GB2173875A - Disc brake caliper - Google Patents

Abstract

A disc brake caliper has a pair of arms 36, 37 pivoted to a base member 32. The arms carry brakepad assemblies 30, 31 and the disc engaging surfaces of the brakepads are maintained parallel to the disc surfaces by resilient links 50, 51, each forming part of a parallelogram linkage and able to deform to take account uneven wear of the associated brakepad surface. <IMAGE>

Description

SPECIFICATION Brake caliper assembly This invention relates to disc brake calipers.

Such calipers comprise a base member and a pair of caliper arms pivoted to the base member. Each arm carries a brake pad assembly pivoted to the arm and each such assembly carries a brake pad having a surface to engage the disc.

It is desirable that as the brake pads move into engagement with the surfaces of the disc during braking operation, the disc-engaging surfaces of the pads should be parallel to the disc surfaces.

It is known to rely on friction in the pivotal connection between the arms and the brake pad assemblies so that, as the brake pad assemblies leave engagement with the disc surfaces with the engaging surfaces are parallel, they will remain in the correct position until the next operation. However if the brake pad assemblies do become misaligned uneven wear occurs.

It is also known to have rigid parallelogram linkages to maintain the brake pad assemblies parallel as the caliper is operated. This has a disadvantage that if the brake pads are unevenly worn or the disc misaligned uneven wear of the pads takes place because the links are rigid.

It is an object of the present invention to provide a disc brake caliper in which there is a parallelogram linkage but the links are resilient so that although the pads will first come into engagement with the disc surfaces in the correct orientation, if they are unevenly worn the links will be permitted to change their effective lengths so that the pads engage the disc surfaces over the whole surfaces of the pads.

According to the invention, therefore, we provide a disc brake caliper comprising a base member; a pair of caliper arms pivoted to the base member; a brake pad assembly pivoted to each arm; a brake pad in each assembly having a surface to engage a disc; a pair of links each pivoted at one end to a respective brake pad assembly and at the other end to the base member so as to form a parallelogram linkage with the assembly, the arm on which the assembly is mounted and the base member; the links acting, when the brake pads are unworn, to hold the disc-engaging surfaces thereof parallel to the disc surfaces as such surfaces move towards engagement in use; the effective lengths of the links being variable against a resilient bias, thus permitting said disc-engaging surfaces to make contact over substantially the whole of their areas with the disc even if there has been uneven wear of the disc-engaging surfaces.

Preferably each link is resiliently deformable so as to effect changes in its effective length.

Each link may comprise a piece of resilient wire having ends pivotally received in apertures in the base member and in a brake pad assembly. Each link may be provided between said ends with a resilient loop portion.

The invention will now be described in detail by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of a brake pad assembly; Figure 2 is an elevation of the assembly of Figure 1 showing its relationship to a disc with the latter cut away; Figure 3 is a perspective view of a brake pad; Figure 4 is a perspective view of a disc brake caliper; Figure 5 is a detail section showing the means for pivoting the arms of the caliper of Figure 4; and Figure 6 is a detail view showing a modification of the caliper of Figures 4 and 5.

Referring now to Figures 1 to 3, the brake pad assembly is indicated generally at 10 and comprises a holder 11 which is a casting in light alloy and which has on the rear face thereof two trunnions 12 provided with aligned apertures 13.

The face of the casting remote from the trunnions 12 is formed with a recess 14 as shown in Figure 2. The recess has end wall portions 15 and side wall portions 16. The side wall portions have inclined end parts 17.

An opening 18 is provided between each pair of end wall portions 15.

A brake pad is indicated generally at 19 and comprises a block 20 of friction material to one face of which is bonded a metal strip 21.

The strip is bonded in position during manufacture of the pad. The pad is of a shape closely to fit within the recess 14 having a periphery comprising end walls 22 and side walls 23, the latter being of a shape to correspond with the side walls 16 of the recess 14.

The metal strip 21 provides means for releasably securing the brake pad in the holder 10 and has T-shaped end portions 24 each comprising a stem 25 and a cross member 26.

As clearly shown in Figures 1 and 2, the brake pad 19 can be placed within the recess 14 in the holder 10 and secured in position by bending over the end portions 24 so that the stems 25 lie in the openings 18 and the cross members 26 lie against the rear surfaces of wall portions 15. The cross members 26 and the surfaces of the wall portions 15 provide cooperating securing means for releasably securing the pad in the holder.

Thus when the pad is worn, the end portions 24 can be bent back to the position shown in Figure 3, the worn pad removed, a new pad fitted into the recess and held there by deforming the end portions 24. The gauge of the metal strip 21 is preferably such that the strips can be deformed by finger pressure making it easy to instal and remove the brake pads.

Figure 2 shows the disc 27 of a brake and it will be seen that the inclined end parts 17 of the pad are provided so as to avoid the pad overlapping the disc at the outer periphery thereof. The wall portions 15 and 16 of the recess 14 cooperate with the end walls 22 and the side walls 23 of the pad so as to restrain movement of the pad relative to the holder in two pairs of opposite directions, i.e.

vertically and horizontally in Figure 2, one pair of said directions being perpendicular to the other pair of said directions.

Thus the brake pad is substantially surrounded by the wall portions of the holder, most of the braking force being taken by the pairs of wall portions 15 with the wall portions 16 preventing sideways movement of the pad and the pad being held in position in the holder so that it moves away from the disc with the holder, by the deformed end portions 24.

Referring now to Figure 4, this shows a complete brake caliper into which the brake pad assemblies of Figures 1 to 3 are fitted.

There are two such assemblies indicated at 30 and 31 in Figure 4. The caliper comprises a base member 32 having two pairs of upper and lower flanges. One such pair is indicated at 33 and 34. The upper flange of the other pair is indicated at 35.

Between the flanges 33 and 34 is pivoted an arm 36 and an arm 37 is pivoted between the upper (35) and lower flanges on the other side of the base member. The arms are pivoted in an identical fashion as shown in Figure 5 for the arm 36. Referring to Figure 5, a sleeve 38 is received in a bore 39 in the arm and provides a pivot for the arm. The lower end of the sleeve is received in a bore 40 in the flange 34, the bore having a shoulder 41 and continuing in a counter-bore 42. The upper end of the sleeve 38 stands proud of the upper surface of the flange 33 as shown at 43 and a bolt 44 passes through the sleeve 38 and the flange 34 and also through a support 45. The bolt has a head 46 which engages a plate 47, described below, which in turn engages the upper end of the sleeve 38, and a nut 48.

It will be seen that the sleeve 38 provides a pivot for the arm 36. The bolt 44 serves to hold the caliper to the support 45 and is prevented from pinching the flanges 33 and 34 together to nip the arm 36 by virtue of the fact that the sleeve 38 stands proud of the upper flange 33 at 43.

The brake pad assemblies 30 and 31 are pivoted to the ends of the arms 36 and 37 by pivot pins one of which is shown at 49, the pivot pins passing through the apertures 13 in the trunnions 12 of the holder 10.

Each of the brake pad assemblies 30 and 31 is controlled in its position by similar links 50 and 51. Referring to the link 50 by way of example, it has two aligned portions 52 and 53 connected by a resilient U-shaped loop 54.

The end portion 52 has an end 55 which is at right angles to the portion 52 and is pivotally received in an aperture in the upper trunnion 12 as shown in Figure 1. The end portion 53 similarly has an end 56 which is pivoted in the upper flange 33. As shown in Figure 5, the plate 47 overlies the end portion 53 and retains the links in position while allowing them to pivot.

The brake pad assemblies 30 and 31 are moved together to apply the brake pads to the disc by means of a thruster 57 of any convenient type which is secured by nuts 58 to the arm 36 and has a rod 59 engaging the arm 37. The thruster may be operated by fluid pressure to extend the rod 59 to move the right-hand end of the arms in Figure 4 apart thus moving the brake pads carried by the assemblies 30 and 31 into engagement with a disc (not shown) positioned between the assemblies 30 and 31. The arms are pulled back to an off position by means of tension springs 60 and 61 connected to pins 62 and 63 on the arms 37 and 36 respectively, the tension springs being anchored to a common projection 64 carried by a bracket 65 bolted to the upper flange 33.

The links 50 and 51 form, with the arms 36 and 37, parallelogram linkages. Thus, taking for example the arm 36 and the link 51, the arm is pivoted on the bolt 44 and sleeve 38 and the brake pad assembly 30 is pivoted on the pivot pin 49. The ends of the link 51 are pivotally mounted in the flange 33 and the trunnion 12 of the pad assembly 30 in such manner that, as the arms 36 and 37 move to bring the brake pads towards the disc, the brake pad engaging surfaces are retained parallel to the disc surfaces. Thus the distance between the two pivot points on the brake pad holder, i.e. the pivot point of the brake pad holder on the arm 36 and the pivot point of the link 51 on the holder is equal to the distance between the pivot point provided by the longitudinal axis of the bolt 44 and the pivot point of the link 51 on the flange 33.

It follows that when the brake pad surfaces are unworn they will be held so as to engage the disc surfaces in the correct positions parallel to the disc surfaces. However if the surfaces become unevenly worn, the resilient loops 54 in the links 50 and 51 may be deformed after the brake pads have engaged the disc so as to ensure full contact of the brake pad surfaces with the disc surfaces. If the links 50 and 51 are stressed due to uneven wear of the pads, the links will tend to redistribute the braking force across the area of the pad surface tending to even out the wear.

If the caliper is mounted as shown in Figure 4 relative to the disc with the axes of the bolts 44 vertical then there is no force tending to pivot either of the arms 36, 37 so that its brake pad assembly engages a disc when the caliper is in the off position with the arms 36 and 37 withdrawn by the springs 60 and 61.

However if the caliper is mounted, for example at a twelve o'clock position on a disc with the pivot axes of the arms horizontal, the weight of the thruster 57 secured to the arm 36 will tend to pivot the arm so as to bring the brake pad assembly 30 into engagement with the disc which is undesirable when the caliper is in an off position. Because of the springs 60 and 61 both arms 36 and 37 will pivot in the same direction. This may be prevented by the arrangement shown in Figure 6 in which the bracket 65 carries a bolt 66 which is adjustable in a sleeve 67 and may be adjusted to prevent the arm 37 from pivoting in a clockwise direction in Figure 6 to a sufficient extent to allow the arm 36 also to pivot in a clockwise direction to bring the brake pad carried by the arm into engagement with the disc. The arms will be held together by the springs 60 and 61 so that the arm 37 engages the end of the rod 59 and the arms will thus move together.

Claims (10)

1. A disc brake caliper comprising: a base member; a pair of caliper arms pivoted to the base member; a brake pad assembly pivoted to each arm; a brake pad in each assembly having a surface to engage a disc; a pair of links each pivoted at one end to a respective brake pad assembly and at the other end to the base member so as to form a parallelogram linkage with the assembly, the arm on which the assembly is mounted and the base member; the links acting, when the brake pads are unworn, to hold the disc-engaging surfaces thereof parallel to the disc surfaces as such surfaces move towards engagement in use;; the effective lengths of the links being variable against a resilient biast thus permitting said disc-engaging surfaces to make contact over substantially the whole of their areas with the disc even if there has been uneven wear of the disc-engaging surfaces.

2. A caliper as claimed in Claim 1 in which each link is resiliently deformable so as to effect changes in its effective length.

3. A caliper as claimed in Claim 2 in which each link comprises a piece of resilient wire having ends pivotally received in apertures in the base member and a brakepad assembly.

4. A caliper as Claimed in Claim 3 in which each said link is provided, between said ends, with a resilient loop portion.

5. A caliper as claimed in Claim 4 in which the loop is U-shaped.

6. A caliper as claimed in any preceding claim in which there is provided stop means engageable with at least one of the arms to limit movement of the brakepad assembly carried by said arm a direction away from the disc.

7. A caliper as claimed in any preceding claim including two tension springs each mounted between the base member and a respective arm to urge the brakepads apart.

8. A disc brake caliper having parallelogram links substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

9. A disc brake caliper substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

10. A disc brake caliper according to Claim 9 but modified substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.