Abstract:
A variable displacement vane-type fluid pump is provided which permits improved regulation of the pump discharge such that the pump can meet the various requirements of lubrication for internal combustion engines at all speeds with minimized use of power. Of course, the vane pump may also be utilized in a wide range of power transmission and other fluid distribution applications. The variable displacement vane pump of the invention may utilize both hydrostatic and mechanical assistance in radially positioning its vanes to ensure efficient and quiet operation of the pump and to facilitate priming of the pump. The vane pump of the invention may also use both hydrostatic and mechanical actuators to control the position of its containment ring or eccentric ring and hence, regulate the output of the pump. According to yet another aspect of the present invention, to prevent inlet flow restriction or cavitation, a valve may be provided to permit some of the pump outlet or discharge flow to bleed into the pump inlet to provide needed velocity and energy to the fluid flow into the pump inlet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/255,629, titled “Variable Displacement Pump and Method,” filed Dec. 12, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to fluid pumps and more particularly to a variable displacement vane pump. 
     BACKGROUND OF THE INVENTION 
     Hydraulic power transmission assemblies and fluid distribution systems may utilize a vane-type pump. Such pumps typically have a rotor with a plurality of circumferentially spaced vanes rotatably carried by the rotor and slidable relative thereto in slots provided in the rotor. The rotor and vanes cooperate with the internal contour of a containment ring or eccentric ring eccentrically mounted relative to an axis of the rotor and vanes to create fluid chambers between the containment ring or eccentric ring, rotor and vanes. Due to the eccentricity between the containment ring or eccentric ring and the rotor and vanes, the fluid chambers change in volume as they are moved with the rotating rotor and become larger in volume as they are moved across an inlet port and smaller in volume across an outlet port. To vary the eccentricity between the containment ring or eccentric ring and the rotor, the containment ring or eccentric ring may be pivoted upon a fixed axis in a pump housing. Pivoting the containment ring or eccentric ring varies the change in volume of the fluid chambers in use of the pump and hence, varies the displacement characteristic of the pump. 
     Side plates carried by the pump housing enclose the containment ring or eccentric ring, the rotor and the vanes, and provide passages through which fluid flows to and from the rotor and vanes. These passages, along with timing grooves and the containment ring or eccentric ring contour define pump cycles or zones, namely a fill or inlet zone, a precompression zone from the inlet to the outlet, a displacement or discharge zone, and a decompression zone from the outlet to the inlet. 
     In current vane-type pumps, the containment ring or eccentric ring is pivoted and oriented by a fluid pressure signal applied to a piston or directly to the containment ring which pivots the containment ring or eccentric ring against the bias of a fixed spring. In other words, a single fluid pressure signal is used to pivot the containment ring or eccentric ring. Accordingly, the control of the containment ring or eccentric ring is essentially limited to a pressure relief type control wherein the containment ring or eccentric ring is pivoted against the bias of the spring only when a sufficient pressure is applied to the piston or containment ring or eccentric ring. When the fluid pressure applied to the piston is not sufficient to move the containment ring or eccentric ring against the bias of a fixed spring, the position of the containment ring or eccentric ring is determined by the spring which limits to one regulation profile characteristic. 
     Additionally, it has been recognized that for efficient and quiet operation of a vane-type pump it is desirable to maintain the vanes in continuous contact with the containment ring or eccentric ring. Some vane-type pumps depend upon centrifugal force to maintain the contact between the vanes and the containment ring or eccentric ring. These pumps may lack positive and continuous contact between the vane and containment ring or eccentric ring resulting in adverse wear and decreased pump performance. One method to improve the contact between the vanes and the containment ring or eccentric ring involves applying a discharge fluid pressure to chambers or slots in the rotor in which the vanes are received. The fluid pressure drives the vanes radially outwardly and into contact with the containment ring or eccentric ring. However, in at least some conditions, the vanes have a tendency to remain in the rotor slots and the centrifugal force of the spinning rotor is not sufficient to overcome the viscous drag force on the vanes. Without the vanes extending radially outwardly from the rotor, the rotating rotor displaces little if any fluid such that there is little or no discharge pressure. Accordingly, there is little or no discharge pressure communicated to the vane slots and tending to force the vanes radially outwardly from the rotor. Hence, the pump will not prime. 
     SUMMARY OF THE INVENTION 
     A variable displacement vane-type fluid pump is provided which has a regulated discharge controlled at least in part by a pair of pilot pressure signals. Desirably, the vane pump of the invention permits improved regulation of the pump discharge such that the pump can meet the various requirements of lubrication for internal combustion engines at all speeds. Of course, the vane pump may also be utilized in power transmission and other fluid distribution applications. The variable displacement vane pump of the invention may utilize both hydrostatic and mechanical assistance in radially positioning its vanes to ensure efficient and quiet operation of the pump and to facilitate priming of the pump. The vane pump of the invention may also use both hydrostatic and mechanical actuators to control the position of its containment ring or eccentric ring and hence, regulate the output of the pump. According to yet another aspect of the present invention, to prevent inlet flow restriction or cavitation, a valve may be provided to permit some of the pump outlet or discharge flow to exhaust into the pump inlet to provide needed velocity energy to the fluid flow in the pump inlet. 
     To achieve the dual pilot pressure regulation of the pump output the vane pump has a pair of actuators each operable to position the containment ring or eccentric ring as desired. In one embodiment of the invention, the actuators are opposed pistons that are each actuated by a separate pilot pressure signal to pivot the cam as a function of the pressure signals. In another embodiment, a seal may be provided between the containment ring or eccentric ring and the pump housing defining separate chambers, the chambers receive pressurized fluid bearing directly on the containment ring or eccentric ring to position it and function as the actuators without any pistons between the fluid signal and the containment ring or eccentric ring. In any of the embodiments, the cam may be biased in one or both directions of its pivotal movement, such as by one or more springs. 
     To ensure priming of the pump and development of discharge pressure, one or more rings lie adjacent to the rotor radially inwardly of the vanes to ensure that at least some of the vanes extend radially outwardly beyond the rotor and in contact with the contoured ring at all times. Preferably, hydrostatic pressure is employed in chambers behind the vanes to provide full extension of the vanes and maintain them in continuous contact with the containment ring or eccentric ring. 
     Accordingly, some of the objects, features and advantages of this invention include providing an eccentric vane pump which enables improved control of the pump discharge, ensures priming of the pump, reduces inlet flow restriction and cavitation, enables pressure signals from two or more points in the hydraulic circuit to be used to regulate pump discharge, strategically positions the cam and its pivot to minimize movement in the direction perpendicular to the desired direction of movement of the eccentric ring as it pivots, is of relatively simple design and economical manufacture and assembly, is durable, reliable and has a long and useful life in service. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments, appending claims and accompanying drawings in which: 
         FIG. 1  is a perspective view of a variable displacement eccentric vane pump according to the present invention; 
         FIG. 2  is a perspective view of the vane pump of  FIG. 1  with a side plate removed to show the internal components of the pump; 
         FIG. 3  is a plan view of the pump as in  FIG. 2  illustrating the containment ring or eccentric ring in its zero-displacement position; 
         FIG. 4  is a plan view of the pump as in  FIG. 2  illustrating the containment ring or eccentric ring in its maximum-displacement position; 
         FIG. 5  is a diagrammatic sectional view of a variable target dual pilot regulation valve which pivots the containment ring or eccentric ring of the pump according to one aspect of the present invention; 
         FIG. 6  is an enlarged, fragmentary sectional view illustrating a portion of the rotor and a vane according to the present invention; 
         FIG. 7  is an enlarged, fragmentary sectional view of the rotor and vane illustrating a seal between the vane and rotor when the vane is tilted within its slot in the rotor; 
         FIG. 8  is a schematic representation of the hydraulic circuit of the vane pump of an embodiment of this invention including completing a 3-way variable target dual pilot regulation valve; 
         FIG. 9  is a schematic representation of the hydraulic circuit of a vane pump according to the present invention including a 3-way regulation valve and an anti-cavitation valve; and 
         FIG. 10  is a diagrammatic view of the containment ring or eccentric ring of the vane pump in its zero-displacement and maximum-displacement positions. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIGS. 1-3  illustrate a variable displacement vane pump  10  having a rotor  12  and associated vanes  14  driven for rotation to draw fluid through a pump inlet  16 , increase the pressure of the fluid, and discharge the fluid under pressure from an outlet  18  of the pump  10 . A containment ring or eccentric ring  20  is carried by a housing  22  of the pump  10  and is pivoted relative to the rotor  12  to vary the displacement of the pump. Such a pump  10  is widely used in a plurality of fluid applications including engine lubrication and power transmission applications. 
     The housing  22  preferably comprises a central body  24  defining an internal chamber  26  in which the containment ring or eccentric ring  20  and rotor  12  are received. The housing  22  further includes a pair of end plates  28 , 30  on opposed, flat sides of the central body  24  to enclose the chamber  26 . A groove  32  formed in an internal surface  34  of the central body  24  is constructed to receive a pivot pin  36  between the containment ring or eccentric ring  20  and housing  22  to permit and control pivotal movement of the containment ring or eccentric ring  20  relative to the housing  22 . Spaced from the groove  32  and preferably at a generally diametrically opposed location, a seat surface  38  is provided in the central body  24 . The seat surface  38  is engageable with the containment ring or eccentric ring  20  in at least certain positions of the containment ring or eccentric ring to provide a fluid tight seal between them. One or both of the containment ring or eccentric ring  20  and central body  24  may carry an elastomeric or other type seal  40  that defines at least in part the seat surface. 
     The containment ring or eccentric ring  20  is annular having an opening  41  and is received within the chamber  26  of the housing  22 . The containment ring or eccentric ring  20  has a groove  42  in its exterior surface which receives in part the pivot pin  36  to permit pivotal movement between the containment ring or eccentric ring  20  and central body  24 . Such pivotal movement of the containment ring or eccentric ring  20  is limited by engagement of the exterior surface of the containment ring or eccentric ring  20  with the interior surface  34  of the central body  24 . As viewed in  FIGS. 4 and 10 , the containment ring or eccentric ring  20  is pivoted counterclockwise into engagement with the housing  22  in its first position wherein the pump  10  has its maximum displacement. As best shown in  FIGS. 3 and 10 , the containment ring or eccentric ring  20  may be pivoted clockwise from its first position to a second position in which the pump  10  has its minimum displacement. Of course, the containment ring or eccentric ring  20  may be operated in any orientation between and including its first and second positions to vary the displacement of the pump, as desired. The containment ring or eccentric ring  20  has an internal surface which is generally circular, but may be contoured or off-centered to improve or alter the pump  10  performance. The containment ring or eccentric ring  20  may also have a second groove  44  in its exterior surface adapted to carry the seal  40  engageable with the internal surface  34  of the central body  24  to provide a fluid tight seal between the containment ring or eccentric ring  20  and central body  24 . The fluid tight seal essentially separates the chamber  26  into two portions  26   a ,  26   b  on either side of the seal to enable a pressure differential to be generated between the separated chamber portions  26   a ,  26   b . The pressure differential may be used to pivot the containment ring or eccentric ring  20  between or to its first and second positions to control the pump displacement. 
     To move fluid through the pump  10 , a rotating displacement group  50  is provided in the housing  22 . The rotating displacement group  50  comprises a central drive shaft  52 , the rotor  12  which is carried and driven for rotation by the drive shaft  52 , and a plurality of vanes  14  slidably carried by the rotor  12  for co-rotation with the rotor  12 . The drive shaft  52  is fixed in position for rotation about its own axis  53 . The rotor  12  is fixed to the drive shaft  52  for co-rotation therewith about the axis of the shaft  52 . 
     As shown, the rotor  12  is a generally cylindrical member having a plurality of circumferentially spaced apart and axially and radially extending slots  54  that are open to an exterior surface  56  of the rotor  12  and which terminate inwardly of the exterior surface  56 . Each slot  54  is constructed to slidably receive a separate vane  14  so that the vanes are movable relative to the rotor  12  between retracted and extended positions. Each slot  54  in the rotor  12  preferably terminates at a small chamber  58  constructed to receive pressurized fluid. The pressurized fluid in a chamber  58  acts on the vane  14  in the associated slot  54  to cause the vane  14  to slide radially outwardly until it engages the internal surface  34  of the containment ring or eccentric ring  20 . Preferably, during operation of the pump  10 , the fluid pressure within the chamber  58  and slot  54  is sufficient to maintain substantially continuous contact between the vanes  14  and the internal surface of the containment ring or eccentric ring  20 . 
     In accordance with one aspect of the present invention, a vane extension member  60  is movably positioned on the rotor  12  to engage one or more of the vanes  14  and cause such vanes  14  to extend radially outwardly beyond the periphery of the rotor  12 . This facilitates priming the pump  10  by ensuring that at least two of the vanes  14  extend beyond the periphery of the rotor  12  at all times. Without the extension member  60  the vanes  14  may tend to remain in their retracted position, not extending beyond the exterior  56  of the rotor  12 , such that subsequent turning of the rotor  12  without any vanes  14  extending outwardly therefrom, does not displace sufficient fluid to prime the pump  10  and increase the pump output pressure. Accordingly, no fluid pressure is generated in the chambers  58  or slots  54  of the rotor  12  and therefore no pressure acts on the vanes  14  causing them to extend outwardly and the pump  10  will not prime. Such a condition may be encountered, for example, in mobile and automotive applications when starting a cold vehicle in cold weather such as during a cold start of an automobile. 
     In the embodiment shown in  FIG. 2 , the vane extension member  60  is a ring slidably received in an annular recess  62  formed in an end face of the rotor  12  and having a diameter sufficient to ensure that at least two of the vanes  14  extends beyond the periphery of the rotor  12  at all times. The recess  62  provides an outer shoulder  64  and an inner shoulder  66  between which the ring  60  may slide. The ring  60  slides in the recess  62  when acted on by vanes  14  which are radially inwardly displaced via engagement with the containment ring or eccentric ring  20  thereby pushing the ring  60  towards the diametrically opposed vanes  14  causing them to extend beyond the periphery of the rotor  12 . The ring  60  is retained between the rotor  12  and the adjacent side plate of the housing  22  in assembly of the pump  10 . A second ring may be provided on the opposite face of the rotor, if desired. 
     Desirably, as shown in  FIGS. 6 and 7 , the slots  54  in the rotor  12  are sized to permit a fluid film to form on the leading and trailing faces  68 ,  69  of each vane  14 . The fluid film supports the vanes  14  as the rotor  12  rotates. The fluid film prevents a wear of the fluid slot effectively seating a bearing surface. Additionally, the size of the slots  54  is desired to prevent vane tilt while still slowing fluid to enter a contact seal between the rotor  12  and vanes  14  in the areas of their contact should vane tilting occur, to the extent that any vane tilting is present. The contact seals maintain the pressurized fluid acting on the vanes  14  and prevents it from leaking or flowing out of the slots  54 . Such leakage is otherwise likely to occur due to the pressure differential between the fluid in the chambers  58  and slots  54  which is at pump outlet pressure and lower pressure portions of the pump cycle (nearly all but at the outlet of the pump). By preventing this leakage, it is ensured that a sufficient hydrostatic force biases the vanes  14  radially outwardly toward the containment ring or eccentric ring  20  to improve the continuity of the contact between the vanes  14  and the containment ring or eccentric ring  20 . 
     To displace fluid, the containment ring or eccentric ring  20  is mounted eccentrically relative to the drive shaft  52  and rotor  12 . This eccentricity creates a varying clearance or gap between the containment ring or eccentric ring  20  and the rotor  12 . The varying clearing creates fluid pumping chambers  70 , between adjacent vanes  14 , the rotor  12  and the internal surface of the containment ring or eccentric ring  20 , which have a variable volume as they are rotated in use. Specifically, each pumping chamber  70  increases in volume during a portion of its rotational movement, thereby creating a drop in pressure in that pumping chamber  70  tending to draw fluid therein. After reaching a maximum volume, each pumping chamber  70  then begins to decrease in volume increasing the pressure therein until the pumping chamber is registered with an outlet and fluid is forced through said outlet at the discharge pressure of the pump  10 . Thus, the eccentricity provides enlarging and decreasing pumping chambers  70  which provide both a decreased pressure to draw fluid in through the inlet of the pump  10  and thereafter increase the pressure of the fluid and discharge it from the outlet of the pump  10  under pressure. 
     The degree of the eccentricity determines the operational characteristics of the pump  10 , with more eccentricity providing higher flow rate of the fluid through the pump  10  and less eccentricity providing a lower flow rate in pressure of the fluid. In a so-called “zero displacement position” or the second position of the containment ring or eccentric ring  20  shown in  FIG. 3 , the opening  41  is essentially coaxially aligned with the rotor  12  so that the fluid pumping chambers  70  have an essentially constant volume throughout their rotation. In this orientation, the pumping chambers  70  do not enlarge to draw flow therein nor do they become smaller in volume to increase the pressure of fluid therein creating a minimum performance condition or a zero displacement condition of the pump  10 . When the containment ring or eccentric ring  20  is in its first or maximum displacement position the pumping chambers  70  vary in size between their maximum volume and minimum volume as the rotor  12  rotates providing increased pump displacement. 
     As shown in  FIGS. 3 and 4 , to control the pivoting and location of the containment ring or eccentric ring  20  a pair of pistons  72 ,  74  may be utilized with the pistons  72 ,  74  operable in opposed directions to pivot the containment ring or eccentric ring  20  between its first and second positions. Desirably, each piston  72 ,  74  may be responsive to different fluid pressure signals that may be taken from two different points in the fluid circuit, one of which must come from the regulating valve. Accordingly, two different portions of the fluid circuit may be used to control the displacement of the containment ring or eccentric ring  20 , and hence the operation and displacement of the pump  10 . The pistons  72 ,  74  may be of different sizes as desired to vary the force on the pistons from the pressurized fluid signals. Further, one or both of the pistons  72 ,  74  may be a spool type valve biased by a spring, or other mechanism to aid in controlling the movement of the containment ring or eccentric ring  20  and operation of the pump. As an alternative, if a seal  40  is provided between the containment ring or eccentric ring  20  and housing  22 , a controlled volume of fluid under pressure may be disposed directly in the chamber portions  26   a ,  26   b  defined on opposite sides of the seal  40 . Fluid at different volumes and pressures may be provided on either side of the seal  40  to control the movement of the containment ring or eccentric ring  20 . Of course, any combination of these actuators may be used to control the movement and position of the containment ring or eccentric ring  20  in use of the pump  10 . 
     Desirably, as best shown in  FIG. 10 , in accordance with a further aspect of the present invention, the axis  76  about which the containment ring or eccentric ring  20  is pivoted is located to provide an essentially linear movement of the containment ring or eccentric ring  20  between its first and second positions. To do so, the containment ring or eccentric ring  20  is pivoted about an axis  76  which is offset from the drive shaft axis  53  by one-half of the distance of travel in the direction of eccentricity of the containment ring or eccentric ring  20  between its first and second positions. In other words, the pivot axis  76  of the containment ring or eccentric ring  20  is offset from the drive shaft axis  53  by one-half of the maximum eccentricity of the containment ring or eccentric ring  20  relative to the drive shaft axis  53 , and hence, relative to the rotor  12 . The pivoting movement of the containment ring or eccentric ring  20  occurs along an at least somewhat arcuate path. By positioning the pivot axis  76  of the containment ring or eccentric ring  20  as described, the path of movement of the containment ring or eccentric ring  20  becomes essentially linear between its first and second positions. Non-linear or compound movement of the containment ring or eccentric ring  20  affects the gap or clearance between the rotor  12  and the containment ring or eccentric ring  20 . The performance and operating characteristics of the pump  10  are influenced by this gap or clearance. Accordingly, the non-linear movement of the containment ring or eccentric ring  20  when it is pivoted can vary the size of the fluid chambers throughout the pump  10 , and importantly, in the area of the inlet  16  and outlet  18  of the pump. For example, the pumping chambers  70  may become slightly larger in volume as they approach the outlet  18  reducing the pressure of fluid therein and causing inefficient pressurization of the fluid at the discharge port. Desirably, offsetting the pivot axis  76  of the containment ring or eccentric ring  20  in accordance with this invention provides a movement of the containment ring or eccentric ring  20  which reduces such centrality errors and facilitates control of the pump operating characteristics to improve pump performance and efficiency. The arrangement of the invention also permits a more simple pump design with a center point of the containment ring or eccentric ring opening  41  moving along an essentially linear path. Further, the pump  10  should operate with less airborne or fluid borne noise. 
     Preferably, to control the application of fluid pressure signals to the actuators that in turn control the movement of the containment ring or eccentric ring  20 , a single control valve  80  reacts to two pilot pressure signals and their application to the actuators. As shown in  FIG. 5 , the control valve  80  has a spool portion  82  with a plurality of annular grooves and lands between adjacent grooves providing sealing engagement with a bore  84  in which the spool portion  82  is received. The valve  80  also has a piston portion  86  comprising an outer sleeve  88  and an inner piston  90  slidably carried by the sleeve  88 . A first spring  92  is disposed between the plunger  90  and the spool portion  82  to yieldably bias the position of the spool portion  82  and a second spring  94  is disposed between the sleeve  88  and the plunger  90  to yieldably bias the plunger  90  away from the sleeve  88 . 
     As shown in  FIGS. 5 and 8 , the valve  80  has a first inlet  96  through which fluid discharged from the pump  10  is communicated with a chamber  98  in which the plunger  90  is received to provide a force acting on the plunger  90  in a direction opposing the biasing force of the second spring  94 . A second inlet  100  communicates fluid discharged from the pump  10  with the spool portion  82 . A third inlet  102  communicates fluid pressure from a downstream fluid circuit source from a second portion of the fluid circuit with a chamber  104  defined between the plunger  90  and outer sleeve  88 . A fourth inlet  106  communicates the second portion of the fluid circuit with an end  108  of the spool portion  82  located opposite the plunger  90 . In addition to the inlets, the valve  80  has a first outlet  110  communicating with a sump or reservoir  112 , a second outlet  114  communicating with the first actuator  74 , and a third outlet  116  communicating with the second actuator  72 . As discussed above, the first and second actuators  72 ,  74  control movement of the containment ring or eccentric ring  20  to vary the displacement of the pump  10 . 
     In more detail, the plunger  90  has a cylindrical body  120  with a blind bore  122  therein to receive and retain one end of the first spring  92 . An enlarged head  124  at one end of the plunger  90  is closely slidably received in the chamber  98 , which may be formed in, for example, the pump housing  22 , and is constructed to engage the outer sleeve  88  to limit movement of the plunger  90  in that direction. The outer sleeve  88  is preferably press-fit or otherwise fixed against movement in the chamber  98 . The outer sleeve  88  has a bore  126  which slidably receives the body  120  of the plunger  90 , a radially inwardly extending rim  128  at one end to limit movement of the spool portion  82  toward the plunger  90 , and a reduced diameter opposite end  130  defining the annular chamber  104  in which the second spring  94  is received. The annular chamber  104  may also receive fluid under pressure which acts on the plunger  90 . 
     The spool portion  82  is generally cylindrical and is received in the bore  84  of a body, such as the pump housing  22 . The spool portion  82  has a blind bore  132 , is open at one end  134  and is closed at its other end  108 . A first recess  136  in the exterior of the spool portion  82  leads to one or more passages  139  which open into the blind bore  132 . The first recess  136  is selectively aligned with the third outlet  116  to permit the controlled volume of pressurized fluid, keeping the displacement high at the second actuator  72  (chamber  26   a ) to vent back through the spool portion  82  via the first recess  136 , corresponding passages  139  blind bore  132  and the first outlet  110  leading to the sump or reservoir  112 . This reduces the volume and pressure of fluid at the second actuator  72  (chamber  26   a ). Likewise, the spool portion  82  has a second recess  140  which leads to corresponding passages  142  opening into the blind bore  132  and which is selectively alignable with the second outlet  114  to permit fluid controlled volume of pressurized fluid, keeping the displacement low at the first actuator  74  (chamber  26   b ) to vent back through the valve  80  via the second recess  140 , corresponding passages  142 , blind bore  132  and first outlet  110  to the sump or reservoir  112 . 
     The spool portion  82  also has a third recess  144  disposed between the first and second recesses  136 ,  140  and generally aligned with the second inlet  100 . The third recess  144  has an axial length greater than the distance between the second inlet  100  and the second outlet  114  and greater than the distance between the second inlet  100  and the third outlet  116 . Accordingly, when the spool portion  82  is sufficiently displaced toward the plunger portion  86 , the third recess  144  communicates the second outlet  114  with the second inlet  100  to enable fluid at discharge pressure to flow through the second outlet  114  from the second inlet  100 . This increases the volume and pressure of fluid acting on the first actuator  74 . Likewise, when the spool portion  82  is displaced sufficiently away from the plunger portion  86 , the third recess  144  communicates the second inlet  100  with the third outlet  116  to permit fluid at pump discharge pressure to flow through the third outlet  116  from the second inlet  100 . This increases volume and pressure of fluid acting on the second actuator  72 . From the above it can be seen that displacement of the spool portion  82  controls venting of the displacement control chamber through the first and second recesses  136 ,  140 , respectively, when they are aligned with the second and third outlets  114 ,  116 , respectively. Displacement of the spool portion  82  also permits charging or increasing of the pilot pressure signals through the third recess  144  when it is aligned with the second and third outlets  114 ,  116 , respectively. 
     Desirably, the displacement of the spool portion  82  may be controlled at least in part by two separate fluid signals from two separate portions of the fluid circuit. As shown, fluid at pump discharge pressure is provided to chamber  98  so that it is applied to the head  124  of the plunger  90  and tends to displace the plunger  90  toward the spool portion  82 . This provides a force (transmitted through the first spring  92 ) tending to displace the spool portion  82 . This force is countered, at least in part, by the second spring  94  and the fluid pressure signal from a second point in the fluid circuit which is applied to the distal end  108  of the spool portion  82  and to the chamber  104  between the outer sleeve  88  and plunger  90  which acts on the head  124  of the plunger  90  in a direction tending to separate the plunger from the outer sleeve. The movement of the spool portion  82  can be controlled as desired by choosing appropriate springs  92 ,  94 , fluid pressure signals and/or relative surface areas of the plunger head  124  and spool portion end  108  upon which the pressure signals act. Desirably, to facilitate calibration of the valve  80 , the second spring  94  may be selected to control the initial or at rest compression of the first spring  92  to control the force it applies to the spool portion  82  and plunger  90 . 
     In response to these various forces provided by the springs  92 ,  94  and the fluid pressure signals acting on the plunger  90  and the spool portion  82 , the spool portion  82  is moved to register desired recesses with desired inlet or outlet ports to control the flow of fluid to and from the first and second actuators  72 ,  74  (or chamber  26   a / 26   b ). More specifically, as viewed in  FIG. 5 , when the spool portion  82  is driven downwardly, the third recess  144  bridges the gap between the second inlet  100  and the third outlet  116  so that pressurized fluid discharged from the pump  10  is provided to the second actuator  72 . This movement of the spool portion  82  preferably also aligns the second recess  140  with the second outlet  114  to vent the volume and pressure of fluid at the first actuator  74  to the sump or reservoir  112 . Accordingly, the containment ring or eccentric ring  20  will be displaced by the second actuator  72  toward its first position increasing the displacement of the pump  10 . The spool  82  operates with the bore  84  and outlets to behave as what is commonly known as a “4-way directional valve.” As the spool portion  82  is driven upwardly, as viewed in  FIG. 5 , the third recess  144  will bridge the gap between the second inlet  100  and the second outlet  114  providing fluid at pump discharge pressure to the first actuator  74 . This movement of the spool portion  82  preferably also aligns the first recess  136  with the third outlet  116  to vent the volume of and pressure of fluid at the second actuator  72  to the sump or reservoir  112 . Accordingly, the containment ring or eccentric ring  20  will be moved toward its second position decreasing the displacement of the pump  10 . In this manner, the relative controlled volume and pressures are controlled by two separate pressure signals which may be taken from two different portions of the fluid circuit. In the embodiment shown, a first pressure signal is the fluid discharged from the pump  10  and a second pressure signal is from a downstream fluid circuit source. In this manner, the efficiency and performance of the pump can be improved through more capable control. 
     As best shown in  FIG. 9 , an inlet flow valve  150  in the fluid circuit may be provided to selectively permit fluid at pump discharge pressure to flow back into the pump inlet  16  when the pump  10  is operating at speeds wherein atmospheric pressure is insufficient to fill the inlet port  16  of the pump  10  with fluid. This reduces cavitation and overcomes any restriction of fluid flow to the inlet  16  of the pump  10  or any lack of fluid potential energy. To accomplish this, the inlet flow valve  150  may be a spool type valve slidably received in a bore  152  of a body, such as the pump housing  22 , so that it is in communication with the fluid discharged from the pump outlet  18 . As shown, the fluid circuit comprises the pump  10 , with the pump outlet  18  leading to an engine lubrication circuit  154  through a supply passage  156  which is connected to the bore  152  containing the inlet flow valve  150 . Downstream of the engine lubrication circuit  154 , fluid is returned to a reservoir  112  with a portion of such fluid routed through a pilot fluid passage  158  leading to the inlet flow valve  150  to provide a pilot pressure signal on the inlet flow valve  150 , if desired. A spring  159  may also be provided to bias the inlet flow valve  150 . From the reservoir, fluid is supplied through an inlet passage  160  to the inlet  16  of the fuel pump  10 . The inlet passage  160  can pass through the bore  152  containing the inlet flow valve  150  and is separated from the supply passage  156  by a land  162  of the inlet flow valve  150  which provides an essentially fluid tight seal with the body. 
     Accordingly, the fluid discharged from the pump  10  acts on the land  162  by way of passage  156  in communication with from outlet line  157  and tends to displace the inlet flow valve  150  in a direction opposed by the spring  159  and the pilot pressure signal applied to the inlet flow valve  150  through the pilot fluid passage  158 . When the pressure of fluid discharged from the pump  10  is high enough, to overcome the spring and pilot pressure from passage  158 , the inlet flow valve  150  will be displaced so that its land  162  will be moved far enough to open the inlet passage  160  permitting communication between the supply passage  156  and inlet passage  160  through the bore  152  and passage  161 , as shown in FIG.  9 . Thus, a portion of the fluid discharged from the pump  10  is fed back into the inlet  16  of the pump  10  along with fluid supplied from the reservoir  112  for the reasons stated above. This aspirated flow of pressurized fluid into the inlet  16  supercharges the pump inlet to ensure that the pump  10  is pumping liquid and not air or gas. This prevents cavitation and improves the pump efficiency and performance. 
     The purpose of the valve  150  and its supercharging effect is to convert available pressure energy into velocity energy at the inlet to provide supercharging. 
     Accordingly, the pump  10  incorporates many features which facilitate the design and operation of the pump, enable vastly improved control over the pump operating parameters and output, and improve overall pump performance and efficiency. Desirably, the vane pump of the invention can meet the various requirements of lubrication for internal combustion engines at all speeds. Of course, the vane pump may also be utilized in power transmission and other fluid distribution applications. 
     Finally, while preferred embodiments of the invention have been described in some detail herein, the scope of the invention is defined by the claims which follow. Modifications of and applications for the inventive pump which are entirely within the spirit and scope of the invention will be readily apparent to those skilled in the art.