Abstract:
A brake carrier for a heavy vehicle disc brake includes an actuating side carrier portion including a support for an actuating side brake pad having a first material having a first property. The brake carrier also includes a separate reaction side carrier portion having a support for a reaction side brake pad for securement to the actuating side carrier portion. The actuating side carrier portion includes a first material having a first property, and the reaction side carrier portion includes a second material having a second property, wherein the second property differs from the first property.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to United Kingdom Patent Application No. GB 0618416.2 filed on Sep. 19, 2006. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a brake carrier, in particular, a carrier for a heavy vehicle disc brake. 
     Heavy vehicles, such as rigid body trucks, tractor and semi-trailer trucks, and buses may be braked on their steered and unsteered axles, driven and undriven axles by either drum brakes or disc brakes. Drum brake linings and their associated actuation mechanisms are supported on fixed axles or the steering knuckles of steered axles by a bracket welded directly to the axle, which has all the required mounting parts, or via an intermediate bracket welded to the axle with a number of mounting holes for the bolts of a separate support for the linings and actuation mechanism. 
     In the latter case, it is known to provide an adapter plate that is bolted to this intermediate bracket in order that a brake carrier of a sliding caliper disc brake may be mounted to an axle otherwise intended to mount drum brakes. This is particularly useful when a vehicle originally fitted with drum brakes is to be updated to have disc brakes as it enables the original axles to be retained without complex modifications. 
     Disadvantageously, this arrangement adds to the overall weight of the axle and brake without a corresponding increase in strength, and results in additional fixing bolts being used in locations where they are not readily accessible when the axle is installed on a vehicle. 
     Furthermore, it has become apparent in recent years that as clamp forces, and hence frictional forces, in heavy vehicle brakes rise, it is increasingly difficult to produce a brake carrier that is sufficiently strong, light and compact to transmit this load to the vehicle axle, particularly on the actuating side thereof. 
     The present invention seeks to overcome, or at least mitigate the problems of the prior art. 
     SUMMARY OF THE INVENTION 
     Accordingly, one aspect of the present invention provides a brake carrier for a heavy vehicle disc brake, the brake carrier including an actuating side carrier portion including a support for an actuating side brake pad and a separate reaction side carrier portion including a support for a reaction side brake pad for securement to the actuating side carrier portion. The actuating side carrier portion includes a first material having a first property, and the reaction side carrier portion includes a second material having a second property, wherein the second property differs from the first property. 
     A second aspect of the present invention provides a brake carrier for a heavy vehicle disc brake including an actuating side carrier portion including a mounting formation for mounting the actuating side carrier portion to a drum brake bracket and a support for an actuating side brake pad. The brake carrier includes a separate reaction side carrier portion securable to the actuating side carrier portion including a support for a reaction side brake pad. 
     A third aspect of the present invention provides a method of making a carrier having an actuating side portion and a separate reaction side portion. The method includes the steps of: 1) manufacturing the actuating side portion to comprise a first material having a first property, 2) manufacturing the reaction side portion to comprise a second material having a second property distinct from the first property, and 3) assembling the actuating side portion and the reaction side portion together to form a complete carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of a prior art disc brake carrier and adapter assembly; 
         FIG. 2  is an exploded perspective view of a brake carrier and adapter assembly according to one embodiment of the present invention; 
         FIG. 3  is a perspective view of the carrier of  FIG. 2  in an assembled state; 
         FIG. 3A  is a cross-section through the carrier of  FIG. 3  on line  3 A- 3 A; 
         FIG. 4  is a perspective view of the carrier of  FIG. 2  when assembled to an adapter plate; 
         FIG. 5  is an exploded perspective view of a carrier according to a second embodiment of the present invention and a vehicle axle; and 
         FIG. 6  is an exploded perspective view of a portion of a carrier according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , a typical prior art assembly  8  for mounting a carrier  24  of a sliding caliper disc brake (caliper not shown) to an axle  10  having an intermediate bracket  12  intended originally for mounting a drum brake (not shown) to the axle  10 . 
     The axle  10  in this embodiment has a circular cross-section, which defines an axis A, and is shown with the wheel-end portion for the mounting of a wheel bearing and hub omitted for clarity. In other embodiments, the axle  10  may have a square or other suitable cross-section. 
     An intermediate bracket  12  is welded to the axle  10  in the form of a ring extending around a radially outer surface thereof and is provided with a plurality (in this case  15 ) bores  14  therethrough in a direction parallel to the axis A. 
     An adapter plate  16  has a circular aperture  21  therein dimensioned to fit over the axle  10 , and a ring portion  17  surrounds the circular aperture  21 . The ring portion  17  includes a plurality of bores  18  (also  15  in this embodiment) that are aligned with the corresponding bores  14  in the intermediate bracket  12 . The intermediate bracket  12  and the adapter plate  16  are secured together by bolts (usually 6; not shown) inserted through the bores  14  and  18 . 
     The adapter plate  16  further includes first and second wing portions  20  extending in generally opposing directions transverse the axis A. A group of three through-bores  22  is arranged on each wing portion  20  in a triangular configuration, also in a direction parallel to the axis A. An area of the face of the adapter plate  16 , not visible in  FIG. 1 , is machined flat in a plane transverse the axis A. 
     A known, the one-piece “closed frame” carrier  24  is secured to the adapter plate  16  by the insertion of bolts (not shown) through the through bores  22  and into corresponding threaded bores  34  provided in one face of the carrier  24 . Areas  38  of the carrier  24  surrounding the threaded bores  34  (hatched in  FIG. 1 ) are machined flat so that good, accurate contact between the carrier  24  and the adapter plate  16  is achieved. 
     The carrier  24  includes an actuating side portion  26  (or inboard portion) having a supporting recess  30  for an actuating side brake pad (not shown), a relatively thin actuating side bridge portion  31  defining the radially innermost portion of the supporting recess  30 , and threaded bores  36  on either side of the supporting recess  30  for guide pins (not shown) to slidably mount a brake caliper thereon (not shown). 
     The carrier  24  further includes a reaction side portion  28  (or outboard portion) cast integrally with the actuating side portion  26  and spaced therefrom by arms  29  positioned to extend over the brake disc or rotor (not shown) in use. The reaction side portion  28  includes a supporting recess  32  for the reaction side brake pad (not shown), with a relatively thin reaction side bridge portion  33  defining the radially innermost portion of the supporting recess  32 . 
     When the brake is fully assembled and is applied to slow rotation of the wheel with which it is associated, the actuating side brake pad is directly urged towards the rotor by an actuating mechanism (not shown) housed in the caliper, and the reaction side brake pad is indirectly urged towards the rotor by virtue of a reaction load through the sliding caliper as the actuating side brake pad contacts the rotor. This clamps the rotor between the brake pads and generates circumferential friction or drag torque load that slows the rotor and the wheel. This circumferential load is transmitted from the brake pads to the actuating and reaction side portions of the carrier  24 , and then to the axle  10  via the adapter plate  16  and the intermediate bracket  12 . 
     Prior art carriers  24  are manufactured in a casting process of iron or steel and therefore have substantially homogeneous material properties. As noted above, various areas, such as mating faces  35 , are machined to obtain a smooth surface, as casting inevitably results in a relatively rough surface. The weakest area of the carrier  24  under braking drag loads has been found to be the actuating side bridge portion  31 , as limited space is available at this location, and the thickness of the actuating side bridge portion  31  is typically minimized. Thus, in order to increase an amount of frictional load that can be applied by the brake, it is desirable to increase the strength of the actuating side bridge portion  31 , without increasing its dimensions. 
     Referring to  FIGS. 2 and 3 , a carrier  124  according to a first embodiment of the present invention is shown. Like parts has been labelled by like numerals with the addition of the prefix “1”. Only those differences with respect to the prior art are discussed in great depth. 
     The carrier  124  includes an actuating side portion  126  and a separate reaction side portion  128 . The actuating side portion  126  includes a recess  130  for accommodating an actuating side brake pad and threaded bores  136  for caliper guide pins (not shown). The reaction side portion  128  includes a recess  132  for a reaction side brake pad (not shown) and arms  129 . 
     With reference to  FIG. 3A , the reaction side portion  128  includes a transverse mating face  140  arranged to contact a corresponding face  150  of the actuating side portion  126 . The reaction side portion  128  further includes circumferential faces  142  and  146  that contact corresponding faces  144  and  148  of the actuating side portion  126 . As a result, when the actuating side portion  126  and the reaction side portion  128  are brought together as shown in  FIG. 3 , the actuating side portion  126  and the reaction side portion  128  are keyed together in a circumferential direction in order that the drag loads from the reaction side pad are effectively transmitted to the actuating side portion  126 . 
     When brought together, four bores  134  of the actuating side portion  126  align with four threaded bores  135  of the reaction side portion  128 , as do two smaller bores  137  and  139  of the reaction side portion  128  and the actuation side portion  126 , respectively. The side portions  126  and  128  are secured together by bolts (not shown) inserted into the bores  134 ,  135 ,  137  and  139 . 
     The actuating side portion  126  has a less complex shape than the reaction side portion  128 . Thus, the actuating side portion  126  is manufactured relatively cost-effectively using a forging process, e.g., forged steel. Advantageously, forging results in a stronger and more durable (tougher) actuating side portion  126 , thereby providing a bridge portion  131  that can withstand increased loads. Beneficially, forging inherently results in a finished product with a smoother surface than casting. Thus, the surfaces  138 ,  144 ,  148 ,  150  and the actuation side abutment surfaces  152  of the recess  130  may not require machining, or the amount of machining may be reduced. Additionally, it is common for abutment surfaces of cast carriers to require induction hardening in order to withstand the rigours of supporting the brake pads in use. As forging results in a tougher end product, induction hardening of the actuating side abutment surfaces  152  may not be required. As a result, the use of a two portion carrier may surprisingly not result in significantly increased manufacturing costs, or may even result in reduced costs compared to a integral carrier, contrary to what might normally be expected. 
     With reference to  FIG. 4 , the part count and assembly cost of the carrier  124  of the first embodiment of the present invention may be minimized by using the same bolts to secure the actuating side portion  126  and the reaction side portion  128  of the carrier  124  together, as are also used to secure the carrier  124  to the adapter plate  16  or to a steering knuckle (not shown) of an axle via the bores  22 ,  134  and  135 . 
     Turning now to  FIG. 5 , a second embodiment of the present invention is illustrated, with similar parts denoted by the same reference numerals, with the addition of the prefix “ 2 ”. Again, only differences with respect to the prior art and first embodiment are discussed in great depth. The actuating side carrier portion includes an integral mounting formation  218  for mounting the actuating side carrier portion to one of an axle, a steering knuckle or a suspension component, the integral mounting formation  218  being a mounting for a drum brake bracket. 
     A carrier  224  of the second embodiment includes a reaction side portion  228  similar to that of the first embodiment, except that it omits the circumferential mating faces and includes a single transverse face  240 . 
     An actuating side portion  226  of the carrier  224  is however integrally formed with the adapter plate, such that the actuating side portion  226  of the carrier  224  is secured directly to the intermediate bracket  12  by bolts (not shown) through the bores  14  of the intermediate bracket  12  and bores  218  of the carrier  224 . The bolts transmit the circumferential load from the reaction side brake pad to the actuating side portion  226  of the carrier  224  due to the omission of circumferential mating faces. 
     In this embodiment, the actuating side portion  226  of the carrier  224  is formed by forging from steel, whereas the reaction side portion  228  is cast from iron. Forging of the actuating side portion  226  remains feasible due to its relatively simple shape, despite the addition of the ring portion  221 . 
     The second embodiment further simplifies the construction of the carrier  224  by eliminating a component and removing a number of contact faces. Furthermore, it saves weight by eliminating a duplication of material, specifically around the bridge  231  of the actuating side portion  226 . 
       FIG. 6  illustrates a third embodiment of the present invention, which is a further variant of the first embodiment and in which like numerals reference similar parts, but with the addition of the prefix “3”, and only differences with respect to the first embodiment are discussed in great depth. 
     In the third embodiment, a similar principle of constructing the carrier is used as in the first embodiment, except that the bolting together of the actuating side portion  326  and the reaction side portion  328 , together with the adapter plate  316 , is achieved in the radial direction rather than the axial direction. Specifically, the adapter plate  316  is provided with a first and second coplanar adapter plate surfaces  343  (only one shown in  FIG. 6 ) having a pair of tangential radial bores  322  provided therein, and the radial bores  322  extend substantially perpendicular to a longitudinal axis A of the axle  10 . As such, the plane on which the surfaces lie is a chord of an imaginary circle whose center is the axis A. 
     The reaction side portion  328  is provided with first and second complimentary carrier mating surfaces  341  (again, only one shown in  FIG. 6 ) and aligned bores  335 . In addition, opposing the carrier mating surfaces  341  and parallel thereto are third and fourth carrier surfaces  340  configured to contact the first and second surfaces  350  of the actuating side portion  326  of the carrier  324 . Further, threaded bores (not visible) extend into the actuating side portion  326  such that all three components may be held together. Thus, the arms  329  of the reaction side portion  328  are sandwiched between the adapter plate surfaces  343  and the actuating side portion  326  and are securely bolted together by bolts  337 . 
     To enhance the rigidity of the connections, the reaction side portion  338  is provided with a further abutment surface  347  extending transverse to the axis of the axle  10  and is arranged to contact a corresponding surface of the adapter plate  316  (not visible). In addition, the actuating side portion  326  is provided with a surface  344  extending parallel to the axis A of the axle  10  and which is arranged to contact a corresponding surface  342  of the reaction side portion  328 . By bolting the components together tangentially (i.e., substantially transverse to axis A), access to the heads of the bolts  337  may be improved during installation and disassembly for maintenance. 
     In alternative embodiments, the order of the adapter plate  316 , the reaction side portion  328  and the actuating side portion  326  may be altered, so that, for example, the actuating side portion  326  may be sandwiched between the adapter plate  316  and the reaction side portion  328 , or the adapter plate  316  may be sandwiched between the other two portions. Furthermore, the second embodiment of the present invention illustrated in  FIG. 5  may be adapted to provide for tangential bolting, rather than axial bolting, in which the reaction side portion  228  may be secured to the integral actuating side portion via tangential bolts and tangential mating surfaces. In addition, the arrangement may be altered such that the bolts are secured in a radially inward rather than radially outward direction, and the corresponding pairs of surfaces may be angled with respect to each other, rather than being coplanar. 
     In other embodiments of the present invention, certain advantages of the carrier shown in  FIG. 5  can be retained without the use of differing materials for the actuating side portion and the reaction side portions. For example, both portions may be cast, or both may be forged and the advantages of reduced material, part count, weight, and of ease of assembly are retained. Indeed, manufacturing a carrier from two portions makes it technically feasible to forge both portions such that both portions may require no or minimal machining, and no or minimal induction hardening or the like. 
     In addition, a two-portion carrier enables the reaction portion to be unbolted and removed with the caliper remaining in-situ on the guide pins. The geometry of the brake can be such that a normal one-piece brake rotor can be removed without removing the caliper. This is advantageous from a servicing point of view as it reduces maintenance time and the problems associated with lifting a heavy caliper once it is removed. 
     Numerous changes may be made within the scope of the present invention. Other ways of altering the material properties of the actuating portion to enhance its strength and durability may be employed. For example, a reinforcing bar may be provided in the actuating bridge, and the remainder of the actuating portion cast around the bar. The carrier may be adapted for any suitable fixing arrangement to an axle or steering knuckle, including, in the case of the first embodiment, direct welding to the axle. Alternative forms of mating faces for the actuating and reaction side portions may be employed. 
     The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.