FRICTION PAD FOR USE IN DISC BRAKE

Abstract: A friction pad for use in a disc brake including a backing plate (8) and a lining member (22) secured to the front surface of the backing plate is provided. The backing plate includes a cavity (21) formed in the front surface of the backing plate for receiving therein a portion of the lining member, and a protrusion (9) on the reverse surface of the backing plate located at a position corresponding to the cavity and projecting outwardly from the reverse surface of the backing plate. The cavity and protrusion are both formed by press working. The cavity (21) includes a first recess (21 a ) formed in the front surface of the backing plate in a depressed manner and having a side wall (23) and a bottom wall (24), and a second recess (21 b ) formed in the bottom wall of a first recess and having a side wall (25). The portion (E) interconnecting the bottom wall of the first recess and the side wall of the second recess includes a convex surface (26) protruding into the inside of the cavity.

Description: This invention relates to a friction pad for use in a disc brake in which a lining member is secured to a surface of a backing plate. A friction pad for a disc brake is disclosed in, for example, Japanese Utility Model Public Disclosure [KOKAI] No. 63-104738. The friction pad disclosed in this Utility Model includes a lining member secured to a surface of a backing plate by means of suitable means, such as an adhesive. A cavity is formed in the surface of the backing plate onto which the lining member is secured. The lining member is designed so that a portion of the lining member may be embedded in the cavity of the backing plate. The cavity may be formed during a press working of the backing plate. The opposite surface of the backing plate is provided with a protrusion at a position corresponding to the cavity, the protrusion being protruded by extruding a portion of the material of the backing plate. According to this prior art friction pad, the inner peripheral wall of the cavity tapers in one direction, whereas the protrusion is columnar, i.e., the protrusion has a cylindrical outer periphery, so as to be fitted within a through hole in a brake caliper of the disc brake. A torque applied to the lining member from a brake disc upon braking is transmitted to the backing plate by virtue of a resistance of a fixing means such as an adhesive disposed between the backing plate and the lining member and a shearing resistance of the portion of the lining member which is embedded in the cavity. The torque is further transmitted from the backing plate through the protrusion to the caliper, thus the caliper finally receives the torque. In the above Utility Model, a cavity and protrusion each are formed at three positions, two of the three protrusions being fitted within respective holes of the caliper, the remaining one serving to secure a retainer spring at a position which restricts free movement of the friction pad relative to the caliper. It will be appreciated that a larger and deeper cavity is advantageous in terms of obtaining a high shearing resistance of the lining member. With the construction of the above prior art friction pad, however, making the cavity A larger and deeper would cause the wall thickness t of the base portion of the protrusion B to be thinner as shown in Fig. 1, thus resulting in a backing plate which tends to be easily broken during a press working and a considerable reduction in the strength of the backing plate. Wall thickness of the base portion is especially reduced at the base portion of the protrusion which is fitted within the through hole of the caliper since a relief groove is formed around the base portion of the protrusion for the purpose of ensuring that the protrusion is fitted in the through hole of the caliper. If it is intended to obtain a sufficient wall thickness t of the base portion of the protrusion, a height h of the protrusion B becomes smaller as shown in Fig. 2, thus disadvantageously reducing the effective area of the protrusion for transmitting torque to the caliper. The invention is aimed at advantageously eliminating the above deficiencies experienced in the prior art. Accordingly, the object of the invention is to increase the strength of the backing plate by maintaining the wall thickness of the base portion of the protrusion B of the backing plate by a sufficient amount, while at the same time achieving high shearing resistance of the lining member by forming a larger and deeper cavity. In order to achieve the above objects, the present invention provides a friction pad for use in a disc brake including a backing plate and a lining member secured to the front surface of the backing plate, the backing plate including a cavity formed in the front surface of the backing plate for receiving therein a portion of the lining member, and a protrusion on the back surface of the backing plate located at a position corresponding to the cavity and projecting outwardly from the back surface of the backing plate, the cavity and protrusion being formed by press working, the cavity including a first recess formed in the front surface of the backing plate in a depressed manner and having a side wall and a bottom wall, and a second recess formed in the bottom wall of the first recess and having a side wall, the portion interconnecting the bottom wall of the first recess and the side wall of the second recess including a convex surface protruding into the inside of the cavity. In one embodiment of the invention, the side wall of the first recess and the side wall of the second recess both are configured in a tapered manner. According to another embodiment of the invention, the side wall of the first recess taper with a first angle and the side wall of the second recess taper with a second angle, the first angle being larger than the second angle. According to further embodiment of the invention, the depth of the first recess is smaller than the thickness of the backing plate, while the lowermost portion of the side wall of the first recess is located outwardly of the base portion of the protrusion adjacent to the back surface of the backing plate. According to still a further embodiment of the invention, the uppermost portion of the side wall of the second recess adjacent to the convex surface is located inward of the base portion of the protrusion. Figs. 1 and 2 are sectional views of a prior art friction pad illustrating relationship between a height of a protrusion of the friction pad and a wall thickness of the base portion of the protrusion; Fig. 3 is a sectional view of a main part of a friction pad for a disc brake according to one embodiment of the invention; Fig. 4 is a front view fully illustrating the friction pad of Fig. 3; Fig. 5 is a top plan view of Fig. 4; Fig. 6 is a cross-sectional view along line 6-6 in Fig. 4; Fig. 7 is a part-sectional view of a disc brake to which a friction pad according to one embodiment of the invention is applied; and Fig. 8 is a front view of Fig. 7 with the omission of one pawl thereof. A friction pad for use in a disc brake according to one embodiment of the invention will be explained herein-below with reference to the attached Figs. 3 through 8. First, a construction of a disc brake to which the friction pad of the invention is applied will be explained with reference to Figs. 7 and 8. The disc brake includes a brake caliper 2 straddling a brake disc 1. The caliper 2 is provided with a cylinder 4 housing therein a piston for driving an inner friction pad 3 and two claw portions 6 supporting an outer friction pad 5 at the backside thereof. The cylinder 4 and the two claw portions 6 each are oppositely disposed at either side of the brake disc 1. The inner friction pad 3 is supported by a plate-like carrier 7 with its tabs 3a formed on the opposite side edges thereof being fitted within respective grooves 7a formed in opposing inner side surfaces of the carrier 7. The outer friction pad 5 includes two protrusions 9 integrally formed on the reverse side surface of a backing plate 8 and is supported by the caliper 2 with the protrusions 9 being received in a space 10 defined between the two claw portions 6 of the caliper 2. The outer surface 11 of each of the protrusions 9 is in contact with a torque receiving surface 12 at the inner surface of the corresponding claw portion 6, while a retainer spring 13 for resiliently engaging with the back surface of each of the claw portions 6 is fixedly disposed between the protrusions 9. It should be noted that the caliper 2 is arranged so as to be displaceable along a bolt 14 and a pin 15 secured to the carrier 7. Returning now to Figs. 3 through 6, each of the protrusions 9 is formed on the reverse side surface of the backing plate 8 simultaneously when a corresponding cavity 21 is formed in the front surface of the backing plate 8 by means of press working. When each cavity 21 is formed, a portion of the material of the backing plate 8 is extruded outwardly from the reverse surface of the backing plate 8 to form the corresponding protrusion 9 having an outer wall surface substantially vertical to the reverse surface of the backing plate 8. The cavity 21 includes a first recess of a larger diameter or larger area and a second recess of a smaller diameter or smaller area formed in the bottom of the first recess. A wall surface of each of the recesses is configured so as to be tapered. Specifically, as shown in Fig. 3, a first recess 21a is formed in the front surface 8a of the backing plate 8 onto which a lining member 22 is secured, the first recess 21a being of a larger area and having a depth less than the wall thickness of the backing plate 8. Side wall surface 23 of the first recess 21a tapers inwardly and downwardly as shown in the figure. A second recess 21b of a smaller area is formed in the bottom of the first recess 21a, the side wall surface 25 of the second recess also tapering in the same manner as that of the side wall surface 23 of the first recess 21a. A convex surface 26 is formed along the portion connecting the bottom 24 of the first recess 21a and the side wall surface 25 of the second recess 21b, the convex surface protruding into the interior of the cavity 21. The lowermost portion of the side wall surface 23 as indicated by D in Fig. 3, i.e., the intersection between the side wall surface 23 and the bottom wall 24, is located radially outward of the outer circumferential wall of a protrusion 9 with respect to the longitudinal axis of a protrusion 9. The uppermost portion of the side wall surface 25 as indicated by E in Fig. 3, i.e., the portion interconnecting the side wall surface 25 and the convex surface 26, is located radially inward of the outer circumferential wall of a protrusion 9 with respect to the longitudinal axis of a protrusion 9. In the illustrated embodiment, the side wall surface 23 tapers with an angle greater than that by which the side wall surface 25 tapers so as to define a relatively large opening area. A protrusion 9 is formed with a groove 27 which extends around the periphery of the base portion of a protrusion 9 and which serves to ensure contact between a protrusion 9 and the torque receiving surface 12 of the claw portion 6 of the caliper 2. It should be noted that the contour of each of the protrusions 9 and the cavity 21 is not circular but is substantially polygonal as shown in Fig. 4 and that each associated protrusion 9 and cavity 21 are similar in shape. As illustrated in Figs. 4 and 8, the backing plate 8 is provided with mould bores 28 extending therethrough at a position outward of each of the protrusions 9. A portion of the lining member 22 extends into each mould bore 28 so as to be fitted therein. According to the friction pad 5 having the above construction, the cavity 21 can be formed to have a relatively large area and depth, while providing the base portion of a protrusion 9 with a wall thickness of a sufficient amount. Consequently, the amount of the portion of the lining member 22 to be filled within the cavity 21 is increased, whereby a shearing resistance exerted by that portion can be advantageously increased, while providing the protrusions 9 with a sufficient height so as to perform reliable transmission of torque, thus greatly improving braking characteristics of the disc brake. The above construction also contributes to the prevention of a reduction in the strength of the backing plate 8. It should also be noted that, according to the embodiment of the invention, the backing plate 8 is formed with the mould bores 28 which allow a portion of the lining member 22 to be fitted therein, thus further increasing the shearing resistance of the lining member 22. It will be appreciated, however, that the mould bores 28 may be eliminated, since a considerable amount of the lining member 22 is filled in the cavity 21 and therefore a sufficient shearing resistance could be obtained thereby. In the above embodiment, the first recess and the second recess are configured so that the side wall surfaces thereof taper in different angles. It should be noted, however, that they can be configured so that the side wall surfaces thereof will taper at an identical angle.

Claims: A friction pad (3, 5) for use in a disc brake including a backing plate (8) and a lining member (22) secured to the front surface (8a) of the backing plate (8), said backing plate (8) including a cavity (21) formed in the front surface (8a) of the backing plate (8) for receiving therein a portion of said lining member (22), and a protrusion (9) on the reverse surface of said backing plate (8) located at a position corresponding to said cavity (21) and projecting outwardly from the reverse surface of said backing plate (8), said cavity (21) and said protrusion (9) being formed by press working; said cavity (21) including a first recess (21a) formed in the front surface (8a) of said backing plate (8) in a depressed manner and having a side wall (23) and a bottom wall (24), and a second recess (21b) formed in said bottom wall (24) of said first recess (21a) and having a side wall (25); and a portion (26) interconnecting said bottom wall (24) of said first recess (21a) and said side wall (25) of said second recess (21b) including a convex surface protruding into the inside of said cavity (21). The friction pad according to claim 1, characterised in that said side wall (23) of said first recess (21a) and said side wall (25) of said second recess (21b) both are configured in a tapered manner. The friction pad according to claim 2, characterised in that said side wall (23) of said first recess (21a) taper with a first angle and said side wall (25) of said second recess (21b) taper with a second angle, said first angle being larger than said second angle. The friction pad according to claim 1, characterised in that the depth of said first recess (21a) is smaller than the thickness of said backing plate (8), and wherein the lowermost portion of side side wall (23) of said first recess (21a) is located outwardly of the base portion of said protrusion (9) adjacent to said reverse surface of said backing plate (8). The friction pad according to claim 4, characterised in that the uppermost portion of said side wall (25) of said second recess (21b) adjacent to said convex surface (26) is located inward of the base portion of said protrusion (9). The friction pad according to claim 1, characterised in that said protrusion (9) includes a base portion adjacent to said reverse surface of said backing plate (8), and wherein said reverse surface is formed with a groove (27) arranged in an encircling relationship with said base portion. The friction pad according to claim 1, characterised in that said friction pad (5) is adapted for use in a disc brake including a carrier (7) attached to a non-rotational part of a vehicle, and a caliper (2) slidably supported by said carrier (7), wherein said caliper (2) includes claw portion (6) arranged in abutment with said reverse surface of said backing plate (8) for supporting said friction pad (5), and wherein said protrusion (9) of said backing plate (8) of said friction pad (5) is arranged in abutment with said claw portion (6) so as to transmit a braking torque exerted to said friction pad (3, 5) upon actuation of the disc brake to said claw portion (6) of said caliper (2). The friction pad according to claim 1, characterised in that the protrusion (9) has a non-circular cross-section and includes an arcuate side surface, and said cavity (21) has a cross-section of a shape similar to that of said protrusion (9).

Inventors: AKIYAMA, ATSUSHI, FUKUDA, HISAO, KOBAYASHI, KINZO
Applicants: TOKICO LTD.
Application year: 1990
Main classification: F16D65
IPC codes: F16D69, A47G9, F16D65