Abstract:
A pad spring that fits on a brake carrier of a disc brake resiliently restrains one end of a disc brake pad in the carrier from movement in a radial direction. The pad spring has an abutment surface that supports one end of the pad and resiliently restraining movement thereof. The abutment surface is harder or softer than the backplate of the brake pad contacting the abutment surface to provide a wearing surface. The pad spring is configured to permit the brake disc pad to be mounted to the brake carrier in a radially inward direction while the disc brake in an assembled state.

Description:
REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present invention claims priority to United Kingdom Patent Application No. 0214705.6, filed Jun. 26, 2002.  
         TECHNICAL FIELD  
         [0002]    The present invention relates to a pad spring and to a disc brake incorporating a pad spring. More particularly, the present invention relates to a pad spring that fits to a pad carrier of a disc brake.  
         BACKGROUND OF THE INVENTION  
         [0003]    Currently known disc brakes (shown in FIGS. 1 through 3) comprise a disc or rotor  20  mounted to a wheel hub for rotation with a vehicle wheel. A brake carrier  12 , made from cast iron or steel, is fixed relative to the axis of rotation of the rotor  20  and is secured to a non-rotating portion of the vehicle (e.g. the vehicle suspension). A brake caliper comprising a bridge  16  secured to a housing  14  is slidably mounted on the carrier  12  to allow for movement parallel to the axis of rotation of the rotor  20 . An actuator  18  communicates with one or more pistons or tappets (not shown) provided in housing  14  to apply the force required for the brake to function.  
           [0004]    A pair of brake pads  22  comprising friction material  36  are mounted to a solid stamped, cut or cast iron or steel backplate  34  and are positioned either side of the rotor  20  with the friction material  36  facing the planar faces of the rotor  20 . The backplates  34  of the pads  22  are seated on vertical and horizontal abutment regions  28  and  30 , respectively, which are provided in openings  32  of the carrier  12  to restrain the pads  22  from rotational and inward radial movement, respectively. In a typical floating caliper type brake, one of the backplates  34  engages with the piston(s), either directly or via a spreader plate, to distribute the load. Braking is achieved when the actuator causes the piston(s) to push one of the pads  22  toward the rotor  20 . Because the caliper is able to “float” on the carrier, this causes an equal frictional braking load to be applied by both pads  22 .  
           [0005]    Outward radial movement of the pads  22  is restricted by elongate pad springs  24 , which seat in formations provided in the upper edge of the backplate and which are held down at their approximate center by a pad strap  26  that spans an opening between the bridge  16  and housing  14 . The resilient restraint provided by the pad springs  24  limits the tendency of the pads  22  to rattle against the abutment regions  28  and  30  when a braking load is applied or when the vehicle is driving along an uneven surface. However, the restraint also permits axial movement of the pads  22  toward the rotor  20  during braking.  
           [0006]    Despite the provision of pad springs  24 , it has hitherto been preferable to harden and machine areas X of the regions  28  and  30  to limit damage that may be caused to the carrier  12  by repeated impacts of the backplate  34  therewith (due to vibrations caused by uneven road surfaces and the like in a primarily radial direction, and brake drag forces in a circumferential direction) that would otherwise shorten the service life of the carrier  12 .  
           [0007]    This need for machining and hardening, as well as the need to provide a pad strap  26  inevitably increases the cost of the overall disc brake assembly and results in a bulkier brake.  
           [0008]    There is a desire for a brake assembly having a simplified structure and that minimizes damage to the carrier due to repeated contact with the backplate.  
         SUMMARY OF THE INVENTION  
         [0009]    One embodiment of the invention is directed to a pad spring that fits to a brake carrier of a disc brake and that is capable of resiliently restraining one end of a disc brake pad in the carrier from movement in a radial direction (e.g., radially outward and/or inward). The pad spring further comprises an abutment surface arranged so that it supports one end of the pad and restrains movement of the pad. The abutment surface has a different hardness (e.g., is harder or softer) than the hardness of a backplate of the brake pad that contacts the pad spring.  
           [0010]    Another embodiment of the present invention is directed to a disc brake carrier assembly comprising a disc brake carrier and a disc brake pad retained in the disc brake carrier by two pad springs, said pad springs being capable of each restraining one end respectively of said disc brake pad in said carrier from movement in a radial direction. The pad springs have an abutment surface that is capable of supporting one end of the pad and restraining movement of the pad. The abutment surface has a different hardness than the backplate of the brake pad that contacts the pad spring.  
           [0011]    The invention is also directed to a kit of parts comprising a disc brake pad and two pad springs having the characteristics described above.  
           [0012]    Yet a further embodiment of the present invention is directed a pad spring that fits to a brake carrier of a disc brake comprising the carrier and a rotor. The pad spring resiliently restrains one end of a brake disc pad in the carrier from movement in a radial direction. The pad spring is configured to permit the brake disc pad to be mounted to the brake carrier in an inward radial direction with the pad spring fitted thereto while the disc brake in an assembled state.  
           [0013]    Another embodiment of the present invention is a disc brake comprising a disc brake carrier, a rotor, and at least one disc brake pad retained in the carrier by two pad springs. The pad springs are capable of each restraining one end of the disc brake pad in said carrier to prevent movement of the brake pad in a radial direction. The pad springs may be configured in a brake pad subassembly comprising the disc brake pad and the pad springs. The subassembly can then be mounted to the brake carrier in a radially inward direction while the disc brake is in an assembled state.  
           [0014]    A further embodiment of the present invention is directed to a method of fitting a disc brake pad to an assembled disc brake comprising a carrier and a rotor. The method comprises securing first and second pad springs to each end of the disc brake pad to form a brake pad subassembly, mounting the subassembly radially inwardly into the brake carrier, and securing the pad springs to the carrier to restrain the brake pad from movement in a radial direction relative to the carrier.  
           [0015]    Other embodiments of the invention will be apparent from the description and claims below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0017]    [0017]FIG. 1 is a plan view of a prior art disc brake assembly;  
         [0018]    [0018]FIG. 2 is a side elevation of the assembly of FIG. 1;  
         [0019]    [0019]FIG. 3 is an exploded view of a portion of the carrier and one brake pad and a pad spring of FIGS. 1 and 2;  
         [0020]    [0020]FIG. 4 is a plan view of a disc brake assembly incorporating a pad spring according to one embodiment of the present invention;  
         [0021]    [0021]FIG. 5 is a side elevation of the assembly of FIG. 4;  
         [0022]    [0022]FIG. 6 is an exploded view of a portion of the carrier, and one brake pad and pad spring of FIGS. 4 and 5;  
         [0023]    [0023]FIG. 7 is a perspective view of the pad spring of FIG. 6;  
         [0024]    [0024]FIG. 8 is an exploded view of a portion of a carrier and brake pad with a pad spring according to another embodiment of the present invention;  
         [0025]    [0025]FIG. 9 is an exploded view of a portion of a carrier and brake pad with a pad spring according to a further embodiment of the present invention;  
         [0026]    [0026]FIG. 10 is a perspective view of a component for use with another embodiment of the present invention;  
         [0027]    [0027]FIG. 11 is an exploded view of a portion of a carrier and brake pad with a pad spring according to a yet another embodiment of the present invention;  
         [0028]    [0028]FIG. 12 and FIG. 13 a  are views of a pad spring and pin according to a further embodiment of the present invention;  
         [0029]    [0029]FIG. 13 b  is a pin according to another embodiment of the present invention;  
         [0030]    [0030]FIG. 14 is an exploded perspective view of a portion of a carrier with a pad spring according to a further embodiment of the present invention;  
         [0031]    [0031]FIG. 15 is an exploded perspective view of a portion of a carrier with a pad spring according to another embodiment of the present invention;  
         [0032]    [0032]FIG. 16 is a plan view of a disc brake assembly incorporating pad springs according to a further embodiment of the present invention;  
         [0033]    [0033]FIG. 17 is a side elevation of the assembly of FIG. 16; and  
         [0034]    [0034]FIG. 18 is a perspective view of one of the pad springs shown in FIGS. 16 and 17. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    [0035]FIGS. 4, 5 and  6  illustrate a disc brake assembly  110  incorporating pad springs  138  according to one embodiment of the present invention. Where possible, like numerals have been used for equivalent parts to the prior art assembly with the addition of the prefix “I”.  
         [0036]    It can be seen from FIGS. 4 and 5 that the conventional pad springs have been dispensed with and replaced by four pad springs  138  according to an embodiment of the present invention. Because the pad springs  138  are fitted at each end of the brake pads, the pad strap  26  of the prior art is unnecessary in the brake assembly. Other than the adaptations described herein for fitting the pad springs of the present invention, the brake pads, caliper, carrier and rotor used with the pad springs of the present invention are largely conventional.  
         [0037]    [0037]FIGS. 6 and 7 illustrate the shape of the pad springs  138  and the way they can be secured to the brake carrier  112 . In this embodiment, the pad spring  138  comprises a vertical abutment surface  146  arranged to contact a corresponding vertical surface  128  of the carrier. The pad spring  138  also has a through bore  145 . A horizontal pad support leg  148  extends from the lower edge of the vertical abutment surface  146  at substantially 90 degrees thereto, and a spring portion  150  of the pad spring extends from an upper edge of the vertical abutment surface  128  in substantially the same direction as the horizontal pad support leg  148 . In this embodiment, the support leg  148  provides a cantilevered support of the lower edge of the pad. In other embodiments, the support leg  148  may act as an abutment surface disposed between the pad and a surface of the carrier. In this embodiment, the spring portion  150  has been formed to engage with a recess provided at one end of the upper face  135  of the backplate  134 .  
         [0038]    The pad springs  138  are preferably manufactured from spring steel or any other material having suitably resilient properties. It has been found that for the abutment and support surfaces to function effectively, the hardness of the material used for the pad springs  138  should be different (e.g., higher or lower) than the hardness of the brake pad backplate  134  material. In one embodiment, the abutment surface and support leg  146  and  148  may be made from an inherently tough or hard material (relative to the material of the backplate  134  of brake pad  112 ) and/or may be heat treated, induction treated or worked to impart the necessary toughness and/or hardness to withstand impact loads from the backplate  134  during use. Radial impact loads on the support leg  148  occur primarily due to vibration of the brake during vehicle motion. Circumferential loads occur primarily due to drag forces on the pad when the brake is applied. In this embodiment, the abutment surface  146  and support leg  148  are both harder than the backplate  134 .  
         [0039]    Alternatively, the vertical abutment surface  146  and the horizontal pad support leg  148  may be formed from a material that is inherently soft and malleable relative to the material properties of the backplate  134 . In this case, the material in the abutment surface  146  and support leg  148  may be left untreated to simply act as sacrificial material that is replaced once its associated brake pad  122  is worn out and also replaced. In a preferred embodiment, the portions of the pad springs  138  are formed integrally from a single piece of material. The spring abutment and support surfaces  146  and  148  are preferably harder than the carrier and/or backplate in this embodiment. In one example, a suitable range of hardness in the abutment surface  146  and/or support leg  148  has been found to be 380 to 560 HB.  
         [0040]    Each brake pad  122  is preferably fitted into the carrier  112  by first clipping the pad springs  138  to either end of the backplate  134  in the position shown in FIG. 6. The pads  122  and pad springs  138  are then slid into the openings  132  provided in the carrier  112  until the hole  145  in the spring  138  is aligned with a corresponding through bore  140  on the carrier. A fastener, such as a pin or attachment bolt  144 , is then fitted through the bore  140  and hole  145  to secure the springs  138  in place. The bore  140  and/or hole  145  may be threaded to retain the spring  138  and hold the pad  122  in place more securely. As shown in FIG. 6, a cutaway or slot  142  may be provided in the end face pad  137  of the backplate  134  and friction material  136  to allow the pad  122  to slide forward and backward (when viewed in the direction shown in FIG. 6) to contact the rotor  120  of the brake assembly  110  during use.  
         [0041]    It should be appreciated that, unlike prior art pad springs, the pad springs  138  of the present invention are fitted directly to the carrier  112  of a disc brake instead of being restrained by a pad strap that is in turn secured to the housing  114  and bridge  116  of the brake. It should also be appreciated that the width of the pad springs  138  should be sufficient to retain the pads  122  throughout the entire extent of their travel towards the rotor  120  as the friction material in the pads  122  is progressively worn away.  
         [0042]    The interaction of the support leg  148  with the spring portion  150  of the pad spring  138  achieves the same or similar resilient pad retaining effect as prior art pad spring and strap arrangements. It should further be appreciated that the arrangement shown in FIG. 6 permits the pad  122  to be replaced while the brake assembly  110  remains fitted to the vehicle because the opening  132  in the carrier  112  and the outer opening of the bore  140  on the carrier  112  is normally accessible even when the brake assembly  110  is still fitted on the vehicle.  
         [0043]    [0043]FIG. 8 shows a pad spring according to another embodiment of the present invention with like parts being designated by like numerals with the addition of the prefix “2”. In this embodiment, the through hole  245  has been formed with a lip  247  turned toward the backplate  234 . The lip  247  may be threaded using a swaging process or the like, thereby providing a greater amount of threaded area on the spring to achieve a more secure connection to the carrier  212 . Again, a slot  242  is provided in the pad  222  to accommodate the bolt  244  and lip  247 . As an alternative, the lip  247  may be turned away from the backplate  234 , with a vertical slot being provided in the carrier  212  to enable the spring  238  to be slid in vertically, thereby negating the need for a slot  242  in the pad  222 .  
         [0044]    [0044]FIG. 9 illustrates a third embodiment of the present invention in which like parts are again designated by like numerals but with the prefix “3”. In this embodiment, a retention piece, such as a nut  352 , is used in conjunction with a fastener  344  to secure the spring  338  to the carrier  312 . To simplify the fitting procedure, the slot  342  is preferably dimensioned to prevent rotation of the nut as it is secured to the bolt  344  while still permitting sliding movement of pads  322  towards the rotor while fitted in the brake assembly.  
         [0045]    An alternative to the nut  352  is illustrated in FIG. 10. In this embodiment, two through bores (not shown) are provided in the carrier through which two bolts are fitted. A plate  456  having two threaded apertures  457  that are mutually spaced by the same distance as the through bores on the carrier acts as the retention piece, replacing the two nuts that would otherwise secure the spring to the carrier.  
         [0046]    [0046]FIG. 11 illustrates an embodiment of the pad spring where the pad support leg has been omitted. In this embodiment, a nut  552  or a nut plate similar to that of FIG. 10 is used to resist inward radial movement of the pad  522  due to engagement of the nut or nut plate  552  in the slot  542  of the pad  522 .  
         [0047]    [0047]FIGS. 12, 13A and  13 B illustrate yet another an alternative securement arrangement of the spring  638  in which like parts are designated by like numerals with the addition of the prefix “6”. In this embodiment, the through bore  640  extends along an axis perpendicular to the plane of the paper. The pad spring  638  has a pair of holes  645  corresponding to the through bore  640  and that are disposed on a pair of wings  660  extending toward the carrier  612  from vertical edges of the vertical abutment surface  646 . The carrier  612  and spring  638  are then secured together by a pin  644 , as shown in FIG. 13A, with axial movement thereof being restricted by a pair of clips  662 . Alternatively, the through bore  640  may be threaded and the bolt  744  shown in FIG. 13B is used in conjunction with a clip  762  to prevent the bolt  744  from working loose.  
         [0048]    [0048]FIGS. 14 and 15 illustrate eighth and ninth embodiments of the present invention respectively. In these embodiments, the pad springs  838  and  938  have a pair of resilient spring legs  860 ,  960  extending from the clip to engage with either slot  864 , recess  865  (shown for convenience on the same Figure as slot  864 ) or cut-outs  964   a  and  964   b  to clip the pad springs  838 ,  938  into place on the carrier  812  and  912 . This structure eliminates the need to have a spanner or the like for fitting. To make fitting the pad springs  838 ,  938  easier, the upper end of the carrier  812 ,  912  may be tapered such that the spring legs  860 ,  960  slide easily onto the carrier.  
         [0049]    A tenth embodiment of the present invention is shown in FIGS. 16, 17 and  18 . In this embodiment, the springs  1038  are fitted at each end of a pad  1022 , but the spring portion  1050  comprises an extension  1070 . As shown in FIGS. 16 and 17, the extension  1070  is arranged to extend over the bridge  1016  and/or housing  1014  of the brake. The bridge  1016  and housing  1014  are thereby resiliently loaded against the carrier  1012 . This minimizes any rattling of the bridge and housing that may occur due to play in the slidable mounting of the bridge/housing  1016 / 1014  on the carrier  1012 .  
         [0050]    It is apparent that the pad springs of the present invention have a number of advantages over prior art springs. For example, the invention eliminates the need for hardening of carrier abutments because impact loading of the brake pads is taken by the abutment and/or support surfaces of the pad spring rather than the carrier directly. Also, the spring element is self-contained in the pad support, eliminating the need for a separate structure for retaining the pads. Furthermore, by eliminating the retaining pad strap and bolt, more clearance between the brake and wheel is created, potentially allowing more material to be added to the casting for the bridge and thereby permitting the brake to be strengthened. In addition, the pad springs enable brake pads to be fitted and removed in a radial direction while the brake is assembled, particularly while the caliper is assembled to the carrier. This makes brake servicing easier.  
         [0051]    It should be appreciated that the various terms used to describe the orientation of the various components has been used for convenience and ease of explanation, and that brakes incorporating springs according to the present invention may be fitted in numerous orientations on a particular vehicle. It must also be appreciated that numerous changes may be made within the scope of the present invention. For example, the extended spring portion may be applied to springs having any one of the various means of attachment disclosed in the preceding embodiments and a variety of the features such as the removal of the support leg may be combined with features of the other embodiments. Furthermore, the pad spring may be used in conjunction with a standard pad spring to retain brake pads in a radially inward direction only and not a radially outward direction. An advantage of this configuration is that it may protect the abutment regions of the brake carrier, thereby potentially negating the need for these regions to be hardened, and thus potentially reducing manufacturing costs, and/or extending the service life of the carrier.  
         [0052]    It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.