Abstract:
A brake pad assembly including a molded material affixed to a backing plate which has opposing faces, at least one non-circular opening through its thickness, and tab-like extensions or some other structure for locating and supporting the backing plate in a vehicle brake system. The molded material extends over both opposed faces of the backing plate by extrusion through the openings to provide a unitary structure wherein molded material at one side of the backing plate functions as a friction-generating pad material and the molded material at the opposite side functions as a shim-like noise attenuating element. The number, configuration, and placement of the openings through the thickness of the backing plate is varied to alter the noise attenuating properties of the assembly, further reducing the tendency for modal locking of brake components.

Description:
[0001]    This divisional application claims priority to U.S. Provisional Application No. 60/511,898 filed Oct. 16, 2003 and U.S. Utility application Ser. No. 10/967,040, filed Oct. 15, 2004. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to brake friction pad assemblies such as are used in various automotive vehicle brake applications, including disc brake systems and drum brake systems. These systems may be utilized in automobiles, trucks, buses, off road equipment, airplanes, industrial machinery, etc. More particularly, it concerns an improved brake friction pad assembly structured to significantly reduce brake noise generated during brake system operation, and methods of making the improved brake friction pad assembly. 
         [0004]    2. Related Art 
         [0005]    Vibrations in a brake friction pad assembly generated during brake system operation frequently result in an audible squealing noise which may be objectionable and/or alarming to an operator, even though the noise may not result from any functionally problematic condition. In some situations, vibrations in a brake friction pad assembly may even contribute to premature or uneven wear of the abrasion surfaces. In any event, excessive brake vibration and noise is generally undesirable and many prior art techniques have been proposed for reducing or dampening vibrations in a brake friction pad assembly. 
         [0006]    Notable examples of prior art attempts to reduce noise in a brake pad assembly include cutting sinusoidal grooves in the backing plate, as shown in U.S. Pat. No. 6,283,258 to Chen et al., and sculpturing of the friction-generating pad as shown in U.S. Pat. No. 5,456,339 to Zeng. These prior art techniques introduce undesirable side effects, however, such as increasing the time cycle of the fabrication process and/or adding cost to the brake/drum assembly. 
         [0007]    One particularly effective method of attenuating brake noise without introducing these undesirable side effects consists of incorporating a shim onto the rear surface of the backing plate. The shim can be integrally molded from the flow of mix extruded through openings in the backing plate, as shown in U.S. Pat. No. 5,413,194 to Kulis, Jr. et al., hereby incorporated by reference in its entirety, or affixed in a subsequent operation. In the &#39;194 Kulis, Jr. patent, the friction material mix or under-layer mix flows via an extrusion process into the openings in the backing plate, and in an alternative embodiment flows behind the backing plate to form an integral noise shim. 
         [0008]    In the &#39;194 Kulis, Jr. patent, the extrusion openings in the backing plate through which the friction material mix or under-layer mix flows are circular. The circular holes are utilized due to ease of manufacture through a punch process and the low cost of readily available round-shaped punch tools. In some braking applications, vibrations traversing the length of the backing plate are a source of objectionable brake noise generation, and the shim on the rear surface of the backing plate is not sufficient to satisfactorily attenuate the objectionable vibrations. 
         [0009]    Accordingly, within a friction brake pad assembly having extrusion openings in the backing plate into which the friction material mix or under-layer mix are pressed during the forming operation, such as shown in the &#39;194 Kulis, Jr. patent, there exists a need to provide additional noise attenuating properties without introducing features that increase the cost of the backing plate nor increase the time cycle of the fabrication process. 
       SUMMARY OF THE INVENTION 
       [0010]    A brake friction pad assembly according to this invention comprises a rigid backing plate having a length and a thickness between opposed first and second faces. The backing plate is capable of transmitting vibrations along its length and width. The backing plate includes a primary extrusion opening extending between its opposed faces. A friction-generating pad element made from a molded material is pressed into contact with the first face of the backing plate such that the molded material fills the primary extrusion opening. The primary extrusion opening has a non-circular shape so that vibrations traveling the length of the backing plate are substantially dampened upon encountering the non-circular shape of said primary extrusion opening. 
         [0011]    The invention also contemplates a method of dampening vibrations traveling through a brake friction pad assembly for a caliper-type vehicular disc brake system comprising the steps of: forming a rigid backing plate with a primary extrusion opening extending there through and at least two spaced mounting features on generally opposing sides of the primary extrusion opening; pressing a molded material onto a first face of the backing plate to form a friction-generating pad element and simultaneously filling the primary extrusion opening with the molded material; generating vibrations in the backing plate between the spaced mounting features; and forcing the vibrations to travel in a non-arcuate path as they find their way around the periphery of the primary extrusion opening to thereby dampen the vibrations within the friction pad assembly. 
         [0012]    It has been discovered that in friction brake pad assembly having extrusion openings in the backing plate into which the friction material mix or an under-layer mix are pressed during the forming operation, vibrations traveling across the backing plate will be substantially dampened by forming the primary extrusion opening with a non-circular shape. It is hypothesized that this advantageous effect is realized by the introduction of reflecting surfaces caused by the non-circular peripheral edges of the primary extrusion opening. This is in contrast to the prior art circular openings which are believed to allow mechanical waves to flow too efficiently around their periphery as they travel across the length and/or width of the backing plate. 
         [0013]    In alternative embodiments of the present invention, the number, configuration, and placement of the extrusion openings through the thickness of the backing plate are varied to alter the natural vibrational frequency and noise attenuating properties of the friction brake pad assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein: 
           [0015]      FIG. 1  is a cut-away perspective view a brake pad assembly according to the subject invention in which the friction-generating pad element is fabricated from a first material mixture formulation, and the noise-damping pad element is fabricated from a second material mixture formulation; 
           [0016]      FIG. 2  is a simplified cross-sectional view of a brake pad assembly in which the friction-generating pad element and the noise-damping pad element are fabricated from the same material mixture formulation; 
           [0017]      FIG. 3  is a simplified cross-sectional view of a brake pad assembly which does not include a integrally molded noise-damping pad element; 
           [0018]      FIG. 4  is a front elevation view of a brake pad assembly of the present invention wherein the primary extrusion opening is formed in the shape of an elongated slot and a secondary extrusion opening is formed in the shape of an elongated slot non-parallel to the orientation of the primary extrusion opening; 
           [0019]      FIG. 5  is a front elevation view as in  FIG. 4  wherein the primary extrusion opening and three secondary extrusion openings are formed in the shape of pairs of parallel elongated slots; 
           [0020]      FIG. 6  is a front elevation view as in  FIG. 5  wherein the primary extrusion opening and three secondary extrusion openings are formed in the shape of pairs of perpendicular elongated slots; 
           [0021]      FIG. 7  is a front elevation view as in  FIG. 4  wherein the primary extrusion opening is formed in the shape of a “T”, and a secondary extrusion opening is formed in the shape of a “T” mirrored in orientation to the primary extrusion opening; and 
           [0022]      FIG. 8  is a front elevation view as in  FIG. 4  wherein the primary extrusion opening is formed in the shape of an “H”, and a secondary extrusion opening is formed in the shape of an “H” mirrored in orientation to the primary extrusion opening. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a disc brake friction pad assembly according the subject invention is generally shown at  10  in  FIG. 1 . 
         [0024]    The assembly  10  includes a rigid backing plate  12 , which in the preferred embodiment is made from a steel material. The backing plate  10  has a length and a thickness between opposed first  14  and second  16  faces. The first face  14  is that surface of the backing plate  12  presented toward a rotor when operationally mounted in a vehicular caliper-type braking assembly. The first face  14  is generally planar and second face  16  is also generally planar and parallel to the first face  14 . The backing plate  12  further includes a top edge  18  and bottom edge  20  spaced from the top edge  18 . The top  18  and bottom  20  edges extend lengthwise of the backing plate  12  and form its upper and lower peripheral boundaries when operationally mounted in a vehicular caliper-type braking assembly. At least two spaced mounting features  22  are formed in the backing plate  12  for supporting the assembly  10  within a brake caliper system. In  FIG. 1 , the mounting features are illustrated as simple profile features of the backing plate  12 , whereas in  FIGS. 4-8  the mounting features  22  are shown as lug-shaped ears extending in opposite lengthwise directions from the backing plate  12 . Other mounting feature configurations are possible, as will be dictated by the brake system design. 
         [0025]    The backing plate  12  also includes a primary extrusion opening, generally indicated at  24 , extending between its opposed first  14  and second  16  faces. The primary extrusion opening  24  is non-circular in shape, and may be skewed in its orientation relative to the top  18  and bottom  20  edges. The primary extrusion opening  24  is described in greater detail below. 
         [0026]    A molded material, generally indicated at  26 , is pressed into contact with the first face  14  of the backing plate  12  such that the molded material  26  forms a friction-generating pad element  28  over the first face  14  while simultaneously filling the primary extrusion opening  24 . As shown in FIGS.  1  and  4 - 8 , the friction-generating pad element  28  can be formed in two or more distinct segments on the backing plate  12 , or in a single section as shown in  FIGS. 2 and 3 . In the case of two or more segments, depending upon the magnitude of expected braking system noise-damping requirements, each pad segment may have different planar configurations, different planar areas, or different thicknesses. Thus, the friction-generating pad element  28  can include contour features  30  on its engagement surface to further tune the noise attenuating characteristics of the assembly  10 . Although not necessary, it is preferable that each such friction-generating pad segment  28  be associated with a different extrusion opening  24  in the backing plate  12 . 
         [0027]    Preferably, although not necessarily, a noise-damping pad element  32  overlies and contacts a substantial portion of the second face  16  of said backing plate, as shown in  FIG. 1 . The noise-damping pad element  32  is joined to the friction-generating pad element  28  by the molded material  26  contained within the primary extrusion opening  24 . 
         [0028]    As shown in  FIG. 1 , the friction-generating pad element  28  can be fabricated from a first material mixture formulation  34 , whereas the molded material  26  contained within the primary extrusion opening  24  and the noise-damping pad element  32  is fabricated from a common, generally homogenous second material mixture formulation  36  having more readily flowable extrusion properties than the first material mixture formulation  34 . Examples of suitable first  34  and second  36  material mixture formulations of the molded material  26  may be had by reference to the above-referenced U.S. Pat. No. 5,413,194 to Kulis, Jr. et al. Regardless of the material selected for the second material mixture formulation  36 , its properties should be chosen to provide the properties of a thermal insulator and/or vibration attenuation. 
         [0029]    Although not shown in the Figures, one or more optional additional intermediate layers of molding material  26  can be introduced, each integrally joined with one another and to the backing plate  12  at the time of material molding. The intermediate layer will typically have either thermal resistive properties and/or noise attenuating properties. 
         [0030]    As shown in  FIG. 2 , the molded material  26  may comprise a common, generally homogenous material mixture formulation forming both the friction-generating pad element  28  and the noise-damping pad element  32 . 
         [0031]      FIG. 3  illustrates another embodiment of the invention wherein the noise-damping pad element is not formed integrally with the friction-generating pad element  28 . In this situation, the noise-damping pad element can be formed separately and affixed in a subsequent operation, or omitted entirely depending upon the application and circumstances. The novel advantages of the present invention are realized in the embodiment of  FIG. 3  by way of the primary extrusion opening  24  in the backing plate  12  by which vibrations traveling from one end of the backing plate  12  to the other will be substantially dampened as more fully described below. 
         [0032]    Referring now to  FIG. 4 , the backing plate  12  is shown including a secondary extrusion opening  38  adjacent the primary extrusion opening  24 . The secondary extrusion opening  38  is filled with the molded material  26  at the same time of filling the primary extrusion opening  24 . Preferably, the secondary extrusion opening  38  also has a non-circular shape, and in the case of  FIG. 4  is formed in the shape of an elongated slot having an orientation on the backing plate  12  which is mirrored, or in this case generally perpendicular to, the orientation of the primary extrusion opening  24 . Although in this Figure the friction-generating pad element  28  is shown segmented with the primary  24  and secondary  38  extrusion openings associated with respective segments, it will be appreciated that this extrusion opening configuration could be equally effective with a non-segmented friction-generating pad element  28 . 
         [0033]      FIG. 5  illustrates a slightly different configuration of the extrusion openings, wherein three secondary extrusion openings  38  are formed in the backing plate  12 , together with the primary extrusion opening  24 . In this example, one of the secondary extrusion openings  38  is arranged as a pair with the primary extrusion opening  24  in which they take the shape of parallel elongated slots associated with a respective segment of the friction-generation pad element  28 . The other two secondary extrusion openings  38  are themselves arranged as a parallel pair and associates with the other segment of the friction-generating pad element  28 . 
         [0034]      FIGS. 7 and 8  illustrate yet additional shape configurations and orientations for the primary  24  and secondary  38  extrusion openings. For example, in  FIG. 7  the primary extrusion opening  24  is formed in the general shape of a “T”, and the secondary extrusion opening  38  is also formed in the general shape of a “T”, but mirrored in orientation to the primary extrusion opening  24 . In  FIG. 8 , the primary extrusion opening  24  is formed in the general shape of an “H”, and the secondary extrusion opening  38  is also formed in the general shape of an “H”, but mirrored in orientation to the primary extrusion opening  24 . These foregoing examples are merely suggestive of the shape configurations possible for the extrusion openings  24 ,  38 . And, although in each example the secondary extrusion opening  38  is shown in a mirrored orientation relative to the primary extrusion opening  24 , such is not a necessary design relationship. 
         [0035]    In all of these examples, however, the extrusion openings  24 ,  38  are shown including at least one linear edge  40  which has been oriented substantially non-parallel to either of the top  18  and bottom  20  edges of the backing plate  12 . This feature is believed to enhance the noise-damping effects of the present invention. Specifically, vibrations traveling the length of the backing plate are substantially dampened upon encountering the non-circular shape of the extrusion openings  24 ,  38  and are further attenuated by reflecting off the linear edge  40 . 
         [0036]    Another beneficial feature common to the examples consists of the preferred absence of any sharp corners, both concave and convex, in the extrusion openings  24 ,  38 . Referring again to  FIGS. 4-8 , each extrusion opening  24 ,  38  is shown including at least two concave corners  42 . The concave corners  42  are provided with radii of curvature; in the preferred embodiment the radii of curvature are at least as large as the thickness of the backing plate  12  however tighter radii can be used to beneficial effect as well. Similarly,  FIGS. 7 and 8  reflect examples in which each extrusion opening  24 ,  38  includes at least one convex corner  44 . The convex corner  44  also has a radius of curvature. These radii of curvature for corners  42 ,  44  within the shape of the extrusion openings  24 ,  38  function to both reduce stress concentrations within the backing plate and facilitate the formation technique of punching with a durable, low cost tool rather than EDM or laser cutting. 
         [0037]    The friction brake pad assembly  10  having extrusion openings  24 ,  38  in the backing plate  12  into which the molded material  24  are pressed during the forming operation has been found to substantially and beneficially alter the vibrations traveling from one end of the backing plate  12  to the other end. It is believed that these beneficial effects are achieved by forming the extrusion openings  24 ,  38  with a non-circular shape. The non-circular shapes can be optimally configured to reduce a tendency for modal locking of the brake friction pad assembly  10  during use, without overstressing the structural integrity of the backing plate  12 . Different numbers, configurations, and placements of the extrusion openings  24 ,  38  in the backing plate  12  have different noise attenuating benefits during brake applications. Preferably, the number, configuration, and placement of the extrusion openings  24 ,  38  are selected and perfected to alter the natural vibrational frequency of the backing plate  12 , and thus reduce the tendency for modal locking of the brake components, which is likely a source of brake noise during vehicle brake usage. An additional benefit of the large surface area occupied by the extrusion openings  24 ,  38  in the backing plate  12  is the increased amount of noise-damping material  26  present on the brake assembly  10 . 
         [0038]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, the novel features of the invention can be practiced in combination with one or more prior art style circular openings in the backing plate  12 . For example, as shown in  FIG. 4 , the non-circular extrusion opening  24  can be paired with a circular opening  46  to achieve added benefit, and thereby take the form of a second extrusion opening. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.