Abstract:
A disc clutch assembly is provided that includes first and second sets of generally annular plates spaced alternately with one another. The plates of the first set have a friction interface. The first and second sets of plates are selectively engagable with one another at the friction interface for transferring torque loads. Separating devices are in contact with the plates radially inward of the friction interface. The separating devices are configured to bias the respective ones of the first and second sets of plates apart from one another when not selectively engaged.

Description:
TECHNICAL FIELD 
     The invention relates to a disc clutch assembly. 
     BACKGROUND OF THE INVENTION 
     Disc clutches, such as rotating-type clutches and brake-type clutches used in transmissions, have sets of closely spaced plates that are selectively engagable with one another to transmit torque loads. The plates generate significant amounts of heat, and require cooling and lubrication. The lubricated plates tend to generate drag, causing considerable spin losses. 
     SUMMARY OF THE INVENTION 
     A disc clutch assembly is provided that includes first and second sets of clutch plates spaced alternately and coaxial with one another. The plates of the first set have a friction material on a first portion of an outer surface thereof. The first and second sets of plates are selectively engagable with one another at the first portions of the first set for transferring torque loads. Separating devices are configured to bias the first and second sets of clutch plates apart from one another when not selectively engaged, thus reducing drag. Because the separating devices separate plates of the first set from plates of the second set, superior drag reduction is accomplished. Additionally, because the separating devices contact the plates of the first set at a portion that does not have friction material, i.e., at a portion with a lower coefficient of friction, drag due to the separating devices is minimal. 
     The plates of the first set may be referred to as friction plates and the plates of the second set may be referred to as reaction plates. In one embodiment, the separating devices may be flexible tabs integral with the friction plates that extend axially outward. For example, three integral tabs may extend axially outward in one direction, and three others may extend axially outward in an opposing direction. The integral tabs may be at a splined inner circumference of the friction plate. In another embodiment, the separating devices may be annular wave springs. With either embodiment, it may be optimal if the separating devices extend axially beyond the friction material not less than 0.5 mm and not more than 1.0 mm. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective exploded view of a first embodiment of a disc clutch assembly; 
         FIG. 2  is a schematic perspective fragmentary view of a portion of the disc clutch assembly of  FIG. 1 ; 
         FIG. 3  is a schematic perspective cross-sectional and fragmentary view of a portion of the disc clutch assembly of  FIGS. 1 and 2 ; 
         FIG. 4  is a schematic perspective exploded view of a second embodiment of a disc clutch assembly; and 
         FIG. 5  is a schematic perspective cross-sectional and fragmentary view of a portion of the disc clutch assembly of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Referring to  FIG. 1 , a disc clutch assembly  10  is illustrated having a first set of clutch plates which are annular friction plates  12 . As further explained below, the friction plates  12  are selectively engagable with a second set of clutch plates, which are annular reaction plates  13 , to transmit torque loads, and, when not engaged, are separated from the reaction plates  13  via separating devices to minimize drag. The annular friction plates  12  each have a core  14  with opposing side faces  15 A,  15 B ((see  FIG. 3 ) also referred to as an outer surface) with a radially outer portion  16  on which a friction material  18  is adhered, bonded, or otherwise secured. The friction material  18  has an average thickness t. As best illustrated in  FIG. 2 , the friction material  18  does not cover a radially inner portion  20  of each of the friction plates  12 . As used herein, the radially outer portion  16  is a first portion of the outer surface  15 A,  15 B, and the radially inner portion  20  is a second portion of the outer surface  15 A,  15 B. 
     Referring again to  FIG. 1 , the reaction plates  13  are spaced to alternate axially with the friction plates  12  (i.e., such that a friction plate  12  has an axially adjacent reaction plate  13  on either side thereof). The reaction plates  13  and the friction plates  12  are coaxial about a center axis  26  shown in  FIG. 1 . The friction plates  12  each have a splined inner circumference  28  at which they may be operatively connected with an outwardly splined shaft or hub, represented at  30  in  FIG. 3 . The reaction plates  13  have a splined outer circumference  32  at which they may be connected to an inwardly splined component represented schematically at  34  in  FIG. 3 , which may be a hub or housing. The shaft  30  may rotate, in which case the friction plates  12  rotate commonly with the shaft  30 . If component  34  is a rotatable hub, the reaction plates  13  rotate with the component  34 , in which case the disc clutch is a rotating-type clutch. If component  34  is a stationary housing, the reaction plates  13  are stationary with component  34 , in which case the disc clutch  10  is a stationary-type clutch (i.e., a brake-type clutch). 
     Referring to  FIGS. 1-3 , the friction plates  12  each have separating devices in the form of integral tabs  40 A,  40 B spaced around the splined inner circumference  28  and extending axially in opposite directions (those extending in one direction referred to as  40 A and those extending in the opposing direction referred to as  40 B). The tabs  40 A,  40 B are positioned in lieu of a spline  42 , and as best shown in  FIG. 2 , do not extend as far radially inward as the splines  42  so that the tabs  40 A,  40 B will not contact the shaft  30 . In the embodiment of  FIGS. 1-3 , the tabs  40 A,  40 B are spaced evenly about the inner circumference  28 , with a total of six tabs on each friction plate  12 , with three of the tabs extending axially in one direction and three of the tabs extending axially in the opposing direction. Although some of the tabs are obscured from view in  FIG. 1 , all six tabs are shown on the rightmost friction plate  12 , with some of the tabs shown in phantom. (Tabs  40 A,  40 B that are obscured on the other friction plates  12  are not shown in phantom for clarity in the drawing.) Other arrangements or another number of tabs may be used within the scope of the claimed invention. 
     The tabs  40 A,  40 B extend in alternate axial directions sequentially around the inner circumference  28 .  FIG. 2  shows a portion of a friction plate  12 , with one tab, referred to as  40 A, extending in a first axially direction (upward in the view of  FIG. 2 ) and one of the tabs, referred to as  40 B, extending in a second axial direction (downward in the view of  FIG. 2 ). The tabs  40 A,  40 B are flexible, and are biased to the axial positions shown in  FIGS. 1 and 2 , but flex under pressure when the plates  12 ,  13  are engaged. 
     As shown in  FIG. 1 , the friction plates  12  are rotated relative to one another such that the tabs  40 A,  40 B on any one of the friction plates  12  do not necessarily align with the tabs  40 A,  40 B on the next axially positioned friction plate  12 . This evenly distributes the axial forces exerted by the tabs  40 A,  40 B on the adjacent reaction plates  13 . However, the tabs  40 A and  40 B on the respective friction plates  12  may be aligned as shown in the assembled cross-sectional view of  FIG. 3 . 
     The reaction plates  13  include an apply plate labeled  13 A (i.e., the reaction plate  13  shown at the left side of  FIG. 3 ), typically of a wider width than the others, that is axially movable in response to hydraulic pressure to move all of the plates  12 ,  13  in closer relation axially, with the apply plates engaging the reaction plates at the friction material  18 . In  FIG. 3 , the disc clutch assembly  10  is shown in an unengaged state, as is apparent by the slight gaps  44  between the friction material  18  and the reaction plates  13 . The gaps  44  shown are with the friction material  18  at its starting thickness t; however, if the friction material  18  wears slightly, the gaps  44  will grow in size accordingly. The flexible tabs  40 A,  40 B may extend axially outward 0.5 mm to 1.0 mm beyond the friction material  18  so that the gap is 0.5 mm to 1.0 mm. The respective tabs  40 A,  40 B at the radially inner portions  20  of the friction plates  12  are shown in contact with the reaction plates  13  and bias the adjacent reaction plates  13  apart from the friction plates  12 . Specifically, the tabs  40 A,  40 B bias the reaction plates  13  away from contact with the radially outer portion  16  of the friction plates  12  with the friction material  18  thereon. Although only one tab  40 A or  40 B is visible per friction plate  12  in  FIG. 3 , as discussed with respect to  FIG. 1 , there are multiple additional tabs  40 A,  40 B extending axially in either direction from each friction plate  12 , such that the reaction plates  13  on either side of the respective friction plate  12  are biased axially away. The tabs  40 A,  40 B are flexible such that axial movement of the apply plate  13 A toward the adjacent friction plate  12  overcomes the bias of the tabs  40 A,  40 B sufficiently to compress the tabs axially inward toward greater radial alignment with the radially outer portions  16  of the friction plates  12 . 
     Second Embodiment 
     Referring to  FIG. 4 , a disc clutch assembly  110  is illustrated having a first set of clutch plates which are annular friction plates  112 . As further explained below, the friction plates  112  are selectively engagable with a second set of clutch plates, annular reaction plates  113 , including an apply plate  113 A, to transmit torque loads, and, when not engaged, are separated from the reaction plates  113  via separating devices  140  to minimize drag. The annular friction plates  112  each have a core  114  with opposing side faces  115 A,  115 B (see  FIG. 5 ) (also referred to as an outer surface) with a radially outer portion  116  on which a friction material  118  is adhered, bonded, or otherwise secured. The friction material  118  has an average thickness t. As best illustrated in  FIG. 5 , the friction material  118  does not cover a radially inner portion  120  of each of the friction plates  12 . As used herein, the radially outer portion  116  is a first portion of the outer surface  115 A,  115 B and the radially inner portion  120  is a second portion of the outer surface  115 A,  115 B. 
     Referring again to  FIG. 4 , the reaction plates  113  alternate axially with the friction plates  112  (i.e., such that a friction plate  112  has an axially adjacent reaction plate  113  on either side thereof). The reaction plates  113  and the friction plates  112  are coaxial about a center axis  126  shown in  FIG. 4 . The friction plates  112  each have a splined inner circumference  128  at which they may be operatively connected with an outwardly splined shaft or hub. The reaction plates  113  have a splined outer circumference  132  at which they may be connected to an inwardly splined component, which may be a hub or housing. The shaft connected with the friction plates  112  may rotate, in which case the friction plates  112  rotate commonly with the shaft. If the component is a rotatable hub, the reaction plates  113  rotate with the component splined thereto in which case the disc clutch  110  is a rotating-type clutch. If the component is a stationary housing, the reaction plates  113  are stationary with the component splined thereto, in which case the disc clutch  110  is a stationary-type clutch (i.e., a brake-type clutch). 
     Referring to  FIGS. 4-5 , separating devices in the form of annular wave springs  140  are sized to contact the radially inner portion  120  of a respective one of the friction plates  112  and an adjacent respective one of the reaction plates  113 . The annular wave springs  140  have a slight wave pattern about the entire circumference thereof such that the wave spring  140  is sufficient in amplitude to extend axially between and in contact with the adjacent reaction plate  113  and radially inner portion  120  of the friction plate  112  when the disc clutch  110  is not engaged. Specifically, a first side surface  150  of one of the wave springs  140  contacts the reaction plate  113  and an opposing second side surface  152  of the wave spring  140  contacts the friction plate  112 . Additionally, the overall axial distance between the side surfaces  150 ,  152  is sufficiently larger than the thickness t of the friction material  118  such that the wave spring  140  separates the friction plate  112  and friction material  118  from contact with the adjacent reaction plate  113  when the disc clutch  110  is not engaged, so that a gap  144  exists therebetween when the disc clutch  110  is not engaged. Preferably, the annular wave springs  140  are sized to extend axially outward beyond the friction material  118  so that the gap  144  is 0.5 mm to 1.0 mm. The gaps  144  shown are with the friction material  118  at its starting thickness t; however, if the friction material  118  wears slightly, the gaps  144  will grow in size accordingly. The total number of waves about the circumference of the wave spring  140  may be selected to result in the desired flexibility (i.e., resistance to compression) of the wave springs  140  as desired. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.