Patent Publication Number: US-6655936-B2

Title: Rotary vane pump with under-vane pump

Description:
TECHNICAL FIELD 
     The present invention relates to hydraulic vane type pumps and, more particularly, to such pumps having under-vane pressure to assist vane extension. 
     DESCRIPTION OF THE PRIOR ART 
     Prior art power steering pumps have provided an exclusive flow path for the under-vane fluid in a vane type pump to improve cold priming. This exclusive flow path is from under the vanes in the pressure or discharge quadrant through a groove in the thrust plate to under the vanes in the inlet quadrant. The pressure plate has a groove in the inlet quadrant, which communicates the under-vane fluid in the inlet quadrant with the discharge flow of the pump. While this structure provides fast priming, it also induces high under-vane pressure when the system operating temperature is at the normal level, and the pump is operating within the normal speed range. This high under-vane pressure can induce early wear and reduces the overall life of the pump. 
     Further, in other prior art pumps, at particular operating conditions, the centrifugal force acting on the vanes is inadequate to insure the vane remains in contact with the internal contour of the pump ring. At all pump speeds, the pump outlet pressure in the high pressure area of the ring discharge is equal to the under-vane pressure which results in a floating vane condition at the ring contour. If a vane pump is operating at a relatively low speed, an external pressure can equalize or overcome the centrifugal force on the vanes and resulting under-vane pressure. This situation results in a reduced pumping efficiency along with noises from the floating vane condition. 
     Another prior art assembly disclosed in U.S. Pat. No. 4,386,891 to Riefel, et al discloses a rotary hydraulic vane pump with under-vane passage for assisting in priming. This assembly includes grooves in the thrust and pressure plates with the groove in the pressure plate being in communication with the discharge flow of the pump. The grooves incorporate restrictions to the under-vane fluid flow between the discharge and inlet positions of the vanes with the restriction in the thrust plate permitting more fluid flow than the restriction in the pressure plate to insure that most of the fluid will pass through the rotor under the vanes in the inlet to assist in vane extension. The grooves on the pressure plate are also isolated from one another in the direction of the low-to-high pressure transition. 
     SUMMARY OF THE INVENTION 
     The present invention provides a vane pump comprising a housing. The vane pump further comprises a rotating group including a ported thrust plate seated on the housing. The ported thrust plate includes a pair of thrust plate passageways thereon. The rotating group further includes a ported pressure plate having a pair of pressure plate passageways thereon. The rotating group also includes a cam ring disposed between the pressure plate and the thrust plate. The vane pump further comprises an oval-shaped wall on the cam ring cooperating with the pressure plate and the thrust plate to define a rotor chamber in the rotating group. 
     The vane pump further comprises a rotor supported in the rotor chamber for rotation about a longitudinal axis of the vane pump. The vane pump further includes a plurality of radial vane slots in the rotor. Each of the vane slots defines an under-vane cavity. The thrust plate passageways and the pressure plate passageways are axially aligned with the under-vane cavities. The vane pump further comprises a plurality of flat vanes slideable in respective ones of said vane slots. Each of the thrust plate passageways includes two generally kidney-shaped passages joined by a restricted passage. Each of the thrust plate passageways is isolated from fluid communication with the next adjacent thrust plate passage. 
     It is, therefore, an object of the present invention to provide an under-vane pump separating the low-to-high pressure regions of the vane pump. This is accomplished by closing the low-to-high pressure transition in the thrust plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1 is a cross-sectional elevational view of a power steering pump; 
     FIG. 2 is a sectional view taken along lines  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken along lines  3 — 3  of FIG. 1; and 
     FIG. 4 is a sectional view taken along lines  4 — 4  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     A power steering pump is generally indicated at  10  in FIG.  1 . The pump  10  includes a housing  12  and a cover  14 . The housing  12  has a substantially cylindrical inner space  16  in which is disposed a rotating group generally indicated at  15 . The rotating group comprises a thrust plate or first plate  18 , a cam ring  20 , and a pressure plate or second plate  22 . The rotating group  15  is stationary relative to the housing  10 . The components of the rotating group are shown in more detail in FIGS. 2 through 4. 
     A hold-down spring  24  and end cap  26  are also provided. The end cap  26  is restrained in the housing by a locking ring  28 . The thrust plate  18 , cam ring  20 , and pressure plate  22  are maintained in axial and angular alignment by a pair of dowel pins  30  which extend from openings (not shown) in the housing  12  to the end cap  26 . That is, the dowel pins  30  prevent relative rotation between the thrust plate  18 , cam ring  20  and pressure plate  22  about a longitudinal axis of the vane pump  10 . A rotor  32  is rotatably disposed within an oval-shaped opening in a cam ring  20 . The oval-shaped opening defines a rotor chamber in the rotating group  15 . More specifically, the rotor chamber is defined by the oval-shaped opening in the cam ring  20 , the thrust plate  18  and pressure plate  22 . The thrust plate  18  and the pressure plate  22  close the axial ends of the oval shaped opening. 
     The rotor  32  has a plurality of vanes slots  34  therein. The vane slots  34  extend radially on the rotor. Each vane slot  34  has vane member  36  slideably disposed therein. Each vane member  36  is adapted to move radially outwardly of the slot  34  to engage the inner surface  37  of the cam ring  20  such that a fluid chamber is formed between adjacent of the vane members  36 . In this manner, the vane members or vanes  36  form the fluid chambers which expand in each of a pair a diagonally opposite inlet sectors and collapse in each of a pair of diagonally opposite discharge sectors in conventional fashion. 
     As best seen in FIG. 3, each vane slot  34  extends radially inwardly sufficient for providing a space  38  for fluid under the vane. The thrust plate  18  and pressure plate  22  cooperate with the rotor and cam ring  20  to define the axial extent of the fluid chambers formed between adjacent vane members  36 . 
     The thrust plate  18  has a pair of diametrically opposed inlet ports  39  and a pair of diametrically opposed discharge ports  40 . The discharge ports  40  are recessed ports only and preferably do not extend entirely through the width of the thrust plate  18 . The inlet ports  39  are angularly offset from the discharge ports  40 . 
     Similarly, the pressure plate  22  includes a pair of diametrically opposed inlet ports  42  and a pair of diametrically opposed discharge ports  44 . The inlet ports  42  are angularly offset from the discharge ports  44 . The inlet ports  42  on the pressure plate  22  are axially aligned with the inlet ports  39  on the thrust plate  18 . Similarly, the discharge ports  44  on the pressure plate  22  are axially aligned with the discharge ports  40  on the thrust plate  18 . The discharge ports  40  and  44  are also in fluid communication through a pair of apertures  46  in the cam ring  20  (FIG.  3 ). As shown, the apertures  46  comprise elongated slots extending through the cam ring  20 . It will be appreciated that the apertures  46  may take any configuration which allows for fluid communication between the discharge ports  40 ,  44 . 
     The hold-down spring  24  creates a sufficient force to maintain the pressure plate  22 , cam ring  20  and thrust plate  18  in the abutting relationship shown in FIG.  1 . The dowel pins  30  prevent relative rotation between these members. The rotor  32  has a central spline portion  48  which is drivingly connected to a drive shaft  50  adapted to be driven by a source of motive power such as an internal combustion engine. 
     The drive shaft  50  rotates about a longitudinal axis. As the drive shaft  50  rotates, the rotor  32  rotates, causing the chambers between adjacent vanes  36  to expand and contract in a well-known manner. Fluid will enter between adjacent vanes  36  when aligned with inlet ports  39  and  42  and will be discharged when adjacent vanes  36  are aligned with discharged ports  40  and  44 . The discharge ports  40  and  44  are open to the space between pressure plate  22  and end cap  26 . The fluid communication between the ports  40  and  44  to the open space between the pressure plate  22  and end cap  26  is through a pair of schematically represented passages  57  in the pressure plate. 
     Fluid in the space is discharged through a passage  52  to a conventional flow control and pressure regulator valve  54  which permits a predetermined about of fluid to be delivered from the pump to a discharge port, not shown, while the remainder of the fluid returns to the inlet ports  38  and  42  through a passage  56 . The operation of the flow control valve  54  is well known. 
     As the vanes  34  pass adjacent the inlet ports  39  and  42 , they extend to the greatest radial degree. In this inlet area, the fluid is at its relatively lowest pressure. As the rotor  32  rotates in the direction of the arrow “A” on FIG. 3 from the inlet area, the vanes  36  are forced radially inwardly within the slot  34 . This effectively reduces the area of the fluid chamber defined between adjacent vanes  36 , causing the fluid within the chamber to reach a relatively higher pressure. 
     The fluid disposed in the vane slots  34  on the underside of the vanes  36  in the space  38  also undergoes a pumping action. The fluid under the vanes  36  in the discharge area or quadrant, that is, the vanes passing adjacent ports  40  and  44 , is forced from under the vanes because the vanes  36  are receding into the slots  34 . Simultaneously, the vanes  36  in the inlet area or quadrant, that is, the vanes  36  passing adjacent inlet ports  39  and  42 , are extending thereby providing a space which must be filled with fluid. 
     To communicate the fluid from under the vanes  36  in the discharge quadrant to under the vanes  36  in the inlet quadrant, fluid passageways in both the thrust plate  18  and pressure plate  22  are provided. As best seen in FIG. 4, there is a pair of passageways in the first or thrust plate  18 . Each passageway in the thrust plate  18  comprises two generally kidney-shaped passageways  58 ,  59 . The first kidney-shaped passageway  58  is aligned in the radial direction with the discharge port  40 . The second kidney-shaped passageway  59  is aligned in the radial direction with the inlet passage  39 . The passageways  58  and  59  are axially aligned with the radially inner end of the slots  34 . The generally kidney-shaped passageways and  58  and  59  do not extend through the width of the thrust plate  18 . Rather, each of the passageways comprise a groove in the thrust plate  18 . 
     Adjacent pairs of associated passageways  58 ,  59  are connected at one adjacent end by a restriction passage or metering groove  60 . The restriction passage or metering grooves  60  are used for pressure control in the discharge or high-pressure under-vane area and allow excess fluid to flow to the inlet or low-pressure area. The passageways  58 ,  59  are further blocked from communicating with one another at their opposite adjacent end. This blockage creates an under-vane pump within the pump  10  and can best be described as separating the low-to-high pressure transition of the thrust plate  18 . By closing the low-to-high pressure transition in the plates, a controlled volume of fluid is maintained in the high-pressure under-vane region. this trapped volume of fluid is used to increase the pressure at the under-vane area because the fluid is not allowed to flow back to the low-pressure area. As stated above, because the fluid being pumped in non-compressible, as the vanes  36  sweep through the high-pressure region, the volume is decreased in the under-vane area. In previous designs, once the vanes reached the high-pressure region, the discharge pressure was greater than the intake pressure, which caused the vane to slide back in the slots and leave the inner surface of the pressure plate  22 . By blocking the area of the thrust plate set forth above, the high-pressure fluid is not allowed to pass to the low-pressure area by overcoming the vane force. 
     The pressure plate  22  has a plurality of kidney-shaped passages  66 ,  68  axially aligned with the passages  59 ,  58  of the thrust plate  18 . Each passage  66 ,  68  is isolated from the adjacent such passage such that they do not communicate with one another. The passages  66 ,  68  are preferably formed as depressions or grooves in the face of the pressure plate  22  and thus do not extend fully through the pressure plate. The passages  66 , may include an opening or port  69  communicating with the space  16  and axially aligned with the passages  58  of the thrust plate  18 . 
     It is also noted that the thrust plate blockage preferably coincides with the blockage in the pressure plate  22 , as set forth above. The thrust plate blockage or isolation, as set forth above, terminates at the beginning of the metering groove or restriction passage  62  prior to discharge. 
     One style vane pump  10  has been discussed above and shown in the drawings. It will be appreciated that within the scope of the present invention, any configuration for the vane pump may be used. 
     The invention has been described in an illustrative manner as to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood that the invention may be practiced otherwise as is specifically claimed.