GB2122291A

GB2122291A - Drum brake

Info

Publication number: GB2122291A
Application number: GB08217981A
Authority: GB
Inventors: Ronald Peter Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1982-06-22
Filing date: 1982-06-22
Publication date: 1984-01-11
Also published as: GB2122291B

Abstract

A brake shoe (3) of an internal shoe drum brake is secured to its support plate (2) by means of an anchor which limits the amount by which the shoe (3) can lift away from plate (2). The anchor comprises a clip (11) and a pin (10) having a shank which extends from the plate (2) and through an opening (17) in a web (8) of the shoe (3). In order to assemble the anchor, the clip is pushed over the free end (19) of the pin shank and is slid down the pin to its desired position, the clip frictionally gripping the pin. The clip (11) wedges in the opening (17) in the brake shoe, so that if the brake shoe (3) starts to lift off from the plate (2) the clip is caused to grip the pin (10) more tightly. <IMAGE>

Description

SPECIFICATION Drum brake This invention relates to an internal shoe drum brake comprising a brake shoe mounted on a support plate for movement across the plate towards and away from the internal surface of a brake drum.

Such brakes are commonly used to brake rotation of vehicle road wheels, and typical examples of such brakes are described in U.K. Patent Specifications Nos. 681,765; 698,457; 899,061; 1,341,548 and 2,039,644. The brakes described in these Specifications each comprise two arcuate brake shoes disposed opposite one another on the support plate with each shoe carrying a friction lining facing the adjacent internal cylindrical surface of the brake drum. One end of each brake shoe (or, in some cases, both ends) is engaged by the piston of a hydraulic ram which when actuated forces its associated shoe to move across the surface of the support plate into engagement with the brake drum. Return tension springs serve to bias the shoes to move away from the drum when the brakes are released.

The shoes are of "T"-section, each comprising a web to which the return springs are attached and which lies generally parallel to the support plate, and a cylindrical surface carrying the brake lining and lying perpendicular to the support plate.

It has been found that during operation of such brakes, the brake shoes tend to lift away from the support plate when they are pressed against the brake drum. In order to limit the amount by which each brake shoe can lift away from the support plate, each shoe is anchored to the plate by means of a pin which extends from the support plate and through an opening or hole in the web of the shoe. In the arrangement shown in U.K. Patent Specification No 681,765, the pin is rigidly connected to the support plate, and the free end of the pin which extends through a slot in the web of the shoe is screwthreaded. A washer is placed over the end of the screw-threaded pin, and a nut is then screwed onto the pin to hold the washer in place against the brake shoe web. When the brake is being assembled, it is necessary to adjust the nut.If the nut is tightened too much, it will force the shoe against the support plate causing friction, wear, and incorrect operation. If the nut is not tightened enough, the shoe will be able to lift away from the support plate to an undesired extent. After the nut is correctly adjusted, it must be locked in position by a split pin.

Although operation of the shoe anchoring means just described is satisfactory, the assembly of the nut on the pin and its subsequent adjustment and locking in position is time consuming. Forthis reason, the usual current practice is to dispense with the nut, and to use instead a compression spring disposed between the free end of the pin and the web of the brake shoe to bias the shoe towards the support plate. Such an arrangement is described in U. K. Patent Specification No. 899,061 in which the compression spring is U-shaped and fits between the shoe web and a head formed on the free end of the pin.

A similar arrangement is shown in U. K. Patent Specification No. 1,342,548, where the compression spring is a coil spring held in place by a washer engaged with a head formed at the free end of the pin.

Although the two shoe anchoring arrangements just described can be assembled relatively easily and are effective to prevent brake shoe lift off, they have the disadvantage that they tend to produce annoying noises, such as screeching, which noises result from the shoes being spring biased into contact with the support plate. With a view to overcoming the problem of brake noise, it has been proposed in U. K.

Patent Specification No. 2,039,644 to mount a layer of brake lining material on the support plate, and to make the brake lining material on the brake shoes wide enough to overlap the shoe edge adjacent the support plate so that the friction between the brake shoe and the support plate takes place between two layers of brake lining material. This solution to the problem of brake noise obviously makes the brakes more expensive to produce.

An object of the present invention is to provide an improved means for anchoring a brake shoe to a support plate which is inexpensive to manufacture and assemble, and which avoids the problem of brake noise.

According to the present invention there is provided an internal shoe drum brake comprising a brake shoe mounted on a support plate for movement across the plate towards and away from the internal surface of a brake drum, the shoe being secured to the support plate by means of an anchor which limits the amount by which the shoe can lift away from the support plate, the anchor comprising a pin, and a clip which frictionally grips a shank of the pin.

In a preferred embodiment, the anchor can be assembled merely by sliding the clip along a shank of the pin to a desired position to determine the length of the anchor, the clip automatically locking itself in position on the pin shank by friction so that the need for special locking means is avoided.

A preferred embodiment of brake according to the invention will now be described byway of example and with reference to the accompanying drawings in which Figure lisa plan view of an internal shoe drum brake according to the invention, Figure 2 is a cross-sectional view on a larger scale on the line II - II in Figure 2, and Figure 3 is a large scale perspective view of a clip used in the brake of Figures 1 and 2.

The brake shown in the drawings is in most respects of conventional design and will therefore be described only briefly. It comprises a brake drum 1 fast with a vehicle wheel (not shown) which is to be braked. The brake drum 1 overlies a brake support plate 2 on which two brake shoes 3 are mounted for pivoting about a pin 4. The shoes can be pivoted to actuate the brake by means of a hydraulic ram, i.e. a brake cylinder 5 which is mounted rigidly on the plate 2.

In order to actuate the brake, hydraulic fluid is supplied under pressure to a central chamber of the cylinder 5 to act on two pistons (not shown) disposed one at each end of the cylinder. The pistons act on the brake shoes 3 urging them to pivot about the pin 4 and move across the face of the plate 2.

Friction linings 6 carried by the shoes 3 engage the drum 1 to brake its rotation as shown in Figure 1.

Two tension springs 7 are connected to the shoes to bias them towards a brake release position in which the shoes are spaced from the brake drum.

As shown in Figure 2, each brake shoe is T-shaped in cross-section, comprising a web 8 to which the return springs 7 are connected and which lies generally parallel to the support plate 2, and a cylindrical surface 9 to which the brake lining is bonded. The brake as thus far described is of conventional design.

As mentioned above, when the brakes are applied, the shoes tend to "lift-off", i.e. they tend to move away from the plate 2 in the direction of the arrow A (Figure 2). In order to restrain brake shoe lift off, each shoe is secured to the plate 2 by means of an anchor comprising a pin 10 and clip 11. Each clip 11, best seen in Figure 3, is made of spring steel. It comprises a base wall 12 having a central circular opening 13, a pair of upwardly diverging side walls 14 extending from a pair of opposite edges of the base wall, and a pair of inwardly directed top walls 15 extending from the top edges of the side walls 14. The top walls 15 terminate short of meeting each other, and are formed with V-notches 16 facing one another. These notched top walls 15from jaws which grip the pin 10 when the anchor device is assembled.

In order to assemble the anchor, the pin 10 is passed through a circular opening 16 in the plate 2 and through a rectangular larger opening 17 in the web 8 of the brake shoe. The pin 10 has an enlarged head 18 which is too large to pass through the opening 16 in the plate 2, so that the pin is anchored to the plate. The length of the pin 10 is such that a free end region 19 of the pin extends beyond the web 8. The clip 11 is then passed base first over the free end 19 of the pin 10 so that the pin passes through the aperture 13 in the base of the clip 11 and then through the opening between the jaws formed by the notched walls 15.The cross-sectional dimension of the pin 10, i.e. the diameter in the case of the round pin illustrated, is such that the pin fits with a clearance through the aperture 13 in the base wall of the clip, but is a force fit into the jaws at the top of the clip. The clip is forced down along the pin until it reaches a position in which it extends through the slot 17 in the web 8, lying partly above and partly below such slot.

The size of the clip relative to the slot 17 in the brake shove web is such that the lower part of the clip can pass through the slot 17 in the web 8, but the diverging side walls of the clip engage the sides of the slot 17 to define an end position of the clip 11 beyond whichit cannot be forced along the pin.

When assembling the anchor, it is preferred that the clip should not be forced down the pin to its fullest extent, so that the shoe is not forced down onto the support plate 2 in the brake release position shown in Figure 2. The fact that the clip is not forced all the way along the pin 10 is the reason for the sight clearance shown in Figure 2 between the head 18 of the pin and the plate 2.

It is important that this small clearance should be left, since otherwise the brake shoe would be forced down onto the support plate 2 when the brakes are applied. The pin 10 can pivot about its head 18 when the brake shoe moves in the direction of arrow B when the brakes are applied, but since the length of the anchor is fixed, this would tend to pull the shoe down onto the plate 2 if the anchor were too short.

Unlike some previously known brake shoe anchors which are spring loaded, the anchor just described does not normally exert any force on its associated brake shoe, so that the brake shoe is not forced against its support plate, and problems of brake noise are avoided. However, in the event of the brake shoe starting to lift off in the direction of arrow A, then the clip 11 will engage the side walls of the slot 17 in the brake shoe web 8 and limit brake lift off to a very small amount. There is little risk of the clip sliding along the pin under the action of brake lift off force, because the walls of the web surrounding the slot 17 act on the diverging side walls 14 of the clip to tend to close the jaws at the top of the clip more tightly onto the pin 10 to increase its friction grip on the pin. To enhance the grip of the clip upon the pin, the pin shank could be grooved, ribbed or patterned, instead of smooth.

The anchor is relatively cheap to manufacture, and can be assembled much more easily than known anchors of the type comprising a nut, bolt, and split pin.

Claims

1. An internal shoe drum brake comprising a brake shoe mounted on a support plate for movement across the plate towards and away from the internal suface of a brake drum, the shoe being secured to the support plate by means of an anchor which limits the amount by which the shoe can lift away from the support plate, the anchor comprising a pin, and a clip which frictionally grips a shank of the pin.

2. A brake according to claim 1, in which the anchor is assembled by sliding the clip along the shank of the pin to a desired position to determined the length of the anchor.

3. A brake according to claim 1 or claim 2, in which the length of the anchor is such that, at least in the released position of the brake shoe, the anchor does not bias the brake shoe into contact with the support plate.

4. A brake according to any preceding claim, in which, in the event of the brake shoe lifting away from the support plate during braking, it exerts a force on the anchor which tends to increase the frictional force retaining the clip in position on the pin.

5. A brake according to any preceding claim, in which the shank of the pin extends from the support plate through an opening in a web of the brake shoe with a free end region of the shank extending on the side of the web remote from the support plate, the clip also extending through the opening in the brake shoe web.

6. A brake according to claim 5, in which the clip has a tapered external surface and is adapted to wedge in the opening in the brake shoe web whereby to limit brake shoe lift off.

7. A brake according to claim 6, in which the clip has a base wall having an opening through which the pin shank passes, a pair of upwardly diverging side walls extending from a pair of opposite edges of the base wall, and a pair of inwardly directed top walls extending from the top edges of the side walls, the top walls terminating short of meeting each other and forming jaws which grip the pin shank, the base wall of the clip lying on the side of the brake shoe web adjacent the support plate, and the top walls of the clip lying on the side of the brake shoe web remote from the support plate, the arrangement being such that in the event of the brake shoe lifting away from the support plate the diverging side walls of the clip are squeezed together to increase the grip of jaws on the pin shank.

8. A brake according to any one of claims 5 to 7, in which the pin shank passes through an opening in the support plate, and in which the pin is formed with an enlarged head which is too large to pass through such opening, the pin being arranged to pivot relative to the support plate during actuation of the brake.

9. A brake according to any preceding claim, in which the clip is made of spring steel.

10. A brake substantially as described herein with reference to the accompanying drawings.