Abstract:
An actuator ( 13 ) device for a disc brake ( 4 ) is provided comprising a rotary actuator ( 13 ) operable, via a force transmission device ( 17, 18 ), to move a friction element ( 2 ) of the brake, in use, into engagement with a rotary brake disc ( 4 ), and a thrust member ( 17 A,  18 A) arranged to transmit force from the actuator ( 13 ) to the force transmission device ( 17, 18 ), the actuator ( 13 ) being arranged to engage the thrust member ( 17 A,  18 A) in a manner such as to prevent rotation of the latter.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an actuator device for a disc brake, primarily for a motor vehicle, the device including a rotary actuator operable, via a force transmission device, to move a friction element of the brake, in use, into engagement with a rotary brake disc. The invention also embraces a disc brake incorporating such an actuator device. 
     SUMMARY OF THE INVENTION 
     Our earlier specification W097/01045 discloses an arrangement in which a thrust member, through which force is transmitted from the actuator to the force transmission device, is held against rotation by engagement with a plate extending between the thrust member and a further such member carried by an adjacent force transmission device associated with the actuator. This arrangement is satisfactory in very large brakes, but cannot easily be accommodated in smaller brakes in which there may be insufficient space in the region of the force transmission device for the convenient incorporation of the aforementioned anti-rotational arrangement. 
     According to the present invention, an actuator device for a disc brake comprises a rotary actuator operable, via a force transmission device, to move a friction element of the brake, in use, into engagement with a rotary brake disc, and a thrust member arranged to transmit force from the actuator to the force transmission device, the actuator being arranged to engage the thrust member in a manner such as to prevent rotation of the latter. 
     Conveniently, the thrust member is received within a recess of the actuator and a defining wall of the recess engages the thrust member to prevent rotation thereof. 
     Typically, the force transmission device includes a pair of threadedly interengaged elements forming part of an extensible adjuster strut, one of the elements being held against rotation by a non-circular formation carried by the thrust member, conveniently in the form of an elongate stem extending into a complementary bore of the element. 
     From another aspect of the invention, there is provided a disc brake incorporating the aforesaid actuator device. 
     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 an end view of one form of the disc brake of the present invention; 
     FIG. 2 is a view from above, partly in cross-section, of the brake of FIG. 1; 
     FIG. 3 is a side view, partly in cross-section, of the brake shown in FIGS. 1 and 2, and 
     FIG. 4 is an enlarged view of a component of the brake of FIGS. 1 to  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The disc brake illustrated in the drawings has a fixed carrier  1  which carries a pair of friction elements, shown as pads  2 ,  3 , disposed respectively at either side of a brake disc  4 , the carrier serving to mount the brake on a vehicle and to absorb torque sustained by the pads during a braking operation. A clamp member or calliper  5  straddles the brake disc and is mounted on the carrier so as to be slidable axially of the brake disc relative to the carrier, by way of pins  6 , in conventional manner. The calliper 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 perform an angular reciprocal swinging movement, as indicated by the arrows, under the action of a thrust member of the power actuator which, with the latter mounted on the face  8 , extends through an opening  11  of the housing into engagement with a recess  12  of the lever  10 . The lever is integral with or attached to a rotary actuating member  13  which is rotatably supported within the calliper by way of a pair of needle bearing assemblies  14 . The member  13  is recessed to house respective cylindrical rollers  15 ,  16 , the axes of which are offset from the rotary axis of the actuating member  13  and form an eccentric actuating arrangement with the rollers  15  and  16  bearing against respective thrust members  17 A,  18 A of adjacent thrust assemblies shown as adjustable tappet assemblies indicated generally at  17  and  18 . Rotation of the lever  10  and its connected member  13  causes actuating thrust to be applied via the tappet assemblies to the directly actuated friction element  2  and, by reaction via the calliper  5 , to the indirectly actuated friction element  3 . 
     An adjuster assembly is indicated generally at  19  and may be of any appropriate conventional type needing no detailed description for the purpose of this invention. The adjuster responds to excessive movement of the friction elements  2 ,  3  and produces resultant rotation of an adjuster shaft  20  which, via an output gear  21  rotates a pair of input gears  22 ,  23  associated respectively with the adjustable tappet assemblies  17 ,  18 . 
     The tappet assemblies are of identical construction and operation and only the assembly  17  will be described in sufficient detail for a full understanding of the invention. This assembly has an outer sleeve  24  which is internally threaded at  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 sleeve  24 . The shaft and sleeve form between them an adjuster strut of variable length. The shaft  25  is provided, at its outer end, with a tappet head  26  which is releasably coupled to the shaft -o as, conveniently, to be freely rotatable relative to the latter. Operation of the adjuster  19  causes rotation of the outer sleeve  24  by way of the gear  21  and, in order to cause the inner shaft  25  to move axially so as to extend the adjuster strut to compensate 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 sleeve  24 , with an elongate stem  27  of non-circular cross-section which extends within the hollow shaft  25 , the internal surface of which forms a complementary bore. As best seen in FIG. 4, the stem  27  is provided with opposed flat surfaces  27 A for engagement with corresponding surfaces within the shaft  25 . 
     As can be seen more clearly from FIG. 4, the thrust member  17 A is of generally rectangular form with four flat edge surfaces  17 B. The thrust member is housed within a recess in the actuating member  13 , which provides at least one planar surface  13 A which engages the adjacent planar surface  17 B of the thrust member so as to hold the thrust member against rotation. This in turn, via the stem  27 , prevents rotation of the inner shaft  25 , so that when the outer sleeve  24  is rotated by the adjuster  19 , the inner shaft performs an axial adjusting movement in a direction such as to extend the strut and thereby compensate for wear of the adjacent friction element. As can be seen from FIG. 3, with the lever  10  in its illustrated rest position, a shaded area A, representing surface  13 A of the actuating member, overlaps the surface  17 B of the thrust member  17 A to prevent rotation of the latter. 
     It will be seen that this arrangement for preventing rotation of the inner shaft  25  is accommodated within the normal dimensions of the actuating member  13  and is therefore compact and particularly suitable for use in a brake of relatively small dimensions. 
     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.