GB1597405A - Pressure medium operable disc brake - Google Patents

Description

(54) PRESSURE MEDIUM OPERABLE DISC BRAKE (71) We, WABCO FAHRZEUGBREMSEN 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.

Disc brakes, which have today become an accepted element in passenger vehicle design, are increasingly being used in goods vehicles, particularly in the lower and middle weight classes having all-hydraulic or combination (hydraulic/pneumatic) brake systems.

Disc brakes for use on commercial or goods vehicles of the heavier weight classes having wholly compressed air brake systems have been disclosed in published German Patent Applications Nos. P 24 42 971 and P 24 41 605. These disc brakes are socalled "full circle" disc brakes comprising a rotatable, externally open, two-part brake housing, and brake rings carrying the brake pads. The brake rings are disposed between the two halves of the housing so as to be rigidly non-rotatable but free to move axially by a pneumatic means of actuation located between the brake rings, the latter being circumferentially supported by a stationary brake support which surrounds the brake housing. The pneumatic means of actuation located between the brake rings is in the form of an annular cylinder with an annular piston slidably mounted therein, the cross section of the annular cylinder having a shape somewhat like that of a letter "W" lying on its side.

However, a "dead" volume is produced in the annular cylinder by the wear of the disc brake pads, With full circle disc brakes of the size used on heavy goods vehicles this "dead" volume is of the order of 0.15 litres per wheel per mm pad wear, so that 4/5 of the amount of wear permitted, representing approximately 8 mm, gives a maximum increase in the "dead" volume of some 1.20 litres.

With a closed hydraulic system for an all-hydraulic or a compressed air piloted hydraulic brake installation, the extra requirement in pressure fluid, arising from pad wear and its consequent increase in dead volume, can be covered by simple means such as, for example, building in correspondingly larger top-up tanks.

With wholly compressed air brake installations however, the dead volume caused by the wear on the brake pads has to be filled with additional air at each use of the brakes -- which means that the compressor has to supply more and more compressed air as increasing pad wear takes increasing amounts of air from the receiver and this has to be made up. It would help to build in air compressors with larger swept volume and possibly also larger air receivers to increase the amount of compressed air in the system but, however, in most cases, this cannot be done because of lack of space in the vehicle and/or for economic reasons.

Moreover, it would not be possible, because of the large dead volume, to build up the air pressure in the annular cylinder in the required time.

With pressure fluid operated disc brakes having integral booster springs according to published German Patent Application No.

25 10 193, the springs lose compression, and hence force, as pad wear increases.

U.K. Patent Specification No. 1,516,519 describes and claims a pressure medium operable disc brake having an actuation mechanism comprising an annular cylinder member and an annular piston member axially slideable 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 actua tion 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.

In an embodiment of the invention of U.K. Patent Specification No. 1,516,519, the adjustment is provided by a camming or a wedge arrangement comprising two adjustment rings, in contact with each other through inclined faces and disposed between the annular piston member and a thrust collar which, during brake application, transmits movement of the piston member to the respective brake ring. During brake release, the return movement of the thrust collar is limited by a clamping ring which locks the thrust collar to the annular cylinder member: to this end, the clamping ring has projections which project into grooves in the thrust collar. A disadvantage of this arrangement, however, is that there is relatively great wear on the projections of the clamping ring, which limits the amount of adjustment, and hence the operating safety of the wear compensating device cannot always be assured. Furthermore, it is a considerable disadvantage that when new linings have to be fitted to the brake, the clamping ring must first of all be turned to withdraw the clamping ring projections from their hold and so allow the necessary movement of piston and thrust collar towards each other to give enough space to fit new brake linings. After the new linings have been fitted, the clamping ring must be turned back into the operating position or else operational certainty cannot be ensured.

The present invention provides 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 break lining said compensating device including two adjustment rings urged into mutual contact across in dined surfaces or planes to provide a camming effect, and a friction element compirsing a sleeve which encases and is in surface contact with one of the said two adjustment rings, the friction element being operable during brake release to hold the said one adjustment ring frictionally fast with one of said annular members and thereby to limit axial movement of the ring, the other of said rings being axially movable with axial movement of the other of said annular members.

By way of example, embodiments of this invention will now be described with reference to the accompanying drawings of which: Fig. 1 shows schematically in axial crosssection a disc brake according to the present invention; Fig. 2 shows similarly a modification of the embodiment of Fig. 1; and Fig. 3 is a partly-sectional perspective view of the embodiment of Fig. 2.

Referring to Fig. 1, a vehicle axle (not shown) carries a hub 1 on bearings. A road wheel 2 is fixed by means of wheel bolts and wheel nuts to the hub 1. Bolts 3 connect the wheel 2 to the brake discs 4 and 4a which form a housing with the hub 1. Brake pad (or lining) carriers 5 and Sc with brake pads 6 and 6a thereon are arranged between the brake discs 4 and 4a, and by means of extensions are carried on a support 7 connected to the axle housing tube 8 by screws (not shown).

An annular or ring-shaped actuating unit is located between the pad carriers 5 and Sc and consists of 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 the automatic wear compensating device comprising two adjuster rings 12 and 13, a friction element 14, a spring 15 and a clamping or locking ring 16.

The chamber 17 between the closed end of annular cylinder 9 and the face of the brake piston 10 is connected via its coupling passage or port 17a to a brake valve (not shown) and thus serves as a service brake chamber, whilst the chamber 18 formed between the inner faces of the brake pistons 10 and 11 has a connection via its coupling passage and port 1 8a to a hand brake valve (also not shown) and thus acts as a parking brake chamber.

A plate spring 19 is located between the face of the brake piston 11 and the face which is effectively connected to brake piston 10 and opposes the pressure in chamber 18.

A spring 20 is connected by one end to the brake piston 10 and by its other end to the adjuster ring 12 (see Fig. 3). The adjuster ring 12 carries inclined faces which abut against complementary inclined faces on adjuster ring 13. The inclined faces on rings 12 and 13 are, in each case provided adjacent the ring's periphery and are directed in planes transverse to radial planes of the disc brake.

In the coupling or interfacial engagement between brake piston 11 and adjuster ring 12, ball bearings 21 are introduced to re duce the friction and these are retained in position by means of a ball bearing cage 22.

So long as the brake is not actuated, the adjuster ring 12 with its inclined faces lies up against the inclined faces of the adjuster ring 13 because of the orsional force from spring 20.

The operation of the disc brake and its automatic wear compensating device is as follows: Upon operation of the service brake, chamber 17 is fed with compressed air through its connection 17cm. The ring cylinder 9 acts directly upon the pad carrier 5a on one side, while the brake piston 10 gives a reaction thrust through the brake piston 11 and the ball bearings 21 onto the adjuster rings 12 and 13, connected by their inclined faces, which act upon the other pad carried 5. The parking brake is actuated by evacuating chamber 18 through its connection 1 8a. The spring 19 acts between the brake piston 10 and the brake piston 11 to separate them and effect a like operational cycle as described above for the service brake operation. The friction element 14 of the automatic clearance adjustment device moves in the same direction as the adjuster ring 13 until it comes up against the locking ring 16. This compresses or loads the spring 15.

As the brake pads 6 and 6a wear, the clearance "a" is taken up first of all when the brake is actuated and the piston has to make a correspondingly greater stroke to maintain the braking force so that the adjuster ring 13 moves to the right relative to the friction element 14 by the amount of the wear. When the brake is released and the pressure in chamber 17 consequently drops, the spring 15 unloads by the amount "a" and transmits this movement via the friction coupling to the adjuster ring 13.

The stroke which the piston 10 had to make because of pad wear will not allow the piston 10 to return completely to its starting point. The force of spring 20, which acts between the piston 10 and the adjuster ring 12, can now turn adjuster ring 12 which in this position is freed from braking force. Because of the rotational movement, the inclined faces of the adjuster ring 12 slide on the similar inclined faces of the adjuster ring 13 which is now held stationary by the frictional force from friction element 14 and this in such a way that there is a camming or wedging effect between parts 13 and 12. This effect is transmitted through the friction reducing ball bearings 21 and parking brake chamber 18 and/or piston 11 causing a return of the piston 10 to its original starting position.

When chamber 17 is once more loaded, the piston 10 has only got to travel through the clearance distance "a" until the pads 6 and 6a come into contact.

The clearance adjustment as described, takes place in the same way with a parking brake operation through the stroke of the plate spring 19. The fact that the distance "a" can be continuously adjusted provides both a constant travel for spring 19 and consequently a constant force for spring 19.

Fig. 2 shows a modification of the embodiment of Fig. 1 in which a spring 23, which abuts against a securing ring 24 provides the return force for pistons 10 and 11, so that the spring 20 can be of smaller size and the forces at the friction coupling between the adjustment ring 13 and the friction element 14 can be less. A further advantage is that the friction on pistons 10 and 11 cannot influence the clearance adjustment.

It will be appreciated that because of its surfacial or flat connection with the adjuster ring 13, the friction element 14 (which has a large surface and forms the casing of the automtaic wear compensating device 12, 13) is subject to much less wear than the clamping ring projections which effected a comparable function in the prior proposal of Specification No. 1 516 519. To renew the brake pads all that is required is that the thrust components are pushed back and, for this, a simple lever will suffice. After pushing in the new pads, a single operation of the brake is sufficient to render the disc brake once more ready for use.

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 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 break lining, said compensating device including two adjustment rings urged into mutual contact across inclined surfaces or planes to provide a camming effect, and a friction element comprising a sleeve which encases and is in surface contact with one of the said two adjustment rings, the friction element being operable during brake release to hold the said one adjustment ring frictionally fast with one of said annular members and thereby to limit axial movement of the ring, the other of said rings being axially movable with axial movement of the other of said annular members.

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. duce the friction and these are retained in position by means of a ball bearing cage 22. So long as the brake is not actuated, the adjuster ring 12 with its inclined faces lies up against the inclined faces of the adjuster ring 13 because of the orsional force from spring 20. The operation of the disc brake and its automatic wear compensating device is as follows: Upon operation of the service brake, chamber 17 is fed with compressed air through its connection 17cm. The ring cylinder 9 acts directly upon the pad carrier 5a on one side, while the brake piston 10 gives a reaction thrust through the brake piston 11 and the ball bearings 21 onto the adjuster rings 12 and 13, connected by their inclined faces, which act upon the other pad carried 5. The parking brake is actuated by evacuating chamber 18 through its connection 1 8a. The spring 19 acts between the brake piston 10 and the brake piston 11 to separate them and effect a like operational cycle as described above for the service brake operation. The friction element 14 of the automatic clearance adjustment device moves in the same direction as the adjuster ring 13 until it comes up against the locking ring 16. This compresses or loads the spring 15. As the brake pads 6 and 6a wear, the clearance "a" is taken up first of all when the brake is actuated and the piston has to make a correspondingly greater stroke to maintain the braking force so that the adjuster ring 13 moves to the right relative to the friction element 14 by the amount of the wear. When the brake is released and the pressure in chamber 17 consequently drops, the spring 15 unloads by the amount "a" and transmits this movement via the friction coupling to the adjuster ring 13. The stroke which the piston 10 had to make because of pad wear will not allow the piston 10 to return completely to its starting point. The force of spring 20, which acts between the piston 10 and the adjuster ring 12, can now turn adjuster ring 12 which in this position is freed from braking force. Because of the rotational movement, the inclined faces of the adjuster ring 12 slide on the similar inclined faces of the adjuster ring 13 which is now held stationary by the frictional force from friction element 14 and this in such a way that there is a camming or wedging effect between parts 13 and 12. This effect is transmitted through the friction reducing ball bearings 21 and parking brake chamber 18 and/or piston 11 causing a return of the piston 10 to its original starting position. When chamber 17 is once more loaded, the piston 10 has only got to travel through the clearance distance "a" until the pads 6 and 6a come into contact. The clearance adjustment as described, takes place in the same way with a parking brake operation through the stroke of the plate spring 19. The fact that the distance "a" can be continuously adjusted provides both a constant travel for spring 19 and consequently a constant force for spring 19. Fig. 2 shows a modification of the embodiment of Fig. 1 in which a spring 23, which abuts against a securing ring 24 provides the return force for pistons 10 and 11, so that the spring 20 can be of smaller size and the forces at the friction coupling between the adjustment ring 13 and the friction element 14 can be less. A further advantage is that the friction on pistons 10 and 11 cannot influence the clearance adjustment. It will be appreciated that because of its surfacial or flat connection with the adjuster ring 13, the friction element 14 (which has a large surface and forms the casing of the automtaic wear compensating device 12, 13) is subject to much less wear than the clamping ring projections which effected a comparable function in the prior proposal of Specification No. 1 516 519. To renew the brake pads all that is required is that the thrust components are pushed back and, for this, a simple lever will suffice. After pushing in the new pads, a single operation of the brake is sufficient to render the disc brake once more ready for use. 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 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 break lining, said compensating device including two adjustment rings urged into mutual contact across inclined surfaces or planes to provide a camming effect, and a friction element comprising a sleeve which encases and is in surface contact with one of the said two adjustment rings, the friction element being operable during brake release to hold the said one adjustment ring frictionally fast with one of said annular members and thereby to limit axial movement of the ring, the other of said rings being axially movable with axial movement of the other of said annular members.

2. A disc brake according to Claim 1,

wherein the two adjustment rings are urged into said mutual contact by spring means acting between one of said rings and one of said annular members.

3. A disc brake according to either preceding claim, wherein the two adjustment rings are relatively rotatable to effect said camming effect and consequential wear compensation, and wherein a rotary bearing device is disposed between the aforesaid other ring and the aforesaid other annular member.

4. A disk brake according to any preceding claim, comprising a stop member positioned to limit movement of the friction element in frictional engagement of said one ring it encompasses, yet permit further movement of said one ring, during brake application.

5. A disc brake according to Claim 4, comprising spring means arranged to act on the frictional element upon a brake application.

6. A disc brake according to any preceding claim, comprising spring means for assisting the relative return movement of the two members upon brake release.

7. A pressure medium operable disc brake, substantially as hereinbefore described with reference to and/or as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.

8. 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 one of the preceding Claims.