GB2168439A

GB2168439A - A disc brake actuator with slack adjustment

Info

Publication number: GB2168439A
Application number: GB08528829A
Authority: GB
Inventors: Wolfgang Endler
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1984-12-14
Filing date: 1985-11-22
Publication date: 1986-06-18
Also published as: DE3445564A1; FR2574885B1; GB8528829D0; FR2574885A1; IT8523183A0; IT1186432B; GB2168439B

Abstract

A disc brake actuator comprises a thrust member (23) which is adjustable in length to take up slack and which is constituted by an adjusting spindle (25) and an adjusting nut (24) engaging in each other through a non-reversible thread (26) and a rotatably supported actuating member (12), which transmits, via a device (16, 17) for the conversion of a rotary motion into an axial motion, an axial brake applying force to the nut of the thrust member in order to axially urge the latter against brake piston (2). When a predetermined brake clearance is exceeded a rotatable follower device (43) is engaged by the actuating member (12) through a lost-motion coupling (46, 47), and, via a unidirectionally acting coupling, in particular with a free-wheel coupling (52), transmits the rotation of the follower device (43) to the spindle (25) of the thrust member thus effecting adjustment to take up slack. In order to ease the resetting of the adjusting apparatus and to eliminate expansions of the calliper during the adjusting operation, a friction coupling (57) is arranged between the unidirectionally acting coupling (52) and the thrust member (23), said friction coupling transmitting torques up to a defined amount to the thrust member (23) and being ineffective instead beyond that amount of torque. <IMAGE>

Description

SPECIFICATION Adjusting apparatus for a disc brake This invention relates to an adjusting apparatus for a disc brake, in particular for automotive vehicles, with a thrust member which is adjustable in length end comprises an adjusting spindle and an adjusting nut engaging in each other through a non-reversible thread, with a rotatably supported actuating member, a device for the conversion of a rotary motion into an axial motion, an axially movable element of said device making catch at the thrust member in order to axially urge the latter against a brake actuating member, with a rotatable follower device engaged by the actuating member through a lost-motion coupling, and with a unidirectionally acting coupling, in particular with a free-wheel coupling, to transmit the rotation of the follower device to the movable element of the thrust member.

An adjusting apparatus of this kind is known from West German patent application published without examination, No.

2,507,012. In this apparatus, within a housing forming part of a brake caliper, there is arranged a two-part bushing configured in the shape of a cylindrical helical bushing and received in a bore of the housing. One part of the bushing is fixed to the housing, that is to say, by a stay bolt in a rear wall of the housing, whereas a second part of the bushing is adjustable in the axial direction with respect to the first bushing part owing to a complementary helical configuration of the two ends facing each other of the two parts of the bushing. A split roller bearing is arranged in between the two parts of the bushing. A head attachment starts from the adjustable bushing part in the radial direction and penetrates through the side wall of the housing. the head attachment is connectible to an actuating apparatus through a connecting-rod linkage.By moving the head attachment in circumferential direction, the adjustable bushing part can be rotated relative to the other bushing part, and, due to the helical configuration of the ends facing each other of the bushing parts, it is itself being adjusted in the axial direction at and relative to the stationary bushing part in such a manner that brake shoes can be applied against opposed front faces of a brake disc. For the purpose, the front end of the adjustable bushing part makes catch, through a roller bearing, at a thrust-member assembly comprised of two elements (adjusting spindle and adjusting nut) arranged paraxially. The adjusting spindle is screwed to the adjusting nut and-being hindered from performing a rotating motion-is capable of urging a brake shoe against a brake disc.

The prior-art apparatus furthermore presents a driving bushing which is arranged between the two-part bushing and the adjusting nut and is coupled to the latter through a unidirectionally acting coupling. In a radial end flange of the driving member, axially directed notches are configured at intermediate distance in circumferential direction. A follower fastened to the rotatable bushing part is received in one of these notches. If on actuation of the brake the rotation of the bushing part is not sufficient to make the follower travel the full width of the distance of adjustment permitted by a notch, then there will not take place any adjustment whatsoever.When the friction linings are worn the follower will, however, come in abutment against one side of the notch and will rotate the driving member, through the unidirectionally acting coupling, with respect to the external element of the thrust-member assembly. When the brake is released the return spring in the actuating apparatus will effect the follower to take support at the other side of the notch and the driving member to rotate jointly with the external element of the thrustmember assembly. That rotation results in an increase of the effective length of the thrustmember assembly, since the adjusting spindle is hindered from an adjustment in axial direction, for example because of its being abutted against a brake shoe.

In this prior-art apparatus, a particular device is necessary to restore the adjusting apparatus into its initial position again, which is, for example, necessary in the event of a change of the brake linings. This is attained in that the driving member, which is non-rotatably arranged with respect to the actuating member in normal operation, is axially slidable, so that on an axial slide of the driving member the follower pin serving for non-rotatable coupling comes to engage in a circumferential groove and the driving member so becomes rotatable relative to the actuating member. In this way, the adjusting nut can be turned in the direction of resetting, which is prevented, during normal operation, by the unidirectionally acting coupling and by the circumstance that the driving member and the actuating member are non-rotatably coupled to each other.Since the driving member is axially slidable against the force of a spring, it will be necessary to simultaneously bring to bear an axial force and a rotary motion in order to reset the adjusting apparatus, so that the resetting operation is relatively complicated.

The present invention has, therefore, an object to create an adjusting apparatus of the type mentioned in the beginning in which the resetting operation is simplified. Furthermore, the unfavourable effect of the elasticity in the caliper bridge and linings is to be eliminated by means of the inventive adjusting apparatus.

According to the present invention there is provided an adjusting apparatus for a disc brake, in particular for automotive vehicles, with a thrust member which is adjustable in length and comprises an adjusting spindle and an adjusting nut engaging in each other through a non-reversible thread, with a rotatably supported actuating member, a device for the conversion of a rotary motion into an axial motion, an axially movable element of said device making catch at said thrust member in order to axially urge the latter against a brake actuating member, with a rotatable follower device engaged by the said actuating member through a lost-motion coupling, and with a unidirectionally acting coupling, in particular with a free-wheel coupling, to transmit the rotation of said follower device to the movable element of said thrust member, characterised in that a friction coupling is arranged between the said unidirectionally acting coupling and the said thrust member, which said friction coupling transmits torques up to a defined amount to the said thrust member and which is ineffective beyond that amount of torque.

In this way, an adjusting apparatus is created in which the rotary motion required for the adjustment is transmitted in a clamping direction, through a locked, unidirectionally acting coupling and a friction coupling, to the threaded spindle in such a manner that adjustment takes place during clamping. In the course of the build-up of the clamping force, an increasing friction torque comes about in the thread of the thrust member which, within the range of expansion, exceeds the friction torque of the coupling, as a result whereof the friction coupling slips and does not continue to transmit the initiated rotary motion. The adjusting operation is thus transposed into the range of application before the beginning of the expansion and an adjustment of the expansion travel is prevented.When the linings have to be changed the threaded spindle may then be reset by simply turning the adjusting spindle.

According to preferred embodiments of the invention, the coupling member of the friction coupling may be configured in the shape of a friction cone or may present a plane friction surface in the case of minor friction torques having to be transmitted.

Expediently, a spring, in particular a cup spring, is provided to apply the coupling force in the axial direction, said spring being suitably dimensioned to reach the necessary friction torque of the friction coupling.

Developing further the teachings of the present invention, a shaft is provided to transmit the rotary motion from the actuating member via the couplings to the rotatable element of the thrust member, to which shaft the hollow adjusting spindle is non-rotatably and axially slidably coupled. The said shaft may very expediently form a bearing section on which a bushing is rotatably arranged which is part of the follower device.

For easy transmission to that bushing of the rotary motion of the actuating member, said bushing is advantageously furnished with a radially extending flange section which is formed with a recess engaged by a pin or similar means rigidly coupled to the actuating member. In this context, the said recess is sized such in the circumferential direction that the actuating member is rotatable to an extent that the device for the conversion of a rotary motion into an axial motion is movable in forward direction in accordance with the normal distance of brake application and wear without any rotation of the bushing and, as a consequence, any adjusting operation coming about.

The free-wheel coupling may be positioned on the bushing in order to attain a particularly compact set-up.

In further versions, it is envisaged that the coupling element is non-rotatably coupled to the rotatable element of the thrust member.

For that purpose, it is expediently arranged on the shaft.

A cage which surrounds the free-wheel coupling may be provided in order to fix the coupling member in the axial direction.

In a further version, the couplings are arranged in a recess of the actuating member in order to realise as short as possible a design.

An embodiment of the present invention will now be described with reference to the accompanying sectional drawing.

The drawing shows a longitudinal section through a part of a disc brake housing 1 within which an actuating device with adjusting apparatus for a brake piston 2 is accommodated. The brake piston 2 having a cupshaped configuration is axially slidably arranged in an axial bore 3 of the brake housing 1, with the bottom 4 of the brake piston 2 facing an intermediate member 5 against which it is abutted. The intermediate member 5 is abutted, in its turn, against the backplate 6 of a brake lining 7, so that, on an axial slide of the brake piston 2, the brake lining 7, too, is slid in the axial direction through the intermediate member 5 in order to be urged against a brake disc (not shown in the drawing). When the brake lining 7 is applied against the brake disc a force of reaction is brought about which slides the brake housing 1 in the opposite direction, as a result whereof a stem (not shown in the drawing) of the brake housing 1 urges a brake lining (not shown in the drawing) positioned on the other side of the brake disc against that other side of the brake disc. A dust boot 8 is provided to protect the bore 3 from soiling, said boot being secured in grooves of the brake housing 1 and of the brake piston 2.

Into the brake housing 1, a pin 9 is screwed which extends in the radial direction into an axial recess 10 of the brake piston 2, so that the latter is non-rotatable with respect to the brake housing 1.

An actuating member 12 is rotatably supported in an end-side bore 11 of the brake housing 1 for the actuation of the brake. The actuating member 12 comprises a cylindrical bearing section 13 and an actuating lever 14.

Said cylindrical bearing section 13 extends through the bore 11 into the bore 3 where it is abutted, with its front side, against a device 15 which serves to convert the rotary motion of the actuating member 12 into an axial motion. The said device 15 is constituted by a roller ramp in this embodiment which comprises two ramp elements 16, 17 with rollers 18 positioned in between. The ramp element 16 facing the actuating member 12 is nonrotatably coupled to the latter by means of screws 19, as a result whereof any rotary motion of said actuating member 12 directly results in a rotation of the ramp element 16.

The other ramp element 17 is arranged nonrotatably, and this is attained by the pin 9 engaging in a corresponding recess 20 of said ramp element 17. Said recess 20 is directed axially, so that the ramp element 17 is allowed to perform an axial motion, but no rotary motion. A roller bearing 22 is located between the bottom 21 of the bore 3 and the ramp element 16.

With its ramp element 17, said roller ramp 15 acts against a thrust member 23 which is adjustable in length and is formed by an adjusting nut 24 and an adjusting spindle 25 engaging with each other through a non-reversible thread 26. Said adjusting nut 24 comprises an axially extending shaft section 27 and a radially extending flange section 28.

Said adjusting spindle 25 also comprises an axial shaft section 29 and a radial flange section 30. Said flange sections 28, 30 of the adjusting nut and of the adjusting spindle face the bottom 4 of the brake piston 2. In this context, the flange section 30 of the adjusting spindle 25 is abutted, with its front end 31, against the bottom 4 of the brake piston 2 and is coupled to the brake piston through an antistrip lock 32. The shaft sections 27, 29 of the adjusting nut 24 and of the adjusting spindle 25 extend through central bores 33, 34 which are provided in the ramp elements 16, 17, toward the actuating member 12, their ends being positioned in a cylindrical recess 35 of the actuating member 12. At the outer circumference of the shaft section 27 of the adjusting nut 24, there is provided a circular groove 36 in which a ring 37 is retained.At said ring, a compression spring 38 takes support whose other end is in abutment against a shoulder 39 of the ramp element 16. The adjusting nut 24 is thereby urged, with one front surface of its flange section 28, against one front surface of the ramp element 17 and is there retained in abutment.

The couplings provided according to the present invention are also accommodated in the recess 35 of the actuating member 12. In the hollow adjusting spindle 25, a toothed shaft 40 is arranged which comprises a toothed (splined) section 41 substantially accommodated in the hollow adjusting spindle 25 in order to couple said toothed shaft 40 in an axially slidable but non-rotatable manner to the adjusting spindle 25, and a bearing section 42 projecting from the hollow adjusting spindle 25 in the direction of the actuating member 12. A bushing 43 is rotatably positioned on the bearing section 42 of the toothed shaft 40. Said bushing 43 comprises an axially extending cylindrical section 44 and a radially extending flange section 45.In said flange section 45 of said bushing 43, a recess 46 is provided which extends over a part of the circumference of the flange section 45 and is engaged by a pin 47 fixed in the sctuating member 12.

For its fixation in the axial direction, the bushing 43 is abutted, with a shoulder 48, against a shoulder 49 of the toothed shaft 40 configured at the transition between the toothed section 41 and the bearing section 42, and is secured on the other side by means of a ring 50 retained in a circular groove 51 of the bearing section 42. On the cylindrical section 44 of the bushing 43, there is provided a unidirectionally acting coupling 52 which constituted by a needle roller-type free-wheel in this instance. The external coupling ring 53 of the coupling 52 is formed with a cone 54 which interacts with a cone 55 configured at a coupling element 56 so as to form a friction coupling 57 jointly with the latter. The coupling element 56 is positioned non-rotatably but axially slidably on the toothed shaft 40 through a toothing 58.

The coupling element 56 is retained inthe axial direction by a cage 59 which engages, with flange sections 60, 61, in corresponding recesses provided in the coupling element 56, on one side, and in the bushing 43, on the other side. Between the flange section 45 of the bushing 43 and the coupling ring 53, a cup spring 62 is arranged which urges the coupling ring 53 agianst the coupling element 56 in order to effect a frictional engagement between the cone 54 and the cone 55. A compression spring 63 is arranged in a recess 64 provided on the inner side of the adjusting nut 24 and takes support at a shoulder of the adjusting nut, on one side, and at the coupling element 56, on the other side.At the end of the bearing section 42 of the toothed shaft 40, a recess 65 is provided having a hexagonal recessed hole for introduction of a mating tool to turn the toothed shaft 40.

There now follows a description of the method of operation of the actuating device and of the adjusting apparatus: On a rotation of the actuating member 12 and of the ramp element 16 which is rigidly coupled to it, the two ramp elements 16 and 17 will be rotated relative to each other since the ramp element 17 is retained non-rotatably.

As a result, the non-rotatable ramp element 17 will be forced to perform an axial motion which is transmitted to the adjusting nut 24 being, in its turn, retained non-rotatably by means of a pin 66. The axial motion will then be transmitted by the adjusting nut 24, through the non-reversible thread 26, to the adjusting spindle 25 which acts, through the brake piston 2 and the intermediate member 5, against the brake lining 7 so as to urge the latter against the brake disc (not shown in the drawing). The aforesaid motion is against the force of the compression spring 38. When, on account of the wear of the brake linings, the actuating member 12 exceeds a defined angle of rotation, then the pin 47 will come in abutment against a lateral boundary of the recess 46, so that the bushing 43 will be carried along.Through the locked free-wheel 52 and the friction coupling 57, the rotary motion will be transmitted to the toothed shaft 40 which will turn the adjusting spindle 25 by a corresponding angle. A friction torque will arise at the flanks of the adjusting thread 26 in the course of build-up of the clamping force. At a defined clamping force, which may, for example, amount to 3,000 to 5,000 N, the friction torque will exceed that of the friction coupling 57 which then slips. No further motion out of the expansion travel will, thus, any longer be transmitted. After the operation of the brake, the actuating member 12 will be turned in the opposite sense. This rotary motion will not affect the adjusting apparatus since the unidirectionally acting coupling 52 wheels freely in this sense. In order to restore the mechanical actuating device into its initial position in the event of a change of the brake linings, it will suffice, upon removal of a screw plug 68 sealing the opening 67 in the actuating member 12, to insert a hexagon wrench in the recess 65 at the end of the toothed shaft 40 in order to turn the latter back to the stop.

Claims

1. An adjusting apparatus for a disc brake, in particular for automotive vehicles, with a thrust member which is adjustable in length and comprises an adjusting spindle and an adjusting nut engaging in each other through non-reversible thread, with a rotatably sup- ported actuating member, a device for the conversion of a rotary motion into an axial motion, an axially movable element of said device making catch at said thrust member in order to axially urge the latter against a brake actuating member, with a rotatable follower device engaged by the said actuating member through a lost-motion coupling, and with a unidirectionally acting coupling, in particular with a free-wheel coupling, to transmit the rotation of said follower device to the movable element of said thrust member, characterised in that a friction coupling (57) is arranged between the said unidirectionally acting coupling (52) and the said thrust member (23), which said friction coupling (57) transmits torques up to a defined amount to the said thrust member (23) and which is ineffective beyond that amount of torque.

2. An adjusting apparatus as claimed in claim 1, characterised in that the said friction coupling (57) comprises a coupling member with friction cone.

3. An adjusting apparatus as claimed in claim 1, characterised in that the said friction coupling comprises a coupling member with a plane friction surface.

4. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that a spring, in particular a cup spring (62), is provided to apply the coupling force in the axial direction.

5. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that a shaft (40) is provided to transmit the rotary motion from the said actuating member (12) via the said couplings (52, 57) to the said thrust member (23), to which said shaft (40) the said hollow adjusting spindle (25) is non-rotatably and axially slidably coupled.

6. An adjusting apparatus as claimed in claim 5, characterised in that the said shaft (40) forms a bearing section (42) on which a bushing (43), which js part of the said follower device, is rotatably arranged.

7. An adjusting apparatus as claimed in claim 6, characterised in that the said bushing (43) is furnished with a radially extending flange section (45) which is formed with a recess (46) engaged by a pin (47) rigidly coupled to the said actuating member (12).

8. An adjusting apparatus as claimed in claim 6 or claim 7, characterised in that the said free-wheel coupling (52) is positioned on the said bushing (43).

9. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that the coupling element (56) is arranged on the said shaft (40).

10. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that the said Coupling element (56) is axially retained by a cage (59) which surrounds the said free-wheel coupling (52).

11. An adjusting apparatus as claimed in any one of the preceding claims, characterised in that the said couplings (52, 57) are arranged in a recess (35) of the said actuating member (12).

12. An adjusting apparatus for a disc brake substantially as herein described with reference to and as illustrated in the accompanying drawing.