Abstract:
A variable displacement sliding vane pump comprising a pump body, inlet and outlet ports formed in said pump body, a drive shaft rotatably mounted in said pump body, a rotor driven by said drive shaft and co-axially aligned therewith, a plurality of radially extending vanes slidably disposed in said rotor, a pivot disposed in said pump body, a slide pivotally disposed on said pivot in said pump body and having a central axis eccentric to the axis of said rotor, a plurality of fluid chambers defined by said rotor, said vanes, and said slide that are successively connected to said inlet and outlet ports, a spring acting on said slide to urge said slide in one direction, a first chamber and a second chamber, each suitable for receiving a fluid pressure and each disposed between said pump body and an outer surface of said slide, the first chamber in fluid communication with a pump outlet discharge pressure, and a valve operable to selectively pressurize and depressurize the second chamber.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a variable displacement sliding vane pump having a slide whose position is controlled by a differential pressure between a constant pressure source and a variable pressure source, the differential pressure equilibrating a spring force applied to the slide to establish a desired flow rate and pressure.  
       BACKGROUND OF THE INVENTION  
       [0002]     A lubrication system for an engine pressurizes and distributes lubrication fluid to the engine lubrication circuits. It employs a rotor and a slide with multiple vanes and cavities which can vary the volume of fluid delivered to the oil circuits.  
         [0003]     The slide is eccentrically offset from the rotor to create fluid chambers defined by the vanes, rotor, and inner surface of the slide. A compression spring positions the slide to create large fluid chambers as the default. When the engine requires less volume of fluid or less oil pressure by the pump, a pressure regulator directs fluid from the pump output line to a regulating chamber in the pump. Pressure in the regulating chamber pivots the slide against the force of the spring to more closely align the centers of the rotor and slide, thereby reducing the size of the fluid chambers. This reduces the amount of fluid drawn into the pump from the fluid reservoir and likewise, the amount of fluid output by the pump and thereby reduces the oil pressure as well.  
         [0004]     There are two ways to control pump output. The first way is to direct line pressure to the regulating chamber via the pressure regulator to decrease pump output. The second way is to remove pressure from the regulating chamber via the pressure regulator by exhausting fluid to increase pump output.  
         [0005]     Representative of the art is U.S. Pat. No. 4,342,545 (1982) to Schuster 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.  
         [0006]     What is needed is a variable displacement sliding vane pump having a slide whose position is controlled by a differential pressure between a constant pressure source and a variable pressure source, the differential pressure equilibrating a spring force applied to the slide to establish a desired flow rate and pressure. The present invention meets this need.  
       SUMMARY OF THE INVENTION  
       [0007]     The primary aspect of the invention is to provide a variable displacement sliding vane pump having a slide whose position is controlled by a differential pressure between a constant pressure source and a variable pressure source, the differential pressure equilibrating a spring force applied to the slide to establish a desired flow rate and pressure.  
         [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 variable displacement sliding vane pump comprising a pump body, inlet and outlet ports formed in said pump body, a drive shaft rotatably mounted in said pump body, a rotor driven by said drive shaft and co-axially aligned therewith, a plurality of radially extending vanes slidably disposed in said rotor, a pivot disposed in said pump body, a slide pivotally disposed on said pivot in said pump body and having a central axis eccentric to the axis of said rotor, a plurality of fluid chambers defined by said rotor, said vanes, and said slide that are successively connected to said inlet and outlet ports, a spring acting on said slide to urge said slide in one direction, a first chamber and a second chamber, each suitable for receiving a fluid pressure and each disposed between said pump body and an outer surface of said slide, the first chamber in fluid communication with a pump outlet discharge pressure, and a valve operable to selectively pressurize and depressurize the second chamber. 
     
    
     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 front view of the pump with outer cover removed.  
         [0012]      FIG. 2  is an exploded view of the pump.  
         [0013]      FIG. 3  is a front view of the pump body without the outer cover, slide, rotor and vanes.  
         [0014]      FIG. 4  is a top/plan view of the pump rotor.  
         [0015]      FIG. 5  is a plan view of the pump slide.  
         [0016]      FIG. 6  is a schematic diagram of the pump fluid circuit.  
         [0017]      FIG. 7  is a graph depicting the pump performance including pump flow rate and pressure.  
         [0018]      FIG. 8  is a side view of an electric valve.  
         [0019]      FIG. 9  is a graph depicting the pump performance including pump flow rate and pressure. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]      FIG. 1  is a front view of the pump with outer cover removed. The inventive pump  100  comprises body  10 . Body  10  defines a cavity  11  within which is disposed slide  12  and rotor  13 . A plurality of sliding vanes  14  are radially disposed about rotor  13 . Each vane  14  extends radially from a slot  15  in rotor  13 . Each vane  14  is moveable within each slot  15 .  
         [0021]     Pump shaft  16  is rotatably mounted in body  10 . A splined end  160  of pump shaft  16  engages rotor  13 . As rotor  13  rotates vanes  14  are urged outwardly by a pair of vane control rings  17  and centripetal force into a sliding engagement with inner surface  120  of slide  12 .  
         [0022]     Slide  12  is pivotally engaged with the body at a pivot member  18 . Slide  12  pivots at pivot member  18  within cavity  11  thereby describing an arc which defines the operating range of motion of slide  12 .  
         [0023]     The position of each vane  14  is a function of the position of slide  12  with respect to ring  17 . Ring  17  occupies a space determined by the ends of vanes  14 . Ring  17  is substantially concentric with inner surface  120 .  
         [0024]     The position of ring  17  with respect to rotor  13  determines the radial position of each vane  14  in each slot  15 , which in turn, determines a given slide  12  position as compared to the position of the axis of rotation of rotor  13 . This relationship determines the volume of each of the chambers  21  between the inlet port  19  and the outlet port  20  for a given engine speed and hence a given slide  12  position.  
         [0025]     Body  12  defines a pair of kidney shaped ports  19 ,  20  which comprise an inlet port and an outlet port, respectively, for the pump  100 . A plurality of chambers  21  are formed by the vanes  14 , rotor  13  and inner surface  120 . Chambers  21  rotate with rotor  13  and expand and contract during rotation, as is well-known in vane type pumps.  
         [0026]     Inlet port  19  accepts fluid from a source or reservoir such as an engine oil system, not shown, and passes the fluid to the chambers  21  in turn as rotor  13  rotates. Vanes  14  move the fluid in chambers  21  from the inlet port  19  to the outlet port  20 . As can be seen in  FIG. 1 , if the pump rotor  13  is rotating in a counterclockwise direction, chambers  21  are continually expanding thereby creating a low pressure region which causes an inflow of fluid in the area of inlet port  19  and are contracting thereby increasing fluid pressure which causes an outflow of fluid in the area of the outlet port  20 .  
         [0027]     The position of slide  12  is established by the combined effect of the control pressure in each for two chambers, namely, chamber  22  and chamber  23  acting in balance with the spring force from spring  31 . Chamber  22  extends about a portion of the outer circumference of slide  12  from seal member  24  disposed in a groove  26  to seal member  25  disposed in a groove  27 , each formed in slide  12 . Each seal member  24  and  25  is urged outwardly against surface  28  by a resilient backing member  29 ,  30  respectively. Chamber  23  extends about a portion of the outer circumference of slide  12  from seal member  24  to pivot member  18 .  
         [0028]     Spring  31  acts in opposition to the sum of the fluid pressures in chambers  22  and  23  such that as the total pressure in chambers  22  and  23  increases, and therefore the torque of the slide around the pivot member increases, the pump slide  12  will move clockwise about pivot member  18 . The combined torque caused by the pressure in chamber  22 ,  23  is balanced by the spring force of spring  31 .  
         [0029]     The fluid pressure in chamber  22  is supplied by fluid in ultimate communication with the outlet port  20  of pump  100  and is therefore subject to the outlet pressure of pump  100  or from a feedback channel to the engine gallery, see  FIG. 5 . The fluid pressure in chamber  23  is supplied by fluid communication with a second pressure source also connected to the outlet port  20  of pump  100 . The fluid pressure in chamber  22  is proportional to the outlet pressure of pump  100 . The fluid pressure in chamber  23  is dependent upon the speed of the pump  100 , namely, for certain operating regimes below a predetermined pump speed the pressure in chamber  23  is automatically vented to ambient, for example, an oil storage reservoir. Above a predetermined speed the pressure in chamber  23  is equivalent to the pressure in chamber  22 . This is also referred to as the “switching point” and can be set at any speed depending upon the application. The sum of the pressures, and therefore torque, in chambers  22  and  23  determine the position of slide  12 . The position of slide  12  determines the outlet pressure and flow rate of the pump.  
         [0030]     Under most operating conditions, the axis of slide  12 , and therefore of inner surface  120 , moves between position  32  during low engine speed conditions to position  33  during high engine speed conditions. As vanes  14  are rotated from the inlet port  19  to outlet port  20  a pressure transition takes place with the chambers  21 .  
         [0031]     Since the inner surface  120  is subjected to the internal pressure generation in chambers  21 , slide  12  is inherently unbalanced during operation. The net resultant reaction force due to the internal pressure generation passes through the central axis of inner surface  120 . It will be appreciated that the reaction forces always provides a counterclockwise moment about axis  18  which is in opposition to the clockwise moment generated by the control pressure in chambers  22  and  23 .  
         [0032]     The pressures in chamber  22 ,  23  are balanced against the force of spring  31  so that the displacement of the pump, and as a result the flow, may be adjusted by varying the chamber pressures. The inventive pump controls both displacement and oil flow for two or more outlet pressure levels based upon the pump outlet pressure or the engine gallery pressure.  
         [0033]     Typically the desirable pressure level in the pump for each chamber is the pressure level required to produce the proper oil flow and pressure for all engine speeds and load conditions. In some cases, at lower rpm&#39;s the engine does not require a high oil pressure level, therefore a somewhat lower pressure is acceptable, and therefore the flow is reduced as well. The lower operating pressure and flow is achieved by pressurizing chamber  23 .  
         [0034]     The required magnitude of the lower oil pressure depends upon different engine parameters, including whether it is a gas or diesel engine, the engine complexity, engine speed and load.  
         [0035]     The inventive pump provides two levels of control. The first is pressure control over a given speed range due to the variable vane pump function. The second is based upon the ability of the pump to change between two (or more) pressure levels by use of two (or more) pressure chambers  22 ,  23 , controlling the position of slide  12 .  
         [0036]     A cover  70  is secured to the housing  10  by a plurality of fasteners  37 . Leakage from the chambers  21  radially outwardly past the cover  70  is prevented by surface to surface contact.  
         [0037]      FIG. 2  is an exploded view of the pump. The position of ring  17  with respect to rotor  13  determines the radial position of each vane  14  in each slot  15 , which in turn, determines a slide  12  position as compared to the position of the axis of rotation of rotor  13 . An inner edge  14   a  of each vane  14  bears upon the outer surface  17   a  of ring  17 . An outer edge  14   b  of each vane  14  also bears upon and slides upon inner surface  120  of slide  12 . The pump may use a single spring  31 , or it may use for example, two springs  31   a  and  31   b.    
         [0038]      FIG. 3  is a front view of the pump body without the outer cover, slide, rotor and vanes. Inlet port  19  and outlet port  20  are disposed in body  10 . Conduit  34  transmits pressure from the main oil gallery  204  to chamber  22 , see  FIG. 5 . Conduit  35  transmits pressure from the main oil gallery  204  to chamber  23 , see  FIG. 5 . Conduit  34  is exposed to pump outlet pressure or engine gallery oil pressure during all pump operating conditions. The fluid pressure in conduit  35  is determined by the position of valve  207 , see  FIG. 1 .  
         [0039]      FIG. 4  is a top plan view of the pump rotor. Rotor  13  comprises slots  15  which are oriented radially about the outer circumference. A vane  14  is slidingly engaged in each slot  15 . Drive shaft  16  engages rotor  13  through splined hole  36 . Drive shaft  16  may also be press fit in hole  36 . Each slot  15  comprises a radial length sufficient to accommodate the entire range of movement of each vane  14 . During operation of the pump each vane  14  moves radially a predetermined distance which distance is dependent upon the position of rings  17  with respect to rotor  13 .  
         [0040]      FIG. 5  is a plan view of the pump slide. Slide  12  comprises inner surface  120 . An outer edge of each vane  14  slidingly engages inner surface  120 . Inner surface  120  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  121 . Groove  26  and groove  27  each receive seal members  24 ,  25  respectively, for sealing a fluid pressure within each chamber  23 ,  22  respectively. Spring  31  bears upon surface  122 . Seal members  24 ,  25  may comprise any material having a suitable compatibility with the pump fluid, for example, synthetic and/or natural rubbers.  
         [0041]      FIG. 6  is an example schematic diagram of the pump fluid circuit  200 . Fluid conduit  201  connects pump outlet port  20  to an oil filter  202 , oil cooler  203  and to a main oil gallery  204 . The main oil gallery  204  is exposed to the outlet pressure of pump  100 , subject to friction losses normal to any fluid system. Main oil gallery  204  is also connected to the engine oil system  210 . This system is offered only as an example and does not depict the varieties of engine oil systems to which the inventive pump and system may be applied.  
         [0042]     Connected to the main oil gallery  204  is conduit  205  which connects to chamber  22  through conduit  34 , see  FIG. 1 . Connected to conduit  205  is conduit  209 . Conduit  209  is connected to electric valve  207 , see  FIG. 7 . Valve  207  is used to selectively connect or disconnect conduit  209  through conduit  206  to conduit  35  and chamber  23  in  FIG. 1 , with the fluid pressure in conduit  205 . Valve  207  is preferably contained within body  10 . Valve  207  is shown in  FIG. 5  schematically separate from pump  100  for ease of illustration. However, valve  207  may also be separated from pump body  100  as schematically shown in  FIG. 5  in order to accommodate variable physical constraints as required by system space requirements. Valve  207  may also comprise a mechanical valve known in the art, for example, a valve which regulates a downstream pressure based upon an upstream pressure commonly known as a pressure regulating valve.  
         [0043]     The total force exerted against spring  31  by slide  12  is the sum of the torques created by the fluid pressure in chamber  22  plus the fluid pressure in chamber  23 , both acting about pivot member  18 .  
         [0044]     At or less than a first operating speed, valve  207  is OPEN thereby allowing the engine gallery pressure to enter chamber  23 . The pressure in chamber  23  and combined with the pressure in chamber  22  causes slide  12  to pivot about pivot member  18  an arcuate distance to a position where the torque caused by the combined pressures in chambers  22 ,  23  is balanced by the spring force of spring  31 . The pump characteristics with slide  12  in this position are shown by portion “A” of  FIG. 7 . The pressure in chamber  22  and  23  is proportional to the pump speed. As the engine speed, and thereby pump speed, increase so does the pressure in the chambers  22 ,  23 . In this operating condition the pump output is a flow and pressure that is less than the flow and pressure of the pump with the valve  207  closed (chamber  23  depressurized) at the same engine speed. In portion “A” the position of slide  12 , and thereby of the pump output flow and pressure, is a function of the pressure in both chambers  22 ,  23 .  
         [0045]     At an operating condition greater than the first operating speed, valve  207  is closed thereby venting chamber  23  to ambient pressure (approximately 1 bar). The pressure in chamber  22  causes slide  12  to pivot about pivot member  18  an arcuate distance to an equilibrium position where the torque caused by the pressure in chamber  22  is balanced by the spring force of spring  31 . Slide  12  pivots because as the pump speed increases, the pressure in chamber  22  also increases, thereby increasing the force exerted against spring  31 . The pump characteristics with slide  12  in this position are shown by portion B of  FIG. 7 . The operating regime in portion B can also be characterized as a passive mode since chamber  23  is vented to atmospheric pressure and the entire pivot movement and position of slide  12  is determined by the level of pressurization of chamber  22 .  
         [0046]     In an alternate embodiment valve  207  may be opened to a partial position thereby causing slide  12  to move to a position that is intermediate position A and position B, causing an intermediate outlet pressure and flow. Placing valve  207  in any position between fully open and fully closed allows the pressure in chamber  23  to be variable, thereby providing a range of slide positions for a given pump outlet pressure.  
         [0047]     In the case of a failure of valve  207 , the pump will continue to operate in a passive mode (chamber  23  depressurized) while meeting all oil requirements of the engine. The passive operating mode is still more efficient that a fixed displacement pump. With valve  207  in operation the instant invention provides incremental horsepower reduction over the passive design.  
         [0048]      FIG. 7  is an example graph depicting the pump performance including pump flow rate and pressure. A range of engine speeds is represented on the x-axis and a range of pump outlet pressures is represented on the y-axis. A range of pump flow rates is also represented on the second y-axis in liters per minute.  
         [0049]     The engine speed range is from 0 RPM to 8000 RPM. The outlet pressure range is from 0 bar to 6.00 bar. The pump flow rate range is from 0 liters/minute to 90.00 liters/minute.  
         [0050]     For the purposes of illustration an engine speed of ˜3,500 RPM is selected to demonstrate the characteristics of the inventive pump. The transition between operating conditions “A” and “B” is depicted as the “switching point” in the center of the curves in the graph.  
         [0051]     For engine speeds less than ˜3,500 RPM the maximum pump outlet pressure is approximately 2.6 bar. The maximum flow rate is approximately 20.0 liters/minute.  
         [0052]     For engine speeds greater than ˜3,500 RPM the pump outlet pressure quickly transitions up to a minimum outlet pressure of approximately 4.9 bar at 7,500 RPM. The flow rate transitions to a maximum of approximately 28.0 liters/minute at 7,500 RPM.  
         [0053]     At the transition point the step change in pressure is approximately 1.6 bar. The step change in flow is approximately 5 l/min.  
         [0054]     The performance transition is caused by slide  12  pivoting about pivot  18  caused by deactivation of valve  207  venting chamber  23  to ambient atmospheric conditions. Valve  207  is controlled by an electric signal transmitted by an engine ECU, for example. Upon reaching the predetermined engine speed, in this case ˜3,5.00 RPM, ECU  208  (see  FIG. 6 ) signals valve  207  to close, thereby pressurizing chamber  23  with fluid pressure equal to that in the main oil gallery  204 .  
         [0055]     As described previously, the pressures in chambers  22 ,  23  create a torque and hence force which is greater than the combination of the force of the spring  31  and the fluid force in chambers  21 , thereby causing spring  31  to compress. This causes slide  12  to pivot. By pivoting in the clockwise direction the flow rate and outlet pressure are each substantially decreased at the predetermined engine speed because pump displacement is reduced.  
         [0056]     For the purposes of comparison, the dashed lines in portion A of  FIG. 7  below ˜3,500 RPM depict the behavior of the outlet pressure and flow rate of a pump in the case where the position of slide  12  is only controlled by a single pressure chamber. In the single chamber case, at relatively low engine speeds, say only slightly greater than idle (˜1,500 RPM), the pump would operate at a comparatively elevated outlet pressure and flow rate not otherwise required by the engine. This is inefficient. The inventive pump provides only the required amount of flow and pressure for efficient operation at reduced engine speeds. This equates to considerable energy savings in the system. However, at elevated engine speeds the pump can quickly and precisely transition to higher flow rates and outlet pressures necessary to meet engine demands.  
         [0057]      FIG. 8  is a side view of an electric valve. Valve  207  is engaged with the body  10  of the pump. Valve  207  is connected to the electrical harness of the engine or vehicle (not shown). An electrical connector (not shown) engages the valve  207  at socket  208 . When valve  207  is de-activated, pressure is vented from chamber  23 , thereby causing the pump to operate in region “A”. When valve  207  is activated fluid pressure is admitted to chamber  23  from nozzle  211 , thereby causing the pump to operate in region “B”. In order to avoid engine failure caused by inadequate fluid pressure at high speed, the valve must be electrically de-activated to vent pressure from chamber  23 . This results in the fail safe situation at high speed, namely, chamber  23  is vented upon electrical failure of valve  207 .  
         [0058]      FIG. 9  is a graph depicting the pump performance including pump flow rate and pressure. A range of engine speeds is represented on the x-axis and a range of pump outlet pressures is represented on the y-axis. A range of pump flow rates is also represented on the second y-axis.  
         [0059]     The engine speed range is from 0 RPM to 8000 RPM. The outlet pressure range is from 0 bar to 6.00 bar. The pump flow rate range is from 0 liters/minute to 90 liters/minute.  
         [0060]     For the purposes of illustration an engine speed of ˜2,000 RPM is selected to demonstrate the characteristics of the inventive pump. The transition between operating conditions “A” and “B” is depicted as the “switching point” at approximately 2,000 RPM.  
         [0061]     In this example, valve  207  is OFF at start up and for engine speeds less than 2,000 RPM, namely, chamber  23  is unpressurized and vented to ambient. For engine speeds less than approximately 2,000 RPM the maximum pump outlet pressure (Line Pressure) is approximately 3.6 bar. The maximum flow rate (Flow Rate) is approximately 25.0 liters/minute.  
         [0062]     For engine speeds greater than approximately 2,000 RPM the pump outlet pressure (Line Pressure) quickly transitions down to a minimum outlet pressure of approximately 2.4 bar at 2,000 RPM up to 3.2 bar at approximately 7,500 RPM. The flow rate (Flow Rate) transitions to a maximum of approximately 23.0 liters/minute at 7,500 RPM.  
         [0063]     At the transition point the step change in pressure is approximately 1.4 bar. The step change in flow is approximately 5 l/min.  
         [0064]     The performance transition in this example is caused by slide  12  pivoting about pivot  18  caused by activation of valve  207  thereby pressuring chamber  23 . Valve  207  is controlled by an electric signal transmitted by an engine ECU, for example. Upon reaching the predetermined engine speed, in this case approximately 2,000 RPM, ECU  208  (see  FIG. 6 ) signals valve  207  to close, thereby pressurizing chamber  23  with fluid pressure equal to that in the main oil gallery  204 . In the event of a failure of valve  207  chamber  23  would depressurize thereby putting the pump in high discharge pressure mode.  
         [0065]     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.