Abstract:
A clutch assembly and clutch plates utilized therein is provided which gives smooth engagement and high holding torque. The friction facing has differing coefficients of friction and different heights. Also claimed is a method of manufacture and a clutch assembly with a piston contacting the friction pack radially displaced from a radial centreline of the friction facings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/759,172 filed Jan. 13, 2006 and U.S. Provisional Application No. 60/855,786 filed Nov. 1, 2006, the entire specifications of which are expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the present invention is that of clutch assemblies and friction plates used therein. More particularly the present invention relates to clutch assemblies and friction plates used in automotive transmissions. 
       BACKGROUND OF THE INVENTION 
       [0003]    In many modern automotive automatic transmissions, particularly of the design known as Lepelltier layout, a single clutch in the transmission will be required to perform its function under widely different conditions, depending on the gear ratio in which the transmission is functioning. There is a need to have good smooth engagement properties in one gear with low torque capacity requirements, and very high holding torque requirements while engaged in another gear. 
       SUMMARY OF THE INVENTION 
       [0004]    To meet the aforementioned need, the present invention provides a clutch assembly having good smooth engagement properties in one gear with low torque capacity requirements, and very high holding torque requirements while engaged in another gear. The present invention additionally provides friction plates that are highly useful in such clutch assemblies. 
         [0005]    Other features of the invention will become more apparent to those skilled in the art as the invention is further revealed in the accompanying drawings and detailed description of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a partial sectional view of a clutch assembly of the present invention. 
           [0007]      FIG. 2  is an operational view of the clutch assembly of  FIG. 1 . 
           [0008]      FIG. 3  is a front elevational view of a preferred embodiment friction plate of the present invention. 
           [0009]      FIG. 4  is a view taken along line  4 - 4  of  FIG. 3 . 
           [0010]      FIG. 5  is a front elevational view of an alternate preferred embodiment friction plate of the present invention. 
           [0011]      FIG. 6  is a view taken along line  6 - 6  of  FIG. 5 . 
           [0012]      FIGS. 7 and 8  are schematic views illustrating the use of the friction plate shown in  FIG. 1 . 
           [0013]      FIG. 9  is a side elevational view of an alternate preferred embodiment friction plate of the present invention. 
           [0014]      FIG. 10  is a front elevational view of an alternate preferred embodiment friction plate of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Referring to  FIG. 1  a clutch assembly  7  of the present invention is provided. The clutch has two rotating members provided by a hub  10  and clutch housing  12 . The clutch housing  12  mounts a plurality of axially moveable pressure plates  14 . The pressure plates  14  have a splined connection along their outer diameter with the clutch housing  14 . A snap ring  16  provides a stop for the pressure plates  14 . Juxtaposing the pressure plates  14  are a plurality of friction plates  18  having their inner diameters mounted on a splined portion of the hub  10 . At least one of the friction plates  18  and preferably all of them has a friction facing  20  with multiple coefficients of friction. 
         [0016]    The friction plate  18  has a friction facing  20  with a radially inward first friction facing  22  of a first height  24  and a first coefficient of friction. The friction plate  18  also has a radially outward second friction facing  26  having a second lower height  28  and a second coefficient of friction that is higher than the first coefficient of friction. 
         [0017]    A piston  30  mounted in the clutch housing  12  is provided for actuating the friction pack provided by the pressure plates  14  and friction plates  18 . The piston  30  contacts one of the pressure plates  14  along a radially outward portion of the pressure plates  14  displaced radially outward of a radial centerline  34  of the friction plate friction facing  20 . 
         [0018]    Upon initial actuation of the piston  30 , the radial inner portion of the pressure plates  14  contacts the first friction facings  22 . Separation still exists between the pressure plates  14  and the second friction facings  26 . Accordingly, the clutch  7  exhibits the characteristic of a clutch with smooth shifting qualities due to the first friction facing  22 . Upon further actuation of the piston  30 , the friction pack experiences a contracting axial deflection along its outer radial plane of rotation. The deflection will be a function of contact of the piston  30  with the pressure plates  14  outward of the of the radial centerline  34  of the friction plate facing  20  and a compression of the first friction facing  22  due to the gap with the second friction facings  26 . The aforementioned deflection increases the pressure upon the first friction facing  22  compressing the same. Further pressure by the piston  30  required when the clutch  7  is in a high torque holding operation causes the second friction facing  26  to additionally be engaged by the pressure plates  14  ( FIG. 2 ). The additional frictional engagement with the second friction facings  26  with its increased coefficient of friction greatly enhances the clutch&#39;s  7  holding torque. 
         [0019]    Referring to  FIG. 9 , an alternate embodiment friction plate  107  is provided having a first facing  110  and a second facing  112 . The first friction facing  110  and the second friction facing  112  have the same height. The second friction facing  112  has a higher coefficient of friction. When the friction plate  107  is used in clutch  7 , the contracting radial deflections of the clutch assembly increases the proportion of the piston load carried by facing  112  relative to facing  110 . The proportionally increased force carried by facing  112  increases the torque carrying capacity of the clutch assembly. This effect can also be enhanced by having the modulus of compression of facing  110  and  112  different with friction facing  110  having a lower modulus of compressibility (less stiff). The aforementioned facing  22  and  26  ( FIGS. 1 and 2 ) can also have a differential modulus of compressibility contributing to the differential loading due to the contracting axial deflection. 
         [0020]    Referring to  FIG. 10 , an alternate embodiment friction plate  157  is provided having a first friction facing  158  that encompasses a plurality of button second friction facings  160 . The second friction facing  160  has a greater coefficient of friction and modulus of compressibility than the first friction facing  158 . The second friction facing  160  has a lower height. In operation, the friction plate  157  functions in a manner to those friction plates previously described. The second friction facings  160  tend to run hotter when engaged with a pressure plate an accordingly encircled by an oil groove  164  that intersects the radial edges  166  and  168  of the facing. 
         [0021]    Referring to  FIGS. 3 and 4 , a preferred embodiment friction plate  207  useful in the clutch assembly of the present invention and other conventional clutches is shown. The friction plate  207  in the present example is a wet type friction plate. The friction plate  207  has a core plate  210 . The core plate  210  is typically fabricated from carbon steel or plastic. An inner diameter of the core plate  210  has spline teeth  12  to provide a torsional interface with a drive member. In another embodiment (not shown), the core plate  210  may be connected with a torsional damper. In still another embodiment (not shown), the core plate may have spline teeth on an outer diameter. 
         [0022]    Connected along a major continuous circumference of the core plate  210  on at least one side, and as shown both sides, is a first friction facing  214 . The first friction facing  214  is typically a fiber type friction facing such as BW  1777  or BW  4300  or other suitable material. The first facing  214  typically has a static coefficient of friction in the range of 0.12 to 0.14 and a dynamic coefficient of friction in range of 0.14 to 0.16. The first facing  214  can be connected with the core  210  by adhesives or other suitable techniques. The first facing  214  can have a height  218  preferably in the range of 0.4 to 1.0 mm. 
         [0023]    Radially separated outward from a first facing  214  and connected with the core plate  210  along a major continuous circumference is a second facing  222 . The second facing  222  may be similarly fabricated as the material in the first facing  214 , or of an alternate composition and fabrication, but in either case having a different coefficient of friction. In the example shown in  FIG. 1  the second facing  222  has a higher static coefficient of friction in the range of 0.16 to 0.22 and a dynamic coefficient of friction in the range of 0.15 to 0.22. The second facing  222  has a height  224  preferably in the range of 0.05 mm to 0.15 less than the height  218  of the first facing  214 . 
         [0024]    Referring to  FIGS. 5 and 6 , an alternate preferred embodiment friction plate  237  has a unitary friction disc providing a first facing  238  integrally formed with a second facing  244 . The first facing  238  is radially separated by a groove  240  from the second facing  244 . The core plate  210  can be identical to the core plate previously described for friction plate  237 . The facings  238  and  244  are fabricated from a fiber based friction material and have heights  245  and  247  comparable to those previously described. The fiber based friction material can be a fibrous material with or without various additives to modify its frictional characteristics. The second facing  244  has a higher static and dynamic coefficient of friction due to being saturated with a higher concentration of friction modifying saturant. Examples of such a saturant are phenolic, epoxy, polyimide, or silicone materials, blends thereof, or other suitable materials. Saturation levels vary from 5-60 percent by weight with higher concentrations typically enhancing friction properties. The groove  240  is provided to aid in the prevention of wicking of the saturant from the second facing  244  to the first facing  238  during fabrication. The groove  240  can be formed or milled into the facings before, after, or during connection of the facings with the core plate  210 . The presence of the groove  240  allows the manufacture of friction plates with different frictional properties for different transmissions or different locations within a transmission or clutch pack using the same common materials. The specific frictional characteristics on any given friction plate can be custom selected by simply determining the saturation concentration of the separate friction facings. The saturating operation can be performed before or after connection of the facings with the core plate  210 . 
         [0025]    In operation ( FIGS. 7 and 8 ), the friction plate  207  (friction facing being shown on only one side of the friction plate  207  for illustrative purposes only) is torsionally connected with a first rotating member  262 . A rotating disc  264  is provided which is torsionally connected with a second shaft  68 . The disc  264  and the friction plate  207  can move axially relative to one another to torsionally engage. Upon initial engagement, the disc  264  first contacts the first facing  214  without contacting the second facing  222 . This above noted action allows smooth initial engagement for a gearshift operation. The increased pressure to the disc  264  compresses the first friction facing  214  to a height of the second friction facing  222  and begins to engage the second facing  222 . The disc  264  then engages with both facings  214  and  222  to provide a high holding torque. Differences in the coefficients of friction, surface area, radial widths and radius of the facings  214 ,  222  can be specified so that either facings may transmit more torque when both facings  214 ,  222  are engaged with the disc  264 . In most applications, the deformation of the first facing  214  should be such that under clutch engagement pressures it compresses to the facing thickness of the second facing  222 . The deformation characteristics of the second facing  222  are such that as additional pressure is applied to the locked up clutch pack, the majority of the additional load is carried on the second facing  222 . 
         [0026]    While preferred embodiments of the present invention have been disclosed, it is to be understood it has been described by way of example only, and various modifications can be made without departing from the spirit and scope of the invention as it is encompassed in the following claims.