Abstract:
A brake pad assembly is provided. A brake backing plate has a generally planar body with at least one mold hole. A generally planar shim is affixed to a first face of the backing plate. The shim has at least one integral hook that extends into the at least one mold hole in the backing plate. A friction material is molded onto a second opposite face of the backing plate, and fills the at least one mold hole to thereby embed the hook and retain the shim against the backing plate. A method of making a brake pad assembly is also provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to brake pads for automobiles. 
       BACKGROUND OF THE INVENTION 
       [0002]    A brake pad generally is made up of two components—a backing plate and an attached pad of friction material. In one style of brake pad, the friction material is molded onto the backing plate and fills holes in the backing plate to hold the two components together. 
         [0003]    To address the problem of brake noise and squeal, manufacturers often provide a shim on the side of the backing plate opposite the friction material. A shim is a relatively thin sheet of metal that serves as a barrier and insulator between the brake backing plate and the brake piston. Various methods of attaching such shims have been suggested—adhesive, clips, and rivets, among others. A problem of these various approaches is that they require excessive manufacturing and assembly steps. 
         [0004]    It has also been proposed to use the friction material itself as a shim insulator. Thus, when molding friction material to the backing plate, a portion of the friction material is allowed to seep through the backing plate and extend over the back surface of the backing plate where it hardens and forms a shim layer. Although this is a relatively easy manufacturing process with relatively few assembly steps, there is some doubt as to the effectiveness of the shim portion as the friction material is not designed with noise damping as its primary objective, and the overall assembly may simply vibrate together thus losing the point of the shim. 
         [0005]    To address these drawbacks in the prior art while providing other advantages, the present invention uses the friction material as an attachment platform for embedding a shim to attach it to the brake backing plate. Hooks are provided on the shim to further enhance the embedment. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first aspect of the invention, a brake pad assembly is provided. A generally planar shim is affixed to a first face of a brake backing plate. The brake backing plate has a generally planar body with at least one mold hole. The shim has at least one integral hook that extends into the at least one mold hole in the backing plate. A friction material is molded onto a second opposite face of the backing plate, and fills the at least one mold hole to thereby embed the hook and retain the shim against the backing plate. 
         [0007]    Preferably, the hook has a downward extending segment and a return segment. For example, the hook may have a generally J-shaped profile. The hook may have a flat bottom and then a return. Alternatively, the hook may have a rounded bottom and then a return. 
         [0008]    Preferably, the hook is cut and bent from the shim, so that there is a hole in the shim adjacent to the hook. This hole provides another fillable area for the friction material. That is, the friction material can also fill the hole in the shim when it fills the one or more mold holes in the backing plate. Preferably, the friction material fills the hole without extending behind or beyond the shim. The friction material may or may not be precisely level with the surface of the shim. A level surface may provide some advantage in reducing rattle and vibration when the piston strikes the shim on the backing plate. 
         [0009]    According to a second aspect of the invention, a method of making a brake pad assembly is provided: 
         [0010]    (1) First, a generally planar shim is affixed to a first face of a brake backing plate, the backing plate having a generally planar body with at least one mold hole, the shim having at least one integral hook that extends into the at least one mold hole in the backing plate; and 
         [0011]    (2) Then, a friction material is molded onto a second opposite face of the backing plate, such that the friction material fills the at least one mold hole thereby embedding the hook and retaining the shim against the backing plate once the friction material has cured. 
         [0012]    Preferably, the molding step further comprises completely surrounding the hook with friction material. 
         [0013]    According to a third aspect of the invention, a method of making a brake pad assembly is provided: 
         [0014]    (1) First, a generally planar shim is placed into a shaped mold; 
         [0015]    (2) Then, a brake backing plate is placed adjacent to the shim in the mold, the backing plate having a generally planar body with at least one mold hole, the shim having at least one integral hook that extends into the at least one mold hole in the backing plate; 
         [0016]    (3) Then, a flowable friction material is pressed into the mold so that it forms a friction pad onto an outer face of the backing plate, and proceeds to fill the at least one mold hole and embed the hook in the friction material; and 
         [0017]    (4) Finally, the friction material is allowed to cure so that the shim is retained to the backing plate by the embedded hook. 
         [0018]    The shaped mold preferably includes a relief pocket for the shim. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a front view of a shim according to the present invention. 
           [0020]      FIG. 2  is a back view of the shim of  FIG. 1 . 
           [0021]      FIG. 3  is a side view of the shim of  FIG. 1 , 
           [0022]      FIG. 3A  is a detailed view of the hook area of the shim shown in  FIG. 3 , 
           [0023]      FIG. 4  is a front (shim-side) view of a brake pad assembly according to the present invention. 
           [0024]      FIG. 5  is a back (friction-side) view of the brake pad assembly of  FIG. 4 . 
           [0025]      FIG. 6  is a cross-sectional view of a brake backing plate according to the present invention along line A-A of the plate portion of the assembly shown in  FIG. 4 . 
           [0026]      FIG. 7  is a sectional view of a mold according to the present invention. 
           [0027]      FIG. 8  is a sectional view of a brake pad assembly in the mold. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    A shim is a relatively thin sheet of metal that serves as a barrier and insulator between the brake backing plate and the piston. The present shim  10  is provided with at least one hook  40 . The shim  10  is shown generally at  FIGS. 1 and 2 . The front/outer (i.e. piston-facing) face  20  of the shim is shown in  FIG. 1 . The back/inner (i.e. backing plate-facing) face  50  of the shim is shown in  FIG. 2 . Hooks  40  protrude from the shim surface (three are shown in the drawings, but any number of hooks is possible). The hooks  40  (which are preferably integral, being formed from the material of the shim itself) are adjacent to holes  30  in the shim (each hook  40  preferably having a corresponding hole  30 ). The hooks  40  may be cut and bent out of the material of the shim  10 , and thus each hole  30  may be simply the cut area from which the hook  40  was raised. Alternatively, the hooks  40  may be separate pieces attached to the shim  10 , or they may be raised from the shim material by some other process. The holes  30  are not necessary to the functioning of the shim, but may add to the retention by providing another area into which friction material may enter and harden. 
         [0029]    The hook  40  itself is best seen in  FIG. 3  and in detail in  FIG. 3A . Preferably, the hook is bent at an angle from the general plane of the rest of the shim body. The bend  90  may be perpendicular to the shim body, although it is not necessary that it have a precise right angle. The shape of the hook is preferably something like a letter J (although variants are also envisioned shaped more like a truncated letter V). A more-or-less straight downward first portion or segment  60  is preferably followed by a more-or-less curved bottom and upwardly extending second portion or segment  70 , terminating at a flat or pointed terminal end  80 . (Alternatively, although not shown, all or a portion of the first segment may be round, and all or a portion of the second segment may be straight or flat.) The overall length of the hook from bend  90  to terminal end  80  is preferably between approximately 7 to 8 mm. The overall downward reach of the hook is preferably between approximately 4 to 5 mm. The overall width of the hook  40  is preferably between approximately 3 to 5 mm. 
         [0030]    The shim  10  is preferably made from a thin steel sheet (thickness preferably less than about  2  mm). It may have one or more coatings applied (such as anti-rust or anti-fingerprint coatings). The shim may also be painted, enameled, printed or embossed (all as well-known in the art). The shim may be a multi-layered composite (such as a steel core with one or more non-metallic layers—e.g. rubber or elastomer). 
         [0031]    An example of a typical brake backing plate  110  to which the shim may be attached is shown in sectional view in  FIG. 6 . The backing plate  110  has at least one mold hole  150  that extends through the plate from the first (friction-facing) surface  140  to second (shim-facing) surface  120 . Such plates are commonly known as “I.M.” or “integrally molded” plates in the industry. Methods of making such plates (with round holes, or other shapes of throughbores) are well-known. Typical plate thickness is between approximately 5 to 6 mm. 
         [0032]    The hook(s) in the shim are intended to align with (and extend into, and optionally all the way through) the mold hole(s)  150  in the backing plate  110 . It is preferred if the hooks  40  are somewhat spaced away from the edges of the mold holes  150  of the backing plate  110  (this allows the hooks  40  to be completely submerged in and surrounded by friction material  130 ). Alternatively, the hook  40  may touch the edge of the mold hole  150  (or even grip onto the edge). The hooks  40  may face all in one direction or in multiple directions (e.g. opposite each other). Each hook may point towards the interior of its corresponding mold hole or away. 
         [0033]    In  FIG. 4 , an assembled view of the plate  110  and shim  10  is shown. The shim  10  preferably covers most of the surface  120  of the backing plate  110 , although clearance for attachment edges may be provided in certain styles of plates (e.g. where “ears” are provided on each side for mounting of the plate into a brake caliper). One advantage of the present shim is that no edge-mounting hooks are necessary on the shim for the attachment to the backing plate. The shim does not wrap around the edges of the plate. Thus, a clear border may be provided around the backing plate. 
         [0034]    The arrangement for molding the brake pad assembly is shown in section in  FIG. 8 . The brake pad assembly  100  is preferably molded in a friction mold using a flash-molding or positive-molding process. The mold surface  170  preferably has a recessed or indented portion  180  (as shown in  FIG. 7 ). Into this recess (or relief pocket), the shim is placed (with hook(s) facing outward from the mold surface). Then, the backing plate  110  is preferably mounted over the shim  10 , so that the hook(s) protrude into the mold hole(s) of the backing plate  110 . It will be understood that the shim and backing plate may be assembled together in advance before insertion together into the mold. The shim  10  may be pre-treated with an adhesive (such as a thermoset resin), which then activates and adheres the shim to the backing plate  110  under mold conditions. 
         [0035]    A measured portion or cake or puck of friction material  130  is applied to the surface  140  of the backing plate  110  in the mold. Pressure is applied to the friction material  130 , so that the material softens and is driven smoothly into the mold hole(s)  150 . It flows into the hole(s)  150  and also extends into any hole(s)  30  in the shim  10 , stopping at the surface of the recess  180 . The hook (preferably fully surrounded with friction material) is thus embedded. As the friction material  130  cools and hardens, the embedded hook  40  serves to lock the shim  10  to the brake pad. The shape of the hook (with its up-turned second portion  70 ) particularly serves to resist delamination of the shim from the backing plate, in contrast to a shim attached by adhesive alone. 
         [0036]    The finished brake pad assembly  100  has a friction pad of material  130  on the front side  140  of the backing plate (as shown in  FIG. 5 ). 
         [0037]    Although not shown in the drawings, another embodiment is contemplated using a longer hook that extends completely through the mold hole in the backing plate. The finished dimensions of the hook not critical provided that it is capable of extending into the friction material and being retained within it. It is also contemplated that multiple hooks could be used for each mold hole (or each single hook could have multiple hooked ends). Various design options are possible. 
         [0038]    The foregoing description illustrates only certain preferred embodiments of the invention. The invention is not limited to the foregoing examples. That is, persons skilled in the art will appreciate and understand that modifications and variations are, or will be, possible to utilize and carry out the teachings of the invention described herein. Accordingly, all suitable modifications, variations and equivalents may be resorted to, and such modifications, variations and equivalents are intended to fall within the scope of the invention as described and within the scope of the claims.