Title of Invention

AUTOMATIC BRAKE ADJUSTER

Abstract

An automtic adjuster has a strut with a pair of threadedly engaged strut parts (13, 14), the length of the strut being variable by relative rotation between the parts under the influence of an adjuster device responding to excessive shoe wear, the adjuster device includes an adjuster element (1B) operatively connected lo one of the strul parts and having a formation (36) connecting it to a uni-directional device (3.5) acting to prevent de-adjusting movement of the adjuster element whilst permitting adjusting movement thereof, A manual adjuster shats (24) is normally held in a non-operative position and provides, a formation (27, 28) for cooperation with that on the adjuster element, movement of the shalt to engage the formations causing the uni-directional device to free THE adjuster element for de-adjusting rnovement PRICE: THIRTY RUPEES

Full Text

This Invention relates to an automatic brake adjuster, primarily for a vehicle brake, operable to maintain a substantially constant clearance between the braking surfaces respectively of a braking element and a rota table braking member of the brake, the adjuster being of the kind conprising a strut having two parts between which there is a non-reversible screw threaded connection permitting the effective length of the strut to be increased by relative rotation between the parts under the influence of an adjuster device operable in response to the occurrence of excessive clearance between said surfaces. One form of adjuster of this kind as applied to a shoe drum brake is known and it is an object of the present invention to improve and simplify certain aspects of such an adjuster. According to the invention, an automatic brake adjuster comprises a strut having two parts between which there is a non-reversible screw threaded connectionpermitting the effective length of the strut to be increased by relative rotation between the parts under the influence of an adjuster device operable in response to the occurrence of excessive clearance between said surfaces, the adjuster device including an adjuster element operatively connected to one of the strut parts and providing a first connecting formation serving to connect the element to a unidirectional device acting to prevent movement of the adjuster element in a direction such as to cause de-adjustment of the strut, whilst permitting movement thereof in a direction allowing strut adjustment , and a manual adjuster shaft normally held in a non-operative position and providing a second formation capable of forming a rotary driving connection with the first formation when the shaft is moved to an operative position, the arrangement being such that as the first and second formations are brought into engagement to form said driving connection, the uni-directional device is caused to free the adjuster element for movement in a de-adjustment direction by operation of the manual adjuster shaft. According to another aspect of the invention, an automatic brake adjuster comprises a strut having two parts between which there is a non-reversible screw threaded connection permitting the effective length of the strut to be increased by relative rotation between the parts under the influence of an adjuster device operable in response to the occurrence of excessive clearance between braking surfece of a brake characterised in that the adjuster device having an adjuster element rotatably mounted in a housing of the adjuster and being separate from and operatively connected to one of the stait parts, and a unidirectional device contained within the adjuster housing and acting to prevent movement of the adjuster element in a direction such as to cause de-adjustment of the strut, whilst permitting movement thereof in a direction allowing strut adjustment, the unidirectional device having a tootlied element movable with the adjuster element and a relatively fixed housing element containing the toothed element and having a ratchet formation engaged with the toothed element. Preferably, the housing element and toothed element are arranged to form a self-contained unit for assembly into the adjuster. The invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is an elevation of part of a vehicle internal shoe drum brake with the drum removed. Figure 2 is a longitudinal cross-section of an actuator installed in the brake of Figure 1; Figure 3 is a fragmentary view, partly in cross-section, of part of an automatic adjuster of the invention installed in the actuator of Figure 2; Figure 4 is a reduced scale exploded view of part of the adjuster of Figure 3; Figure 5 is a fragmentary view, partly in cross-section, of an alternative form of the adjuster of the invention and Figure 6 is a reduced scale escploded view of part of the adjuster of Figure 5, The shoe drum brake illustrated in Figure 1 has a pair of arcuate brake shoes 1 and 2 mounted on a backplate 3, each shoe having a friction lining 4 for braking engagement with a surrounding rotatable drum (not shown) • The brake is of the leading/trailing type, having an actuator 5 of appro¬priate type* illustrated as a cam actuator mounted on the backplate 3 between one pair of adjacent shoe ends and an abutment device 6 also mounted on or formed integrally with the backplate and disposed between the other pair of adjacent shoe ends* in conventional manner. As can be seen more clearly from Figure 2, the actuator 5 comprises a housing 7 adapted to be fixed to the backplate 3, usually by bolts or the like. A rotary cam 8 is mounted for rotation within the housing 7 and co-operates via struts 9 and inserts 10 with respective tappets*indicated generally at 11, 12, the inserts being press-fitted within the tappets. Each tappet 11, 12 incorporates an adjustable machanism which includes an internally threaded nut 13 through which extends a correspondingly threaded spigot 14 projecting from a larger diameter head portion 15 of the tappet, the nut and spigot together constituting a strut of which the length may be varied by relative rotation of the nut and spigot in order to alter the retracted position of the adjacent brake shoe in response to wear of the shoe friction lining. The adjacent shoe abuts the nut 13, thereby effectively preventing rotation of the latter, so that, in this embodimant, the length of the strut is variable by rotating the spigot 14 in the manner to be described. The external surface of the head 15 is formed with helical gear teeth 16 which mesh with similar teeth 17 on an end portion of an adjuster member in the form of a spigot 18 mo'.'nted in the housing 7 for rotation about an axis at right angles to that of the tappet 11, One particular form of the adjuster member and its associated mechanism is illustrated in more detail in Figures 3 and 4, The spigot 18 is provided with axlally spaced journal portions 18A, 18B which are engaged respectively in correspondingly sized portions of a through bore 19 of the housing to mount the shaft rotatably therein. The helical teeth 17 are arranged between the spigot portions 18A, 18B and mesh with the teeth 16 of the tappet head 15 (Figure 2) , as described above. A further cylindrical spigot portion 18C projects from the portion 18B and lies closely within an aperture formed in an end wall of a hollow cam 20 which lies within the bore 19 closely adjacent the wall thereof and acts to support the shaft 18 axlally of the housing. The free end of the cam 20 is provided with one or more axial tongues 20A each of which engages within a complementary peripheral formation 21 on an end closure member 22 at the outer end of the bore 19 so that the cam 20 is held thereby against rotation. Alternatively, the cam 20 may be foreshortened to lie just clear of the end member 22 and thus be free to rotate, A cylindrical extension 23 of the member 22 acts as a rotairy bearing for a manual adjuster shaft 24 having an enlarged head 25 lying within the bore 19 adjacent the end member 22. The head 25 is provided with castellations 26 resulting from the formation on its inner end portion of a pair of mutually perpendicular slots 21, 28, for the purpose to be described. The outer end of the shaft 24 is provided with a hexagonal formation 29 to which a spanner or the like may be applied to turn the shaft, when required for manual adjustment. Arranged within the cam 20 is an inner hollow generally cylindrical cam 30 having a base 31 through which is formed a circular opening 32, As can be seen more clearly from Figure 4, the cam 30 is provided with three equi-angularly spaced slots 33 in its peripheral wall forming arms 33A, and the base 31 is slit radially from its outer edge over a short distance within the peripheral extent of each slot 33, the respective base portions at corresponding sides of each radial slitting being inwardly upset to form downwardly projecting teeth 34. A generally plate-like ratchet member 35 is housed within the cam 30 and is rotationally coupled to the adjuster shaft 18 by a nose 36 of generally oblong cross-section projecting from the inner end of the shaft into engagement with a correspondingly shaped slot 36A in the ratchet member. The ratchet member 35 is provided around its periphery with teeth 37 which co-operate with the down¬wardly projecting teeth 34 of the caro 30, against the base 31 of which the ratchet member lies. An additional ratchet conponent in the form of a ratchet plate 38 is disposed at the opposite side of the ratchet member 35 and is slit and upset in a similar manner to the base of the cam 30 in order to provide teeth 39 projecting ratchet member towards the for engagement with the teeth thereof. The teeth 39 are arranged in relation to those 34 of the cam 30 so that each tooth 39 lies between a different pair of teeth 34 and equl-dlstantly from the teeth of each pair, thereby effectively making available six equi-spaced teeth for co-operation with the teeth 37 of the ratchet member 35. The ratchet plate 38 has an axially projecting flange 40 which rests on the inner end of the adjuster shaft 24 and a spring 41 acts between the inner end of the cam 20 and the outer surface of the can 30 to urge the assembly 30, 35, 38 towards the inner end of the shaft 24 and thereby hold the latter against the inner end of the closure member 22, The ratchet plate 38 has three radial arms 38A spaced angularly so as to lie within the slots 33 of the cam 30 and thereby couple the plate 38 rotationally to the cam 30, In an alternative arrangement, the spring 41 is arranged as illustrated in Figure 3 and an additional spring acts between the inner end of the shaft 24 and the ratchet plate 38, loading plate 38 against the ratchet member 35 and hence the member 35 against the cam 30 to increase the load on the ratchet components. It also urges the shaft 24 against the inner end of the closure member 22, For manual operation, both springs partially collapse to permit engagement of the formations 27 or 28 of the shaft 24 with the adjuster shaft formation 36 and also freeing of the cam 30 from the member 22 to disable the ratchet mechanism. One advantage of the present arrangement is that the cam 30, ratchet member 35 and ratchet plate 38 may be assembled together to form a self-contained unit for subsequent assembly into the outer cage 20, This is achieved by forming one or more pips 42 in the arms 33A of the ca^" 30 and forcing the coroponents 35 and 38 into the cam 30 past the pips, which are capable of limited radially out¬ward displacement due to the resilience of the arms 33A, Resilient recovery of the arms returns the pips inwardly to perform the aforesaid retaining function. This arrange¬ment considerably facilitates assembly of the adjuster on an assembly line. A further sub-assembly can be formed by first inserting the sub-assembly 30, 35, 38 within the cam 20 and then securing the cams 30 and 20 to the end cap 22 after assembly of the shaft 24 in the latter, the cam 20 being press-fitted on to the end cap. This enables the entire adjuster mechanism and manual adjuster shaft to be assembled into the housing 5 as a unit and the required connections to be made with the adjuster shaft 18 already placed therein. This further improves assembly rates on an assembly line. Actuation of the brake by rotation of the cam 8 causes the tappets 11 and 12 to be urged outwardly in order to separate the shoes 1 and 2 into braking engagement with the brake drum, A predetermined amount of backlash is provided between the teeth 16 and 17 respectively on the tappet head portion 15 and adjuster shaft 18, and by other clearances in the mechanism, in order to permit sufficient separation of the shoes to take up the maximum desired shoe to drum clearance without causing operation of the automatic adjuster. When wear of the friction linings 4 becones such that the shoe movement exceeds this maximum clearance, the corresponding excessive axial movement of the tappet 11 causes the adjuster shaft 18 to rotate and thereby in turn rotate the ratchet member 35 disposed between the teeth respectively on the cam 30 and ratchet plate 38, Since the ratchet wheel engages with the three spaced teeth on the cam 30, or those on the ratchet plate 38, a relatively small excessive lining wear will cause the ratchet wheel to click past one or more of these sets of teeth alternately, providing a fine, degree of adjustment. When the brake is released, the adjuster shaft 18 is held stationary in a new position by the ratchet wheel locking against either the cam 30 or ratchet plate 38, This causes the axial return movement of the adjuster tappet to wind out the tappet screw 11 In a direction such as to lengthen the strut 11, 13 and retain the retracted shoe in a new outwardly adjusted position. When manual de-adjustment is required, the manual adjuster shaft 24 is pushed inwardly and by bearing against the cylindircal part 40 of the ratchet plate 38, pushes the whole of the assembly 38, 35, 30 inwardly against the spring 41, enabling the nose 36 of the adjuster shaft 18 to engage within one of the slots 27, 28 of the shaft 24 and thereby provide a driving coupling between the shafts 24 and 18, Simultaneously, the free ends of the legs 33A of the cam 30 become disengaged from the end member 22, leaving the aforesaid assembly free for rotation. The interconnected shafts 24 and 18 may now be rotated in an appropriate direction in order to effect de-adjustment by applying a suitable tool to the hexagonal formation 29 at the outer end of the shaft 24. When the axially inward force on the shaft 24 is released, the spring 41 acts to restore the coiTtponents to their rest positions illustrated in Fugure 3. In the alternative embodiment described in Figures 5 and 6, the general arrangement of the adjuster shaft 18, the manual adjuster shaft 24 and end member 22 are generally similar to the corresponding items in Figure 3, but the adjuster mechanism itself is considerably sinplified. The mechanism again includes an outer cage 20 which, at its inner end, surrounds the cylindrical boss 18C of the adjuster shaft 18, and extends longitudinally as far as the end member 22, where castellated portions 20A of its outer periphery engage in corresponding grooves formed in the end member to preclude rotation thereof, the cage being press-fitted onto the end member for axial retention also. Alternatively or additionally, the outer end portion of the cage may be formed with radially inwardly formed tags for engagement in the grooves of the end member. The main component of the adjuster mechanism is a ratchet wheel 50 which includes a cylindrical boss 51 and a peri¬pheral radial flange 52 of which the outerperipheral edge is formed with ratchet teeth 53. The ratchet wheel is urged longitudinally of the housing by a spring 54 of which one end engages the end of the cage 20 and the other surrounds the boss 51 of the ratchet wheel and engages the flange 52 thereof to urge the wheel against the adjacent end of the manual adjuster shaft 24 and thereby maintain this shaft in its rest position against the inner surface of the end member 22. The cage 20 is formed at a first axial distance with a plurality of ,e,g. three equi-angularly spaced inwardly directed teeth 55 located so that all three of the ratchet teeth 55 engage with the teeth 53 at any one time. At another axial location nearer to its free end, the cam 20 is formed a further plurality of inwardly, directed teeth 56 which, in the same way as the pips 42 of the previous embodiment, enable the ratchet wheel to be assembled through the open end of the cam by resilient deformation of the teeth 56 and be retained by these teeth following their resilient recovery. The cage 20 thereby encapsulates the ratchet wheel 50 and the spring 54 to form a self-contained assembly, as before. As can be seen more clearly from Figure 6, the boss 51 of the ratchet wheel 50 is provided with a generally rectangular opening 57 which matches the cross-sectional form of the nose 36 of the adjuster shaft 18 so as to be rotationally connected to the latter. The operation of the adjuster is imilar to that described previously, in that excessive outward movement of the actuator tappet causes rotation of the adjuster shaft 18 and ratchet wheel 51, causing the teeth 53 to click over the teeth 56 on the cam. Once this occurs, return move¬ment of the adjuster shaft is precluded, causing rotation of the adjuster tappet upon brake retraction to lengthen the adjuster strut and set a new retracted position of the brake shoe, as described previously. Manual de-adjustment is effected by pushing the shaft 24 and conse- quently the ratchet wheel 50 axially inwardly against the action of the spring 44, until one of the slots 27, 28 of the cruciform arrangement at the inner end of the adjuster shaft engages with the nose 36, which now projects beyond the inner end of the ratchet wheel. The ratchet wheel will now have moved axially inwardly far enough to move the teeth 4 3 clear of the teeth 4 5, permitting the wheel and adjuster shaft to be rotated freely in either direction, but usually in the de-adjustment direction. Release of the shaft enables the components to return to their rest positions shown in Figure 5. We Claim 1. An automatic brake adjuster comprising a strut having two parts between which there is a non-reversible screw threaded connection permitting the effective length of the strut to be increased by relative rotation between the parts under the influence of an adjuster device operable in response to the occurrence of excessive clearance between braking surfaces of a brake, characterised in that the adjuster device having an adjuster element rotatably mounted in a housing of the adjuster and being separate from and operatively connected to one of the strut parts, and a unidirectional device contained within the adjuster housing and acting to prevent movement of the adjuster element in a direction such as to cause de-adjustment of the strut, whilst permitting movement thereof in a direction allowing strut adjustment, the unidirectional device having a toothed element movable with the adjuster element and a relatively fixed housing element containing the toothed element and having a ratchet formation engaged with the toothed element 2. An adjuster according to Claim 1, wherein the housing element and toothed element are arranged to form a self-contained unit for assembly into the adjuster housing. 3. An adjuster according to Claim 1 or Claim 2, wherein a first part of the ratchet formation of the housing element is on an axially facing wall of the latter which forms a first ratchet element at one side of the toothed element a second ratchet element being disposed within the housing element and having a second part of the ratchet formation thereon at the other side of the toothed element. 4. An adjuster according to Claim 3, wherein the toothed element, housing element and second ratchet element are arranged to form a self-contained assembly. 5. An adjuster according to Claim 3 or Claim 4, wherein the second ratchet element is keyed to the housing element by at least one projecting formation thereof engaging in a corresponding opening in the housing element. 6. An adjuster according to any one of Claims 3 to 5, wherein the toothed element has a series of teeth around its periphery, each of a plurality of ratchet formations of each ratchet element respectively being arranged to engage different teeth of the toothed element successively. 7. An adjuster according to Claim 1 or Claim 2. wherein the toothed element has peripheral generally radially projecting ratchet teeth engaging generally radially inwardly projecting teeth formed on the surrounding housing element. 8. An adjuster according to Claim 7, wherein the toothed element has a boss providing a rotary connection with the adjuster element and a generally radial peripheral flange carrying the projecting teeth, 9. An adjuster according to Claim 7 or Claim 8, wherein the housing element has at least one further generally radially inwardly projecting information axially spaced from the ratchet teeth and serving to retain the toothed element within the housing element. 10. An automatic brake adjuster according to any one of Claims 1 to 6 and 7 to 9, wherein the adjuster element provides a first connecting formation serving to connect the element to the uni-directional device, and a manual adjuster shaft normally held in a non-operative position provides a second connecting formation capable of forming a rotary driving connection with the first formation when the shaft is moved to an operative position, the arrangement being such that as the first and second formations are brought into engagement to form said driving connection , the uni-directional device is caused to free the adjuster element for movement in a de-adjustment direction by operation of the manual adjuster shaft. 11. An adjuster according to Claim 10, wherein the said first connecting formation connects the adjuster element to the toothed element of the unidirectional device, the anrangement being such that movement of the manual adjuster shaft to bring the first and second formations into operative engagement moves the housing element to a position in which it is free for rotation with the toothed element , thereby freeing the adjuster element for movement in a de-adjustment direction. 12. An adjuster according to Claim 11, wherein the toothed element has radially projecting teeth which cooperate with teeth on an axially facing surface of the housing element. 13. An adjuster according to Claims 11 or Claim 12, wherein the toothed element has radially projecting teeth which cooperate with teeth on a radially facing surface of the housing element. 14. An adjuster according to any one of Claims 10, 11 or 13, wherein the housing element is a hollow sleeve surrounding the toothed element. 15. An adjuster according to any one of the claims 11 to 14, wherein the toothed element and housing element are arranged to form a self-contained assembly, 16. An automatic brake adjuster substantially as hereinbefore described with reference to Figures 2,3 and 4 or Figures 2.5 and 6 of the accompanying drawings.

Documents:

1410-mas-1995 abstract.jpg

1410-mas-1995 abstract.pdf

1410-mas-1995 claims.pdf

1410-mas-1995 correspondence-others.pdf

1410-mas-1995 correspondence-po.pdf

1410-mas-1995 description (complete).pdf

1410-mas-1995 drawings.pdf

1410-mas-1995 form-13.pdf

1410-mas-1995 form-2.pdf

1410-mas-1995 form-4.pdf

1410-mas-1995 form-6.pdf

1410-mas-1995 form-62.pdf

1410mas95.jpg