CA2427951A1

CA2427951A1 - Friction plate return mechanism

Info

Publication number: CA2427951A1
Application number: CA002427951A
Authority: CA
Inventors: Jean Pierre Crevier; Benoit Raymond
Original assignee: NEWTECH BRAKE Corp Inc
Current assignee: Individual
Priority date: 1999-11-15
Filing date: 2000-11-15
Publication date: 2001-05-25

Abstract

A brake shoe return mechanism (10, 110) is provided for disengaging a brake shoe (26a, 26b) from frictional contact with a rotor disk in a brake assembly for vehicles. The mechanism includes a pin (36, 136) slidably received in a casing (34, 134) that is mounted to the vehicle. The pin (36, 136) is biased by a spring (44,144) to a rear position and is frictionally connected using a retaining washer (58, 158) to the brake shoe (26) to move the brake shoe (26) rearwardly away from the rotor disk (18) when a braking force is removed from the brake shoe (26). Another retaining washer (56,156) is received within the casing and axially movable in a predetermined distance. This retaining washer (56, 156) is also frictionally connected to the pin (36, 136) for permitting the pin (36, 136) freely moving forwardly with the brake shoe (26) during a braking action, but stopping the pin (36,136) in a rearward movement together with the brake shoe (26) except moving together with the retaining washer (56, 156) over the predetermined distance.

Description

FRICTION PLATE RETURN MECHANISM
Technical Field The present invention relates to a disk brake for vehicles and more particularly to improvements in friction plate return mechanisms for s disengaging brake shoe from frictional contact with a rotor disk in the disk brake assembly.
Background Art The friction plate return mechanism of the present invention is used in disk brakes for vehicles of the type described in the applicant's PCT
to patent application PCT/CA97/01014, entitled IMPROVED DISK BRAKE
ASSEMBLY and published as W098/29671 in the inventor's name, Yvon Rancourt, on July 9, 1998.
The disk brake assembly for a vehicle as described in the appli-cant's PCT publication W098/29671 generally includes a housing mounted to 15 the vehicle, an annular rotor disk within the housing, and means mounting the disk to the wheel. The disk has at least a first radial planar annular friction surface and the housing includes a first annular brake shoe provided adjacent the first friction surface of the disk. The brake shoe is axially movable towards and away from the first friction surface and is restrained from rotating with the 2 o disk. An annular fluid expandable bladder extends between the first annular brake shoe and a radial wall of the housing, so that upon expansion of the bladder the first brake shoe moves axially to frictionally engage the first fric-tion surface of the disk. There are provided means for disengaging the first brake shoe from frictional contact with the first friction surface of the rotor disk, 2s which is a rolling seal provided between an axially generated surface of the brake shoe and an axially generated cylindrical surface of the first radial wall of the housing such that the rolling seal can store energy when force is being applied on the brake shoe to frictionally engage the frictional surface of the rotor disk, and the stored energy is sufficient to retract the brake shoe from the first friction surface of the rotor disk when the applied force is removed from the brake shoe.
The disk brake works well. Improvements regarding the disen-gaging means, however, are desired because adjustment has to be done to compensate for the increasing of the travel distance of the brake shoe during a break action. The increasing of the travel distance is a result of the wearing of the friction surface of the disk. When the travel distance of the brake shoe increases, the rolling seal is more resiliently deformed to store more energy so that more braking force is needed to overcome the resistance from the 1 o deformed rolling seal.
Disclosure of the Invention It is an aim of the present invention to provide a friction plate return mechanism for the disk brake of the type described above, which over-comes the shortcomings in the prior art.
It is another aim of the present invention to provide a friction plate return mechanism for a disk brake which is enabled to be self-adjusted to maintain a substantially constant travel distance of the brake shoe regard-less of the wearing of the friction surface of the rotor disk.
It is a further aim of the present invention to provide a brake 2 o shoe return mechanism which can be self-adjusted to maintain a substantially constant maximum amount of energy which may be stored by the mechanism to retract the brake shoe so that a braking force applied to the brake shoe is kept constant regardless of the wearing of the friction surface of the rotor disk.
In accordance with one aspect of the invention, there is a brake shoe return apparatus for a disk brake assembly wherein a rotor disk rotates in a housing about an axis and a brake shoe moves towards the rotor disk for frictional engagement therewith, the brake shoe return comprising: a link member slidable relative to the housing and in a to and fro direction parallel to 3 o the axis of rotation of the rotor disk and associatd with the brake shoe;
resil-ient means associated with the link member for urging the link member away from the rotor disk; a connecting member to link the brake shoe with the link member and frictionally connected with the moving member to move the link member together with the brake shoe in a forward movement towards the rotor disk during a braking action when a forward pressure is applied to the s brake shoe until the resilient means overcomes the forward pressure and returns the link member and the brake shoe to a position where the brake shoe is disengaged from the rotor disk.
In another aspect of the invention there is a brake shoe return apparatus for a disk brake assembly wherein a rotor disk rotates in a housing to about an axis and a brake shoe moves towards the rotor disk for frictional engagement therewith, the brake shoe return comprising: a link member slidable relative to the housing and in a to and fro direction parallel to the axis of rotation of the rotor disk and associatd with the brake shoe; resilient means associated with the link member for urging the link member away from the 15 rotor disk; a friction device associated with the housing and slidable relative to the housing in the forward and rearward direction within a predetermined travel; the friction device being frictionally connected to the link member, the link member and the friction device permitting the link member to move together with the brake shoe in the forward direction during a brake action 2 o with little frictional resistance from the friction device when the friction device is restrained, while a maximum friction force in the opposite direction between the friction device and the link member prevents the link member from moving in the rearward direction relative to the friction device so that the brake shoe and the link member can only move away from the rotor disk in the rearward 2s direction together with the friction device within the predetermined travel when a brake force is removed from the brake shoe.
In a specific embodiment of the present invention, a casing is provided, and both the link member and the friction device are made from a metal retaining washer. Each retaining washer includes a flat ring and a 3 o plurality of finger members extending from the flat ring inwardly and forwardly.
The finger members are circumferentially positioned and the ends of the finger members define an aperture slightly smaller than the exterior of a pin, which acts as the moving member. The ends of the finger members are enabled to be resiliently displaced to permit the pin to be inserted from a rear side through the retaining washer, and the finger members grip the exterior of the pin to prevent the pin from moving in a rearward direction relative to the retaining washer. However, the pin is enabled to be moved in rearward direc tion relative to the retaining washer or the retaining washer is enabled to be moved in the forward direction relative to the pin when the force to move the pin or the retaining washer is greater than the friction force between the finger 1o members and the exterior of the pin.
The other retaining washer acting as the friction device surrounds the exterior of the pin and is contained within a chamber of the housing. The periphery of the chamber is defined by a circumferentially extending groove, which receives the flat ring of the retaining washer. The 15 retaining washer is axially movable within the chamber and the axial move-ment is limited by the width of the groove. The retaining washer is moved together with the pin in the forward direction in a brake action until the flat ring abuts a front side of the groove, and permits the pin to slide through the retaining washer to continue the forward movement. When the braking force 2 o is removed and the pin moves in the rearward direction under the spring force, the retaining washer is moved together with the pin in the rearward direction until the flat ring abuts the rear side of the groove to stop the rear-ward movement of the pin. The spring force is never greater than the friction force between the finger members and the exterior of the pin and therefore, 2 s the finger members are able to grip the pin firmly and to stop the rearward movement.
The friction plate return mechanism according to the present invention presents an advantageous self-adjustment function to compensate for brake wearing so that both the traveling distance of the brake shoe and the 3 o braking force applied on the brake shoe are maintained constant during the service life of the disk brake assembly.

Brief Descripton of the Drawings Having thus described the nature of the invention, the invention will now be described in detail, having reference to the accompanying draw-ings in which:
s Figure 1 is a partial sectional view of a disk brake incorporating a preferred embodiment of the invention;
Figure 2 is an exploded perspective view of the embodiment in Figure 1;
Figure 3 is a front view of the retaining washer used in the 1 o embodiment in Figure 1;
Figure 4 is a cross-sectional view taken along line 4-4 in Figure 3; and Figure 5 is a perspective view, partly in cross- section of another embodiment of the present invention.
15 Mode for Carrying Out the Invention Referring now to the drawings, and particularly to Figure 1, a friction plate return mechanism 10 is installed to a disk brake 14 for an auto-mobile. The disk brake 14 is not a part of the invention and many different types of disk brakes may incorporate the embodiment of the invention.
2 o Therefore, the disk brake is described merely with its basic structure to illus-trate the braking operation of the disk brake using the friction plate return mechanism 10. The disk brake 14 generally includes a housing 16 mounted to the automobile, an annular rotor disk 18 within the housing, and mounting member 20 for mounting the disk 18 to the wheel 22 of the automobile. The 2 s disk 18 has at least a radial planar annular frictional surface 24 and the hous-ing includes an annular brake shoe 26 provided adjacent the friction surface 18 of the disk. The brake shoe 26 has a backing plate 26a and a brake shoe lining 26b. The brake shoe 26 is movable axially towards and away from the frictional surface 24 but is restrained from rotating with the disk 18. The 3 o housing 16 includes an annular radial wall 28 parallel to the brake shoe 26, and an annular fluid expandable bladder 30 with a fitting member 32 extend-ing between the annular brake shoe 26 and the annular radial wall 28. When the brake fluid is pumped into the inside of the bladder 30, the expansion of the bladder 30 moves the brake shoe 26 axially to frictionally engage the fric-tional surface 24 of the disk 18. The friction plate return mechanism 10 is used to move the brake shoe 26 for disengaging from frictional contact with the frictional surface 24 of the rotor disk 18 upon release of the brake fluid from the bladder 30.
The friction plate return mechanism 10 includes a cylindrical 1 o casing 34 and a pin 36 which are more clearly illustrated in Figure 2. The cylindrical casing 34 is closed at the rear end 38 and has a central opening at the front end 42. The pin 36 is slidably received within the casing 34 and a front portion of the pin 36 protrudes forwardly from the central opening 40. A
spiral spring 44 is contained within a bigger chamber 46, and positioned between a front wall 48 of the chamber 46 and an enlarged pin head 50 such that the pin 36 is biased to a rear position in which the pin head 50 contacts the closed end 38 of the cylindrical housing. An enlarged rear portion 52 of the pin 36 prevents the pin 36 from overprotruding forwardly from the cylindri-cal casing when it abuts the front wall 48 of the chamber 46.
2 o A smaller chamber 54 is defined within the cylindrical casing 34 near the front end 42, and the central opening 40 extends axially through the chamber 54.
Two retaining washers 56 and 58 are provided. The structure and size of the retaining washer 56, 58 are identical and more clearly illus-trated in Figures 3 and 4. The retaining washer 56 or 58 is made from an inte-gral metal plate having a central aperture. The metal plate includes an annular outer section forming a flat ring 60 and an annular inner portion forming a plurality of finger members 62 which are circumferentially spaced apart from one another by a plurality of radially extending cuts 64. The finger members 3 0 62 are bent in permanent deformation in one direction, which is referred to as a forward direction hereinafter. The final opening 66 defined by the ends of the finger members 62 is slightly smaller than the exterior of the pin 36. The finger members 36 are enabled to be resiliently deformed slightly to permit the pin 36 to be inserted from the rear side of the retaining washer 56 there-through. However, if the pin 36 is to be moved in the rearward direction rela-tive to the retaining washer 56, the friction force between the exterior of the pin 36 of the finger members 62 is in a trend to move the ends of the finger members 62 together with the pin 36 to further grip the pin 36 and stop the movement thereof. When the pin 36 is moved in the rearward direction by a force greater than or equal to the maximum friction force between the exterior of the pin and the finger members, the retaining washer 56 or 58 is no longer able to stop the rearward movement of the pin 36.
The retaining washer 58 abuts the brake shoe backing plate 26a and engages a front portion of the pin 36 extending therethrough as shown in Figure 1. When brake fluid is pumped into the bladder 30 and the backing plate 26a is moved forward with the brake lining 26b towards the frictional surface 24 of the rotor disk 18, the retaining washer 58 grips the pin 36 to move together with the backing plate 26a in the forward direction against the spring force applied on the pin head 50. After the brake action is completed and the brake fluid is released from the bladder 30, the spring force acting on 2 o the pin head 50 moves the pin 36 with retaining washer 58 to move the back-ing plate 26a rearwardly in order to disengage the brake lining 26b from frictional contact with the frictional surface 24.
As the frictional surface 24 wears out, the brake shoe 26 has to travel a longer distance from its original position to engage the frictional 2s surface 24. That means the pin 36 would have to travel together with the backing plate 26a over a longer distance and the spring 44 would be more compressed to produce greater spring forces acting on the pinhead 50. Prac-tically, the spring forces acting on the pin head 50 will never be greater than the maximum friction force between the retaining washer 58 and the pin 36 3 o and therefore, the spring force is able to move the pin 36 together with the _g_ backing plate 26a in the rearward direction for disengagement from the friction surface 24.
The retaining washer 56 is mounted on the pin 36 and received in the chamber 54 of the cylindrical casing 34. The periphery of the chamber s 54 is defined by a circumferentially extending groove 68 for receiving the flat ring 60 of the retaining washer 56 and permitting the retaining washer 56 to be axially movable within a range of the width of the groove 68. The retaining washer 56 acts as a self-adjustable friction device, compensating for the positional change of the frictional surface 24 caused by the wear over a period of time of performance. When the pin 36 is moved by the backing plate 26a in the forward braking action, the retaining washer 56 is freely moved together with the pin 36, until the flat ring 60 of the retaining washer 56 abuts the front side of the groove 68. However, the retaining washer 56 stopped by the front side of the groove 68 does not stop the pin 36 in the forward movement and the pin 36 stops only when the brake lining 26b frictionally engages the friction surface 24.
It is noted, that in this stage, the friction force between the pin 36 and the retaining washer 56 is relatively small and the pin 36 will continue its travel, entrained by the backing plate 26a beyond the initial travel in view of 2o the wear on the lining 26b and friction surface 24. Thus, although the washer 56 is prevented from travel beyond the front side of the groove 68, the pin will continue its travel. The fingers on the washer will then engage the pin 36 at a new position.
When the braking action is completed and the brake fluid is 2s released from the bladder 30, the backing plate 26 is pulled away from the frictional surface 24 of the disk 18 by the pin 36 under the spring force.
Both the retaining washers 56, 58 are the driven members in the rearward move-ment of the pin 36, and the backing plate 26b moves in the rearward direction.
The backing plate 26a is moved away from the frictional surface 3 0 24 over a short distance determined by the corresponding travel of the washer 56 within the width of the groove 68 because the retaining washer 56 abuts _g_ the rear side of the groove 68 during its rearward movement together with the pin 36 and the friction force between the pin 36 and the retaining washer 56 stops the pin 36 and thus the backing plate 26a. The travel of the pin 36 against the spring 44 will remain the same although the pin 36 and the back s ing plate will be closer to the disk 18 relative to the housing 22.
In a further embodiment of the present invention as shown in Figure 5, the reference numerals which correspond to elements having an equivalent in the previous embodiment have been raised by one hundred.
Thus, a return mechanism 110 is shown having a cylindrical to housing 134. A pin 136 is slidable axially through the cylindrical housing and a compression spring 144 is concentric with pin 136. The housing is closed at the rearward end thereof by a threaded sleeve 170.
The pin 136 is connected to the backing plate (not shown) by the retaining bracket 158 which includes an abutment flange 158a, a sleeve 15 158b which in turn is held by a friction sleeve 159. A washer 157 abuts against the backing plate, sandwiching the backing plate against the friction sleeve 159.
The retention washers 156a, 156b, and 156c are located on pin 136 (at the place of the pin head 50 in the embodiment of Figure 1 to 4).
2 o Thus, washers 156a serve both the purpose of the former pinhead 50 and the retaining washer 56. The washers 156a, 156b and 156c are spaced apart by spacers 157a, 157b, 157c which in turn are contained within a cylindrical cage 151 with an annular radial wall 152. The spring 144 abuts against the radial wall 152. The multiple retaining washers 156a, 156b, 156c have limited axial 25 travel within the cylindrical recess portion 168 in the housing 134. The recess portion 168 corresponds to the groove 68 in the embodiment of Figures 1 to 4 and the operation of the retaining washers 156 within the recessed portion 168 would be similar to that described with respect to the washer 56 in groove 68.
3o Accordingly, the pin 136 follows the forward movement of the breakshoe backing plate (engaged between the friction sleeve 159) causing the cylindrical cage 151 to move axially with washers 156 until the radial wall 152 abuts the forward shoulder forming the recess 168. If there is pronounced wear on the brake linings or the friction surface of the rotor disk, the backing plate will continue its travel, drawing the pin 136 through the s openings formed in the retention washers 156, in the direction of low frictional resistance. When the brakes are released, the pin 136 will be withdrawn under the urging of the spring 144 thereby pulling back the backing plate and thus the brake liner from the friction surface of the disk brake. However, the pin will have advanced slightly in relation to the washers 156 and thus will not to return fully to its initial position in the housing 134. Thus the pin 136 is in a position with the backing plate for travel with compensation for wear.
The above-described embodiments are examples for illustration of the principle of the invention. Any type of link member, which can be fric-tionally connected with the pin 36, can be used to replace the retaining 15 washer 58. Any type of friction device able to be frictionally connected to the pin 36 may be used to replace the retaining washer 56. However, the frictional features of the friction device in opposite directions must be different so that the maximum friction force in one direction is much smaller than the friction force in the opposite direction to permit the pin 36 to slide forward with little 2 o resistance while the maximum friction force in the opposite direction is suffi-cient to overcome the spring force acting on the pin 36 to stop the pin 36 in its rearward movement.
Other modifications or changes without departing from the prin-cipal of the present invention will be obvious to those skilled in the art.
The 2s embodiment described above is exemplary and not intended to limit the scope of the invention, which will be solely defined and limited by the appended claims.

Claims

CLAIMS:

1. ~A brake shoe return apparatus for a disk brake assembly wherein a rotor disk rotates in a housing about an axis and a brake shoe moves towards the rotor disk for frictional engagement therewith, the brake shoe return comprising:
a link member slidable relative to the housing and in a to and fro direc-tion parallel to the axis of rotation of the rotor disk and associatd with the brake shoe;
resilient means associated with the link member for urging the link member away from the rotor disk;
a connecting member to link the brake shoe with the link member and frictionally connected with the moving member to move the link member together with the brake shoe in a forward movement towards the rotor disk during a braking action when a forward pressure is applied to the brake shoe until the resilient means overcomes the forward pressure and returns the link member and the brake shoe to a position where the brake shoe is disengaged from the rotor disk.

2. A brake shoe return apparatus includes a housing, a friction device movable between first and second stops on the housing, a link mem-ber, connected to the brake shoe, mounted to the friction device and displaceable, by the brake shoe in a forward direction, along a first axis, towards a brake shoe friction engagement position with a rotor disk rotatable in the housing; the link member carrying the friction device along towards the first stop, the friction device having minimal frictional engagement on the link member when the link member slides forward beyond the position where the friction device is retained by the first stop, to displace the friction device on the link member, a spring in the housing for returning the link member and the brake shoe from the brake shoe friction engagement position towards a rear-ward position where the friction device abuts the second stop and halts the return displacement of the link member because of the substantial frictional resistance of the friction device on the link member in the return direction whereby the travel of the brake shoe corresponds to the distance between the first stop and the second stop and when wear is exhibited on the brake shoe and/or the rotor disk, the link member is adjusted for the relative displacement of travel of the brake shoe due to the wear.

3. A brake shoe return as defined in claim 2 wherein the housing includes a casing in the form of an elongated cylindrical wall and the link member is a cylindrical pin slidable along a second axis parallel to the first axis in the cylindrical housing and a compression spring is provided within the cylindrical housing acting against an abutment member mounted on the pin urging the pin toward a rearward direction, the friction device including a retention washer having engagement fingers in the forward direction, the washer being secluded in a groove defining the first and second stops respectively corresponding to the travel whereby when the pin is drawn by the brake shoe towards the rotor disk beyond its normal travel to compensate for wear, it will slide in the forward direction through the retention washer when the retention washer is abutting the first stop, but on the return, the retention washer will prevent the pin from returning to its initial position when the washer abuts the second stop, thereby slightly precompressing the spring.

4. A brake shoe return apparatus as defined in claim 2, wherein the link member slides in a chamber formed within the housing and retention washers are mounted on the pin within the housing chamber and said first and second stop are provided in the chamber to engage the retention wash-ers whereby the pin will move forward beyond the first stop relative to the retention washers but will be prevented from moving rearwardly to its initial position when the washers abut the second stop in order to compensate for the wear.

5. A brake shoe return apparatus for a disk brake assembly wherein a rotor disk rotates in a housing about an axis and a brake shoe moves towards the rotor disk for frictional engagement therewith, the brake shoe return comprising:
a link member slidable relative to the housing and in a to and fro direc-tion parallel to the axis of rotation of the rotor disk and associatd with the brake shoe;
resilient means associated with the link member for urging the link member away from the rotor disk;
a friction device associated with the housing and slidable relative to the housing in the forward and rearward direction within a predetermined travel;
the friction device being frictionally connected to the link member, the link member and the friction device permitting the link member to move together with the brake shoe in the forward direction during a brake action with a little frictional resistance from the friction device when the friction device is restrained, while a maximum friction force in the opposite direction between the link member and the friction device prevents the link member from moving in the rearward direction relative to the friction device so that the brake shoe and the link member can only move away from the rotor disk in the rearward direction together with the friction device within the predetermined distance when a brake force is removed from the brake shoe.