Abstract:
A vane pump comprising a case, a rotor disposed in the case, the rotor having a bore, a plurality of vanes radially moveable with respect to the rotor extend from the rotor, a drive shaft engaged with the bore, a second shaft fixedly connected to the case and extending from the case to slidingly engage the bore, a land extending from each end of the rotor, each land cooperating with the case to seal a fluid flow, and each land further axially controlling a rotor position within the case by a sliding engagement, and the drive shaft retainable in a predetermined position with respect to the case.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a vane pump, and more particularly, to a vane pump having a rotor having a position that is axially controlled between case cavity walls and a shaft engaged with the rotor. 
       BACKGROUND OF THE INVENTION 
       [0002]    Pumps are staple engineering components used in a variety of applications to transfer fluid. They are available in a wide range of sizes and capacities to suit particular applications. One typical application is that of supplying lubricating oil in an automotive engine. Vane pumps are used widely in engine oil and transmission oil pumping applications. Vane pumps comprise vanes slidably engaged with a rotor. The vanes move radially in the rotor while also sliding along the inner surface of an eccentric cavity in a pump casing. 
         [0003]    In engine oil applications the reliable operation of the pump is paramount to avoid catastrophic failure of the engine. On the other hand a reduction in both the cost, weight and energy requirements of the pump is demanded to meet automotive manufacturer&#39;s objectives. 
         [0004]    Conventionally, pumps have a rotor supported within a housing on a pair of bearings. The bearings are located on opposite walls of the housing and the rotor has an integral shaft supported in those bearings. The shaft is usually press fit into the rotor which can cause significant stress to be imposed on the rotor. This arrangement may require an exotic material to withstand the stresses caused by the press fit while ensuring torque transmission at cold temperatures. It also requires careful alignment of the bearings that are located in independent housings of the pump to permit the shaft to be rotated freely within the bearings. Any misalignment in the bearings can cause the rotor to be tilted within the housing, causing premature wear and/or increased or decreased clearance with a consequent loss of efficiency or mechanical drag. Similarly, misalignment of the bearings imposes side loads upon the shaft which inhibits rotation and increases the torque required to drive the pump and thereby an increase in fuel consumption when used in an automotive environment. As such the conventional pumps do not readily meet the increasingly stringent requirements for enhanced efficiency and lower costs. 
         [0005]    Representative of the art is U.S. Pat. No. 5,964,584 discloses a vane pump for liquids is comprised of a slotted rotor supported in a stator, wherein radially displaceable vanes are slidingly disposed, which can be pressed slidingly supported while acted upon by centrifugal force, spring tension or otherwise by compressive force against a stator inside wall, in said process delivery cells are formed which expand or narrow in a crescent-like fashion and the entry of the liquid takes place through a hollow concentric stator and the filling of the vane cells from the inside to the outside. The rotor is shaftless and of tubular construction, both sides are extended beyond the operating area determined by the vanes and the rotor is supported with the extensions in the outer stator, while the rotor possesses continuous vane slots from the internal to the external diameter. In the area of the rotor extensions, the frame of the stator possesses on its surface hydraulic effective surfaces acted upon by the operating pressure and/or pressure-relieved directed against the rotor for the at least partial compensation or avoidance of radially occurring forces. 
         [0006]    What is needed is a vane pump having a rotor having a position that is axially controlled between case cavity walls and a shaft engaged with the rotor. The present invention meets this need. 
       SUMMARY OF THE INVENTION 
       [0007]    The primary aspect of the invention is to provide a vane pump having a rotor having a position that is axially controlled between case cavity walls and a shaft engaged with the rotor. 
         [0008]    Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
         [0009]    The invention comprises a vane pump comprising a case, a rotor disposed in the case, the rotor having a bore, a plurality of vanes radially moveable with respect to the rotor extend from the rotor, a drive shaft engaged with the bore, a second shaft fixedly connected to the case and extending from the case to slidingly engage the bore, a land extending from each end of the rotor, each land cooperating with the case to seal a fluid flow, and each land further axially controlling a rotor position within the case by a sliding engagement, and the drive shaft retainable in a predetermined position with respect to the case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
           [0011]      FIG. 1  is a cross-sectional view of the vane pump installed on an internal combustion engine. 
           [0012]      FIG. 2  is a cross-sectional detail of the vane pump shown in  FIG. 1 . 
           [0013]      FIG. 3  is a perspective view of a rotor used in the vane pump. 
           [0014]      FIG. 4  is a cross-sectional detail of the vane pump shown in  FIG. 1 . 
           [0015]      FIG. 5  is a perspective view of the shaft. 
           [0016]      FIG. 6  is a plan view of the connection between the shaft and the rotor. 
           [0017]      FIG. 7  is a detail of  FIG. 6 . 
           [0018]      FIG. 8  is an exploded view of the pump. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]      FIG. 1  is a cross-sectional view of the vane pump installed on an internal combustion engine. Pump  10  is mounted to an engine block B. Pump  10  delivers oil from an outlet  12  to internal oil galleries G. Oil is supplied from a sump S to the pump suction at inlet  14 . 
         [0020]    Pump  10  is driven by drive shaft  90 . Drive shaft  90  is connected to a camshaft (not shown) or similar engine power take-off. The details of the engine form no part of the invention and the supply of oil to the pump and the delivery of oil from the pump  10  is per engine requirements. 
         [0021]    A hydraulic seal known in the art is disposed between shaft  90  and case portion surface  22 . 
         [0022]      FIG. 2  is a cross-sectional detail of the vane pump shown in  FIG. 1 . Referring to  FIG. 1  and  FIG. 2 , shaft  46  is press fit into case  30 . To provide the necessary bearing surface, shaft  46  extends into rotor  60  approximately 50% to 90% of the distance between the inner walls  34 ,  38 . Walls  34 ,  38  are substantially planar and are parallel to each other, thereby defining opposite sides of cavity  18 . In the preferred embodiment the shaft extends in excess of approximately 75% of the distance between the walls  34 ,  38 . 
         [0023]    Rotor  60  is located within the cavity  18 . Cavity  18  is formed between case portions  20  and  30 . 
         [0024]    Rotor  60  is typically a powdered metal component as shown in  FIG. 3 . Rotor  60  may also be machined from billet or cast with equal performance. Rotor  60  is generally cylindrical with a series of radial slots  62 , see  FIG. 3 . Each slot  62  cooperatively and slidingly receives a vane  64 . Vanes  64  slidingly engage with the peripheral wall  36  of cavity  18 . Rotor  60  is formed with a radially outer peripheral land  74  and a radially inner peripheral land  76  extending around the bore  70  at both ends. 
         [0025]    Rotor  60  further comprises a bore  70  which receives a bushing  78 . Bushing  78  is press fit into bore  70 . Bushing  78  provides a bearing surface for rotation of the rotor  60  on the shaft  46 . Bushing  78  is typically a metal backed nylon bushing that is a close sliding fit on the shaft  46 . In an alternate embodiment bushing  78  may be omitted. In the alternate embodiment wherein bushing  78  is omitted, shaft  46  has a sliding fit within bore  70 , thereby allowing rotor  60  to spin on shaft  46 . Some minor lateral movement of rotor  60  with respect to shaft  46  can occur without adversely affecting operation of the pump. 
         [0026]    An end of bore  70  is formed in the shape of a hexagonal socket  86 . Socket  86  comprises a close fit on a drive shaft  90 . Shaft  90  projects through an aperture  21  in case  20 . Close contact along each of the flanks of the hexagonal drive shaft is preferably obtained. This enhances the torque transmitting capabilities of the connection to the drive shaft, thereby permitting a shorter socket for a desired torque. 
         [0027]    To assemble the pump  10 , shaft  46  is pressed into bore  50  in case  30 . Bushing  78  is press fit into the rotor  60 . Rotor  60  and bushing  78  are then slipped onto the shaft  46 . End  47  of shaft  46  is adjacent to but does not contact shoulder  87  at the intersection of the socket  86  and bore  70 . This feature locates rotor  60  radially on shaft  46 . Case  20  is then secured to case  30  using fasteners  40 . Drive shaft  90  is inserted into the aperture  21  and into socket  86 . 
         [0028]    In operation, rotation of rotor  60  by drive shaft  90  causes fluid to be displaced from the inlet  14  to the outlet  12  by movement of vanes  64 . The peripheral lands  74 ,  76  on the opposed end faces the rotor  60  provide dynamic seals between the ends of rotor  60  and cavity  18 , thereby inhibiting leakage past the end walls  34 ,  38 , which improves hydraulic efficiency. Lands  74 ,  76  eliminate the need for separate secondary seals. Each land  74 ,  76  axially locate and control the rotor location within the cavity  18  during operation. The “axial” direction is parallel to the axis of rotation of the rotor. It should be noted that shaft  90  only transmits torque to the rotor, and it does not serve as a means of locating and positioning rotor  60  within the cavity  18 . This function is performed by the lands  74 ,  76  and shaft  46 . It will be noted that a single bushing is utilized on the surface of the shaft  46  so that alignment of spaced bearings is not otherwise required. Moreover, the provision of the bushing  78  engaged with shaft  46  allows the rotor to “float” in the cavity  18  which allows the rotor to find a natural equilibrium during operation within the cavity. This in turn allows the clearance between the end walls  34 ,  38  defining the cavity  18  to be further reduced compared to the use of a pair of bearings at each end of a shaft, again, enhancing the hydraulic efficiency. Put another way, rotor  60  is similar to a “bearing” as it spins and floats between walls  34 ,  38 . 
         [0029]    Use of a hexagonal socket  86  in rotor  60  avoids the need for heat treating of the rotor  60  to prevent “round out” of the socket. The simple sliding fit of the rotor  60  on the shaft  46  also avoids the need for exotic materials otherwise necessary for the rotor to withstand the press fit of a conventional shaft arrangement. 
         [0030]    The arrangement of the pump described above eliminates the potential misalignment of a pair of bearings that may be conventionally used, which facilitates manufacture and assembly. Although the clearances are tighter, the instant arrangement easily accommodates a normal engine operating temperature range of approximately −40° C. to +130° C. whilst maintaining reduced tolerances. A reduction in driving torque in the range of approximately 5% to 10% can be achieved by the inventive pump as compared to conventional arrangements. 
         [0031]      FIG. 3  is a perspective view of a rotor used in the vane pump. Rotor  60  comprises socket  86  and radial slots  62 . Each radial slot  62  slidingly receives a vane  64 , see  FIG. 2 . Each vane  64  moves freely within each slot  62 , while the movement is constrained by the inner surfaces of case  20  and case  30 . Lands  74 ,  76  are disposed about a circumference of rotor  60 . 
         [0032]    In the preferred embodiment rotor  60  comprises a powdered metal or alloy compact. This allows the inventive design to take advantage of the “as pressed” geometry for the rotor. The green rotor compact is then sintered using known methods. Consequently, the rotor only requires minor surface finishing for final operating clearances. 
         [0033]      FIG. 4  is a cross-sectional detail of the vane pump shown in  FIG. 1 . Drive shaft engages aperture  21  with a loose fit having a relatively large clearance between the shaft  90  and the inner surface  22  of aperture  21 , for example, from approximately 1 to 3 mms. Drive shaft  90  is loosely secured in case  20  by means of a circumferential groove (surface feature)  94  in shaft  90 . Snap ring  98  is disposed a circumferential groove (surface feature)  100  within case  20 . Groove  100  is a sufficient depth to allow ring  98  to expand as shaft  90  is inserted. 
         [0034]    Once the shaft  90  is inserted though aperture  21 , ring  98  engages with groove  94 . The diameter “D” of ring  98  exceeds the radial gap “RG”. This inhibits further axial movement to the shaft  90  with respect to case  20 , thereby mechanically retaining the shaft in the case and avoiding loss of engagement of shaft  90  with socket  86  in rotor  60  during shipping. It will be noted that the shaft  90  is freely rotatable in case  20  with limited axial movement to accommodate connection to the engine and ensure no interference or contact with the shaft  46  once the pump is completely installed. 
         [0035]      FIG. 5  is a perspective view of the shaft. Bushing  78  is shown engaged with shaft  46 . Rotor  60  is omitted form this view. Shaft  46  is press fit into case  30 . 
         [0036]      FIG. 6  is a plan view of the connection between the shaft and the rotor. Hexagonal socket  86  is engaged with drive shaft  90 . Shaft  90  has a hexagonal form which comprises six flats  901 . Each of the six sides of socket  86  are split mid-point and angled with respect to the shaft  90  by angle “B”. Angle “B” between adjacent surfaces  861  and  862  is in the range of approximately +0° to approximately 15°. Therefore, hexagonal socket  86  comprises six pairs of adjacent surfaces  861  and  862 . Surfaces  861  disposed opposite each other across the socket are separated by dimension “A”. Dimension “A” also applies to opposing surfaces  862 . 
         [0037]    Clearance between the socket  86  and the shaft  90  is compensated for with the “B” angle to provide an area contact rather than a line contact between shaft  90  and socket  86 , see  FIG. 7 . The area contact increases the torque that can be transmitted before the material stress limit is reached. This is an improvement over the prior art which teaches a simple line contact between the corners of the shaft  90  and the hexagonal socket  86  which can be caused by manufacturing variances. 
         [0038]      FIG. 7  is a detail of  FIG. 6 . Surface  901  is in area contact with surface  862 . 
         [0039]      FIG. 8  is an exploded view of the pump. Rotor  60  and member  120  are disposed within case  30  and case  20 . Slide  120  comprises inner surface  121 . An outer edge of each vane  64  slidingly engages inner surface  121 . Inner surface  121  is cylindrical, but the shape of the surface can be slightly distorted to accommodate design geometries, for example to an oval or egg-shaped form. Pivot  18  engages detent  124 . Groove  122  receives seal member  240  for sealing a fluid pressure within chamber  23 . Spring  310  bears upon member  311  and surface  128 . Seal member  240  may comprise any material having a suitable compatibility with the pump fluid, for example, synthetic and/or natural rubbers. Oil pressure is used to adjust a position of slide  120  within case  20 . Oil pressure is applied to a surface  312  to impart a force against the force of spring  310 , thereby adjusting the pump output. Rings  641  and  642  control the position of each vane  64 . 
         [0040]    Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.