A drum brake assembly

Abstract: A drum brake assembly has brake shoes (2) and (3) within a rotatable drum (1). The shoes (2) and (3) are displaceable to effect braking by an hydraulic ram (7) and free ends (9) of the shoes react against an abutment (10). This reaction is effected through a layer of viscoelastic damping material and metal plate laminate (110) which may be carried by either the brake shoes or the abutment (10). The viscoelastic layer may be bonded between steel plates and secured by a spring clip to either the brake shoe or the abutment (10). Alternatively the viscoelastic layer may be bonded to the abutment (10). The laminate (110) can be accommodated within a recess in the abutment (10). The provision of the viscoelastic layers through which the brake shoes react on the abutment (10) alleviates the development of noise or squeal during use of the brake assembly.

Description: TECHNICAL FIELD & BACKGROUND ART The present invention relates to a drum brake assembly and is primarily concerned with such assemblies as are known for vehicle braking and which have a rotatable brake drum within which is located a brake shoe. More particularly the invention concerns brake assemblies of the kind in which the shoe is displaceable into engagement with the interior cylindrical surface of the drum for braking purposes, for example by actuation of a hydraulic ram, and during braking a freely mounted end of shoe reacts by abutment against a plate on which that end pivots as the shoe is displaced. Examples of drum brake assemblies of the type aforementioned are disclosed in French Patents FR-A-1 497 559 (Ferodo) and FR-A-872 912 (Auto Union AG). FR-A-1 497 559 proposes a drum brake assembly comprising a rotatable brake drum, a brake shoe therein and actuating means for displacing the shoe into engagement with the interior cylindrical surface of the brake drum to effect braking. The brake shoe has a free end remote from the actuating means which reacts with an abutment, the abutment being fixed relative to the rotation of the drum, so that the free end of the shoe is in direct sliding contact with a plate which is interposed between the free end of the shoe and the abutment and further interposed between the plate and the abutment is a resilient damping material through which the said reaction is effected to alleviate noise of operation of the assembly. FR-A-872 912 proposes a similar brake assembly to that discussed above but in this case the free ends of two brake shoes are resiliently damped by an elastic cover on the abutment means. Without a damping material disposed between the brake shoe and abutment means the operation of a drum brake assembly of the kind discussed above results, occasionally, in the development of vibrations producing noise or brake squeal which is generally regarded as disconcerting and unacceptable. It is therefore desirable to incorporate this damping material in a brake assembly. However, not all brake assemblies, similar to those discussed above, utilize the damping material and for those that do the damping material can be worn away over time. It is therefore an object of the present invention to provide a drum brake assembly of the kind referred to in which the development of noise during use of the assembly is alleviated by the incorporation of damping material in a manner which allows said damping material to be readily fitted. STATEMENT OF INVENTION AND ADVANTAGES According to the present invention there is provided a drum brake assembly comprising a rotatable brake drum having an interior cylindrical surface; a brake shoe within the drum; actuating means for displacing the shoe into engagement with said cylindrical surface for braking the drum; said shoe having a free end remote from the actuating means which free end reacts during braking against an abutment relative to which the drum is rotatable, the free end of the shoe being in direct abutting and sliding contact with a plate which is interposed between said free end and the abutment, and interposed between said plate and abutment is a resilient damping material through which said reaction is effected to alleviate noise of operation of the assembly, CHARACTERISED IN THAT the resilient damping material is bonded or adhesively secured to said plate to form a laminate therewith, said laminate being removably interposed between the free end of the brake shoe and the abutment and having a clip which engages the brake shoe or the abutment for retaining the laminate in said interposed position. In a conventional drum brake assembly of the kind specified the abutment is in the form of a steel plate, anvil or similar part against which the shoe reacts and this reaction is by direct metal-to-metal abutting contact between the shoe and the abutment. By the present invention, however, the reaction of the shoe against the abutment is through the medium of the resilient damping material and the introduction of a relatively thin layer of such a material has been found to result in a considerable reduction in the level of noise or squeal which is generated during operation of the break assembly. The resilient damping material is preferably a layer of viscoelastic material (such as a natural or synthetic rubber) where it is believed that viscosity of the material absorbs energy to provide the required damping characteristics and the elasticity of the material maintains its structure and ensures that it will return to a predetermined form following temporary compression. A preferred example of the resilient damping material is the elastomeric material sold under the Trade Mark BUNA-N. In conventional drum brake assemblies there are usually two brake shoes of generally arcuate shape positioned diametrically opposite to each other within the drum so that a hydraulic piston and cylinder ram can act simultaneously on both shoes at one common end of those shoes to apply the brake while the other common and free ends of the shoes can react against the abutment during operation of the brake. With such a conventional assembly there is what is known in the art as a leading brake shoe and it is preferred that at least this leading brake shoe reacts against the abutment through the resilient damping material and plate combination - usually however, both brake shoes will react against the abutment through respective resilient damping material and plate combinations. The resilient damping material is likely to be an extremely thin layer (say in the range 0.2 to 0.5 millimetres thickness) and may be carried either by the brake shoe or the abutment. Conventionally the edge of a steel web on the brake shoe will be urged into direct abutment with a flat face of the abutment anvil or other part so it is likely to be more convenient to locate the resilient damping material so that it is retained on the flat face of the abutment rather than on the brake shoe web. It is preferred that the laminate comprises the damping material sandwiched between two opposed metallic plates and bonded or adhesively secured to both of those plates so that the shoe reacts against the abutment through the metal plate/damping material laminate. The unit provided by the laminate of the resilient damping material sandwiched between opposed metallic plates can form a relatively thin shim (typically each plate could have a thickness in the range 0.2 to 0.5 millimetres sandwiching a thin layer of damping material as aforementioned) so that the shim could be incorporated in existing drum brake assemblies of conventional form with very little or no modification being required to those assemblies. DRAWINGS Embodiments of drum brake assemblies constructed in accordance with the present invention will now be described by way of reference only, with reference to the accompanying illustrative drawings, in which :- Figure 1 diagrammatically illustrates the general form of the drum brake assemblies and in particular the location of the resilient damping material in such an assembly which has a leading brake shoe and a trailing brake shoe; Figures 2 and 3 show perspective views of two examples of a laminate containing the damping material clipped onto an abutment of the assembly of Figure 1; Figure 4 shows a modified form of drum brake assembly having two leading brake shoes and the location of the resilient damping material. DETAILED DESCRIPTION OF DRAWINGS The components of the drum brake assembly shown in Figure 1 will, in the main, be recognisable by those familiar with the present art as comprising a cylindrical drum 1 rotatable with a vehicle wheel and within which is mounted a pair of non-rotatable brake shoes 2 and 3. Each brake shoe has a generally arcuate form and comprises a substantially part-cylindrical steel platform 4 on the convex side of which is carried a friction braking material 5 while the concave side of the platform has an integral steel reinforcing web 6. The shoes 2 and 3 are positioned diametrically opposite to each other within the drum 1 and an hydraulic ram or piston and cylinder device 7 is disposed to act between one pair of adjacent common ends 8 of the webs 6. Disposed between the other pair of adjacent common free ends 9 of the webs 6 is an abutment in the form of a steel anvil or plate 10. The ram 7 and abutment 10 are non-rotatably secured to a back plate 100 of the assembly. During use of the drum brake assembly in conventional manner the brake shoes 2 and 3 are displaced simultaneously radially outwardly in Figure 1 by operation of the hydraulic ram 7 to move the braking material 5 into frictional engagement with the cylindrical interior wall of the drum 1 to brake the rotating drum. In response to the actuation of the ram 7 and the braking of the drum 1, the shoes 2 and 3 can react against and pivot on the abutment 10. In a conventional assembly this latter reaction would be by the edges of the free ends 9 of the steel webs 6 directly abutting and sliding on the anvil or the plate 10. By the present invention however a resilient damping material and plate laminate 110 is interposed between the free end 9 of each brake shoe and the abutment 10. Consequently each brake shoe can react against the abutment 10 through the medium of the resilient damping material and plate laminate 110 and it has been found that this alleviates the development of noise or squeal during operation of the assembly (such noise being believed to be attributable in part to vibration in the shoes). Figures 2 and 3 illustrate two ways in which resilient damping material consisting of a layer 11 of viscoelastic material (such as Nitrile Rubber) can be incorporated in the assembly of Figure 1. For a typical brake assembly the layer 11 is likely to have a thickness in the order of 0.25 millimetres. In the embodiment of Figure 2 the layer 11 of viscoelastic material is sandwiched and bonded between opposed steel plates 12 and 12a to form a laminate. However, here the plate 12 is formed of spring steel and is generally U-shaped to have legs 12b by which the laminated shim is clipped to engage opposed side edges of the abutment 10 and firmly retain the shim on the abutment (preferably with the plate 12a in face-to-face abutment with the face 10a). In Figure 2 the edge of web end 9 is intended to slidingly abut the plate 12 and to react through the layer 11 in the laminate against the abutment 10. Typically the plates 12 and 12a will have a thickness in the order of 0.35mm. It will be realised however that the laminate/clip component may be of a reverse structure whereby the spring legs 12b are arranged to clip on to the web end 9 of the brake shoe so that end 9 will slidingly abut the plate 12a to react through that plate and successively through the viscoelastlc layer 11 and the steel plate 12 against the abutment 10. The visco elastic layer 11 in Figure 3 is incorporated as part of a laminated spring clip component which is attached to the abutment 10 in a similar manner to the Figure 2 embodiment. However, in Figure 3 it will be seen that the laminated clip is formed by two substantially complementary "U" shaped spring steel plates between which is disposed and bonded a "U" shaped layer of the visco elastic material 11. More particularly, the inner of the "U" shaped plates has opposed legs 12b' and a bridging portion 12a', the latter of which abuts the face 10a of the abutment 10 in a similar manner to the plate 12a in Figure 2. Although the aforegoing embodiments indicate the visco elastic material as being retained or maintained on a rectangularly shaped abutment anvil or plate 10, it will be appreciated that the abutment is not necessarily in the form of a plate or a rectangular shape. The vehicle to which the drum brake assembly shown in Figure 1 is fitted will usually have a direction of movement which results in the drum 1 rotating in the direction of arrow X and under these conditions the brake shoe 2 will be regarded as the leading shoe and the brake shoe 3 as the trailing shoe. Tests have indicated that the provision of the resilient damping material 11 is most beneficial for the leading brake shoe and it is likely that there will be applications of the present invention where it is considered unnecessary to provide the resilient damping material for a trailing brake shoe. Figure 4 shows a modified form of drum brake assembly in which the two diametrically opposed brake shoes are mounted within the drum 1 and each of these brake shoes 2 leads with regard to the direction of rotation for the drum indicated by the arrow X. Two hydraulic rams 20 and 21 are provided for displacing, one each, the shoes 2. More particularly, the ram 20 is disposed between the opposed adjacent ends 8 and 9 of the two shoes while the ram 21 is disposed between the opposite adjacent ends 9 and 8 respectively of the shoes. Each ram comprises a cylinder 22 which is secured relative to the back plate 100 and a piston 23 which acts on the adjacent end 8 of the respective shoes 2 so that when the rams are actuated as shown in Figure 6 the pistons 23 can simultaneously displace the shoes in an anti-clockwise direction in that Figure to brake the drum 1. During such braking and/or actuation of the rams 20 and 21 the free ends 9 of the shoes 2 react against the abutments 10 through the visco elastic damping layer and metal plate laminates 110. Each abutment 10 in Figure 4 conveniently comprises the cylinder 22 of the ram which is located adjacent to the respective shoe free end 9 while the visco elastic layer and plate laminate may be secured to or carried on the cylinder 22 or on a mounting part for that cylinder in the manner previously discussed with reference to Figures 2 and 3.

Claims: A drum brake assembly comprising a rotatable brake drum (1) having an interior cylindrical surface; a brake shoe (2) within the drum (1); actuating means (7) for displacing the shoe (2) into engagement with said cylindrical surface for braking the drum (1); said shoe (2) having a free end (9) remote from the actuating means (7) which free end reacts during braking against an abutment (10) relative to which the drum (1) is rotatable, the free end (9) of the shoe being in direct abutting and sliding contact with a plate (12) which is interposed between said free end (9) and the abutment (10), and interposed between said plate (12) and abutment (10) is a resilient damping material (11) through which said reaction is effected to alleviate noise of operation of the assembly, CHARACTERISED IN THAT the resilient damping material (11) is bonded or adhesively secured to said plate (12) to form a laminate therewith, said laminate being removably interposed between the free end (9) of the brake shoe and the abutment (10) and having a clip (12 b ) which engages the brake shoe (2) or the abutment (10) for retaining the laminate in said interposed position. An assembly as claimed in claim 1 in which the resilient damping material (11) comprises a viscoelastic rubber. An assembly as claimed in either claim 1 or claim 2 in which the resilient damping material (11) comprises a layer having a thickness in the range 0.2 to 0.5 millimetres. An assembly as claimed in any one of the preceding claims in which the laminate comprises the damping material (11), said plate (12) and an opposing second plate (12 a ), the damping material being sandwiched between said first (12) and second (12 a ) plates and being bonded or adhesively secured to both said plates. An assembly as claimed in any one of the preceding claims in which the clip (12 b ) is integrally formed with the or a plate (12) of said laminate. An assembly as claimed in claim 5 in which said plate (12) is of substantially "U" shape to present opposed legs (12 b ) which form the clip and between which legs the brake shoe (2) or abutment (10) is received for retaining the laminate. An assembly as claimed in either claim 5 or claim 6 when appendant to claim 4 in which the clip (12 b , 12 b' ) is integrally formed with both said opposing first and second plates (12, 12 a ). An assembly as claimed in claim 7 in which both said opposed first and second plates (12, 12 a ) are of substantially "U" shape with one said plate being received in substantially complementary manner within the other to present opposed legs (12 b 12 b' ) which form the clip between which the brake shoe (2) or abutment (10) is received for retaining the laminate. An assembly as claimed in claim 8 in which the resilient damping material (11) is in the form of a "U" shaped layer extending in substantially complementary manner between the opposed "U" shaped first and second plates (12, 12 a ). An assembly as claimed in claim 5 or in any one of claims 6 to 9 when appendant to claim 5 in which the plate or plates with which the clip (12 b ) is integrally formed is of spring metal. An assembly as claimed in any one of the preceding claims in which the or each plate (12, 12 a ) of said laminate has a thickness in the range 0.2 to 0.5 millimetres. An assembly as claimed in any one of the preceding claims in which the brake shoe (2) is of substantially arcuate shape and comprises a part cylindrical platform (4) on the convex side of which platform (4) is carried a friction braking material (5) and on the concave side of which platform is an integral web (6) and wherein one end (8) of the shoe (6) is acted on by said actuating means (7) and the opposite free end (9) of the shoe reacts through the laminate against the abutment. An assembly as claimed in claim 12 and having two said brake shoes (2) positioned substantially diametrically opposite to each other within the drum. An assembly as claimed in claim 13 in which said one ends (8) of the respective shoes (2, 3) are adjacent to each other and said actuating means (7) is disposed between said one ends (8) to act simultaneously on both shoes (2, 3), said opposite free ends (9) of the respective shoes (2, 3) are adjacent to each other and said abutment (10) is disposed between said opposite ends (9), and wherein at least one of said opposite free ends (9) of the brake shoes (2, 3) reacts on the abutment (10) through said laminate. An assembly as claimed in claim 14 and having a leading brake shoe and a trailing brake shoe and in which at least the leading brake shoe reacts on the abutment (10) through the laminate. An assembly as claimed in claim 13 in which said one end (8) of one shoe (2) is adjacent to said opposite free end (9) of the second shoe (2) and said opposite free end (9) of the one shoe (2) is adjacent to the one end (8) of the second shoe (2); a said actuating means (21) and a said abutment (10) are disposed between each of said adjacent one end (8) and opposite free end (9) so that both brake shoes (2) can be displaced simultaneously by the said actuatinq means (21) acting on the said one ends (8) of the respective brake shoes (2) and both brake shoes are leading, and each said opposite free end (9) of the brake shoes (2) reacts on the respective abutments (10) through a said laminate. An assembly as claimed in claim 16 in which each actuating means (21) comprises a fluid pressure operated piston and cylinder device. An assembly as claimed in claim 17 in which the abutments (10) comprise the cylinders (22) of the respective actuating devices.

Inventors: LANG ALLAN MICHAEL, LANG, ALLAN MICHAEL
Applicants: BBA GROUP PLC, BBA GROUP PLC.
Application year: 1989
Main classification: F16D65
IPC codes: F16D65, F16D51