GB2036898A

GB2036898A - Disc Brakes

Info

Publication number: GB2036898A
Application number: GB7843294A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-11-06
Filing date: 1978-11-06
Publication date: 1980-07-02
Also published as: JPS5565734A; AU5218479A; FR2441098A1; DE7931220U1; IN149243B; ES485744A1; IT7950743A0; IT1162431B; GB2036898B

Abstract

The pads (4) of a disc brake assembly are held symmetrically relative to guide surfaces (14) of a carrier by springs (9) which clip over the backing plate (5) of each pad (4). The springs (9) each comprise two arms (10) which depend from a bridge portion (11) and resiliently grip the backing plate The edges (13) of the arms are bent out of the plane of the arms (10) and frictionally engage the surfaces (14). During limited forward movement of the pad (4) towards the disc the frictional engagement holds the edge of the springs (9) in position and the springs resiliently deform. When the brakes are released the springs (9) relax, thus retracting the pads (4) clear of the disc. Forward movement beyond a predetermined amount causes the springs (9) to slip on the carrier so that the amount of retraction remains substantially constant. The springs (9) include a portion (12) which biases the pads (4) into contact with the carrier guide surfaces (3). <IMAGE>

Description

SPECIFICATION Disc Brakes This invention relates to disc brakes, and more particularly to a disc brake incorporating a retraction spring for retracting the brake pads clear of the disc after each operation of the brakes.

In a disc brake assembly in which a pair of oppositely directed brake pads are mounted to slide in guides and are forced into engagement with opposite sides of the brake disc by suitable means, for example a hydraulic actuator, the danger exists that at the end of each application of the brakes at least one of the pads will remain in contact with the rotating disc unless it is positively retracted from engagement with the disc. If the pad remains in engagement with the disc unwanted braking action occurs producing undesirable heat and leading to rapid wear of the friction lining of the brake pads and noisy operation.

A disc brake having no means of positively retracting the pads from contact with the disc is described in British patent specification no.

1,501,394.

It has been proposed to overcome this problem by attaching a brake pad to the adjacent piston of the hydraulic actuator provided to operate the brake. Such attachment being by means of a spring secured to the rear face of the pad which engages in a groove formed in the inside of the piston. This system is, however, not entirely satisfactory since it considerably adds to the cost of manufacture of the brake pads and necessitates additional machining of the piston.

Further, this system is not wholly suitable in braking systems employing a single hydraulic actuator located on one side only of the disc since in such cases retraction will only be provided for the pad on the hydraulic actuator side of the disc.

Further, in such systems unless an entirely redundant coupling spring is provided on the pad located on the side of the disc remote from the actuator, the pad on this side will be different from that located on the actuator side and the pads will accordingly not be interchangeable. This again adds to the cost of the system. This construction also leads to difficulty in removing the pads.

Because the brake pads must, in order to move freely, be a loose fit in their guides, a problem which arises with prior art systems is that the pads tend to rattle in their guides. Various proposals for springs to bias the pad against the support in order to prevent this rattling have been made. For example, our co-pending British patent application 36802/78 describes a spring attached to a projection formed on top of the backing plate of a brake pad. Two substantially oppositely directed free arms of the spring engage the caliper of the disc brake assembly and when the pad is in position in the caliper the springs bias the pad downwardly, reducing the sideways rattle of the pads.Such arrangements have the disadvantage that they require projections formed on the back plate, and this leads to additional expense not only because additional material must be provided on the back plate but because the more complicated shape leads to less efficient utilization of the sheet material from which the backing plate blanks are stamped. Other proposals for seating anti-rattle springs have included the machining of recesses in the back plate. Whilst such systems avoid the difficulties associated with providing a projection on the back plate, the machining of the recess is an additional manufacturing step and again adds to the cost of the pads.

It will be appreciated that a further disadvantage of this system in which the pads are loosely guided is that the pads will always be forced in the same circumferential direction when braking effort is applied and the vehicle to which the brakes are fitted is moving forward. This constant stressing of the pads to one side of the carrier in which they are mounted can lead to seizure of the brake pad in position, and accordingly to failure or serious impairment of efficiency of the brakes.

According to one feature of the present invention there is provided a disc brake assembly comprising a carrier member in which at least one brake pad is mounted for sliding movement towards and away from a brake disc, the or each such brake pads having a plate portion which extends at each of two opposite sides of the pad to a position adjacent the carrier member, wherein a spring is secured to the plate portion at each of said two opposite sides thereof, and the 1 springs of the or each brake pad extend into frictional engagement with the carrier member, the arrangement being such that upon movement of the or each pad towards the disc the respective springs are stressed and upon release of the brake applying effort the springs will relax by moving the brake pads away from the disc.

In such a brake assembly not only are the brake pads automatically retracted from engagement with the disc at the end of each application of the brakes, but the springs of each pad can be arranged to maintain that pad centrally relative to the aperture in the carrier member in which it is mounted. This helps to reduce the possibility of the pads seizing in the carrier member.

Preferably, the springs are arranged such that if the forward travel of the brake pad from its relaxed position to its fully engaged position exceeds a predetermined amount (for example 0.013 mm) the frictional engagement between the springs and the carrier member will be overcome and the springs will slide along the surface of the carrier member by approximately the amount which the forward movement of the brake pad exceeded the predetermined amount.

When the brakes are next released the brakes will be retracted only by the predetermined amount since the springs have moved slightly forward along the carrier member. Thus, as brake pad wear occurs and the plate portion of the brake pad moves progressively nearer the disc the springs slide along the carrier member to ensure that in all states of wear of the pad, the pads are retracted by the same predetermined amount from the surface of the disc after each application of the brakes. The sliding movement of the springs against the carrier member assists in scraping accumulated deposits of road dirt and friction lining material, etc. From the surface of the carrier member, and this again helps in preventing the pad seizing in position.

Preferably, each spring includes a portion which extends radially outwardly (relative to the axis of rotation of the disc) from the pad to engage a portion of the caliper member and thereby apply a spring bias to the pad biasing the pad radially inwardly. Such bias assists in preventing the pad from rattling.

Advantageously, each spring includes a pair of jaws which grip opposite sides of the plate portion to hold the spring in place. The spring may advantageously be a unitary structure cut and bent from suitable sheet material.

The above and further features and advantages of the invention will become clear from the following description of an embodiment thereof, given by way of example only, reference being had to the accompanying drawings, wherein: Figure 1 is an elevational view, partly in crosssection, of part of a disc brake assembly; Figure 2 is a section on the line Il-Il of Figure 1; Figures 3 and 4 are respectively an elevational view and an end view of the spring of the assembly of Figure 1; and Figure 5 shows a blank from which the spring of Figures 3 and 4 is formed.

The brake assembly 1 shown in the drawings comprises a carrier member 2 which defines a pair of guide surfaces 3 (only one of which is shown in the drawings) on which are slidably mounted a pair of brake pads 4. The brake assembly 1 is generally as described in our British patent specification no. 1,501,394.

The brake pads 4 are a relatively loose fit in the carrier member and in use are acted upon by suitable force means to apply them against the opposite surfaces of a rotating brake disc which is angularly fast with the wheel of a motor vehicle.

The force means may comprise a single hydraulic piston-and-cylinder assembly which acts directly on one brake pad to apply it against one side of the disc, and indirectly by way of a caliper member against the other pad. Each brake pad comprises a backing plate portion 5 through which is bonded a friction lining 6 as will be well understood by those in the art.

On each side of the brake pad a spring 9 is located, the spring 9 being held in place by arms 10 thereof which resiliently grip opposite faces of the plate portion 5.

The spring 9 which is best illustrated in Figures 3 and 4 includes a bridge portion 11 from which the arms 10 depend and an upwardly extending portion 12 extending from one edge of the bridge portion 1 The arms 10 terminate at one edge in outwardly flared projections 13. As can be seen from Figure 2, when the springs 9 are correctly positioned over the plate portion 5, the projections 13 extend beyond the lateral edge of the plate portion 5 into engagement with the wall 14 of the guide surfaces 3.

It will be noted that since tha projections 1 3 engage the guide surfaces 3 on both lateral sides of the brake pad in a symmetrical manner, the springs will have the effect of maintaining the brake pad in a central position relative to the guides 3, thereby assisting in the prevention of seizing of the brake pads in the guides.

Upon actuation of the force means to apply the brakes, the pads will be moved towards each other, i.e. the pad illustrated in Figure 2 will be moved in the direction of the arrow of Figure 2.

Upon such movement the extreme right-hand end (as viewed in Figure 2) of the leading projection 1 3 will, by virtue of the frictional engagement between the projections 1 3 and the wall 14, act as a fixed pivot point, that is to say this extreme right-hand end will not move relative to the guide surfaces 3. Accordingly, movement of the brake pad will cause the leading arm 10 and projection 13 to resiliently deform into a stressed state.

During this movement the trailing arm 10 and projection 1 3 will either be bent slightly away from the backing pad (by virtue of the frictional engagement of the trailing projection 13 with the wall 14) or will not be deformed at all since the trailing projection 1 3 is free to slide along the wall 14. When the brakes are released the leading arm 10 and projection 1 3 will relax into the position shown in Figure 2 and because the extreme righthand end of the projection 13 is fixed relative to the wall 14 this will cause the brake pad to be retracted. The amount of retraction will be determined by the dimensions of the spring, but can conveniently be arranged to be approximately 0.013 mm.Accordingly, at each application of the brakes the pad will be moved forward 0.013 mm into engagement with the disc, and at the end of each application the pad will be retracted by this distance clear of the disc.

As the friction lining material wears the distance the pad must be advanced into braking contact with the disc increases. When this distance exceeds a predetermined amount the leading arm 10 and projection 13 will be fully stressed before the brake pad is in full braking engagement with the disc. Further forward movement of the brake pad by the force means will then cause the extreme right-hand edge of the leading projection to slide relative to the wall 14 by a small amount. When the braking force is subsequently removed, the pad will again be retracted by the dimension predetermined by the spring, that is to say 0.013 mm in the example given above. Thus, the retraction mechanism is "self-adjusting" and the pad is always retracted by approximately a predetermined amount, regardless of pad wear.

It will be noted from Figure 1 that when the spring is in position the upstanding portion 12 of the spring is deformed and is in sliding engagement with a portion 1 5 of the caliper.

Since the portion of the carrier 1 5 is relatively fixed, the spring portion 12 tends to exert a downward bias on the pad 4. This downward bias holds the pads firmly in engagement with the guide surfaces 3 and helps to prevent the pads rattling. It will be noted from Figures 3 and 4 that the portion 12 includes rolled-over edge portions 1 6 to give rounded edges to the portion 12 and assists sliding on the caliper portion 1 5.

It will be noted that the spring 9 is symmetrical about the centre plane of the plate portion 5 and accordingly the springs at opposite ends of the pad are identical and interchangeable. Further, the springs are secured to the plate portion 5 by simply pressing them in place, the resilience of the arms 10 serving to hold the springs in position until the pads are located in the carrier member, after which the springs cannot be accidentally displaced. Thus, the use of the described springs does not require any special machining of the brake pads, and the springs themselves, being all identical, are relatively simple and straightforward to manufacture. The springs are preferably manufactured from suitable resilient material, for example stainless steel and can be formed from the blank 17 shown in Figure 5, the blank being suitably stamped from sheet material.

It will be noted that the sliding action of the projections 1 3 along the wall 14 as the brake lining wears has the effect of scraping any accumulated deposits 1 8 from the wall 14, and this again helps to prevent seizure of the brake pads.

It will be seen therefore that the above described spring which can be formed cheaply and fitted without the provision of any special projections or machine recesses in the pad serves the three functions of ensuring retraction of the pads from the disc after each brake application, preventing rattling of the pads by biasing the pads radially inwardly into engagement with the guide surfaces 3, and helping to prevent seizure of the brake pads by centralising the pads within the carrier member and scraping accumulated deposits from the guide surfaces.

It will be noted that the spring of the above described device serves as an audible warning of excess friction lining wear. As the friction lining wears the leading projections 1 3 approach the disc, and eventually contact the disc when the amount of friction lining material remaining on the abutment plate is less than the amount by which the free end of the projections 1 3 are spaced from the plate portion 5. The engagement of the spring with the disc provides an audible warning that very little friction lining material remains. It will be noted that this warning system is effective even if the plate portion is made of plastics material and would accordingly not itself give any audible warning if it were to contact the disc.

Claims

1. A disc brake assembly comprising a carrier member in which at least one brake pad is mounted for sliding movement towards and away from a brake disc, the or each such brake pad having a plate portion which extends at each of two opposite sides of the pad to a position adjacent the carrier member, wherein a spring is secured to the plate portion at each of said two opposite sides thereof, and the springs of the or each brake pad extend into frictional engagement with the carrier member, the arrangement being such that upon movement of the or each pad towards the disc the respective springs are stressed and upon release of the brake applying effort the springs will relax by moving the brake pads away from the disc.

2. A disc brake assembly according to claim 1 wherein each spring comprises a pair of arms which resiliently grip opposite faces of the plate portion.

3. A disc brake assembly according to claim 2 wherein the portion of the spring which extends into frictional engagement with the carrier member is a projection extending from one side of one of the arms.

4. A disc brake assembly according to claim 3 wherein the projection and the associated arm are each planar with the plane of the projection extending obliquely to the plane of the arm.

5. A disc brake assembly according to any preceding claim wherein the frictional engagement between the springs of a brake pad and the carrier member is overcome when the pad is advanced towards the disc by more than a predetermined amount permitting the springs to slide relative to the carrier member.

6. A disc brake assembly according to any preceding claim wherein each spring includes an upstanding portion which is resiliently deformed as the pads are installed to bias the pads into engagement with guide surfaces on the carrier member.

7. A disc brake assembly according to claim 6 when appendant to claim 2 or claim 3 wherein the arms of each spring are interconnected by a bridge portion which spans an edge of the plate portion and from which the upstanding portion extends.

8. A disc brake assembly according to any preceding claim wherein the springs are each symmetrical about the central plane of their associated plate portion.

9. A disc brake assembly according to any preceding claim wherein the springs are all identical and hold the or each brake pad centrally between the pad guide surfaces of the carrier member.

1 0. A disc brake assembly according to any preceding claim wherein each spring is a unitary structure stamped from stainless steel.

11. A disc brake assembly, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.