GB1596324A

GB1596324A - Pressure medium operable disc brake

Info

Publication number: GB1596324A
Application number: GB874678A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-07-30
Filing date: 1978-03-06
Publication date: 1981-08-26
Also published as: DE2734518C2; DE2734518A1

Description

(54) PRESSURE MEDIUM OPERABLE DISC BRAKE (71) We, WABCO FAHRZEUG- BREMSEN GmbH (formerly Wabco Westinghouse GmbH), a German Company, of 3 Hannover 91, Postfach 911280, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:--- This invention relates to a pressure medium operable disc brake, particularly for a motor vehicle, and provides a modification of or improvement in the invention of U.K. Patent Specification No.

1,516,519.

According to U.K. Patent Application No. 44247/75, Specification No. 1,516,519, there is provided a pressure medium operable disc brake having an actuation mechanism comprising an annular cylinder member and an annular piston member axially slidable therein, and an expansible wear compensating device between one of the said members and a brake ring of the disc brake for transmitting movement of that member to the brake ring, said expansible wear compensating device in use compensating automatically upon brake actuation and release, for lengthening of the stroke of the mechanism resulting from wear of the brake lining effecting consequential widening of the gap between the annular member and the brake ring.

Specifically, one embodiment of said U.K.

Patent Specification No. 1,516,519 discloses a compensating device including two adjusting rings operatively linked through oblique faces and disposed between the said one annular member and a thrust collar held in the brake ring.

Since however the oblique faces of the adjusting rings must, by reason of their mode of working, be in self-locking engagement, it is necessary for the angle included by these oblique faces with the radial plane of the axle to be such that locking through a self-locking action is ensured at minimum values of the coefficient of friction y. In this context it is required that the ,values remain as constant as possible or that any variations in the ,values are kept within the narrowest possible limits which can normally only be achieved by a special surface treatment or by applications of a coating on the oblique faces.

Variations in the value of N affect to a considerable extent the forces which have to be applied during brake release. It is therefore, considered desirable to provide a compensating device in which there is no need for adhering to narrow-tolerance values nor for an expensive treatment of the oblique surfaces by means of special methods.

According to the present invention there is provided a pressure medium operable disc brake having an actuation mechanism comprising an annular cylinder member and an annular piston member axially slidable therein, and an expansible wear compensating device between one of the said members and a brake ring of the disc brake to transmit movement of that member to the brake ring and to compensate automatically, upon brake actuation and release, for lengthening of the stroke of the mechanism resulting from wear of the brake lining, said expansible wear compensating device comprising two relatively rotatable rings having complementary oblique surfaces facing and engaging one another such that relative rotation of the two rings in one direction can increase the axial length occupied by the said device and effect a consequential widening of the gap between said one annular member and the said brake ring, the brake ring being located between said one annular member and externally disposed releasable locking means operable to lock the two rings of the compensating device against relative rotation in the opposite direction.

By way of example, embodiments of the present invention will now be described with reference to the accompanying drawings of which: Fig. 1 shows schematically in axial crosssection a compressed air operated disc brake according to this invention with a service brake circuit and a spring brake actuated parking or auxiliary brake circuit, and with an automatic compensating device having a locking device located outside the disc brake, Fig. 2 shows similarly substantially the same disc brake as shown in Fig. 1, but with a modified locking device, and Fig. 3 is a partly-sectioned perspective view of parts of the embodiment of Fig. 2.

A hub 1 mounted on the vehicle axle (not shown) has a road wheel 2 fixed thereto by wheel studs and wheel mounting nuts. A dise brake housing or casing, comprising brake discs 4 and 4a is attached to the hub 1 by means of bolts 3. Brake lining carriers 5 and 5a with linings 6 and 6a are arranged between the brake discs 4 and 4a. These carriers are supported by extensions thereof on supports 7 which are fixed by bolts or other means (not shown) to the axle tube 8.

An annular actuating unit is disposed between the lining carriers 5 and 5a, this unit comprising an annular cylinder 9, an annular piston 10 serving as the brake piston of the service brake, an annular piston 11 serving as the brake piston of the parking brake, and an automatic compensating device comprising two adjusting rings 12 and 13, a friction element 14, a spring 15 and a circlip or locking ring 16.

The chamber 17 between the closed end of annular cylinder 9 and the end face of brake piston 10 is the usual service brake chamber and is connected through its passage and port 17a with a brake valve which is not shown. The chamber 18 bounded by the inner surfaces of the brake piston 10 and of the brake piston 11 is the parking brake chamber and is connected through its passage and port 18a with a hand brake valve (also not shown).

A cup spring or plate spring 19 is positioned between the end face of the brake piston 11 and the surface which is operatively connected with the brake piston 10 so as to provide a spring force countering the pressure in the chamber 18.

One end of a spring 20 is connected to the brake piston 10 and its other end to the adjusting ring 12 (see Fig. 3). The latter has oblique surfaces which abut against complementary oblique surfaces of the adjusting ring 13. The inclined or oblique surfaces of rings 12, 13 are in each case provided adjacent the ring's outer periphery and are directed in planes transverse to radial plane of the disc brake. Caged ball or roller bearings 21 are provided in the operative connection between the brake piston 11 and the adjusting ring 12.

As long as the brake is not applied, the adjusting ring 12 abuts with its oblique surfaces against the oblique surfaces of the adjusting ring 13 as the result of the twisting force exercised by the spring 20.

The oblique surfaces on the adjusting rings 12, 13 are designed so as to exclude a self-locking action between the rings so that tans , or tan , where ct is the angle of the oblique surfaces to the radial plane and y is the coefficient of friction between the coacting oblique surfaces.

The resultant torque produced on the adjusting ring 12 under load is transmitted to one end of a part-cylindrical lever 23 rotatably connected to the adjusting ring 12.

The lever 23 is provided at its other end with ratchet teeth engaged by a peg 24 held in mesh with the ratchet teeth by a spring 25.

The peg 24 and the spring 25 are secured to an extension of the brake carrier 7 by means of a screw 26.

In the modification shown in Fig. 2, the torque produced under load on the adjustment ring 12 is transmitted via gear teeth 27a (Fig. 3) on the adjustment ring 12 and a pinion 27 on one end of a shaft 28 to a radially-directed -ratchet pin 35 mounted on the other end of shaft 28. The shaft 28 is guided in a bush 29 connected to the axle tube 8. This bush has teeth 30 on its end face which are engaged by toothing on the end face of a sleeve 31. An unscrewable cap 32 forces the sleeve 31 against the bush 29 and brings the teeth into interlocked engagement. Internal gearing of the sleeve is engaged by the ratchet pin 35 under the action of a spring 34 supported on a sleeve 33. Thus pin 35 transmits the torque from the shaft 28 through the sleeve 31 onto the bush 29 connected with the axle shaft 8.

The mode of working of the disc brake and its automatic clearance adjustment or compensating device is as follows: The chamber 17 is pressurised via 17a on application of the service brake. The annular cylinder 9 acts directly upon the brake lining carrier 5a on the one side whilst the brake piston 10 transmits, through the brake piston 11 and the ball bearings 21 onto the adjustment rings 12, 13, abutting against each other through their oblique surfaces, the force of reaction which acts on the other side upon the other brake lining carrier 5. The parking brake is activated by venting or bleeding of the chamber 18 through its port 18a. The spring 19 acts forcibly between the brake piston 10 and the brake piston 11 to separate them and effect a similar operational sequence as described in connection with a service brake application. The friction element 14 of the automatic clearance compensation/adjustment unit moves, with the adjusting ring 13 it encompasses and frictionally engages, in the same direction as the adjusting ring 13 until the friction element 14 abuts against the circlip 16. The spring 15 is compressed or loaded during this movement.

In the event of wear of the brake linings 6 and 6a, the clearance travel "a" is initially overcome on brake application and the piston describes an appropriately longer stroke to maintain the braking force, the adjustment ring 13 being displaced to the right relative to the friction element 14 by a distance equalling the amount of wear.

When the brakes are released as a result of lowering the fluid pressure in chamber 17, the spring 15 is relieved by the amount "a" and transmits this movement to the adjustment ring 13 through the frictional engagement of ring 13 and element 14.

The stroke the piston 10 had to travel to achieve full return to its original setting is incomplete by the amount it had to travel as the result of lining wear. The adjustment ring 12, which in this condition is relieved from the braking force, is now able to turn, i.e. move angularly, relative to the adjustment ring 13 under the action of the spring 20 tensioned between the piston 10 and the adjustment ring 12, the adjustment ring 13 remaining stationary due to the frictional force exercised by the friction element 14. The oblique surfaces of the adjustment ring 12 therefore slide over the co-operating oblique surfaces of the adjusting ring 13 and thereby axially expand or separate the parts 13 and 12. This axial expansion acts through the frictionreducing ball bearings 21 and the parking brake chamber 18 and/or piston 11 to return the piston 10 to its starting setting.

In a fresh pressurisation of the chamber 17, the piston 10 need only describe the clearance travel "a" before effecting a reengagement of the brakes by the linings 6 and 6a.

The described clearance compensation/adjustment is effected in the same way in a parking brake application by a stroke of the cup or plate spring 19. The stepless adjustment of the dimension "a" ensures in the same way a constant spring excursion or stroke and consequently a constant spring force.

For mechanical, i.e. manual, release of the spring actuated brake (e.g. following emergency actuation), the screw 26 (Fig. 1) is turned until the pin 24 releases the lever 23 so that the adjustment rings 12, 13 can be turned against the force of the spring 20 until the excursion of the spring 19 is compensated. Friction is reduced by the ball bearings 21 guided in the cage 22. The undercut of the gearing teeth on the lever 23 corresponds to the clearance.

In the arrangement according to Fig. 2 the gearing 30 is released by slight withdrawal or pulling-off of the sleeve 31 after unscrewing of the cover 32 so that readjustment can be effected in the way described in conjunction with Fig. 1. Also no further twisting by the amount of the undercut of the gearing is required. The undercut of the internal toothing of the sleeve 31 corresponds to the clearance travel of the brake member of the disc brake. It will be noted that the gearing is enclosed or encapsulated towards the outside to ensure better sealing of the brake. In this arrangement, the length of the arc of the circle of the internal toothing of the adjustment ring (12) in engagement with the pinion (27) is such as to permit complete release of the brakes.

The expense of a special surface treatment of the oblique surfaces is eliminated through the provision outside the disc brake of a locking device or catch which replaces the direct self-locking engagement between the oblique surfaces of the adjusting rings in U.K. Patent Specification No. 1,516,519.

Another benefit derived from this is that more uniform power or force transmission can be achieved by the larger number of oblique surfaces on a given circumference which can be derived from using a larger angle.

The feature of arranging the catch externally makes it possible to achieve a simplified release sequence of the spring brake actuators in the event of failure of the pressure medium supply without any need for the direct engagement of levers, gear wheels or cams with the adjusting unit.

WHAT WE CLAIM IS: 1. A pressure medium operable disc brake having an actuation mechanism comprising an annular cylinder member and an annular piston member axially slid able therein, and an expansible wear compensating device between one of the said members and a brake ring of the disc brake to transmit movement of that member to the brake ring and to compensate automatically, upon brake actuation and release, for lengthening of the stroke of the mechanism resulting from wear of the brake lining, said expansible wear compensating device comprising two relatively rotatable rings having complementary oblique surfaces facing and engaging one another such that relative rotation of the two rings in one direction can increase the axial length occupied by the said device and effect a consequential widening of the gap between said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. described in connection with a service brake application. The friction element 14 of the automatic clearance compensation/adjustment unit moves, with the adjusting ring 13 it encompasses and frictionally engages, in the same direction as the adjusting ring 13 until the friction element 14 abuts against the circlip 16. The spring 15 is compressed or loaded during this movement. In the event of wear of the brake linings 6 and 6a, the clearance travel "a" is initially overcome on brake application and the piston describes an appropriately longer stroke to maintain the braking force, the adjustment ring 13 being displaced to the right relative to the friction element 14 by a distance equalling the amount of wear. When the brakes are released as a result of lowering the fluid pressure in chamber 17, the spring 15 is relieved by the amount "a" and transmits this movement to the adjustment ring 13 through the frictional engagement of ring 13 and element 14. The stroke the piston 10 had to travel to achieve full return to its original setting is incomplete by the amount it had to travel as the result of lining wear. The adjustment ring 12, which in this condition is relieved from the braking force, is now able to turn, i.e. move angularly, relative to the adjustment ring 13 under the action of the spring 20 tensioned between the piston 10 and the adjustment ring 12, the adjustment ring 13 remaining stationary due to the frictional force exercised by the friction element 14. The oblique surfaces of the adjustment ring 12 therefore slide over the co-operating oblique surfaces of the adjusting ring 13 and thereby axially expand or separate the parts 13 and 12. This axial expansion acts through the frictionreducing ball bearings 21 and the parking brake chamber 18 and/or piston 11 to return the piston 10 to its starting setting. In a fresh pressurisation of the chamber 17, the piston 10 need only describe the clearance travel "a" before effecting a reengagement of the brakes by the linings 6 and 6a. The described clearance compensation/adjustment is effected in the same way in a parking brake application by a stroke of the cup or plate spring 19. The stepless adjustment of the dimension "a" ensures in the same way a constant spring excursion or stroke and consequently a constant spring force. For mechanical, i.e. manual, release of the spring actuated brake (e.g. following emergency actuation), the screw 26 (Fig. 1) is turned until the pin 24 releases the lever 23 so that the adjustment rings 12, 13 can be turned against the force of the spring 20 until the excursion of the spring 19 is compensated. Friction is reduced by the ball bearings 21 guided in the cage 22. The undercut of the gearing teeth on the lever 23 corresponds to the clearance. In the arrangement according to Fig. 2 the gearing 30 is released by slight withdrawal or pulling-off of the sleeve 31 after unscrewing of the cover 32 so that readjustment can be effected in the way described in conjunction with Fig. 1. Also no further twisting by the amount of the undercut of the gearing is required. The undercut of the internal toothing of the sleeve 31 corresponds to the clearance travel of the brake member of the disc brake. It will be noted that the gearing is enclosed or encapsulated towards the outside to ensure better sealing of the brake. In this arrangement, the length of the arc of the circle of the internal toothing of the adjustment ring (12) in engagement with the pinion (27) is such as to permit complete release of the brakes. The expense of a special surface treatment of the oblique surfaces is eliminated through the provision outside the disc brake of a locking device or catch which replaces the direct self-locking engagement between the oblique surfaces of the adjusting rings in U.K. Patent Specification No. 1,516,519. Another benefit derived from this is that more uniform power or force transmission can be achieved by the larger number of oblique surfaces on a given circumference which can be derived from using a larger angle. The feature of arranging the catch externally makes it possible to achieve a simplified release sequence of the spring brake actuators in the event of failure of the pressure medium supply without any need for the direct engagement of levers, gear wheels or cams with the adjusting unit. WHAT WE CLAIM IS:

1. A pressure medium operable disc brake having an actuation mechanism comprising an annular cylinder member and an annular piston member axially slid able therein, and an expansible wear compensating device between one of the said members and a brake ring of the disc brake to transmit movement of that member to the brake ring and to compensate automatically, upon brake actuation and release, for lengthening of the stroke of the mechanism resulting from wear of the brake lining, said expansible wear compensating device comprising two relatively rotatable rings having complementary oblique surfaces facing and engaging one another such that relative rotation of the two rings in one direction can increase the axial length occupied by the said device and effect a consequential widening of the gap between said

one annular member and the said brake ring, brake ring being located between said one annular member and externally disposed releasable locking means operable to lock the two rings of the compensating device against relative rotation in the opposite direction.

2. A disc brake according to Claim 1, wherein the locking means is coupled to a movable one of the said two rings via a lever, one end of the lever engaging the said one of the two rings and the other end of the lever being provided with teeth engageable by the locking means.

3. A disc brake according to Claim 2, wherein the locking means comprises a pin, peg or pawl that is spring urged into engagement of said toothed other end of the lever.

4. A disc brake according to Claim 3, wherein the pin, peg or pawl is provided with teeth for entry between the teeth of said other end of the lever.

5. A disc brake according to Claim 3 or Claim 4, wherein the pin, peg or pawl and the spring means urging it are retained in position by screw means arranged for ad Justing the force of said spring means upon the pin, peg or pawl and hence the latter's degree of extension into or towards said toothed other end of the lever.

6. A disc brake according to any one of Claims 2 to 5, wherein the space between adjacent teeth at said other end of the lever corresponds to the clearance desired between said one member and said brake ring.

7. A disc brake according to Claim 1, wherein the locking means is coupled to a movable one of the said two rings via a shaft mounted pinion wheel in mesh with gear teeth provided on the said one of the two rings. ~~~~~~~~~~~~~~~~~~

8. A disc brake according to Claim 7, wherein the shaft extends through a fixed bush having a radial face thereof provided with gear teeth engaged by teeth provided on a sleeve that is mounted on the pinion shaft.

9. A disc brake according to Claim 8, wherein the sleeve is housed within a rotatable cap that is screw-threadedly connected to the bush whereby, upon unscrewing the cap, the inter-engagement of the teeth of the bush and sleeve can be released.

10. A disc brake according to Claim 8 or Claim 9, wherein the sleeve is internally provided with teeth engageable by a springurged pin, peg or pawl.

11. A disc brake according to Claim 10, wherein the end of the pin, peg or pawl engaging the sleeve's internal teeth is correspondingly toothed.

12. A disc brake according to Claim l0br Claim 11, wherein the space between adjacent internal teeth of the sleeve corresponds to the clearance desired between said one member and said brake ring.

13. A disc brake substantially as herein described with reference to and/or as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.

14. For a vehicle, a pressure medium operable service brake system and a pressure medium operable parking and/or auxiliary or emergency brake system, the systems incorporating a disc brake according to any preceding claim.