DISC BRAKES

This invention relates to disc brakes and in particular, though not exclusively, to such brakes designed to provide a handbrake function.

Disc brakes are well known which comprise:- a support structure for attachment to a vehicle; a caliper which spans an associated disc and is supported for sliding relative to the disc on the support structure; the caliper including an actuation piston which is moveable within the caliper in a direction generally parallel to an axis of rotation of the associated disc to move a first brake pad into contact with a first side of the associated disc and to cause sliding displacement of the calliper relative to the support structure to draw a second brake pad into contact with the other side of the disc.

Such disc brakes are hereinafter referred to as being of the kind specified.

It is an object of the present invention to provide a disc brake of the kind specified which is relatively cheap to manufacture and which can therefore provide an economical handbrake function.

Thus in accordance with the present invention there is provided a disc brake of the kind specified in which the sliding displacement of the caliper relative to the support structure is guided by the engagement of the piston in a bore in the support structure, the piston also being housed in a bore in the calliper and being moved relative to the calliper to apply the brake by a ball and ramp expander mechanism.

This provides a disc brake construction which is particularly suitable for the provision of a handbrake function.

The ball and ramp expander mechanism may comprise first and second confronting ramp members with pairs of co-operating ball ramp pockets each containing an actuating ball, one of the ramp members being rotatable to apply the brake and one of the ramp members reacting against an axial support bearing supported against an axially adjustable adjuster member, the axially adjustable adjuster member allowing adjustment of a retracted position of the piston in the caliper bore to adjust the pad to disc clearance when the brake is released.

Conveniently the axially adjustable adjuster member may comprise an externally threaded nut which is in screw-threaded engagement with an internally threaded portion of the caliper bore and is rotatable in the bore to adjust the retracted position of the piston.

The externally threaded nut conveniently also has a formation engageable by a spanner or similar tool to rotate the nut in the bore.

A return spring for the ball and ramp expander may be housed within the piston.

A brake actuating lever is preferably rotationally connected with one of the ramp members.

The support structure may have an inverted U-shaped portion with one arm of the inverted U-shaped section designed to be located on one side of the disc and the other arm of the inverted U-shaped portion designed to be located on the other side of the disc with a brake pad located and supported in each respective arm of the inverted U-shaped portion.

Preferably guide means on the caliper may co-operate with guide means on the support structure to prevent rotation of the caliper relative to the support structure when the brake is applied.

Conveniently the caliper may be provided with a pair of circumferentiafiy extending forks which each engage a respective guide pin carried by the support structure which extends generally parallel to the axis of rotation of the associated disc.

One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 and figure 2 both show perspective views of a disc brake in accordance with the present invention, and

Figure 3 shows a cross section through the disc brake of figures 1 and 2.

Referring to the drawings, a disc brake 10 has a support structure in the form of a support bracket 11 which is bolted to the suspension of an associated vehicle via holes 12. The support bracket 11 is of inverted U-shaped form with an inner arm 11a which includes the attachment holes 12 and an outer arm 11b which is disposed on the other side of the brake disc 13 which is shown diagrammatically in figure 3.

Mounted on the support bracket 11 is a caliper body 14 which supports an actuating piston 15 in a bore 16. The piston 15 also slides in a bore 17 in the support bracket arm 11a and thus guides the caliper body 14 for sliding relative to the disc 13 as indicated by arrow X in figure 3.

Mounted on either side of the disc 13 are brake pads 18a and 18b. Pad 18a is brought into contact with a disc by direct contact from piston 15 and pad 18b is brought into contact with the disc by sliding of the caliper body which draws the pad 18b into contact with the disc via limb 19 of the caliper body.

As will be appreciated, the pads 18a and 18b are supported during braking by recesses formed in the support bracket arms 11a and 11b respectively.

Rotation of the caliper body 14 relative to the support bracket 11 is resisted by a pair of forks 20 formed on the caliper body which engage guide pins 21 carried on the support bracket 11. Forks 20 slide on pins 21 when the brake is applied and released.

A set screw 22 enters a slot 23 formed in piston 15 to prevent rotation of the piston 15 relative to the bore 16 in the caliper body.

The piston 15 is moved axially relative to the caliper body 14 by a ball and ramp expander mechanism 24 which comprises confronting ramp members 25 and 26 which include pairs of cooperating ramp pockets 25a and 26a respectively each containing an actuating ball 27.

Ramp member 25 is rotated relative to ramp member 26 by an actuating lever 28 which is operated by a cable 28a with the outer sheath 28b of the cable supported on a reaction member 29 as indicated diagrammatically in dotted detail in figure 2.

Ramp member 25 is screw threaded onto a bolt 30 at 31 and mounts a return spring 32 within piston 15. Spring 32 acts between a head 33 of bolt 31 and an abutment surface 34 on the piston 15 to provide a return force which returns the ball and ramp expander mechanism 24 to its non actuating position when the actuating lever 28 is released. A clamping nut 30a holds the bolt 30, the lever 28 and the ramp member 25 in a fixed position relative to each other. A cap 15a seals the inside of piston 15.

Ramp member 25 is axially supported by thrust bearing 35 which reacts against an adjuster member 36 which is in screw threaded engagement at 37 with the bore 16 in the caliper body. The axial position of adjuster member 36 in the screw threaded bore 37 is adjustable by using a spanner or other suitable tool on flats 38 provided on the outer end of adjuster member 36.

As will be appreciated the axial position of adjuster member 36 in screw threaded bore 37 determines the position to which piston 15 is drawn by spring 32 when the

actuating lever 28 is released. Thus as the pads 18a, 18b wear, the position of piston 15 in bore 37 is adjusted towards the disc 13 to compensate for the pad wear.

In order to access the flats 38 on adjuster member 36 a rubber sealing bellows 39 must be first displaced axially towards the end rim 40 of the caliper body.

A further sealing bellows 41 is provided between the support bracket 11 and the caliper body 14.

As will be appreciated the disc brake of the present invention provides a simple but effective braking mechanism in which the sliding of the caliper body 14 relative to the support bracket 11 is simply and efficiently achieved by the sliding of piston 15 in the bore 17 in limb 11a of the support bracket. This provides a caliper construction which is particularly suitable for use as a hand brake for a vehicle.