Abstract:
A friction clutch pack exhibiting improved high speed stability includes a first plurality of friction plates or discs preferably having friction material on both faces interleaved with a second plurality of thicker reaction plates or discs. The friction plates comprise a formed core plate having multiple obliquely oriented or angularly offset sinusoidal waves. Male splines around the periphery of each friction plate engage complementary splines on a cylindrical housing. The reaction plates are flat and thicker than the friction plates and include female splines around an inner opening which engage complementary splines on a shaft or quill.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/734,684, filed Dec. 7, 2012, which is hereby incorporated in its entirety herein by reference. 
    
    
     FIELD 
     The present disclosure relates to friction plates for wet clutches and more particularly to friction plates for wet friction clutches having improved high speed stability and performance. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Wet friction clutches, or more properly wet friction clutch packs, which comprise a first plurality of friction plates or discs interleaved with a second plurality of thicker reaction plates or discs connected to respective input and output members, are nearly universal components of modern multiple planetary gear automatic motor vehicle transmissions. The activation or relaxation or one or typically more than one such clutch in a predetermined sequence, steps the transmission through upshifts and downshifts. 
     Frequently during such operation, wet friction clutches are subjected to relatively high differential, i.e., input to output, speeds. In certain clutches and certain applications, dramatically increased spin losses have been observed when the differential speed increases beyond a certain magnitude. This non-linear spin loss increase has been attributed to instabilities of the rotating friction plates which result from gyroscopic tumbling of the plates. 
     The use of core plates with a shallow circumferential sinusoidal profile is state of the art for spin loss reduction at low relative (differential) speeds. However, it is believed that this approach is unsatisfactory at high relative speeds because the sinusoidal geometry essentially conforms to the first deformation mode of the plates. 
     There have been many other proposed solutions to this problem, all of which lead to other inefficiencies or difficulties. 
     The present invention is directed to an improved friction clutch configuration that reduces high differential speed instabilities and spin losses. 
     SUMMARY 
     The present invention provides a friction clutch pack having a first plurality of friction plates or discs preferably having friction material on both faces interleaved with a second plurality of thicker reaction plates or discs. The friction plates comprise a formed core plate having multiple obliquely oriented or angularly offset sinusoidal waves. Male splines around the periphery of each friction plate engage complementary splines on a cylindrical housing. The reaction plates are flat and thicker than the friction plates and include female splines around an inner opening which engage complementary splines on a shaft or quill. Of course, the invention comprehends a friction clutch pack in which the male splines are disposed on the reaction plates and the female splines are disposed on the friction plates or discs. A friction clutch pack assembly incorporating friction plates or discs according to the present invention exhibits improved high differential speed stability and reduced spin losses. 
     Thus it is an aspect of the present invention to provide a friction clutch pack which exhibits improved high differential speed performance. 
     It is a further aspect of the present invention to provide a friction clutch pack which exhibits reduced high differential speed instability and spin loss. 
     It is a still further aspect of the present invention to provide a friction clutch pack having friction plates which include a core plate with multiple angularly offset sinusoidal waves. 
     It is a still further aspect of the present invention to provide a friction clutch pack having friction plates which include a core plate with multiple obliquely oriented sinusoidal waves. 
     It is a still further aspect of the present invention to provide a friction clutch pack having friction plates which include a core plate with angularly offset sinusoidal waves and friction material affixed thereto. 
     It is a still further aspect of the present invention to provide a friction clutch pack having friction plates which include a core plate with obliquely oriented sinusoidal waves and friction material affixed thereto. 
     It is a still further aspect of the present invention to provide a friction clutch pack having friction plates which include a core plate with angularly offset sinusoidal waves and male splines disposed about its periphery. 
     It is a still further aspect of the present invention to provide a friction clutch pack having friction plates which include a core plate with obliquely oriented sinusoidal waves and male splines disposed about its periphery. 
     It is a still further aspect of the present invention to provide a friction clutch pack having flat reaction plates which include female splines disposed within an inner opening. 
     Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a sectional view of a portion of an automatic motor vehicle transmission including a wet friction clutch pack and operator incorporating the present invention; 
         FIG. 2  is a plan view of a prior art friction plate having sinusoidal waves aligned with geometric axes, i.e., lines of radius, of the plate; 
         FIG. 3  is a side elevational view of the front half of a prior art friction plate having sinusoidal waves aligned with geometric axes, i.e., lines of radius, of the plate; 
         FIG. 4  is an enlarged, full sectional view of a prior art friction plate having sinusoidal waves aligned with geometric axes, i.e., lines of radius, of the plate taken along line  4 - 4  of  FIG. 2 ; 
         FIG. 5  is a plan view of a friction plate according to the present invention having angularly offset or obliquely oriented sinusoidal waves; 
         FIG. 6  is a side elevational view of a friction plate according to the present invention having angularly offset or obliquely oriented sinusoidal waves; and 
         FIG. 7  is an enlarged, full sectional view of a friction plate according to the present invention having angularly offset or obliquely oriented sinusoidal waves taken along line  7 - 7  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIG. 1 , a portion of an automatic motor vehicle transmission is illustrated and generally designated by the reference number  10 . The automatic transmission  10  typically includes a plurality of nested, concentric shafts and quills, one of which, a first quill  12 , is illustrated in  FIG. 1 , a plurality of planetary gear assemblies, one of which, a first planetary gear assembly  20  is illustrated in  FIG. 1  and a plurality of friction pack clutch assemblies, one of which, a first friction pack clutch assembly  40  is also illustrated in  FIG. 1 . The first quill  12  is coupled through interengaging male and female splines  14  to a stationary or rotating drive plate or disc  16  and defines a sun gear  22  of the first planetary gear assembly  20 . The first planetary gear assembly  20  also includes a planet gear carrier  24  which supports a plurality of shafts  26  (one of which is illustrated in  FIG. 1 ) which, in turn, support a like plurality of needle bearing assemblies  28  and a respective plurality of planet gears  32  (one of both being illustrated in  FIG. 1 ). The planet gears  32  are in constant mesh with the sun gear  22  and a ring gear  34 . The ring gear  34  is secured to an adjacent circular member  36  of the transmission  10  which may be a drive member, a driven member or a stationary member. 
     The planetary gear assembly  20  just described is a simple planetary gear assembly (having a single planet gear  32  between the sun gear  22  and ring gear  34 ). It should be appreciated that the invention is not limited for use therewith and that a compound planetary gear assembly (having pairs of planet gears between the sun gear and ring gear) is also wholly suitable for use with the present invention. 
     The friction clutch pack assembly  40  is disposed outside and generally in radial alignment with the first planetary gear assembly  20 . The outer surface of the ring gear  34  includes male splines  42  which are engaged by complementary female splines  44  on a plurality of reaction plates  46 . Interleaved with the reaction plates  46  are a plurality of friction plates or discs  48 . The friction plates or discs  48 , which are often referred to as a core since friction material is generally attached to one or both surfaces or faces thereof, include male splines  52  which are engaged by complementary female splines  54  on the inner surface of an axially extending flange or shoulder  56  of the planet gear carrier  24 . As best illustrated in  FIG. 5 , the friction plates or discs  48  include an annulus or band of friction material  58  on each face or surface. 
     It should be understood that with regard to the plurality of reaction plates  46  having a smaller diameter and internal (female) splines  44  and the plurality of interleaved friction plates or discs  48  of somewhat larger diameter having external (male) splines  52  described directly above, the relative diameters and locations of the splines may be interchanged such that the reaction plates have a larger diameter and external (male) splines which engage a shoulder or a housing and the friction plates or discs have a smaller diameter and internal (female) splines which engage a gear, a shaft or a hub. 
     At one end of the interleaved reaction plates  46  and clutch plates  48 , the left end in  FIG. 1  (adjacent the wall of the planet gear carrier  24 ), is a circular backing plate  62  against which the plates  46  and  48  are compressed. At the opposite end of the interleaved plates  46  and  48 , to the right in  FIG. 1 , is an apply plate  64  which is retained in position by a snap ring  66  or similar component. The apply plate  64  evenly applies compressive force to the interleaved clutch plates  46  and  48  generated by, for example, a hydraulic or electric operator  68  which is transmitted through a thrust bearing  69  to the apply plate  64 . 
     It will be appreciated that the foregoing description of a location and application for the present invention is exemplary and illustrative only. It should be understood that the present invention will find wide application in any power transmission device of any nature in which friction clutch pack assemblies are utilized. 
     Referring now to  FIGS. 2 ,  3  and  4 , a prior art friction plate or disc  70  is illustrated. The friction plate or disc  70 , according to previous practice, includes sinusoidal curves or waves  72  that align with the geometric axes of the disc, that is, with lines of radius. The prior art friction plate or disc  70  typically includes friction material  74  on both faces and male splines  76  about its periphery. The edge-on view of  FIG. 3  clarifies that the arrangement of the sinusoidal waves or curves  72  of the prior art friction plate or disc  70  are like those of a conventional wave washer.  FIG. 4  also illustrates this orientation of the waves  72  in the prior art friction plate or disc  70  whereby a radial cutting plane, the line  4 - 4  of  FIG. 2 , reveals that the displaced or offset wave  72  is at an essentially constant axial offset from the nominal plane  78  of the plate or disc  70  along a line of radius. 
     It should be appreciated that the extent of axial offset, that is, the height of the sinusoidal waves or curves  72  has been exaggerated for purposes of explanation in the foregoing drawing figures. 
     Unfortunately, as noted above, this conventional, prior art arrangement of the sinusoidal waves or curves  72  essentially conforms to the first mode of structural vibration and deformation of the prior art plate or disc  70 , exciting the first order resonant frequency of the plate or disc  70  and thus exacerbates rather than cures or reduces the problem of friction plate deformation and increased drag at high differential rotational speeds. 
     Referring now to  FIGS. 5 ,  6  and  7 , the friction plate or disc  48  according to the present invention is illustrated. Here, the sinusoidal waves or curves  82  are angularly offset or obliquely oriented relative to lines of radius. Thus, as illustrated in  FIG. 6 , the waves or curves  82  do not align with radial lines. With regard to  FIG. 7 , note the oblique or angular orientation of the cutting plane  7 - 7  in  FIG. 5  which, in a manner similar to  FIG. 4 , presents the axially displaced or offset wave  82  at an essentially constant distance from the nominal plane  84  of the plate or disc  48 . Once again, it should be appreciated that the extent of axial offset, that is, the height of the sinusoidal waves or curves  82  has been exaggerated for purposes of explanation in  FIGS. 6 and 7 . 
     The angle of offset of the sinusoidal waves or curves  82  in  FIGS. 5 ,  6  and  7  is 45° but it should be understood that this angle may be adjusted over a relatively wide range, for example, 30° to 60° of offset from a line of radius and possibly wider depending upon engineering variables relating to the friction clutch pack assembly  40  and the friction clutch plates or discs  48  such as their maximum speed, both engaged and disengaged, the thickness, stiffness and material of the friction plate or disc  48 , the type and thickness of the friction material  58  and other variables. Similarly, the number of sinusoidal waves or curves  82  may be greater or lesser than the four illustrated in  FIGS. 5 ,  6  and  7 . For example, three, five, six, eight, ten or twelve waves or curves  82  may be formed in a plate or disc  48 . Typically, smaller numbers of waves or curves  82  will be utilized with relatively smaller diameter plates or discs  48  and larger numbers of waves or curves  82  will be utilized with relatively larger diameter plates or discs  48 . 
     The description of the present invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be, and are, within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.