Abstract:
The present invention provides an improved fluid management system for dual and other multiple clutch assemblies having fluid-operated pistons and fluid operated balance chambers offsetting the undesired pressures exerted by fluids within the piston chamber induced by centrifugal forces. Among other improvements, the system provides an effective and cost efficient arrangement of fluid supply channels and supply openings capable of maintaining desired fluid levels in the balance chambers under low, otherwise insufficient, flow rate conditions. In another aspect, the system provides a reservoir for the balance chambers under conditions where the fluid flow is stopped or interrupted.

Description:
1. FIELD OF THE INVENTION  
       [0001]     The invention relates generally to a clutch mechanism for a transmission utilizing oil or other fluid systems such as those used in automotive dual clutch transmissions.  
       2. BACKGROUND  
       [0002]     One form of automotive transmissions utilizes a dual clutch system to transmit torque to a gear box or other gear shifting mechanism. Such dual clutch systems may be used in manual, an assisted manual or automatic transmissions. Dual clutch systems typically are provided with a single torque input from the engine that is transferred by the clutch to one of a pair of shafts out of the clutch to the transmission gear box.  
         [0003]     The torque input is transferred to the output shafts through a pair of selectively engageable, compressible stacks of clutch disks. Such dual clutch systems typically have a first and a second clutch stack, and each stack has a set of driving disks and a set of driven disks. The driving disks are operatively connected to the torque input, and the driven disks are operatively connected to one of the output shafts. In the gear box, the output shafts provide torque to different gear sets. For example, one of the clutch stack/output shafts can provide torque to the even numbered gears in the gear box and the other shaft can to provide torque to the odd numbered gears and a reverse gear.  
         [0004]     By selectively compressing the disc stacks, the operator or operating system frictionally engages the driving disks and the driven disks to transmit torque to the preselected gears. The amount of torque transfer will depend on degree to which the disks are engaged, the engine speed and other related factors. Because one disk stack is inactive while the other stack is engaged, an additional gear may be selected in the gear box and engaged to the output shift connected to the inactive clutch stack. The gear shift is accomplished by disengaging the active stack and activating the inactive stack that is already engaged with the new gear. Thus, the time required to shift to the new, pre-selected gear can be reduced, clutch engagement and disengagement interruptions can be reduced, and a smoother gear shift can be accomplished.  
         [0005]     Many dual clutch systems position the first and second clutch arrangements radially with respect to each other. In others systems, the first and second clutch arrangements are positioned parallel to each other along the principal axis of rotation of the clutch mechanism.  
         [0006]     In many dual clutch systems, the clutch output shafts are concentrically arranged with respect to each other. One example of such an arrangement uses a first inner clutch output shaft connected to a one of clutch stacks and positioned within a hollow second, outer clutch output shaft, that is connected to the other clutch stack. The selective activation of either the first or the second clutch stacks allows for the torque input from, for example, an engine drive shaft to one of the inner or outer output shafts.  
         [0007]     Each clutch stack can be hydraulically activated by radially extending annular pistons. The pistons often extend from a location proximate a clutch support to the outer clutch plates of each of their clutch stacks. The pistons together with an annular cylinder and/or inner walls of the clutch define a pressure chamber for each piston. When a flow of fluid (typically a transmission oil) is applied to the pressure chamber and thus to one of the pistons, the piston contacts the clutch stack with a force sufficient to compress and frictionally engage the discs of the clutch stack.  
         [0008]     In operation, the torque input to the clutch is transmitted through the entire clutch, rotating the clutch around a central axis. In some instances, the clutch also rotates around a stationary shaft(s), and in other systems the shafts also may rotate. As a result, the clutch rotation exerts centrifugal force on the oil or other fluids in the clutch and the pressure chambers. The amount of centrifugal force at a particular point in the pressure chamber will vary with the rotational speed of the assembly, the engine and the fluid&#39;s distance from the clutch axis of rotation. In many applications, the effects of such centrifugal forces cause the fluids within the pressure chamber exert unwanted pressure on the pistons. This undesirable pressure tends to urge the piston to self-engage with its respective plate stack or to resist the disengagement of the piston from the plate stack.  
         [0009]     Accordingly, in many systems, it is desirable to provide a balancing force against the piston sufficient to reduce or offset the effect of centrifugal forces on the fluids in the pressure chambers. One design for compensating for the effect of the centrifugal force in the pressure chamber provides a balance chamber on the opposite side of the piston. This balance chamber is supplied with a transmission fluid and/or oil that also is subject to the centrifugal forces generated by the rotation of the clutch. The fluid is supplied in an amount sufficient to generate a pressure opposing and offsetting that exerted by the fluid in the pressure chamber. In many systems, the result is a general reduction or cancellation of the opposing pressures, and the net clutch application force will thus be approximately equal to the force exerted by the command pressure sent to the pressure chamber to acuate the clutch.  
         [0010]     In “wet” clutch systems, a consistent flow of an oil, transmission fluid or other lubricating fluid, also is maintained through the clutch. The lubricating fluid flows through supply channels and through the clutch stacks providing lubrication to the clutch disks, seals and other moving parts. This fluid flow further serves an important role in cooling the clutch and particularly the disk stacks.  
         [0011]     The fluid flow for applying pressure to the pistons, for supplying the balance chambers and for lubricating and cooling the clutch assemblies often is directed from a pump or reservoir through a series of channels located in a shaft or support surrounding the clutch output shafts. The channel system provides separate passages for separate functions within the clutch to permit use of different fluid flow rates and/or pressure for those functions.  
         [0012]     For example, the fluid flow rate into the pressure chambers will substantially increase and decrease with the activation and deactivation of the pistons for each clutch stack. The lubricating and cooling fluid flow to the clutch disk stacks also often must be significant, and sometimes greater than that required for the piston or balance chambers. In many dual clutch systems, as a result, it is difficult to efficiently control the fluid flows for each such function.  
         [0013]     This is a concern for the balance chambers as it is desirable to keep the fluid in balance chambers at a preferred level without unduly pressurizing them. If a balance chamber does not contain sufficient fluid, the clutch piston associated with the balance chamber will tend to self-engage the clutch stack as the engine and/or clutch rotational speed increases due to the increasing centrifugal forces. Conversely, if the fluid in the balance chamber is over-pressurized, the associated clutch will tend to self-disengage as the rotational speed of the clutch increases.  
         [0014]     The variability of fluid flow in a dual clutch systems is also of concern in systems with a fixed or stationary fluid supply shafts under low flow rate conditions. The transfer channels in such systems typically are mounted on the upper surfaces of the sleeve and/or shaft. This requires that the fluid move out and into the balance chamber, resisting gravity and other forces that would interfere with the fluid flow. Under such low flow conditions, the fluid flow from those channels may be insufficient to maintain the balance chamber fluid levels at the desired levels.  
         [0015]     Similarly, at times, such as a vehicle launch there may be a need for a reservoir of fluid that can be delivered into balance chambers before the vehicle is fully started and the fluid delivery system is delivering fluids to the clutch. There also may be other instances where the fluid flow is interrupted for a time and a reservoir of fluid to supply the clutch with fluid for the balance chambers is desirable.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention provides an improved fluid management system for clutch assemblies having fluid-operated pistons and fluid operated balance chambers offsetting the undesired pressures exerted by fluids within the piston chamber induced by centrifugal forces. The improved system provides an effective and cost efficient arrangement of fluid supply channels and supply openings capable of maintaining desired fluid levels in the balance chambers at low, otherwise insufficient, flow rate conditions.  
         [0017]     In one aspect, the system utilizes a first supply opening and a second supply opening to the balance chambers, with a supply conduit connection the openings. At low flow rate conditions, a gravity assisted flow of fluids from the first opening, through the supply conduit to the second opening. The second opening is positioned provide a gravity assisted flow of fluids into the balance chambers. The use of the multiple supply openings connected by the supply conduit permits the maintenance of sufficient fluid levels in the balance chambers under low flow rate conditions that otherwise are insufficient for that purpose.  
         [0018]     In another aspect, the system permits the efficient use of common flow channels providing fluid flow for the balance chambers and for lubrication and cooling purposes. In this aspect, the invention permits the maintenance of a consistent desired fluid flow to the balance chambers under conditions where the fluid flow for lubrication and cooling purposes exceeds that preferred for supplying the balance chambers. In yet another aspect, the improved system provides a reservoir of fluid for the balance chambers under conditions where the fluid supply is stopped or interrupted for a period of time.  
         [0019]     In yet another aspect of the system, a dual clutch assembly is provided with a first clutch disk stack and a second clutch disk stack. The clutch is provided with torque input from an engine drive linked to the disk clutch stacks. Each clutch disk stack is associated with a pressure chamber having a piston disposed to reversibly compress the disk stack when the pressure chamber is pressurized with a fluid. The fluids used in the system typically are one or more oils, oils with additives, transmission fluids or other fluids suitable for use in automotive transmissions. Each clutch stack further is associated with a balance chamber disposed to provide pressure against the piston to counteract the effect of centrifugal forces acting on the fluids within the pressure chambers.  
         [0020]     The first and second disk stacks are connected to a first and second clutch output shaft, respectively. The output shafts, in turn, are connected to a gear box. The first clutch output shaft is disposed to transfer torque to and drive one set of gears, and the second output shaft is disposed to transfer torque to and drive another set of gears. The specific combinations of gears driven by each shaft will depend on the specific application.  
         [0021]     In one aspect of the invention, the clutch also is provided with a fluid source, which may, for example, include a reservoir, at least one fluid pump, one or more fluid valves, and a controller that regulates the flow of fluid to the clutch chambers. The fluid source provides the fluid flow necessary to actuate the clutch pistons, provides fluid to the balance chambers and provides a lubricating and cooling flow to the other clutch components. The clutch accordingly is provided with one or more fluid flow channels from the fluid source to the pressure chambers, balance chambers, and the lubrication and cooling paths through the clutch.  
         [0022]     Each fluid channel is provided with channel openings disposed to deliver fluid to one of the clutch pressure chambers, to one or both balance chambers, and/or to the lubrication and cooling paths. In one aspect of the invention, the channels are formed in an sleeve mounted between the clutch output shafts and a clutch hub and/or support carrying one or both of the clutch stack assemblies. The sleeve typically is stationary during operation of the clutch so that when in operation the clutch hub, pressure chambers, balance chambers and disk stacks rotate around the sleeve. Similarly, multiple sleeves or multi-component sleeves may be used for the same purpose, and other alternatives providing fluid channels to the other clutch components may be used in other aspects of the invention.  
         [0023]     In this aspect, the sleeve provides a fluid channel to apply fluid pressure to the first clutch pressure chamber; a channel to apply fluid pressure to the second clutch pressure chamber; and a high capacity channel to supply flow fluid to the lubrication and cooling paths. This aspect of the invention also provides a channel to supply fluid to the balance chambers, as well as additional fluid to the lubrication and cooling paths when the fluid flow exceeds a predetermined level.  
         [0024]     Each channel includes a channel opening in communication with a fluid passage to the appropriate chamber and/or the lubrication and cooling paths. The channel openings are disposed circumferentially around the sleeve, and in different positions relative to the sleeve end to permit a sealing engagement of the opening and the respective fluid passages. The openings to the balance chambers include a first opening in an upper position on the sleeve, and a second opening spaced from the first opening for the supply of fluid to the balance chambers under low fluid pressure conditions.  
         [0025]     The second, low pressure opening is in fluid communication with the first opening via a ring groove. A choke wall or segment at the end of the balance chamber supply channel directs fluid into the ring groove even at low fluid flow rates. The second low pressure opening is located in a position permitting a gravity assist to the flow of fluid to the balance chambers, for example, along a bottom section of the sleeve opposite the first opening. As a result, a consistent fluid flow is available to the balance chamber at fluid pressures that often are inadequate to permit sufficient fluid flow from the first, upper opening to the balance chambers. In conditions where the fluid flow is halted, the ring groove and the additional low pressure balance channel opening also can serve as fluid reservoirs sufficient to provide adequate balancing for small piston movements.  
         [0026]     In this aspect, the fluid management system of the invention allows an overall reduction in fluid flow without a substantive loss in the ability to fill the balance chambers to effective levels under low pressure conditions. The invention also compensates for temporary interruptions in the fluid flow that would have impeded or interfered with the operation of previous systems. As one result, the invention can provide a more responsive clutch under a wide range of operating conditions. The invention, among other advantages, also permits the reduction in fluid flow requirements and volumes for the clutch system. Such reduction can result in reduced fluid resistence in the clutch, reduced fluid system wear and fluid volume requirements, and provide fuel savings and other cost savings to the users. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a partial side elevation, cross sectional view of one aspect of the invention showing the a dual clutch with one arrangement of clutch stacks.  
         [0028]      FIG. 2  is a partial side elevation, cross sectional view of the aspect of the invention shown in  FIG. 1 .  
         [0029]      FIG. 3  is a schematic illustration of the fluid flow system to the pressure chambers, balance chambers, and the lubrication and cooling paths.  
         [0030]      FIG. 4  is a partial side elevation, cross sectional view of the aspect of the invention shown in  FIG. 1  showing the flow of fluid to the pressure chamber for a first clutch stack.  
         [0031]      FIG. 5  is a partial side elevation, cross sectional view of the aspect of the invention shown in  FIG. 1  showing the flow of fluid to the pressure chamber for a second clutch stack.  
         [0032]      FIG. 6  is a partial, side elevation cross sectional view of the aspect of the invention shown in  FIG. 1  showing the flow of fluid to lubrication and cooling paths through the clutch stacks.  
         [0033]      FIG. 7  is a side elevation, cross sectional view of the aspect of the invention shown in  FIG. 1  showing the flow of fluid to the balance chambers and into the lubrication and cooling paths.  
         [0034]      FIGS. 8   a  and  8   b  are an upper perspective view and a lower perspective view, respectively, of a portion of a fluid sleeve as used in the aspect of the invention shown in  FIG. 1  with the channel openings illustrated.  
         [0035]      FIG. 9  is a graph illustrating the effect of the invention on the flow rates directed to the balance chambers and to the lubrication and cooling paths. 
     
    
       [0036]     It should be understood that the above figures are not necessarily to scale. In certain instances, details of the actual structure shown in the Figures which are not necessary for the understanding of the present invention have been omitted. It should also be understood that the Figures are provided to illustrate an example of the invention and that the invention is not necessarily limited to the particular example and aspects discussed herein.  
       DETAILED DESCRIPTION  
       [0037]     One aspect of the invention is shown in  FIG. 1  as employed in a dual clutch  10  with a first outer clutch disk stack  12  and a second inner clutch disk stack  14 . The clutch includes a drive input hub  16  to receive a torque input from an engine draft shaft, fly wheel, torque converter or other engine drive input (not shown). In this example, the drive input hub  16  includes splines  18  to join the torque input source to an outer housing  20 , which is operatively connected to the driving disks of the first  12  and second  14  clutch disk stacks.  
         [0038]     A first clutch output spline  22  is operably connected to the driven disks of the first, outer disk stack  12 , and a second clutch output spline  24  is operably connected to the driven disks of the second, inner disk stack  14 . In a typical application, the second output spline  24  is keyed to a first outer drive shaft to provide driving torque to preselected gears in a gear box (not shown) when the second inner disk stack  14  is actuated. The first output spline  22  similarly is keyed to a second drive shaft (not shown) that typically is disposed within the first drive shaft. The second inner draft shaft is operatively disposed to transfer driving torque from the first outer clutch stack  12  to other, typically complementary gears in the gear box. The drive shafts also may provide driving torque to other sets of gears in the gear box such as a reverse gear.  
         [0039]     Thus, the first  12  and second  14  disk stacks are selectively operable to transmit torque to one or more gears in the gear box in an order, and timed, to provide a desired transition between gears at selected shift points.  
         [0040]     In the example shown in  FIGS. 1 and 2 , the first and second disk stacks  12  and  14  comprise a plurality of intermeshing clutch disks. The first, outer disk stack  12  includes driving clutch disks  30  mounted in a driving disk support  32 . The first disk stack  12  also includes the driven disks  34  disposed between the driving disks  30  and mounted on a driven disk support  36 . The outer driving disks  30  and outer driven disks  34  are reversibly, and compressively movable (typically along one or more keyways) when pressure is exerted against the end driving disk  30   a , with the exception of the end disk  30   b  which is typically fixed.  
         [0041]     The second, inner disk  14  stack similarly includes driving clutch disks  38  mounted in a driving disk support  40 . The second stack  14  further includes the driven disks  42  disposed between the driving disks  40  and mounted on a driven disk support  44 . The inner driving disks  38  and inner driven disks  42  similarly are reversibly, and compressively movable (typically along one or more keyways) when pressure is exerted against the end driving disk  38   a.    
         [0042]     The driving disks  30  and  38 , and the driven disks  34  and  42  may be made a variety of materials suitable for use in clutch applications. Such materials should provide sufficient frictional engagement to efficiently transfer torque from the driving disks  30  and  38  to the driven disks  30  and  42 , and are sufficiently durable to permit the repeated compressive engagement and disengagement of the disk stacks  12  and  14 . Examples of such materials include steel, metal composite materials, disks provided with friction facings and similar friction materials. In this aspect of the invention, the disk stacks also are subject to a flow of lubricating and cooling fluid. According, the disk friction material in this example must be suitable for such a “wet” environment.  
         [0043]     As shown in  FIGS. 1 and 2 , the outer stack driving disk support  32  is attached to a first, outer stack driving plate  46  fixed at one end to the outer housing  20 . The opposite end of the outer stack driving plate  46  is fixed to a clutch support hub  48 . The outer stack driven disk support  36  is attached at one end to an outer stack driven plate  50 , which has the outer stack output shaft spline  22  at its opposite end. The inner driving disk support  44  similarly is attached to one end of a inner stack driving plate  52 . The inner stack driving plate  52  is fixed at its opposite end to the clutch support hub  48 . The inner driven disk support  44  is attached at one end of an inner driven plate  54 , which is in turn fixed at its opposite end to the output shaft spline  24 .  
         [0044]     Accordingly, when the clutch is in operation, driving torque is transferred though the hub  16  and the outer housing  20  to the outer driving plate  46 , and thereby to the the first driving disks  30  and the clutch hub  48 . The clutch hub  48 , in addition transfers driving torque to the inner stack driving plate  54 , and thereby to the inner stack driving disks  38 .  
         [0045]     To actuate the disk stacks  12  and  14 , the first outer stack  12  is provided with a first outer piston  56  selectively shiftable from an first unengaged position to a second position engaging the end driving disk  30   a . When engaged, the outer piston  56  progressively compresses the outer clutch driving disks  30  and driven disks  34  together to progressively transfer driving torque from the driving disks  30  to the driven disks  32 . That driving torque is thereby transmitted by the outer stack driven plates  50  to the outer output shaft spline  22  and its corresponding clutch output shaft.  
         [0046]     Likewise, the second inner stack  14  is provided with a second inner piston  58  selectively shiftable from an unengaged position to a position engaging the end, inner driving disk  38   a . The inner piston  58  progressively compresses the driving disks  38  and driven disks  42  together transferring driving torque from the driving disks  38  to the driven disks  42  and to the inner driven plate  54  and output shaft spline  24 , with its attached output shaft.  
         [0047]     The outer piston  56 , in addition, separates a first outer pressure apply chamber  60  from a first outer pressure balance or compensation chamber  62 . In this example, the balance chamber  62  is formed by a portion of the outer piston  56 , an outer piston support wall  64  and the inner driving plate  52 . A first, outer plate spring  66  is positioned in the outer balance chamber  62  engaging the outer piston  56 . As illustrated in  FIGS. 1 and 2 , the first plate spring  64  biases the outer piston  56  from its engaged position to its unengaged position.  
         [0048]     The inner piston  58  also separates a second inner pressure apply chamber  68  from a second, inner pressure balance or compensation chamber  70 . In this example, the inner balance chamber  70  is formed by a portion of the inner piston  58 , an inner piston support  72  and an inner balance chamber wall  74 . Positioned within the inner pressure compensation chamber  70  are one or more coil springs in a spring carrier  76 . The coil springs  76  bias the inner piston  58  from a position engaging the inner clutch stack  14 , to an unengaged position.  
         [0049]     The first, outer pressure apply chamber  60  is provided with one or more seals  78  that substantially prevent the flow of fluid from the pressure apply chamber  60 , while permitting the reversible movement of the piston  56  from an unengaged to a position engaging the outer disk stack  12 . In this example, the seals are mounted on the first outer piston  56 , and are in sealing engagement with the outer driving plate  46  and the outer piston support wall  64 . The outer balance chamber  62  also is provided with one or more seals  80  that substantially prevent to flow of fluid from the balance chamber  62 . Other sealing arrangements may be used depending on the specific configuration and structure of the pressure apply chamber  60  and piston  56 , and the balance chamber  62 .  
         [0050]     The second, inner pressure apply chamber  68  is provided with one or more seals  82  that substantially prevent the flow of fluid from the inner, pressure apply chamber  68 , while permitting the reversible movement of the second, inner piston  58  from an unengaged to a position engaging the outer disk stack  14 . In this example, the seals are mounted on the second, inner piston  58 , and are in sealing engagement with the inner stack driving plate  52  and the inner piston support wall  72 . The inner balance chamber  70  is provided with one or more seals  84  that substantially prevent to flow of fluid from the balance chamber  62 . Other sealing arrangements may be used, depending on the specific configuration and structure of the pressure apply chamber  68  and piston  58 , and the balance chamber  70 .  
         [0051]     The piston  56  of the first, outer plate clutch stack is shifted from an unengaged position to a position engaging and compressing the first, outer disk stack  12  by the application of fluid pressure in the pressure apply chamber  60 . The fluid pressure is supplied by an increase of fluid flow from an oil pump at the direction of a controller operating a valve as further discussed in connection with  FIG. 3 . Sufficient fluid is supplied to the pressure apply chamber  60  to increase the fluid pressure within the chamber until the biasing force of the spring  66  is overcome and the piston  56  is moved into engagement with the disk stack pressure plate  30   a . Additional fluid is supplied to the pressure chamber  60  to compress the disk stack  12  to provided the desired amount of torque transfer from the driving disks  30  to the driven disks  34 .  
         [0052]     The second inner  58  piston similarly is actuated by the supply of fluid to the second, inner pressure apply chamber  68  from the oil pump, valve and controller system. Sufficient fluid is supplied to the inner, pressure apply chamber  68  to increase the fluid pressure within the chamber overcoming the biasing force of the coil spring assembly  76 . The fluid pressure is increased until the second inner piston  58  is moved into engagement with the inner disk stack pressure plate  38   a , and to compress the disk stack  14  to provide the desired amount of torque transfer from the inner stack driving disks  38  to the inner stack driven disks  42 .  
         [0053]     The first  62  and second  70  balance chambers, in addition, are provided with a fluid flow sufficient to offset the pressures exerted in the outer pressure apply chamber  60  and inner pressure apply chamber  68 , respectively, resulting from the centrifugal force exerted on the fluid in the pressure apply chambers  60  and  68 . As the clutch  10  is rotated by the torque supplied by the engine, the acceleration of the fluid in the pressure apply chambers  60  and  68  tends to exert pressure against the pistons  56  and  58 .  
         [0054]     The pressure increases in the pressure apply chamber  60  and  68  due to centrifugal force will fluctuate depending on the rotational speed of the clutch  10 , and the distance of the fluid from the clutch axis of rotation. The centrifugal force will tend to increase as the engine speed (and clutch rotation) increases and decrease as the engine speed (and clutch rotation) decreases. As discussed above, if such pressure fluctuations are unchecked, then the pistons  56  and  58  may unintentionally engage the disk stacks  12  and  14 , may be subject to undesirable pressure fluctuations while operating the disk stacks, and may experience resistance to disengagement with the disk stacks.  
         [0055]     The balance chambers  62  and  70 , accordingly, are supplied with sufficient fluid to offset the pressure fluctuations in the pressure apply chambers  60  and  68  due to centrifugal forces. Because the fluids in the balance chambers  62  and  70  also are subject centrifugal forces proportionate to those exerted on the fluid in the pressure apply chambers  60  and  68 , they exert pressure against the opposite side of the pistons  56  and  58  respectively. Thus, changes in the rotational speed of the clutch  10  will cause proportionate increases and decreases in pressure in both the pressure apply chambers  60  and  68 , and their respective balance chambers  62  and  70 . By maintaining a sufficient amount of fluid in each balance chamber  62  and  70 , the fluid pressures caused by centrifugal forces in the pressure apply chambers  60  and  68  can be offset by the fluid pressures induced in the balance chambers  62  and  70 .  
         [0056]     In the example shown  FIGS. 1 and 2 , the clutch  10  rotates about a stationary support hub  86 , with a fluid distribution sleeve  88  disposed between the support hub  86  and the clutch output shafts (not shown). A plurality of bearings  90 , which also may act as seals, are positioned between the clutch hub  48  and the support hub  86  permitting the rotation of the clutch  10  around the support hub  86 .  
         [0057]     A plurality of roller bearings  92  are provided between the second inner driven plate  54  and the support hub  86 ; between the driven plate  54  and the first, driven plate  50 ; and between the outer housing  20  and the outer stack driven plate  50 . These roller bearings  92  permit the rotation of the driven plates  50  and  54  relative to each other, relative to the clutch hub  48 , and relative to the support hub  86  and the outer housing  20 . In some aspects of the invention, the roller bearings  92  also may serve as seals to prevent substantial fluid leakage from the clutch.  
         [0058]     The fluid flow for the pressure apply chambers  60  and  68 , the balance chambers  62  and  70 , and cooling and lubrication paths flow from a supply channel  94  that is in communication with an oil pump, valve and controller system. The fluid flows through the distribution sleeve  88  and through a one or more fluid channels in the distribution sleeve  88 . The channels include openings in communication with ports in the clutch hub  48  for the supply of fluid to the pressure and balance chambers.  
         [0059]     For example, the sleeve  88  is provided with a channel having an opening to port  100  in communication with the first pressure applying chamber  60 . Similarly the sleeve  88 , is provided with channels having openings in communication with port  104  to the second pressure apply chamber  68 , and with openings to ports  102  and  106  to the balance chambers  62  and  70 , respectively. The fluid distribution sleeve  88  further includes an opening  108 , typically at a distal end of the sleeve  88 , for the flow of fluid to cooling and lubrication paths and specifically to those for clutch stacks  12  and  14 . The fluid distribution sleeve  88  may define other fluid paths and alternative fluid channels depending on the specific application.  
         [0060]      FIG. 3  is a schematic illustration of the fluid flow system provided by this aspect of the invention. A controller  110  is operatively connected to a fluid pump  112 , and flow valves  114   a ,  114   b ,  114   c  that permit, limit or stop the flow of fluid from the pump  112  and a fluid reservoir (not show). The controller  110 , in this example, is part of an automotive engine control system, and typically includes a microprocessor programed to monitor a variety of data (shifting input from the clutch operator, engine speed, accelerator position, engine and/or vehicle loading, engine temperature, etc.). Other types of controllers may be used in the claimed system, including mechanical, electrical, and combination controllers.  
         [0061]     Based on the controller programing, and input from the operator and vehicle, the controller directs the pump  112  to increase or decrease the fluid flow, and directs the valves  114  to open or close as appropriate for the desired operation of the clutch  10 . In the example shown in  FIG. 3 , the controller may direct the flow of fluid from the pump  112  through the valve  114   a  to a supply fluid flow to the first outer pressure apply chamber  60 , and through valve  114   b  to the second inner pressure apply chamber  68 .  
         [0062]     As shown in  FIGS. 3 and 4 , the fluid controlled by the valve  114   a  flows through a supply channel  116  in the sleeve  88 , through the port  100  in the hubs  48  and  86  to the first outer pressure apply chamber  60 . As mentioned above, as the fluid pressure increases the first outer piston  56  moves into actuating engagement with the first outer disk stack  12 . The reduction of the fluid pressure with the closing of the valve  114   a  similarly permits the spring  66  to disengage the piston  56  from the disk stack  12 .  
         [0063]     As shown in  FIGS. 3 and 5 , the fluid controlled by the valve  114   b  flows through a supply channel  118  in sleeve  88 , through the port  102  in the hubs  48  and  86  and into the second, inner, pressure apply chamber  68 . The increasing fluid pressure urges the second inner piston  58  into actuating engagement with the second inner disk stack  14 . The reduction of the fluid pressure with the closing of the valve  114   b  permits the coil spring  76  to disengage the piston  58  from the disk stack  14 .  
         [0064]     By opening and closing the valves  114   a  and  114   b , the controller may selectively, partially and/or fully engage of the disk stacks  12  and  14  as needed to provide for the smooth transition between gear shifts. In one aspect, this smooth transition is accomplished by pre-engaging the next desired gear in the gear box with the appropriate clutch output shaft. When a gear shift is desired, the fully engaged clutch stack is gradually disengaged by a reduction in fluid pressure to its respective pressure apply chamber. The fluid pressure to the other clutch stack is increased, in sequence or simultaneously, until the required driving and driven disks are fully engaged completing the shift to the next, preselected gear.  
         [0065]     As also illustrated in  FIG. 3, 6  and  7  the controller  110  directs the operation of the valve  114   c  regulating the supply of fluid to the balance chambers  62  and  70 , and the lubrication and cooling paths  124 . In this example, the fluid flow is divided at the splitter  118  into a first, high capacity lubrication and cooling channel  120  and a second balance chamber channel  122 . As illustrated in  FIG. 6 , the high capacity lubrication and cooling channel  120  directs the fluid through the port  108   a  to the lubrication and cooling paths  124 . The fluid flows along the paths  124  through or around the bearings and/or seals  90   a  and  92   a  between the clutch hub  48 , the support hub  86  and the second, inner driven plate  54 . Other lubrication and cooling paths may be used as well depending on the specific application for the system.  
         [0066]     In this example, the lubrication and cooling flow paths  124  extend through openings  126  in the inner driven plate  54  and the inner driven plate support  44 ; through and around the second, inner plate stack  14 ; and through openings  128  in the inner driving plate support  40  and the inner driving disk plate  52 . The lubrication and cooling flow paths  124  also extend through the openings  130  in the outer disk driven plate  50  and outer driven disk support  36 ; through and around the disk stack  12 ; and through openings in the outer driving disk support  32  and the outer driving plate  46 . The continuous flow of the fluid through the lubrication and cooling paths, returning to the fluid reservoir, assisting in the efficient and durable operation of the clutch  10 .  
         [0067]     As shown in  FIGS. 3 and 7 , the balance and lubrication/cooling flow channel  122  directs the fluid flow to the first  102  and second  106  ports for the balance chambers  62  and  70 , respectively. The channel  122 , in addition, is provided with a channel choke or throttle  134  that permits fluid flow through an outlet port  108   b  at the end of the channel  122  to the the lubrication and cooling paths  124  when the fluid flow rate in the channel  122  exceeds a predetermined level. Accordingly, the fluid flow through the channel  122  serves to maintain the fluid levels in both of the balance chambers  62  and  70 , and may further supplement the lubrication and cooling flow though the clutch disk stacks  12  and  14 .  
         [0068]      FIGS. 8   a  and  8   b  show an end portion  88   a  of the fluid supply sleeve  88  providing openings from the fluid supply channels  116 ,  118 ,  120  and  122  to the respective ports  100 ,  102 ,  104 ,  106 , as well as the outlet  108  to the lubrication and cooling paths. As shown in  FIG. 8   a  and  FIG. 4 , the end portion  88   a  of the fluid supply sleeve in this example is provided with an opening  136  from the channel  116  for the supply of fluid to the first outer pressure apply chamber  60  through port  100 . As shown in  FIGS. 5 and 8   a , the end portion  88   a  of the fluid supply sleeve is provided with the opening  138  from the channel  118  to supply fluid to the second, inner pressure apply chamber  68  through port  102 .  
         [0069]     The sleeve end portion  88   a  also is provided with an opening  140  to the high capacity lubricant and coolant channel  120  as shown in  FIGS. 6 and 8   a . The opening  140  extends to the outlet port at the end of the sleeve  108   a  permitting fluid flow to the cooling and lubricating paths  124 . In this example, the high capacity channel opening  140  is sized to provide a fluid flow sufficient to substantially satisfy (and some instances exceed) the lubricating and cooling needs of the disk stacks  12  and  14 .  
         [0070]     The sleeve end portion  88   a  further is provided with an opening  142  to the channel  122  supplying a fluid flow to the balance chambers  62  and  70 , as well as the lubrication and cooling paths  124 . In this example, the opening  142  is located in the upper portion of the sleeve  88 , and is sized to permit the simultaneous flow of fluid into both ports  102  and  106  to balance chambers  62  and  70 . The opening  142  similarly is sized to receive a fluid flow from the balance chambers  62  and  70  through the ports  102  and  106  when the pistons  56  and  58  are actuated reducing the volume of the balance chambers  62  and  70 . The opening  142 , in addition, is sized to provide a flow of fluid through the port  108   b  to the lubrication and cooling paths  142 .  
         [0071]     The flow through port  108   b  is restricted by the choke or throttle  134  to maintain a predetermined amount of fluid in the channel  122  and predetermined fluid flow to the balance chamber  62  and  70 . When the fluid flow through the channel  122  exceeds this predetermined level due to input from the oil pump  112  or fluid flow from the balance chambers  62  and  70 , the fluid passes over the choke  134  and through the port  108   b  into the lubrication and cooling paths  142 .  
         [0072]     As shown in  FIGS. 7   a ,  8   a  and  8   b , the sleeve end portion  88   a  further is provided with a low pressure supply conduit or ring groove  144  and low pressure balance opening  146 . The low pressure supply conduit  144  is in flow communication with the channel  122  and opening  142 , and directs fluid to low pressure balance channel supply opening  146 . The low pressure balance channel opening  146  is in flow communication with a portion of the ports  102  and  106  to the balance chambers  68  and  70 . In this example, the low balance channel opening  146  is located on lower portion of the sleeve  88 , opposite the upper opening  142 .  
         [0073]     The low pressure supply conduit  144  is located near the end of the opening  142  on the upper portion of the sleeve  88 , and extends around the circumference of the sleeve to the low pressure balance chamber supply opening  146 . The low pressure supply conduit  144 , in addition, is located proximate the choke  134  to assist directing fluid into the supply conduit  144 . Thus, when the fluid flow through the channel  122  is at a low rate or pressure, the choke  134  and action of gravity directs a flow of fluid into the low pressure supply conduit  144 . The fluid is thereby directed to the low pressure balance channel opening  146  and is delivered to the portion of the ports  102  and  106  adjacent to the opening  146 , and there through to the balance chambers  62  and  70 .  
         [0074]     Because the low pressure balance channel supply opening  146  is stationary, and below the opening  142 , a fluid flow can be maintained to the balance chambers  62  and  70  even under low pressure/flow conditions where sufficient fluid flow cannot be maintained through the opening  142 . While the explanation for the difference in flow rates through the opening  142  and  146  is not necessary to the invention, it is believed that this efficiency is due to the required upward flow through the opening  142  that is restrained by gravity (as well as the opening size and viscosity of the fluid), and the assist provided by gravity for the fluid flow through the supply conduit  144  and flow from the low pressure opening  146 .  
         [0075]     Thus, in this aspect of the invention, the flow of fluid through the low pressure supply conduit  144  and out of the opening  146  ensures an adequate flow rate to the balance chambers  62  and  70 , which is reinforced by the choke  134  at the end of the upper opening  142 . Accordingly, this aspect of the invention can provide a flow of fluid to the balance chambers under flow rates and conditions that would preclude the effective fluid flow solely through the upper opening  142 .  
         [0076]     The channel openings  136 ,  138 ,  140 ,  142  and  146 , in addition, are disposed circumferentially around the sleeve portion  88   a , and may be staggered in different positions relative to the end of sleeve  88  to permit an effective sealing engagement with the ports  100 ,  102 ,  104 , and  106 . The openings  136 ,  138 ,  140 ,  142  and  146  further are sized to provide the desired maximum flow rate to their respective pressure and balance chambers.  
         [0077]     The operation and benefits of the combined use of the upper opening,  142 , choke  134 , low pressure supply conduit  144  and low pressure opening  146  is illustrated in the example shown in  FIG. 7 . The fluid flow  148  through the channel  122  supplies fluid to both of the balance chambers  62  and  70  via the fluid flow  150  through the upper opening  142  in the sleeve  88 , and the ports  102  and  106 . The fluid flow  152  through the low pressure conduit  144  (which under low pressure conditions may be the primary or only fluid flow) is directed to the low pressure balance channel opening  146 . The fluid flow  154  though the low pressure opening  146  is gravity fed into those portions of the ports  102  and  106  proximate to the low pressure opening  146 . The excess fluid  156 , if any, flows over the choke  134  and into the lubricant and cooling paths  124 .  
         [0078]     Moreover, the upper opening  142 , the low pressure supply conduit  144  and low pressure supply opening  146  can retain sufficient fluid as a supply reservoir to the balance chambers  62  and  70  when the fluid flow rate from the pump is interrupted or stopped. Thus, the feed of this retained fluid through the low pressure opening  146  can ensure that sufficient fluid is available to the balance chambers  62  and  70  to effectively offset the effect of centrifugal forces on the pistons  56  and  58  under those conditions as discussed above.  
         [0079]     The coordinated of fluid flow through balance chamber channel  122  and supply openings  142  and  146 , the high capacity channel  120 , and the port  108   a  can provide increased efficiencies in the operation of the clutch. Because the fluid supply to the balance chambers  62  and  70  may be maintained at low rates and/or pressures, the drag torque due to excess fluid flow and retention in the clutch  10  may be minimized without comprising the operation of the clutch  10 . Furthermore, the capacity to maintain sufficient fluid flow to the balance chambers  62  and  70 , while reducing excesses or surges, reduces the opportunity for under compensating for the effect of centrifugal forces on the pistons  56  and  58  due to inadequate fluid levels in the balance chambers  62  and  70 , or overfilling the balance chambers  62  and  70  and thereby exerting undesired and interfering pressure on the pistons  56  and  58 .  
         [0080]     The graph shown in  FIG. 9  illustrates certain of the advantages of one aspect of the invention. In this example, a consistent fluid flow to the balance chambers  62  and  70  is maintained at relatively low fluid flow rates of between 0 and about 2 liters per minute from the pump  112 , while also providing a fluid flow to the lubrication and cooling paths  124 . As the flow rate from the pump  112  approaches and exceeds 2 liters per minute, the fluid flow to the balance chambers  62  and  70  is maintained at approximately the same flow rate. The additional fluid flow at such higher flow rates is directed through the high capacity channel  120  and through the port  108   b  (through the choke  134 ) at the end of the balance chamber supply channel  122 . Thus, increases in the fluid flow necessary for lubricating and cooling purposes, or due to other fluctuations, do not cause an over supply and excess pressures in the balance chambers  62  an  70  and the consequential adverse effects on the operation of the clutch stacks  12  and  14 .  
         [0081]     In other aspects of the invention, the above described fluid delivery and management system may be adapted for use in dual clutch systems with clutch stacks disposed in a parallel relation, or in dual clutch designs of other configurations. In still other aspects of the invention, the low pressure fluid conduit  144  and low pressure opening  146  may be placed in a variety of locations along the supply channel  122  where the low pressure opening  146  is operatively associated with ports and to the balance chambers.  
         [0082]     While the invention has been described by reference to certain specific descriptive examples which illustrate preferred materials and conditions, it is understood that the invention is not limited thereto. Rather all alternatives, modifications and equivalents within the scope of the invention so described are considered to be within the scope of the appended claims.