GB2239067A

GB2239067A - Sliding caliper disc brake with automatic adjustment means for wear compensation

Info

Publication number: GB2239067A
Application number: GB9025982A
Authority: GB
Inventors: Bernd Rupprecht; Wilfried Strauss; Rainer Baumgartner
Original assignee: Deutsche Perrot Bremse GmbH
Current assignee: Deutsche Perrot Bremse GmbH
Priority date: 1989-12-15
Filing date: 1990-11-29
Publication date: 1991-06-19
Anticipated expiration: 2010-11-29
Also published as: IT1245839B; GB9025982D0; GB2239067B; DE3941540A1; DE3941540C2; IT9022066A1; IT9022066A0

Abstract

When the linings of a sliding caliper disc brake are worn, movement of the piston (2) upon hydraulic actuation results in a threaded sleeve (9) of an automatic wear adjuster being rotated on bearing (14), relative to a threaded spindle (6) fixed to the piston (2), due to the restraining force provided by spring (12). Spring (12) also biasses axially displaceable pressure member (16) directly or indirectly against a cam shaft (21) to prevent slack between them due to rotation of the cam shaft resulting from shoe wear related movement of the caliper housing. The engaging flanks of the threads of the spindle (6) and the sleeve (9) are of differing inclination and permit turning of the sleeve upon hydraulic loading of piston (2) and prevent turning of the sleeve upon mechanical loading of pressure member (16). <IMAGE>

Description

1 :2:2390&,-7 1 SLIDE-SADDLE DISC BRAKE WITH AUTOMATIC ADJUSTMENT MEANS

FOR WEAR COMPENSATION This invention relates to a slide-saddle disc brake with automatic adjustment means comprisinga brake piston, which is displaceable in a cylinder bore of the slide saddle, but mounted to be rotatably secure, and which is hydraulically and/or mechanically loaded for direct operation of a brake shoe, a member of adjustable length comprising an adjustment spindle, which is non-rotatably mounted on the brake piston, and an adjustment sleeve, which is connected to the adjustment spindle by means of a thread, with play, and a pressure spring, which acts between the slide saddle and the adjustment sleeve and loads the adjustment sleeve via the thread to extend the adjustable member, pressure means, which is mounted in the slide saddle to be coaxially displaceable relative to the brake piston but rotatably secure, and mechanical operating means which is capable of displacing the pressure means together with

the adjustment sleeve and the adjustment spindle against the force of the pressure spring. In a slide-saddle disc brake with automatic adjustment means of this type, as described in German 25 Specification DE-OS 21 43 575, the adjustment spindle is connected to the adjustment sleeve via a thread which is not self-inhibiting. The sleeve is supported relative to the slide saddle under the bias of the pressure spring via an

4 1 2 axial roller bearing. Upon hydraulic loading of the brake piston, the adjustment sleeve rotates freely on the adjustment spindle to compensate for wear of the brake lining. Engagement surfaces of both the adjustment sleeve and the pressure means are conical and fit into each other during mechanical operation of the brake. This results in a rotatably secure frictional connection between the pressure means and the adjustment sleeve, which prevents the adjustment sleeve from turning. There is free play between the friction cones of the adjustment sleeve and the pressure means and this has to be overcome upon each mechanical operation of the brake.

In a slide-saddle disc brake, the slide saddle is increasingly displaced towards one side due to wear of the indirectly operated brake lining relative to the brake disc.

This is schematically shown in Fig. 3 of the accompanying drawings where an eccentric shaft 21 is shown to be rotatably mounted in the slide saddle 1 and coupled via an operating lever 22 to an operating bar 23 of a spring-loaded cylinder 24. Rotary movement of the eccentric shaft 21 is transferred via a ram 19 into axial movement of pressure means 16, which acts on the (not shown) adjustment sleeve. With increasing wear of the indirectly operated brake lining, the slide saddle 1 moves to the right as seen in Fig. 3 up to a maximum displacement marked "B". As the operating bar 23 is pivotally connected, at "A", to the operating lever 22, the aforesaid movement of the slide 71 1 3 saddle 1 results in anticlockwise movement of the operating lever 22 and thus of the eccentric shaft 21. An increase in play ("C") between the abutment surfaces of the ram 19, the 5 pressure means 16 and/or the eccentric shaft 21 then occurs. This play adds to the aforementioned operational plays within the adjustable means, and results in an increase in the required mechanical movement to overcome play. This known adjustment arrangement is, accordingly, unsuitable for parking brakes which are operated by spring-loaded cylinders, as such cylinders have only a limited range of movement.

It is an object of the present invention to provide adjustment means suitable for parking brakes which are operated by spring-loaded cylinders.

According to the present invention adjustment means fulfilling this requirement is characterised in that the adjustment sleeve is acted upon by the mechanical operating means by way of freely displaceably mounted pressure means by abutment of even contact surfaces of both the pressure means and the adjustment sleeve, and in that the thread connection between the adjustment spindle and the adjustment sleeve is a specially arranged buttress thread, respective shallow flanks of which have different inclinations, and respective steep flanks of which also have different inclinations, in which respect the shallow flanks engage due to hydraulic loading of the brake piston, and the steep flanks engage due to mechanical loading of the 4 pressure means.

Due to the floating mounting of the adjustment sleeve and of the pressure means, the adjustment movement is transferred to the pressure means, so that no undesirable play between the operational members of the mechanical operating device can occur despite displacement of the slide saddle upon increasing wear of the brake linings.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is an axial cross-section of a section of a hydraulically and mechanically operated slide-saddle disc brake in accordance with the invention; 15 Fig. 2 is an illustration of the mechanical operation of same with unused brake linings; Fig. 3 is an illustration of the mechanical operation of same with displacement of the slide saddle due to wear of the brake linings; 20 Fig. 4 is a more detailed illustration of the adjustment means of this brake; and Fig. 5 is an enlarged illustration of the buttress thread of the adjustment means, shown in use during mechanical operation of the brake. The slide- saddle disc brake shown in Fig. 1 has a brake piston 2 displaceably mounted in a cylinder bore 5 of the slide saddle 1. Sealing and return of the brake piston 2 are achieved in known manner by a roll-back seal 28. An k. A adjustment spindle 6 is non-rotatably mounted, by a nut 26 and a radial collar 8, inside the brake piston 2, which is pot-shaped and has an open area facing towards a brake lining 3.

An adjustment sleeve 9 is rotatably mounted on the adjustment spindle 6 and has a radial collar 10 at one end facing mechanical operating means. In this respect, the adjustment spindle 6 and the adjustment nut 9 are connected via a buttress thread 7, which has a thread play corresponding to the required free play L of the brake, as shown in Fig. 5. This buttress thread 7 is specially constructed to have flanks of different inclinations on the adjustment spindle 6 and on the adjustment sleeve 9, i.e.

flanks and 1 of different shallowness and flanks 8 and B' of different steepness. Engagement of the thread flanks and 1 of different shallow inclination allows turning of the adjustment sleeve 9 on the adjustment spindle 7, whereas engagement of the thread flanks jB and 13' of different steepness inhibits turning of the adjustment sleeve 9 on the adjustment spindle 6.

The adjustment sleeve 9 extends into a narrower diameter portion 11 of the cylinder bore where it is loaded by a pressure spring 12. The pressure spring 12 acts between a support ring 13 mounted inside the cylinder bore 11 and an axial roller bearing 14 which bears against the collar 10 of the adjustment sleeve 9. The cylinder bore 11 also serves to guide both the pressure spring 12 and the i i 6 axial roller bearing 14, so that usual guide-, support- and mounting members, such as spring washers, are dispensed with.

Mounted within a yet narrower diameter portion 15 of the cylinder bore is a pressure member 16, which at one side protrudes a distance L, and abuts the collar 10 of the adjustment sleeve 9, and at its other side has a recess- 17 providing an abutment surface 18 for a ram 19. An eccentric shaf t 21, which is mounted in the slide saddle 1 to be rotatable parallel to the plane of the brake disc 27, is provided with a similar abutment surface 20, against which the ram 19 also abuts. As shown in Figs. 2, 3 and 4 an operating lever 22 is mounted on the eccentric shaft 21 and pivoted at point A to an operating bar 23 of a fixed springloaded cylinder 24.

In other embodiments within the scope of the invention the eccentric shaft 21 could be substituted by a shaft of involute shape which directly abuts a smooth surface of the pressure means, thereby dispensing with the ram 19.

The piston 2 has its interior space 25 filled with oil. In operation, hydraulic pressure applied thereto pushes the piston 2 and the connected adjustment spindle 6 in the direction of brake disc 27 to press the brake lining 3 against the brake disc 27. The reactionary force of the slide saddle 1 brings the indirectly loaded brake lining 4 into abutment against brake disc 27 as well. In this way 7 the piston 2 and its connected adjustment spindle 6 move forwards relative to the adjustment sleeve 9 through the normal free play L, which is defined by the buttress thread 7, and backwards again when the brake is released.

When the brake lining 3 is worn, the piston 2 moves further forward to press it against the disc 27 so that the free play L in buttress thread 7 is exceeded. The shallow, non- self inhibiting thread flanks A ' abut, and the adjustment sleeve 9 simultaneously lifts off from the surf ace of the pressure member 16 which f aces it, by a distance corresponding to the extent of lining wear. At the same time, the slide saddle 1 is displaced to the right as seen in Fig. 1 due to the wear of the indirectly operated brake lining 4. This causes the eccentric shaft 21 to turn contrary to its operating direction, around the fixed point A as shown in Fig. 3.

At this point the adjustment sleeve 9 is turned by the pre-tensional force of the axial roller bearing 14, the pressure member 16. pressure spring 12 is thus which turns back, at the pressure spring 12, acting via so as to again abut the face of As the pre- tensional force of fixed, the adjustment sleeve 9, same time pushes the pressure member 16 further back in the cylinder bore portion 15, so that no play can develop between the pressure member 16, the ram 19 and the eccentric shaft 21, when the eccentric shaft 21 is turned against its operating direction due to the displacement of the slide saddle 1.

8 Consequently, the pressure spring 12 fulfils several functions. By virtue of its pre-tensional force in conjunction with the roll-back seal 28 it reliably returns both the slide saddle 1 and the brake piston 2 to their original positions upon release of pressure. The pressure spring 12 also sets the degree of free play between the adjustment members and forcibly transfers this to the pressure member 16, thereby compensating for any play developed between the mechanical operating members.

The adjustment is infinitely variable, and undesirable turning of the respective components is prevented by the friction which is created between the adjustment sleeve 9 and the pressure member 16 by the pretensional force of the pressure spring 12.

With reference to Figs. 2 and 3, mechanical operation of the brake is aided by a spring-loaded cylinder 24. Turning of the eccentric shaft 21 takes place via the operating bar 23 and the operating lever 22 only after overcoming an idle stroke, caused by the free play. The shaf t 21 pushes the ram 19 which in turn pushes the brake piston 2 axially forward via the pressure member 16, the adjustment sleeve 9, and the adjustment spindle 6, with the thread flanks 8, 8' held in abutment against the pre- tensional force of pressure spring 12, so that the brake lining 3 (and via the reactionary force also the brake lining 4) abut against the brake disc 27. In this state turning of adjustment sleeve 9 relative to the adjustment 1 9 spindle 6 cannot take place, as the friction between the pressure member 16 and adjustment sleeve 9 is greater than the thread friction.

Realignment of the adjustment means after changing the brake lining is done in a simple manner; The end of the adjustment spindle 6 to which the nut 26 is secured is provided with a hexagonal recess 29 into which a key can be inserted to iold the adjustment spindle 6 so that the nut 26 can be released. The adjustment spindle 6 is then screwed into adjustment sleeve 9 whilst the brake piston 2 is pushed fully home into the cylinder bore 5. By retightening the nut 26, the adjustment spindle 6 is again connected to the brake piston 2 in a rotatably secure manner, thus completing the repositioning.

Although the above described and illustrated embodiment is a preferred form of the invention, numerous variations thereof are possible within the scope of the invention.

Claims

CLAIMS:

1. A slide-saddle disc brake with automatic adjustment means comprising a brake piston, which is displaceable in a cylinder bore of the slide saddle, but mounted to be rotatably secure, and which is hydraulically and/or mechanically loaded for direct operation of a brake shoe, member of adjustable length comprising an adjustment spindle, which is non-rotatably mounted on the brake piston, and an adjustment sleeve, which is connected to the adjustment spindle by means of a thread, with play, and a pressure spring, which acts between the slide saddle and the adjustment sleeve and loads the adjustment sleeve via the thread to extend the adjustable member, pressure means, which is mounted in the slide saddle to be coaxially displaceable relative to the brake piston but rotatably secure, and mechanical operating means which is capable of displacing the pressure means together with the adjustment sleeve and the adjustment spindle against the force of the pressure spring, characterised in that the adjustment sleeve is acted upon by the mechanical operating means by way of freely displaceably mounted pressure means by abutment of even contact surfaces of both the pressure means and the adjustment sleeve, and in that the thread connection between the adjustment spindle and the adjustment sleeve is a specially arranged buttress thread, respective shallow flanks of which have different inclinations, and respective steep flanks of which also have different inclinations, in 1 11 which respect the shallow f lanks engage due to hydraulic loading of the brake piston, and the steep flanks engage due to mechanical loading of the pressure means.

2. A slide-saddle disc brake as claimed in claim 1 wherein the pressure spring is supported relative to the slide saddle via a support ring and relative to the adjustment sleeve via an axial roller bearing.

3. A slide-saddle disc brake as claimed in claim 2 10 wherein the pressure spring and the axial roller bearing are guided in the cylinder bore of the slide saddle.

4. A slide-saddle disc brake as claimed in any preceding claim wherein the adjustment spindle is releasably attached to the brake piston by means of a nut.

5. A slide-saddle disc brake as claimed in any preceding claim wherein the mechanical operatingmeans comprises an eccentric shaft which is mounted in the slide saddle and is rotatable around an axis which is perpendicular relative to the cylinder bore, and which is coupled via an operating lever to an operating bar of a spring-loaded cylinder.

6. A slide-saddle disc brake substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

Published 1991 at The Patent Office. State House. 66171 High Holborn. London WC1 R 41P. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Fbint Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid, St Mary Cray. Kent.