GB2122290A - Self adjusting mechanisms for brakes - Google Patents

Abstract

A hydraulic brake self adjuster mechanism to limit the return movement of a hydraulic piston (15) includes a fixed length strut (22), a sleeve (24) having a limited axial sliding movement on the strut, and a ball and ramp mechanism acting between the sleeve and the hydraulic piston (15). The ball and ramp mechanism includes an array of caged balls (29) and co-operating surfaces (27,30) on the sleeve and piston which surfaces are convergent in the direction of return movement of the piston. When the brake is applied and if clearance 'C' exceeds the limited axial play of sleeve (24) on strut (22), which play is set by a pin (34) projecting through elongated holes (36) in strut (22), then the piston (15) will move axially relative to the sleeve (24) but on brake release the balls (29) jam relative movement between piston (15) and sleeve (24). To de-adjust, a lever (37) is rotated so that a cam (38) pushes a bar (33) which carries pin (34). As shown, brake is a disc brake operable hydraulically or mechanically: it may be drum brake. <IMAGE>

Description

SPECIFICATION Self adjusting mechanisms for brakes This invention relates to self adjusting mechanisms for hydraulic brake actuators and in particular but not exclusively for motor vehicle disc brakes.

Accordingly there is provided a hydraulic brake self adjuster mechanism of the type that limits the return movement of a hydraulic actuator piston on release of the brake in order to compensate for brake wear, said adjuster comprising a fixed length strut, a co-axial sleeve slidable along the strut and having an axial lost motion connection therewith, and a ball and ramp mechanism acting between the sleeve and piston and including co-operating surfaces on the sleeve and piston, said surfaces being convergent in the direction of the return movement.

The invention will be described by way of example and with reference to the accompanying drawing which illustrates a cross-section through a disc brake according to this invention.

With reference to the drawing, a disc brake caliper body 11 straddles the outer periphery of a rotatable disc 12. In use the caliper body 11 will be bolted to part of a vehicle stub axle assembly (not shown) and the disc will be secured fast with a road wheel.

The caliper body supports a pair of opposed friction pads 13 on opposite sides of the disc 12. In use the friction pads 13 are each thrust against opposite sides of the disc 12 by a piston 15 in a hydraulic actuator 14. Each piston 15 is cup shaped having its base adjacent the pad 13 and its open end within the actuator 14. When the brakes are released the frictional grip between the piston seals 16 and 17 in the caliper body and each piston 15 serves to return the piston 15 into the actuator 14 and provide an operating clearance 'C' between each pad 13 and its respective side of the disc 12.

The return movement of each of the pistons 15 is limited by an adjuster 21 housed within the cup shaped piston so that as the pad 13 wears the piston 15 return stop is moved towards the disc 12 in order to compensate for the wear.

The adjuster 21 in each actuator 14 is identical and therefore only the adjuster in the left-hand actuator will be described in detail.

The adjuster 21 has a strut 22 of fixed length which is arranged co-axially with the piston 15 and which passes sealingly through the caliper body 11 into the cup shaped piston 15. The strut 22 is held in place relative to the caliper body 11 by a pair of circlips 23 and 23' adjacent each side of the hydraulic actuator wall. A co-axial annular sleeve 24 is fitted onto the strut 22 within the piston 15 and is slidable on the strut for limited axial movement. The sleeve 24 can slide between a shoulder 25 on the inner end portion of the strut 22 and the circulip 23' on the strut adjacent the inner wall surface of the actuator. An annular spring washer 26 is located between the circlip 23 and the sleeve 24 to bias the sleeve towards the shoulder 25.The inner most end portion of the sleeve 24 has an external tapered surface 27 thereon thattapers towards the base of the piston.

The tapered portion 27 of the sleeve carries an annular ball race 28 thereon in which the balls 29 are held together in a circumferential array by a cage which allows the balls 29 some axial and radial movement whilst retaining them in their respective circumferential positions.

The internal cylindrical surface within the mouth of the cup shaped piston 1.5 has a hardened steel bush 30 set therein. The cytinder inner surface of the bush and the tapered surface 27 on the sleeve provide co-operating surfaces that converge in the direction of the return movement of the piston.

The balls 29 act between the two convergent surfaces to form a ball and ramp mechanism. The balls 29 are biased up the tapered surface ie. into the convergent surfaces by a belleville spring washer 31 secured onto the innermost end of the sleeve 24.

The strut 22 is hollow and has a cylindrical bar 33 axially slidable therein. The bar 33 carries a diametral pin 34 thereon that projects through axial elongated holes 36 in the strut 22 and sleeve 24 which accommodates axial movement of the pin 34. The bar 33 can be moved axially by a rotatable handle 37 with cam 38 on its end adjacent the bar and the pin 34 abuts a washer 39 to act on the balls 29 of the ball race.

The disc brake and adjuster operate as follows: When the brakes are applied hydraulically the piston 15 moves outwardly of the actuator 14 to thrust a pad 13 against the disc 12. If the clearance 'C' between the pad 13 and the disc exceeds the limited axial play of the sleeve 24 on the strut 22 the piston 15 will move axially towards the disc relative to the sleeve 24 which is in abutment with the shoulder 25. The spring 31 pushes the balls 29 into the apex of the convergent surfaces 27 and 30 and when the brakes are released the balls 29 jam relative movement between the piston 15 and sleeve 24. The sleeve and piston then move back against the bias of the spring washer 26 for the limit lost motion connection to reform the clearance 'C' between the pad and disc.

In order to de-adjust the brake to change the brake pads 13, the lever 37 is rotated so that the cam 38 pushes the bar 33 towards the pad 13. This moves the pin 34 into abutment with the washer 39 which in turn acts on the balls 29 to push them away from the apex of the surfaces 27 and 30 thereby allowing the pistons 15 to be pushed back into the actuator 14 relative to the sleeve 24.

The rightuhand actuator 14' is also fitted with a hand brake mechanism whereby the actuator may also be mechanically operated to thrust its pad 13 against the disc. The respective strut 22 is axial.ly slidable in the caliper body 11 and has a pair of circlips 43 fitted on the strut on either side of the actuator wall to limit its axial travel. A stack of belleville spring washers 44 act between the caliper body 11 and the external circlip 43' to bias the strut 22 into a brake released position. The external end face of the strut 22 is connected by a link 45 to a rotary cam 46 operated by a hand brake lever 46.

The hand brake is applied by rotating the lever46 clockwise to move the strut 22 towards the piston 15.

The strut 22 then pushes the piston and pad 13 towards the disc 12 to apply the brake.

Whilst the invention has been described by way of example using a disc brake, it is equally applicable to drum brake actuators.

Claims (9)

1. A hydraulic brake self adjuster mechanism of the type that limits the return movement of a hydraulic actuator piston on release of the brake in order to compensate for brake wear, said adjuster comprising a fixed length strut, a co-axial sleeve slidable along the strut and having an axial lost motion connection therewith, and a ball and ramp mechanism acting between the sleeve and piston and including co-operating surfaces on the sleeve and piston, said surfaces being convergent in the direction of the return movement.

2. An adjuster mechanism as claimed in Claim 1, in which the piston is cup shaped and wherein the convergent surfaces comprise a cylindrical surface portion on the internal surface of the cup shaped piston, and a tapered surface on the external surface of the sleeve.

3. An adjuster mechanism as claimed in Claim 1 or Claim 2, wherein the ball and ramp mechanism includes a ball race in which the balls are held together in a circumferential array by a cage which allows the balls some axial and radial play whilst retaining them within the race.

4. An adjuster mechanism as claimed in any preceding claim in which the adjuster mechanism includes a de-adjuster wherein the strut extends sealingly through the actuator body and the deadjuster comprises a co-axial bar axially slidable within the strut and having abutment means thereon for acting on the balls of the ball race to move the balls away from the apex of the convergent surfaces and thereby allow the brake to de-adjust, said bar being operable by means external of the actuator body.

5. An adjuster mechanism as claimed in Claim 4, wherein the abutment means are a diametral pin fixed in the bar and which project through axially elongated holes in the strut and sleeve for abutment against the co-axial annular washer which in turn contacts the balls.

6. An adjuster mechanism as claimed in any preceding claim, wherein the strut extends sealingly through the actuator body and has limited axial movement relative to the actuator body and is connected to a hand brake lever whereby the strut may be moved to apply the brake through the piston and the strut is spring loaded for a return to a brake released position.

7. A disc brake caliper having a hydraulic actuator with a self adjuster mechanism as claimed in any preceding claim.

8. A hydraulic brake self adjuster mechanism substantially as described herein and with reference to the accompanying drawing.

9. A disc brake substantially as described herein and as illustrated in the accompanying drawing.