TECHNICAL FIELD 
       [0001]    The present invention relates to a clutch assembly having a clutch plate with a plurality of internal fluid passages configured for conducting pressurized fluid directly to the friction interface for cooling of the interface and for reducing spin losses. 
       BACKGROUND OF THE INVENTION 
       [0002]    In an automotive transmission, clutch assemblies are commonly used to transmit rotational motion or torque between two rotating members, such as an engine crankshaft and a transmission driveshaft. Standard friction-type clutch assemblies, or friction clutches, include a series of alternating friction and reaction plates that together make up a clutch pack, with the clutch pack being disposed within an outer clutch drum. The friction plate typically has a layer of rough friction material which is bonded or otherwise attached to the primary contact surfaces of a metal core plate, while the reaction plate typically has a relatively smooth contact surface configured to oppose the friction plate when the friction clutch is engaged. The friction clutch is engaged or applied using a controllable hydraulic force supplied by a transmission pump. The force actuates an apply mechanism, such as a clutch-apply piston, to selectively compress the friction and reaction plates of the clutch pack. Once compressed, the alternating plates become interlocked due to the friction forces imparted by the apply force and the friction material, thereby allowing the rotating members to rotate in unison. 
         [0003]    Friction clutches may be of the dry-plate or wet-plate variety, with wet-plate friction clutches providing enhanced thermal performance due to the cooling qualities of the pressurized lubricating fluid. In particular, the enhanced thermal performance is accomplished by passing or directing the pressurized fluid, such as transmission fluid or oil, through and around the mating clutch surfaces to dissipate heat generated by the friction forces in proximity to the friction interface between the surfaces. Lubricated surface cooling of friction clutch plates is often provided via a series of shallow radial channels or grooves along the contact surfaces of the friction plates, with the grooves being pressed into or formed on a separate bonded friction material layer, or defined by the gaps between discrete patches of friction material. However, as such patches and/or surface grooves reduce the total contact area between the mating clutch surfaces, surface temperature may increase along the remaining contact surfaces, resulting in less than optimum overall plate cooling. Also, spin losses may occur while the clutch assembly is disengaged as friction forces create drag between the plates. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, an engageable clutch assembly is provided having a friction interface adapted for use with a pressurized fluid, the assembly comprising at least one clutch plate having at least one internal fluid passage and at least one reaction surface at least partially defining the friction interface, wherein the at least one fluid passages is configured to conduct the pressurized fluid directly to the friction interface for cooling of the friction interface when the clutch assembly is engaging, and for reducing spin losses through the clutch assembly when the clutch assembly is disengaged. 
         [0005]    In one aspect of the invention, there are a plurality of internal fluid passages, with at least one of the fluid passages being plugged at one end to prevent flow of fluid in one direction as needed. 
         [0006]    In another aspect of the invention, the fluid passages include at least one main or primary fluid passage and at least one secondary fluid passage intersecting at least one of the main or primary fluid passages in a perpendicular direction. 
         [0007]    In another aspect of the invention, the thickness of the clutch plate and the diameter of at least one of the primary and secondary fluid passages are proportionately related by a ratio of approximately 2:1. 
         [0008]    In another aspect of the invention, the clutch plate is a unitary friction/reaction plate with friction material on one side. 
         [0009]    In another aspect of the invention, a method is provided for controlling fluid flow at the friction interface of a clutch plate assembly. The method includes providing fluid directly to the friction interface to cool the interface when the clutch plate assembly is engaging, and providing fluid to the friction interface when the clutch plate assembly is disengaged to thereby reduce spin losses through the clutch plate assembly. 
         [0010]    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 
         [0011]      FIG. 1  is an exploded view of a friction clutch assembly having a dual reaction plate and friction plate with a friction interface according to the invention; 
           [0012]      FIG. 2A  is a fragmentary side view of a portion of a reaction plate between adjacent friction plates, each forming a friction interface with the reaction plate according to one embodiment of the invention; 
           [0013]      FIG. 2B  is a fragmentary top view of a portion of the reaction plate according to the invention; 
           [0014]      FIG. 3A  is a fragmentary perspective view of a reaction plate having a blind hole according to a second embodiment of the invention; 
           [0015]      FIG. 3B  is a fragmentary perspective view of a portion of a reaction plate having an alternately oriented blind hole according to the second embodiment of the invention; 
           [0016]      FIG. 3C  is a fragmentary perspective view of a portion of a reaction plate having a selectively pluggable inner orifice according to a third embodiment of the invention; 
           [0017]      FIG. 4A  is an exploded view of a friction clutch assembly having unitary friction/reaction plates according to a fourth embodiment of the invention; and 
           [0018]      FIG. 4B  is a fragmentary side view of a portion of pair of unitary friction/plates forming a friction interface therebetween according to the fourth embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures, there is shown in  FIG. 1  an exploded view of a clutch plate assembly  10  having a friction plate  14  and a reaction plate  18 , and a friction interface  65  therebetween. For simplicity, only one friction plate  14  is shown, however those skilled in the art will recognize that clutch plate assembly  10  may consist of any number of alternately arranged friction plates  14  and reaction plates  18 , depending on the specific clutch application. Friction plate  14  has a core plate  36  having a first and second main surface  28 ,  29 , respectively, the core plate  36  preferably constructed of a suitable grade of stainless steel and having a plurality of inwardly-extending splines  24  configured to mate or interlock with alternating grooves of an adjoining clutch hub (not shown). 
         [0020]    Preferably, first and second main surfaces  28 ,  29  each have a layer of friction material  20 A,  20 B, respectively, which is bonded or otherwise attached to surfaces  28 ,  29  of the core plate  36 , although friction material such as  20 A,  20 B may also be bonded directly to a unitary friction/reaction plate (not shown). The friction material  20 A,  20 B is preferably ring-shaped and sized to cover the primary surface  28 ,  29  of the core plate  36  to which the friction material is bonded, and further includes a plurality of surface fluid channels  16  that separate the friction material layer  20 A,  20 B into substantially equal patches or segments for directing pressurized fluid  15  between the outer diameter  38  and the inner diameter  13  of the core plate  36 , or between the inner diameter  13  and the outer diameter  38 , depending on the design of the clutch assembly  10 . While the friction material  20 A,  20 B as shown in  FIG. 1  have fluid channels  16  as shown, other styles or designs of friction material may also be used within the scope of the invention, including, for example, smooth or grooveless material, or a series of surface channels or grooves that are pressed partially through the thickness of the friction material  20 A,  20 B. 
         [0021]    Friction plate  14  is configured to press against and synchronize with the speed of the mating reaction plate  18  when a controllable source of hydraulic pressure, preferably a positive displacement transmission pump  11 , actuates or engages an apply mechanism such as clutch-apply piston (not shown) to selectively compress the alternating friction plates  14  and reaction plates  18  that make up the clutch assembly  10 . As plates  14 ,  18  become interlocked due to the friction forces imparted by the layer of friction material  20 B, the clutch plate assembly is thereby engaged, and the mating plates  14 ,  18  are permitted to rotate in unison. 
         [0022]    Reaction plate  18  is a preferably circular metallic ring of a suitable grade of stainless steel having an outer and inner diameter  22 ,  12 , respectively, and includes a plurality of outwardly extending splines  32  configured to mate or interlock with a plurality of grooves positioned on the inside surface of a mating clutch drum (not shown). The reaction plate  18  has a first main surface  37  and a reverse or second main surface  39  (see  FIG. 2A ), with main surfaces  37 ,  39  being at least as wide as the width of friction material  20 A,  20 B to allow for maximum frictional contact area between mating plates such as plates  14  and  18 . The reaction plate  18  also has outer and inner lateral or side surfaces  48 ,  58 , respectively, each having a width/height sufficient to provide the reaction plate  18  with adequate bending and surface strength without adding excessive weight for a given clutch application, and with sufficient thickness to accommodate the drilling of fluid passages therein as described hereinbelow. 
         [0023]    Reaction plate  18  is further provided with a plurality of primary fluid passages  42  extending radially inward through the reaction plate  18  from outer lateral surface  48  to inner lateral surface  58 , preferably perpendicularly with respect to the lateral surfaces  48 ,  58  as shown in  FIG. 1  and substantially parallel to the main surfaces  37 ,  39 . Each of primary fluid passages  42  are in fluid communication with a source  11  of pressurized fluid  15  which is configured to deliver the fluid  15  through one of the outer or inner orifices  34 ,  50  of primary fluid passage  42 , depending on the application. Orifices  34 ,  50 , along with primary fluid channels  42 , are preferably circular or cylindrical in shape so as to minimize the effects of fluid friction and are preferably positioned approximately midway up lateral surfaces  48 ,  58  and approximately halfway between main surfaces  37 ,  39  of reaction plate  18 , and approximately midway between each of the outer splines  32 , so as to minimize the amount of material that must be removed from the reaction plate  18  during forming or drilling of the primary fluid passages  42 . However, those skilled in the art will recognize that the location of the outer orifices  34  may be positioned in alternate locations along or around the outer lateral surface  48 . For example, each of outer orifices  34  may be positioned on a respective spline face  33  of an outer spline  32  to thereby increase the area of potential fluid/metal contact for an enhanced fluid cooling effect. 
         [0024]    Turning to  FIG. 2A , which is a side view of a portion of the clutch plate assembly  10 , a reaction plate  18  is disposed between a pair of friction plates  14 A,  14 B, forming or defining a pair of boundary or friction interfaces  65 A,  65 B between the friction plates  14 A,  14 B and the reaction plate  18 , respectively. Outer orifice  34  admits a flow of pressurized fluid  15  from outer lateral surface  48  into the reaction plate  18 , as previously explained herewithin. For delivery of fluid  15  directly to the friction interfaces  65 A,  65 B for the cooling of main surfaces  37 ,  39 , the reaction plate  18  is further provided with a preferably circular or cylindrical secondary fluid passage  62  having a pair of circular or cylindrical first and second orifices  40  and  70 , respectively, each in fluid communication with primary fluid passage  42  through the secondary fluid passage  62 . 
         [0025]    In the preferred embodiment, first and second orifices  40 ,  70  are each positioned on main surfaces  37 ,  39 , respectively, at opposite ends of secondary fluid passage  62  and open to the friction interfaces  65 A,  65 B between reaction plate  18  and friction plates  14 A,  14 B, respectively. First orifice  40  is positioned on the main surface  37  of reaction plate  18  directly above primary fluid passage  42  and approximately midway between the respective outer and inner diameters  22 ,  12  of the reaction plate  18 , and second orifice  70  is positioned on the second primary surface  39  directly below primary fluid passage  42 . While  FIG. 1  shows just one first and second orifice  40 ,  70 , those skilled in the art will recognize that additional orifices substantially identical to first and second orifices  40 ,  70  may be added as needed depending on the size/width of the reaction plate and/or desired cooling/lubricating requirements of a given clutch plate assembly design. 
         [0026]    During a transient high temperature, low relative velocity condition, i.e. the low speed conditions most likely to cause shudder or vibration due to slippage, the secondary fluid passage  62  takes advantage of the relatively low viscosity of the fluid  15  under high temperature conditions to draw the fluid from primary fluid passage  42  directly to the low local pressure region created in proximity to the first and second orifices  34 ,  70 . Without requiring a reduction in contact surface area of the friction material  20 A,  20 B, shudder or vibration at low relative rotational speed is thereby reduced in part by delivering the fluid  15  directly to the friction interfaces  65 A,  65 B as needed. When the clutch assembly  10  is rotating in unison at relatively high rates of speed, the low pressure region formed in proximity to first and second orifices  40 ,  70 , respectively, between the disparately rotating plates  14 ,  18  disappears, and the various plates of the clutch assembly  10  are pressed together, thereby substantially blocking the flow of fluid  15  through the orifices  40 ,  70 . In this manner, loss of excess fluid  15  into the friction interfaces  65 A,  65 B helps to preserve fluid and prevent flooding of the friction interfaces  65 A,  65 B, thus minimizing the hydroplaning effect between friction plates  14 A,  14 B and reaction plate  18 . Those skilled in the art will recognize that when clutch assembly  10  is disengaged, fluid  15  will continue to be fed at line pressure through the orifices  40 ,  70 , which will provide a hydraulic force at the friction interfaces  65 A,  65 B sufficient to separate the various adjacent plates, such as friction plates  14  and reaction plate  18  and reducing or minimizing the spin losses or drag therebetween. 
         [0027]    In a second embodiment shown in  FIG. 3A , a blind primary fluid passage  142  is shown extending or penetrating from the outer lateral surface  48  to a closed or blind end  72  of primary fluid passage  142  which is short of the inner diameter  12  of reaction plate  18 . As configured, fluid  15  may enter the outer orifice  34 , pass through primary fluid passage  142 , and exit first and second orifices  40 ,  70  as previously explained herewithin. However, due to the blind end  72  of primary fluid passage  142 , the fluid  15  is blocked or prevented from passing all the way through to the inner diameter  12 . Fluid  15  is conserved in this manner while still being drawn by the local low pressure zone between plates  14 A,  14 B and  18  through secondary fluid passages  62  to reach the friction interface  65 A,  65 B (see  FIG. 2A ). Alternately, as shown in  FIG. 3B , in situations or configurations in which flow of the fluid  15  initiates from the inner lateral surface  58  of internal diameter  12 , an alternate primary fluid passage  242  may extend or penetrate from the inner diameter  12  to a closed or blind end  74  of primary fluid passage  242 . The blind end  74  is short of the outer diameter  22  of reaction plate  18 . Both blind ends  72  and  74  are preferably positioned approximately ¾ of the distance between the inner diameter  12  and outer diameter  22  of reaction plate  18  to allow for some additional core cooling of reaction plate  18 , although other distances are also within the scope of the invention. 
         [0028]    In a third embodiment as shown in  FIG. 3C , primary fluid passage  42  extends all the way through reaction plate  18  from inner diameter  12  to outer diameter  22 , and is capped or otherwise blocked, preferably by a plug  67  that is inserted into the inner orifice  50 , thus blocking fluid  15  from flowing all the way through reaction plate  18 . This embodiment facilitates a drilling or boring process initiating from within the inner diameter  12  of the reaction plate  18 , as may be required to produce the embodiment of  FIG. 3B , particularly in situations in which the reaction plate  18  is relatively small in diameter. Preferably, the plug  67  is constructed of suitable material such as stainless steel when the plus is to be inserted into inner orifice  50  and secured with epoxy or other adhesive material (not shown) with sufficient strength and materials properties to retain the plug  67  within the inner orifice  50  in the presence of fluid  15  for the operational lifetime of the reaction plate  18 . 
         [0029]    While a multi-plate design is preferred, a fourth embodiment includes unitary friction/reaction plates  110 A,  110 B as shown in  FIG. 4 , which are stacked without a separate core plate  36  (see  FIG. 1 ). Friction material  26  is bonded or attached directly to one surface  137 A,  137 B of each unitary plate  110 A,  110 B, respectively, with each unitary plate  110 A,  110 B having respective alternating internally and externally projecting splines  124 ,  132 . Unitary plate  110 A has an internal orifice  150 A and an external orifice  134 A disposed at either end of at least one primary fluid passage  342 , each of which is intersected by a secondary fluid passage  162  having a single orifice  170 . Likewise, unitary plate  110 B has an internal orifice  150 B and an external orifice  134 B disposed at either end of at least one primary fluid passage  342 , with primary fluid passages  342  being substantially identical to passage  42  as previously described hereinabove (see  FIG. 1 ). In this fourth embodiment, as shown in partial side view in  FIG. 4B , only one friction interface  65 C will be formed relative to each pair of unitary plates  110 A,  110 B, and accordingly, only a single orifice  170  would be required opening thereto from each of primary fluid passages  342 , although multiple secondary passages  162  and orifices  170  may be added as needed to deliver more fluid  15  to the friction interface  65 C as required. Orifices  134 A and  150 A, and primary fluid passage  342  may also be configured using blind or plugged holes as previously described herewithin as the application or clutch design requires. 
         [0030]    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.
A clutch plate assembly is provided having a friction interface and internal fluid passages for delivering pressurized fluid to the friction interface to cool the interface, and to reduce spin losses through the clutch assembly. The fluid passages comprise a plurality of primary passages extending inward from a clutch plate inner or outer diameter, and a plurality of secondary fluid passages intersecting the primary fluid passages for conducting fluid to the friction interface. Fluid is directed to the friction interface during clutch engagement for cooling thereof when the clutch assembly is engaging, and separates the clutch plates to reduce spin losses when the clutch assembly is disengaged. A method is also provided for controlling fluid flow at the friction interface, including providing fluid directly to the interface for cooling when the clutch plate assembly is engaging, and for reducing spin losses when the clutch plate assembly is substantially disengaged.