Abstract:
An improved lubrication system for a ball ramp master clutch and a gear change transmission is disclosed where a lubricant pump is driven by the input shaft to a ball ramp mechanism which, when energized, applies a clamping force on a clutch pack where lubricant is supplied to the pump from a wet sump on the transmission and then lubricant is forced into the clutch assembly and also forced into the gear shaft transmission for eventual return into the sump for recirculation. In an alternate embodiment, a dry sump system is used where the oil flowing out of the transmission is pumped to dry sump where it is then recirculated to the pump.

Description:
RELATED APPLICATIONS 
     This application is related to application U.S. Ser. No. 09/940,821, now issued patent U.S. Pat. No. 6,561,332 entitled Ball Ramp Clutch With Frictional Damping and U.S. Ser. No. 10/143,323 and U.S. Ser. No. 10/143,324 all of which are assigned to the same assignee, Eaton Corporation, as this application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a lubrication system for a vehicle driveline master clutch which utilizes a ball ramp mechanism to load a clutch pack and more specifically to a lubrication system for a vehicle driveline master clutch which utilizes a ball ramp actuator to load a clutch pack where the master clutch includes a lubrication pump to direct fluid flow from a transmission lubricant sump and direct it to the master clutch and through the gear change transmission. 
     PRIOR ART 
     Driveline master clutches commonly use a plurality of springs to clamp a friction disc to an engine flywheel. The clamping springs are normally disposed within a pressure plate assembly which is bolted to the flywheel. The friction discs are splined to rotate with a transmission input shaft which, when rotated, provides motive power to the driveline and wheels of the vehicle. A mechanical linkage operated by a driver is used to control the engagement and disengagement of the master clutch. The clutch is typically a dry clutch when no lubricant is required. The master clutch is typically located between a prime mover such as an internal combustion engine and a gear change transmission. 
     Efforts to automate the operation of the master clutch to eliminate the need for driver operation are currently underway. Thus, it is known to make use of a hydraulic actuator or an electric motor actuator to operate the master clutch release mechanism in response to a control signal generated by a control microprocessor in response to a multiplicity of sensor outputs which are used to determine the vehicle operating conditions and hence the desired operation of the master clutch. Furthermore, the use of a ball ramp actuator to operate a driveline master clutch is known in the art. U.S. Pat. Nos. 5,441,137; 5,469,948; 5,505,285; 5,651,437; 5,810,141; 5,910,061; 5,964,330; and RE 36,502 assigned to the same assignee as this application, all of which are hereby expressly incorporated by reference, disclose methods of using a ball ramp actuator to supply the clamping force on a clutch disc and could, in the alternative, be used to supply a release force against a clutch apply spring. 
     Typically, a ball ramp actuator is activated when an electrical current is supplied to a coil thereby producing an electromagnetic field in a coil pole which applies a retarding force to an armature which rotates with an input shaft. The rotating armature is nonrotatably connected to an annular control ring which has a plurality of control ramps or grooves formed in the face of the control ring which vary in axial depth. An annular activation ring which rotates with an output shaft has a like number of variable depth activation grooves formed therein which oppose those formed in the control ring where a corresponding number of rolling elements are trapped between the control and activation grooves. As a retarding force is applied to the control plate by the armature, the rotational movement of the control plate relative to the activation plate causes the rolling elements to simultaneously traverse the control grooves and the activation grooves thereby causing an increase in separation distance between the control and activation plates which is used to provide a clamping force on a device such as a clutch friction disc. 
     The prior art ball ramp actuators used in the operation of the master clutch or other driveline coupling system such as a differential or transfer case could be improved by improving the flow of lubricating/cooling fluid through the clutch. It would also be an advantage if the clutch lubrication system could make use of the same lubricant as that used in the transmission. It would also be an advantage if the lubrication system for the clutch could be used with either a dry or wet sump transmission lubrication system. 
     SUMMARY OF THE INVENTION 
     The present invention results in an improvement in the lubrication system of a ball ramp clutch which can be used in a variety of vehicle driveline applications to provide a clamping load on a frictional clutch pack. The present invention provides for the common use of the lubricant used in a gear change transmission for use in the ball ramp clutch irrespective of whether it is a dry sump or a wet sump system. This unique solution reduces package size, simplifies the lubrication system, reduces cost and improves performance. 
     The present invention improves the performance and durability of a ball ramp actuated master clutch assembly by eliminating the need for separate lubrication systems for the ball ramp clutch and the gear change transmission. The present invention also improves the performance and durability of a ball ramp actuated master clutch assembly by eliminating one-way clutches with the use of indexing plates to limit the relative rotational travel of the control ring and the actuation ring of the ball ramp actuator which is used to apply an axial clamping load on a clutch pack. One indexing plate limits the rotation of the control ring of the ball ramp mechanism, and a second indexing plate limits the rotation of the activation ring, thereby allowing unidirectional grooves to be used in the control ring and the activation ring. Using the indexing plates of the present invention, the ball ramp mechanism, when energized, can only further compress the clutch pack with clutch slippage thereby preventing any break in clutch engagement when the torque flow in the driveline reverses direction from a drive mode into a driven mode. The torque flow in the driveline is in a drive mode when the engine is supplying power to the input shaft of the clutch assembly and in a driven mode when the engine is absorbing power from the input shaft of the clutch assembly. The indexing plates do not always prevent rotation in an undesired direction as with the one-way clutches disclosed in U.S. Ser. No. 09/940,821 but may permit limited rotation in an undesired manner until the index plates hit against a respective stop formed on the control plate and the activation plate. 
     The present invention also results in an improvement in the operational characteristics of a ball ramp actuator which can be used in a variety of vehicle driveline applications to supply a clamping load to a frictional clutch pack. The present invention provides a unidirectional apply ball ramp function which applies the clutch irregardless of torque flow along with significantly increased frictional damping in the ball ramp mechanism itself to control and stabilize the ball ramp mechanism thereby improving the operation of the master clutch or other driveline device. 
     To improve the operation of the ball ramp mechanism, the stability is improved by significantly increasing the frictional damping using an intermediate plate disposed between the activation plate and the control plate where the intermediate plate rotates with the output shaft and hub and the activation plate rotates with the activation ring and the control plate rotates with the control ring. Either the activation plate or the control plate must slip relative to the intermediate plate (which rotates with the output shaft) for the ball ramp mechanism to increase the clamp load on the clutch pack. Note that the torque flow from the input shaft to the output shaft can be reversed so that the torque flows from the output shaft to the input shaft and the ball ramp clutch assembly will continue to provide the desired functionality. 
     One provision of the present invention is to provide a vehicle master clutch using a ball ramp actuator to load a clutch pack where the master clutch uses a common lubrication system with a gear change transmission. 
     Another provision of the present invention is to provide a vehicle master clutch using a ball ramp actuator to load a clutch pack where the master clutch includes an integral pump to pressure a lubricant flow within a ball ramp mechanism and clutch pack. 
     Another provision of the present invention is to provide a master clutch having a ball ramp mechanism to load a clutch pack where the lubrication system is pressurized using a gerotor pump mounted within the ball ramp master clutch which draws lubricant from a lubricant sump and supplies lubricant to both the clutch and a change gear transmission. 
     Still another provision of the present invention is to provide a ball ramp actuator to actuate a driveline master clutch which is joined to a gear change transmission, both the master clutch and the transmission having an improved lubrication system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a first embodiment of the lubrication system of the present invention using a wet sump; 
     FIG. 2 is a cross-sectional view of a second embodiment of the lubrication system of the present invention using dry sump; 
     FIG. 3 is a cross-sectional view of the clutch assembly of the present invention; 
     FIG. 4 is a sectional view of the clutch assembly of the present invention taken along line IV—IV of FIG. 3; 
     FIG. 5 is an illustrative partial view of the ball ramp mechanism in a nonactivated state taken along line V—V of FIG. 4; 
     FIG. 6 is an illustrative partial view of the ball ramp mechanism in an activated state taken along line III—III of FIG. 4 
     FIG. 7 is a perspective view of the ball ramp mechanism and the indexing plates of the clutch assembly of FIG. 3; 
     FIG. 8 is a perspective view of a portion of the clutch assembly of FIG. 3; 
     FIG. 9 is a sectional perspective view of the clutch assembly of the present invention; and 
     FIG. 10 is a partial perspective view of a third embodiment of the lubrication system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Certain terminology will be used in the following description for convenience in reference only and will not be limiting. 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. 
     Although primarily described for use in a vehicle driveline and more specifically as part of a master clutch/transmission system the present invention can be used to rotationally connect any two rotatable shafts in response to an electronic control signal, using a common lubrication system between two or more devices. Such alternative devices could include differentials, engine retarders, transmission brakes, foundation brakes, inertia brakes, transfer cases and other devices. 
     Now referring to FIG. 1 of the drawings, a cross-sectional partial view of the lubrication system of the present invention is shown. A ball ramp clutch  2  is joined to a prime mover such as an internal combustion engine (not shown) through an input shaft  6  which is frictionally rotationally joined to an output shaft  8  using a ball ramp mechanism  19  to apply a compression load on a clutch pack  26  schematically illustrated in FIG.  1 . The output shaft  8  is nonrotationally connected to the input shaft  9  of a gear change transmission  3 . The housing  10  of the ball ramp clutch  2  is joined to a face plate  5  on one side and to a ball housing  11  and a transmission case  7  at its second side. The face plate  5  is supported by the input shaft  6  through bearing  12 . 
     The lubrication system of the present invention is comprised of a lubrication wet sump  102  which is mounted to or part of the underside of the gear change transmission. A lubricant supply tube  104  has a first end  104 A located within the sump  102 . A second end  104 B of the lubricant supply tube  104  is retained in a lubricant port  41  formed in the face plate  5 . A lubricant pump  38  is positioned within the clutch assembly  2 . As shown in FIG. 1, a gerotor type lubricant pump  38  is positioned to be driven by the input shaft  6 . The lubricant residing in the sump  102  of the gear change transmission  3  is drawn up lubricant supply tube  104  by the pump  38  as it is rotated by the input shaft  6  which is connected to the crankshaft of the engine. The lubricant is pressurized by the pump  38  and forced into the lubricant feed ports  70  into the lubricant distribution channel  100  for distribution into the working elements of the clutch assembly  2  such as into the ball ramp mechanism  19  and into the clutch pack  26  through one or more secondary feed ports  71 . The lubricant that is forced into the workings of the clutch assembly  2  is then allowed to flow back into the sump  102  through the drain  106 . 
     The lubricant pressurized by the pump  38  is also routed through the lubricant distribution channel  100  to a check valve  73 . The check valve  73  prevents the flow of lubricant through the check valve port  72  and into the transmission  3  until the pressure of the lubricant exceeds a pre-set value. Once the lubricant pressure exceeds this pre-set value, the lubricant flows into the inner workings of the transmission  3  such as the transmission input shaft  9  contained within transmission case  7  to lubricate the various rotating elements and eventually make its way back into the sump  102 . Sump  102  is what is known in the art as a wet sump since it has a large open area to the inner workings of the transmission  3  and the lubricant simply drips or drains into the sump  102 . 
     Now referring to FIG. 2, a cross-sectional view of a second embodiment of the lubrication system of the present invention is shown. FIG. 2 illustrates use of the lubrication system with a dry sump  102 ′ where the lubricant is held in a separate container with no generally open top to the inner workings of the transmission  3 ′. 
     The lubrication system of the present invention is comprised of a lubrication wet sump  102 ′ which is mounted to the underside of the gear change transmission  3 ′. A lubricant supply tube  104 ′ has a first end  104 A′ located within the sump  102 ′. A second end  104 B′ of the lubricant supply tube  104 ′ is retained in a lubricant port  41  formed in the face plate  5 . A lubricant pump  38  is positioned within the clutch assembly  2 . As shown in FIG. 1 a gerotor type lubricant pump  38  is positioned to be driven by the input shaft  6 . The lubricant residing in the sump  102 ′ of the gear change transmission  3 ′ is drawn up lubricant supply tube  104 ′ by the pump  38  as it is rotated by the input shaft  6  which is connected to the crank shaft of the engine. The lubricant is pressurized by the pump  38  and forced into the lubricant feed ports  70  into the lubricant distribution channel  100  for distribution into the working elements of the clutch assembly  2  such as into the ball ramp mechanism  19  and into the clutch pack  26  through one or more secondary feed ports  71 . The lubricant that is forced into the workings of the clutch assembly  2  is then allowed to flow back into the sump  102 ′ through the drain  106 ′. 
     The lubricant pressurized by the pump  38  is also routed through the lubricant distribution channel  100  to a check valve  73 . The check valve  73  prevents the flow of lubricant through the check valve port  72  until the pressure of the lubricant exceeds a pre-set value. Once it exceeds this pre-set value the lubricant flows into the inner workings of the transmission  3 ′ to lubricate the various rotating elements and eventually make its way back into the sump  102 ′. Sump  102 ′ is what is known in the art as a dry sump since it has no large open area to the workings of the transmission  3 ′. 
     The lubricant eventually flows into a dry sump drain port  108  where it flows back into the dry sump  102 ′. Drain port  108  is relatively small in cross-sectional area as compared to the opening in the wet sump  102  shown in FIG.  1 . In some systems, an auxiliary pump is used to pump the lubricant out of the transmission  3 ′ and back into the dry sump  102 ′. 
     Now referring to FIG. 3 of the drawings, a cross-sectional view of the clutch assembly  2  of the present invention is shown. An input shaft  6  which rotates about an axis of rotation  4  is normally connected to a power source such as an internal combustion engine (not shown). The clutch assembly  2  functions to frictionally rotationally link the input shaft  6  to an output shaft  8  which, for example, could be linked to the input shaft of a change gear transmission (not shown). In general, the elements which make up the clutch assembly  2  are annularly shaped and rotate about the axis of rotation  4 . The face plate  5  is connected to and together with the housing  10  provides a containment structure for the operating elements and lubricating/cooling fluid of the clutch assembly  2 . The face plate  5  is supported by the input shaft  6  through bearing  12 . The clutch hub  14  is piloted on the input shaft  6  but is nonrotatably connected to the output shaft  8 . The housing  10  can be attached to the case of a gear change transmission or other driveline rotational device (not shown). Splines  15  nonrotatably connect the output shaft  8  and clutch hub  14  to at least one driven disc  28  and also rotatably connect the hub  14  to the intermediate plate  34  through teeth  34 C. Splines  18  formed on a drive hub  16  nonrotatably connect at least one drive disc  30  to the input shaft  6  since the drive hub  16  is attached to the input shaft  6 . The clutch hub  14  is driven by the frictional interaction between the drive discs  30  and the driven discs  28 . Annular wave springs  13  are placed between the driven discs  28  to provide a separation force so that the drive discs  30  and the driven discs  28  separate when the clutch assembly  2  is disengaged to reduce clutch drag in the clutch pack  26 . 
     The ball ramp mechanism  19  is comprised of a control ring  20 , an activation ring  32  and a plurality of rolling elements  45 A,  45 B,  45 C (see FIGS. 3 and 4) positioned to engage and roll along opposed variable depth grooves  35 A,  35 B,  35 C and  37 A,  37 B,  37 C formed in both the control ring  20  and the activation ring  32 , respectively (see FIGS.  3  and  4 ). As the control ring  20  is rotated relative to the activation ring  32 , the rolling elements  45 A,  45 B,  45 C transverse the opposed control ring grooves  35 A,  35 B,  35 C and activation ring grooves  37 A,  37 B,  37 C either increasing or decreasing the separation distance  47  between the control ring  20  and the activation ring  32  depending on the direction of the relative rotation. 
     The thrust bearings  33 A,  33 B,  33 C and  33 D axially position of various components contained in the clutch assembly  2 . The input shaft flange  6 A is axially located by the thrust bearing  33 A. The first index plate  31 A is axially supported through the thrust bearings  33 B and  33 C and the control ring  20  is axially supported through the thrust bearing  33 D acting against the second index plate  31 B which contacts the snap ring  40 . 
     The ball ramp mechanism  19  is comprised of a control ring  20 , an activation ring  32  and a plurality of rolling elements  45 A,  45 B,  45 C (see FIGS. 3 and 4) positioned to engage opposed variable depth grooves  35 A,  35 B,  35 C formed in both the control ring  20  and variable depth grooves  37 A,  37 B,  37 C formed in the activation ring  32 . As the control ring  20  is rotated relative to the activation ring  32 , the rolling elements  45 A,  45 B,  45 C (see FIGS. 3,  4  and  5 ) transverse the opposed control ring grooves  35 A,  35 B,  35 C and activation ring grooves  37 A,  37 B,  37 C thereby either increasing or decreasing the separation distance between the control ring  20  and the activation ring  32  depending on the direction of the relative rotation. The second index plate  31 B limits rotation of the control ring  20  when the first index step  46 A contacts the first control stop  52 A or when the second index step  46 B contacts the second control stop  52 B. Thus, as shown in FIG. 2, the maximum rotation of the control ring  20  relative to the second index plate  31 B is approximately 240 degrees. Since the second index plate  31 B is nonrotatably fixed to the input shaft  6 , through splines  36 , the maximum relative rotation of the control ring  20  relative to the input shaft  6  is also limited by the second index plate  31 B. In a similar manner to the operation of the second index plate  31 B, the first index plate  31 A limits the rotation of the activation ring  32  relative to the input shaft  6  when the first index step  54 A contacts the first activation stop  56 A (see FIG.  5 ). With the use of the index plates  31 A and  31 B, the ball ramp mechanism  19  is activated whenever there is a speed differential between the input shaft  6  and the output shaft  8  irregardless of the direction of the torque flow through the clutch assembly  2  even though the control plate grooves  35 A,  35 B,  35 C and the activation plate grooves  37 A,  37 B,  37 C are unidirectional. A second index plate  31 B contacts thrust bearing  33 D which, in turn, contacts the control ring  20 . Both the first and second index plates  31 A,  31 B are nonrotationally coupled to the input shaft  6  with splines  36 . 
     The pressure plate  22  is attached to the activation extension  24 . As the activation plate  32  is displaced to the right by an increase in separation distance between the control ring  20  and the activation ring  32 , the clutch pack  26  is squeezed by the pressure plate  22  and the drive discs  30  frictionally contact and are frictionally coupled to the driven discs  28 . In this manner, where the ball ramp mechanism  19  is energized, the input shaft  6  is frictionally rotationally coupled to the output shaft  8 . 
     The axial thrust of the clutch hub  14  is borne by the thrust bearing  33 A which rides against the input shaft  6 . The activation extension  24  is axially positioned against the thrust bearing  33 B which, in turn, contacts a face of the first index plate  31 A. A thrust bearing  33 C is positioned between the first index plate  31 A and the activation ring  32 . 
     The intermediate plate  34  is splined to the clutch hub  14  to rotate therewith but allowed to move in an axial direction. The intermediate plate  34  is interposed between an activation plate  39  and an armature  44  where the armature  44  is attached to the control ring  20  and thus its rotation relative to the input shaft  6  is also limited by the second index plate  31 B. Intermediate plate  34  is connected to the output shaft  8  through the clutch hub  14  while the activation ring  32  and the control ring  20  are through the steps  46 A,  46 B,  54 A,  54 B and stops  52 A,  52 B,  56 A,  56 B keyed to the input shaft  6  via the index plates  31 A,  31 B. 
     The activation ring  32  is splined to rotate with the slide sleeve which is splined to rotate with the activation plate  39 . The activation ring  32  can rotate and axially move relative to the input shaft.  6 . Also, the control ring  20  can rotate and axially move relative to the input shaft  6  and relative to the activation plate  39 . Both the control ring  20  and the activation ring  32  are limited in their degree of rotation by the index plates  31 B and  31 A respectively which are splined to the input shaft  6 . Index plate  31 A is trapped between the thrust bearings  33 B and  33 C and limits the rotation of the activation ring  32  relative to the input shaft  6 . Index plate  31 B is trapped between the thrust bearing  33 D and snap ring  40  thereby fixing the axial position of the control ring  20 . 
     The coil assembly  42  is comprised of a multiple turn coil  48  which is partially surrounded by and attached to a stator  49 . Both the coil  48  and the stator  49  remain stationary relative to the housing  10  where the stator  49  is attached to the face plate  5 . The armature  44  is attached to and rotates with the control ring  20  with a slight clearance between the armature (control plate)  44  and the stator  49 . For purposes of this application the term “armature” shall be equivalent to the term “control plate”. When the coil  48  is electrically energized by the control unit  50  through signal wires  51 , an electromagnetic field is established in the stator  49  which is transferred to the armature  44  which, in turn, electromagnetically attracts the intermediate plate  34  and the activation plate  39 . The armature  44 , intermediate plate  34  and activation plate  39  can have friction material attached to at least one of their respective faces where they make contact with an adjacent element. 
     As the electrical current in the coil  48  is increased by the control unit  50 , the strength of the electromagnetic field induced in the armature  44  is increased and the electromagnetic attraction between the armature  44  (also termed a “control plate”) and the intermediate plate  34  and the activation plate  39  increases. If the input shaft  6  is rotating at a slower speed the output shaft  8 , this produces a torque on the control ring  20  and the activation ring  32  in either direction as needed to further activate the ball ramp mechanism  19  thereby increasing the separation distance between the control ring  20  and the activation ring  32  to axially move the pressure plate  22  and increase the clamp force on the clutch pack  26 . The control ring  20  can rotate in either direction relative to the activation ring  32  and the clamping load on the clutch pack  26  will be increased due to the rotational limiting action of the first and second index plates  31 A and  31 B. Slip sleeve  27  functions such that when activation ring  32  axially moves to clamp the clutch pack  26  it doesn&#39;t drag activation plate  39  with it. Thus, slip sleeve  27  allows activation ring  32  to move axially independently of activation plate  39  but joins the two in a rotational sense. The slip sleeve  27  is retained axially relative to control ring  20  by sump ring  27 A but allowed to rotate relative to control ring  20 . 
     Flux slots  44 A and  44 B are formed in the armature  44  to enhance the magnetic field properties of the coil assembly  42 . Likewise, magnetic flux slots  34 A,  34 B are formed in the intermediate plate  34  and one central flux slot  39 A is formed in the activation plate  39 . These flux slots  44 A,  44 B,  34 A,  34 B and  39 A combine to enhance the magnetic flux properties of the armature  44 , the intermediate plate  34  and the activation plate  39  when the coil  48  is electrically energized. In a certain mode of operation, the activation plate  39  slips relative to the intermediate plate  34  and in another mode of operation the armature  44  slips relative to the intermediate plate  34 . In operation, that slippage can switch between the two modes. 
     A fluid pump  38  functions to force a lubricant into the clutch assembly  2  for cooling and lubrication of the various components. The fluid pump  38  can be a gerotor pump as shown or any other type of suitable fluid pump device. The lubricant used for a gear shift transmission could be used for this purpose when the fluid pump  38  also functions to force lubricant into various parts of the transmission as part of a dry sump or wet sump lubricating system. The fluid pump  38  provides a flow of lubricating and cooling lubricant to the clutch assembly  2  which is routed from port  41  into the lubricant distribution channel  100  through the lubricant feed ports  70 . The lubricant distribution channel  100  distributes the fluid to the various components of the clutch assembly  2 . The fluid port  41  allows lubricant to flow into the fluid pump  38 . 
     Now referring to both FIG.  3  and FIG. 4 of the drawings, where FIG. 4 is an elevational view of a portion of the clutch assembly  2 . The elevational view of FIG. 4 is taken looking into the armature  44  from the right side to the left with the faceplate  5  and coil  48  removed from the clutch assembly  2 . Slots  44 A and  44 B formed in the armature  44  are clearly shown in this view. Also, more clearly shown are portions of the corresponding slots  34 A and  34 B formed in the intermediate plate  34 . 
     In a similar manner to the operation of the second index plate  31 B, the first index plate  31 A limits the rotation of the activation ring  32  relative to the input shaft  6  when the first index step  54 A contacts the first activation stop  56 A (see FIG.  5 ). With the use of the index plates  31 A and  31 B, the ball ramp mechanism  19  is activated whenever there is a speed differential between the input shaft  6  and the output shaft  8  irregardless of the direction of the torque flow even though the control plate grooves  35 A,  35 B,  35 C and the activation plate grooves  37 A,  37 B,  37 C are unidirectional. Activation plate  39  is rotationally joined to the input shaft  6  via the index plate  31 B which in one mode, is against a stop  52 A and the control ring  20  and the activation ring  32  are positioned such that the rolling elements  45 A,  45 B,  45 C are at the bottom of their respective grooves while the second index plate is on its stop  56 B but in the opposite direction. 
     Now referring to FIG. 5 of the drawings, more clearly illustrated are the control grooves  35 A,  35 B,  35 C formed in the control ring  20  and the activation grooves  37 A,  37 B,  37 C formed in the activation ring  32 . The control grooves  35 A,  35 B,  35 C at least partially oppose the activation grooves  37 A,  37 B,  37 C and both are of variable depth increasing from one end to the other and extending in opposite relative directions. Rolling elements  45 A,  45 B,  45 C simultaneously contact and roll along respective opposed control grooves  35 A,  35 B,  35 C and activation grooves  37 A,  37 B,  37 C. The rolling elements  45 A,  45 B,  45 C are shown in FIG. 3 in a nonactivated position where each contacts a respective control and activation groove  35 A,  35 B,  35 C;  37 A,  37 B,  37 C at their lowest depth (and minimum overlap) thereby minimizing the axial separation distance  47 . As the ball ramp mechanism  19  is activated by electronically energizing the coil  48 , assuming there exists slippage in the clutch pack  26 , the control ring  20  moves counter-clockwise relative to the activation plate  32  thereby causing the rolling elements  45 A,  45 B,  45 C to transverse the three respective pairs of opposed variable depth control grooves  35 A,  35 B,  35 C and activation grooves  37 A,  37 B,  37 C. As the control plate  20  continues to rotate relative to the activation plate  32 , the separation distance  47  increases thereby increasing the clamp force on the clutch pack  26 . 
     FIG. 5 shows the ball ramp mechanism  19  in a nonactivated state and FIG. 4 shows the ball ramp mechanism  19  in an activated state at about fifty percent travel. In FIG. 3, the rolling element  45 B is positioned at the maximum depth of both the control groove  35 B and the opposed activation groove  37 B and the separation distance  47  is at a minimum. Reference point  41 B is on the activation groove  37 B and reference point  43 B is on the control groove  35 B for use in comparison to their positions in FIG.  4 . 
     In FIG. 6, the rolling element  45 B has traversed both the control groove  35 B and the activation groove  37 B as the control ring  20  has been rotated relative to the activation ring  32 . The separation distance  47  has increased since the rolling element  45 B is now contacting a more shallow portion of both the control groove  35 B and the activation groove  37 B. The relative position of reference points  41 B and  43 B illustrate the relative rotation. 
     Now referring to FIG. 7, a partial perspective exploded view of the ball ramp mechanism  19  of the present invention is shown. The control ring  20  includes at least three control grooves  35 A,  35 B,  35 C which vary in axial depth according to rotational location on the face of the control ring  20  and oppose respective variable depth activation grooves  37 A,  37 B,  37 C (see FIGS. 3 and 4) with rolling elements  45 A,  45 B,  45 C trapped between the respective grooves  35 A,  35 B,  35 C;  37 A,  37 B,  37 C. The grooves  35 A,  35 B,  35 C and  37 A,  37 B,  37 C are shaped and oriented such that upon rotation of the control ring  20  relative to the activation ring  32 , the axial separation distance  47  between the control and activation rings  20 ,  32  is increased or decreased. 
     The rotation of the control ring  20  is limited by action of the second index plate  31 B which is keyed to rotate with the input shaft  6  with keys  60 A and  60 B (not shown) which engage splines  36  (see FIG.  1 ). The rotation of the control ring  20  is stopped relative to the input shaft  6  when either the first index step  46 A contacts the first control stop  52 A or when the second index step  46 B contacts the second control stop  52 B (see FIG.  2 ). 
     Likewise, the rotation of the activation ring  32  is limited by action of the first index plate  31 A which is also keyed to rotate with the input shaft  6  with keys  58 A and  58 B which engage the splines  36 . The rotation of the activation ring  32  is stopped relative to the input shaft  6  when either the first index step  54 A contacts the first activation stop  56 A or when the second index step  54 B contacts the second activation stop  56 B. Note the rotational orientation of the first and second index plates  31 A,  31 B where the second index stop  52 B of the second index plate  31 B is in axial alignment with the first index step  54 A of the first index plate  31 A. Thus, looking from left to right, the activation ring  32  could rotate approximately 240 degrees clockwise and the control ring  20  could rotate approximately 240 degrees counterclockwise relative to the input shaft  6 . The rolling elements  45 A,  45 B,  45 C would traverse their respective control grooves  35 A,  35 B,  35 C and activation grooves  37 A,  37 B,  37 C (not shown) and thereby increase the axial separation distance  47  between the control ring  20  and the activation ring  32  as they rotate relative to each other. Activation plate  39  is rotationally joined to the input shaft  6  via the index plate  31 B which in one mode, is against a stop  52 A and the control ring  20  and the activation ring  32  are positioned such that the rolling elements  45 A,  45 B,  45 C are at the bottom of their respective grooves while the second index plate is on its stop  56 B but in the opposite direction. Intermediate plate  34  is connected to the output shaft  8  through the clutch hub  14  while the activation ring  32  and the control ring  20  are through the steps  46 A,  46 B,  54 A,  54 B and stops  52 A,  52 B,  56 A,  56 B keyed to the input shaft  6  via the index plates  31 A,  31 B. In a certain mode of operation, the activation plate  39  slips relative to the intermediate plate  34  and in another mode of operation the armature  44  slips relative to the intermediate plate  34 . In operation, that slippage can switch between the two modes. 
     FIG. 8 is a partial perspective view of the clutch assembly  2  of the present invention looking from left to right as shown in FIG.  1 . The axis of rotation  4  extends through the clutch assembly  2  and through the centerline of the input shaft  6 . Flange  6 A is shown extending from the input shaft  6 . 
     The slip sleeve  27  has a multiplicity of tooth shapes formed therein to engage the mating teeth formed in activation ring  32 . Slip sleeve  27  functions such that when activation ring  32  axially moves to clamp the clutch pack  26  it doesn&#39;t drag activation plate  39  with it. Thus, slip sleeve  27  allows activation ring  32  to move axially independently of activation plate  39  but joins the two in a rotational sense. The slip sleeve  27  is retained axially relative to control ring  20  by sump ring  27 A but allowed to rotate relative to control ring  20 . The teeth  34 C of the intermediate plate  34  extend to engage the splines  15  formed in the clutch hub  14 . A small portion of the intermediate plate  34  is visible through the slot  39 A formed in the activation plate  39 . The outside surface of the armature  44  is also shown. 
     Now referring to FIG. 9 of the drawings, a cross-sectional perspective view of the clutch assembly  2  of the present invention is shown. An input shaft  6  which rotates about an axis of rotation  4  is normally connected to a power source such as an internal combustion engine (not shown). The clutch assembly  2  functions to frictionally rotationally link the input shaft  6  to an output shaft  8  which, for example, could be the input shaft a change gear transmission. In general, the elements which make up the clutch assembly are annularly shaped and rotate about the axis of rotation  4 . The face plate  5  is connected to and together with the housing  10  provides a containment structure for the operating elements and lubricating/cooling fluid of the clutch assembly  2 . The face plate  5  is supported by the input shaft  6  through bearing  12 . The clutch hub  14  is piloted but not connected to the input shaft  6  and can be nonrotatably connected to some type of driveline device such as a gear change transmission. The housing  10  can be attached to the housing of a gear change transmission (not shown) or other driveline device. Splines  18  formed on a drive hub  16  nonrotatably connect at least one drive disc  30  to the input shaft  6  since the drive hub  16  is attached to the input shaft  6 . 
     Now referring to FIG. 10 of the drawings, a partial perspective view of a third embodiment of the clutch assembly  2  of the present invention is shown which includes a heat exchanger. The face plate  5  of the clutch assembly  2  is partially cut away to more clearly show the fluid pump  38  which pumps lubricant from a lubricant sump through lubricant sump line  62  to a lubricant heat exchanger (not shown) through lubricant pump line  64  which when cooled, is returned to the clutch assembly  2  through the lubricant return line  66 . The input shaft  6  includes a plurality of lubricant flow apertures that distribute the cooling/lubricating lubricant to various sections of the clutch assembly  2 . The fluid pump  38  pumps the lubricating lubricant through at least one lubricant feed ports  70  into the lubricant distribution channel  100  (see FIG. 3) for distribution through a plurality of lubricant distribution apertures also (not shown) into the various internal elements of the clutch assembly  2 . 
     Fluid pump  38  functions to provide a pressurized flow of lubricant through the rotating clutch pack  26  and generally, the ball ramp mechanism  19  to provide both a source of cooling and lubrication. Lubricant return line  66  supplies a flow of lubricant from a heat exchanger (not shown) to the pump  38  which pumps lubricant through the interior of the clutch housing  10  and the lubricant is then drained through a separate lubricant sump line  62 . The lubricant flows to the clutch assembly  2  through lubricant feed ports  70  and flows into the lubricant distribution channel of the input shaft  6  for distribution to the clutch pack  26  through various lubricant apertures (not shown) which are typical illustrative of a well known method to adequately distribute the flow of lubricant. The lubricant sump line  62  extends into a lubricant supply reservoir such as that of a transmission (not shown) and the lubricant is drawn up into the fluid pump  38  where it is pumped to the heat exchanger through lubricant pump line  64  and flows through the heat exchanger and returns to the clutch assembly  2  through the lubricant return line  66 . 
     Operation 
     Consider the situation when the torque flow is from the input shaft  6  to the output shaft  8  where both the input and output shafts  5  are rotating clockwise as viewed from the input shaft  6  and with the coil assembly  42  in an energized state. In a certain mode of operation, the activation plate  39  slips relative to the intermediate plate  34  and in another mode of operation the armature  44  slips relative to the intermediate plate  34 . In operation, that slippage can switch between the two modes. One such condition, when the clutch assembly  2  is used as a master clutch, is encountered in a typical vehicle acceleration mode. The activation ring  32  is stopped from rotating relative to the input shaft  6  by the first index plate  31 A since the first index step  54 A contacts the first activation stop  56 A formed in the activation ring  32  which is keyed to rotate with the input shaft  6  but allowed to move axially relative thereto. Activation plate  39  is rotationally joined to the input shaft  6  via the index plate  31 B which in one mode, is against a stop  52 A and the control ring  20  and the activation ring  32  are positioned such that the rolling elements  45 A,  45 B,  45 C are at the bottom of their respective grooves while the second index plate is on its stop  56 B but in the opposite direction. Intermediate plate  34  is connected to the output shaft  8  through the clutch hub  14  while the activation ring  32  and the control ring  20  are through the steps  46 A,  46 B,  54 A,  54 B and stops  52 A,  52 B,  56 A,  56 B keyed to the input shaft  6  via the index plates  31 A,  31 B. The control ring  20  is allowed to rotate in a clockwise direction relative to the input shaft  6  (and the activation ring  32 ) as the second control stop  52 B moves away from the second index step  46 B thereby causing the rolling elements  45 A,  45 B,  45 C to transverse their respective opposing variable depth control and activation grooves  35 A,  35 B,  35 C;  37 A,  37 B,  37 C to increase the separation distance  47 . This results in an increase in the clamping load on the clutch pack  26  whenever there is relative rotation between the input shaft  6  and the output shaft  8  up to some maximum value. 
     Now consider when the torque flow is reversed and directed from the output shaft  8  to the input shaft  6  and the input and output shafts  6 ,  8  are still rotating clockwise and the coil assembly  42  remains energized. In a certain mode of operation, the activation plate  39  slips relative to the intermediate plate  34  and in another mode of operation the armature  44  slips relative to the intermediate plate  34 . In operation, that slippage can switch between the two modes. This condition occurs in a vehicle master clutch application when the vehicle is in a coast mode and the engine is braking the vehicle. The control ring  20  is stopped from rotating relative to the input shaft  6  by the second index plate  31 B since the first control step  46 B formed in the control ring  20  contacts the second index stop  52 B (see FIG.  4 ). The second index plate  31 B is keyed to rotate with the input shaft  6  but is allowing to move axially leftward relative thereto. Axial movement to the right in FIG. 1 is prevented by the snap ring  40 . The activation ring  32  is allowed to rotate in a clockwise direction relative to the input shaft  6  (and the control ring  20 ) as the second activation stop  56 B moves away from the second index step  54 B (see FIG. 7) thereby causing the rolling elements  45 A,  45 B,  45 C to transverse the opposing variable depth control and activation grooves  35 A,  35 B,  35 C;  37 A,  37 B,  37 C to increase the separation distance  47 . This results in an increase in the clamping load on the clutch pack  26  whenever there is relative rotation between the input shaft  6  and the output shaft  8  up to some maximum value. 
     In general, the input shaft  6  could be any type of rotational input member connected so as to rotate the first and second index plates  31 A,  31 B and the armature  44  and the drive hub  16 . Also, the output shaft  8  could be any type of suitable rotational output member connected to rotate with the clutch hub  14 . The clutch assembly  2  of the present invention works even if the input shaft  6  and the output shaft  8  are reversed in function. In the lubrication system of the present invention, the gerotor pump  38  picks up lubricant from the wet or dry sump and pressurizes it for forced flow into the primary lubricant feed ports  70  and into the lubricant distribution channel  100  for flow into the clutch through secondary feed port  71  and into the check valve port  72 . The check valve  73  provides a blockage of flow at low rotational speeds to maintain proper lubricant distribution. 
     Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example in that numerous changes in the details and construction and combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as now claimed.