GB2326449A - Over-run trailer brakes - Google Patents

Abstract

A trailer brake 2 comprises friction pads 6, 8, a brake disc, and means including a pivoted lever 10 for applying the pads to the disc via an intermediate member 20 which has rear surfaces 26, 28. In the automatic mode, on over-run, trailer hitch (50, Fig.6), which is operative between stops (64, 66), pivots the lever 10 via a cable (72), and a roller (18, Fig.1) on the lever engages the intermediate member. For forward motion, the roller engages surface 26 and the brake is applied, but on reversing of the trailer, pad 8 and member 20 move relative to the caliper 30 to bring surface 28 into register with the roller so as to release the brake. In the manual mode, operation of the hand brake (58), which is not restricted by the stops, actuates the brake to prevent movement of the trailer in both the forward and reverse directions.

Description

IMPROVEMENTS RELATING TO BRAKES This invention relates to disc brakes which are primarily, but not exclusively, designed to be used on trailers.

Small trailers of up to 3500 kg Gross have been known for many years and are a well developed field. It is a legal requirement that trailers in this weight class be fitted with a braking system and consequently such braking systems are well known.

Commonly trailers in this class are fitted with drum brakes which are operated by a mechanism utilising a force applied to the rear of a tractor (a vehicle towing the trailer), by the trailer, when braking is occurring. This force is generated by conservation of the momentum of the trailer; the trailer tries to maintain its velocity when the tractor brakes and so applies a force to the rear of the tractor. This force is usually converted to a displacement by compress ion of a compressible coupling mechanism connecting the trailer to the tractor. In the common braking arrangement this displacement operates a mechanism which applies the brakes of the trailer.

This arrangement works well, but in the simplest arrangement described so far, has its disadvantages. When the tractor is reversing, particularly when reversing up a hill, a force is applied to the rear of the tractor in the same direction as is required to operate the brakes of the trailer during forward braking. Thus, the brakes of the trailer operate and the tractor is prevented from reversing.

This is a well known problem. In the simplest form the displacement occurring in the coupling is prevented by a temporarily engaged blocking member which prevents the brakes being operated whilst the tractor is reversing.

The blocking member must be manually inserted. If a driver of the tractor is on their own they must stop the tractor, get out, and insert the blocking member before being able to reverse. According to current safety legislation if a blocking member is used it must be adapted to remove itself automatically when the tractor starts to travel forward (if this did not occur then the trailer brakes would remain inoperative which is obviously an undesirable situation).

A more advanced solution is to use an "auto-reverse" detection mechanism which is provided in the brake drum. These mechanisms are mechanical and detect the rearward motion of the trailer. When rearward motion is detected the drum brakes are not operated. Such mechanisms have been known for over 25 years.

Traditionally, as discussed, drum brakes are used on trailers in this weight class. However, there are advantages to using disc brakes for trailers.

Trailers are usually neglected; they are left outside, in all weathers, for long periods, and are expected to work when required. Because disc brakes are mechanically much simpler than drum brakes there is less to go wrong. That is disc brakes withstand the abuse of being left outside in all weathers much better that drum brakes.

Further, because they are mechanically much simpler than drum brakes they can be immersed in salt water (useful when launching boats, etc.) with less of an ill effect. Drum brakes do not react well to being immersed into such a hostile medium.

However, to allow disc brakes to be used on a trailer the reversing problem again arises. The mechanism developed to automatically allow reversing works for drum brakes and not with disc brakes. Therefore, the blocking member (previously discussed) must be used to prevent the mechanism which operates the trailer brakes from preventing reversing.

This is not a satisfactory solution.

It is an aim of the present invention to provide a brake which ameliorates the problems discussed above.

According to a first aspect of the invention there is provided a brake comprising a disc, at least two friction members and an activation means, in which said friction members are adapted, in use, to be applied to either side of said disc, said disc is adapted, in use, to rotate in association with a wheel in a forward direction and a reverse direction and said activation means is adapted, in one mode of use, to operate only when the disc is rotating in the forward direction.

For the purposes of this description it is intended that the disc be made to rotate in the forward direction when a trailer or vehicle to which the disc is fitted is moved in a forwards direction.

Said activation means may be adapted, in use, to have two modes of operation in which in the first mode it can be moved from a rest position to an automatic position and a second mode in which it can be moved from the rest position to a manual position both modes being capable of applying said friction means to said disc, wherein when the activation means is moved to the automatic position said friction members are applied to said disc only when said disc is rotating in the forward direction and when said activation means is moved to said manual position said friction members are applied to said disc regardless of the direction of rotation of the disc.

The disc brake may have a floating caliper.

An advantage of the present invention is that by moving the activation means to the manual position, thus ensuring that the friction members can be applied with the disc rotating in either direction, the brake can be activated as required whereas movement of the activation means to the automatic position will result in the brake being applied only if the disc is rotating in one of either the forward or the reverse direction.

The activation means may be a lever which applies the friction members to the disc perhaps by acting on a rear surface of one of the friction members, the active friction member, so providing a simple structure to operate the brake.

Preferably there is provided an intermediate member having at least two operating faces upon one of which faces the activation means, in use, is caused to operate to provide the required modes of operation.

The two operating faces of the intermediate member may be provided as an integral part of a backing member of the active friction member, providing a convenient way of forming the intermediate member.

In such circumstances the backing member may be provided in the form of a pressing, so providing a cost effective backing member.

Alternatively, the intermediate member may be provided as a separate member between the activation means and the active friction member, in which case the intermediate member may be affixed to the active friction member.

The intermediate member may be caused, in use, to move to a forward position when the disc is rotating in a forward direction and move to a reverse position when the disc is rotating in a reverse direction.

Movement of the intermediate member may be by rectilinear movement along a path parallel to a tangent to the disc.

Preferably, the operating faces of the intermediate member may be arranged to be different heights, measured in an axial direction of the disc. The second operating face may be a lower height than the first operating face. An advantage of this is that different forces may be applied to the active friction member, through the intermediate member, by the activation means when it operates on each of the operating faces.

In use, when the activation means is in the automatic position and is co-operating with the second operating face of the intermediate member the brake will not activate when the disc is rotating in the forward or reverse directions. Further, in use, when the activation means is in the automatic position and is co-operating with the first operating face of the intermediate member the brake is activated when the disc is rotating in the forward direction. Yet further, in use, when the activation means is in the manual position the brake will be actuated whether the lever is cooperating with the first or the second operating face of the intermediate member and regardless of the direction of rotation. This arrangement provides the desired mode of operation of the brake.

The active friction member may be adapted, in use, to be caused to move by friction with the disc in a path parallel to a tangent of the disc, between two positions. Movement of the active friction member may cause the intermediate member to move between the forward position and the reverse position. Such an arrangement provides a simple way of arranging for movement of the intermediate member.

When the intermediate member is in the forward position the activation means may operate on the first operating face and when the intermediate member is in the reverse position the activation means may operate in the second operating face.

It is against conventional disc brake design to allow any of the friction members, in this case the active friction member, to move. Such movement is usually thought to be bad because it may lead to increased wear of the friction member due to vibration of the friction members.

Movement of the active friction member may be limited to approximately 25mm relative to the caliper of the brake along a path parallel to a tangent of the disc. Preferably, movement is limited to approximately 15mm. Most preferably, movement is limited to approximately 5mm.

A roller may be provided at an end portion of the activation means so providing a low friction engagement between the activation means and the rear face of the active friction member or the intermediate member.

Preferably, a wear adjustment means is provided in association with the activation means which allows the disc brake to be adjusted to take account of wear of the friction members and disc.

The wear adjustment means may be provided in association with the roller providing a simple manner in which to adjust the brake.

Biasing means may be provided on the activation means which is adapted, in use, to bias the activation means to a position in which the brake does not cause the friction members to co-operate with the disc. An advantage of such a biasing means is that it ensures that the friction members are not caused to co-operate with the disc unless the activation means has been activated so reducing wear of the friction members.

Conveniently, the biasing means is a spring. Most conveniently, the biasing means is a coil spring. The spring may be arranged to be stretched by operation of the lever. Such a biasing means provides a simple yet effective manner in which to ensure the activation means is correctly biased.

Alternatively or additionally a compression spring or a torsion spring may be used as the biasing means.

A resilient member may be provided which biases the active friction member (and optionally the intermediate means) to the forward position. Preferably, the resilient member also acts as an anti-rattle member which secures the friction member in place. Such a resilient member may increase the life of the friction member (and faces to which the friction member abuts) by preventing excessive wear caused by vibration of the friction members and provides means whereby the brake assembly is biased to a position in which the brake operates when the disc is rotating in a forward direction.

Alternatively, but perhaps less preferably, the resilient member may be biased to the reverse position.

In use, the friction members may be arranged so that when the active friction member has moved to cause the intermediate member to be in the forward position the two friction members overlie each other (on opposite sides of the disc) but when the active friction member has moved to cause the intermediate member to be in the reverse position the friction members are displaced from overlying each other.

This arrangement also goes against conventional wisdom in the design of disc brakes. Usually disc brakes are arranged so that the friction members always overlie each other.

In use, so called 'pad drag' or friction occurring between the disc and active friction member in the unactivated disc brake (wherein the friction members are not being forced to co-operate with the disc) may cause the active friction member to move between the forward position and the reverse position depending on the direction of rotation of the disc.

According to a second aspect of the invention there is provided a trailer fitted with a disc brake according to a first aspect of the invention.

An advantage of having a trailer fitted with such a disc brake is that it is better able to withstand the abuse of being left outside and effects of its operating environment than a trailer which is fitted with drum brakes as is customary in the field of trailers in the weight class discussed.

Preferably the trailer is fitted with a plurality of disc brakes.

Preferably, the trailer is provided with a manual operative means and an automatic operative means which move the activation means of the brake to the manual position and the automatic positions respectively. An advantage of such a system is that it is simple to obtain the desired modes of operation from the brake fitted to the trailer by applying the correct operative means.

The manual operative means may be a hand brake and the automatic operative means may be a towing mechanism which applies the brakes depending upon the force the trailer is applying to the rear of a tractor. An advantage of such an arrangement is that the brakes of the trailer are not applied when the tractor is reversing ( in which case the disc of the brake will be rotating in the reverse direction).

The hand brake and the towing mechanism may both activate a linkage which is connected to the activation means of the brake so providing a simple way of operating the brake.

The linkage may be mechanical or may be hydraulic.

The hand brake and the towing mechanism may be arranged so that the towing mechanism causes, in use, a displacement x of the linkage and the hand brake causes, in use, a displacement x + Ax (which is greater than x) of the linkage.

According to a third aspect of the invention there is provided a method of improving the reliability of trailers which comprises providing the trailer with a disc brake according to the first aspect of the invention.

Such a method is beneficial in that disc brakes are much more robust than drum brakes which are traditionally used for trailers. Disc brakes have been not been used to a wide extent on trailers because previously they have experienced the problems hereinbefore discussed.

There now follows a detailed description, to be read with reference to the accompanying drawings, of a disc brake which illustrates the present invention by way of example.

In the accompanying drawings: Figure 1 shows a schematic view of a brake assembly, according to the present invention, in a number of positions; Figure 2 shows a schematic view of the brake assembly of Figure 1 viewed from the direction of arrow X in Figure 1; Figure 3 shows a schematic view of the brake assembly of Figure 1, viewed from the direction of arrow Y in Figure 1; Figure 4 shows an elevation of a front side of the brake assembly of Figure 1; Figure 5 shows an elevation of a rear side of the brake assembly of Figure 1; Figure 6 shows a schematic representation of a hitch mechanism of a trailer adapted to operated the brake assembly of the preceding Figures; Figure 7 show a resilient member which holds friction members of the brake assembly in place; Figure 8 shows a different embodiment of the brake assembly; Figure 9 shows a cross section through a friction member and an intermediate member; and Figure 10 shows a cross section through a friction member and an alternative embodiment of a friction member.

Figures 1 to 5 show a brake assembly according to the present invention from various angles and positions.

A floating caliper disc brake 2 is shown in Figure 1 which has central to it a disc 4 comprising a disc of iron as is know in the art of disc brakes. Either side of the disc 4 there is arranged a friction member: a first friction member 6, and a second, active, friction member 8. The friction members 6, 8 comprise pads and are provided on backing plates 7, 9 as is also commonly know in the art of disc brakes.

To the left of Figure 1, an activation means, or lever 10, is provided. The lever 10 is in the form of an "L" shape, with a pivot, in this case a bolt 12 through a corner of the "L", securing the lever 10 to the disc brake 2.

In Figure 1 the lever 10 is shown in three positions. In solid outline, labelled A is a rest position; in chain outline, labelled B is an automatic position; also in chain outline, labelled C, is a manual position.

Provided at the short arm of the "L" part of the lever 10 is a wear adjustment means 14 comprising an elongate threaded member 16 which is threadably received in the lever 10. Disposed at a first end portion of the elongate member 16 is a roller 18 which abuts an intermediate member 20. Disposed at a second end portion of the elongate member 16, opposite the first end portion, is an adjustment head 22 which is securely attached to the elongate member 16. Part way along the elongate member is a lock nut 24 which abuts a portion of the lever 10.

The intermediate member 20 is disposed between the roller 18 and the second, active, friction member 8 and is affixed to a rear surface 25 of the second, active, friction member 8. The intermediate member 20 has two operating faces; a first operating face 26 and a second operating face 28. The intermediate member 20 can be most clearly seen in Figure 3.

The first operating face 26 of the intermediate member 20 is displaced further from the disc 4 (in axial direction of the disc 4) than the second operating face 28 of the intermediate member 20.

The intermediate member 20 has two positions; a forward position 20', and a reverse position 20" (these are both shown in dotted outline in Figure 1). In the forward position of the intermediate member 20 the first operating face 26 is in contact with the roller 18. In the reverse position of the intermediate member 20 the roller 18 is adjacent to the second operating face 28.

An aluminium "U" shaped housing (caliper) is provided and maintains the working components of the brake assembly in place. The housing works in a manner as is known in the field of disc brakes and traverses the disc 4 so that it holds both the first friction member 6 and second, active, friction member 8 in place.

A coil spring 32 ( or biasing means) is connected between the long side of the "L" part of the lever 10 and the housing 30.

As viewed in Figure 1, displacement of the long "L" part of the lever 10 in a downward direction causes rotation of the lever 10 about the bolt 12. Such rotation applies a force to the intermediate member 20 and second, active, friction member 8 through the roller 18 to activate the brake assembly 2 and cause the friction members 6, 8 to co-operate with the disc 4.

Force applied to the intermediate member 20 applies the second, active, friction member 8 to the disc 4. The reaction force produced by this action causes the housing to move to left of Figure 1 so applying the first friction member 6 to the disc 4. This action is typical for a floating caliper disc brake and will not be described further.

The second, active, friction member 8 and the intermediate member 20 can move along a path parallel to a tangent of the disc.

Figure 4 shows a rear view of the second, active, friction member 8.

Stops 100, 102 are provided on the housing 30 which prevent the second, active, friction member 8 moving beyond certain limits. In the Figure the second, active, friction member 8 is abutting the stop 102 whereas there is a gap 108 between the second, active, friction member 8 and the stop 100.

Figure 5 shows a rear view of the first friction member 6. Further stops 104, 106 are provided to hold the first friction member 6 in place.

The stops 104, 106 abut the first friction member 6 so that no movement (parallel to a tangent to the disc 4) is allowed.

As the skilled man will appreciate there is always a small amount of friction between the disc 4 and the friction members 6, 8. This friction is enough to move the second, active, friction member 8 from abutting one of the stops 102, 100 to abutting the other of the stops 100, 102. This consequently causes movement of the intermediate member 20 between the forward position and the reverse position. (That is "pad drag" acts on the friction members 6, 8 and has sufficient force to cause the second, active, friction member 8 to move along a path parallel to a tangent of the disc 4 according to the direction of rotation of the disc 4).

The action of the disc brake 2 is dependent on the position of the intermediate member 20 and also to the degree of displacement of the lever 10.

When the lever 10 is in the rest position A the brake assembly 2 is always unactivated; no force is applied (apart from that due to pad drag) to the disc 4 by the friction members 6, 8.

When the lever 10 is in position B then depending on the position of the intermediate member 20, force may be exerted on the disc 4 by the friction members 6, 8. If the second operating face 28 of the intermediate member 20 is adjacent the roller 18 then the brake remains unactivated as long as the lever 10 does not move beyond position B. The friction members 6, 8 will only co-operate with the disc 4 when the disc is rotating in a forward direction (i.e. when the intermediate member 20 is in contact with the first operating face 26).

The lever 10 and the intermediate member 20 are arranged so that when the lever 10 is in the automatic position and the intermediate member in the reverse position 20" the roller 18 does not actually touch the second operating face 28. This ensures that no braking occurs.

If however, the first operating face 26 of the intermediate member 20 is in contact with the roller 18 then the brake is applied when the lever 10 is in position B. Force is applied to the second friction member 8 and consequently to the disc 4 (because the intermediate member 20 is thicker at the first operating face 26).

When the lever 10 is moved to the position C (which is equivalent to displacement B plus an extra amount) the brake 2 will be actuated whatever the position of the intermediate member 20 ( whether it is in the forward or reverse positions thus presenting either the first operative face 26 or the second operative face 28 to the roller 18 respectively).

The position of the intermediate member depends on the position of the second, active, friction member 8. Figure 4 shows the second, active, friction member 8 abutting the stop 102. The action of friction of the disc 4 on the second, active, friction member 8 moves the member 8 to this position as shown in the Figure (corresponding to the disc 4 moving in the same direction to the arrow shown in the Figures). Consequently the first operating face 26 of the intermediate member 20 is brought into contact with the roller 18. (Rotation of the disc 4 as shown by the arrows in the Figures corresponds to forwards movement of a trailer to which the brake is attached).

When the trailer reverses, motion of the disc 4 will be in the reverse direction and friction between the disc 4 and the second, active, friction member 8 will cause the member 8 to move parallel to a tangent of the disc 4 so that it abuts the stop 100. This moment causes the intermediate member 20 to move so that the second operating face 28 of the intermediate member 20 is adjacent the roller 18.

Wear of the friction members 6, 8 and of the disc 4 can be compensated for by the wear adjustment means 14. The lock nut 24 can be released and the adjustment head 22 thereafter rotated to alter the position of the roller 18. After adjustment has been made the lock nut 24 is tightened so securing the elongate member 16 (and consequently the roller 18) in position.

As shown in Figure 6 a towing mechanism (automatic operative means) 50 is provided on a trailer (not shown) to operate the disc brake 2.

A rod 52 is provided which runs from the towing mechanism 50 to a reversing lever 70. A cable 72 runs from the reversing lever 70 to the lever 10 of the brake assembly 2. The reversing lever 70 is pivoted about pivot 74.

A hitch 54 couples the trailer to a ball 56 fitted to a rear portion of a tractor. A hand brake lever 58 (manual operative means) is also provided to operate the disc brake 2. A resilient member 60 (a spring in this case) is provided to operate on the hitch 54.

The hitch 54 can move within a housing 62 but its travel is limited by two stops 64, 66 which co-operate with the hitch 54.

As the trailer is being towed by the tractor the trailer will gain momentum. As the tractor brakes a force is exerted on the towing mechanism 50. This force causes the hitch 54 to move within the housing 62. This movement causes the hitch 54 to push the rod 52 and thus moves the reversing lever 70 in an anti-clockwise direction as viewed in the Figure. This rotation pulls the cable 72 and therefore operates the lever 10 of the brake assembly 2.

The stops 64, 66 are arranged in such a way so as to ensure that the lever 10 cannot be caused to move beyond position B by movement of the hitch 54 within the housing 62. That is the stops 64, 66 prevent the cable 72 being moved to such an extent so as to cause the lever 10 to move beyond position B.

However, the amount that the cable 52 can be moved by the hand brake lever 58 is not limited by the stops 64, 66. Therefore by actuating the hand brake lever 58 the lever 10 can moved beyond position B and onto position C.

The displacement caused to the cable 52 is represented by the two lines labelled B and C.

Since the mechanism 50 cannot cause the lever 10 to be moved beyond position B the activation of the brake is dependent upon the position of the intermediate member 20 and therefore dependent upon the direction of rotation of the disc 4. The brake will not operate when the tractor is reversing.

If the hand brake lever 58 is applied, the extra displacement of the cable causes the lever 10 to be moved to position C thus enabling the brake to be applied regardless of the direction of rotation of the disc 4.

Figure 7 shows a similar view of the friction members 6, 8 and disc 4 as Figure 2 (a plan view). However, in Figure 7 a resilient member 110 is provided to bias the friction members 6, 8 in place.

The resilient member 110 is in the form of a 'U' shape, with the bottom of the 'U', to the right of the Figure, turning 360C around an anchor 112. Each of the end portions of the 'U' pass through the backing plates 7, 9 of the friction members 6, 8 through holes 114, 116.

The arm of the 'U' in proximity with the second, active, friction member 8 has incorporated into it a coil tension spring 118.

In use, the resilient member 110 exerts a force holding the friction members 6, 8 away from the disc 4. (In the Figure the second, active, friction member 8 is forced downwards and the first friction member 6 is forced upwards). This force is created due to the turn of the resilient member 110 around the anchor 102. That is there is a force preventing the end portions of the resilient member being brought together to effect braking but not sufficient to prevent the "pad drag" effect.

Further, the coil spring 118 in the arm of the 'U' in proximity to the active friction member 8 biases the second, active, friction member in such a manner as to bias the intermediate member to the forward position, i.e. to the right of Figure 7.

The direction of rotation of the disc 4 is indicated in the Figure, wherein the arrow indicates forward rotation of the disc 4.

Should the disc 4 rotate in the reverse direction, pad drag will cause the second, active, friction member 8 to move to the left of the Figure, causing the coil spring 118 to be extended. Once motion of the disc 4 turns to forward rotation force exerted by the extended spring 118 will cause the second, active, friction member 8 to move to the right as viewed in the Figure. This ensures that friction member 8 is biased to a position in which the intermediate member is in the forward position.

This ensures that the brakes should always operate when the trailer is moved forwards.

Figure 8 shows a similar view of a brake assembly as Figure 1, but a different embodiment. Like parts are referenced similarly to Figure 1.

The lever 10 pivots around the pivot 12. The cable 72 is shown attached to the end portion of the lever 10. The cable 72 is protected by an outer sleeve 80 and a compression spring 82 is disposed between the lever 10 and the sleeve 80. An anchor point 84 is provided which holds an end portion of the sleeve 80.

In use, the compression spring 82 acts as a biasing means, returning the lever 10 to the rest position, position A. It will be noted that no tension spring 32 is provided in Figure 8.

The embodiment shown in Figure 8 is perhaps the preferred embodiment of the biasing means. It should also be noted that the anchor point 84 must be arranged and affixed to an assembly that moves with the brake assembly.

An alternative embodiment to bias the lever 10 to the rest position would be to provide a torsion spring around the pivot 12.

Figures 9 and 10 show cross sections through an active friction member, referenced 8 in both Figures. The second, active, friction member 8 is mounted on a backing plate 200, 202.

In Figure 9, the backing plate 200 has been pressed to create a deformed portion during manufacture forming, integrally with it, the intermediate member 204. In this, perhaps the preferred embodiment of the intermediate member the second operating face 208 is provided by an undeformed portion of the backing plate 200 and the first operating face by the deformed portion of the backing plate 206.

Figure 10 shows a different embodiment in which an intermediate member 210 is provided as a separate member affixed to the rear of the backing plate 202. The first operating face 212 is provided at a higher portion and the second operating face 214 at a lower portion.

In the Figure 8 embodiment a wheel nut is utilised as a lock nut on the wear adjustment means 14. A chamfered portion 87 of the wheel nut 85 co-operates with a suitably dimensioned counter sunk hole 89 in the lever 10.

Adjustment is as described hereinbefore (the wheel nut 85 is slackened, the elongate member rotated to the correct position, and the wheel nut 85 retightened).

It will be realised that the wheel nut 85 could be used instead of the lock nut 24 shown in any of the embodiments described herein.

Claims (43)

1. A brake comprising a disc, at least a first and active friction members and an activation means, in which said friction members are adapted, in use, to be applied to either side of said disc, said disc is adapted, in use, to rotate in association with a wheel in a forward direction and a reverse direction and said activation means is adapted, in one mode of use, to operate only when the disc is rotating in the forward direction.

2. A brake according to claim 1 in which said activation means is adapted, in use, to have two modes of operation in which in the first mode it can be moved from a rest position to an automatic position and a second mode in which it can be moved from the rest position to a manual position both modes being capable of applying said friction means to said disc, wherein when the activation means is moved to the automatic position said friction members are applied to said disc only when said disc is rotating in the forward direction and when said activation means is moved to said manual position said friction members are applied to said disc regardless of the direction of rotation of the disc.

3. A brake according to claim 1 or claim 2 in which the brake has a floating caliper.

4. A brake according to any preceding claim in which the activation means is a lever which applies the friction members to the disc.

5. A brake according to any preceding claim in which the activation means acts on a rear surface of one of the friction members, the active friction member.

6. A brake according to any preceding claim in which there is provided an intermediate member having at least two operating faces upon one of which faces the activation means, in use, is caused to operate.

7. A brake according to claim 6 in which the two operating faces of the intermediate member are provided as an integral part of a backing member of the active friction member.

8. A brake according to claim 7 in which the backing member is provided in the form of a pressing.

9. A brake according to claim 6 in which the intermediate member is provided as a separate member between the activation means and the active friction member.

10. A brake according to claim 9 in which the intermediate member is affixed to the active friction member.

11. A brake according to any of claims 6 to 10 in which the intermediate member is caused, in use, to move to a forward position when the disc is rotating in a forward direction and move to a reverse position when the disc is rotating in a reverse direction.

12. A brake according to claim 11 in which movement of the intermediate member is by rectilinear movement along a path parallel to a tangent to the disc.

13. A brake according to any of claims 6 to 12 in which the operating faces of the intermediate member are arranged to be different heights, measured in an axial direction of the disc.

14. A brake according to claim 13 in which the second operating face is a lower height than the first operating face.

15. A brake according to any preceding claim in which the active friction member is adapted, in use, to be caused to move by friction with the disc in a path parallel to a tangent of the disc, between two positions.

16. A brake according to claim 15 as it depends directly or indirectly on claim 11 in which movement of the active friction member causes the intermediate member to move between the forward position and the reverse position.

17. A brake according to claim 16 in which when the intermediate member is in the forward position the activation means operates on the first operating face and when the intermediate member is in the reverse position the activation means operates on the second operating face.

18. A brake according to any preceding claim in which movement of the active friction member is limited to approximately 25mm relative to the caliper of the brake along a path parallel to a tangent of the disc.

19. A brake according to any of claims 1 to 17 in which movement is limited to approximately 15mm relative to the caliper of the brake along a path parallel to a tangent of the disc.

20. A brake according to any of claims 1 to 17 in which movement is limited to approximately 5mm relative to the caliper of the brake along a path parallel to a tangent of the disc.

21. A brake according to any preceding claim in which a roller is provided at an end portion of the activation means so providing a low friction engagement between the activation means and the surface upon which it operates.

22. A brake according to any preceding claim in which a wear adjustment means is provided in association with the activation means which allows the brake to be adjusted to take account of wear of the friction members and disc.

23. A brake according to claim 22 in which as it depends from claim 21 the wear adjustment means is provided in association with the roller providing a simple manner in which to adjust the brake.

24. A brake according to any preceding claim in which biasing means is provided on the activation means which is adapted, in use, to bias the activation means to a position in which the brake does not cause the friction members to co-operate with the disc.

25. A brake according to claim 24 in which the biasing means is a spring.

26. A brake according to claim 25 in which the biasing means is a coil spring.

27. A brake according to claim 11 or any claim directly or indirectly dependent upon claim 11 in which a resilient member may be provided which biases the active friction member to the forward position.

28. A brake according to claim 27 in which the resilient member biases the intermediate member to the forward position.

29. A brake according to claim 27 or claim 28 in which the resilient member also acts as an anti-rattle member which secures the friction member in place.

30. A brake according to claim 6 or any claim directly or indirectly dependent on claim 6 in which in use, the friction members are arranged so that when the active friction member has moved to cause the intermediate member to be in the forward position the two friction members overlie each other (on opposite sides of the disc) but when the active friction member has moved to cause the intermediate member to be in the reverse position the friction members are displaced from overlying each other.

31. A brake according to claim 11 or any claim directly or indirectly dependent upon claim 11 in which in use, so called 'pad drag' or friction occurring between the disc and active friction member in the unactivated disc brake (wherein the friction members are not being forced to cooperate with the disc) causes the active friction member to move between the forward position and the reverse position depending on the direction of rotation of the disc.

32. A trailer fitted with a brake according to any of claims 1 to 31.

33. A trailer according to claim 32 in which the trailer is fitted with a plurality of said brakes.

34. A trailer according to claim 32 or 33 in which the trailer is provided with a manual operative means and an automatic operative means which move the activation means of the brake to the manual position and the automatic positions respectively.

35. A trailer according to claim 34 in which the manual and automatic operative means both activate a linkage which is connected to the activation means of the brake so providing a simple way of operating the brake.

36. A trailer according to claim 35 in which the manual and automatic operative means are arranged so that the automatic operative means causes, in use, a displacement x of the linkage and the manual operative means causes, in use, a displacement x+Ax of the linkage.

37. A trailer according to claim 36 in which x + Axis greater than x.

38. A trailer according to any of claims 34 to 37 in which the manual operative means is a hand brake.

39. A trailer according to any of claims 34 to 38 in which the automatic operative means is a towing mechanism which applies the brakes depending upon the force the trailer is applying to the rear of a tractor.

40. A method of improving the reliability of trailers which comprises providing the trailer with a brake according to any one of claims 1 to 31.

41. A brake substantially as described herein with reference to the accompanying drawings.

42. A trailer substantially as described herein with reference to the accompanying drawings.

43. A method of improving the reliability of trailers substantially as described herein with reference to the accompanying drawings.