A RETRACTION SEAL FOR A DISC BRAKE

Abstract: A retraction seal (32) for a disc brake is disposed within a caliper groove (34). The retraction seal (32) cooperates with a forward wall (42) of the groove (34) to define a space (72) which substantially prevents the retraction seal (32) from engaging a radially inner edge (80) of the forward wall (42) during braking, thereby preventing nibbling of the retraction seal (32).

Description: This invention relates to a retraction seal for a disc brake wherein a caliper defines a bore for receiving a piston and the bore includes a groove for receiving the retraction seal in an installed condition so that the latter sealingly engages the caliper and the piston. In United States Patent 3,915,461 a retraction seal for a disc brake comprises a square resilient member which is installed within a caliper groove. During braking the retraction seal deflects axially to engage a forward wall of the groove. Consequently, with repeated braking application, it is possible for the retraction seal to be damaged by "nibbling" at a radially inner forward edge, thereby adversely affecting the retraction capabilities of the retraction seal. In DE―A―1 264 889 it has already been proposed a disc brake actuator cylinder and piston arrangement wherein a seal of resilient deformable material and of substantially rectangular cross-section when unstressed is disposed in a groove of trapezoidal cross-section in the cylinder wall so as to take the shape of the groove and thereby to be stressed radially into sealing contact with the piston wall, said groove having substantially parallel side walls and a base inclined thereto. Further, in DE―A―2 326 047 according to the preamble of Claim 1 a similar arrangement of a retraction seal for a disc brake is described, comprising a groove situated in the caliper bore for receiving the piston, which groove includes a forward surface having a first portion extending substantially normal to the direction of movement for the piston during braking and a second portion extending substantially from an inner diameter of the groove to define a first angle relative to the normal direction, and which retraction seal includes a forward wall facing said forward surface, and including an inner section opposite said second portion. In the above mentioned prior art documents, during braking, the fluid pressure generated in a disc brake pressure chamber acts against the retraction seal to bias the latter outwardly into tight engagement with the piston and the edge of the groove at the radially inner and axially outer corner of the groove. The retraction seal tends to creep into the clearance between the wall of caliper bore and the piston and is pinched therebetween. Repeated braking applications cause the radially inner and axially forward portion of the retraction seal to wear or "nibble". It is believed that a uniform gripping engagement between the radially inner surface of the retraction seal and the piston is necessary in order to consistently retract or withdraw the piston into the caliper bore upon termination of braking. Several retraction seals used today adequately retract the piston initially; however, after about a year of vehicle operation the retraction seal is worn or nibbled to such a degree that the engagement between the retraction seal and the piston is no longer uniform. Consequently, retraction is inadequate and the piston opposes separation between an inner friction pad and a rotor or disc upon termination of braking to generate disc brake drag for the vehicle. The retraction seal of the present invention is characterized by the features of Claim 1. The above mentioned various functional and angular relationship between the edges of the groove are necessary to define a seal which functions to provide a sufficient return force on the piston, while at the same time provides a space in which fully accommodates the displaced portion of the seal with some portion of the space remaining. As discussed in the specification, maintenance of this space is critical to the invention, since prior art seals suffered from the problem of "nibbling, which, as the inventor discovered, appears to be caused by displacement of the seal into the interface between the piston and the cylinder wall during braking. The problem is avoided by providing the empty space. It is an advantage of the present invention that the portion of the retraction seal in engagement with the piston remains spaced from the wall of the groove to substantially prevent "nibbing" of the radially inner edge at a foward wall. Furthermore, the retraction seal of the invention provides the advantage of reversible installation. The invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a side cross-sectional view of a disc brake including a retraction seal constructed in accordance with the present invention; Figure 2 is an enlarged view of the circumscribed portion of Figure 1 showing the retraction seal before it is installed; Figure 3 is a view similar to Figure 2 showing the retraction seal disposed within a groove before the piston is disposed within a caliper bore; Figure 4 is an enlarged view of Figure 1; and Figure 5 is a view similar to Figure 4 showing the retraction seal during a brake application. A disc brake 10 includes a caliper 12 movably mounted relative to a disc 14 via suitable means, such as a pin assembly 16. The caliper cooperates with a pair of friction pads 18 and 20 during braking to engage the friction pads 18 and 20 with the disc 14 to retard rotation of the latter. The caliper 12 defines a bore 22 leading from an opening 24 to an end wall 26. A piston 28 is received within the bore 22 and extends from the opening 24 to oppose the friction pad 18. The piston cooperates with the caliper end wall 26 to define a pressure chamber 30 which is capable of receiving fluid pressure from a fluid pressure generator such as a master cylinder (not shown) during a brake application. In order to seal the pressure chamber from the environment and also to provide retraction for the piston 28 upon termination of braking, a retraction seal 32 is disposed within a groove 34 formed on the wall of bore 22 near the opening 24. A dust boot 36 extends between the end of the piston 28 and the wall of the bore 22 to prevent particles from entering the sliding interface defined between the piston 28 and the wall of the bore 28. Turning to Figure 2, the groove 34 includes a bottom surface 40 connecting a forward surface 42 and a rear surface 44. The forward surface includes a tapered corner 46, a first portion 48 extending normal to the direction of movement for the piston 28, and a second portion 50 extending from the bore 22 to an edge 52 formed between the first and second portions. The second portion 50 defines an angle A relative to the wall of bore 22. The rear surface 44 includes tapered corner 54, a tapered first portion 56 and a tapered edge 58 adjoining the wall of bore 22. The forward surface 42 cooperates with the rear surface 44 to define an axial dimension for the groove 34 which increases from a radially outer position to a radially inner position. In Figure 2, the retraction seal 32 is shown overlaying the groove 34 in its uninstalled or free state. The retraction seal 32 defines an outer surface 60 having a radial dimension larger than the radial dimension for the groove 34. An inner surface 62 on the retraction seal 32 defines a radial dimension substantially equal to the radius of the piston 28. The retraction seal 32 includes a forward wall 64 comprising an outer section 66 and an inner section 68. The outer section extends in a normal direction relative to piston movement and the inner section 68 defines an angle B relative to the wall of bore 22. The retraction seal 32 includes a rear wall 70 which is identical to the forward wall 64 so that the retraction seal is reversible for simple installation into the groove 34. The inner section 68 cooperates with the second portion 50 to define a triangular-shaped spacing 72 with angle A being substantially equal to angle B. The rear wall 70 cooperates with the rear surface 44 to define a chamber 73. When the retraction seal is installed in the groove 34, the retraction seal is deformed such that its inner surface 62 defines an interference fit with the piston 28. In Figure 3, it is seen that the edge 74 between the inner section 68 and outer section 66 is substantially aligned with the edge 52. The rear wall 70 is rotated counter-clockwise in response to the taper of the bottom surface 40. When the piston 28 is inserted into the bore 22, the retraction seal 32 is further deformed to be retained within the groove 34. Although the cross-sectional area or volume of spacing 72 is reduced, the inner section 68 retains its cooperation with the second portion 50 in order to define the spacing 72. In particular, the inner section 68 defines the angle C which is slightly greater than the angle B. The angle C opens toward the second portion 50 and the angle A opens toward the inner section 68. The retraction seal 32 defines an axial dimension which substantially decreases from a radially outer position to a radially inner position, so that the smallest axial dimension for the installed retraction seal is located at the engagement with the piston 28. During braking, fluid pressure is communicated to the pressure chamber 30 to bias the piston 28 to the right. In Figure 5 the fluid pressure within chamber 30 is communicated to the chamber 73 by means of a radial spacing between the bore 22 and the piston 28. Fluid pressure within the chamber 73 acts against the rear wall 70 to deform the retraction seal 32 such that the radially inner portion adjacent the inner surface 62 is deflected to the right to move with the piston 28. The dimensions of the spacing 72 before fluid pressure is communicated to the pressure chamber 30, see Figure 4, enable the retraction seal 32 to be deformed during braking in the direction of the forward wall 64 but remain spaced therefrom at the radially inner edge 80. The retraction seal is biased into engagement with a portion of the second portion 50 and the angle thereof relative to the direction of piston movement urges the deformed retraction seal into tight engagement with the piston 28. With the retraction seal 32 remaining spaced from the radially inner edge 80 of forward wall 64, the retraction seal 32 is not subjected to nibbling or wear at the edge 80. Therefore, the inner surface 62 of the retraction seal remains substantially in uniform engagement with the piston 28. Upon termination of braking, the fluid pressure within chambers 30 and 73 is relieved so that the deformed retraction seal will return to its compressed configuration as shown in Figure 4 in response to the inherent resiliency thereof. As the retraction seal is returning to its compressed state, the inner surface 62 is moving to the left so that the engagement between inner surface 62 and piston 28 causes the piston 28 to move to the left to the position shown in Figure 4.

Claims: 1. A retraction seal for a disc brake wherein a caliper (12) defines a bore (24) for receiving a piston (28), the bore includes a groove (34) for receiving the retraction seal (32) in an installed condition so that the latter sealingly engages the caliper and the piston, said retraction seal defining an outer diameter (60) in its free state which is greater than an outer diameter (40) defined by the groove, said retraction seal defining an inner diameter (62) in its free state which is substantially equal to an outer diameter defined by the piston (28), the groove including a forward surface (42) having a first portion (48) extending substantially normal to the direction of movement for the piston during braking and a second substantially planar portion (50) extendind substantially from an inner diameter of the groove to define a first angle (A) relative to the normal direction, said retraction seal including a rear wall (70) and a forward wall (64) facing said forward surface, said forward wall including an inner section (68) opposite said second portion (50) the bore (24) receiving the piston (28) to deform said retraction seal into the groove, said inner section (68) and said second portion (50) cooperate to define a space (72) which permits deformation of said retraction seal (32) into said space (72) during braking in order to generate a resilient restoring force biasing the piston (28) into the bore (24) upon termination of braking, charcterized in that the inner section (68) of the forward wall of the seal is substantially planar and defines a second angle (B) relative to the normal direction, in that said first angle (A) is substantially equal to said second angle (B), in that the volume of said space (72) is sufficiently larger than the portion of said seal (32) displaced into the space (72) during braking so that a portion of said space (72) remains unfilled by said seal (32) even when the piston (28) is fully displaced, in that said retraction seal includes a rear wall (70) having a substantially planar inner section defining an angle of the same value as angle (B) relative to the normal direction such that said inner sections of said forward and rear walls are identical to permit reversible installation of said retraction seal into the groove, the retraction seal defining an axial dimension which substantially decreases from a radially outer position to a radially inner position. 2. The retraction seal of claim 1 in which said second portion (50) and said inner section (68) extend radially inwardly from edges (52, 74) which substantially adjoin each other when said retraction seal is disposed in the groove and engaging the piston, so that said space (72) is substantially triangular shaped in a plane coinciding with the axis for the piston. 3. The retraction seal of claim 2 in which said retraction seal (32) defines a radially outer axial dimension substantially equal to a radially outer axial dimension for the groove, the groove defining a substantially gradually increasing axial dimension over the radial dimension for the groove.

Inventors: RITSEMA, IRVING RAY
Applicants: ALLIED-SIGNAL INC. (A DELAWARE CORPORATION)
Application year: 1983
Main classification: F16D65
IPC codes: F16D55, F16D65, F16J15