WO1997038880A1

WO1997038880A1 - Trailer vehicle brake operating system

Info

Publication number: WO1997038880A1
Application number: PCT/GB1997/001018
Authority: WO
Inventors: John Harvey Milnes
Original assignee: John Harvey Milnes
Priority date: 1996-04-12
Filing date: 1997-04-14
Publication date: 1997-10-23
Also published as: AU2517297A; GB9607603D0

Abstract

The invention provides a trailer vehicle having a braking system, comprising at least one wheel brake and brake-actuating means (90) for applying and releasing the brake or brakes, the vehicle comprising a secondary brake applicator system comprising a ground-engageable member (113) extending from the trailer, said member being operatively connected to the brake actuating means (90) such that when said member engages the ground a force is transmitted to the brake actuating means to cause the brake or brakes to be applied.

Description

Trailer Vehicle Brake Operating System Field of the Invention

This invention relates to systems for operating the braking system of trailer vehicles, in particular to systems for operating the braking sys- tems of trailer vehicles when detached from a towing vehicle. Background to the Invention

Trailer vehicles (hereinafter called trailers) consist of a chassis, at one end of which there is mounted a towing bracket for attachment to a towing vehicle, and at least one axle mounted on the chassis, the or each axle being provided with at least one wheel or tracklaying assembly on each end thereof.

Trailers fall generally into two types, and these types are often known as unbalanced trailers and balanced trailers.

An unbalanced trailer has at least one axle mounted to the chassis to the rear of the centre of the trailer, so that the trailer is front heavy. In use, whilst the major part of the weight of the trailer and its load is car¬ ried by the wheels or track-laying assemblies on which the trailer is mounted, a proportion of the weight is carried by the towing vehicle be¬ cause the trailer is front heavy. When the trailer is removed from the tow- ing vehicle the trailer chassis pivots relative to the axle until the towing bracket comes to rest on the ground. To support the trailer when detached from a towing vehicle a skid, jack or jockey wheel is often located forward of the centre of the trailer.

A balanced trailer has at least two axles mounted to the chassis at spaced apart locations, so that the weight of the trailer is carried by the axles. Balanced trailers may or may not have on one or more of the axles wheels which are steerable. One type of balanced trailer often used for agricultural or road haulage purposes has one or more axles towards the rear of the trailer and an axle towards the front of the trailer. The axle towards the front of the trailer is either mounted on a turntable or has a fixed axle and steerable wheels. A drawbar is connected to the front axle, the towing bracket being part of the drawbar. When the trailer is discon¬ nected from the towing vehicle, the towing bracket comes to rest on the ground. A skid, jack or jockey wheel is sometimes provided to support the drawbar at a convenient height for attachment to a towing vehicle. It is known for the front axle to be removably attachable to the trailer. Such a drawbar and axle assembly is often known as a "dolly".

Generally trailers are equipped with braking systems. This is so that the speed of the trailer can be controlled, both when it is being towed by a towing vehicle and when the trailer is detached therefrom. In most systems, to control the speed of a trailer when it is detached from the towing vehicle, a hand brake which an operator applies manually is provided. The hand brake may operate the trailer's braking system, or may be a separate system. Typically, the braking systems of trailers, such as caravans, suitable for towing behind a car are operated by means of a cable. In these systems the hand brake acts on the cable to apply the brakes. Other trailers, such as agricultural trailers, are commonly pro¬ vided with hydraulic actuators to apply the trailer's brakes. This requires the provision of a separate cable operated hand brake system. Such hand brakes are generally mounted on the drawbar (which forms part of the chassis) of the trailer to the front of the trailer body. In the case of an agri¬ cultural trailer, to apply the hand brake it is necessary for a person, usually the driver of the towing vehicle, to move into the space between the rear of the towing vehicle and the trailer body. This is highly danger¬ ous. Each year many accidents occur when people are in this location. When a trailer unit, comprising a towing vehicle and a trailer, is being operated by one man, the need for the operator to dismount from the vehi¬ cle to apply the hand brake reduces the productivity of the operator.

Many countries require trailers used for road haulage to be equipped with air brakes. Trailers having air brakes may be provided with a cable operated hand brake, and the hand brake may be to the front, the side, and often underneath the trailer body. The operation of a hand brake in such a location is potentially dangerous.

Accidents often occur where a trailer is parked on a slope, and in¬ sufficient braking force is applied, the result being that the trailer runs away down the slope. Also, each year a significant number of trailers be- come detached from towing vehicles. Such detached trailers are out of con¬ trol and present an extreme hazard.

For these reasons it would be desirable to provide a trailer braking system which does not suffer from these disadvantages.

Many types of trailer, especially trailers towed by cars and agricul- tural trailers, are not equipped with a fail safe system to apply the trailer brakes in the event of the trailer becoming detached from the towing vehi¬ cle. This is highly dangerous. Detachment of the trailer often occurs whilst the trailer is being towed. This can be due to failure of a part of the towing assembly (the towing vehicle's towbar and the trailer's drawbar and the means connecting the two) which may be due to poor maintenance, the use of unsuitable materials for components, or human error. The result of a trailer becoming detached from a towing vehicle is often a collision with another vehicle. This can cause not only financial loss, but also personal injury and death. It would therefore be desirable to provide a trailer with a braking system which would mitigate the consequences of a trailer be- coming detached from its towing vehicle. Summary of the Invention

The invention provides a trailer vehicle having a braking system, comprising at least one wheel brake and brake-actuating means for apply¬ ing and releasing the brake or brakes, the vehicle comprising a secondary brake applicator system comprising a ground-engageable member extend¬ ing from the trailer, said member being operatively connected to the brake actuating means such that when said member engages the ground a force is transmitted to the brake actuating means to cause the brake or brakes to be applied. The trailer may be an unbalanced or a balanced trailer.

Preferably, said force is proportional to the force exerted by the ground-engageable member on the ground.

Preferably, the ground-engageable member is operatively connected to the brake actuating means by a control means adapted to control the brake actuating means.

Preferably, when the trailer is coupled to a towing vehicle in a safe position for towing, the ground-engageable member is clear of the ground, and when the trailer is de-coupled from the towing vehicle, the ground- engageable member engages the ground. The control means may be mounted on the chassis of the trailer. Preferably, the control means is mounted on the chassis of the trailer for¬ ward of the or each axle, and more preferably on the drawbar of thereof.

Preferably, the control means comprises a linkage connectable at one end to the ground-engageable member, and at the other end to the brake actuating means. Alternatively, the control means may comprise an electrical or electronic sensor to sense whether the ground-engageable member is in engagement with the ground or not. The control means may be further provided with means to operate the brake actuating means upon receiving a signal from the sensor.

The linkage may be adapted to provide for adjustment of the height of the ground-engageable member relative to the ground and the trailer. Advantageously, the linkage comprises a return spring which biases the control means to its non-brake actuating position. The control means may comprise a source of compressed air, which compressed air is adapted to operate the brake actuating means. The con¬ trol means may be adapted to operate the brake actuating means upon release the compressed air.

The brake actuating means may comprise at least one hydraulic cylinder.

In one embodiment, the brake actuating means comprises a first hydraulic actuating means comprising a piston and cylinder, and a second hydraulic actuating means comprising a piston and cylinder. The first hydraulic actuating means is preferably attached to the control means. The second hydraulic actuating means preferably acts upon the trailer brake or brakes. The first and second hydraulic actuating means are preferably hydraulically connected to each other so that hydraulic fluid can flow therebetween so as to form a brake actuating circuit, the volume of hydraulic fluid contained therein remaining constant. Preferably, in use, when the ground-engageable member engages the ground a force is exerted upon the first hydraulic actuating means causing the piston to move with respect to the cylinder effecting a change in the volume of hy¬ draulic fluid contained therein the said change in volume being accounted for by an equal change in volume of hydraulic fluid contained in the sec¬ ond hydraulic actuating means, which change in volume causes the piston and cylinder of the second hydraulic actuating means to move with respect to each other, which movement applies the brakes.

The first hydraulic actuating means may comprise first and second piston and cylinder assemblies. The first and second piston and cylinder assemblies are preferably connected in series, and more preferably the diameter of the piston of the first piston and cylinder assembly is smaller than the diameter of the piston of the second piston and cylinder assem¬ bly, and still more preferably the diameter of the piston of the first piston and cylinder assembly is 30 to 70 percent smaller than the diameter of the piston of the second piston and cylinder assembly, and advantageously the diameter of the piston of the first piston and cylinder assembly is 50 per¬ cent smaller than the diameter of the piston of the second piston and cyl¬ inder assembly. The second cylinder of the first hydraulic actuating means may be hydraulically connected the second hydraulic actuating means so that hydraulic fluid can flow therebetween. By providing a second piston of increased diameter, the force exertable on the second hydraulic actuat¬ ing means may be increased. The piston of the first piston and cylinder assembly of the first hy¬ draulic actuating means is preferably attached to the control means.

A pressure relief system may be provided in the brake actuating circuit formed by the first hydraulic actuating means the second hydraulic actuating means and the hydraulic connection between the two said means. Preferably, the pressure relief system comprises a pressure relief valve connected in series with an accumulator, the said pressure relief valve and accumulator being connected in series with the brake actuating circuit. An accumulator comprising a pressure relief valve may be provided, and preferably, the accumulator is provided with a pressure gauge.

The brake actuating means may comprise a cable, whereby move¬ ment of the ground-engageable member causes the tension in the said cable to increase, which increase in tension applies the brakes. In one embodiment, there is provided an unbalanced trailer, such as a caravan, with an over-run braking system to operate the wheel brakes, wherein the control means is adapted to act upon the brake actuating means of the over-run braking system.

Preferably, the ground-engageable member is in the form of a skid or a wheel, which wheel may be a castor wheel.

In another embodiment of the invention the brake actuating means comprises at least one hydraulic brake actuator, an hydraulic circuit com¬ prising a plurality of inter-connected bores through which hydraulic fluid may flow, a direction control valve operably connected to the control means and means to pressurize the hydraulic fluid, the hydraulic circuit being connectable to an hydraulic supply and to the or each hydraulic brake actuator, wherein upon engagement of the ground-engagable mem¬ ber with the ground, the control means moves the direction valve to a posi¬ tion which allows hydraulic fluid to flow from means to pressurize the hydraulic fluid to the hydraulic brake actuator. The hydraulic fluid may be a liquid, such as hydraulic oil, or a gas, such as air.

The means to pressurize the hydraulic fluid may be an accumulator, a compressor, which may be electrically powered, or an hydraulic pump, which may be an electrically powered pump. The compressor may be driven by an electric motor. The hydraulic pump may be driven by an electric motor. Where a compressor and an hydraulic pump are provided, they may be driven by separate electric motors or a common electric motor.

The hydraulic supply may be the hydraulic system of the towing vehicle, or an hydraulic supply mounted on the trailer itself. Such an hy¬ draulic supply mounted on the trailer itself may comprise a compressor, and the said compressor may be driven by a motor, for example an electric motor.

Preferably a shuttle valve is provided which permits hydraulic fluid to flow selectively either from the towing vehicle, or from the accumulator to the hydraulic brake actuator. The shuttle valve may also permit the return of fluid from the hydraulic brake actuator to the hydraulic system of the towing vehicle.

Advantageously, a reservoir is provided, the said reservoir receiving any hydraulic fluid returned from the hydraulic brake actuator. The reservoir may be pressurized, and such pressurization may be achieved by resiliently biasing, e.g. spring loading, one wall of the reser¬ voir, so that the hydraulic fluid contained in the reservoir is under suffi¬ cient pressure to return the hydraulic fluid contained therein to the hydraulic system of the towing vehicle.

The accumulator is suitably charged to in excess of 100 bar, and most suitably to 108 bar.

A check valve may be provided which permits hydraulic fluid to flow to the accumulator whilst the direction valve permits hydraulic fluid to flow from the towing vehicle to the hydraulic brake actuator.

A check valve may be provided which prevents hydraulic fluid flow¬ ing from the hydraulic system of the towing vehicle to the reservoir. Pref¬ erably, the same check valve permits return of the hydraulic fluid from the reservoir to the hydraulic system of the towing vehicle. A plurality of accumulators may be provided, and at least two of the said accumulators may be connected in series.

A plurality of reservoirs may be provided, and at least two of the said reservoirs may be connected in series.

The hydraulic circuit is preferably connectable to the hydraulic sys- tem of the towing vehicle by means of a connector which may be adapted to break if the trailer accidentally becomes detached from the towing vehi¬ cle. The hydraulic circuit may be connected to the hydraulic system of the towing vehicle by means of a connector comprising a spool valve which prevents the flow of hydraulic fluid when disconnected from the towing vehicle and permits the flow of hydraulic fluid when connected to the tow¬ ing vehicle. The control means may comprise an electrical, or electronic sensor, such as a pressure sensor, which senses whether the ground engageable- member is in engagement with the ground or not, the sensor providing a signal to an actuator arranged to move the direction valve to permit the flow of hydraulic fluid either from the hydraulic supply, or from the means to pressurize the hydraulic fluid, to the hydraulic brake actuator upon receipt of a signal.

In operation, when the ground-engagable member engages the ground, either because it has been lowered purposely, or because the trailer has become detached from the towing vehicle, the direction control valve prevents hydraulic fluid flowing from the towing vehicle and permits hydraulic fluid to flow from the accumulator to the hydraulic brake actuator.

The invention provides a particularly advantageous system for ap- plying a trailer's brakes, which is simple and relatively inexpensive. Trail¬ ers provided with this braking system are inherently safer than other trailers, since the weight of the trailer causes the trailer's brakes to be applied as soon as the ground-engageable member engages the ground. Furthermore, in one embodiment the braking force increases proportion- ally with the force exerted by the ground-engageable member on the ground, which in turn depends on the weight of the trailer and its contents.

Trailers according to the invention are particularly suitable for tow¬ ing by a tractor equipped with an automatic hitch. Such a tractor and trailer combination allows the operator to be significantly more produc¬ tive, since he does not need to leave the tractor seat when de-coupling the trailer from the tractor. Furthermore, he does not need to enter the danger area between the rear wheels of the tractor and the front of the trailer.

Another advantage of the invention is that a fail safe mechanism for braking the trailer is provided. Brief Description of the Drawings

In the drawings, which illustrate exemplary embodiments of the invention:

Figure 1 is a side view of an unbalanced trailer vehicle brake oper¬ ating system; Figure 2 is a schematic representation of a trailer braking system which may be operated by the system shown in Figure 1;

Figure 3 is a side view of a trailer equipped with the brake operat¬ ing system as shown in Figure 1, with the trailer not attached to a towing vehicle and the brakes applied; Figure 4 is a side view of the trailer as shown in Figure 3, with the trailer in a towing position and the brakes released;

Figure 5 is a front view of the first hydraulic actuating means; Figure 6 is a sectional view along line A-A, of the first hydraulic actuating means shown in Figure 5; Figure 7 is a side view of a trailer chassis having a brake actuating means according to another embodiment of the invention; and

Figure 8 is a view side view of the brake actuating means shown in Figure 7. Detailed Description of the Preferred Embodiments

In Figure 1 a section of a trailer chassis, which in this case is a sec¬ tion of the drawbar, is generally indicated at 1. To the drawbar there is attached a control means 2 and brake actuating means 3. In the following description links provided on one side of drawbar 1 are described. However, the linkage comprises identical links provided on the opposite side of drawbar 1. Where pins are provided for pivotally at¬ taching links to each other or to the drawbar, any suitable pin may be used. Typically, bolts secured by nuts and washers or pins secured by re- movable clips are used.

Control means 2 is provided with a ground-engageable member 4 comprising a skid plate 5 to the upper surface of which are attached brack¬ ets 6 with apertures. The lower surface of skid plate 5 engages the ground to apply the brakes. Control means 2 comprises a linkage made from a plurality of link members. The link member 7 connected to the ground- engageable member 4 comprises two links 8, 9. Each end of link 8 is pro¬ vided with an aperture 10. One end of link 8 is pivotally attached, by means of a pin (not shown) to brackets 6 of ground-engageable member 4. The other end of link 8 is rigidly attached to one end of link 9. Link 9 is provided with apertures to enable attachment to other links or the draw¬ bar by means of pins. Where links 8 and 9 are attached apertures which co-operate with each other, and with a corresponding aperture in the drawbar 1 are provided. Link member 7 is pivotally mounted to drawbar 1 by passing a pin (not shown) through the said apertures. Link 9 is provided with a second aperture 11, to which link 13 is pivotally attached by means of a pin (not shown). At its other end link 13 is provided with a second aperture for attachment to link 14 by means of a pin (not shown), the link 14 also being provided with an aperture to co¬ operate with the said pin. The length of link 13 may be adjustable, so that the height of skid plate 5 of ground-engageable member 4 relative to the ground and the drawbar may be varied.

Link 14 is provided with apertures 15 at each end thereof and an aperture 16. One end of link 14 is pivotally attached to drawbar 1 by means of a pin (not shown) which passes through aperture 15 and draw¬ bar 1. The other end of link 14 is pivotally attached, by means of a pin (not shown) to the piston 31 of the first piston and cylinder arrangement of the first hydraulic actuator 30 (shown in greater detail in Figures 5 and 6), which first hydraulic actuator 30 is a part of the brake actuating means 3.

Link 14 is pivotally connected to one end of link 17 by means of a pin (not shown) passing through aperture 16 and a corresponding aperture in link 17. The other end of link 17 is provided with an aperture 18.

Link 19 is pivotally attached to drawbar 1 by means of a pin (not shown) passing through central aperture 20 and a corresponding aperture in drawbar 1. Each end of link 19 is provided with apertures 21. Link 19 is attached to link 17 by passing a pin through one of the apertures 18 and the lower aperture of apertures 21. To the other end of link 19, there is pivotally mounted a cradle 22. Pivotal attachment is achieved by means of a pins 23 extending outwardly from cradle 22. The movement of skid plate 5 of ground-engageable member 4, towards and away from drawbar 2 therefore causes movement of the hydraulic actuator 30 forwards or back- wards in direction "Y". First hydraulic actuator 30 further comprises second piston and cylinder arrangement 35 which is supported by cradle 22. First and second piston and cylinder arrangements are provided with shut-off valves 32 and 34, to which hydraulic lines 33 may be attached for filling the hydraulic actuators 30, 40 with hydraulic fluid, or for removing hydraulic fluid from the said actuators. Shut-off valve 34 further provides for hydraulic connec¬ tion of the first hydraulic actuator 30 to the second hydraulic actuator 40 by means of hydraulic line 36. Hydraulic connections are not shown in detail as they are well known in the art. A pressure relief valve connected in series with an accumulator may be connected in parallel with hydraulic line 36. Such an arrangement allows the hydraulic pressure in line 36, and hence hydraulic actuators 30 and 40 to be limited. The accumulator is pressurized so that hydraulic fluid contained therein is returned when the pressure in hydraulic line 36 decreases to below a chosen limit. The provi- sion of the pressure relief valve and accumulator allows excessive pres¬ sure, which can occur when the trailer is heavily laden, to be avoided.

Brake actuating means 3 comprises first hydraulic actuator 30 and second hydraulic actuator 40, the said actuator 40 being attached to a fixed point 42. Figure 2 shows second hydraulic actuator 40 connected to a braking system 50 comprising brake shoes 51 held apart by cam 52, and biased together by spring 53. Piston 41 of hydraulic actuator 40 is connected to bar 54, at each end of which there is mounted a lever 55. Each lever 55 is attached to cam 52, and by extending piston 41, cam 52 rotates moving brake shoes 51 apart, thereby applying the brakes. A means to take up wear of brake shoes 51 may also be provided. This may take the form of a threaded adjuster adapted to move mounting point 42, or alternatively the length of piston 41 may be adjustable. The means to take up wear of the brake shoes 51 is not described in detail as such devices are well known to the man skilled in the art, and are readily available.

In use, as the drawbar is lowered, the underside of skid plate 5 en¬ gages the ground, causing link member 7 to pivot about its mounting to the drawbar 1. This pivotal movement pushes link 13 backwards causing link 14 to pivot about is mounting to the drawbar 1, pulling link 17 back¬ wards, causing link 19 to pivot about pivot point 20 and moving the hy¬ draulic actuator 30 forwards in the direction "Y". The pivotal movement of link 14 also pushes piston 31 into cylinder 37 forcing hydraulic fluid through aperture 39 into cavity 38 of second piston and cylinder arrange- ment 35. This forces piston 28 to move in the direction "X" as shown in Figure 6, forcing hydraulic fluid out of cavity 27 via aperture 25 and shut- off valve 34 through hydraulic line 36 and into second hydraulic actuator, thus extending piston 41 and applying the brakes 50.

Referring to Figure 3, which illustrates a trailer 60 comprising a chassis 65 provided with a towing bracket 61 and a trailer body 66, the said chassis being pivotally mounted on a bogey 64 which mounts wheels 63. To the chassis there is attached the trailer brake operating system 70 which is as shown in Figure 1 connected to the braking system 80 as shown in Figure 2. The weight of the trailer is supported by wheels 63, and the skid plate, thereby applying the brakes in the manner described above. Figure 4 shows the trailer illustrated in Figure 3 in a safe towing position, the front end of the trailer being lifted clear of the ground. The towing vehicle would be a tractor equipped with an automatic hitch, and since such a vehicle is well known it is not shown. Referring also to Fig- ures 1,2, 5 and 6, as the drawbar is raised to a position safe for towing as shown in Figure 4, the underside of skid plate 5 disengages the ground, causing link member 7 to pivot about its mounting to the drawbar 1. This pivotal movement pulls link 13 forwards causing link 14 to pivot about is mounting to the drawbar 1. This pivotal movement of link 14 causes hy- draulic actuator 30 to move backwards in direction Y and pulls piston 31 out of cylinder 37 drawing hydraulic fluid through aperture 39 out of cav¬ ity 38 of second piston and cylinder arrangement 35. This forces piston 28 to move in the direction "Z" as shown in Figure 6, drawing hydraulic fluid out of second hydraulic actuator through hydraulic line 36 and into cavity 27, thus retracting piston 41 and releasing the brakes 50.

Drawbar 1 may be provided with a jack to enable the towing bracket 61 to be raised to a suitable height for attachment to a towing vehicle. Such a jack would be necessary where the towing vehicle is not provided with an automatic hitch. Referring now to Figures 7 and 8, there is shown a trailer chassis

118 having a towing bracket 115 mounted on one end of drawbar 114, and an axle mounting wheels 116, the wheels being provided with brakes (not shown) which are actuated by brake actuating ram 117. The chassis 118 is provided with a brake actuating means 90 which comprises a manifold (the outline of which is shown in broken lines), having a plurality of bores 94 to 97 and 103, 104. Bore 94 extends out of the manifold as a pipe which is connected by connection means 93 to a pipe 92 which is in turn connected to the hydraulic system of a towing vehicle, e.g. a tractor, by connecting means 91. Connection means 93 features a point of weakness so that if the trailer becomes detached from the towing vehicle, connection means will fail so that the hydraulic fittings of the towing vehicle are not damaged. A shut-off valve (not shown) may be provided in order to be able to isolate the brake actuating means 90. Such shut-off valves are well known in the art and are therefore not described in detail herein. The shut-off valve may be provided in bore 94 or 95. As can be best seen from Figure 8, bores 95 and 97 are provided with check valves 98 and 99. Bore 97 is provided with an hydraulic accumulator 101 downstream of check valve 99, and downstream of accumulator 101 there is located a two-way valve 102. Shuttle valve 100 mounted in bore 96 permits the flow of hy¬ draulic fluid to the brake actuating ram 117 via bore 103, which fluid emanates either from the towing vehicle or from the accumulator 101. Bore 95 is equipped with an hydraulic fluid reservoir 105 of variable vol¬ ume. One face 106 of reservoir 105 is moveable against the bias of coil spring 107.

Referring to Figure 8, when lever 108 is in the position shown in solid lines the flow of hydraulic fluid from the accumulator 101 down¬ stream through bore 97 is closed off. Hence hydraulic fluid can flow from the hydraulic supply of the towing vehicle through bores 96 and 103 to operate the brakes when the brakes of the towing vehicle are operated. When the trailer is lowered, lever 108 is moved to the position shown in broken lines and hydraulic fluid flows from the accumulator 101 through the two way valve 102 moving the ball in shuttle valve 100 to the left so that fluid flows through the bore 103 to the brake actuating rams 117. When the trailer is raised, the lever 108 returns to the position shown in solid lines shutting off the supply of hydraulic fluid from the accumulator 101. The ball in shuttle valve 100 is still to the left and thus the hydraulic fluid returning from the brake actuating rams 117 as the brakes are re¬ leased flows through bore 96, two-way valve 102 and bores 97, 104 and 95. If the trailer is connected to the hydraulic system of a towing vehicle by pipe 92 the hydraulic fluid will simply return through pipe 92 to the said hydraulic supply. If, however, the shut-off valve (not shown) is closed so as to isolate the manifold 90, e.g. because the trailer has been discon¬ nected from the towing vehicle the hydraulic fluid returning from the brake actuating rams 117 fills the reservoir 105. When the shut-off valve is open and the pipe 92 is re-connected to the hydraulic supply of the tow¬ ing vehicle the hydraulic fluid contained in the reservoir simply returns to the said hydraulic supply. The provision of a reservoir 105 enables a trailer which has been parked to be moved by a towing vehicle without needing to connect to the hydraulic supply of the towing vehicle. Where it is desirable to move a trailer from place to place each time parking the trailer, and where time is of the essence, it may be advantageous to be able to apply and release the brakes without needing to connect the pipe 92 to the hydraulic supply of the towing vehicle. This can be achieved either by providing a plurality of accumulators 101 and a plurality of res¬ ervoir 105, and/or by providing an accumulator and reservoir having larger capacities than accumulator 101 and reservoir 105. Referring now to Figure 7 is particular, a control means to control the brake actuation means is shown, the control means comprising a rod 109 linked at one end to lever 108 of two-way valve 102 and at the other end to a pivotally mounted shoe 111. The shoe 111 is pivotally mounted about a pivot point 112, and the effect of shoe 111 pivoting clockwise is to move rod 109 to the right which causes two-way valve 102 to change posi- tion allowing hydraulic fluid to flow from accumulator 101 to bore 103 via bore 96 and shuttle valve 100. The ball shown in shuttle valve 100 moves to the left due to the increase in pressure caused by the flow of hydraulic fluid from the accumulator 101 and closes off flow of hydraulic fluid through bore 96 from the towing vehicle. The shoe 111 shown in Figure 7 is mounted inside a larger shoe

113. The larger shoe 113 may be the existing shoe of a trailer when the braking system of the invention is fitted as a retro-fit kit to a trailer. Of course, either or both shoes 111, 113 may be comprise a wheel.

In operation, if the trailer accidentally becomes detached from the towing vehicle, or is parked and removed from the towing vehicle, supply of hydraulic fluid to the brake actuation means 90 is disconnected so that hydraulic fluid cannot escape from tube 94. As the drawbar 114 is low¬ ered to the ground shoe 113 engages the ground thus causing shoe 111 to pivot about pivot point 112. This results in lever 108 of two-way valve 102 being moved to permit the flow of hydraulic fluid from the accumulator 101 through bore 103. When the trailer is re-attached to the towing vehi¬ cle the drawbar is lifted upwards lifting shoe 113 clear of the ground, which in turn moves lever 108 and thus changes the position of two-way valve 102 to divert the flow of hydraulic fluid from the accumulator 101 to bore 104 and from there to bore 95 and reservoir 105. The hydraulic brake ram 117 is operated in normal fashion since hydraulic fluid from the hydraulic system of the towing vehicle passes along bore 96 forcing the ball of shuttle valve 100 to the right and allowing flow of fluid through the said valve to bore 103.

As hydraulic fluid flows through bore 96, excess fluid flows through bore 97 and accumulator 101 fills with fluid until it has reached a pres¬ sure of approximately 108 bar. When the pressure in accumulator 101 has reached 108 bar fluid a pressure relief valve releases hydraulic fluid from the accumulator. The accumulator 101 is preferably provided with means to adjust the pressure relief valve, and a pressure gauge so that an opera- tor can check that the accumulator is suitably adjusted or make any nec¬ essary adjustments.

In one embodiment of the invention, where the trailer chassis 118 is provided with a tipping body, which body is tipped by an hydraulic actua¬ tor, an hydraulic connection may be made between the hydraulic supply line to the tipping actuator, and the brake actuating means 90 so as to charge the accumulator 101 each time the trailer body is tipped the accu¬ mulator is charged. Such a hydraulic connection may be in the form of an hydraulic line into bore 97 upstream of accumulator 101. A check valve would be provided in the line to prevent the return of fluid. It will be appreciated by one skilled in the art that the brake actu¬ ating means may either be primed with hydraulic fluid before being first connected to a towing vehicle, or be primed by the operation of the towing vehicles brakes which forces fluid through pipe 92. The manifold may be replaced by pipes and valves without departing from the invention. The embodiment of the invention shown in Figures 7 and 8 is par¬ ticularly advantageous because the hydraulic pressure to operate the brake actuating ram 117 is generated by the pressurization of the accumu¬ lator 101. The control means simply acts as a trip switch to control the supply of fluid to ram 117. This means that the brake actuating means can be used where there is only a low weight on the towing bracket of the trailer (e.g. a balanced trailer or an unbalanced trailer with only a small proportion of the weight carried by the towing vehicle), since only a small amount of weight is required to move the two-way valve 102.

Claims

1) A trailer vehicle having a braking system, comprising at least one wheel brake and brake-actuating means for applying and releasing the brake or brakes, the vehicle comprising a secondary brake applicator system comprising a ground-engageable member extending from the trailer, said member being operatively connected to the brake actuating means such that when said member engages the ground a force is trans¬ mitted to the brake actuating means to cause the brake or brakes to be applied. 2) A trailer according to Claim 1, wherein the ground-engageable member is operatively connected to the brake actuating means by a con¬ trol means adapted to control the brake actuating means.

3) A trailer according to Claim 1 or Claim 2, wherein when the trailer is coupled to a towing vehicle in a safe position for towing, the ground-engageable member is clear of the ground and the brake or brakes are released, and when the trailer is de-coupled from the towing vehicle, the ground-engageable member engages the ground causing the brake or brakes to be applied.

4) A trailer according to Claim 2 or Claim 3, wherein the control means is mounted on the chassis of the trailer.

5) A trailer according to any one of Claims 2 to 4, wherein the control means comprises a linkage connectable at one end to the ground- engageable member, and at the other end to the brake actuating means.

6) A trailer according to any preceding claim, wherein the brake actuating means comprises at least one hydraulic actuating means. 7) A trailer according to Claim 6, wherein the brake actuating means comprises a first hydraulic actuating means comprising a piston and cylinder, and a second hydraulic actuating means comprising a piston and cylinder. 8) A trailer according to Claim 7, wherein the first hydraulic ac¬ tuating means is attached to the control means.

9) A trailer according to Claim 7, wherein the second hydraulic actuating means acts upon the trailer brake or brakes.

10) A trailer according to any of Claims 7 to 9, wherein the first and second hydraulic actuating means are hydraulically connected to each other so that hydraulic fluid can flow therebetween so as to form a brake actuating circuit, the volume of hydraulic fluid contained therein remain¬ ing constant.

11) A trailer according to Claim 10, wherein when the ground- engageable member engages the ground a force is exerted upon the first hydraulic actuating means causing the piston to move with respect to the cylinder effecting a change in the volume of hydraulic fluid contained therein the said change in volume being accounted for by an equal change in volume of hydraulic fluid contained in the second hydraulic actuating means, which change in volume causes the piston and cylinder of the sec¬ ond hydraulic actuating means to move with respect to each other, which movement applies the brakes.

12) A trailer according to any of Claims 7 to 12, wherein the first hydraulic actuating means comprises first and second piston and cylinder assemblies. 13) A trailer according to Claim 12, wherein the first and second piston and cylinder assemblies are connected in series.

14) A trailer according to Claim 13, wherein the diameter of the piston of the first piston and cylinder assembly is smaller than the diame- ter of the piston of the second piston and cylinder assembly.

15) A trailer according to any of Claims 12 to 14, wherein the piston of the first piston and cylinder assembly of the first hydraulic actu¬ ating means is attached to the control means.

16) A trailer according to any of Claims 1 to 5, wherein the brake actuating means comprises a cable, whereby movement of the ground- engageable member causes the tension in the said cable to increase, which increase in tension applies the brakes.

17) A trailer according to Claim 1, wherein the braking system is an over-run braking system, and wherein the control means is adapted to act upon the brake actuating means of the over-run braking system.

18) A trailer according to any of Claims 1 to 5, wherein the brake actuating means comprises at least one hydraulic brake actuator, an hy¬ draulic circuit comprising a plurality of inter-connected bores through which hydraulic fluid may flow, a direction control valve operably con- nected to the control means and means to pressurize the hydraulic fluid, the hydraulic circuit being connectable to an hydraulic supply and to the or each hydraulic brake actuator, wherein upon engagement of the ground-engagable member with the ground, the control means moves the direction valve to a position which allows hydraulic fluid to flow from means to pressurize the hydraulic fluid to the hydraulic brake actuator. 19) A trailer according to Claim 18, wherein the hydraulic fluid is a liquid, or a gas.

20) A trailer according to Claim 18 or 19, wherein the means to pressurize the hydraulic fluid is an accumulator, a plurality of accumula- tors, and/or a compressor, and/or an hydraulic pump.

21) A trailer according to any of Claims 18 to 20, wherein a shut¬ tle valve is provided in the hydraulic circuit which permits hydraulic fluid to flow selectively either from the towing vehicle, or from the accumulator to the hydraulic brake actuator. 22) A trailer according to any of Claims 18 to 21. wherein at least one reservoir is provided, the said reservoir receiving any hydraulic fluid returned from the or each hydraulic brake actuator.

23) A trailer according to Claim 22, wherein one wall of the reser¬ voir is moveable and resiliently biased to exert a pressure on the hydraulic fluid contained in the reservoir.

24) A trailer according to Claim 20, wherein the compressor and/or hydraulic pump are electrically driven.