Abstract:
A seal device for use in sealing between parts of a thrust assembly of a disc brake has a support element ( 31 ) adapted to be carried by a first part ( 25 ) of the thrust assembly, the support element ( 31 ) carrying a seal ( 33 ) arranged so that, with the support element ( 31 ) in its position of use on the first part ( 25 ), the seal ( 33 ) engages a surface of a second part ( 25 ) of the thrust assembly in sealing relationship. Also disclosed is a thrust assembly for a disc brake and a disc brake incorporating such an assembly.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a seal device for use in sealing between parts of a thrust assembly of a disc brake, primarily for a motor vehicle, and to a disc brake incorporating the seal device and thrust assembly. 
   One conventional type of thrust assembly, in the form of an adjustable tappet assembly, has a pair of threadedly interengaged parts forming a strut of which the length can be varied by relative rotation between the parts to perform a brake adjustment, in use. In order to provide the necessary sealing between the relatively rotatable strut parts and between the strut parts and adjacent surfaces, it has been necessary to provide multiple seals, together with inserts for the retention and/or support of the seals, as well as to effect machining of the parts to provide adequate sealing surfaces for engagement by the various seals. Such arrangements are complicated to manufacture and assemble, giving rise to relatively high costs. 
   An object of the invention is to provide a simpler and more cost-effective seal device for use in a thrust assembly of a disc brake, as compared with the aforesaid conventional arrangements. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the invention, a seal device for use in sealing between parts of a thrust assembly of a disc brake comprises a support element adapted to be carried externally by a first part of the thrust assembly, the support element carrying a seal arranged so that, with the support element in its position of use on the first part, the seal engages a surface of a second part of the thrust assembly in sealing relationship. 
   In one convenient arrangement, an outer surface of the support element serves, in use, for engagement by a further seal carried by adjacent structure. 
   Preferably, the support element is in the form of a cap having a generally annular skirt adapted to fit, in use, over an end portion of the first element, the outer surface of the skirt serving for engagement by said further seal. 
   According to another aspect of the invention, a seal device for use in sealing between parts of a thrust assembly of a disc brake comprises a support element adapted to be carried by a first part of the thrust assembly, the support element carrying a seal arranged so that, with the support element in its position of use on the first part, the seal engages a surface of a second part of the thrust assembly in sealing relationship, the support element being arranged so that an outer surface thereof serves, in use, for engagement by a further seal carried by adjacent structure. 
   Preferably, the support element is carried externally by said first part of the thrust assembly and is conveniently in the form of a cap having a generally annular skirt adapted to fit, in use, over an end portion of the first element, the outer surface of the skirt serving for engagement by said further seal. 
   According to a further aspect of the invention, a thrust assembly comprises a pair of relatively movable parts, and a seal device which has a support element carried externally by a first of said parts, the support element carrying a seal arranged to engage a surface of a second of said parts in sealing relationship. 
   Conveniently, an outer surface of the support element provides a sealing surface engaged by a further seal carried by adjacent structure. 
   The support element is preferably in the form of a cap having a generally annular skirt fitted over an end portion of the first element, the outer surface of the skirt providing the sealing surface engaged by the further seal. 
   According to a yet further aspect of the invention a thrust assembly comprises a pair of relatively movable parts, and a seal device which has a support element carried by a first of said parts, the support element carrying a seal arranged to engage a surface of a second of said parts in sealing relationship, the support element being arranged so that an outer surface thereof serves, in use, for engagement by a further seal carried by adjacent structure. 
   Preferably the support element is carried externally by said first part and is conveniently in the form of a cap having a generally annular skirt fitted over an end portion of the first element, the outer surface of the skirt providing the sealing surface engaged by the further seal. 
   The invention will now be described, by way of example, with reference to the accompanying drawings in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view, partly in cross-section, of one form of the brake of the invention; 
       FIG. 2  is a cross-section alone line A—A of  FIG. 1 , and 
       FIG. 3  is an enlarged cross-sectional view of a thrust member forming part of the brake of  FIGS. 1 and 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 and 2  of the drawings, the illustrated disc brake has a fixed carrier  1  which carries a pair of friction elements  2  and  3 , such as friction pads, disposed respectively at either side of a brake disc  4 . The carrier  1  serves to mount the brake on a vehicle and to absorb torque sustained by the pads during a braking operation. A clamp member or caliper  5  straddles the brake disc and is mounted on the carrier  1  so as to be slidable axially of the brake disc relative to the carrier  1 , by way of pins  6 , in conventional manner. The caliper  5  carries an integral housing  7  which is adapted to mount a conventional air or other power actuator (not shown) on an external face  8  thereof. The housing  7  defines a chamber  9  within which a pivotal brake actuating lever  10  may conveniently perform an angular reciprocal swinging movement, as indicated by the arrows ( FIG. 2 ), under the action of a thrust member of the power actuator which, with the latter mounted on the external face  8 , extends through an opening  11  of the housing  7  into engagement with a recess  12  of the brake actuating lever  10 . The brake actuating lever  10  is integral with or attached to a rotary actuating member  13  which is rotatably supported within the caliper by way of a pair of needle bearing assemblies  14 . The rotary actuating member  13  is recessed to house respective cylindrical rollers  15  and  16 , the axes of which are offset from the rotary axis of the rotary actuating member  13  to form an eccentric actuating arrangement with the cylindrical rollers  15  and  16  bearing against respective thrust members  17 A and  18 A of adjacent adjustable tappet assemblies  17  and  18 . Rotation of the brake actuating lever  10  and its connected rotary actuating member  13  causes actuating thrust to be applied via the tappet assemblies to the directly actuated friction element  2 , and by a reaction via the caliper  5 , to the indirectly actuated friction element  3 . 
   The thrust assemblies, illustrated as adjustable tappet assemblies  17  and  18 , are disposed at either side of a center line of the brake passing through the brake actuating lever  10  and are associated with an adjuster assembly  19  which lies laterally offset from and adjacent the adjustable tappet assembly  18 . The adjuster assembly may be of any appropriate conventional type needing no detailed description for the purpose of the present invention. The adjuster responds to excessive movement of the friction elements  2  and  3  and produces resultant rotation of an adjuster shaft  20  which, via an output gear  21  and an intermediate idler gear  21 A, rotates a pair of input gears  22  and  23  associated respectively with the adjustable tappet assemblies  17  and  18 . 
   The adjustable tappet assemblies  17  and  18  are of identical construction and operation, and only the adjustable tappet assembly  17  will be described, with reference to  FIGS. 1 and 3 , in sufficient detail for a full understanding of the present invention. This assembly has an outer sleeve  24  which includes internal threads  24 A and receives a hollow internal shaft  25  having an externally threaded portion  25 A extending over a part of its length for cooperation with the internal thread of the outer sleeve  24 . The hollow internal shaft  25  and the outer sleeve  24  form between them an adjuster strut of variable length. The hollow internal shaft  25  is provided, at its outer end, with a tappet head  26 , which bears against the adjacent friction element  2  and which is releasably coupled to the shaft so as, conveniently, to be freely rotatable relative to the latter. To enable the hollow internal shaft  25  to be moved axially by rotation of the outer sleeve  24  so as to extend the adjuster strut in compensation for wear of the friction elements, it is necessary to lock this shaft against rotary movement. This is achieved, in the present embodiment, by providing the thrust member  17 A, which is engaged over the adjacent end of the outer sleeve  24 , with an elongate stem  27  of non circular cross-section which extends within the hollow internal shaft  25 , of which at least a part  25 B of the internal surface forms a complementary bore. The thrust members  17 A and  18 A of the respective tappet assemblies are each provided with, for example, a generally planar external surface for locking engagement with a corresponding adjacent surface on a fixed plate  28 . 
   The present invention is concerned particularly with improving the sealing arrangement between the outer sleeve  24  and inner shaft  25 . To this end, as can be seen in  FIG. 3 , an end portion of the sleeve  24  adjacent the tappet head  26  is relieved to provide a reduced diameter portion  29 , which carries a support element  31  of a seal device, the element  31  being in the general form of a cap. An annular skirt or flange  30  of the support element is received over the portion  29 , conveniently by press-fitting. The inner shaft  25  extends through a flat annular base  32  of the support element which rests against the adjacent end of the sleeve  24  and carries a seal, of which an annular rim  33  is housed within the portion  32 . An annular lip  34  of the seal engages the outer surface of the shaft  25  in sealing relationship. The support element  31  may conveniently be manufactured from stainless steel. A metal retainer  35  has a first annular portion  36 , which is a press fit in the caliper  5 , and to which is attached a further lip seal  37  engaging the outer surface of the annular skirt  30  of the support element  31 , such outer surface providing a smooth sealing surface for cooperation with the lip seal  37 . The retainer  35  has a further annular portion  38  lying against an adjacent surface of the caliper  5 , the remainder of the retainer forming an annular channel  39  to receive a bead  40  of a main convoluted boot seal  41 , a further bead  42  of which is received within a groove of the tappet head  26 . 
   The above-described sealing device  31  is particularly advantageous in terms of its simplicity and effectiveness in providing a high integrity seal between the sleeve  24  and shaft  25  and also in providing a smooth sealing surface on its cylindrical part  30 , for engagement by the further seal  37 , thereby largely obviating the necessity for high quality expensive machining and/or plating of the outer surface of the sleeve  24  for sealing purposes. 
   It will be understood that the annular lip  34  and the further lip seal  37  may be of any convenient form and retained in any convenient manner on their respective support element  31  and metal retainer  35  which, in turn, may have any convenient shape whilst retaining their essential purpose according to the invention. 
   The flat annular base  32  may conveniently provide stop means for limiting the axial movement of the tappet assembly at extremes of adjustment. 
   The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described. For that reason the following claims should be studied to determine the true scope and content of this invention.