Patent Publication Number: US-2012045355-A1

Title: Variable displacement oil pump

Description:
FIELD OF THE INVENTION 
     The invention relates to a variable displacement oil pump, and more particularly to a variable displacement pivoting slide oil pump having a vane reservoir in continuous fluid communication with a discharge pressure such that the vane is held in abutment with a slide surface. 
     BACKGROUND OF THE INVENTION 
     An oil pump of vane type generally comprises a cam ring having a substantially elliptical cam surface around its inner periphery, a rotor disposed for rotation inside the cam ring, a plurality of vanes fitted in the rotor for reciprocating motion in their associated radially extending slits, and a pair of pressure plate and side plate which act to hold the rotor and the cam therebetween from the opposite sides. As the rotor rotates, the volume of a pump chamber defined between a pair of adjacent vanes increases and decreases, thus serving the suction and discharge of oil. In order to achieve a reliable sliding contact of the vane tip with the cam, a groove is formed in the pressure plate to introduce oil which is discharged from the pump chamber so as to act against the back side of the vane. 
     Representative of the art is U.S. Pat. No. 4,342,545 which discloses A variable displacement vane type pump having a pivotally mounted ring member controllable to vary the eccentricity between the rotor and the ring thus controlling the pump displacement. The ring is positioned on the pivot such that the center thereof is always located in one quadrant relative to axes through the pivot point and the center of the pump rotor to continually maintain the net ring reaction force, due to internal pressure, directed to one side of the pivot connection in opposition to the displacement control pressure, which is impressed on a portion of the outer surface of the ring, whereby control stability throughout the displacement range is improved. 
     What is needed is a variable displacement pivoting slide oil pump having a vane reservoir in continuous fluid communication with a discharge pressure such that the vane is held in abutment with a slide surface. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide a variable displacement pivoting slide oil pump having a vane reservoir in continuous fluid communication with a discharge pressure such that the vane is held in abutment with a slide surface. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises an oil pump comprising a pump body, which oil pump is driven by a driven input shaft, a slide having an internal surface, the slide disposed in the pump body, the slide pivotally moveable by pressurization of a first chamber and second chamber, a rotor disposed for rotation within the slide, a plurality of vanes, each moveably disposed in a radial slot in the rotor, each radial slot in fluid communication with a vane fluid reservoir, wherein first and second pump body portions are disposed on the opposite sides of the slide and the rotor to hold each therebetween thus causing the volume defined by a pair of adjacent vanes to change to perform an oil suction and discharge, wherein the pump body portions comprise a suction region where a pump chamber undergoes a suction stroke, wherein the pump body portions comprise a discharge region where each pump chamber undergoes a discharge stroke and in which a fluid conduit is connected, the pump body portions each comprising a groove, each groove continuously communicating with each vane fluid reservoir, and the fluid conduit in the discharge region communicating with the first groove whereby a discharge pressure is continuously communicated to each vane fluid reservoir to urge each vane into continuous abutment against the slide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is a top plan view of the cam profile. 
         FIG. 2  is a top plan view of the oil pump. 
         FIG. 3  is a top perspective cross-section of the oil pump slide. 
         FIG. 4  is a top perspective cross-section view of the oil pump. 
         FIG. 5  is a top perspective plan view of the oil pump. 
         FIG. 6  is a top perspective plan view of the oil pump. 
         FIG. 7  is a bottom perspective cross-section view of the oil pump. 
         FIG. 8  is an exploded view of the pump. 
         FIG. 9  is a perspective detail of the vane reservoir and slot. 
         FIG. 10  is a plan view of the vane reservoir and slot. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An inventive variable displacement oil pump is disclosed. The advantageous design provides a number of improvements over the prior art. 
     The prior art comprises vane rings that are used to control the position of the sliding vanes, see Fig. ______. The instant oil pump deletes vanes rings. Elimination of vane rings provides benefits including improved volumetric efficiency. This is accomplished by using outlet pressure to maintain slide contact and thereby reduce vane tip clearance leakage. This also allows the rotor counter bores to be eliminated thereby reducing outlet port leakage to the centre of the pump. A pressure ring that is used to feed oil to the rotor root diameter for the vanes will have some oil leakage to the centre of the slide, however, the ring can be increased in diameter reducing the centre leakage. Further, use of a key step in the rotor vane slot reduces the leakage from the ring to the centre even further. The centre ring also feeds oil leakage to the inlet port past the vane slot clearance, rotor endface and vane endface. A balance in the diameter of the feed groove is necessary therefore the ring may have a cam type shape whereas the radius changes through the full circumference of the design. 
     The new design also improves mechanical efficiency by removal of the vane ring which allows the pump to be reduced in diameter for a given drive shaft diameter. The resulting reduction of the torque arm of the outlet pressure reduces the required drive torque, resulting in a more efficient pump. 
     Volumetric efficiency improvements also result in a smaller displacement pump to meet a given operating requirement, further reducing the torque. Elimination of vane rings also eliminates parasitic losses caused by friction through vane ring contact. 
     Further, eliminating the prior art vane rings eliminates the need for the slide internal form to be round. Using a cam profile for the inlet porting increases the area of the inlet and allows more time for the pump to fill. With more time to fill the required inlet vacuum level (inlet head) is decreased thereby moving the cavitation threshold to a higher rotor speed. This also reduces the sensitivity of the pump to fluid aeration levels. 
       FIG. 1  is a top plan view of the cam profile. The inventive oil pump comprises a pump body  100 . Slide  200  is moveably disposed within a pump body cavity. 
     Pump rotor  300  rotates within slide  200  about a pivot  203 . Drive shaft  800  drives rotor  300 . 
     Vanes  301  are moveably disposed within rotor  300 . Each vane  301  may radially extend and retract within a vane slot  302 . Each vane has a sliding engagement with an inner surface of slide  200 . 
     Seals  201  and  202  engage an inner surface of pump body  100 , thereby preventing a flow of oil between a first chamber  101  and a second chamber  102 . In an alternate embodiment seal  201  can be eliminated to provide only one chamber. 
     Coil spring  400  urges slide  200  into a first position. Coil spring  400  is engaged between slide portion  205  and body  100 . 
     First chamber  101  and second chamber  102  each receive oil from the pump discharge. The pressurized oil flows through a fluid conduit  101   a  and fluid conduit  102   a  respectively to each chamber. The pressure in each chamber will counter the coil spring force, thereby causing slide  300  to pivot in a direction D 1  about pivot  203  to a position. A release of pressure in either or both chambers will cause slide  200  to pivot in the opposite direction in response to the coil spring force. 
     The cam profile represents the path the outer edge of each vane during a rotation of the rotor. An increase in cam profile radius corresponds with an increase in volume between adjacent vanes. When corresponding with the inlet porting, the flow area is increased, reducing the pressure drop of the fluid flow into the pump. 
     It can also be seen that the cam profile, surface  204  see  FIG. 4 , is not round or circular when viewed in plan. This is an additional benefit of the use of the pressurized vanes and allows further design flexibility directed to reducing the net fluid inlet head and oil discharge rates. The pressurized vanes readily follow the contour of surface  204 . 
       FIG. 2  is a top plan view of the oil pump. Pump suction  103  conducts oil to the rotor and slide. Pressurized oil is discharged from the pump via discharge  104 . 
     In operation each vane  301  moves radially outward in response to the centripetal force caused by rotation of rotor  300 . Each vane  301  bears upon an inner surface  204  of slide  200 , thereby creating a volume for receiving oil between each adjacent vane. 
     Each vane slot  302  comprises a fluid reservoir  303  and slot  305 . Fluid reservoir  303  has a volume in addition to the vane slot  302 . Each fluid reservoir  303  extends from one side of the rotor to the other. 
     Each slot  305  allows the pressure feed groove to be located further from the centre of the pump, see  FIG. 9  and  FIG. 10 . Each slot  305  is wider than the thickness of each vane  301 . Each fluid reservoir  303  does not need to be round and can be at a larger radius at the outlet port region, and a smaller radius at inlet port region. Slot  305  reduces leakage from the groove to the inlet port of the centre of the pump to the environment. 
     In the prior art, vane rings are used to maintain vane contact with slide surface  204  to ensure the pump is primed during start up and to resist the outlet pressure which would otherwise cause the vanes to be pushed toward the center of the rotor. The inventive pump uses discharge pressure to balance the reaction force and to maintain constant contact between each vane and the slide surface  204 . This is achieved by communicating the discharge pressure directly to each of the vane fluid reservoirs. This also allows slide  200  to optionally have a non-circular shape. 
       FIG. 3  is a top perspective cross-section of the oil pump slide. Each vane  301  engages surface  204 . Each fluid reservoir  303  extends across the rotor from side to side. 
       FIG. 4  is a top perspective cross-section view of the oil pump. Body  100  and rotor  300  are shown installed between body  500  and body  600 . 
     Body  600  comprises a groove  601 . Groove  601  is substantially circular. Groove  601  is located on body  600  such that groove  601  continuously communicates with each vane reservoir  303  throughout the entire rotary path of the rotor  300  and regardless of the pivot position of the slide. In an alternate embodiment, groove  601  may be omitted from the oil pump with out impairing operation. 
     Body  500  comprises a groove  501 . Groove  501  is substantially circular. Groove  501  is located on body  500  such that groove  501  continuously communicates with each vane reservoir  303  throughout the entire rotary path of the rotor  300  and regardless of the pivot position of the slide. 
     In an alternate embodiment groove  501  may be placed instead on the rotor, and extending between each vane fluid reservoir  303 . 
       FIG. 5  is a top perspective plan view of the oil pump. Rotor  300  does not move laterally as slide  200  pivots about  203 . The axis of rotation of rotor  300  does not translate with respect to pump body  100 ,  500 ,  600 . 
     The volume between each set of adjacent vanes changes in a continuous manner as the rotor rotates. Pivoting movement of slide  200  causes the volume at a given rotational position of the rotor for a given set of adjacent vanes to vary as a function of the angular position of the slide. 
       FIG. 6  is a top perspective plan view of the oil pump. The position of slide  200  is shown in the idle position, or “fail safe” position. “Fail safe” refers to the position the slide takes in the event of oil pressure loss to the chamber  101  or chamber  102 . 
     In this position the maximum oil flow is realized. As the pump discharge pressure increases, each chamber  101  and  102  is pressurized in turn, thereby causing the slide to pivot. As the slide pivots the oil flow rate is decreased, thereby reducing the power required to operate the pump, and hence the engine. While the pressure in each chamber  101 ,  102  is variable depending on an operating condition, the pressure in fluid conduit  501  and  601  is limited to the pump discharge pressure. 
     Each chamber  101  and chamber  102  can receive pressure from either the outlet port, the engine block or can be vented to ambient pressure. A valve can be added to switch between chamber  101  or  201  to allow pressure from either chamber to be vented to a lower pressure, thereby allowing either chamber to act alone against the spring force. 
       FIG. 7  is a bottom perspective cross-section view of the oil pump. Fluid conduit  502  communicates the pump discharge  104  pressure with groove  501 . Oil flows from groove  501  and  601  to each fluid reservoir  303  when each vane moves radially outward. The oil discharges from each fluid reservoir  303  back to groove  501  and  601  when each vane moves radially inward. 
       FIG. 8  is an exploded view of the pump. 
       FIG. 9  is a perspective detail of the vane reservoir and slot. Each slot  305  extends across the width of each vane  301 . 
       FIG. 10  is a plan view of the vane reservoir and slot. 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 and method without departing from the spirit and scope of the invention described herein.