Patent Application
20120045355
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.
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.
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.
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.
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.
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 101a and fluid conduit 102a respectively to each chamber. The pressure in each chamber will counter the coil spring force, thereby causing slide 300 to pivot in a direction D1 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
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
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.
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.
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.
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.
