Abstract:
A vane pump includes a cylindrical rotor rotatable inside of an oval-shaped rotor chamber defined by a cam ring around the rotor. A thrust plate and a pressure plate on opposite sides of the cam ring cover the rotor chamber and are squeezed together by a pressure force attributable to fluid in a discharge chamber of the vane pump at a discharge pressure thereof. A first thrust face of the thrust plate is pressed against an end wall of a cavity of a pump housing in which the components are installed. Fluid at the discharge pressure is ported to one or more balance chambers between the thrust plate and the end wall of the housing. The balance chambers are defined by a gasket received in a groove of the first thrust face. Fluid at the discharge pressure within the balance chamber balances a fraction of the pressure force on the thrust plate on an opposite second thrust face thereof attributable to fluid discharged from a rotor chamber in which the rotor operates, in order to place the thrust plate in axial static equilibrium.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is based upon, and claims the benefit of, United States Provisional Patent Application No. 60/181,871 filed Feb. 11, 2000, the disclosure of which are incorporated by reference herein in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    This invention relates to vane pumps.  
           [0004]    2. Related Art  
           [0005]    A vane pump typically includes a cylindrical rotor supported for rotation inside of an oval-shaped rotor chamber defined by a cam ring surrounding the rotor. The cam ring and the rotor define crescent-shaped cavities therebetween which are divided in to a plurality of pump chambers by a corresponding plurality of flat vanes carried in radial vane slots of the rotor. The pump chambers expand into an inlet sector of the crescent-shaped cavities and collapse in a discharge sector of the cavities as the rotor rotates. A thrust plate and a pressure plate are disposed on opposite sides of the cam ring and are squeezed together under spring tension to cover the rotor chamber. An opposite thrust face of the thrust plate is pinned between the cam ring and end wall of the housing. A significant fluid pressure differential is developed across the thrust plate which induces flexure of the thrust plate away from the rotor toward the end wall. A clearance dimension between the housing, thrust plate, and rotor calculated to accommodate such flexure exceeds a corresponding clearance dimension needed for high volumetric efficiency. Fluid leakage from the pump chambers attributable to the extra clearance for flexure of the thrust plate reduces the volumetric efficiency of the vane pump.  
           [0006]    U.S. Pat. No. 6,050,796 discloses a vane pump having a hydraulically balanced rotor for improving the efficiency of the pump. The present invention provides further improvements to vane pumps.  
         SUMMARY OF THE INVENTION AND ADVANTAGES  
         [0007]    A vane pump constructed according to the invention comprises a pump housing having a longitudinal axis, a cavity for hydraulic fluid, and a substantially planar end wall of the housing which is exposed to the cavity. A thrust plate is disposed in the cavity having a first thrust face disposed in adjacent facing relation to the end wall of the housing, and an opposite second thrust face. The thrust face has at least one fluid inlet port communicating with the cavity. A pressure plate is disposed in the cavity in axially space relation to the thrust plate. A cam ring is disposed in the cavity between the thrust plate and pressure plate and has a circumferentially extending inner cam wall defining a rotor chamber of the cavity. A rotor is supported in the rotor chamber for rotation about the longitudinal axis of the housing relative to the inner cam wall of the cam ring. A plurality of vanes are slideably supported by the rotor for radial reciprocation in communication with the inner cam wall of the cam ring to define a plurality of dynamically expanding and diminishing volume sectors of the rotor chamber and which are operative to draw hydraulic fluid into the rotor chamber under low pressure and expel the hydraulic fluid under elevated pressure from the rotor chamber. A resilient gasket is disposed between the first thrust face of the thrust plate and the end wall of the housing to define a sealed balance chamber therebetween.  
           [0008]    Provision of the balance chamber is operative to exert counteracting controlled fluid pressure on the first thrust face to oppose the fluid pressure exerted on the second thrust face so as to support the thrust plate in hydraulic equilibrium within the pump housing. The balance of fluid force on axially opposite sides of the thrust plate minimize or eliminate thrust plate flexure away from the rotor, allowing for tighter dimensional tolerance of the thrust plate and rotor which in turn lessens leakage of high pressure fluid past the thrust plate and lessens the loss of volumetric efficiency associated therewith. When combined with a hydraulically balanced rotor, a pump constructed according to the invention has been shown to improve volumetric efficiency by as much as 57% over traditional vane pumps without such balanced thrust plate and rotor components. 
       
    
    
     THE DRAWINGS  
       [0009]    A presently preferred embodiment of the invention is disclosed in the following description and in the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a longitudinal sectional view of a vane pump constructed according to the invention;  
         [0011]    [0011]FIG. 2 is a sectional view taken generally along lines  2 - 2  of FIG. 1;  
         [0012]    [0012]FIG. 3 is a sectional view taken generally along lines  3 - 3  of FIG. 1;  
         [0013]    [0013]FIG. 4 is a sectional view taken generally along lines  4 - 4  of FIG. 1;  
         [0014]    [0014]FIG. 5 is a fragmentary perspective view of a rotor;  
         [0015]    [0015]FIG. 6 is a fragmentary sectional view taken generally along lines  6 - 6  of FIG. 5;  
         [0016]    [0016]FIG. 7 is a sectional view taken generally along lines  7 - 7  of FIG. 1; and  
         [0017]    [0017]FIG. 8 is an enlarged fragmentary sectional view showing further features of the thrust plate and housing. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Referring now in more detail to the drawings, a vane pump  10  constructed according to the invention includes a pump housing  12  having therein a drive shaft bore  14  open through a first end  16  of the housing  12  and intersecting a flat bottom or end wall  18  of a large counter bore or cavity  20  in a second end  22  of the housing  12 . A control valve bore  24  in the housing  12  communicates with the counter bore  20  through a schematically represented internal passage  26  in the housing  12 . An inlet passage  28  in the housing  12  communicates with a reservoir of fluid (e.g., hydraulic fluid), not shown, and with the internal passage  26  through an aperture  30 .  
         [0019]    A “rotating group”  32  of the vane pump  10  is captured in the cavity  20  between the end wall and a disc-shaped cover  34  closing the open end of the cavity  20 . An annular chamber  36  is defined between a cylindrical side wall  38  of the cavity  20  and the rotating group  32 . A seal ring  40  suppresses fluid linkage between the housing  12  and the cover  34 . The rotating group  32  is stationary relative to the pump housing  12  and includes a thrust plate  42  seated on the flat end wall  18  of the cavity  20 , a pressure plate  44  spaced axially from the thrust plate  42 , and a cam ring  46  disposed in the cavity  20  between the thrust plate  42  and the pressure plate  44 . A plurality of dowel pins  48  traverse the thrust plate  42 , pressure plate  44 , cam ring  46 , and the housing  12  and prevent relative rotational movement therebetween about a longitudinal center line or axis  50  of the pump housing  12 .  
         [0020]    The cam ring  46  has an oval-shaped inner wall  52  that is circumferentially continuous and faces the longitudinal center line  50 . The thrust plate  42  has an aperture or shaft bore  54  in line with the bore  14  of the housing  12 . The thrust plate  42  has a first thrust face  56  facing the end wall  18  of the housing  12  and an axially opposite second thrust face  57  facing and bearing against an end  58  of the cam ring  46 . The pressure plate  44  has a planar side  60  facing and bearing against an end  62  of the cam ring  58  and an annular shoulder  64  on which the cover  34  is seated. The oval-shaped inner wall  52  of the cam ring  46  and the planar sides  57 ,  60  of the thrust plate  42  and pressure plate  44  cooperate in defining a generally oval-shaped rotor chamber  66  of the cavity  20 , as best shown in FIG. 3.  
         [0021]    The cover  34  compresses the rotating group  32  against the end wall  18  of the cavity  20  to seal the rotor chamber  66  against fluid leakage against the planar side  57  of the thrust plate  42  and the end  58  of the cam ring  46  and between the planar side  60  of the pressure plate  44  and the end  62  of the cam ring  46 . A retaining ring  68  is mounted in the cavity  20  to engage and prevent dislodgment of the cover  34  from the cavity  20 . A discharge chamber  70  of the vane pump  10  is defined between the cover  34  and the pressure plate  44  and within the housing  12  around the drive shaft bore  14 . A seal ring  72  suppresses fluid leakage between the cover  34  and the pressure plate  44 .  
         [0022]    A drive shaft  74  is jounaled by a bearing of the pump housing  12  for rotation about the longitudinal axis  50 . A splined inboard end of the drive shaft  74  engages a splined bore  76  of a rotor  78  disposed in the rotor chamber  66  for rotation with the shaft  74  within the rotor chamber  66  about the longitudinal axis  50 . An outboard end (not shown) of the drive shaft  74  is coupled to a rotary drive source, such a motor of a motor vehicle, when the vane pump  10  is employed for providing a source of pressurized fluid for a steering assist fluid motor of a motor vehicle.  
         [0023]    The rotor  78  has a cylindrical outer surface  80  which is symmetric with respect to the longitudinal  50  of the pump  10 . The rotor  78  has a pair of planar end walls  82 A,  82 B disposed in parallel planes perpendicular to the longitudinal axis A. The end walls  82 A,  82 B of the rotor  78  are separated from the planar sides  60 ,  57  of the pressure plate  44  and the thrust plate  42  by respective ones of a pair of clearance dimensions D 1 , D 2 , illustrated in exaggerated fashion in FIG. 6. The outer surface  80  of the rotor  78  cooperates with the inner wall  52  of the cam ring  46  in defining a pair of crescent-shaped cavities  84 A,  84 B of the rotor chamber  66  on radially opposite sides of the rotor  78 , as best illustrated in FIG. 3.  
         [0024]    The rotor  78  is formed with a plurality of radial vane slots  86  which intersect the outer surface  80  and each of the end walls  82 A,  82 B. A corresponding plurality of flat vanes  88  are supported in respective ones of vane slots  86  for sliding radial reciprocation relative to the rotor  78 . Each flat vane  88  has an outboard lateral edge  90  (FIG. 1) bearing against the oval-shaped inner wall  52  of the cam ring  46 , and a pair of radial edges  92  (FIG. 5) separated from the planar side  66  of the pressure plate  46  and the planar side  57  of the thrust plate  44  by clearance dimensions D 1 , D 2 , respectfully (FIG. 6). The vanes  88  divide the crescent-shaped cavities  84 A,  84 B into a plurality of pump chambers  93  (FIG. 3) which expand in each of a pair of diagonally opposite inlet sectors of the crescent-shaped cavities, and collapse in each of a pair of diagonally opposite discharge sectors of the crescent-shaped cavities in conventional fashion concurrent with the direction of rotation R of the rotor  78 .  
         [0025]    The thrust plate  42  has a pair or diametrically opposed notches  94 A,  94 B which are open to the annular chamber  36 . The pressure plate  44  has a pair of diametrically opposed notches  96 A,  96 B which are open to the annular chamber  36 . The notches  94 A,  96 A and  94 B,  96 B are angularly aligned with the inlet sector of the crescent-shaped cavities  84 A,  84 B, respectively. The notches  94 A,  96 A and  94 B,  96 B define first and second inlet ports of the vane pump for directing hydraulic fluid from the chamber  36  into the rotor chamber  66 .  
         [0026]    As shown best in FIGS. 1, 7, and  8 , the thrust plate  42  has a pair of diametrically opposed through ports  98 A,  98 B extending through the plate  42  from in the second thrust face  57  thereof to the first thrust face  56 . The pressure plate  44  has a pair of diametrically opposed shallow recesses or grooves  100 A.  100 B in the planar side  60  thereof which are angularly aligned with the ports  98 A,  98   b,  respectively, and with the discharge sectors of the crescent-shaped cavities  84 A,  84 B, respectively. The shallow grooves  100 A, 100 B communicate with the discharge chamber  70  through a pair of schematically represented passages  102  in the pressure plate  44 , as shown best in FIGS. 1 and 2, and define respective ones of a pair of discharge ports of the vane pump  10 . The discharge chamber  70  communicates with an external device, such as the aforementioned steering assist fluid motor (not shown) through a discharge passage (not shown) in the pump housing  12 .  
         [0027]    As seen best in FIGS. 3, 5, and  6 , the planar end wall  82 A of the rotor is interrupted by an annular groove  106  having a depth dimension D 3  of about 1.0 mm which intersects each of the radial vane slots  86  and faces a groove  107  in the planar side  60  of the pressure plate opposite the inboard ends of the vane slots  86 . Radially outboard of the annular groove  106 , the end wall  82 A of the rotor defines an annular outer land  108  between the annular groove and the cylindrical outer surface  80  of the rotor. The annular outer land  108  is interrupted by each of the radial vane slots and turns toward the longitudinal centerline  50  on opposite sides of each vane slot to define a plurality of pairs of radial lands  110  integral with the outer land. Radially inboard of the annular groove  106 , the end wall  82 A of the rotor defines an annular inner land  112  between the annular groove  106  and the splined bore  76  in the rotor. The surface area of the annular groove  106  between the outer land  108  and the inner land  112  constitutes a reaction portion of the planar end wall  82 A of the rotor having a surface area of at least 30% of the surface area of the planar end wall  82 A.  
         [0028]    The planar end wall  82 B of the rotor is interrupted by an annular groove  114 , FIG. 6, identical to the annular groove  106  in the end wall  82 A facing a groove  115  in the planar side  56  of the thrust plate opposite the inboard ends of the vane slots  86 . The surface area of the annular groove  114  between outer and inner lands corresponding to the outer and inner lands  108 ,  112  constitutes a reaction portion of the planar end wall  82 B of the rotor having a surface area of at least 30% of the surface area of the planar end wall  82 B.  
         [0029]    The groove  106  cooperates with the planar side  60  of the pressure plate in defining an annular first longitudinal balance chamber  116 . The groove  114  cooperates with the planar side  56  of the thrust plate in defining an annular second longitudinal balance chamber  118 . The first longitudinal balance chamber communicates with the discharge chamber  70  through a schematically represented passage  120  in the pressure plate. The second longitudinal balance chamber communicates with the first balance chamber  116  through the vane slots  86  under the vanes  88  therein.  
         [0030]    The annular inner and outer lands  112 ,  108  cooperate with the planar side  60  of the pressure plate in defining fluid seals on opposite sides of the annular groove  106  even though separated by the clearance dimension D 1 . Likewise, the inner and the outer lands on opposite sides of the annular groove  114  in the end wall  82 B of the rotor cooperate with the planar side  56  of the thrust plate in defining fluid seals on opposite sides of the annular groove  114  even though separated from the planar side  56  by the clearance dimension D 2 . The close fit between the vanes  88  and the vane slots  86  suppresses fluid leakage from the balance chambers through the vane slots. The outer lands also separate the first and the second balance chambers from the aforesaid inlet and discharge ports of the vane pump.  
         [0031]    As shown best in FIGS. 1, 7 and  8 , a resilient gasket or seal  122  fabricated of a suitable rubber or synthetic plastic material resistant to hydraulic fluid is disposed between the first thrust face  56  of the thrust plate  42  and the facing end wall  18  of the housing  12 . The gasket  106  is compressed between the thrust plate  42  and housing end wall  18  and defines at least one and preferably at least two bounded, sealed balance chambers  124 A,  124 B which are isolated by the gasket  106  from the chamber  36  and the drive shaft bore  14  of the housing  12 . The thrust plate  42  preferably is formed with grooves  126  in the first thrust face  56  which outline the balance chamber regions  124 A,  124 B. The gasket  122  is accommodated in the grooves  126 , with a sealing portion  128  of the gasket  122  projecting out of the grooves  126  beyond the first thrust face  56  for sealing contact with the end wall  18  of the housing  12 . The grooves  126  and gasket  122  disposed therein are arranged to surround the through ports  98 A,  98 B of the thrust plate  42 , as shown best in FIG. 7, such that the through ports  98 A,  98 B open into the balance chambers  124 A,  124 B on the first thrust face  56  for the containment of high pressure hydraulic fluid at the discharge pressure across an area of the thrust face  56  substantially greater than that of the area occupied by the through ports  98 A,  98 B. The size and shape of the balance chambers  124 A,  124 B are selected to capture within the balance chambers  124 A,  124 B a volume of the high pressure hydraulic fluid under the discharge pressure which is distributed evenly across the area of the first thrust face surface  56  confined by the balance chambers  124 A,  125 B and exerts an axial hydraulic balancing force F 3  (FIGS. 1 and 8) in the axial direction against the first thrust face  56  which is preferably equal to and counteracts the hydraulic fluid force F 4  exerted on the second thrust face  57  from the rotor chamber  66 , so as to balance the thrust plate  42  in hydraulic equilibrium in the direction of the axis  50 , as will be explained in greater detail below.  
         [0032]    In operation, fluid at substantially atmospheric pressure is delivered to the annular chamber  36  around the rotating group through the inlet passage  28 , the aperture  30 , and the internal passage  26  in the pump housing  12 . As the drive shaft  74  rotates the rotor  78 , the expanding pump chamber  93  in the inlet sectors of the crescent-shaped cavities  84 A,  84 B are filled with hydraulic fluid through the inlet ports defined by the notches  94 A,  96 B and  94 A,  96 B. The fluid in the pump chambers is transported by the rotor  78  to the discharge sectors of the crescent-shaped cavities  84 A,  84 B and expelled through the discharge ports  98 A,  98 B of the thrust plate  42  and the recesses  100 A,  100 B of the pressure plate  44  into the discharge chamber  70 . The fluid pressure prevailing in the discharge chamber  70  is a high discharge pressure of the vane pump  10 . The discharge chamber  70  is connected to the aforementioned steering assist fluid motor or similar device through a flow control valve, not shown, in the bore  24  of the housing  12 . The flow control valve maintains a substantially rate of fluid flow from the vane pump  10  by recirculating a fraction of the fluid expelled from the pump chambers back through the annular chamber  36  around the rotating group through the internal passage  26  and the pump housing  12 .  
         [0033]    The fluid in the discharge chamber induces a net pressure force on the pressure plate  44  represented by a schematic force vector F 1 , FIG. 1, which reacts evenly across the exposed area of the pressure plate. The net pressure force represented by the schematic vector F 1  thrusts the rotating group toward the flat bottom  18  of the counterbore  20  for enhanced suppression of fluid leakage from between the planar side of the thrust plate and the end  58  of the cam ring and between the planar side of the pressure plate and the end  62  of the cam ring.  
         [0034]    At the same time, fluid at the discharge pressure of the pump is conducted or ported to the annular first balance chamber  116  through the passages  102  and  120  in the pressure plate and from the first balance chamber into the second balance chamber  118  through the vane slots  86  under of the flat vanes  88 . The fluid pressure under the flat vanes thrusts the outboard lateral edges  90  of the vanes against the oval-shaped wall  52  of the cam ring to suppress fluid leakage from the pump chambers  93  between the vanes and the oval-shaped wall.  
         [0035]    The fluid pressure in the first balance chamber  116  of the rotor  78  induces a net pressure force on the pressure plate represented by a schematic force vector F 2  opposite to the net pressure force represented by the schematic vector F 1 . The fraction of the net pressure force represented by the schematic vector F 1 , reacting on the pressure plate within the silhouette of the oval-shaped rotor chamber  66  is effectively offset or balanced by the net pressure force represented by the schematic vector F 2  because the reaction portion of the planar end wall  82 A of the rotor constitutes a substantial fraction of the area of the silhouette of the rotor chamber  66 . Accordingly, the flexure of the pressure plate  44  into the rotor chamber characteristic of the prior van pumps referred to above is substantially reduced so that the clearance dimension D 1  is smaller than corresponding clearance dimensions in such prior van pumps for improved volumetric efficiency.  
         [0036]    The fluid pressure in the first balance chamber  116  also reacts against the reaction portion of the planar end wall  82 A of the rotor and thrusts the rotor toward thrust plate. Concurrently, however, the same fluid pressure in the annular second balance chamber  118  reacts against the reaction portion of the opposite end wall  82 B of the rotor and thrusts the rotor toward the pressure plate. Because the reaction portions of the planar first and second end walls of the rotor are equal, the net pressure force on the rotor attributable to fluid in the annular first balance chamber equal s the net pressure force on the rotor attributable to fluid in the annular second balance chamber. Accordingly, the rotor is suspended longitudinally in static equilibrium between the planar sides of the pressure plate and the thrust plate with the substantially equal clearance dimensions D 1 , D 2  minimizing both sliding friction and fluid leakage between the rotor and the flat vanes thereon and the planar sides of the thrust plate and the pressure plate.  
         [0037]    The fluid in the discharge sectors exerts a hydraulic pressure force F 3  on the second thrust face  57  of thrust plate  42  which urges the thrust plate  42  axially away from the rotor  78  and cam ring  46  toward the end wall  18  of the housing  12 .  
         [0038]    The balance chambers  124 A,  124 B defined on the opposite first thrust face  56  of the thrust plate  42  enclose a sealed space in fluid communication with fluid at the discharge pressure through the ports  98 A,  98 B in the thrust plate  42  and through flow passages  136 A,  136 B formed in the housing  12  (FIGS.  1  and  8 ) which extend from the discharge chamber  70  through the end wall  18  for porting the high pressure hydraulic fluid to the sealed balance chambers  124 A,  124 B to exert the counteracting balance force vector F 4  in opposition to the opposing force vector F 3 . As mentioned, the size and shape of the balance chambers  124 A,  124 B and thus the shape of the grooves  126  and gasket  122  are engineered to provide a counteracting force F 4  to the opposing force F 3  so as to balance the thrust plate  42 , placing it in a state of hydraulic equilibrium in the axial direction within the cavity  20  of the housing  12 . One such shape is illustrated in FIG. 7, although it will be appreciated that the invention is not limited to this particular gasket configuration. The gasket  122  of the illustrated embodiment includes an outer perimeter portion  130 A,  130 B which generally traces but is spaced inwardly of the outer perimeter of the thrust plate  42  so as to isolate the chambers  124 A,  124 B from the thrust plate notches  94 A,  94 B and the dowel pins  48 . The gasket  122  includes an inner perimeter seal portion  132 A,  132 B which encircles the drive shaft bore  54  of the thrust plate  42 . The outer and inner seal portions are joined by a transverse bridge portion  134  to partition the area between the outer and inner perimeter portions into a pair of adjacent balance chamber portions denoted as  124 A,  124 B. Each balance chamber portion  124 A,  124 B has associated therewith the aforementioned fluid passages  136 A,  136 B fluid inlet port of the housing  12  (FIGS. 1 and 8) for communicating the high pressure hydraulic fluid into the chamber portions  124 A,  124 B. The gasket  122  keeps the high pressure fluid from escaping the balance chambers  124 A,  124 B into the chamber  36  or drive shaft bore  14 . Accordingly, the thrust plate  42  is supported axially in static equilibrium, minimizing or altogether eliminating axial distortion of the thrust plate  42  and fluid leakage between the flat vanes  88  and the second thrust face  57  of the thrust plate  42 , thereby increasing the volumetric efficiency of the vane pump  10 .  
         [0039]    The hydraulically balanced thrust plate  42  has been surprisingly shown to perform best when used in combination with the hydraulically balanced rotor  78 . The balanced thrust plate  42  has shown to improve volumetric efficiency of a vane pump by about 20% when used with a conventional non-hydraulically balanced rotor. A gain in volumetric efficiency of about 58% was shown when the hydraulically balanced thrust plate  42  was used together with the hydraulically balanced rotor  78 .  
         [0040]    The disclosed embodiments are representative of presently preferred forms of the invention, but are intended to be illustrative rather than definitive thereof. The invention is defined in the claims.