GB1600998A - Disc brake piston retraction means - Google Patents

Description

(54) DISC BRAKE PISTON RETRACTION MEANS (71) I, REGINALD JOSEPH DOR MER, a British Subject of 2, Trumpers Way, Hanwell, London W7 20A, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: The object of this invention is to provide improved retraction means for a friction pad operating piston of a fluid pressure operated disc brake caliper whereby simplicity of construction and ease of assembly are obtained and also a self adjusting action.

According to this invention piston retraction means on or for a disc brake caliper comprises a body containing return spring means and also a coiled spring acted upon by said return spring means, said coiled spring being adapted to have a gripping fit about a rear cylindrical extension of a friction pad operating piston of a disc brake caliper in order to provide an abutment on said piston extension for the return spring means to effect retraction of the piston, the gripping fit which the coil spring is adapted to have about the piston extension being such that the piston extension is able to move axially relative to the coiled spring on operative movement of the piston exceeding maximum yielding movement of the return spring loading means as a result of pad wear so that the piston extension and piston are advanced in relation to the coiled spring and remain so advanced in order to provide automatic take up adjustment for pad wear.

In practice the construction and arrangement is as follows, reference being had to the accompanying drawing which is a detail sectional view of that part of a disc brake caliper containing a friction pad piston and fitted with a retraction unit according to this invention.

In the usual manner the cylinder bore 10 of the caliper 1 receives a piston 2 carrying a friction pad 3 for application against the disc 4, the piston 2 being arranged for fluid pressure (e.g. hydraulic) operation for this purpose. A rear co-axial cylindrical extension or tailpiece 20 of the piston 2 extends from the caliper 1 and receives the retraction unit 5.

This unit 5 consists of a body 50 bored at 51 to fit the piston tailpiece 20 and counter bored at 52 to accommodate a coil spring 53 which has a gripping fit about the tailpiece 20. The body 50 is further counter bored at 54 to accommodate return spring means shown consisting of two Belleville washers 56 acting between the coil spring 53 and a circlip 57 which retains the washers 56 in the counterbore 54 in the head 55 of the body 50. A washer 58 is shown interposed between the Belleville washers 56 and coil spring 53.

The internal bore of the coil spring 53 is honed or otherwise formed to provide a flat 530 on the turns for gripping contact with the piston tailpiece 20 whilst a leg 531 at the front end of the spring engages a recess 510 in the bore 51 to prevent rotation of the spring 53 relative to the body 50. The rear end of the spring 53 is preferably ground so as to seat against the shoulder 520 of its counter bore 52.

The assembled unit 5 can be simply fitted on the protruding portion of the piston tailpiece 20 with a screwing action, i.e. until the head 55 of the body 50 abuts the adjacent face 11 of the caliper body 1. Once in position in this way the grip of the coil spring 53 about the tailpiece 20 is such that it has a considerable resistance against axial movement along the latter so that on application of the friction pad 3 by hydraulic fluid pressure on the piston 2, forward movement of the coil spring 53 with the tailpiece 20 compresses the Belleville washers 56. Conversely on release of the brake the Belleville washers 56 act against the forward end of the coil spring 53 to retract the piston 2 and friction pad 3. At all times the action is such as to maintain the head 55 firmly against the face 11.

As wear of the friction pad 3 takes place, the pad 3 and piston 2 are required to move an increasing axial distance, causing increasing compression of the Belleville washers 56. When this axial movement is sufficiently great to produce maximum compression of the Belleville washers, the hydraulic pressure acting on the piston is able to overcome the grip of the coil spring 53 on the tailpiece 20 resulting in forward movement of the tailpiece 20 relative to the coil spring 53. As a result, the piston 2 and pad 3 are advanced relative to the coil spring 53 and remain so advanced on retraction by re-assertion of the Belleville washers 56.

In this way automatic adjustment is provided since the pad 3 is advanced as wear takes place so as to maintain a required minimum pad to disc clearance when the brake is released. In addition to such adjustment it will be appreciated that the retraction unit is of simple construction and can be readily fitted or removed e.g. for replacement.

By way of practical example the coil spring 53 may consist of a "Flexal" (Registered Trade Mark) 17 SWG (.056") close wound spring in E.N. 49C R3 steel having an outside diameter of .520" and an internal diameter of .408" honed to .420" diameter at the interval flat 530 of the turns. However these dimensions may be varied according to requirements and the size of brake involved.

WHAT I CLAIM IS: 1. Piston retraction means on or for a disc brake caliper comprising a body containing return spring means and also a coiled spring acted upon by said return spring means, said coiled spring being adapted to have a gripping fit about a rear cylindrical extension of a friction pad operating piston of a disc brake caliper in order to provide an abutment on said piston extension for the return spring means to effect retraction of the piston the gripping fit which the coil spring is adapted to have about the piston extension being such that the piston extension is able to move axially relative to the coiled spring on operative movement of the piston exceeding maximum yielding movement of the return spring loading means as a result of pad wear so that the piston extension and piston are advanced in relation to the coiled spring and remain so advanced in order to provide automatic take up adjustment for pad wear.

2. Piston retraction means according to claim 1 wherein the turns of the coiled spring at the internal bore thereof are formed with a flat surface for gripping contact with the rear cylindrical extension of a said piston.

3. Piston retraction means according to claim 1, 2 or 2 wherein the body is provided with an axial bore containing the coiled spring and a further axial bore containing the return spring means acting on the coiled spring.

4. Piston retraction means according to any of the preceding claims wherein a washer is interposed between opposed ends of the return spring means and the coiled spring.

5. Piston retraction means according to any of the preceding claims wherein the return spring means consists of one or more Belleville washers.

6. Piston retraction means according to any of the preceding claims wherein the coiled spring is restrained against rotation relative to the body.

7. Piston retraction means according to claim 6 wherein an end leg of the coiled spring engages a recess in the body to prevent its rotation relative to the body.

8. Piston retraction means according to any of the preceding claims wherein the return spring means and the coiled spring are contained in the body whereby the retraction means can be mounted in position of use by pushing the body onto a said rear cylindrical extension of a friction pad operating piston of a disc brake caliper so as to engage the coil spring with a gripping fit about the piston extension the body being further adapted to abut a body part of a said disc brake caliper.

9. Piston retractions means on or for a disc brake caliper substantially as herein described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. the coil spring 53 to retract the piston 2 and friction pad 3. At all times the action is such as to maintain the head 55 firmly against the face 11. As wear of the friction pad 3 takes place, the pad 3 and piston 2 are required to move an increasing axial distance, causing increasing compression of the Belleville washers 56. When this axial movement is sufficiently great to produce maximum compression of the Belleville washers, the hydraulic pressure acting on the piston is able to overcome the grip of the coil spring 53 on the tailpiece 20 resulting in forward movement of the tailpiece 20 relative to the coil spring 53. As a result, the piston 2 and pad 3 are advanced relative to the coil spring 53 and remain so advanced on retraction by re-assertion of the Belleville washers 56. In this way automatic adjustment is provided since the pad 3 is advanced as wear takes place so as to maintain a required minimum pad to disc clearance when the brake is released. In addition to such adjustment it will be appreciated that the retraction unit is of simple construction and can be readily fitted or removed e.g. for replacement. By way of practical example the coil spring 53 may consist of a "Flexal" (Registered Trade Mark) 17 SWG (.056") close wound spring in E.N. 49C R3 steel having an outside diameter of .520" and an internal diameter of .408" honed to .420" diameter at the interval flat 530 of the turns. However these dimensions may be varied according to requirements and the size of brake involved. WHAT I CLAIM IS:

1. Piston retraction means on or for a disc brake caliper comprising a body containing return spring means and also a coiled spring acted upon by said return spring means, said coiled spring being adapted to have a gripping fit about a rear cylindrical extension of a friction pad operating piston of a disc brake caliper in order to provide an abutment on said piston extension for the return spring means to effect retraction of the piston the gripping fit which the coil spring is adapted to have about the piston extension being such that the piston extension is able to move axially relative to the coiled spring on operative movement of the piston exceeding maximum yielding movement of the return spring loading means as a result of pad wear so that the piston extension and piston are advanced in relation to the coiled spring and remain so advanced in order to provide automatic take up adjustment for pad wear.

2. Piston retraction means according to claim 1 wherein the turns of the coiled spring at the internal bore thereof are formed with a flat surface for gripping contact with the rear cylindrical extension of a said piston.

3. Piston retraction means according to claim 1, 2 or 2 wherein the body is provided with an axial bore containing the coiled spring and a further axial bore containing the return spring means acting on the coiled spring.

4. Piston retraction means according to any of the preceding claims wherein a washer is interposed between opposed ends of the return spring means and the coiled spring.

5. Piston retraction means according to any of the preceding claims wherein the return spring means consists of one or more Belleville washers.

6. Piston retraction means according to any of the preceding claims wherein the coiled spring is restrained against rotation relative to the body.

7. Piston retraction means according to claim 6 wherein an end leg of the coiled spring engages a recess in the body to prevent its rotation relative to the body.

8. Piston retraction means according to any of the preceding claims wherein the return spring means and the coiled spring are contained in the body whereby the retraction means can be mounted in position of use by pushing the body onto a said rear cylindrical extension of a friction pad operating piston of a disc brake caliper so as to engage the coil spring with a gripping fit about the piston extension the body being further adapted to abut a body part of a said disc brake caliper.

9. Piston retractions means on or for a disc brake caliper substantially as herein described with reference to the accompanying drawing.