulic pressure.

12. A system according to Claim 11, wherein the pressure relief valve is actuated through an electrical switch responsive to reversing motion.

13. A system according to Claim 11, wherein the pressure relief valve is actuated through a connection or switch responsive to engagement of reverse gear of the towing vehicle.

14. An overrun braking system for a trailer including a hydraulic master cylinder and ram assembly coupled with the towing mechanism whereby the ram is operated on trailer overrun relative to the towing vehicle, and wherein a first set of trailer wheel brakes are operated by a hydraulic cylinder assembly operatively coupled with the master cylinder wherein lost motion is provided in the trailer wheel brake assembly which actuates a hydraulic pressure relief valve on reverse motion of the trailer which takes up the lost motion, a second set of wheel brakes being operatively coupled with a manually actuated hand brake means, the second set of brakes being independent of the first set.

15. An overrun braking system in accordance with any preceding Claim wherein the wheel brake assembly is mounted through cooperating pegs and slots permitting limited linear movement forming the lost motion said slots allowing movement in both a radial and a tangential direction of the brake disc.

16. An overrun braking system for a trailer in accordance with any preceding Claim, wherein the brake assembly comprises a double pot (piston) hydraulic disc brake unit, one piston being connected in a hydraulic circuit operated through the overrun system, the other piston being coupled with an independent circuit having a separate actuating means.

17. An overrun braking system for a vehicle as described herein and exemplified and with reference to the drawings.

18. A trailer adapted to function and incorporating a system as claimed herein or as exemplified with reference to the drawings.

19. A tractor vehicle and trailer combination including a system as described herein and exemplified or as claimed herein.