IMPROVEMENTS RELATING TO FRICTION PAD ASSEMBLIES

Abstract: The present specification discloses a friction pad assembly comprising a planar backing plate (2) to which a pad (3) of friction material is secured. To resiliently hold the pad assembly in position in a disc brake a resilient spring (19) is secured in the assembly. In known brakes the spring (19) projects beyond the profile and sides of the backing plate (2) and thus requires space within the overall design, available space being limited and critical to brake design. The present invention provides a friction pad assembly (1) wherein an edge region (9) of the backing plate has two recesses (13) located symmetrically about a centre line (11) of the assembly with a resilient leaf spring (19) secured across each recess (13). In use, in a disc brake retaining pins engage against the springs (19) to hold the assembly in position. This pad assembly design thus minimises the required space by locating the resilient pad anti-rattle springs within the profile and sides of the backing plate (2), and by using the necessarily relatively short springs (19), the tendency for the springs (19) to be buckled or distorted, or affected by heat, is minimised.

Description: The present invention relates to a friction pad assembly for use in a disc brake, and a disc brake incorporating such a friction pad assembly. In particular the present invention relates to a friction pad assembly comprising a planar backing plate to which a pad of friction material is secured. To resiliently hold such a friction pad assembly in a disc brake it is known to secure a wire or leaf spring to the backing plate e.g., by a pin, rivet or clip-type arrangement, the spring engaging part of the disc brake and biassing the friction pad assembly against another part of the disc brake. In this way pad rattle is at least reduced. The majority of such springs are attached to the backing plate in a way in which they protrude either radially outwardly of the backing plate, thus increasing the swept form of the pad profile and restricting cooling air flow above the pads, or attached so that they lie to the front or the rear of the backing plate. Any such offset positioning of the spring may of course result in spurious loading of the pad assembly, which may have adverse effects. Furthermore in order to allow for the offset spring arrangement the disc brake, i.e. caliper housing, may have to have cast recesses to accommodate the spring. This all adds to the overall size, complexity and cost of the brake. Also in certain cases the spring is detachable from the backing plate. This is disadvantageous. Another known type of friction pad assembly incorporates an elongate leaf spring which extends across a recess provided in the upper edge region of the backing plate, the spring being flexed and held between opposite ends of the recess. Such constructions are disclosed in FR-A-2461161 and EP-A-0158385. However, again, this type of construction causes the flexed spring to require additional space in the brake construction. A further brake construction disclosed in EP-A-0336103 utilises a single wire spring which engages in two small recesses in the upper edge of the baking plate of each of the two friction pad assemblies, the wire spring merely engaging in the recesses so that the spring maintains its position relative to the respective backing plates. It will be appreciated that because of the size of a commercial wehicle disc brake and consequently the size and weight of the friction pads, fairly hefty springs have to be used to prevent unwanted vibration and rattle. Accordingly the above spring arrangements as used on cars have to be made correspondingly bigger to compensate. However these designs do not lend themselves to such an increase in size and the above mentioned problems and disadvantages are amplified. The aim of the present invention is to provide a friction pad assembly incorporating a pad anti-rattle spring which is located within the confines of the front and rear faces of the backing plate i.e., is not offset, and within the radially outer edge of the backing plate so that the spring does not require special modification of the caliper housing and does not affect the swept profile of the pad assembly, and to also provide a disc brake incorporating such a friction pad assembly. According to the present invention there is provided a friction pad assembly comprising a backing plate to which a pad of friction material is secured, a recess being formed in an edge region of the backing plate with a resilient spring extending between opposite end regions of the recess, characterised in that at least two recesses located in spaced relationship to one another, are provided in the edge region, an elongate spring being provided for each recess, each recess being stepped at each end to provide a shoulder on which an end region of a spring is supported, each spring being thus maintained above the base of a recess. In a preferred embodiment of the present invention the backing plate has two side edges, an upper edge and a lower edge, the pad assembly resting in a disc brake on its lower edge. The upper edge has two recesses symmetrically located about the centre line or axis of symmetry of the pad assembly. To secure the leaf springs in position, the said end regions of the leaf spring each include a region of reduced width which engages in a respective slot formed in the region of the backing plate continuous to the recess, the regions of the backing plate defining the slot being bent together to fixedly retain the spring. The leaf spring is thus within the confines of the front and rear faces of the backing plate, i.e., not offset, and radially within the edge of the backing plate. Thus the swept form of the pad assembly is minimized and because the spring(s) are so confined the manufacture and machining of the caliper housing may be simplified, i.e. the backing plate can abut a corresponding machined surface on the caliper housing without areas of the housing having to be recessed to accommodate the spring(s). In use, the above described friction pad assemblies are located in a caliper housing of a disc brake, mechanically or hydraulically actuated, and are held down against supporting surfaces preferably by a U-shaped retention pin which is secured to the caliper housing. Each arm of the U-shaped retention pin engages one of the leaf springs on each friction pad assembly, so as to deflect the leaf spring radially inwardly on assembly, thus loading the friction pad assemblies against the supporting surfaces. Alternatively the U-shaped retention pin may be replaced by two separate pins. By using a pair of relatively short leaf springs the required optimum loading can be achieved with at least the springs being located within the swept profile of the backing plate, and possibly also the pin or pins when the friction pad assembly is installed in a brake. Further, by utilising two relatively short leaf springs there is only a small thermal effect and a minimal tendency for the springs to buckle or twist. The concept of two recesses and leaf springs may also be used on a force transmitting member located between an actuator of the brake and the friction pad assembly nearer to the actuator. In this way the previously mentioned U-shaped retention pin or pair of pins can additionally bias the force transmitting member against guide surfaces to avoid unwanted vibration. The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a preferred embodiment of the present invention; Fig. 2 is a front view of the embodiment of Fig. 1; Fig. 3 is a partially cutaway front view of part of the embodiment of Fig. 1; Fig. 4 is a plan view of a leaf spring for use in the embodiment of Figs. 1 to 3; Fig. 5 is a plan view of a disc brake incorporating friction pad assemblies constructed according to Figs. 1 to 4; and Fig. 6 is a sectional view of part of the brake shown in Fig.5. A preferred embodiment of the present invention is illustrated in Figs. 1 to 5 of the accompanying drawings. As best seen in Figs. 1 to 4, this preferred embodiment of friction pad assembly 1 comprises a planar backing plate 2 to which a pad 3 of friction material is secured. The backing plate 2 is generally rectangular (see Fig. 2) and has two parallel side edges 5, a lower edge 7 and an upper edge 9. The friction pad assembly is symmetrical about a centre line 11 and has a recess 13 formed in the upper edge 9 symmetrically on each side of the centre line 11. Each recess 13 extends through the complete thickness of the backing plate 2 and has a base 15 with a stepped region adjacent to each end wall 16, the stepped regions forming shoulders 17 on which the end regions of an elongate leaf spring 19 rest. Each end wall 16 is provided with a slot 21, each slot having facing walls 23. As seen in Fig. 4, the leaf spring 19 has a reduced width region 25 at each end, these reduced width regions 25 each engaging in a slot 21. To retain the reduced width regions 25 in said slots, the facing walls 23 are bent towards each other during manufacture of the friction pad assembly. In this way each leaf spring 19 is supported across a recess 13, above the base 15 thereof. In use, as can be seen in Figs. 5 and 6, two friction pad assemblies 1 are located in a caliper housing 27 with the side edges and lower edge 7 engaged on supporting surfaces provided by guides 29. The lower edge 7 is loaded against the guides 29 by a U-shaped retention pin 31 which is secured to the caliper housing 27, the U-shaped pin 31 having two arms 33 which each engage and deflect a leaf spring 19 on each of the friction pad assemblies. As an alternative to the U-shaped retention pin 31, two parallel pins secured to the caliper housing can be used. As can be seen in Fig, 5, the principle of a leaf spring 34 extending across a recess is also used in a force transmitting member 35, the force transmitting member 35 being located between an actuator of the brake, which is located in actuator housing 37, and the friction pad assembly 1 which is nearer to the actuator. The arms 33 of the U-shaped retention pin 31 additionally engage the leaf spring 34 and thus load the force transmitting member 35 against its guides to avoid unwanted vibration. As will be appreciated from the accompanying drawings, especially Figs. 1, 2 and 6, the positively secured leaf spring(s) 19; 34 are radially within the profile of the friction pad assembly and within the confines of the front and rear faces of the backing plate 2. Also by using the relatively short leaf springs 19,34, illustrated, the required optimum loading is achieved and any tendency for the leaf spring to buckle or distort, and/or to be affected by heat, is minimised. The illustrated design also enables the arms 33 of the pin 31 to be within the swept profile of the backing plate 2. The swept profile of the pad assembly is therefore unaffected by the provision of the leaf springs, and the caliper housing of the brake thus requires no specific design. Further, as the springs are not offset with regard to the backing plate, no spurious moments of force are applied to the friction pad assembly. The present invention thus provides a simple friction pad assembly which is cheap to manufacture and which has clear advantages both by virtue of its operation and by virtue of the fact that no specific brake design features are required.

Claims: 1. A friction pad assembly comprising a backing plate (2) to which a pad (3) of friction material is secured, a recess (13) being formed in an edge region (9) of the backing plate (2) with a resilient spring extending between opposite end regions of the recess (13), characterised in that at least two recesses (13) located in spaced relationship to one another, are provided in the edge region (9), an elongate spring (19) being provided for each recess (13), each recess (13) being stepped at each end to provide a shoulder (17) on which an end region of a spring (19) is supported, each spring (19) being thus maintained above the base (15) of a recess (13). 2. An assembly as claimed in claim 1, wherein two recesses (13) are located symmetrically about a centre line (11) of the assembly. 3. An assembly as claimed in claim 1 or 2, wherein the said ends of the recesses (13) are each provided with a slot (21) into which an end portion of one of the springs (13) engages, the sides (23) of the slot (21) being deformed to retain the spring (13) in position. 4. An assembly as claimed in any one of claims 1 to 3, wherein each spring (19) is an elongate leaf spring. 5. An assembly as claimed in any one of claims 1 to 4, wherein each spring (19) is located within the confines of the front and rear faces of the planar backing plate (2). 6. An assembly as claimed in any one of claims 1 to 5, wherein each spring (19) is located within a recess (13). 7. A disc brake incorporating a friction pad assembly (1) as claimed in any one of the preceding claims, with a retaining pin (31) engaging against each resilient spring (19) to resiliently hold the friction pad assembly (1) in position in the brake (27).

Inventors: GODDARD, CHRISTOPHER HUGH, THOMPSON, RICHARD EDGAR
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1989
Main classification: F16D65
IPC codes: F16D69, F16D65, F16D55