GB1602068A

GB1602068A - Pressure medium operable disc brakes

Info

Publication number: GB1602068A
Application number: GB20228/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-07-15
Filing date: 1978-05-17
Publication date: 1981-11-04
Also published as: FR2397565B1; FR2397565A1; JPS5420269A; DE2731999C2; IT1203192B; DE2731999A1; IT7868685A0

Description

(54) IMPROVEMENTS IN OR RELATING TO PRESSURE MEDIUM OPERABLE DISC BRAKES (71) We, WABCO FAARZEUG 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 par ticularly described in and by the following statement: This invention relates to a pressure medium operable disc brake, e.g. for a motor vehicle.

In German Offenlegungsschrift 25 10 193 (U.K. Patent Specification No. 1,516,519) there is described a combination of a pres- sure medium operable disc service brake with a spring actuator operable parking brake (or auxiliary brake) having a gradatable braking action, the actuation mechanism for the two brakes being accommodated together in the casing of the disc brake. In German Offenlegungsschrift 25 08 771 (U.K. Patent Specification No. 1,516,519) such a combination is described having an expansible wear compensating or re-setting device which automatically compensates for the larger strokes of the brake member brought about by the wear of the brake pads. Specifically one embodiment of the invention of U.K. Patent Specification No. 1,516,519 has the wear compensating or resetting device characterised by an expansible device comprising two adjustment rings operatively linked via a plurality of inclined surfaces.

It is desirable, inter alia to meet official regulations, that some arrangement should be provided for releasing the spring actuatoroperated auxiliary brake in the event of failure of the normal brake release action.

According to this invention, there is provided a pressure medium operable disc brake having an actuation mechanism comprising an annular piston-andcylinder assembly operable to actuate and release the brake, and an expansible wear-compensating device for transmitting movement of one of the said members to a brake lining carrier of the disc brake, said expansible wear compensat- ing device in use compensating automatically, upon brake actuation and release, for lengthening of the stroke of the mechanism as a result of brake lining wear, the said device comprising two adjustment rings urged into mutual contact across inclined surfaces or planes arranged such that relative rotation of the rings alters the axial length occupied by the rings, and resilient means biasing the rings for relative rotation in one direction to increase the said axial length, the brake being provided with means for rotating the rings relative to one another in the opposite direction against the force of said means to an extent sufficient to ensure complete release of the brake.

In one embodiment of the invention, one of the rings is provided with at least one abutment arranged to be radially congruent with an arc of tooth-like projections provided on a relatively non-rotatable member, whereby the said one of the rings can be rotated by a lever engaging the abutment surface and successive ones of the tooth-like projections, the angular extent of the arc of projections being at least sufficient to ensure complete release of the brake.

In another embodiment of the invention, one of the rings is provided with an arc of gear teeth for meshing engagement with a pinion provided on one end of a rotatable shaft, whereby the said one of the rings can be rotated by rotating the shaft, the angular extent of the arc of gear teeth being at least sufficient to ensure complete release of the brake.

In yet another embodiment of the invention, one of the rings is provided with a lever-like extension for engagement with a cam provided on one end of a rotatable shaft, whereby the said one of the rings can be rotated by rotating the shaft, the cam being so shaped that the relative rotation of the rings is sufficient to ensure complete release of the brake.

By way of non-limiting example, embodiments of this invention will now be described with reference to the accompanying drawings of which: Fig. 1 is a schematic radial cross-section of a disc brake embodying this invention, which can be released by means of a lever, Fig. la is perspective view of part of the disc brake of Fig. 1, Fig. 2 is a schematic radial cross-section of a disc brake embodying this invention, which can be released by means of a rotatable toothed shaft, and Fig. 3 is a schematic radial cross-section of a disc brake embodying this invention, which can be released by means of a rotatable shaft on which a cam is mounted.

Referring to Fig. 1, a hub 1 is mounted via bearings on a vehicle axle (not shown) and a wheel 2 is fixed to the hub 1 by means of wheel bolts and wheel nuts (not shown).

Bolts 3 connect the hub 1 to a casing comprising the brake discs 4 and 4a. Brake lining carriers 5 and 5a with linings 6 and 6a of frictional material are arranged between the brake discs 4 and 4a. These carriers are supported through extensions on carriers 7 which are connected by means of bolts (not shown) with the stationary axle housing 8.

Between the lining carriers 5 and 5a is an annular actuation mechanism comprising an annular cylinder 9, an annular service brake piston 10, an annular parking brake piston 11 and an automatic resetting or wear compensating device comprising two adjustment rings 12 and 13, a friction element 14, a spring 15 and a circlip 16.

The chamber 17 located between the annular cylinder 9 and the end face of the brake piston 10 provides a service brake chamber connected through its port 17a with a brake valve (not shown). The chamber 18 formed by the mutually facing interior faces of the brake piston 10 and the brake piston 11 provides a parking brake chamber connected through its port 18a with hand brake valve (also not shown).

A plate or cup spring 19 acting against the pressure in chamber 18 is arranged between the end face of the brake piston 11 and the adjacent end face of the brake piston 10. A spring 20 is connected by one end (not shown) to the brake piston 10 and its other end is connected to the adjustment ring 12. The latter has oblique faces on the side adjacent the ring 13 and abutting against complementary oblique faces on the adjustment ring 13.

To reduce friction, cage-mounted bearings such as balls 21 or rollers are inserted between brake piston 11 and the adjustment ring 12.

The brake piston 10 has radially-directed, rib-like projections 23 serving as contacts or abutments and providing recesses between them for alignment with a recess 24 in the adjustment ring 12. When so aligned, a lever can be inserted for turning or twisting of the adjustment ring by applying force to the lever in a tangential direction.

Whilst the brake system is inoperative, the oblique faces of the adjustment ring 12 will abut against the oblique faces of the adujstment ring 13 as a result of the twisting force applied by the spring 20.

The mode of working of the disc brake and its automatic clearance resetting unit is as follows: On application of the service brake the chamber 17 is pressurised through its port 17a. The annular cylinder 9 acts directly upon the brake lining carrier 5a on one side whilst the brake piston 10 transmits the force of reaction through the brake pistons 11 and the ball bearings 21 to the adjustment rings 12, 13 which transmit the force to the other brake lining carrier 5. The parking brake is triggered off by venting or bleeding of the chamber 18 through its port 18a. The spring 19 moves the brake piston 10 relative to and away from the brake piston 11 and the operational sequence effected in connection with a service brake application is repeated.

The friction element 14 of the automatic clearance resetting unit moves co-directionally with the adjustment ring 13 it frictionally engages until, as shown in Fig. 1, it abuts against the circlip 16 which is fast with the cylinder 9. In the course of this movement the spring 15 is loaded or compressed.

On wear of the brake linings 6 and 6a the clearance travel "a" is overcome on the first brake application and the piston travels a correspondingly greater stroke to maintain the braking force whereby the resetting ring 13 is displaced to the right (when viewed as in Fig. 1) relative to the friction element 14 by the amount of wear. On release of the brakes and the thereby resultant decrease in the pressure in chamber 17, the spring 15 relaxes by the amount "a" and transmits this movement to the resetting ring 13 by means of the friction element 14. The return movement of the piston 10 leaves it short of its initial position by a distance equal to the stroke it had to travel to compensate for lining wear. The located spring 20 acting between the piston 10 and the resetting ring 12 is now able to turn the resetting ring 12 which latter, in this condition is relieved from the braking force. Due to the turning movement, the oblique faces of the resetting ring 12 slide along the above-mentioned oblique faces of the resetting ring 13 (that is maintained stationary due to the frictional force from the friction element 14) such that an expanding action between parts 12 and 13 takes place. This expansion acts through the fric tion reducing balls 21 and the parking brake piston 11 and/or chamber 18 to effect a restoration of the piston 10 to its original starting position.

On renewed pressurisation of the chamber 17 the stroke of piston 10 need only be the clearance "a" until the linings 6, 6a abut the brake discs 4, 4n respectively.

The above described clearance adjustment or compensation occurs in the same way during a parking brake application by means of an extension of the plate spring 19. The stepless resetting of the amount "a" ensures likewise a constant spring extension and consequently a constant spring force.

In the event of failure of the parking brake circuit, i.e. impossibility of pressurisation of the chamber 18 for releasing of the parking brake, a lever is inserted from outside the disc brake into the recess 24 in the resetting ring 12 and is swivelled tangentially whereby the projections 23 of the non-rotatable piston 10 act during the swivel movement of the lever as abutments or fulcrums. The resetting ring 12 is in this way rotated in the release direction in relation to the brake piston 10 which is held securely against rotation in relation to the brake lining carrier 7. The resetting ring 12 may be rotated until complete release of the brakes is achieved by applying the lever several times against successive ones of the ribs 23.

In the embodiment of Fig. 2 the resetting ring 12 is circumferentially provided with a toothed portion 25 engaged by a pinion 26 which, for brake release following a failure, is rotated by means of a standard key fitting onto an appropriately sectioned end 27 of a shaft 29 held in an extension 28 of the axle tube 8.

In another embodiment shown in Fig. 3, the resetting rings 12, 13 have lever-like extensions 12a, 13a disposed one each side of a cam 30 mounted on one end of a shaft 29a. The other end of shaft 29a is appropriately sectioned for engagement by a standard key which on rotation rotates cam 30 to move apart the two lever like extensions 12a and 13a of the resetting rings 12 and 13 and thus imparts opposite rotary movements to the resetting rings 12, 13 so that the brakes maintained at braking setting by the spring actuators are released.

It will be appreciated that the above described embodiments of this invention are simple to operate.

WHAT WE CLAIM IS:- 1. A pressure medium operable disc brake having an actuation mechanism comprising an annular piston-and-cylinder assembly operable to actuate and release the brake, and an expansible wear-compensating device for transmitting movement of one of the said members to a brake lining carrier of the disc brake, said expansible wear compensating device in use compensating automatically, upon brake actuation and release, for lengthening of the stroke of the machanism as a result of brake lining wear, the said device comprising two adjustment rings urged into mutual contact across inclined surfaces or planes arranged such that relative rotation of the rings alters the axial length occupied by the rings, and resilient means biasing the rings for relative rotation in one direction to increase the said axial length, the brake being provided with means for rotating the rings relative to one another in the opposite direction against the force of said means to an extent sufficient to ensure complete release of the brake.

2. A disc brake according to Claim 1, wherein one of the rings is provided with at least one abutment arranged to be radially congruent with an arc of tooth-like projections provided on a relatively non-rotatable member, whereby the said one of the rings can be rotated by a lever engaging the abutment surface and successive ones of the toothlike projections, the angular extent of the arc of projections being at least sufficient to ensure complete release of the brake.

3. A disc brake according to Claim 2, wherein the abutment surface is provided on the radially inner end surface of the said one ring.

4. A disc brake according to Claim 1, wherein one of the rings is provided with an arc of gear teeth for meshing engagement with a pinion provided on one end of a rotatable shaft, whereby the said one of the rings can be rotated by rotating the shaft, the angular extent of the arc of gear teeth being at least sufficient to ensure complete release of the brake.

5. A disc brake according to Claim 4, wherein the gear teeth are provided on the radially inner end surface of the said one ring.

6. A disc brake according to Claim 1, wherein at least one of the rings is provided with a lever-like extension for engagement with a cam provided on one end of a rotatable shaft, whereby the said one of the rings can be rotated by rotating the shaft, the cam being so shaped that the relative rotation of the rings is sufficient to ensure complete release of the brake.

7. A disc brake according to Claim 6, wherein a said lever-like extension extends radially inwardly from the radially inner end surface of each of said rings, the two leverlike extensions engaging one each side of the cam so as to move apart upon rotation of the cam by the shaft.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tion reducing balls 21 and the parking brake piston 11 and/or chamber 18 to effect a restoration of the piston 10 to its original starting position. On renewed pressurisation of the chamber 17 the stroke of piston 10 need only be the clearance "a" until the linings 6, 6a abut the brake discs 4, 4n respectively. The above described clearance adjustment or compensation occurs in the same way during a parking brake application by means of an extension of the plate spring 19. The stepless resetting of the amount "a" ensures likewise a constant spring extension and consequently a constant spring force. In the event of failure of the parking brake circuit, i.e. impossibility of pressurisation of the chamber 18 for releasing of the parking brake, a lever is inserted from outside the disc brake into the recess 24 in the resetting ring 12 and is swivelled tangentially whereby the projections 23 of the non-rotatable piston 10 act during the swivel movement of the lever as abutments or fulcrums. The resetting ring 12 is in this way rotated in the release direction in relation to the brake piston 10 which is held securely against rotation in relation to the brake lining carrier 7. The resetting ring 12 may be rotated until complete release of the brakes is achieved by applying the lever several times against successive ones of the ribs 23. In the embodiment of Fig. 2 the resetting ring 12 is circumferentially provided with a toothed portion 25 engaged by a pinion 26 which, for brake release following a failure, is rotated by means of a standard key fitting onto an appropriately sectioned end 27 of a shaft 29 held in an extension 28 of the axle tube 8. In another embodiment shown in Fig. 3, the resetting rings 12, 13 have lever-like extensions 12a, 13a disposed one each side of a cam 30 mounted on one end of a shaft 29a. The other end of shaft 29a is appropriately sectioned for engagement by a standard key which on rotation rotates cam 30 to move apart the two lever like extensions 12a and 13a of the resetting rings 12 and 13 and thus imparts opposite rotary movements to the resetting rings 12, 13 so that the brakes maintained at braking setting by the spring actuators are released. It will be appreciated that the above described embodiments of this invention are simple to operate. WHAT WE CLAIM IS:-

1. A pressure medium operable disc brake having an actuation mechanism comprising an annular piston-and-cylinder assembly operable to actuate and release the brake, and an expansible wear-compensating device for transmitting movement of one of the said members to a brake lining carrier of the disc brake, said expansible wear compensating device in use compensating automatically, upon brake actuation and release, for lengthening of the stroke of the machanism as a result of brake lining wear, the said device comprising two adjustment rings urged into mutual contact across inclined surfaces or planes arranged such that relative rotation of the rings alters the axial length occupied by the rings, and resilient means biasing the rings for relative rotation in one direction to increase the said axial length, the brake being provided with means for rotating the rings relative to one another in the opposite direction against the force of said means to an extent sufficient to ensure complete release of the brake.

8. A disc brake substantially as herein des

cribed with reference to, and as illustrated in, Figs. 1 and la, or Fig. 2, or Fig. 3 the accompanying drawings.

9. A motor vehicle having a disc brake according to Claim 8.