GB2058973A

GB2058973A - Disc brake assembly

Info

Publication number: GB2058973A
Application number: GB8028177A
Authority: GB
Original assignee: SAUER ACHSENFAB
Current assignee: SAUER ACHSENFAB
Priority date: 1979-09-04
Filing date: 1980-09-01
Publication date: 1981-04-15
Also published as: GB2058973B; DE2935647B2; DE2935647C3; FR2464406A1; DE2935647A1

Abstract

The assembly is for use in commercial vehicles having a compressed air supply and comprises a floating yoke (3) which houses an hydraulic force gearing system (9, 10, 18) for applying the brake pads (11) to the wheel disc (2) which system is actuated by supply of compressed air to a cylinder (4). A membrane (19) of the cylinder (4) acts via a thrust rod 17, a working piston (9), hydraulic fluid chamber (18) and brake piston (10) on one pad (11), the other pad (11) being actuated by reaction on yoke (3). Ratio of areas of pistons (9, 10) determines the gearing. The arrangement provides automatic wear adjustment by passage of hydraulic fluid from a reservoir (14) into chamber (18). <IMAGE>

Description

SPECIFICATION Floating yoke disc brake The invention relates to disc brakes for commercial vehicles, in particular lorries and trailers, having a compressed-air supply.

Known fixed yoke disc brakes are unsuitable for heavy commercial vehicles, in particular lorries and trailers, because such brakes must be capable of sustained brake action and the brake lining and brake disc must therefore be sized for greater strength. In addition, the fixed yoke disc brake lacks the necessary depth of fitting space for application on both sides. Due to the closeness, on both sides, of the sealing elements and the brake fluid to the hot zone of the brake disc, the fixed yoke disc brake also lacks an adequate resistance to thermal stress.

Attempts have already been made to solve these problems by the use of floating yoke disc brakes with a clamping system facing away from the wheel hub. In this case, a brake yoke mounted in guide rails on a brake anchor was displaced by mechanical operation via rod actuators which are known from the drum brake and act on a spindle or a key system. This mechanical force transmission requires great constructional effort and leads to poor efficiency and to extensive hysteresis in actuation. Direct actuation of the disc brake by means of compressed air has failed due to the low pressure of the pneumatic brake assembly and the small space available for the brake cylinder. Moreover, in known floating yoke disc brakes, the yoke guides are so short that oblique running of the brake linings can frequently be found.A further disadvantage is that the yoke must be removed for dismantling the wheel hub with the brake disc.

According to the present invention a disc brake assembly for commercial vehicles comprises a brake yoke; hydraulic force gearing for applying brake pads to a wheel disc; and means for applying compressed air to actuate the hydraulic force gearing, the yoke being mounted for axial movement relative to the wheel disc and includes a section extending over a said wheel disc carrying a brake pad, whereby actuation of the assembly displaces the yoke and applies a brake pad to both sides of the disc. The brake yoke section which reaches over the disc to provide braking action on both sides, is preferably a separate, removable part. This permits removal of the wheel hub and the brake disc without completely dismantling the floating yoke.

Assemblies according to the invention can substantially relieve the problems of the prior art. They may be of simple construction and reliable mode of action, while enabling high efficiency and low hysteresis in actuation to be obtained. A pneumatic cylinder mechanism is normally mounted on the brake yoke to provide the source of compressed air.

It will be appreciated from the foregoing that the invention essentially combines the pneumatic and hydraulic application of pressure in each brake yoke associated with a wheel, with effective force gearing. Preferably, the hydraulic force gearing comprises a working piston coupled to the compressed air supply means for compressing hydraulic fluid in a cylinder against a brake piston to urge the pad against a said wheel disc, the assembly including a spring continuously biasing the working piston towards its deactuated position. The degree of force gearing is determined by the ratio between the areas of the working and the brake pistons.

A large support base for the floating yoke in the preferred embodiment is obtained with three-point mounting or multi-point mounting, when the brake yoke has at least two guide bolts, whereby the brake yoke is axially displaceably held in corresponding holes in a brake anchor which is normally located close to the brake disc, is fixed to the wheel axle and preferably has the shape of a collar. The brake yoke may also be axially displaceably held at an axial spacing from the brake anchor in a bearing which is rigidly mounted on the wheel axle, preferably close to the compressed-air supply, and preferably also has the shape of a collar.

The invention will now be described by way of example and with reference to the accompanying drawing which shows a section through a floating yoke disc brake embodying the invention.

A brake disc 2 is bolted, secure against rotation, to the wheel hub 1 of the wheel axle 6. The brake disc 2 can be designed with or without internal ventilation. A brake yoke 3 is axially displaceably mounted on the wheel axle 6. For this purpose, the brake yoke 3 has at least two guide bolts 5 which are mounted, axially displaceably together with the yoke 3, in corresponding holes in a brake anchor 7 which, close to the brake disc 2, is formed as a collar on the wheel axle 6. At an axial spacing therefrom, that end of the brake yoke 3 which faces away from the brake disc 2 is again axially displaceably mounted, close to a compressed-air cylinder 4 flanged there to the brake yoke 3, with the aid of a bearing 8 which has the shape of a collar and is fixed to the wheel axle 6.On that side of the brake yoke 3 which faces the brake disc 2, the brake yoke carries an angled separate brake yoke section 1 2 which is flanged on by means of screw bolts 1 3 and reaches over the brake disc 2 on the wheel hub side. On the inner surface, facing the brake disc 2, of the brake yoke section 12, there is the brake lining 11 on the wheel hub side. The compressed-air brake cylinder 4, flanged to that end of the brake yoke 3 which faces away from the wheel hub, acts with the aid of a membrane 1 9 on a working piston 9, which is supported against a compression spring 16 by means of a foot 20 located on the rear of a thrust rod 17, and hence acts on a volume of brake fluid present in a brake fluid chamber 1 8 of the same cross-section.Via the volume of brake fluid, the working piston 9 presses on a brake piston 10 which is mounted in the brake yoke 3, coaxially and likewise displaceably in the axial direction, and the brake lining 11, facing away from the wheel hub, is provided on that side of the brake piston which faces the brake disc 2. The working piston 9 has a crosssectional area which corresponds to the brake fluid chamber 1 8 but is smaller than the cross-sectional area of the brake piston 10.

The ratio of the areas of the working piston 9 and of the brake piston 10 determines the hydraulic force gearing of the floating yoke disc brake. The brake fluid chamber 18 is in flow connection with a brake fluid reservoir 14 via an upper balancing bore 1 5 of smaller cross-section. On actuation of the brake, the balancing bore 1 5 is overrun by the working piston 9 and is thus closed. On release of the brakes and on retraction of the working piston 9 due to the action of a eompression spring 16, the balancing bore 1 5 is freed again.

Further brake fluid can therefore be drawn from the brake fluid reservoir 14 into the brake fluid chamber 18, so that manual readjustment of the brake in the case of abrasion of the lining is not necessary. When the brake lining 11 is pressed, due to the actuation of the brake piston 10, against that side of the brake disc 2 which faces away from the wheel hub, the brake lining 11 carried by the brake yoke section 12 is also pressed, because of the reaction on the brake yoke 3 in floating mount, against that side of the brake disc 2 which faces the wheel hub, so that the brake action and the wear of the lining are uniform.

After the end of the brake stroke, the clearance for ventiiation between the brake disc 2 and the brake linings 11 is restored, in a manner known per se, under the action of the reduced pressure generated in the brake fluid chamber 1 8 by the retraction of the working piston 9.

Claims

1. A disc brake assembly for commercial vehicles having a compressed air supply means, which assembly comprises a brake yoke; hydraulic force gearing for applying brake pads to a wheel disc; and means for applying compressed air to actuate the hydraulic force gearing, the yoke being mounted for axial movement relative to the wheel disc and includes a section extending over a said wheel disc carrying a brake pad, whereby actuation of the assembly displaces the yoke and applies a brake pad to both sides of the disc.

2. A disc brake according to Claim 1 wherein the brake yoke has at least two guide bolts at one end thereof, located in a brake anchor fixed relative to the axis of a said wheel disc, and is slidably supported at the other end in a bearing which is also fixed relative to the disc axis.

3. A disc brake according to Claim 2 wherein the brake anchor and the bearing are mounted on a wheel axle.

4. A disc brake according to any preceding Claim wherein said brake yoke section is a separate, removable part.

5. A disc brake according to any preceding Claim wherein the hydraulic force gearing comprises a working piston coupled to the compressed air supply means for compressing hydraulic fluid in a cylinder against a brake piston to urge the pad against a said wheel disc, the assembly including a spring continuously biasing the working piston towards its deactuated position.

6. A disc brake according to Claim 5 including a brake fluid reservoir connected to the cylinder by means of a bore communicating with the cylinder at an axial location in the path of the working piston.

7. A disc brake according to any preceding Claim including a pneumatic cylinder mechanism for actuating the hydraulic force gearing.

8. A disc brake assembly substantially as described herein with reference to the accompanying drawing.