DISC BRAKE SHOE ASSEMBLIES

Abstract: A disc brake shoe assembly (30) includes a noise insulator sheet (40) that is secured to a brake shoe backing plate (32) and on brake actuation is engaged by an annular end portion of the disc brake piston (24) or by a caliper leg (l4). This engagement by the actuator piston gives rise to one or more high-pressure areas (50,52) which could cause the insulation layer to buckle and separate from the backing plate. By the provision of slots or lances (64,66,68 and 70) through the insulator sheet immediately adjacent the high-pressure areas, a discontinuity is provided which prevents such buckling and separation.

Description: The invention relates to disc brake shoe assemblies. The invention is more particularly concerned with disc brake shoe assemblies having an insulator secured to one side of an inboard disc brake shoe and arranged to have the annular end of a disc brake piston, or portions of the caliper housing in the case of an outboard shoe, engaging the insulator to act on the brake shoe for brake actuation, for example as disclosed in US-A-3 885 65l. A difficulty which occurs with disc brake shoe assemblies of this kind is that a discontinuity in deformation of the insulator tends to be caused by reason of the piston or the caliper housing causing high-pressure loading of the insulator, so that the unloaded portions of the insulator may not remain secured to the backing plate. The present invention is concerned with a disc brake shoe assembly having the potential to avoid this difficulty. To this end, a disc brake shoe assembly in accordance with the present invention is characterised by the combination of features specified in claim l. In a disc brake shoe assembly in accordance with the present invention, therefore, the high-pressure loading of the annular surface of the piston which engages the shoe through the insulator is prevented from deforming the insulator by the provision of one or more slots formed through the insulator immediately adjacent to but laterally outwardly from the high-pressure load area of the insulator. Such slot or slots provide a discontinuity in the deformation of the insulator which may result from the high pressure load exerted on the insulator by the piston during brake actuation, and this discontinuity permits the unloaded areas of the insulator to remain firmly secured to the backing plate and therefore to be fully effective in providing the required insulating action. The invention is applicable to outboard shoes engaged by the outboard leg of a sliding caliper housing; however, the detailed description which follows is specifically concerned with the inboard shoe and piston construction. Overall, and within the scope of the claims, the invention is applicable to all shoes and insulators subject to high-pressure loading, and therefore references in certain claims hereof to disc brake actuating members may refer to either an actuating piston or a caliper leg, as shown in the drawing. It is well known to use heat and/or noise insulators between a disc brake piston and the backing plate of a disc brake shoe assembly. Insulators which are formed of layers of steel and adhesive have been found to be particularly effective for noise insulation purposes. Such insulators are formed as sheets which are cut to the same shape as that of the backing plate and are secured to the backing plate by rivets or adhesive, or both. If for any reason an area of the insulator becomes detached from the backing plate, the insulating action of the insulator is lessened. One of the causes of such detachment has been found to be deformation of the insulator at the high-pressure load area where the piston engages the insulator and transmits relatively high forces therethrough during brake actuation. the provision of one or more discontinuity-forming slots through the insulator immediately adjacent the high-pressure area, in conformity with the present invention, the buckling and detachment effects of any such deformation can be substantially eliminated so that the unloaded portions of the insulator may remain secured to the backing plate even though the high-pressure area portions of the insulator are deformed. The slots providing such discontinuity may conform to the shape of the high-pressure area and be positioned immediately adjacent thereto, or may have other shapes which substantially conform to such shape. For example, the disc brake piston is commonly circular, with an annular end engaging the insulator, and therefore with this configuration the slots forming the discontinuity could usefully be correspondingly arcuate. In some constructions the slots may be formed as one or more straight-line slots positioned in a tangent-like fashion but spaced slightly radially from the high-pressure area. When the insulator is secured to the backing plate by means of rivets, the discontinuity slots may terminate before they intersect the insulator openings through which the rivets pass, or in other instances the slots may intersect such openings so that the slots and the rivet openings are formed in the insulator as in effect a common opening. The slots may be formed as cuts or lances, or they may be formed with the removal of a small amount of material. It is desirable to form the slots with enlarged ends, particularly if the slots are formed as cuts or lances, so as to relieve the stress at the ends of the slots and therefore prevent the slots from opening further than desired. The slots may be positioned radially outwardly of the high-pressure area, and slots may also be provided radially inwardly thereof to protect the portion of the insulator which is positioned radially inwardly of the high-pressure area. In the drawing: Figure l is a fragmentary cross-sectional view, with parts broken away, of a disc brake assembly having disc brake shoe assemblies provided with insulators in conformity with the invention; Figure 2 is a fragmentary enlarged view in the direction of arrows 2--2 of Figure l, showing in elevation an inboard portion of the disc brake assembly together with an insulator in conformity with the invention, with parts broken away; Figure 3 is a fragmentary sectional view in the direction of arrows 3--3 of Figure 2, showing the disc brake shoe assembly having the embodiment of the invention illustrated in Figure 2; Figure 4 is a fragmentary view similar to Figure 2 but illustrating a second embodiment of the invention; and Figure 5 is another fragmentary view similar to Figure 2, but illustrating a third embodiment of the invention. With reference now to the drawing, a disc brake assembly l0 includes a caliper l2 having legs l4 and l6 joined by a bridge section l8. The caliper extends over a rotary disc 20 to be braked. The caliper leg l6 has a cylinder 22 formed therein in which a disc brake piston 24 is reciprocably received. The piston 24 is illustrated as being the usual cup-shaped piston having an annular end 26 opening towards the disc 20. An outboard brake shoe assembly 28 is secured to the caliper leg l4 so as to be frictionally engageable with one side of the disc 20. The assembly 28 includes a sheet-like insulator 29 secured to a backing plate 32 and engaged under high-pressure loading by portions of the caliper leg l4 when the brake assembly is actuated. The inboard brake shoe assembly 30 is positioned between the annular end 26 of the piston 24 and the other side of the disc 20 so as to be movable by the piston into friction engagement with the disc 20 when the brake is actuated. Further description of the invention relates to the inboard brake shoe assembly 30, but the inventive concept is likewise applicable to the outboard shoe assembly 28. The inboard brake shoe assembly 30 includes the backing plate 32, with a friction pad 34 being secured to one side 36 of the backing plate. The other side 38 of the backing plate has a sheet-like insulator 40 secured thereto. The insulator 40 may be secured by adhesive, or by the use of rivets such as integral rivets 42, or both. The insulator 40 may be a noise insulator, or a heat insulator, or both: it preferably covers substantially the entire side 38 of the backing plate 32. In the form of a noise insulator, the insulator 40 is preferably constructed of multiple layers, layers 44 and 46 being made of sheets of steel joined together by an adhesive layer 48, which is preferably of a visco-elastic material. Details of the construction of the inboard shoe assembly 30 are better illustrated in Figure 3. The annular end 26 of the piston normally engages the brake shoe assembly 30 at two arcuate high-pressure areas of piston engagement 50 and 52 which are radially opposite each other relative to the piston axis 54. The high-pressure areas 50 and 52 are shown in Figures 2 to 5, from which it will be evident that the total area of the two high-pressure areas 50 and 52, which is the portion of the shoe assembly 30 actually engaged by the annular end 26 of the piston, is relatively small in relation to the total area of the insulator 40. The inboard brake shoe assembly 30, and therefore the insulator 40, is divided by the high-pressure areas 50 and 52 so that there are radially outward portions 56 and 58 of the total area of the insulator 40 which are respectively radially outward, and therefore laterally outward, of the high-pressure areas 50 and 52. The insulator 40 also has a radially inner portion 60 which is positioned radially inwardly of the arcuate high-pressure areas 50 and 52. Thus the high-pressure areas 50 and 52 are clearly limited in surface area relative to the other area portions 56, 58 and 60 of the insulator. When the insulator 40 is secured to the backing plate 32 by means of rivets 42, the insulator is provided with openings 62 through which the rivets 42 extend. These openings are positioned radially outwardly of the high-pressure arcuate areas 50 and 52 so that the rivet heads are also positioned outwardly of the area of contact of the annular end 26 of the piston with the insulator 40. It has been found that over a period of time, the many brake actuations involved, particularly heavy brake actuations, may cause some deformation of the insulator 40 in the immediate vicinity of the high-pressure areas 50 and 52 of piston engagement. Such deformation is illustrated in Figure 3, with the portion of the radially inner portion 60 of the insulator immediately adjacent the high-pressure areas 50 and 52 being illustrated as having been deformed, the deformation being shown in an exaggerated style for clarity and emphasis. It has been found particularly desirable to keep the insulator 40 secured to the side 38 of the backing plate in surface engagement therewith at all times so that the insulator may perform with maximum efficiency. In order to do this, it is therefore necessary to prevent deformation of adjacent areas, and particularly any buckling and consequent separation of the insulator from the backing plate caused by such deformation. Therefore, in conformity with the invention, cuts or slots are formed through the insulator immediately adjacent the high-pressure areas 50 and 52, the cuts or slots providing deformation discontinuity in the insulator and therefore permitting the portions of the insulator beyond the cuts or slots to remain secured to the backing plate because those portions are not subjected to buckling or other deformation caused by high-pressure loading of the piston. As is more particularly shown in Figures 2 and 3, slots 64 and 66 as aforesaid are provided laterally outwardly from the high-pressure area 50 but immediately adjacent that area, and are also positioned on either side of an opening 62 in the insulator through which one of the rivets 42 extends. Similar slots 68 and 70 are provided laterally outwardly of the high-pressure area 52. The slots are formed in the laterally outward portions 56 and 58 of the insulator 40. The slots 64, 66, 68 and 70 are illustrated as having closed ends so that they are spaced from the openings 62 receiving the rivets 42, and they are also spaced inwardly from the outer edges of the insulator 40. The slots are preferably provided with stress-relieved ends, illustrated as being slightly enlarged slot portions having a circular conformation. This is particularly important if the slots are formed as lances or cuts through the insulator rather than being formed by removal of material. The arcuate slots of Figures 2 and 3 are illustrated as being concentrically outwardly of the high-pressure areas 50 and 52, with the slot arc also being based on the axis 54. As can be seen in Figure 3, the high-pressure areas 50 and 52 may cause deformation or buckling of the immediately adjacent portions of the insulator, with separation of the insulator from engagement with the side 38 of the backing plate. By providing the slots as a deformation discontinuity, the outer portions 56 and 58 of the insulator 40 are not adversely affected by the deformation or buckling, and remain tightly secured to the surface 38 of the backing plate 32 Figure 4 shows a slot arrangement in which slots 72 and 74 are also provided in the radially inner portion 60 of the insulator, radially inwardly of the high-pressure areas 50 and 52. These slots, constructed similarly to the outer slots, therefore provide deformation discontinuity for the radially inner portion 60 and minimise buckling and separation of the insulator from the backing plate in the area covered by the inner portion 60. Inner slots corresponding to the slots 72 and 74 may likewise be provided in any other of the embodiments illustrated. Figure 4 also shows a modification of the slots 64, 66, 68 and 70 whereby the inner ends of the slots extend into the openings 62. The arrangement shown in Figure 5 has slots 76, 78, 80 and 82 formed in the insulator which are similar to the slots 64, 66, 68 and 70. However, the slots of Figure 5 are illustrated as being straight-line slots which are positioned radially outwardly of the high-pressure areas 50 and 52 but in a tangent-like spaced arrangement relative to the arc of the outer side of those areas. In all instances, it is preferable that the cuts or slots extend entirely through the insulator 40 from one side thereof engaged by the annular end of the piston to the other side thereof secured to the side 38 of the brake shoe. In some instances only a single slot may be provided in place of the two slots per side illustrated in Figures 2 and 5.

Claims: 1. A disc brake shoe assembly having a backing plate (32), a friction pad (34) secured to one side (36) of the backing plate (32), and an insulator layer (40) secured to the other side (38) of the backing plate (32), the insulator (40) having a high-pressure area (50,52) of disc brake actuating member contact subject to high pressure loading during brake actuation, with a portion of the insulator (40) positioned laterally from the high-pressure area (50,52) and subject to no direct pressure loading from the disc brake actuating member during brake actuation, characterised in that an arrangement is provided for preventing deformation of the insulator (40) resulting from high-pressure loading of the high-pressure area (50,52) by the disc brake actuating member during brake actuation and consequent buckling and detachment of at least a portion of the insulator (40) from the backing plate (32) with resulting decreased insulating capability of the insulator (40), the arrangement comprising at least one slot (64,66,68,70) that is formed through the insulator (40) immediately adjacent to but laterally away from the high-pressure area (50,52) and is effective to provide a discontinuity in the deformation of the insulator (40) resulting from high-pressure loading and permitting the laterally-positioned portion of the insulator (40) to remain secured to the backing plate (32). 2. A disc brake shoe assembly according to claim l, characterised in that the disc brake actuating member comprises a disc brake actuating piston (24). 3. A disc brake shoe assembly according to claim l, characterised in that the assembly is in the form of an outboard disc brake shoe assembly (28) that is subject to the action of a disc brake caliper (l2) constituting the disc brake actuating member. 4. A disc brake shoe assembly according to any one of claims l to 3, characterised in that the laterally-positioned portion of the insulator layer (40) subject to no direct pressure loading from the disc brake actuating member during brake actuation is positioned laterally outwardly from the high-pressure area (50,52), and the said at least one slot (64,66,68,70) is formed through the insulator layer (40) immediately adjacent to but laterally outwardly of the high-pressure area (50,52). 5. A disc brake shoe assembly according to any one of claims l to 4, characterised in that the insulator layer (40) comprises an insulator sheet, the high-pressure area (50,52) of disc brake actuating member contact of the insulator sheet (40) comprises a limited surface area of the insulator sheet (40) conforming to the area of the disc brake actuating member which is in brake-actuating force-transmitting contact with the insulator sheet (40) during brake actuation, the portion of the insulator sheet subject to no direct pressure loading from the disc brake actuating member during brake actuation comprises another area of the insulator sheet (40) not engageable by the disc brake actuating member, the said another area adjoins the said limited surface area and is laterally displaced therefrom, and the said at least one slot (64,66,68,70) is formed through the insulator sheet (40) in the said another area at a location adjacent to the said limited surface area, and is effective to prevent deformation of the said another area of the insulator sheet (40) by high pressure area loading through the disc brake actuating member and thereby prevent detachment of the said another area of the insulator sheet (40) from the backing plate (32). 6. A disc brake shoe assembly according to claim l, in a disc brake assembly including a brake-actuating piston (24) having an annular end, and a rotary disc (20) that is selectively frictionally engageable by the friction pad (34) of the disc brake shoe assembly (28,30) for braking the disc (20), characterised in that the insulator layer (40) comprises an insulator sheet substantially covering the said other side (38) of the backing plate (32), the annular end of the piston (24) engages the insulator sheet (40) throughout the high-pressure area (50,52) of disc brake actuating member contact, the said area conforming to the annular end of the piston (24) where the annular end of the piston (24) engages the insulator sheet (40) so that the high-pressure area (50,52) includes at least one circumferentially extending arcuate section with a first portion of the insulator sheet (40) radially within the said at least one circumferentially extending arcuate section and at least a second portion of the insulator sheet (40) radially outwardly of the said at least one circumferentially extending arcuate section, and the said at least one slot (64,66,68,70) is formed in the said at least a second portion of the insulator sheet (40) and extends through the insulator sheet (40) from the side (38) thereof engaged by the annular end of the piston (24) to the side (36) thereof secured to the brake backing plate (32), the said at least one slot (64,66,68,70) being disposed adjacent to the said at least one circumferentially extending arcuate section of the high-pressure area (50,52) and providing a deformation discontinuity as aforesaid between the high-pressure area (50,52) and substantially the whole of the said at least a second portion of the insulator sheet (40) laterally outwardly from the high-pressure area (50,52). 7. A disc brake shoe assembly according to claim 6, characterised in that the said at least one slot (64,66,68,70) is arcuate. 8. A disc brake shoe assembly according to claim 6 or 7, characterised in that the said at least one slot (64,66,68,70) is closed at the ends thereof. 9. A disc brake shoe assembly according to claim 6, characterised in that the said at least one slot (64,66,68,70) comprises a plurality of slot sections at least one of which is closed at the ends thereof. l0. A disc brake shoe assembly according to claim 6, characterised in that the said at least one slot comprises one or more straight-line slots (76,78,80,82). 11. A disc brake shoe assembly according to claim 6, characterised in that the high-pressure area (50,52) is composed of two arcuate sections, the second portion of the insulator sheet (40) is composed of two oppositely positioned sections of insulator sheet (40), and the said at least one slot (64,66,68,70) comprises one or more slots in each of the two oppositely positioned sections of the insulator sheet (40). 12. A disc brake shoe assembly according to any one of claims l to ll, characterised in that the insulator (40) is a noise insulator made of multiple layers including a first layer (44) of steel bonded to a second layer of steel (46) by means of a visco-elastic adhesive (48).

Inventors: MYERS, WILLIAM KEITH
Applicants: GENERAL MOTORS CORPORATION
Application year: 1986
Main classification: F16D65
IPC codes: F16D65, F16D55