Patent Abstract:
A variable displacement vane pump includes, but is not limited to inlet and outlet ports in a pump body, a drive shaft rotatably mounted in the pump body, a rotor driven by the drive shaft and radially extending vanes slidably disposed in the rotor. A slide is pivotally disposed on a pivot and has a central axis eccentric to the axis of the rotor. Chambers are defined by the rotor, the vanes and the slide that are successively connected to the inlet and outlet ports. A resilient member is pivotally engaged with the slide and acts on the slide to urge the slide in one direction.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to British Patent Application No. 0907687.8, filed May 5, 2009, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a variable displacement vane pump and, in particular, to a variable displacement vane pump of an engine lubrication system of an automotive vehicle. 
     BACKGROUND 
     The lubrication system of an engine pressurizes and distributes lubrication fluid, e.g. oil, to the engine lubrication circuits by use of a pump such as a variable displacement vane pump (VDVP). A variable displacement sliding vane pump may employ a rotor and a slide with multiple radially extending slidable vanes and cavities which can vary the volume of fluid delivered to the lubrication circuits. 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. 
     U.S. Pat. No. 6,763,797 discloses a variable displacement pump in which pump outlet pressure is used to bias the position of a slide (also referred to as a cam ring), thereby changing the eccentricity of the slide with respect to the rotor axis and consequently varying the pump displacement. By varying the pump displacement relative to pump outlet pressure, the pump outlet pressure can be controlled based on engine flow requirements. The pressure regulation characteristics of the pump are determined by calibrating a reaction spring that counterbalances the hydraulic forces acting on the slide. 
     However, further improvements to variable displacement vane pumps and, in particular, variable displacement vane pumps with a pivotable slide for use in engine lubrication systems are desirable. In addition, other improvements, desirable features and characteristics are desirable and will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     Embodiments of the present invention provide a variable displacement vane pump with a pivotable slide in which a resilient member urged against the slide is pivotally engaged with the slide. 
     The pivotable engagement between the resilient member and the slide is used to reduce the stress on the resilient member when the slide pivots against the resilient member and reduce the occurrence of bending and buckling of the resilient member. Consequently, the durability of the spring and the variable displacement vane pump can be increased. Furthermore, the occurrence of buckling due to the increased wear on the spring as a result of its installation may be reduced. Since the spring rate can be increased, fuel consumption should be able to be reduced as well. 
     The variable displacement vane pump may comprise the following; a pump body, inlet and outlet ports in said pump body, a drive shaft rotatably mounted in said pump body, a rotor driven by said drive shaft and a plurality of radially extending vanes slidably disposed in said rotor. The variable displacement vane pump may also comprise a pivot disposed in said pump body, a slide pivotally disposed on said pivot and having a central axis eccentric to the axis of said rotor and 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 resilient member acts on said slide to urge said slide in one direction and a pressure control chamber is disposed between said pump body and an outer surface of said slide. As mentioned above, the resilient member is pivotally engaged with the slide. 
     In an embodiment, the resilient member is biased between the pump body and the slide to urge the slide in one direction. The resilient member may be biased as to urge the slide into an end position of its pivotable range. In one embodiment, the resilient member is biased between the pump body and a tab protruding from the outer surface of the slide. 
     In one embodiment, the resilient member is pivoted about a pivot at the pump body upon pivoting of the slide against the resilient member. 
     The resilient member may comprise a spring such as a solenoid-wound spring which has a longitudinal axis. 
     The spring may further comprise a seat in pivotable engagement with the slide. The seat may also be in slidable engagement with the slide. 
     In one embodiment, the seat comprises a convex outer surface in slidable engagement with a concave surface positioned on the slide. The convex outer surface of the seat and the concave surface of the slide may be in form-locking engagement with one another. 
     In one embodiment, the seat further includes a guiding pin extending from a flat inner surface opposing said convex surface. The guiding pin is accommodated within said spring. The guiding pin may have a longitudinal axis which extends generally parallel to or along the longitudinal axis of the solenoid spring if the resilient member comprises a solenoid spring. The flat inner surface of the seat may be generally perpendicular to the longitudinal axis of the spring and the longitudinal axis of the guiding pin. The guiding pin may have a length which is less than the length of the uncompressed spring so as to allow the spring to be compressed by the slide when in the mounted condition. 
     In an embodiment, the spring is biased against the flat inner surface of the seat and urges the seat against the slide. If the seat has an outer convex surface, this outer convex surface may be urged against a concave surface positioned on the slide by the spring which is biased against the flat inner surface of the seat. 
     In an embodiment, the longitudinal axis of the spring is pivoted about a point at the pump body upon pivoting of the slide against the seat. 
     In a further embodiment, the outer surface of the seat slidably engages with the slide as the longitudinal axis of the spring is pivoted about a point on the pump body due to the pivoting of the slide against the seat. This sliding engagement between the seat of the spring and the slide enables the flat inner surface of the seat to be orientated in a more perpendicular fashion with respect to the longitudinal axis of the spring and be orientated in a more parallel fashion with the respect to the end face of the spring than in an arrangement in which no slidable engagement is provided between spring and slide. This further reduces the stress on the spring and may lead to an increase in the durability of the spring and the pump. 
     A lubrication system of an engine of an automotive vehicle is also provided which comprises a variable displacement vane pump according to one of the previous embodiments. The lubrication medium pumped by the pump may be oil. 
     However, the variable displacement vane pump according to one of the previous embodiments is not limited to use in lubrication systems of automotive vehicle engines but can also be used to pump other types of liquids or gases, for example, air in other applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  illustrates a cross-sectional view of a variable displacement vane pump according to an embodiment of the present invention, 
         FIG. 2  illustrates a three-dimensional view of a portion of the variable displacement vane pump of  FIG. 1 ; 
         FIG. 3  illustrates a detailed view of the pivotable spring of the variable displacement vane pump of  FIG. 1 ; 
         FIG. 4  illustrates a cross-sectional view of a comparison variable displacement vane pump; 
         FIG. 5  illustrates the pivotable spring and slide of  FIG. 1 ; 
         FIG. 6  illustrates the angular displacement of the pivotable spring and the slide of  FIG. 5 ; 
         FIG. 7  illustrates a detailed view of the pivotable spring of  FIG. 6 ; and 
         FIG. 8  illustrates a schematic view of the pivotable spring of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
       FIG. 1  illustrates a cross-sectional view of a variable displacement vane pump  10  according to an embodiment of the present invention. The variable displacement vane pump  10  includes a pivotable slide  11  which is urged in one direction by a resilient member in the form of a solenoid spring  12 . A three-dimensional view of the spring  12  and slide  11  is illustrated in  FIG. 2  and the movement of the spring  12  with respect to the slide  11  is illustrated in  FIG. 3 . 
     The variable displacement vane pump  10  may be used to supply lubrication medium to the lubrication system of an internal combustion engine. However, the variable displacement vane pump  10  is not limited to this use and may be used to pump other liquids or gases, for example, air in other applications. 
     The variable displacement vane pump  10  includes a housing  13 . A rotor  14  having a plurality of radially extending slidable vanes  15  is rotatable in the housing  13  on a fixed axis  16 . The rotor  14  may be driven by a cross-axis hex shaft drive of the engine or other suitable driving means powered by the engine. The slidable vanes  15  internally engage the slide  11  to define pumping chambers  17  within the slide  11 . 
     The slide  11  is pivotally connected to the housing wall  18  by a pivot  19  and is pivotable about pivot  19  in the plane of the slide  11  to vary the displacement of the pumping chambers  17  by moving the position of the slidable vanes  15 . The displacement of the pump  10  is proportional to the eccentricity of the slide  11  relative to the axis  16  of the rotor  14 . 
     When the pump  10  is at rest, the slide  11  is urged by the spring  12  into a position of maximum eccentricity relative to the rotor  14 . When the pump operates with the slide  11  in this position, the displacement of the pump is at its maximum value. As the slide  11  pivots away from a position of maximum eccentricity, indicated by arrow  29  in the drawings, the displacement of the pump is reduced and the output flow of the pump generally decreases. When the center of the slide  11  is pivoted to a position at which it is aligned with the axis  16  of the rotor  14 , the slide  11  is at approximately 0% eccentricity (i.e., approximately 100% from its maximum eccentricity) and the pump  10  operates at zero displacement. 
     A non-illustrated oil inlet port is formed on an inlet side of the housing  13  and a non-illustrated pressurized oil outlet port is formed on an opposite outlet side of the housing  13 . The inlet and outlet ports communicate with the pumping chambers  17  preferably on opposite bottom and top sides of the rotor  14  in order to prevent entrapment of gases in the pumping chambers  17 . Rotation of the rotor  14  at some level of eccentricity causes the pumping chambers  17  to expand. This change in chamber volume in turn causes a decompression of the pumping chambers which causes oil to be sucked into the pumping chambers  17  through the inlet port and then pushed out of the pumping chambers  17  through the outlet port as the chambers contract. 
     The spring  12  is a solenoid-wound spring having a longitudinal axis  20 . The spring  12  is biased between the pump housing  13  and the slide  11 , in particular a tab  30  extending from the outer surface of the slide  11 . The spring is accommodated within a generally tubular cut out in the housing  13 . 
     The resilient member comprises, in addition to the spring  12 , a guiding pin  21  with an integral seat  22 . The guiding pin  21  has a length which is less than that of the installed solenoid spring  12  and is positioned concentrically within the spring  12  so that it extends generally long the longitudinal axis  20  of the spring  12 . The seat  22  has an outer convex surface  23  and a flat inner surface  24  opposing the outer convex surface  23 . The flat inner surface  24  extends generally perpendicularly to the length of the guiding pin  21  and the longitudinal axis  20  of the spring  12 . The end face  25  of the spring  12  is generally parallel to the flat surface  24  of the seat  22 . 
     The outer convex surface  23  of the seat  22  is in slidable engagement with a concave surface  26  positioned in a surface of the tab  30  protruding from the outer surface of the pivotable slide  11 . This sliding engagement is indicated in  FIG. 3  by the arrow  31 . 
     The guiding pin  21  and the spring  12  are pivotable about a pivot  27  positioned at the pump housing  13  so that the longitudinal axis  20  of the spring  12  has an excursion path due to the movement of the slide  11  against the spring  12 . 
       FIG. 4  illustrates a cross-sectional view of a comparison variable displacement vane pump  10 ′ with a pivotable slide  11 ′. In this comparison variable displacement vane pump  10 ′ the resilient member comprises only a spring  12 ′ which extends between a flat surface  26 ′ of the tab  30 ′ of the slide  11 ′. The flat surface  26 ′ is generally perpendicular to the longitudinal axis  20 ′ of the spring  12 ′ and parallel to the end face  25 ′ of the spring  12 ′. 
       FIG. 5  illustrates the operation of the spring  12  and pivotable slide  11  of the variable displacement pump illustrated in  FIG. 1 . Three positions of the spring  12  and slide  11  are illustrated in  FIG. 5  and  FIG. 6 . The angular displacement of the spring  12  and the slide  11  about their respective pivot points  27 ;  19  are illustrated in  FIG. 6 ,  FIG. 7  and  FIG. 8  for particular positions. 
     One end point of the pivotable range of the slide  11  is illustrated in the drawings by reference number  28 . When the slide  11  is in end position  28 , the guiding pin  21  and spring  12  are arranged so that their longitudinal axis  20  is generally perpendicular to the pump housing  13 . The end position  28  may, typically, be defined as the position of the slide  11  at which the fluid chambers  17  have their largest volume. 
     As the slide  11  is pivoted anticlockwise about pivot  19  in the plane of the slide  11 , the spring  12  is compressed and the concave surface  26  of the tab  30  slidably engages with the outer convex surface  23  of the seat  22  thus causing the guiding pin  21  and spring  12  to pivot clockwise about pivot point  27  at the pump housing  13 . As the angular displacement of the slide  11  increases, i.e., the slide  11  pivots further in the anticlockwise direction, the guiding pin  21 , seat  22  and spring  12  further pivots in the clockwise direction. 
     Due to the pivoting action of the guiding pin  21 , the flat surface  24  of the seat  22  remains more parallel with respect to the end face  25  of the spring  12  and more perpendicular to the longitudinal axis  20  of the spring  12  than would be the case if the slidable arrangement of the seat  22  and tab  30  were omitted. This reduction in the change in the angle between the end face  25  of the spring  12  and the surface against which it is biased reduces the stress on the spring  12  so that the likelihood of the spring  12  buckling is reduced. The durability and lifetime of the spring  12  and the pump may be increased. 
       FIG. 6  to  FIG. 8  illustrate two angular displacements of the slide  11  away from the end position  28  for the pump  10  of  FIG. 1  provided with a pivotable spring  12 . When the slide  11  is pivoted by 4° anticlockwise from the end position  28 , the longitudinal axis  20  of the guiding pin  21  and spring  12  is caused to pivot approximately 3° in the clockwise direction. The flat surface  24  of the seat  22  is caused to pivot approximately 2.5° clockwise. 
     When the slide  11  is pivoted by approximately 8° anticlockwise from the end position  28 , the longitudinal axis  20  of the guiding pin  21  and spring  12  caused to pivot approximately 6.7° in the clockwise direction. The flat surface  24  of the seat  22  is caused to pivot approximately 6.2° clockwise. 
     A comparison of the path of excursion for the spring  12  with a seat  22  at the slide side as well as for the spring  12 ′ of the comparison pump  10 ′ is illustrated in  FIG. 8 . The excursion for the spring  12  with a seat  22  at the slide side is indicated by the solid lines  32  and the excursion for a spring  12 ′ in the comparison pump  10 ′ of  FIG. 4  is illustrated by dashed lines  33 . 
     The excursion of the pivotable spring  12  with guiding pin and seat  22  is slidable engagement with the slide  11  is linear. In contrast, the spring  12 ′ of the comparison pump  10 ′ has a non-linear excursion with a maximum displacement region. Furthermore, the displacement of the spring  12 ′ of the comparison pump  10 ′ is greater that that of the spring  12  arrangement according to an embodiment of the present invention. 
     For the comparison pump  10 ′ illustrated in  FIG. 4 , an angular displacement of the slide  11 ′ of approximately 4° causes the longitudinal axis of the spring to be displaced by approximately 7° and the flat face of the seat is caused to pivot approximately 4.5° clockwise. 
     For a slide angular displacement of approximately 8°, the longitudinal axis of the spring is displaced by approximately 14.7° and the flat face of the seat is caused to pivot approximately 8.5° clockwise if the end face of the spring  12 ′ engages with a non-slidable flat surface of the tab  30 ′. The spring  12 ′ is subjected to greater stress than in the arrangement according to an embodiment of the present invention and buckling of the spring is more likely to occur as a result. 
     While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

Technology Classification (CPC): 5