Abstract:
A clutch button is provided including a friction pad having first and second surfaces. The friction pad has a radial outer and inner edges. The friction pad also has first and second upper outward circumferential edges adjacent to the radial outer edge. The friction pad has first and second lower outward circumferential edges adjacent to the radial inner edge. The friction pad has first and second inward circumferential outer edges joining the respective first and second outward upper and lower circumferential edges. The friction pad has a first groove formed in the first surface extending from the first upper outward circumferential edge to one of the second upper and lower outward circumferential edges. A second groove is formed in the first surface extending from the first lower outward circumferential edge to the other one of the second upper or lower circumferential edges the first groove does not extend to. A backing plate is bonded to the second surface.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a friction button for fastening to a clutch disc. More specifically, the present invention relates to a friction button for fastening to a clutch disc where grooves and/or contours are formed in a face of the clutch button for improved clutch release.  
           [0003]    2. Description of the Prior Art  
           [0004]    Typically, a plurality of clutch buttons are fastened to a motor vehicle clutch disc. The clutch disc assembly is used in a clutch assembly to transmit drive forces from a prime mover such as an internal combustion engine to an input shaft of a transmission, which in turn multiplies the torque by a selected gear ratio and transmits it to an output shaft such as a vehicle driveshaft. Prior art clutch buttons often have a backing plate on which a friction material is fixedly disposed. The buttons are spaced circumferentially about the clutch disc with the friction material facing outwardly. The buttons are commonly fixed to the disc by riveting the backing plates to the disc. The disc is selectively engaged with a drive disc, commonly a flywheel, to transmit a rotational driving force to an output shaft. A spring loaded engagement member, such as a pressure plate, presses the clutch disc against the drive disc in the engaged condition. The frictional engagement causes the clutch disc to rotate with the flywheel. Commonly, the friction material has both a smooth continuous inner face which is bonded to the backing plate and a smooth continuous outer face which contacts the drive disc (flywheel or pressure plate).  
           [0005]    One problem with the prior art clutch assemblies is that the clutch disc tends to remain in contact with either the flywheel or the pressure plate even if the clutch is disengaged, especially when the clutch is at an elevated temperature. The resultant undesired frictional drag on the clutch disc causes difficulty in the selecting the desired transmission gear ratio.  
           [0006]    Configuring the friction material to facilitate cooling is believed to facilitate certain aspects of clutch performance. Indeed, it is known to provide a spacing between portions of the clutch button friction material to facilitate cooling of the friction material. U.S. Pat. No. 5,158,165, assigned to the assignee of this application, discloses spacing portions of friction material from each other to form a central void to facilitate air movement therebetween for improved cooling of the clutch button. It is also known to provide a plurality of radially extending grooves in the face of a friction material to facilitate fluid movement across the face for improved cooling of the friction material and of the structure to which it is mounted. However, while the known spacings and grooves facilitate cooling, they are not well suited to facilitating the separation of the disc from the pressure plate and flywheel.  
           [0007]    It would be desirable to provide a clutch which features a low drag torque on the clutch disc when the clutch is disengaged. Enhancing separation of the clutch disc from the drive disc (flywheel) when the clutch is disengaged would yield this result.  
         SUMMARY OF THE INVENTION  
         [0008]    According to the present invention there is provided a disc type clutch for rotationally coupling a drive disc which flywheel or pressure plate to a shaft (transmission input shaft) having an enhanced separation action of the clutch disc from the flywheel when the clutch is disengaged. Friction material in the form of a plurality of friction pads are bonded to a backing plate to form a clutch button or bonded directly to the clutch disc to form a clutch disc assembly. The clutch buttons of the present invention have circumferential grooves formed in the face of the button which aid in the separation of the clutch disc assembly from the flywheel due to the aerodynamic forces generated by airflow through the separate grooves. A secondary effect is that operating temperature of the clutch disc assembly and especially the clutch buttons are reduced due to the additional cooling airflow created by the grooves formed in the face of the friction material that contacts the flywheel and/or pressure plate when the clutch is engaged.  
           [0009]    The circumferential orientation of the grooves increases the aerodynamic forces that enhance the separation characteristics of the clutch disc from the flywheel and/or pressure plate. Also, the volume of air flowing through the grooves is increased as compared to prior art designs using radial grooves.  
           [0010]    One provision of the present invention is to enhance the separation characteristics of a clutch disc from a drive disc.  
           [0011]    Another provision of the present invention is to enhance the separation characteristics of a clutch disc from a drive disc by using aerodynamic forces.  
           [0012]    Another provision of the present invention is to enhance the separation characteristics of a clutch disc from a drive disc by using aerodynamic forces generated by at circumferential grooves formed in a friction button attached to the clutch disc.  
           [0013]    Another provision of the present invention is to increase the cooling of a clutch disc by increasing the airflow across the surface of the clutch button attached to the clutch disc.  
           [0014]    Still another provision of the present invention is to increase the cooling of a clutch disc by increasing the airflow across the surface of a clutch button attached to the clutch disc with at least two circumferential grooves formed in a face of said clutch button.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a side elevational view of the clutch button of the present invention attached to a friction disc;  
         [0016]    [0016]FIG. 2 is a front elevational view of a first preferred embodiment clutch button of the present invention;  
         [0017]    [0017]FIG. 3 is a side sectional view of a clutch button shown in FIG. 2 taken in the direction of arrows III;  
         [0018]    [0018]FIG. 4 is a front elevational view of a first alternative preferred embodiment of the clutch button of the present invention; and  
         [0019]    [0019]FIG. 5 is a front elevational view of a second alternative embodiment of the clutch button of the present invention.  
         [0020]    [0020]FIG. 6 is a front elevational view of a third alternative embodiment of the clutch button of the present invention.  
         [0021]    [0021]FIG. 7 is a side elevational view of the third alternative embodiment of the clutch button of the present invention.  
         [0022]    [0022]FIG. 8 is a front elevational view of a fourth alternative embodiment of the clutch friction pad of the present invention.  
         [0023]    [0023]FIG. 9 is a front elevational view of a fifth alternative embodiment of the clutch button of the present invention.  
         [0024]    [0024]FIG. 10 is a broken-out perspective view of a portion of the clutch button of FIG. 9.  
         [0025]    [0025]FIG. 11 is a front elevational view of a sixth embodiment of the clutch button of the present invention.  
         [0026]    [0026]FIG. 12 is a broken-out perspective view of a portion of the clutch button of FIG. 11. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    Certain terminology will be used in the following description for convenience in reference only and will not be limiting. For example, the terms “forward” and “rearward” will refer to directions forward and rearward of a transmission as normally mounted in a vehicle. The terms “rightward” and “leftward” will refer to directions in the drawings in connection with which the terminology is used. The terms “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the apparatus. The terms “upward” and “downward” will refer to directions as taken in the drawings in connection with which the terminology is used. All foregoing terms mentioned above include the normal derivatives and equivalents thereof.  
         [0028]    Referring to FIG. 1 of the drawings, a partial cross-sectional view of a clutch/transmission assembly  4  is shown. An engine flywheel  6  is rotatably coupled to a clutch cover  8 . A gear change transmission  10  is nonrotatably mounted to a bellhousing  11  which is mounted to an engine block (not shown). The transmission  10  is driven through the rotation of a transmission input shaft  12  about an axis  7  which eventually rotates a transmission drive yoke  14  which is attached to the balance of the vehicle driveline (not shown).  
         [0029]    Now referring to FIG. 2 of the drawings, a front elevational view of a clutch button  18  of the present invention is shown. A friction pad  20  is bonded or otherwise attached to a backing plate  22  to form the clutch button  18 . The clutch button  18  is riveted or otherwise attached to a clutch disc  16  (FIG. 1) to form a clutch disc assembly  15 .  
         [0030]    The transmission input shaft  12  is rotated by the flywheel  6  through frictional engagement of a clutch disc assembly  15  with flywheel  6 . The clutch disc assembly  15  is typically nonrotatably slideably mounted to the input shaft  12  of the gear change transmission  10  and disposed between the engine flywheel  4  and a clutch pressure plate  13 . Commonly shaft  12  and disc assembly  15  have complementary mating splines enabling disc assembly  15  to axially slide along shaft  12  while rotating as a unit therewith.  
         [0031]    [0031]FIG. 2 is a front elevational view of a clutch button  18  of the present invention. The clutch button  18  includes a friction pad  20  composed of friction material bonded to a backing plate  22  using known methods. The friction pad  20  is preferably formed of ceramics but other known friction materials may be used for this invention. The clutch button  18  is attached to the clutch disc  16  using an attachment means such as rivets placed through the mounting apertures  24  formed in the backing plate  22  and into the clutch disc  16 . Disc  16  is integrated into disc assembly  15 . According to the present invention, first groove  26  and second groove  28  are formed in the face of the friction pad  20 . The friction pad  20  has a radial outer edge  30  and a radial inner edge  31  and inward circumferential outer edges  32 A and  32 B. The inward circumferential outer edge  32 A is joined to the radial outer edge  30  by upper outward circumferential edge  33 A and to the radial inner edge  31  by lower outward circumferential edge  33 B. The inward circumferential outer edge  32 B is joined to the radial outer edge  30  by upper outward circumferential edge  33 C and to the radial inner edge  31  by lower outward circumferential edge  33 D.  
         [0032]    Now referring to FIG. 3 of the drawings, a cross-sectional view of the clutch button of the present invention in the direction of arrows III of FIG. 2 is shown. The friction pad  20  is bonded to the backing plate  22  and has both first and second grooves  26 ,  28  formed therein. The second groove  28  is shown having a cross-sectional groove width W and a cross-sectional groove depth D. An exemplary dimension for the groove width W is 0.090 inches (2.3 mm) and a corresponding groove depth D is 0.060 inches (1.5 mm) in a friction pad  20  that has a thickness T of 0.165 inches (4.2 mm). Alternative dimensions for the groove width W and groove depth D can be selected as determined for a particular clutch design.  
         [0033]    Referring once again to FIG. 2, the first groove  26  extends to connect the upper outward circumferential edge  33 A with the upper outward circumferential edge  33 C and curves towards the radial inner edge  31  near the midpoint. In a similar fashion, but curving toward the radial outer edge  30  at its midpoint, the second groove  28  extends to connect the lower outward circumferential edge  33 B with the lower outward circumferential edge  33 D. Thus, the first groove  26  and the second groove  28  curve toward one another to achieve a minimum separation distance at approximately the center of the friction pad  20 . Neither groove  26  nor groove  28  are concentric with axis  7  to prevent the development of a corresponding ridge on the pressure plate  13  and the flywheel  6 .  
         [0034]    Now referring to FIG. 4, a front elevation view of a first alternative embodiment of the clutch button  18 A is shown. The friction pad  20 A is bonded to the backing plate  22  where the friction pad  20 A differs from the friction pad  20  shown in FIG. 2 in that the first and second grooves  26 ,  28  have been modified to cross at approximately the lower central section of the friction pad  20 A. A first groove  34  which extends in a substantially straight manner connects the upper outward circumferential edge  33 A with the lower outward circumferential edge  33 D while a second groove  36  extends in a substantially straight manner to connect the lower outward circumferential edge  33 B with the upper outward circumferential edge  33 C crossing the first groove  34  in the process.  
         [0035]    Now referring to FIG. 5, a second alternative embodiment of the clutch button  18 B of the present invention is shown. A friction pad  20 B is bonded or otherwise attached to a backing plate  22  which is riveted to a clutch disc  16  through mounting apertures  24 . The friction pad  20 B includes a radial outer edge  30  and a radial inner edge  31 . Forming the left side of the friction pad  20 B is a first upper outward circumferential edge  33 A which joins a first inward circumferential outer edge  32 A which joins a first lower outward circumferential edge  33 B. Forming the right side of the friction pad  20 B is a second upper outward circumferential edge  33 C which joins a second inward circumferential outer edge  32 B which joins a second lower outward circumferential edge  33 D.  
         [0036]    A first curvilinear groove  34 ′ generally runs from the first upper outward circumferential edge  33 A to the second lower outward circumferential edge  33 D while a second curvilinear groove  36 ′ generally runs from the first lower outward circumferential edge  33 B to the second upper outward circumferential edge  33 C.  
         [0037]    In FIG. 5, the first groove  34 ′ is comprised of a section  34 ′A which generally has a center of curvature which lies below the clutch button  18 B which is joined to a section  34 ′B which generally has a center of curvature which lies above the clutch button  18 B. In a similar manner, the second groove  36 ′ is comprised of a section  36 ′A which generally has a center of curvature which lies below the clutch button  18 B which is joined to a section  36 ′B which generally has a center of curvature which lies above the clutch button  18 B. The first groove  34 ′ intersects the second groove  36 ′ at approximately the center of the friction pad  20 B.  
         [0038]    Referring to FIGS. 6 and 7, a third alternative embodiment clutch button  18 C is presented. The button  18 C has a first groove  126  and an intersecting second groove  128 . Friction pad  120  has a radial outer edge  130  and a radial inner edge  131 . The friction pad  120  also has inward circumferential outer edges  132 A and  132 B on its outer face. The inward circumferential edge  132 A is adjoined to the radial outer edge  130  by upper outward circumferential edge  133 A and to the radial inner edge  131  by lower outward circumferential edge  133 B. The inward circumferential outer edge  132 B is joined to the radial outer edge  130  by upper outward circumferential edge  133 C. The inward circumferential outer edge  132 B is joined into the radial inner edge  131  by lower outward circumferential edge  133 D. The pad  120  has a tapered or scalloped leading edge portion  144 . The pad has a tapered trailing edge portion  146 .  
         [0039]    In operation, the clutch disc rotates in the direction of arrow  156  shown in FIG. 7. Air is forced toward flywheel  6  and into grooves  126  and  128  by the tapered portion  144  of the friction pad. The clutch button  18 C along the sides of its backing plate  122  has a portion  148  which is not covered by the pad  120 . The portion  148  of the backing plate has extending therethrough apertures  124  to allow attachment of the button  18 C to the clutch disc  16 . Since tapered portions  144  and  146  are on both the leading and trailing ends, the clutch button  18 C can be used on either side of the clutch disc  16 .  
         [0040]    [0040]FIG. 8 shows another embodiment of a friction pad  220 . The friction pad  220  has a radial outer edge  230  of radius R1 centered at point  260 , and a radial inner edge  231  centered at a point  262 . Outer edges  232 A and  232 B fall on straight lines extending from point  262 , separated by approximately 40° from each other. Inward circumferential outer edge  232 A is connected to radial outer edge  230  by upper outward circumferential edge  233 A, and to radial inner edge  231  by lower outward circumferential edge  233 B. Inward circumferential outer edge  232 B is connected to radial outer edge  230  by upper outward circumferential edge  233 C, and to radial inner edge  231  by lower outward circumferential edge  233 D.  
         [0041]    First groove  234  extends diagonally across pad  220  from edge  233 A to edge  233 D. Second groove  236  extends diagonally across pad  220  from edge  233 B to edge  233 C, intersecting first groove  234 . Grooves  234  and  236  are not straight. Each of  234  and  236  have two distinct radii of curvature. A centerline  264  of a first groove portion  234 A of groove  234  has a radius of R3, centered at point  266 . A centerline  268  of a second groove portion  234 B of groove  234  has a radius of R4, centered at point  270 . Centerlines  264  and  268  are continuous, with portions  234 A and  234 B being correspondingly continuous. A centerline  272  of a first groove portion  236 A of groove  236  has a radius of R5, centered at point  274 . A centerline  276  of a second groove portion  236 B of groove  236  has a radius of R6, centered at point  278 .  
         [0042]    An exemplary value for radii R3 through R6 is 5.000 inches (127 mm). Exemplary values for radii R1 and R2 are 6.377 inches (162.0 mm) and 6.375 inches (161.9 mm) respectively. Point  278  is offset from point  260  by L 1  and L 2 . Point  270  is offset from point  260  by L 3  and L 4 . Exemplary values of L 1 , L 2 , L 3  and L 4  are 2.753 inches (69.93 mm), 3.095 inches (78.61 mm), 2.928 inches ( 74 . 37  mm) and 11.322 inches (287.58 mm) respectively. Points  266  and  274  are similarly spaced from point  260 .  
         [0043]    [0043]FIGS. 9 and 10 show yet another alternative embodiment of a clutch button  318 . A first groove  334  and a second groove  336  cross a friction pad  320  in essentially the same manner in which grooves  234  and  236  cross friction pad  220 . However, the leading and trailing edge portions  344  and  346  respectively have a radiused taper which is intended to force air between the friction pad  320  and the pressure plate. Air forced therebetween will help separate the two parts, reducing clutch drag.  
         [0044]    [0044]FIGS. 11 and 12 show a further alternative embodiment of a clutch button  418 . A first groove  434  and a second groove  436  cross a friction pad  420  in essentially the same manner in which grooves  234  and  236  cross friction pad  220 . However, the leading and trailing edge portions  444  and  446  respectively have a scalloped taper which tapers downwardly toward backing plate  422  as well as inwardly toward the center of friction pad  420  from start points proximate to the intersection of grooves  234  and  236  with leading and trailing edge portions  444  and  446 . The scalloped edge portions  444  and  446  are intended to force air between friction pad  420  and the pressure plate. Air forced therebetween will help separate the two parts, reducing clutch drag.  
         [0045]    Clutch drag is an undesired characteristic of clutch operation using prior art clutch buttons. After disengagement, the clutch disc will in some instances continue to contact or drag against one of the pressure plate and the engine flywheel. The clutch drag results in difficult shifting of the transmission between gear ratios since power is still being transferred through the dragging clutch disc to the transmission input shaft. The present invention operates to significantly reduce the amount of clutch drag by using aerodynamic forces generated when grooves are formed in the surface of the friction pads and by providing an optimal cooling flow path for air. Air flow through the grooves facilitates separation of the clutch disc from the clutch pressure plate and the engine flywheel, thereby reducing the clutch disc drag and facilitating transmission shifting. Tapered portions  144  and  146  further facilitate separation of the disc assembly from both the pressure plate and the flywheel by directing a greater flow of air therebetween.  
         [0046]    As noted above, the grooves formed in the friction pad also increase cooling of the friction pad. Clutch drag tends to increase with higher operating temperatures. The cooling effect of the friction pad grooves thus serves to reduce clutch drag.  
         [0047]    The embodiments disclosed herein have been discussed for the purposes of familiarizing the reader with the novel aspects of the invention. Although preferred embodiments of the invention have been shown and disclosed, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of the invention as described in the following claims. Examples of such variations include providing an enlarged opening or mouth for the grooves which tapers to the narrower width W of the grooves and employing radiused corners at the ends of the grooves and at the intersection of the grooves to facilitate molding of the grooves in the friction material.