Abstract:
A variable output pump system is provided, the pump system having a first positive displacement pump; a pump drive operably coupled to the first positive displacement pump, wherein the pump drive operates the first positive displacement pump to have a first output profile during a first operating range and a second output profile during a second operating range, the pump drive having a hydraulic release being configured to decrease the second output profile as a hydraulic pressure increases.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the following U.S. Provisional Applications Ser. No. 61/057,801 filed May 30, 2008; Ser. No. 61,059,069 filed Jun. 5, 2008; and Ser. No. 61/150,225 filed Feb. 5, 2009, the contents each of which are incorporated herein by reference thereto. 
     
    
     BACKGROUND 
       [0002]    Exemplary embodiments of the present invention relate to fluid pumps, in particular a variable output pump system comprising a positive displacement pump and a variable speed ratio drive system. 
         [0003]    Positive displacement pumps are generally used in automotive and industrial applications due to their comparatively low overall cost and the packaging space requirements for such pumps. One example is an internal tip sealing gear type pump commonly known as a gerotor pump. These pumps (positive displacement gerotors and equivalents thereof) are configured to maintain oil pressure under certain conditions (e.g., high oil temperatures and engine idle rpm), however these same pumps without a variable speed ratio connection to the engine typically produce excess oil at elevated rpms. In order to address this concern, variable speed drives could be provided. However, current art variable speed drives are costly and require significant additional packaging space. Also, variable displacement pumps suitable for direct driving are costly and require significant additional packaging space. 
         [0004]    Accordingly, it is desirable to provide a low cost, compact variable speed drive for a positive displacement pump such as a gerotor, the variable speed drive having a drive speed ratio that is capable of being managed as a function of the required oil pressure, and having capacity for long term continuous duty operation without performance degradation. 
         [0005]    The utilization of multiple friction members in a clutchpack is desirable in order to provide the most practical ratios of power dissipation to packaging space and to cost. Current art clutches often utilize engineered friction materials such as paper and/or carbon fiber composites in resin matrices comprising phenolics or the like to gain favorable stick-slip characteristics. These engineered friction materials typically exhibit heat aging characteristics that degrade overall performance with time. Current art clutches also typically comprise smooth steel friction members interleaved with engineered friction material-surfaced friction members having lubrication grooves that provide fluid communication, for the outward flow of heat dissipating lubricant between hub area spaces (where cooling lube is most easily introduced) and the spaces outside of the friction members where it escapes. The between-grooves areas comprising the engineered friction materials are thus typically in continual contact with their smooth mating friction members, and therefore exhibit lubricant masking, a property that fosters heat buildup and therefore the heat aging and reduction of remaining life thereby engendered. 
         [0006]    Stability of performance, over time and tribological wear, of wet friction members subjected to extended-duration high slip speed operation has been difficult to obtain at low component cost since the removal of asbestos from product offerings for reasons of environmental health. Many innovations, such as carbon fiber and nanocarbon structure-enhanced paper-based phenolic composites have been proposed and developed as friction materials. Many such materials are localized to a surface layer and so by definition are subject to change as wear erodes or consumes the surface layer. 
         [0007]    The transfer of slip-related heat from the friction surfaces to the lubricant of a wet clutch system depends on the ability of the lubricant to interact, in thermal contact, with the friction surfaces in sufficient flow volumes as to preclude localized overheating. The customary means of providing lubricant replenishment to friction surfaces, i.e. the aforementioned provision of grooves in the friction surfaces of only one of the two friction member types, has the drawbacks of groove flow area being reduced by wear over time, and also being limited by friction member thickness, while lacking the ability to hold significant lubricant volume in cooling contact with the friction surfaces while also providing for the free flow of same radially outward. It also has the aforementioned drawback that the friction contact areas themselves, i.e. those between the lubricant grooves, are self-masking, preventing the free flow of lubricant into cooling contact with the working areas most needful of cooling. 
       SUMMARY OF THE INVENTION 
       [0008]    In one exemplary embodiment of the present invention, a variable output pump system is provided, the pump system having a first positive displacement pump; a pump drive operably coupled to the first positive displacement pump, wherein the pump drive operates the first positive displacement pump to have a first output profile during a first operating range and a second output profile during a second operating range, the pump drive having a hydraulic release being configured to decrease the second output profile as a hydraulic pressure increases. 
         [0009]    In accordance with another exemplary embodiment of the invention, a variable output pump system is provided, the pump system having a pressure-regulated slip drive for varying the output of at least one positive displacement pump. The pressure-regulated slip drive has at least one biasing member for providing a biasing force that tends to cause frictional engagement of at least a pair of engagement surfaces, and the pressure-regulated slip drive also has a fluid cavity in fluid communication with a fluid being pumped by the pump. The pressure of the fluid in the fluid cavity opposes the biasing force of the biasing member tending to engage the pair of engagement surfaces, thereby affecting the magnitude of the torque transmitted from one of the engagement surfaces to the other, thereby affecting the speed ratio between the engagement surfaces, and thus the output of the pump. The torque transmitted between engagement surfaces is preferably due to Coulomb friction during startup phases only, i.e. before fluid pressure is developed, thereafter transitioning to viscous oil film shearing between physically separated engagement surfaces of sufficient area and radius in order to avoid the wear inherent to Coulomb friction. The engagement surfaces are preferably formed with interactive lubricant passages that enable continually repeated flushing of the entirety of the contact areas of both members, for improved cooling and power dissipation capacity. 
         [0010]    In still another exemplary embodiment, a pressure-regulated slip drive for varying the output of a pump is provided, the pressure-regulated slip drive comprising: at least one biasing member for providing a biasing force to a sealingly mobile load control member that tends to cause frictional engagement of at least a pair of engagement surfaces; a fluid cavity in fluid communication with a fluid being pumped by the pump, the fluid cavity being disposed between a surface of a sealingly mobile load control member and a pressure containment member, wherein the pressure of the fluid in the fluid cavity opposes the biasing force of the biasing member tending to engage the engagement surfaces, thereby affecting the output of the pump in similar manner. 
         [0011]    In still another exemplary embodiment, a method for varying the output of a positive displacement pump is provided, the method comprising: driving a contact surface coupled to a first pump of the pump system with a pressure-regulated slip drive by rotating an engagement surface of the pressure-regulated slip drive in a first direction about an axis, wherein viscous shear of a fluid disposed between the engagement surface and the contact surface couples the engagement surface to the contact surface; and decreasing an output of the first pump by moving the engagement surface away from the contact surface as a pressure of a fluid pumped by the pump system moves a moveable load control member coupled to the engagement surface. 
         [0012]    In still another exemplary embodiment, a method for varying the output of a positive displacement pump is provided, the method comprising: biasing at least one frictional engagement surface of a pressure-regulated slip drive towards frictional engagement with another frictional engagement surface with a biasing force in order to drive the pump. The biasing force is applied to a sealingly mobile load control member. Opposing the biasing force applied to the sealingly mobile load control member by fluid pressure in a fluid cavity disposed between a surface of the sealingly mobile load control member and a pressure containment member causes a reduction in the amount of the biasing towards frictional engagement of the at least two frictional engagement surfaces and thereby affects the output of the pump. 
         [0013]    In still another exemplary embodiment, a variable output pump system is provided, the system comprising: a positive displacement pump and means for varying the output of the pump by control of fluid pressure in a fluid cavity in order to either increase or decrease an amount of torque being applied to the pump, thereby affecting the output of the pump. 
         [0014]    Additional features and advantages of the various aspects of exemplary embodiments of the present invention will become more readily apparent from the following detailed description in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional view of an exemplary embodiment of the present invention; 
           [0016]      FIG. 2  is a cross-sectional view of an alternative exemplary embodiment of the present invention; 
           [0017]      FIG. 3  is schematic illustration of an alternative exemplary embodiment of the present invention; and 
           [0018]      FIG. 4  is a cross sectional schematic illustration of another alternative exemplary embodiment of the present invention. 
           [0019]      FIG. 5  is a cross sectional schematic illustration of yet another alternative exemplary embodiment of the present invention. 
           [0020]      FIG. 6  schematically illustrates engagement members in accordance with an alternative exemplary embodiment of the present invention; 
           [0021]      FIG. 7  is a schematic representation illustrating an operational position of the engagement members illustrated in  FIG. 6 . 
           [0022]      FIG. 8  is a schematic representation of the contact areas between the engagement members illustrated in  FIG. 7 . 
           [0023]      FIG. 9  is a view along lines  9 - 9  of  FIG. 7 . 
           [0024]      FIG. 9A  is another partial cross-sectional view along lines  9 - 9  of  FIG. 7 . 
           [0025]      FIG. 10  is an enlarged portion of the pump system illustrated in  FIG. 9 . 
           [0026]      FIG. 11  is another enlarged portion of the pump system illustrated in  FIG. 9 . 
           [0027]      FIG. 12  is a graph illustrating output of the pump system with respect to engine speed and potential energy savings. 
       
    
    
       [0028]    Although the drawings represent varied embodiments and features of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain exemplary embodiments of the present invention. The exemplification set forth herein illustrates several aspects of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0029]    Exemplary embodiments of the present invention relate to a system comprising a low cost slip drive unit for the pressure-controlled driving of a positive displacement oil pump. The slip drive unit utilizes a predetermined axial clamping load that is applied to friction drive surfaces via a resilient biasing member (e.g., at least one Belleville disc spring or equivalents thereof). The axial clamping load is then reduced by hydraulic pressure that overcomes the biasing force of the biasing member to allow slippage of the friction drive surfaces, as needed, after a predetermined control pressure is attained, so as to limit pump speed to that which is necessary to maintain the predetermined pressure. 
         [0030]    In one exemplary embodiment, the control pressure is taken from a remote branch of the lubrication network such as a balance shaft bearing, in order to assure that the desired pressure is available to all components downstream of the flow restrictions of, for example, those of the oil filter and its flow circuit. The control fluid pressure acts against at least one face area of an axially-mobile load control member to oppose the predetermined axial clamping load by applying a compression force to the resilient member, thereby to reduce the clamping load being applied to the friction drive surfaces, or the proximities of the friction drive surfaces with respect to one another, as a function of the control pressure. The controlled slippage allows the positive displacement pump to rotate more slowly than the shaft which drives it, i.e. at just the speed required for the maintenance of the target pressure, and thus self-adjusts the speed ratio of the pump with respect to its drive shaft to control system pressure despite fluid viscosity variation, or in the case of variations in engine permeability, for example the opening of piston cooling jets or the cycling of variable valve timing camshaft phasers, or when engine speed exceeds that at which sufficient oil pressure is developed. 
         [0031]    The following patent application Ser. No. 11/110,476 entitled: Device for Controlling Parasitic Losses in a Fluid Pump, the contents of which are incorporated herein by reference thereto uses a self-releasing wrap spring on an outside diameter of a drive hub; however this approach is in reality torque-regulated instead of pressure-regulated as claimed, so cannot be relied upon for overcoming the high startup torque magnitudes that are required to move oil under cold start conditions. 
         [0032]      FIG. 1  illustrates an exemplary embodiment of the present invention namely, a variable output pump system  10  having a pressure-regulated axial force-applying slip drive unit  12 , which in one embodiment can be used to capture an inner rotor  14  of a balance shaft-driven gerotor pump. The drive illustrated in  FIG. 1  has a minimalist structure that lacks axial “float”, and therefore captures the gerotor&#39;s inner rotor  14  in substantially fixed axial relationship to the balance shaft. This captured relationship may be useful for the synergistic elimination of balance shaft thrust control faces elsewhere, the gerotor&#39;s inner rotor&#39;s sealing lands  16  doing double duty to also provide this functionality at probable cost savings. The gerotor pump in this figure features a so-called “piloted” inner rotor, its pilot extension  18  having its small diameter end face  20  in friction-driven contact, under axial preload in the direction of arrow  22 , from paired Belleville disc springs or any other equivalent biasing device  24 , with the illustrated embodiment of the inventive hydraulically regulated slip drive unit. The opposing end of the gerotor&#39;s inner rotor is preferably captured by a shoulder  26  of similar diameter on the drive shaft  28 , wherein the inner rotor is captured, under the axial force, between similar-area faces having a diameter smaller than the minimum radius of the inner rotor&#39;s sealing area. Here a friction drive face  30  engages a face (slotted or otherwise)  20  of the exemplary piloted gerotor pump when the spring  24  provides the biasing force in the direction of arrow  22 . Once oil or fluid is received in a chamber or oil pressure cavity  32  via an oil feed path  34  in fluid communication with the oil pressure cavity, a resultant force in a direction opposite to arrow  22  causes the faces  20  and  30  to be less forcefully engaged (or disengaged), wherein the pump output is reduced. It should be understood that the force-applying load control member  36  having friction drive face  30  may be extended to engage a non-piloted gerotor without affecting the scope of the invention. The noise, vibration and harshness (NVH) benefits of a piloted inner rotor may indeed be obtained naturally by the firmness of the connection of the inner rotor to the drive shaft as provided by such an extended type force-applying unit, thus avoiding the cost and efficiency penalties inherent to piloted gerotors. 
         [0033]    Where radial compactness of the pressure-regulated axial force-applying unit is desired, the friction drive surfaces on one or both sides of the pump rotor may be conical in configuration, whereby greater torque capacity is obtained, at a slight manufacturing cost penalty, for a given axial force. The use of conical seats for connectivity between the drive shaft, the slip drive unit, and the inner rotor preferably locate the female cones in the gerotor to avoid the added process costs of an extended pilot diameter on the gerotor. Such cones or friction faces preferably will be interrupted by lube grooves that, in conjunction with an oil feed passage in communication with oil feed path  34 , maintain full presence of lubrication, and accompanying cooling, of the drive seats or faces. 
         [0034]    Where further radial compactness of the pressure-regulated axial force-applying unit is desired, and/or when greater power handling capacity is needed for a given force-applying unit package size, a multiple disc clutch pack type friction apparatus may be preferred. Friction members (or “clutch discs” or “clutch plates”) are alternatingly attached, with axial mobility as needed to transfer clamp loads through the pack or/and to allow separation between friction members, to inner and outer anti-rotation features such as splines, flats, or lobes, as is known in the art. This use of multiple friction members may increase torque capacity for any given clamping load, by increasing friction radius, and also, optionally, by sharing torque loads amongst more friction surfaces, thus enabling reduction in the axial clamping load, or the proximities of the friction drive surfaces with respect to one another, required for a given torque capacity. A reduction in the required predetermined clamping load or proximities may thus be controlled (or unloaded or opposed) by correspondingly smaller pressure reaction area at given fluid pressure, thereby enabling compactness in terms of piston diameter. Multiple friction interfaces, operating at lower clamping force or proximities, are generally more robust in terms of heat transfer as the associated lower contact pressures, or increased proximities, enable operation by fluid shear forces alone, rather than potentially requiring actual friction surface contact while slipping. The obtaining of these significant performance benefits comes at cost of an added inner torque transfer member which relocates the slip interfaces from being with respect to the pump inner rotor itself, to being with respect to an outer torque transfer member which drivingly engages the pump drive sleeve, or “inner torque transmitting member”, by means of friction members disposed therebetween. 
         [0035]    Referring now to  FIG. 2  an alternative embodiment of the present invention is illustrated. Here a variable output pump system  38  has a pressure regulated drive system  40  that uses a multiple disc clutch pack to provide the torque transfer to a positive displacement pump. The pressure-regulated slip drive system  40  comprises an outer torque transmitting member  42  that is coupled for location, and for receipt of torque, to a drive shaft  44  and captures at least one preferably Belleville spring or resilient urging member  46 , hereafter called Belleville spring, so that a predetermined static force of resilient preload in the direction of arrow  47  urges a sealingly mobile load control member  48  in the direction of arrow  47  such that an outwardly connected mobile pressure plate  50  and at least one axially mobile inwardly connected friction member  52  is urged towards an outwardly connected fixed pressure plate  56  in order to drive the pump with the drive shaft  44 . In addition, a plurality of axially mobile outwardly connected friction members, engagement members or clutch discs  54  may be added to the mobile pressure plate  50  and the fixed pressure plate  56 , in mating pairings with additional inwardly connected friction members, engagement members or clutch discs  52 , to help provide torque transfer when the pressure plate is urged in the direction of arrow  47 . 
         [0036]    The fixed pressure plate  56  is located with respect to the outer torque transmitting member  42  in order to supply the reaction force of spring preload forces as transmitted by the mobile pressure plate  50 . Mobile pressure plate  50  and fixed pressure plate  56 , as well as the axially mobile outwardly connected friction members  54  where present, sandwich the axially mobile inwardly connected friction members  52  and are in torque transmitting, preferably splined, relationship with the outer torque transmitting member  42 . The axially mobile inwardly connected friction members  52  are in torque transmitting, preferably splined, relationship with an inner torque transmitting member or drive sleeve  58  and are also preferably formed with oil passages, between their inner surfaces and corresponding passages in their mating outwardly connected friction members  50 ,  56 , and  54  where present, in order to allow generally outward oil flow and thus provide cooling and assure consistency of oil film presence between the inwardly connected friction members  52  and outwardly connected members  50 ,  56 , and  54  where present, during periods of contact with relative motion, for power dissipation and wear resistance. 
         [0037]    As illustrated, an oil pressure capturing chamber  60  is formed between the sealingly mobile load control member  48  and a static pressure containment member  62  that is sealingly captured with respect to the outer torque transmitting member  42  so as to supply an oil pressure reaction area. The oil pressure that is introduced into the oil pressure chamber  60  acts against the sealingly mobile load control member  48  in a direction opposite to arrow  47  in order to oppose the predetermined static force of the resilient preload from the at least one Belleville spring  46 , thus reducing the axial clamp load applied to the axially mobile inwardly connected friction members  52 , between mobile pressure plate  50  and fixed pressure plate  56 , and axially mobile outwardly connected friction members  54  where present, thereby reducing the friction force and thus the torque transmitting capability of the axially mobile inwardly connected friction members  52 , mobile pressure plate  50 , fixed pressure plate  56 , and axially mobile outwardly connected friction members  54  where present, which connect the drive shaft  44  to the inner torque transmitting member  58  via the outer torque transmitting member  42 . The inner torque transmitting member  58  is in driving communication, via at least one drive feature  96 , with an inner rotor member  64  of an oil pump that, in conjunction with an outer rotor member  66  and the pump housing  68 , transfers fluid volumes from an intake passage (not shown) to a discharge passage (not shown). This transfer of fluid volume occurs under pressure when resisted by flow restriction, ordinarily that of a consumptive load which requires pressurization, such as the lubrication passage network of an engine. 
         [0038]    A sample, or “pilot” pressure (hereafter “control pressure”) from a location either upstream of, or within, the consumptive load is supplied to the oil pressure chamber  60 , preferably by means of a control pressure feed hole  70  in the drive shaft  44  and at least one pressure feed cross hole  72 , which are aided in pressure capture by a plug  74 . It is to be understood that the control pressure may be supplied by means of a regulator, or by non-passive means such as a control device or pump without departing from the scope of the present invention. 
         [0039]    Since the inner torque transmitting member  58  is subject to relative rotary motion with respect to the drive shaft  44  and thus the other members of the slip drive unit (except for axially mobile inwardly connected friction members  52 ), the use of pressure seals which are suited to such rotary motion is preferred for the sealing mobilities required with respect to it. Pressure seals  76 , for example, are arrayed to capture the control pressure for the pressure chamber  60  with robustness to relative rotary motion between the sealingly mobile load control member  48  and the inner torque transmitting member  58 , such that at least one pressure transfer passage  78  in sealingly mobile load control member  48  may receive pressurized fluid from the at least one pressure feed cross hole  72 , via at least one pressure transfer hole  80 , for communication of fluid pressure with pressure chamber  60 . 
         [0040]    The clutch disc array is preferably also cooled and lubricated actively by means of at least one cooling flow cross hole  82  and at least one preferably flow throttling transfer hole  84 , the cooling flow being captured by a pressure seal  86  for escape, for example and in one non-limiting embodiment through at least one cooling flow escape hole  88 , after passage radially outward through the friction face grooves  90 . The uninterrupted communication of oil pressure between the pressure feed cross hole  72  and the pressure transfer hole  80 , and of oil flow between the cooling flow cross hole  82  and the throttling transfer hole  84 , is preferably assured, despite rotary relative motion, by localized grooves  92  and  94 , respectively. It should be understood that the preferable friction face lube grooves  90  could, either alternatively or also, be formed in the friction faces of the outwardly connected friction members, and in preferred embodiments to be described later, both type friction members are interactively slotted to maximize power dissipation capacity and durability. 
         [0041]    The inner torque transmitting member  58  drives the oil pump by means of at least one pump driving feature  96  such as face splines or “dogs” that preferably transmit the drive torque without generating axial reaction forces. 
         [0042]    Sealing, with axial mobility as required, between the members that are not subject to relative rotary motion is preferably provided by O-rings  65  as illustrated. 
         [0043]    Referring now to  FIG. 3  another alternative exemplary embodiment of the present invention is illustrated, here the system comprises a pressure-regulated slip-driven pump and a direct drive positive displacement pump each being driven by the same drive shaft. The parallel-output combination of the disclosed pressure-regulated slip-driven pump with at least one direct drive positive displacement pump (always driven when drive shaft is rotating) offers the opportunity to size the pump displacements such that within ordinary operating conditions the slip-driven pump becomes virtually disengaged, and so the system drive torque is reduced to little more than that of the parallel-output directly-driven pump, permitting power consumption to be reduced to the maximum possible extent 
         [0044]    It is to be understood that the direct drive positive displacement pump of this embodiment may be driven by a separate shaft, and thus also at a non-unit speed ratio with respect to the slip-driven pump&#39;s drive shaft, and may alternatively comprise multiple directly driven pumps. 
         [0045]    In still another alternative exemplary embodiment and referring to  FIG. 4 , a dual pump system is provided wherein one pump is directly driven by a first drive and another pump is driven by a separate second drive which applies its torque through the pressure-regulated slip drive of exemplary embodiments of the present invention. As illustrated in  FIG. 4 , the slip drive unit supplies torque to the pump through a single inwardly connected friction member  52  disposed between the mobile pressure plate  50  and the fixed pressure plate  56 . In still another alternative exemplary embodiment, as few as two friction surfaces supply the torque to the pump, non-limiting examples include the mobile pressure plate  50  and inwardly connected friction member  52  or any equivalents thereof Of course, numerous other configurations are considered to be within the scope of exemplary embodiments of the present invention. It should be also understood that in accordance with exemplary embodiments of the present invention a single pump, whether slip-driven or direct-driven, could be replaced by a plurality of pumps. 
         [0046]    Referring now to  FIGS. 5-11  another alternative exemplary embodiment of the present invention is illustrated. Here,  FIG. 5  is a cross sectional view of the slip-driven pump of a multiple pump system such as described previously in embodiments of  FIG. 3  and/or  FIG. 4 . Schematically illustrated are friction member separating devices  98 , which are interposed between an outward portion of the friction members  50 ,  54 , and  56 . The separating devices  98  are packaged radially outside the inwardly-connected friction members  52  of the slip-drive unit. Of course, other locations are contemplated to be within the scope of exemplary embodiments of the present invention. 
         [0047]    During start up, the Belleville springpack  46  urges the load control member  48  to hold the friction members together, for Coulomb friction-based driving, which is illustrated in the upper half of  FIG. 5 . In the lower half of  FIG. 5  the load control member  48  is shown fully shifted leftward by pressure captured in oil pressure chamber  60 , having compressed the Belleville springpack  46  and thus releasing the clutchpack to have maximal typical friction member separation, as illustrated by fluid film gaps  100 , for minimal drive torque transmission between the drive shaft  44  and the driven element  64  of the pump. In cases of such complete disconnection of the slip-driven pump of a multiple pump system, it is possible to include a one-way check valve in the discharge passage of the slip-driven pump so that system pressure is unable to escape through the slip-driven pump by motoring it backwards of its drive direction, however another strategy simply engineers the slip drive unit&#39;s minimum torque transmissibility (i.e., that of full disengagement) to match the torque required to back motor the slip driven pump, thereby avoiding the cost of the one-way check valve. This minimum value of torque transmissibility is provided by limitation on the magnitude of separation between mating engagement members, thereby limiting the minimum value that viscous shearing forces between the engagement members may attain. 
         [0048]    This  FIG. 5  embodiment also shows a shorter drive sleeve, or inner torque transmitting member  58 , which may help reduce manufacturing costs. In this exemplary embodiment the pressure seals  76  directly contact shaft  44 , the pressure transfer holes  80  and the preferably flow throttling transfer holes  84  are eliminated, along with grooves  92  and  94 . Throttling of clutch plate coolant flow is in this exemplary embodiment preferably provided by flow throttling annular gap  85 . 
         [0049]      FIG. 6  illustrates another alternative exemplary embodiment of the present invention wherein interactive voids, perforations, slots or grooves ( 102 ,  104 ,  106  and  108 ) in the mating or facing surfaces of the friction members ( 50 ,  52 ,  54 ,  56 ) or completely through the same are configured such that the entirety of the contact areas of between each adjacent friction member is, at least once per revolution of relative motion of the associated friction members, directly flushed by lubricant that is permitted free unmasked access to these contact areas enroute outward from the hub spaces. The arrangement and shape of such lube flow features is in one embodiment engineered to result in uniform-with-radius circumferential contact lengths, in terms of angular sums, to assure uniform with radius friction member wear rates, and the periodicity of such lube flow features is preferably Vernier in nature and with boundary shapes free from coincidence, to guard against any abruptness of interaction during their relative rotary motion when in contact; homogeneous friction member materials having both excellent thermal conductivity and wear properties, for example  4032  high silicon aluminum alloy, interleaved with preferably wear-resistant (for example nitrocarburized) ferrous alloys. Light enough loading of friction surfaces, by means of friction member area and effective radius, preferably enables virtually all operation, after a Coulomb friction-dependent startup mode before fluid pressure becomes available, to be characterized by viscous film shearing between proximate but substantially non-contacting friction surfaces. Slippage between friction members while driving by Coulomb friction necessarily produces wear and thus change of properties, clutchpack preload force at the very least, as incrementally thinner friction members act to reduce the preload magnitude (or installed compression force) of clutchpack actuating springs. The use of viscous film shearing forces rather than Coulomb friction allows the friction surfaces to be substantially wear-free after an initial break-in period to equalize film thicknesses across all friction members. Wave springs or other friction member separating devices  98  (See  FIGS. 9-11 ) are used to assure that the film thicknesses or gaps between friction members enlarge uniformly, or substantially so, as the preferably Belleville clutchpack actuating springs are compressed by the axially mobile load control member, allowing the friction members to separate. 
         [0050]    Exemplary mating friction members  52 ,  54 ,  50 ,  56  preferably have contact areas formed by voids or perforations that interact, in angularly Vernier fashion, to form axially serpentine radial oil flow paths whereby cooling lubricant entering the friction face annular contact region through the radial oil flush slots  102  in the inwardly-connected friction members  52 , directly flushes and cools exposed areas of the mating outwardly-connected friction members&#39;  54 ,  50 ,  56  contact faces, but then must cross over a friction interface (preferably a plane, but alternatively non-planar, such as conical), to one side or the other of the members  52  in order to further progress radially outward outside the member&#39;s  52  cross section by passing through the interactive voids  106  in members  54 ,  50 ,  56 . A non-limiting path is illustrated with arrows  101  in  FIG. 7 . From these sides of the friction interfaces the lubricant directly flushes and cools areas of the member&#39;s  52  contact faces exposed by the voids in member  54 ,  50 ,  56 . Finally, enroute to its radial escape it can once again cross over a friction interface to rejoin in one of the notches  104  in the periphery of a member  52 , wherein it directly flushes and cools other exposed areas of the members  54 ,  50 ,  56 . Arrows  103  illustrate oil flow paths that due to the angular configuration of at least two of members  50 ,  52 ,  54  and  56  with respect to each other do not extend all the way to the outward radial periphery of members however, and as the members rotate with respect to each other the different flow paths  101  and  103  are formed (e.g., some extending to the outer periphery (paths  101 ) and some that do not (paths  103 ). 
         [0051]    The shapes and areas of the exemplary voids or perforations are preferably engineered to maintain substantially uniform, with radius, total circumferential arc lengths of angular contact, in order to result in substantially uniform with radius rates of wear. It is to be understood that while perforated friction members have been illustrated, the axially outwardmost friction members  50 ,  56  of the clutchpack are preferably formed with blind-bottom voids or recesses of similarly engineered projected shape and areas, to prevent unwanted axial escape of cooling lubricant and the resultant underflushing and undercooling of mating part contact areas. It is to be further understood that while perforated friction members have been illustrated as being preferable, the inventive provision of interactive flow passages that enable direct wetting of the entirety of both faces of a friction member pair while forcing lubricant across the boundary between the faces in order to progress radially outward may be provided by blind-bottom voids or recesses in both friction member pairs as well as by perforations between the boundary surfaces of one or both friction members. 
         [0052]      FIG. 7  shows the mating clutch friction member contact areas of the exemplary  FIG. 6  friction members superimposed, to show their instantaneous contact pattern illustrated by the circumferentially hatched lines in  FIG. 7 . The contact pattern preferably changes continually, with relative rotary motion, in Vernier fashion by virtue of the repeat patterns of the two friction members differing in odd-even fashion. The circumferential arcs  110  which characterize the various areas of this contact pattern preferably have length sums that coincide, in terms of angle subtended, for wear uniformity with radius. 
         [0053]      FIG. 8  is a graphical representation of the total contact areas between the two friction plates illustrated in  FIG. 7  wherein circumferential arcs  110  correspond to the hatched lines or contact areas between the two friction members (illustrated in  FIG. 7 ) wherein each arc has been rotated to eliminate gaps in order to illustrate the concept of being summed angularly. These exemplary contact patterns show preliminary, but not full, optimization in terms of angular arc length sum uniformity with radius, for the purpose of substantial uniformity of wear. The exemplary pattern is but one of countless possibilities whereby the inventive concept of full flushing of mating contact surfaces, preferably with substantially uniform with radius angular contact, may be employed. 
         [0054]      FIGS. 9 and 9A  are views along lines  9 - 9  of  FIG. 7  showing at least members  52  and  54  in a cross-sectional perspective view.  FIG. 9A  illustrates one member  52  and  54  in a non-cross-sectional view. 
         [0055]      FIGS. 10 and 11  are enlarged portions of  FIG. 9  wherein fluid capture zones C (fluid paths  103 ) are illustrated in  FIG. 10  while fluid transfer passages P (fluid paths  101 ) are illustrated in  FIG. 11 . Of course, the fluid paths are merely illustrated as non-limiting examples. 
         [0056]      FIG. 12  is a graph illustrating output of the preferred multiple pump (i.e. such as illustrated in  FIGS. 3˜5 ) embodiment of the pump system with respect to engine speed (e.g., an engine driving the pump system) and potential energy savings in one non-limiting example. Plot  150  represents the output (flow in liters per minute) of the slip driven pump. As shown the slip drive pump&#39;s output will initially increase until the clutch members or members sufficiently separate (e.g., fluid pressure in cavity  60  increases) and the output is reduced. Plot  160  represents the output (flow in liters per minute) of the direct driven pump. As shown the direct drive pump&#39;s output will increases gradually with respect to engine speed. 
         [0057]    Plot or line  170  shows the combined output of the slip driven pump and the direct driven pump, while the dashed lines of plots  150  and  170  illustrate the output of the slip drive and the combined output if the slip drive was not able to reduce output as engine speed increased and the pressure of the fluid in the cavity increased. Shaded area  180  represents potential energy savings with the slip drive pump system of an exemplary embodiment of the present invention as opposed to a non-slip driven system. While numerous embodiments may be configured to achieve the inventive functionality of pressure control of a friction drive for a positive displacement pump, the apparatus described herein is to be understood as being for illustrative purposes only, and thus not limiting in scope. Exemplary embodiments of the present invention use hydraulic pressure to downwardly modulate a predetermined resilient force applied to friction drive surfaces in an apparatus used for driving a fluid pump at a variable speed ratio of 1.0 or less with respect to a driving shaft, as a function of such fluid pressure. Additionally, exemplary embodiments of the present invention are related to a variable output pump having a pressure-regulated slip drive for use in an internal combustion engine, or a balance shaft apparatus therefor. 
         [0058]    As used herein, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. In addition, it is noted that the terms “bottom” and “top” are used herein, unless otherwise noted, merely for convenience of description, and are not limited to any one position or spatial orientation. 
         [0059]    The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). 
         [0060]    While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.