GB2399607A

GB2399607A - Wear adjuster for brake shoe

Info

Publication number: GB2399607A
Application number: GB0405782A
Authority: GB
Inventors: Glynn Ashman; Grahame Hickin
Original assignee: TRW Ltd
Current assignee: TRW Ltd
Priority date: 2003-03-18
Filing date: 2004-03-16
Publication date: 2004-09-22
Anticipated expiration: 2024-03-16
Also published as: GB0405782D0; GB2399607B; GB0306139D0

Abstract

A brake shoe 10 having on its first side a friction pad 16, and at least one pin 24 on its second side, said pin 24 having a cross section wherein a first dimension along first direction is larger than a second dimension along a second transverse direction, there being received on each pin 24 a spring clip 26 to enable the shoe 10 to be mounted, wherein each spring clip 26 comprises an opening 38 such that the pin 24 can be inserted thereinto, the clip 26 and pin 24 being configured such that the spring clip 26 can be arranged on the pin 24 in a first orientation with relatively no engagement with the pin 24, and a second orientation with a larger engagement with the pin 24. How a pin goes form the first orientation to the second is observed in Figs. 27a-27c; pin 100 and spring clip 126.

Description

A RETRACTION MECHANISM

This invention relates in general to vehicle disc brake assemblies and in particular to an improved structure for a retraction mechanism adapted for use in such a vehicle disc brake assembly.

Most vehicles are equipped with a brake system for retarding or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies are typically actuated by hydraulic or pneumatic pressure generated when an operator of the vehicle depresses a brake pedal. The structures of these drum brake assemblies and disc brake assemblies, as well as the actuators therefor are well known in the art.

A typical disc brake assembly includes an anchor bracket which is secured to a fixed, non-rotatable component of the vehicle. A pair of brake shoes is supported on the anchor bracket for sliding movement relative thereto.

The brake shoes have respective friction pads which are disposed on opposite sides of a brake disc. The disc, in turn, is connected to the wheel of the vehicle for rotation therewith. To effect braking action, the brake shoes are moved inwardly toward one another so as to frictionally engage the opposed sides of the disc. Such frictional engagement causes retarding or stopping of the rotational movement of the disc and, therefore, the wheel of the vehicle in a controlled manner.

To accomplish this, the disc brake assembly further includes a caliper assembly for selectively moving the brake shoes into frictional engagement with the brake disc. The caliper assembly typically includes guide pins or other components to slidably support a caliper housing relative to the fixed anchor bracket. The caliper housing is generally C- shaped, having an inboard leg disposed adjacent the inboard brake shoe and an outboard leg disposed adjacent to the outboard brake shoe. One or more hydraulically or pneumatically actuated pistons are provided in respective cylindrical recesses formed in the caliper inboard leg adjacent to the inboard brake shoe. When the brake pedal is depressed, the piston and the inboard leg of the caliper are urged apart from one another.

Specifically, the piston is urged outwardly, while the outboard leg of the caliper is urged inwardly. As mentioned above, the piston is disposed adjacent to the inboard brake shoe and, therefore, urges it outwardly toward the inner side of the disc. Because the caliper is slidably mounted on the pins of the anchor bracket, the caliper outboard leg (and, thus, the outboard brake shoe disposed adjacent thereto) are urged inwardly toward the outer side of the disc. As a result, the brake shoes frictionally engage the opposed sides of the disc.

Frequently, an annular roll-back seal is provided within the cylindrical recess in contact with the outer surface of the piston. The roll-back seal is conventional in the art and performs several functions. First, the roll- back seal provides a seal to define the extent of the cylindrical recess within which the piston is disposed. Second, the roll-back seal is designed to retract the piston inwardly away from the disc by a predetermined distance from the fully engaged position when the brake pedal is released after being depressed. To accomplish this, the rollback seal frictionally engages the outer surface of the piston, resiliently resisting movement thereof when the brake pedal is depressed. Thus, when the operator of the vehicle releases the brake pedal, the resilience of the roll-back seal causes the piston to retract within the cylindrical recess and out of contact with the inboard brake shoe.

With repeated usage, the friction pads of the brake shoes wear and become increasingly thinner. When this occurs, the piston and the caliper must move greater distances relative to one another to effect the same braking action as when the friction pads were new. Despite this increased distance of movement of the piston in the outboard direction, it is desirable that the roll-back seal retract the piston only by the same predetermined distance away from the disc in the inboard direction.

Thus, known roll-back seals are designed to accommodate increased movement of the piston in the outboard direction when the brake pedal is depressed, but to retract the piston inwardly by approximately the same predetermined distance when the brake pedal is subsequently released.

Ideally, when the brake pedal is released, the brake shoes should also be spread apart from one another to prevent any incidental frictional engagement with the disc. If the brake shoes are not moved from engagement with the disc, one or more of the following can occur: disc thickness variation of the disc caused by residual drag of the brake shoes which can cause brake judder; rattle of the brake shoes; squeal of the caliper caused by structural variations; increase of fuel consumption; and inconsistent short pedal feel. To accomplish this, it is known to provide the disc brake assembly with one or more retraction mechanisms for moving the brake shoes apart from one another to prevent frictional engagement with the disc when the brake pedal is released.

Further, due to fluctuations in an axial direction of the brake disc due to irregularities thereof, it is possible for the brake shoe to contact only a region of the brake pad. This regional contact of the brake disc can lead to localised wear of the disc, which can increase the problems discussed above.

For example, U.S. Patent Nos. 4,364,455 to Oshima, 4,491,204 to Dirauf et al., 4,629,037 to Madzgalla et al., 4,658,938 to Thiel et al, 4,867,280 to Von Gruenberg et al., 4,940,119 to Kondo et al., 5,069,313 to Kato et al., 5,249,647 to Kobayashi et al., and 5,251,727 to Loemer et al. and Great Britain 747,972 to Dunlop Rubber all disclose disc brake assemblies which include a retraction mechanism structure.

According to a first aspect of the invention there is provided a brake shoe which carries, on a first side of the shoe, a friction pad, the shoe also comprising one or more pins provided on a second side of the shoe, opposite the first side, and the or each pin having a cross section comprising a first dimension along a first direction and a second dimension, less than the first, along a second direction transverse the first direction, there being received on the or each pin a spring clip arranged to allow the shoe to be mounted.

Such an arrangement is advantageous because the different dimensions may allow the clips to be more easily fitted to the pins.

The second dimension may be provided between at least one substantially flat surface and another surface.

Conveniently, the first direction is substantially transverse the first direction. Such an arrangement is advantageous since it may maximise the separation of the first and second directions.

In the preferred embodiment, two pins are provided on the brake shoe.

The provision of two pins is convenient because it may allow the shoe to be located in a housing more readily than if a single pin were provided.

Preferably, each pin comprises two flat surfaces with the second dimension being provided between the flat surfaces. Such an arrangement is convenient because it may allow a spring clip which may be arranged to be received on the pin to be oriented and fitted to the pin more readily than if a single flat is provided. Further, the provision of the two flats may make the pin more easy to manufacture. The pin may be manufactured by pressing, or otherwise compressing, a round or substantially round pin.

Each pin may comprise a region, generally an end region, of greater cross section than the remainder of the pin. Such an arrangement is convenient because it may allow the pin to be received in an opening within the brake shoe without passing through the opening. Conveniently, the opening in the brake shoe is of complementary dimensions to the pin such that the pin can be inserted into the opening. It is advantageous to provide the region of greater cross section at an end region of the pin such that the pin does not protrude from the first side of the brake shoe. It is likely that travel, and thus wear of the brake shoe, may be limited if the pin protrudes from the first side.

The opening in the brake shoe is advantageously provided by stamping the brake shoe. Such an arrangement is convenient because it is a cheaper machining operation when compared to processes such as drilling an as such may reduce the cost of the brake shoe.

Each spring clip comprises an opening such that the pin can be inserted thereinto. Conveniently, the opening has at least one, and preferably two, flat sides.

In the preferred embodiment, the flat sides of the opening in the spring clip are further apart than the widest dimension of the or each pin. Such an arrangement is convenient since it allows the pin to readily be inserted onto the pin.

The opening in the spring clip may also comprise at least one, and preferably two, curved sides.

In the preferred embodiment, the curved sides are arranged such that they provide tangs which function in a similar manner to the tangs of a star washer should the pin be oriented in the opening such the pin engages at least one of the curved sides. Generally, the pin will engage the curved surfaces should the widest dimension be oriented toward the curved surfaces.

The clip and pin arrangement may be fabricated such that the spring clip can be passed on the pin, in a first orientation, with relatively no engagement with the pin and subsequently moved to a second orientation relative to the pin in which relatively large engagement occurs between the two. Such an arrangement is convenient because it allows the clip to be placed on the pin. Movement from the first orientation to the second orientation may occur by rotation.

The engagement of the clip with the pin may be such that the clip is prevented from sliding along the pin towards the brake shoe. This may be achieved by providing a spring clip which is similar to a star washer and includes one or more tangs which are bent out of the plane of the spring clip towards the brake shoe assembly and project into the opening through which the pin passes to resiliently engage the pin.

A pin may be provided at each end region of the brake shoe, each pin carrying a respective spring clip The spring clip may be fabricated from a material which is harder than the material of the pin. Such a material selection is advantageous because it helps to ensure that should any wear occur on the or each pin or the spring clip then it is the or each pin that wears. Should the spring clip wear then the ability of the clip to grip the pin is likely to be reduced.

Conveniently, the clip is fabricated from a material having a thickness of roughly lmm, since it has been found that such a thickness can provided the return forces necessary to return or roll back the brake shoe during use. Of course, other thicknesses may be possible. For example roughly any of the following thicknesses may be appropriate: 0. 6mm; 0.7mm; 0.8mm; O.9mm; l.lmm; 1.2mm; 1.3mm; 1.4mm.

According to a second aspect of the invention there is provided a kit of parts arranged to provide a brake shoe according to the first aspect of the invention, the kit comprising a backing plate having a friction pad on a first side, at least one pin arranged to be fitted to the backing plate and at least one clip arranged to be received on the pin.

The pin and/or spring clip may have any of the features discussed in relation to the first aspect of the invention.

The kit may comprise a tool according to the sixth aspect of the invention.

According to a third aspect the invention provides a disc brake assembly comprising an anchor bracket, a brake shoe which carries a friction pad and a piston slidably connected to the anchor bracket which is arranged such that upon movement of the piston relative to the anchor bracket the piston acts upon the brake shoe to move the shoe into contact with a brake disc, and in which the assembly further includes a retraction mechanism which is adapted to retract the brake shoe from the disc when the piston is retracted, the retraction mechanism comprising at least one pin secured to one of the friction pad and the anchor bracket, the pin having at least one flat surface, and a spring clip fixed relative to the pin which acts between the pin and the other one of the anchor bracket and the friction pad, deformation of the spring clip as the pad is moved towards the disc providing a returning force to pull the friction lining away from the disc when the piston is retracted.

By anchor bracket we may mean any portion of the brake assembly which in use is fixed relative to the bore of the piston. The bracket may be fixed to the vehicle body or may be provided with a degree of "float" relative to the vehicle body.

The invention may thus provide a brake assembly which includes a simple and reliable mechanism for retracting the friction pad from the disc. A low number of parts are required which simplifies the assembly of the brake assembly.

A first portion of pin may be secured to the brake shoe and the spring clip may then be in contact with the anchor bracket. Of course, the opposite may be true, with the pin fixed relative to the bracket and the spring clip contacting the brake shoe.

In a most preferred embodiment, the spring clip may comprise a resilient plate, conveniently of metal, having an opening through which the pin passes and defining at least one wing which is in contact with the anchor bracket, the wing deforming resiliently as the friction pad moves towards the disc. The spring clip can therefore be considered to be a type of resiliently deformable star washer fitted onto the pin The spring clip may define at least two wings which extend in opposing directions away from the opening, with each wing in contact with the anchor bracket. This spring clip is preferably in direct resilient engagement with the pin.

By way of the engagement between the pin and the clip, the clip is fixed in position relative to the pin during normal use but is adapted to slide along the pin in the event that the displacement of the pad relative to the anchor bracket due to wear of the friction lining produces a deformation of the spring clip which exceeds a predefined limit. This provides a mechanism for the automatic adjustment of the amount of return provided to the friction lining as it wears or is otherwise deformed.

For ease of construction, the predefined limit may be substantially dependent upon the shape and location of the spring clip which is arranged such that a force required to move the clip along the pin is only provided when the spring clip is deformed in excess of a predefined amount.

In the most preferred arrangement envisaged by the applicant, the engagement of the spring clip with the pin is such that the force required to move the clip along the pin away from the friction lining is greater than that required to move it along the pin towards the friction lining.

Indeed the engagement of the pin and the clip may be arranged such that in normal use the spring clip is permitted to move along the pin in only a single direction.

The retraction device may also provide a biasing force to the friction pad as it is displaced in a direction normal to the plane of the disc relative to the anchor bracket, the biasing force being provided by deformation of a portion of the spring clip. Such displacement may occur as the friction lining contacts the disc and is dragged around by the rotation of the disc.

Whilst only a single retraction mechanism has been described so far it is preferred that two retraction mechanisms are provided which are located at or adjacent each end of the brake shoe. In this way, each end of the pad is retracted from the disc.

The anchor bracket may have many forms as will be readily understood to the man skilled in the art, and indeed more than one piston may be provided for movement of the brake shoe.

The pin and/or spring clip may have any of the features and associated advantages described in relation to the first aspect of the invention.

Each spring clip may be arranged to exert roughly 600N of force between the anchor bracket and the brake shoe. Such a force is advantageous since forces of this magnitude allow the piston to be forces away from a brake disc acted upon by the brake assembly. Forcing the piston away from the disc in this manner is advantageous because it can help to alleviate problems associated with the friction pads contacting a brake disc during non braking use of the brake assembly.

The pin may have a diameter of roughly 3mm. For example, the pin may have a diameter of roughly 3.00mm to roughly 3.20mm, perhaps roughly 3.08mm, or roughly 3.11mm. It has been found that for a particular combination of pin diameter and spring clip thickness then the force exerted by the clip in order to return the brake shoe may be roughly constant. Any excess force may cause the pin to slide through the clip thus keeping the force at the desired level.

In other, perhaps less preferred embodiments, the pin may have a diameter of roughly any of the following: 2mm, 4mm, 5mm.

According to a fourth aspect the invention provides a brake shoe assembly for use in a disc brake assembly according to the third aspect of the invention.

According to a fifth aspect the invention provides a brake shoe assembly which includes a brake shoe assembly adapted for use in a disc brake assembly having at least one pin, having at least one flat surface, secured to the brake shoe which carries a spring clip, the spring clip cooperating with the pin through a sliding frictional engagement and having at least one deformable wing which is adapted to contact an anchor bracket of the disc brake assembly, and whereby the engagement between the clip and the pin is such that the clip is fixed relative to the pin until a force applied to the clip exceeds a predetermined limit whereby the clip is adapted to slide along the pin away from the brake shoe.

The retraction device may provide a positive retraction device for a disc brake assembly incorporating which may provide anti-rattle and antisqueal features for the disc brake pads supported on the disc brake assembly. The retraction device may have two pins or rods anchored to each brake pad and a clip, preferably self-setting, fitted on the pins or rods. The pins or rods may provide abutments and the pin or rods may compel the pads to float on the abutments and thus may stops the pads from rattling and which may also add a damped load to the brake carrier which may help to stop structural vibrations of the carrier reducing squeal.

When the brakes are applied, the clips deform so that when the brakes are released the clip "springs back" to its original form thereby pushing the pads and the brake piston back to their associated original "brake off" positions. This predetermined movement is designed into the clip and pin technology. The retraction device of this invention preferably does not rely on a roll-back seal to pull the piston into the bore and allow a running clearance between the pads and the disc because such rollback is famously invariable. The retraction device of this invention is operative to push the pads and the piston back a controlled amount and providing that the rollback is small will produce a consistent short pedal travel.

Alternatively, if piston roll-back is not a consideration of the retraction device of this invention but rather is near zero, then the clips of this invention can be used to control the pad to disc clearance and thus maintain good control over the pedal travel. If piston roll-back is a consideration, then the roll-back seal is not used for roll-back or if it is, it is secondary to the retraction device. If this is the case, the roll back seal may have a surface texture or can be coated in such a manner that it provides not any or very little roll-back function.

In operation, when the brake is applied the pads move in two directions.

In the longitudinal direction, the clip distorts until the pad is grounded against the carrier. In the axial direction, the pad moves toward the disc.

If the axial movement of the pad is greater than the clip deformation, either through pad wear, high pressure, etc., then clip preferably slides on the pin. The amount of axial movement of the clip on the pin may be controlled by the shape/structure of the clip. Alternatively, it is possible to "reverse" this invention and have the rod anchored on the bracket and the clip reacting against the pad. This invention will work on any single sided or opposed piston caliper. Another advantage of this invention is that the pad to carrier clearance can be increased. This will prevent pad seizure in the carrier gap.

A further advantage of the retraction mechanism is that it may increase the life of the friction pad. It will be appreciated that the life of a friction pad is a function of the amount of time it contacts the disc. Further, it is a function of the temperature of the disc. Therefore, if the friction pad is not brought out of engagement as efficiently as may be desired then the friction pad is not only in contact with the disc for longer, but the temperature of the pad may also increase. These two factors may shorten the life of the pad and as such, by trying to alleviate the problem of the friction pads contacting the disc, the life of the friction pads may be increased.

According to a sixth aspect of the invention there is provided a tool arranged to allow a clip to be rotated relative to a pin.

The tool may comprise a clip engaging portion arranged to receive a clip therein and a lever means arranged to provide sufficient force to rotate the clip relative to the pin.

The lever means may comprise a lever, or may alternatively comprise a motor, whether electrical, hydraulic, pneumatic or the like.

Some embodiments of the invention are illustrated in the accompanying drawings in which: Figure 1 illustrates a portion of a disc brake assembly including a retraction mechanism according to the invention; Figure 2 illustrated a portion of the disc brake assembly taken along line 2-2 of Figure 1; Figure 3 illustrates a portion of the disc brake assembly taken along line 3-3 of Figure 1; Figure 4 illustrates the condition of the retraction mechanism when the brakes are not applied; Figure 5 illustrates the condition of the retraction mechanism when the brakes are applied; Figure 6 illustrates another view of the retraction mechanism when the brakes are not applied; Figure 7 illustrates another view of the retraction mechanism when the brakes are applied; Figure 8 to 11 illustrates various views of the retraction mechanism when the brakes are either applied or not applied; Figures 12 to 14 illustrates various views of the retraction mechanism when the brakes are either applied or not applied, showing an alternate construction of the carrier; Figure 15 is a view of a carrier member; Figure 16 is a view of a portion of a brake shoe assembly; Figures 17 to 21 are various views of the clip of the retraction mechanism; Figure 22 is a view of the pin of the retraction mechanism; Figure 23 to 25 show views of a pin according to a further embodiment of the invention; Figure 26 shows a clip according to the embodiment of the invention of Figures 23 to 25; Figure 27 shows steps in a method of placing the pin of Figures 23 to 25 into the clip of Figure 26; and Figure 28 shows a portion of a backing plate into which the pin of Figures 23 to 25 can be inserted.

Referring now to the drawings, there is illustrated in Figs. 1 through 3 a portion of a disc brake assembly including a brake shoe assembly 10 and an abutment 12 of a carrier member (shown in Fig. 15 at 11). The brake shoe assembly 10 includes a backing plate 14 having a lining 16, which provides a friction pad, attached thereto. The backing plate 14 includes a pair of opposed ends (only one of such ends is illustrated at 18), which are slidably disposed in a slot 20 of the carrier abutment 12.

A retraction mechanism 22 is carried by the disc brake assembly. The retraction mechanism 22 includes a pin 24 and a clip 26. The pin 24 is secured to each of the ends 18 of the backing plate 14 by a suitable manner. The pin 24 can be a roll pin or a serrated pin which is disposed in an opening 28 provided in the end 18. The clip 26 is preferably formed from spring steel or stainless steel and is disposed on or fitted to the pin 24. The clip 26 includes a side leg or extension 30, a pair of opposed upper and lower arms 34A and 34B, prongs 32, and a center opening 38. Also, in Figure 1, an upper brake shoe to carrier bracket abutment is shown at C 1 and a lower brake shoe to carrier bracket abutment is shown at C2. However, either the upper abutment C1, the lower abutment C2 or both can be present depending upon the particular brake shoe assembly 10 design. Alternatively, a brake shoe to carrier bracket abutment can be at the end 18 of the backing plate 14, as shown at C3 in Fig. 2.

Figure 2 shows that leg 30 of the clip 26 contacts an adjacent surface of the carrier abutment 12. As a result of this, the clip 26 can be useful in reducing anti-rattle of the brake shoe assembly 10 in a longitudinal direction and in damping squeal of the caliper (not shown) of the disc brake assembly.

Figure 3 shows that the clip 26 is preferably provided with one or more prongs 32 which grip an outer surface of the pin 24. The prongs 32 are operative to retain the clip 26 on the pin 24 and allow movement of the clip 26 relative to the pin 24 in only one direction. Also, in Figure 3, reference character X indicates the amount of movement of the brake shoe when the disc brake assembly is actuated.

Figures 4 and 5 illustrate the condition of the retraction mechanism 22 when the brake is not applied (Figure 4) and when the brake is applied (Figure 5). As shown therein, when the brake is applied, the clip 26 moves or deforms as shown in Figure 5.

Figures 6 and 7 also illustrate the condition of the retraction mechanism 22 when the brake is not applied (Figure 6) and when the brake is applied (Figure 7). As shown therein, when the brake is applied, the clip 26 moves or deforms as shown in Figure 7. In particular, when the brake is applied, the arms 34A and 34B of the clip 26 deform or flatten as shown in Figure 7. Also, the prongs 32 can act like a clutch and allow the rod 24 to pass through in the direction of arrow 40 and adjust its position to take up pad wear. When the brakes are no longer applied, the clip 26 will return to its original position shown in Figure 6 moving the pad away from contact with the brake disc. Also, as shown in Figure 7, a slight panting of the clip 26 in the region 26A can also tend to spring back the clip when the brake is released.

Figures 8 through 11 also illustrate the condition of the retraction mechanism 22 when the brake is not applied (Figure 8) and possible positions when the brake is applied (Figure 9, 10 and 11). As shown therein, when the brake is not applied, the clip 26 is hard against the carrier 22 to prevent rattle as shown in Figure 8 at Points A and B. As shown in Figure 9, when the brake is applied, the clip 26 moves or deforms so that the clip arms 26A and 26B are flattened against the adjacent surface of the carrier abutment 12. As shown in Figure 10, the prongs 32 of the clip 26 can pant and allow the rod 24 to pass through and adjust its position to take up pad wear. Also, as shown in Figure 11, the clip arms 26A and 26B can flatten and then pivot at Point A on the carrier abutment 12.

Figures 12 through 14 also illustrate the condition of the retraction mechanism 22 when the brake is not applied (Figure 12) and possible positions when the brake is applied (Figures 13 and 14). Also, in this embodiment, the carrier abutment 12 has a chamfer surface 12A. As showntherein, when the brake is not applied, the clip 26 is hard against the chamber surface 12A of the carrier 22 to prevent rattle as shown in Figure 12. As shown in Figure 13, when the brake is applied, the clip 26 moves or deforms so that the clip arms 26A and 26B are flattened against the adjacent surface of the carrier abutment 12. As shown in Figure 14, the prongs 32 of the clip 26 can pant and allow the rod 24 to pass through and adjust its position to take up pad wear.

Figure 15 shows the carrier member 11, and Figure 16 shows the brake shoe assembly 14. Figures 17 through 21 show various views of the clip 26 of the retraction mechanism, and Figure 22 shows the pin 24 of the retraction mechanism.

In one embodiment which could be described in relation to the Figures above, the pin 24 is threadably received in the ends 18 of the backing plate. Before the pin 24 is screwed into the backing plate, the clip 26 is placed onto the pin 24. Once the clip 26 is on the pin 24 then the pin 24 is screwed into a complementary hole in the backing plate 18. It will be appreciated, due to the nature of the clip 26, that it would not be possible to screw the pin 24 into the backing plate 18 and the slide the clip 26 thereon because of the one way nature that the clip 26 can slide along the pin 24. It will be appreciated that creating screw threaded members may not be as cheap a process as may be desired.

In a further embodiment, as described in relation to Figures 23 to 28 a further design of pin 100 is shown. The pin 100 comprises a clip engaging portion 102 and a base portion 104. The clip engaging portion 102 has a first 106 and second 108 substantially flat side on opposite sides thereof. The base portion 104 is of a larger cross section than the pin engaging portion 102. The pin 100 may be fabricated by stamping, or otherwise pressing a roughly circular cross section rod and is thus, cheaper to manufacture than a pin 24 with a screw threaded portion. As shown in the Figures, the pin has a width of y at a widest part of the clip engaging portion 102.

Figure 24 shows an end elevation of the pin 100 viewed from the end opposite the base portion 104. Figure 25 shows a side elevation of the pin 100.

Figure 28 shows a portion of the backing plate 18, which has previously been described, but modified to receive the pin 100 of Figures 23 to 25.

A hole 150 is provided within the backing plate 18 through which the pin 100 can be passed. The hole 150 has a shape that is roughly complementary to the pin 100 and thus there is a portion 152 arranged to receive the clip engaging portion 102 of the pin 100. The hole 152 also has a portion of larger cross section 154 arranged to receive the base portion 104 of the pin. The hole 150 may be formed in the backing plate using one or more stamping operations and as such may be provided more cheaply than having to drill and tap a hole.

It should be noted that the backing plate 18 has a depth x, which is less than the length of the pin 100. Therefore, when the pin 100 is inserted into the hole 150 the length of the pin 100 beyond x from the base portion 104 thereof protrudes beyond an upper surface of the backing plate 18 as shown in Figure 28. This upper surface would be the opposite face to that having the friction pad thereon.

A clip 126 according to this second embodiment of the invention is shown in Figure 26. It will be seen that the clip 126 of Figure 26 is largely similar to that described above and like parts will not be described further. However, the opening 138 at a centre region of the clip 126 has been changed. The opening 138 now has a first 140 and a second 142 flat region, which function as will be described hereinafter. The distance between the first and the second flat regions 140, 142 is y or more preferably slightly greater than y, the maximum width of the pin 100.

The opening 138 also has two curved regions 144, 146 that are provided at the end of teeth 148,149 and the distance between the two curved regions 144, 146 is less than y. The distance y may provide a first dimension which can be seen is greater than the distance between the two flat surfaces of the pin 100. The distance between the two flat surfaces provides a second dimension which is less than the first and orthogonal thereto.

Since the pin 100 is slightly narrower than the width between the first and second 140, 142 flat regions of the opening 138 the pin 100 can be inserted will little resistance with the widest part oriented toward the flat regions 140, 142.

As will be explained in relation to Figure 27 this arrangement of the clip 126 and pin 100 can allow the clip 126 to be readily placed onto the pin 100. The clip 126 is oriented relative to the pin 100 such that the widest part of the pin is aligned between the first 140 and second 142 flat regions of the clip 126. Thus, the clip 126 can be passed onto the pin 100.

Next, as can be seen illustrated in Figure 27b, the clip 126 is rotated relative to the pin 100 by roughly 90 . This moves the widest dimension of the pin 100 between the two curved surfaces 148, 149 which engage the pin 100 and hold the clip 126 thereon. In this orientation, the clip 126 and pin 100 function much as described in relation to the embodiment described in relation to Figures 1 to 22. However, it will be appreciated that in the embodiment described in relation to Figures 23 to 28 the pin can be inserted into the backing plate 18, before the clip is placed thereon.

Claims

1. A brake shoe which carries, on a first side of the shoe, a friction pad, the shoe also comprising one or more pins provided on a second side of the shoe, opposite the first side, and the or each pin having a cross section comprising a first dimension along a first direction and a second dimension, less than the first, along a second direction transverse the first direction, there being received on the or each pin a spring clip arranged to allow the shoe to be mounted, and in which the or each spring clip comprises an opening such that the pin can be inserted thereinto, the clip and pin being configured such that the spring clip can be arranged on the pin in a first orientation with relatively no engagement with the pin and subsequently moved to a second orientation relative to the pin in which the clip has a relatively larger engagement with the pin.

2. A brake shoe according to claim 1 in which movement from the first orientation to the second orientation occurs by rotation.

3. A brake shoe according to any preceding claim in which an opening in the brake shoe arranged to allow a pin to be inserted thereinto is provided by stamping the brake shoe.

4. A brake shoe according to any preceding claim in which the or each pin comprises a flat region.

5. A brake shoe according to claim 4 in which the region is an end region.

6. A brake shoe according to any preceding claim in which the second direction is substantially transverse the first direction.

7. A brake shoe according to any preceding claim which comprises two pins.

8. A brake shoe according to any preceding claim in which the or each spring clip is fabricated from a material which is harder than the material of the pin.

9. A tool arranged to allow a spring clip to be rotated relative to a pin of a brake shoe according to any preceding claim which comprises a clip engaging portion arranged to receive a clip therein and a lever means arranged to provide sufficient force to rotate the clip relative to the pin.

10. A kit of parts arranged to provide a brake shoe according to any of claims 1 to 8, the kit comprising a backing plate having a friction pad on a first side, at least one pin arranged to be fitted to the backing plate and at least one clip arranged to be received on the pin.

11. A kit according to claim 10 which includes a tool according to claim 9.

12. A disc brake assembly comprising an anchor bracket, a brake shoe which carries a friction pad and a piston slidably connected to the anchor bracket which is arranged such that, upon movement of the piston relative to the anchor bracket, the piston acts upon the brake shoe to move the shoe into contact with a brake disc, and in which the assembly further includes a retraction mechanism which is adapted to retract the brake shoe from the disc when the piston is retracted, the retraction mechanism comprising at least one pin secured to one of the friction pad and the anchor bracket, the pin having at least one flat surface, and a spring clip fixed relative to the pin which acts between the pin and the other one of the anchor bracket and the friction pad, the disc brake assembly being arranged such that deformation of the spring clip as the pad is moved towards the disc provides a returning force to pull the friction lining away from the disc when the piston is retracted.

13. A disc brake assembly according to claim 12 in which the spring clip comprises a resilient plate having an opening through which the pin passes and defining at least one wing which is in contact with the anchor bracket, the or each wing being arranged to deform resiliently as the friction pad moves towards the disc.

14. A disc brake assembly according to claim 13 in which the spring clip comprises at least two wings which extend in opposing directions away from the opening, such that each wing is in contact with the anchor bracket.

15. A disc brake assembly according to any of claims 12 to 14 in which the engagement of the pin and the clip may be arranged such that in normal use the spring clip is permitted to move along the pin in only a single direction.

16. A disc brake assembly according to claim 13 or claim 14 which further comprises a second retraction mechanism wherein the two retraction mechanisms are provided which are located at or adjacent, each end of the brake shoe.

17. A disc brake assembly according to any one of claims 13 to 15 in which the pin and/or spring clip has any of the features of claims 1 to 8.

18. A brake shoe assembly adapted for use in a disc brake assembly having at least one pin having at least one flat surface secured to the brake shoe which carries a spring clip, the spring clip co-operating with the pin through a sliding frictional engagement and having at least one deformable wing which is adapted to contact an anchor bracket of the disc brake assembly, and whereby the engagement between the clip and the pin is such that the clip is fixed relative to the pin until a force applied to the clip exceeds a predetermined limit whereby the clip is adapted to slide along the pin away from the brake shoe.

19. A brake shoe substantially as described herein and as illustrated in the accompanying Figures 1 to 28.

20. A kit of parts arranged to provide a brake shoe substantially as described herein and as illustrated in the accompanying Figures 1 to 28.

21. A disc brake assembly substantially as described herein and as illustrated in the accompanying Figures 1 to 28.

22. A brake shoe assembly substantially as described herein and as illustrated in the accompanying Figures 1 to 28.

Amendments to the claims have been filed as follows 1. A brake shoe which carries, on a first side of the shoe, a friction pad, the shoe also comprising one or more pins provided on a second side of the shoe, opposite the first side, and the or each pin having a cross section comprising a first dimension along a first direction and a second dimension, less than the first, along a second direction transverse the first direction, there being received on the or each pin a spring clip arranged to allow the shoe to be mounted, and in which the or each spring clip comprises an opening such that the pin can be inserted thereinto, the clip and pin being configured such that the spring clip can be arranged on the pin in a first orientation with relatively no engagement with the pin and subsequently moved to a second orientation relative to the pin in which the clip has a relatively larger engagement with the pin, and being configured such that the clip is prevented from sliding along the pin towards the brake shoe.

A brake shoe according to claim 4 in which the region is an end region.

NAG

7. A brake shoe according to any preceding claim which comprises two pins.

11. A kit according to claim 10 which includes a tool according to claim 9.

12. A disc brake assembly comprising an anchor bracket, a brake shoe which carries a friction pad and a piston slidably connected to the anchor bracket which is arranged such that, upon movement of the piston relative to the anchor bracket, the piston acts upon the brake shoe to move the shoe into contact with a brake disc, and in which the assembly further includes a retraction mechanism which is adapted to retract the brake shoe from the disc when the piston is retracted, the retraction mechanism comprising at least one pin secured to one of the friction pad and the anchor bracket, the pin having at least one flat surface, and a spring clip fixed relative to the pin which acts between the pin and the other one of the anchor bracket and the friction pad, the disc brake assembly being arranged such that deformation of the spring clip as the pad is moved towards the disc provides a returning force to pull the friction lining away from the disc when the piston is retracted, and the engagement of the clip with the pin being such that the clip is prevented from sliding along the pin towards the brake shoe.

16. A disc brake assembly according to claim 13 or claim 14 which further comprises a second retraction mechanism wherein the two retraction mechanisms are provided which are located at or adjacent, each end of the brake shoe. l

18. A brake shoe assembly adapted for use in a disc brake assembly having at least one pin having at least one flat surface secured to the brake shoe which carries a spring clip, the spring clip co-operating with the pin through a sliding frictional engagement and having at least one deformable wing which is adapted to contact an anchor bracket of the disc brake assembly, and whereby the engagement between the clip and the pin is such that the clip is fixed relative to the pin until a force applied to the clip exceeds a predetermined limit whereby the clip is adapted to slide along the pin away from the brake shoe, the engagement being such that the clip is prevented from sliding along the pin towards the brake shoe.

19. A brake shoe substantially as described herein and as illustrated in the accompanying Figures I to 28.