Abstract:
A power steering pump having a plate disposed between a first surface and an intake chamber, wherein an intake flow channel defined by the first surface is in fluid communication with the intake chamber through an opening extending through the plate, the plate opening having opposed terminal ends. The intake flow channel defined by the first surface is configured to direct fluid flow through the plate opening into the intake chamber at a location through the plate opening that is intermediate and spaced from the two terminal ends of the plate opening. Also, a power steering pump having a plate disposed between a first surface and a pair of intake chambers, wherein a pair of intake flow channels defined by the first surface are in fluid communication with the intake chambers through a corresponding pair of openings extending through the plate. A pressure balancing fluid communication channel extends between the pair of intake flow channels to provide fluid communication between areas of the two intake flow channels where each intake flow channel is in communication with an opening extending through the plate, the pressure balancing fluid channel tending to equalize the fluid pressure in the two intake flow channels at the areas where they communicate with the plate openings.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Applications Ser. Nos. 61/124,096 and 61/124,095, both filed Apr. 12, 2008, the disclosures of which are both hereby expressly incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to hydraulic pumps and, more particularly, to hydraulic pumps suitable for use in a vehicular power steering application. 
         [0004]    2. Description of the Related Art 
         [0005]    Many modern vehicles have hydraulic power assisted steering systems having a power steering pump for circulating the hydraulic fluid within the system. The power steering circuit typically includes a reservoir from which hydraulic fluid is fed to the pump. Fluid discharged by the pump is used to operate a steering gear and then returns to the reservoir. The reservoir not only collects hydraulic fluid for intake by the pump but also typically conditions the hydraulic fluid by de-aerating and filtering the hydraulic fluid. The reservoir may also act as a thermal sink and cool the fluid. Fluid from the reservoir is fed to the pump and the cycle is repeated. The pump will often generate more fluid flow than is necessary for operation of the steering gear and the pump will typically include a flow control valve that re-circulates excess flow from the discharge to the intake channels of the pump. 
         [0006]      FIG. 1  presents a simplified schematic diagram of a power steering system  20  for a vehicle. Power steering system  20  includes a pump  22  which discharges fluid into a hydraulic line  24  leading to steering gear  26 . Hydraulic fluid flows through the circuit from steering gear  26  to reservoir  28  where it is de-aerated and filtered prior to returning to pump  22 . A flow control valve  30  diverts fluid from discharge line  24  of pump  22  to intake line  32  of pump  22  when pump  22  is producing excessive fluid flow. Although flow control valve  30  is presented as an external valve in the schematic depiction shown in  FIG. 1 , valve  30  is physically located within the housing of pump  22 . 
         [0007]    For many vehicles, the power steering pump shaft typically has a pulley that is driven by a belt that is also coupled to a pulley on the vehicle crankshaft. It is also known to drive the power steering pump by an electrical motor. 
         [0008]    A variety of different types of power steering pumps are known in the art and four general types of pumps that can be used for such power steering pumps include vane, roller, slipper and gear pumps. Vane-type steering pumps are in common use in contemporary vehicles and examples of vane-type steering pumps are disclosed in U.S. Pat. No. 6,913,446 B2 issued to Nissen et al.; U.S. Pat. No. 6,899,528 B2 issued to Youngpeter et al.; U.S. Pat. No. 6,857,863 B1 issued to Modrzejewski et al.; and U.S. Pat. No. 6,666,670 B1 issued to Hartman et al., the disclosures of which are hereby incorporated herein by reference. 
         [0009]      FIG. 2  is a simplified exploded view of pump  22  which is a high flow vane pump. Pump  22  includes a housing  34  which in the illustrated embodiment is a cast aluminum housing or other suitable material. A drive shaft  36  extends through housing  34  and thrust plate  38  into interior housing volume  40 . A rotor  42  is mounted on shaft  36  within housing volume  40  and includes slots  44  in which vanes  46  are located. A pump rotating group including camming ring  48  is schematically depicted in  FIG. 3  and is located within housing volume  40 . Camming ring  48  surrounds rotor  42 , vanes  46  and chambers  50 . (Camming ring  48  is not shown in  FIG. 2 .) An end plate assembly  52  seals the end of housing volume  40  opposite thrust plate  38  and is secured within housing  34  by a retaining ring  54  or other suitable means. The general operating principles of vane-type pumps such as pump  22  are well known to those having ordinary skill in the art. 
         [0010]      FIGS. 4 and 5  illustrate prior art pump  22   a,  a known, commercialized embodiment of vane-type pump  22 . In pump  22   a,  thrust plate  38  has first and second openings  56 ,  58  through which hydraulic fluid flows into an intake chamber. Openings  56 ,  58  are oblong, and each has opposed terminal ends  60 . Relative to each opening  56 ,  58 , one terminal end  60  is downstream of the other terminal end  60  relative to fluid flowing through the intake flow channel. It is noted that vanes  46  subdivide that portion of housing volume  40  within camming ring  48  into separate chambers  50  and that first and second thrust plate openings  56 ,  58  are in communication with two separate chambers  50 . When these separate chambers  50  are in communication with openings  56 ,  58  they function as intake chambers, taking in hydraulic fluid. As shaft  36  rotates rotor  42  and vanes  46 , the chambers  50  which had just functioned as intake chambers receiving fluid flowing through openings  56 ,  58 , rotate out of communication with openings  56 ,  58  and begin to function as discharge chambers. After rotating out of communication with openings  56 ,  58 , chambers  50  are rotated into communication with discharge ports and become progressively smaller thereby increasing the pressure of the fluid and discharging the fluid through the discharge ports. 
         [0011]    Pump  22   a  is configured such that fluid entering a chamber  50  through one of openings  56 ,  58  is discharged through a discharge port after rotation through an angle of approximately 90 degrees about the axis of shaft  36 . 
         [0012]    Thrust plate  38  is seated against surface  62  formed by housing  34  and which is best seen in  FIG. 5 . An intake flow channel  64  is formed in surface  62  and has a generally V-shaped configuration when viewed along the rotational axis of shaft  36  as depicted in  FIG. 5 . Intake line  32  of pump  22  feeds into flow channel  64  through an opening  66  near the apex of the V-shape of channel  64 . The fluid flowing into channel  64  through opening  66  is then divided into two flow channels  68 ,  70  which form the two separate legs of V-shaped channel  64 . Intake channels  68 ,  70  respectively lead to terminal areas  72 ,  74  which are in fluid communication with openings  56 ,  58  in thrust plate  38 . Terminal areas  72 ,  74  of intake channels  68 ,  70  each have a shape and size that generally conforms to their respective opening  56 ,  58  in thrust plate  38  such that substantially all of the area of an opening  56 ,  58  is positioned above or over the respective terminal area  72 ,  74 . In operation, fluid flows from opening  66  through channels  68 ,  70  and then from terminal areas  72 ,  74  through openings  56 ,  58  in thrust plate  38  into separate chambers  50 . 
         [0013]    While many adequate steering pump designs such as pump  22   a  are known in the art, a steering pump having improved fluid flow and/or pressure balancing characteristics, which reduce the variability and magnitude of pressures within the pump, and provide noise reduction, increased durability, and the opportunity for cost saving benefits, remains desirable. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention provides a steering pump design which improves its internal fluid flow and/or pressure balancing characteristics and provides a more durable and quietly operating pump. 
         [0015]    The present invention provides, in one form thereof, a power steering pump including a first surface, an intake flow channel defined by the first surface, a chamber into which fluid is received, and a plate disposed between the first surface and the chamber. The plate is provided with an opening extending therethrough, the plate opening having opposed terminal ends, one terminal end being downstream of the other relative to the flow of fluid through the intake flow channel. The intake flow channel is in fluid communication with the chamber through the plate opening, and the intake flow channel is configured to direct fluid flow through the plate opening into the chamber at a location intermediate and spaced from the terminal ends of the plate opening. 
         [0016]    The present invention provides, in another form thereof, a power steering pump including a first surface, a pair of intake flow channels being defined by the first surface, a pair of chambers into which fluid is received, and a plate disposed between the first surface and the pair of chambers. The plate is provided with a pair of openings, each opening extending through the plate, and each of the pair of intake flow channels is in fluid communication with one of the chambers through one of the plate openings. The two intake flow channels are in fluid communication with each other through a pressure balancing fluid communication channel extending therebetween at areas in which the intake flow channels are respectively in fluid communication with one of the pair of plate openings. The pressure of fluid in the intake flow channels at these areas tending toward equalization through the pressure balancing fluid communication channel. 
         [0017]    The present invention also provides, in another form thereof, a vane-type power steering pump including a first surface, a pair of chambers into which fluid is received, a thrust plate disposed between the first surface and the pair of chambers, and a pair of intake flow channels defined by the first surface and the thrust plate. The thrust plate is provided with a pair of openings, each opening extending therethrough, the thrust plate openings each having opposed terminal ends, one terminal end being downstream of the other relative to the flow of fluid through the respective intake flow channel. Each of the pair of intake flow channels is in fluid communication with one of the chambers through one of the thrust plate openings, and is configured to direct fluid flow through the respective thrust plate opening into the respective chamber at a location intermediate and spaced from the terminal ends of the thrust plate opening. The pump also includes a pressure balancing fluid communication channel extending between the pair of intake flow channels, the pair of intake flow channels being in fluid communication with each other through the pressure balancing fluid communication channel at areas in which the intake flow channels are respectively in fluid communication with one of the pair of thrust plate openings. The pressure of fluid in the intake flow channels at these areas tending toward equalization through the pressure balancing fluid communication channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a schematic view of a hydraulic steering circuit; 
           [0020]      FIG. 2  is an exploded side view of a vane-type power steering pump; 
           [0021]      FIG. 3  is an end view of the rotating group of the pump of  FIG. 2 ; 
           [0022]      FIG. 4  is an end view of the interior housing volume of a prior art vane-type pump with the rotor removed and showing the thrust plate; 
           [0023]      FIG. 5  is the same view as  FIG. 4  but with the thrust plate removed; 
           [0024]      FIG. 6  is an end view of the interior housing volume of a first embodiment of a vane-type pump with the rotor removed and showing the thrust plate; 
           [0025]      FIG. 7  is the same view as  FIG. 6  but with the thrust plate removed; 
           [0026]      FIG. 8  is an enlarged, fragmentary view of a cross section taken along line  8 - 8  of  FIG. 6 , showing the intake flow channel, thrust plate and intake chamber; 
           [0027]      FIG. 8A  is an enlarged, fragmentary view of a cross section taken along line  8 A- 8 A of  FIG. 6 , showing the intake flow channel, thrust plate and intake chamber; 
           [0028]      FIG. 9  is a cross sectional view taken along line  9 - 9  of  FIG. 6 ; 
           [0029]      FIG. 10  is a perspective cross sectional view taken along line  10 - 10  of  FIG. 6 ; 
           [0030]      FIG. 11  is a graphical representation of fluid pressure within the prior art pump of  FIGS. 4 and 5  as computed by a flow model of the pump operating at 8500 rpm; 
           [0031]      FIG. 12  is a graphical representation of fluid pressure within the first pump embodiment of  FIGS. 6 and 7  as computed by a flow model of the pump operating at 8500 rpm; 
           [0032]      FIG. 13  is a graphical representation of fluid pressure within the prior art pump of  FIGS. 4 and 5  as computed by a flow model of the pump operating at 3500 rpm; 
           [0033]      FIG. 14  is a graphical representation of fluid pressure within the first pump embodiment of  FIGS. 6 and 7  as computed by a flow model of the pump operating at 3500 rpm; 
           [0034]      FIG. 15  is an end view of the interior housing volume of a second embodiment of a vane-type pump with the rotor removed and showing the thrust plate; 
           [0035]      FIG. 16  is the same view as  FIG. 15  but with the thrust plate removed; 
           [0036]      FIG. 17  is an end view of the interior housing volume of a third embodiment of a vane-type pump with the rotor removed and showing the thrust plate; 
           [0037]      FIG. 18  is the same view as  FIG. 17  but with the thrust plate removed; 
           [0038]      FIG. 19  is an enlarged, fragmentary view of a cross section taken along line  19 - 19  of  FIG. 17 , showing the intake flow channel, thrust plate and intake chamber; 
           [0039]      FIG. 19A  is an enlarged, fragmentary view of a cross section taken along line  19 A- 19 A of  FIG. 17 , showing the intake flow channel, thrust plate and intake chamber; 
           [0040]      FIG. 20  is a cross sectional view taken along line  20 - 20  of  FIG. 17 ; 
           [0041]      FIG. 21  is a perspective cross sectional view taken along line  21 - 21  of  FIG. 17 ; 
           [0042]      FIG. 22  is a graphical representation of fluid pressure within the prior art pump of  FIGS. 4 and 5 , as computed by a flow model of the pump operating at a high speed; and 
           [0043]      FIG. 23  is a graphical representation of fluid pressure within the second pump embodiment of  FIGS. 15 and 16 , as computed by a flow model of the pump operating at a high speed. 
       
    
    
       [0044]    Corresponding reference characters indicate corresponding parts throughout the several views. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
         [0045]    Moreover, it is to be noted that the Figures are not necessarily drawn to scale and are necessarily not drawn to the same scale. In particular, the scale of some of the elements of the Figures is greatly exaggerated to emphasize characteristics of the elements. Elements shown in more than one Figure that may be similarly configured have been indicated using the same reference numerals. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0046]      FIGS. 6 and 7  illustrate pump  22   b,  a first embodiment of pump  22  in accordance with the present invention. Pump  22   b  is substantially identical to pump  22   a  except for the configuration of the intake flow channel in surface  62 . Intake flow channel  76  of pump  22   b  receives hydraulic fluid through opening  78 . Channel  76  has a first channel leg  80  and a second channel leg  82  which include respective terminal area  84 ,  86  which is respectively positioned below or under an opening  56 ,  58  in thrust plate  38 . Terminal areas  84 ,  86 , however, do not conform to the shape of the overlying openings  56 ,  58  in thrust plate  38 . Instead, terminal areas  84 ,  86  underlie approximately one half of openings  56 ,  58 . Channels  80 ,  82  have a depth of approximately 10 mm where such channels  80 ,  82  underlie a solid portion of thrust plate  38 . Beginning near the point at which channels  80 ,  82  begin to underlie openings  56 ,  58 , the bottom surface  88  of channels  80 ,  82  begins to slope upwards or toward thrust plate  38 . These transition zones are marked  90  and can be seen in  FIG. 7 . The bottom of channels  80 ,  82 , from transition zones  90  to the terminal ends  92  of terminal areas  84 ,  86 , forms an upwardly sloped surface  94 . Substantially flat bottom surface  88  is joined to sloped surface  94  through transition zone  90 . The slope of surface  94  in channel  80  forms a 36 degree angle with a line extending along bottom surface  88  upstream of transition zone  90  and parallel with thrust plate  38  as depicted by angle  96  in  FIG. 8 . The slope of surface  94  in channel  82  is similar and forms a 40 degree angle with a line extending along bottom surface  88  upstream of transition zone  90  and parallel with thrust plate  38  as depicted by angle  96  in  FIG. 8A . Although specific channel geometry has been described herein, the present invention is not limited to this geometry and various other intake flow channels can be employed with the present invention. 
         [0047]    Terminal ends  92  of channels  80 ,  82  are located approximately midway between opposite terminal ends  60  of openings  56 ,  58  in thrust plate  38 . Ends  60  of openings  56 ,  58  are located at approximately the same radial distance from the longitudinal axis of shaft  36  and at different angular positions about the shaft axis. The depth of channels  80 ,  82  is approximately 2 mm at channel ends  92 . As shown in  FIGS. 8 and 8A , the provision of an upwardly sloping channel bottom and the introduction of the fluid flow from the channel into the thrust plate opening  56 ,  58  at a point intermediate and spaced from opposed terminal ends  60  of each thrust plate opening  56 ,  58  directs the fluid flow, indicated by arrow  98  in  FIGS. 8 and 8A , through the openings  56 ,  58  in a direction that is at an acute or obtuse angle (depending on how measured) to the plane of thrust plate  38 . This relatively smooth redirection of the fluid flow from channels  80 ,  82  through openings  56 ,  58  reduces the turbulence of the fluid flow at this location in pump  22   b  in comparison to that of the fluid flow into chambers  50  from channels  68 ,  70  formed in surface  62  of prior art pump  22   a  which each lead to a terminal end surface oriented generally perpendicular to the fluid flow direction and defined by the terminal end  100  of each channel  68 ,  70  together with one terminal end  60  of its respective thrust plate opening. 
         [0048]      FIGS. 9 and 10  provide cross-sectional views of pump housing  34  and thrust plate  38 . A discharge passage  102  in housing  34  can be seen in  FIG. 9 . 
         [0049]    Flow model analyses of prior art pump  22   a  and first embodiment pump  22   b  were conducted at operating speeds of 8500 rpm and 3500 rpm and the fluid pressure values obtained by these analyses are presented in  FIGS. 11 through 14 .  FIG. 11  displays the results of operating prior art pump  22   a  at a shaft speed of 8500 rpm while  FIG. 12  displays the results of operating first embodiment pump  22   b  at the same shaft speed of 8500 rpm. The pressure in the intake fluid line immediately upstream of opening  66  ( FIG. 5 ) in prior art pump  22   a  was approximately 19.5 pounds per square inch gauge (psig), whereas the pressure in the intake fluid line immediately upstream of opening  78  ( FIG. 7 ) in first embodiment pump  22   b  was approximately 20.9 psig. 
         [0050]    The vertically extending rectangle located at the right in each of  FIGS. 11 through 14  is a legend and displays the shading or cross-hatching used to represent the different, indicated pressure values in psig. The horizontally extending shaded or cross-hatched rectangles located near the top and bottom of each of these Figures represent the fluid pressure on vanes  46  which face compression volumes or chambers  50  into which fluid is entering from thrust plate openings  56  (topmost rectangle) and  58  (bottommost rectangle). 
         [0051]    As can be seen by a comparison of  FIGS. 11 and 12 , the range between highest and lowest pressures acting on vanes  46  is greater, and the distribution of different pressures acting on vanes  46  is more varied, with the intake flow channel configuration of prior art pump  22   a  ( FIG. 11 ), than with the intake flow channel configuration of first embodiment pump  22   b  ( FIG. 12 ). 
         [0052]    Similarly,  FIG. 13  displays the results of operating prior art pump  22   a  at a shaft speed of 3500 rpm while  FIG. 14  displays the results of operating pump  22   b  at the same shaft speed of 3500 rpm. The pressure in the intake fluid line immediately upstream of opening  66  ( FIG. 5 ) in prior art pump  22   a  was approximately 7 psig, whereas the pressure in the intake fluid line immediately upstream of opening  78  ( FIG. 7 ) in first embodiment pump  22   b  was approximately 6 psig. At this lower operating speed, the intake flow channel configuration of pump  22   b  once again provides a comparatively smaller range and a more consistent and uniform distribution of pressures on vanes  46 . The reduced pressure variation resulting from the intake flow channel configuration of first embodiment pump  22   b  has also been found to provide a more quietly operating pump than that resulting from the intake flow channel configuration of prior art pump  22   a.  It is also thought that the more uniform distribution of pressures generated by the intake flow channel configuration of first embodiment pump  22   b  will provide a comparatively more reliable and longer lasting pump than by that of prior art pump  22   a.    
         [0053]    Another aspect of the present invention provides a pump  22  modified to have a fluid communication channel to equalize pressure between terminal areas  72  and  74  of channel  64  of prior art pump  22   a,  or terminal areas  84  and  86  of channel  76  of first pump embodiment  22   b.    
         [0054]    Referring to  FIGS. 15 and 16 , pump  22   c  is a second embodiment of pump  22  in accordance with the present invention. Pump  22   c  is substantially identical to prior art pump  22   a  except for the inclusion of fluid communication channel  106  formed in surface  62  that extends between terminal areas  72  and  74  of intake flow channel legs  68  and  70 . As in prior art pump  22   a,  in second embodiment pump  22   c  fluid flows from channels  68 ,  70  through openings  56 ,  58  into intake chambers  50 . In pump  22   c,  fluid is also communicated between the terminal areas of channels  68  and  70  proximate their terminal ends through groove  106 . 
         [0055]    Referring to  FIGS. 17 and 18 , pump  22   d  is a third embodiment of pump  22  in accordance with the present invention. Pump  22   d  is substantially identical to first embodiment pump  22   b  except for the inclusion of fluid communication channel  106  in surface  62  that extends between terminal areas  84  and  86  of intake flow channel legs  80  and  82 . As in first embodiment pump  22   b,  in third embodiment pump  22   d  fluid flows from channels  80 ,  82  through openings  56 ,  58  into intake chambers  50 . In pump  22   d,  fluid is also communicated between the terminal areas of channels  80  and  82  proximate their terminal ends  92  through groove  106 . Views of pump  22   d  shown in  FIGS. 19 ,  19 A,  20  and  21  are substantially identical to views of pump  22   b  shown in  FIGS. 8 ,  8 A,  9  and  10 , with the exception of depicting groove  106  formed in surface  62 . 
         [0056]    Groove  106  acts as a pressure balancing fluid communication channel providing fluid communication between areas  72 ,  74  of flow channels  68 ,  70  in second embodiment pump  22   c,  and areas  84 ,  86  of flow channels  80 ,  82  in third embodiment pump  22   d.  In pumps  22   c  and  22   d,  groove  106  is advantageously positioned so that it communicates with the terminal areas at the point in the terminal areas where these areas experience the highest fluid pressure values, e.g., the terminal ends of such areas. 
         [0057]    The illustrated groove  106  in pump  22   c  and pump  22   d  has a semi-circular cross-section with a depth of approximately 3 mm and a width of approximately 3.5 mm, the present invention is not, however, limited to a specific sized groove or channel  106 . It is also noted that while the illustrated pressure balancing fluid communication channel  106  is formed by a groove located in surface  62  other fluid communication passages may also be employed with the present invention. 
         [0058]    The presence of pressure balancing groove  106  tends to equalize the pressure in areas  72 ,  74  or  84 ,  86  proximate the location at which hydraulic fluid is communicated to intake chamber  50 . The presence of pressure balancing groove  106  has been found to reduce the fluid pressure within the intake line. This reduction in pressure is thought to enhance the durability of the pump. It might also provide the opportunity for cost reductions through the use of a relatively thinner housing  34  and thereby providing material cost savings. 
         [0059]    Flow model analyses of a second embodiment pump  22   c  (having pressure balancing groove  106 ) and a prior art pump  22   a  (otherwise identical but having no pressure balancing groove) were conducted at common operating speeds. Fluid pressure values obtained by these analyses at high compressor speeds are presented in  FIGS. 22 and 23 . 
         [0060]      FIG. 22  displays the results of operating prior art pump  22   a  (having no pressure reducing groove) at a shaft speed of 8500 rpm, while  FIG. 23  displays the results of operating second embodiment pump  22   c  (having pressure reducing groove  106 ) at the same shaft speed of 8500 rpm. The vertically extending rectangle located at the lower right in each of  FIGS. 22 and 23  is a legend and displays the shading or cross-hatching used to represent the different, indicated pressure values in psig. The results of the analyses indicate that, under similar conditions, the pressure in the intake fluid line immediately upstream of opening  66  ( FIG. 5 ) in prior art pump  22   a  was approximately 19.5 psig, whereas the pressure in the intake fluid line immediately upstream of opening  66  ( FIG. 16 ) in second embodiment pump  22   c  was approximately 5.2 psig. 
         [0061]    Similarly, the modeling results of operating prior art pump  22   a  and second embodiment pump  22   c  each at a shaft speed of 3500 rpm, while not graphically depicted herein, included the pressure in the intake fluid line immediately upstream of opening  66  ( FIG. 5 ) in prior art pump  22   a  being approximately 7 psig, whereas the pressure in the intake fluid line immediately upstream of opening  66  ( FIG. 16 ) in second embodiment pump  22   c  was approximately 1 psig. 
         [0062]    While the reduction in the intake fluid pressure obtained by the use of a pressure groove  106  in second embodiment pump  22   c  or third embodiment pump  22   d  is thought to increase pump durability and longevity relative to prior art pump  22   a  or first embodiment pump  22   b,  respectively, it is also thought to relatively increase turbulence in respective terminal areas  72 ,  74  and  84 ,  86  which thereby negates some of the advantages that terminal areas  84 ,  86  of first embodiment pump  22   b  provides over terminal areas  72 ,  74  of prior art pump  22   a.    
         [0063]    Although the illustrated embodiments of second embodiment pump  22   c  and third embodiment pump  22   d  respectively show pressure balancing groove  106  providing fluid communication between their respective terminal areas  72 ,  74  and  84 ,  86 , alternative configurations are also contemplated. For example, a pressure balancing groove  106  connect with the intake flow channels at alternative locations, or be used with much differently configured intake fluid lines. 
         [0064]    Although the intake flow channels  64 ,  76  and/or pressure balancing groove  106  of the illustrated first, second and third embodiments of a pump  22  in accordance with the present invention are all formed in housing  34 , alternative means of defining channels  64 ,  76 ,  106  may also be used. For example, channels  64 ,  76 ,  106  could be formed in a part that is separate from both the thrust plate  38  and housing  34 , or, they could be formed in surface  104  of thrust plate  38  that faces away from chambers  50 , or some combination thereof, e.g., formed by mating grooves located both in housing  34  and in surface  104  of thrust plate  38  that faces away from chambers  50 . 
         [0065]    While this invention has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.