GB2304387A

GB2304387A - Brake adjuster mechanism

Info

Publication number: GB2304387A
Application number: GB9616688A
Authority: GB
Inventors: Paul Roberts
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1995-08-18
Filing date: 1996-08-07
Publication date: 1997-03-19
Anticipated expiration: 2016-08-07
Also published as: GB2304387B; GB9616688D0; GB9516922D0; DE19632917A1; DE19632917B4

Description

2304387 1 BRAKE ADJUSTER MECHANISM This invention relates to an adjuster

mechanism for a brake, primarily for use on a vehicle, and having an adjuster shaft of which an end portion is accessible from the exterior and operable to re-wind or cle- adjust the adjuster to permit removal and replacement of the brake friction elements and/or other servicing procedures.

In some conventional adjuster mechanisms having such a de-adjustment facility, there is a danger of excessive manual de-adjustment of the mechanism leading to locking together of internal components thereof, resulting in the mechanism becoming inoperative in normal use.

An attempt has been made to solve this problem by providing a weakness or rupture point in the adjuster shaft of such a mechanism so that shearing takes place at a predetermined excessive torque applied to the shaft in the de-adjustment direction. This is disadvantageous in that the sheared shaft has to be replaced, requiring stripping and re-building of the adjuster after each shaft shearing.

An object of the invention is to provide an adjuster mechanism in which the application of excessive torque to the adjuster components, which may result in damage to the adjuster or other components, is prevented in a simple and convenient manner.

According to the invention, an adjuster mechanism comprises a housing containing an adjuster shaft of which an end portion is accessible from the exterior of the housing and operable to re-wind or de-adjust the 2 adjuster, and a torque-applying element engaged or engageable with the adjuster shaft and via which torque may be applied to the shaft for rewind or de-adjustment, the element being such that the application via the element to the shaft of re-wind torque of a predetermined value results in deformation of the element in such a manner as to prevent or reduce further torque application to the shaft.

The element is preferably in the form of a plug fitting closely within a part of the adjuster housing surrounding a portion of the adjuster shaft, the plug having a first formation engaged or engagable with a formation on the adjuster shaft portion to form a first connection, and a second formation accessible from the exterior of the housing for engagement by a torque-applying tool to form a second connection, said first and/or second connection being interrupted by deformation of the element upon the application to the adjuster shaft of torque higher than the predetermined value. The torque at which such interruption occurs is lower than that which would cause jamming of or damage to the adjuster or other brake components.

Conveniently, the element may be yieldably urged away from a position in which it forms the first connection.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is a side view, partly in cross-section, of part of an adjuster mechanism of the invention; 3 Figure 2 is a perspective view of a component of the mechanism of Figure 1; Figure 3 is a view similar to Figure 1 illustrating an alternative embodiment; Figure 4 is a view similar to Figures 1 and 2 illustrating another alternative embodiment, and Figure 5 is a view similar to Figures 1, 3 and 4 illustrating a further alternative embodiment.

Figures 1 and 2 illustrate part of a brake adjuster mechanism, of which an adjuster shaft 1 can be seen rotatably mounted within an adjuster housing 2. The lower end of the shaft 1 extends into cooperative relationship with components of an automatic adjuster which may be of any appropriate conventional kind and will not be further described. An upper end portion of the shaft 1 forms a square drive formation 3 for the purpose to be described. The housing 2 is provided with an internal cavity 4 surrounding the upper end portion of the shaft 1, which cavity may contain a seal (not shown) acting between the shaft and housing. The open end of the cavity is closed by a plug 5 which is formed with a peripheral groove 6 containing a resilient ring 7, of rubber or elastomeric material, forming a seal between the plug and adjacent wall of the housing 2. The plug 5 is formed with an internal square cavity 3A complementary with and receiving therein the square formation 3.

As can be seen more clearly from Figure 2, the plug 5 has a peripheral surrounding flange 8 which rests against an upper surface of the housing 4 2 when the plug is installed, as illustrated in Figure 1. The plug 5 has a generally cylindrical portion 9 extending longitudinally from the flange 8 and having the groove 6 formed therein. The lower end part of the cylindrical portion 9 is divided by a plurality of equi-spaced longitudinal slots 10 to form a plurality of legs 11, each of which is provided with a radially out-turned flange portion 12. The plug 5 is installed in the cavity 4 of the housing 2 by resiliently radially inwardly deforming the legs 11 sufficiently to enable the plug to enter the cavity and sliding it inwardly until the flange portions 12 arrive opposite to an internal groove 13 formed in the cavity wall, into which the flange portions snapengage upon resilient recovery of the legs to render the plug captive within the housing. The spacing between the flange portions 12 and flange 8 is chosen so that the flange 8 comes to bear against the end of the housing when the plug is inserted sufficiently to achieve the aforesaid snap engagement. Insertion of the plug also brings the formation 3 into driving engagement within the complementary opening 3A of the plug. The portion 5A of the plug extending upwardly of the flange 8 is of hexagonal form for engagement by an appropriate turning tool, such as a spanner.

In the particular embodiment described, the plug and adjuster shaft 1 are in permanent driving engagement and rotate together during normal operation of the adjuster. When it is desired to wind back the adjuster in order to de-adjust it, the spanner is applied to the hexagonal formation 5A and the plug 5, together with the shaft 1, are rotated in the de-adjust direction. The material of the plug is chosen so that, for a particular size of hexagon, the plastic will deform at a predetermined torque, selected to be less than that which may result in jamming of the adjuster, causing the spanner to slip and thereby preventing continued rotation of the adjuster shaft. This process will have rendered the plug unserviceable, necessitating its removal from the brake housing, together with its seal 7, a new plug and seal being installed as part of the servicing procedure. It will be seen that the use of the plug in the aforesaid manner avoids overloading and jamming of adjuster components so that the adjuster remains intact and does not necessaril require dismantling and rebuilding as part of a servicing procedure.

In the alternative embodiment illustrated in Figure 3, the square formation 3 of the adjuster shaft 1 is replaced with a cylindrical end portion 14 having a splined external surface 15 engaged with internal splines 16A formed in the plug 5. In this arrangement, resilient legs 16 at the lower end of the plug have in-turned portions 17 engaged within groove 18 of the adjuster shaft below the formation 15. Upon the occurrence of excessive torque during a de-adjust operation, the force applied via the splines to the legs 16 causes the latter to flex outwardly and prevent drive from the plug 5 being applied to the shaft 1.

Figure 4 illustrates another alternative embodiment in which the arrangement of the shaft 1 is similar to that illustrated in Figure 1 in that it carries a square section drive formation 3 at its upper end for engagement with a complementary recess 3A in the plug 5. The remaining details of the plug 5 are also similar to that of Figure 1. The principal difference as compared with the Figure 1 arrangement is that the adjuster housing 2 is formed with opposed internal shoulders 2A, 213 and the plug 5 is urged upwardly by a spring 20 to a position governed by abutment of the legs 16 of the plug against the shoulder 2A, the spring acting between the legs and the shoulder 2B. In its illustrated position, the plug 5 is disengaged from the adjuster shaft 1 which can 6 therefore rotate freely independently of the plug when operational. When a brake de-adjustment operation is required, the plug 5 is depressed inwardly against the action of the spring 20 to engage the recess 3A with the adjuster shaft formation 3, enabling the adjuster to be wound back by application of a spanner to the projecting portion of the plug 5 until the hexagonal formation deforms, at a predetermined torque, to preclude further de-adjustment, as previously.

The further alternative embodiment illustrated in Figure 5 has an adjuster shaft similar to that illustrated in Figure 3 with a splined free end portion 15 which normally resides within a cavity 21 of the plug 5 of larger diameter than the splined portion 15. The plug 5 is provided, above the portion 15, with a further cavity 22 containing a spring 23 which acts between the base 24 of that cavity and the top of the portion 15, thereby urging the plug and adjuster shaft apart to the extent limited by engagement of the legs 16 of the plug with the underside of a flange 25 on the adjuster shaft. For a de-adjustment operation, the plug is urged inwardly against the action of the spring 23 to bring internal splines 26 of the cavity 24 into engagement with the externally splined portion 15 of the adjuster shaft, enabling the latter to be rotated by application of rotational force to the plug by way of a spanner, for example. The splined portion 15 is arranged to slip relative to the splines 26 as a result of deformation of the plug material at a predetermined torque, thereby preventing jamming of the adjuster in the manner referred to previously.

in a further alternative embodiment, the shaft 1 may be an auxiliary manual adjuster shaft normally disengaged from the adjuster but moved axially into engagement therewith to effect de-adjustment. In such an 7 arrangement, the plug and shaft may be permanently engaged and moved together axially when de-adjustment is required, protection against overadjustment resulting from deformation of the plug material, as previously.

It will be understood that the mechanism of the invention may vary in many respects from the embodiments described above. For example, the plug may be provided with any convenient number of legs having any convenient shape for engagement with the housing or adjuster shaft and the external form of the plug for engagement by an appropriate turning tool may have any suitable alternative form such as splines or slots.

The invention will be seen to solve the problem of excessive adjuster torque during de-adjustment in a particularly simple and convenient manner by ensuring that the adjuster shaft itself is not excessively rotationally loaded. A further advantage of the described embodiments that the result is achieved by adaptation of a plug which normally acts solely as a dust cover.

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Claims

1. An adjuster mechanism comprising a housing containing an adjuster shaft of which an end portion is accessible from the exterior of the housing and operable to re-wind or de-adjust the adjuster, and a torque-applying element engaged or engageable with the adjuster shaft and via which torque may be applied to the shaft for re-wind or de adjustment, the element being such that the application via the element to the shaft of re-wind torque of a predetermined value results in deformation of the element in such a manner as to prevent or reduce further torque application to the shaft.

2. An adjuster mechanism according to Claim 1, wherein the element is in the form of a plug fitting closely within a part of the adjuster housing surrounding a portion of the adjuster shaft, the plug having a first formation engaged or engagable with a formation on the adjuster shaft portion to form a first connection, and a second formation accessible from the exterior of the housing for engagement by a torqueapplying tool to form a second connection, said first and/or second connection being interrupted by deformation of the element upon the application to the adjuster shaft of the predetermined re-wind torque.

3. An adjuster mechanism according to Claim 1, or Claim 2, wherein the element is provided with longitudinally extending resilient legs arranged so as to be deformed during insertion of the element into the housing and to recover resiliently to bring portions thereof into a locking position in which they co-act with a surface within the housing or on the shaft serving to retain the plug permanently in the housing.

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4. An adjuster mechanism according to Claim 3, wherein the element is retained with said first formation in permanent engagement with the shaft formation.

5. An adjuster mechanism according to Claim 2, wherein the element is permanently retained within the housing and resiliently urged to a position in which said first and second formations are mutually disengaged, the element being movable longitudinally within the housing to bring the formations into engagement when de-adjustment is required.

6. An adjuster mechanism according to any one of Claims 1, 2, 5 and 5, wherein the element is retained permanently within the housing by the cooperation of an inwardly projecting portion thereof with a formation on the shaft.

7. An adjuster mechanism according to Claim 3, wherein the element is provided with a radially projecting flange spaced longitudinally from the leg portions so as to lie against an outer axially facing surface of the housing when said portions are in their locking positions.