Patent Publication Number: US-8118575-B2

Title: Variable displacement vane pump with enhanced discharge port

Description:
The application claims the benefits of U.S. Provisional Application No. 61/047,801, filed Apr. 25, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a variable displacement vane pump. More specifically, the present invention relates to a variable displacement vane pump which includes an enhanced discharge port designed to improve energy efficiency of the pump. 
     BACKGROUND OF THE INVENTION 
     Until recently, fixed displacement pumps have conventionally been employed as lubrication oil pumps for internal combustion engines. To prevent possibly damaging oversupply of lubrication oil under some operating conditions, pressure relief valves or other control mechanisms have been used to route the oversupply of oil from the output of the pump back to a reservoir or the pump inlet. 
     While such systems have proven to be reliable and inexpensive, they suffer from a disadvantage in that energy is used by the pump to pressurize the oversupply of oil which is merely redirected to the pump inlet or reservoir by the control mechanism, and this energy is wasted, reducing the energy efficiency of the pump. 
     More recently, variable displacement vane pumps have been considered for use as lubrication oil pumps for internal combustion engines. By providing a suitable control mechanism to alter the displacement of the pump to provide only the amount of pressurized lubrication oil necessary for proper operation of the engine, no energy is required to pressurize unneeded oil and thus the energy efficiency of the pump, and the internal combustion engine, can be improved. 
     However, conventional designs of variable displacement vane pumps have proven to be less energy efficient than desired, especially at high displacement operating conditions. 
     It is desired to have a variable displacement vane pump which has an improved operating energy efficiency compared to conventional variable displacement vane pumps. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel variable displacement vane pump which obviates or mitigates at least one disadvantage of the prior art. 
     According to a first aspect of the present invention, there is provided a variable displacement vane pump, comprising: a rotor having a set of radially extending vanes; a control ring having an inner surface against which the vanes abut, adjacent vanes forming pumping chambers with the control ring and the rotor and the control ring being moveable about a pivot to alter the eccentricity of the axis of rotation of the vanes and the axis of rotation of the rotor to change the displacement of the pump; an inlet port to introduce working fluid from a pump inlet to the pumping chambers; a discharge port located downstream of the inlet port, with respect to the direction of rotation of the rotor, to transfer pressurized working fluid from the pumping chambers to a pump outlet; and a discharge recess formed in at least one of the upper and lower surfaces of the control ring adjacent the discharge port and in fluid communication with the discharge port to form an enhanced discharge port. 
     The present invention provides a variable displacement vane pump which includes an enhanced discharge port. The enhanced discharge port provides additional volume for pressurized fluid to exit the enhanced discharge port and reduces areas of high pressure in the discharge port which would otherwise occur as the pressurized working fluid reverses its direction of flow to enter the discharge port. By reducing the areas of high pressure, the back torque on the pump rotor is reduced and the energy efficiency of the pump is enhanced. In one embodiment, the pivot for the pump control ring is located radially outwardly from a conventional location, to allow for a discharge recess to be formed in the control ring, adjacent the discharge port, and extending past the pivot to the pump outlet. The combination of the discharge port and the discharge recess form an enhanced discharge port. In a second embodiment, the discharge recess is formed in the control ring around the pivot and a seal is provided on the control ring to inhibit leakage of pressurized working fluid past the control ring. In a third embodiment, a secondary discharge port is provided adjacent the discharge recess formed in the control ring and pressurized working fluid in the discharge recess can exit the discharge recess through the secondary discharge port which is in fluid communication with the pump outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
         FIG. 1  shows a cross section through a prior art variable displacement vane pump; 
         FIG. 2  shows an enlarged view of a portion of the discharge port of the pump of  FIG. 1  showing the flow of working fluid; 
         FIG. 3  shows a perspective view of a portion of a cross section taken along line  3 - 3  of  FIG. 1 ; 
         FIG. 4  shows a cross section through a variable displacement vane pump in accordance with the present invention; 
         FIG. 5  shows a perspective view of a portion of a cross section taken along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  shows an enlarged view of a portion of the discharge port of the pump of  FIG. 4  showing the flow of working fluid; 
         FIG. 7  shows a cross section through another variable displacement vane pump in accordance with the present invention; 
         FIG. 8  shows an enlarged view of a portion of the discharge port of the pump of  FIG. 7  showing the flow of working fluid; 
         FIG. 9  a cross section through another variable displacement vane pump in accordance with the present invention; and 
         FIG. 10  shows an enlarged view of a portion of the discharge port of the pump of  FIG. 9  showing the flow of working fluid. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A prior art variable displacement vane pump is indicated generally at  20  in  FIG. 1 . Pump  20  includes a pump housing  24  and a rotor  28  which is located within a cavity  32  in housing  24 . A control ring  36  is also located within cavity  32  and control ring  36  pivots about a pivot  40  to alter the degree of eccentricity of a set of vanes  44  extending from rotor  28  to change the displacement of pump  20 . 
     As is well known to those of skill in the art, as rotor  28  turns (in the direction indicated by arrow  48 ), working fluid from an inlet port  52 , which is connected to a pump inlet  56 , is drawn into the pump chambers formed between adjacent vanes  44 , rotor  28  and control ring  36 . As rotor  28  turns, the volume of each of these pump chambers first increases, drawing working fluid into the pump chambers from inlet port  52 , and then decreases as the pump chamber is brought into fluid connection with a discharge port  60  that is connected to a pump outlet  64 . This decreasing volume results in the pressurization of the working fluid supplied to discharge port  60 . 
     By pivoting control ring  36  about pivot  40 , the eccentricity between the rotational center of vanes  44  and the rotational center of control ring  36  can be altered to vary the change in the volume of the pump chambers during a revolution of pump  20 , thus varying its displacement. In  FIG. 1 , control ring  36  of pump  20  is in its maximum eccentricity position, i.e.—at the point of maximum volumetric displacement. 
     One of the known optimizations for vane pumps is the provision of a recess  68 , referred to as a “teardrop recess” in the upper and lower surfaces of control ring  36  adjacent the narrowest end (i.e.—the downstream end) of discharge port  60 . As the rotation of rotor  28  moves each vane  44 , in turn, towards the downstream end of discharge port  60 , the pressurized working fluid must undergo a reversal of its direction to exit discharge port  60 , as indicated by the arrows in  FIG. 2 . 
     While recess  68  provides some additional flow area which assists in achieving the necessary reversal in direction of the working fluid, the present inventors have determined that a significant pressure increase occurs at the narrowest end  72  of discharge port  60  as the working fluid undergoes the reversal of direction. In particular, the narrowness of end  72  (most clearly seen in  FIG. 3 ) strongly inhibits the necessary reversal of the pressurized working fluid, resulting in a significant pressure increase. This pressure increase results in a back torque force being applied to rotor  28  and requires additional input torque to be applied to rotor  28  to overcome the back torque. 
     Further, as the width of recess  68  necessarily tapers such that recess  68  ends at  76 , adjacent pivot  40 , to ensure for adequate sealing surfaces for control ring  36 , the flow of working fluid through this area  76  is restricted which also contributes to the pressure increase and the back torque. Further still, the resulting back pressure increases with the viscosity of the working fluid and thus start up and/or cold operating conditions, especially at high displacement setting for the pump, will exacerbate the back torque. 
     As will be apparent to those of skill in the art, providing the input torque necessary to counteract the back torque results in an increased operating energy requirement for pump  20 , with no useful benefit being obtained, thus decreasing the overall energy efficiency of pump  20 . 
     An embodiment of a variable displacement vane pump, in accordance with the present invention, is indicated generally at  100  in  FIGS. 4 ,  5  and  6 . Similar to prior art pump  20 , pump  100  includes a pump housing  104  and a rotor  108  which is located within a cavity  112  in housing  104 . A control ring  116  is also located within cavity  112  and control ring  116  pivots about a pivot  120  to alter the degree of eccentricity of a set of vanes  124  extending from rotor  108  to change the displacement of pump  100 . 
     As rotor  108  turns, in the direction indicated by arrow  128 , working fluid is introduced to the pumping chambers formed between adjacent vanes  124 , rotor  108  and control ring  116  via an inlet port  132  which is in fluid communication with a pump inlet  136 . Working fluid which has been pressurized within the pumping chambers exits those chambers via a discharge port  140  which is in fluid communication with a pump outlet  144  via a passage  148 . 
     Unlike prior art pump  20 , in pump  100  control ring  116  includes a discharge recess  152  which is adjacent to the narrowest end  156  of discharge port  140 . Discharge recess  152  has a greater radial width than comparable prior art teardrop recesses  60 . Further, unlike teardrop recesses, discharge recess  152  extends from the narrowest end  156  of discharge port  140  past pivot  120  toward the upstream end of discharge port  140  and passage  148 . In this manner, discharge port  140  and discharge recess  152  combine to serve as an enhanced discharge port, best seen in  FIG. 5 . 
     To permit the large width and long length of discharge recess  152 , pivot  120  has been moved radially outward, with respect to the center of rotation of rotor  108 , such that sufficient material is still available at the top and bottom surfaces of control ring  116  adjacent pivot  120  to provide a sealing surface between control ring  116  and the upper and/or lower surfaces of chamber  112  and/or any covers (such as cover  160  shown in  FIG. 5 ) which are used to enclose chamber  112 . By moving pivot  120  radially outward and by providing discharge recess  152 , the width  158  of the resulting enhanced discharge port can be significantly greater than the discharge port of prior art pump  20  (as shown in  FIG. 3 ). 
       FIG. 6  shows the reversal of the direction of the working fluid, as indicated by the arrows, in the enhanced discharge port of pump  100 . As is apparent, the relatively large width of discharge recess  152  at narrowest end  156  of discharge port  140  and the radially outward placement of pivot  120  results in a significantly increased volume within which pressurized working fluid can achieve the necessary change of direction. Further, by extending discharge recess  152  past pivot  120 , undue constrictions in the flow path of the pressurized working fluid from narrowest end  156  to passage  148  are avoided. 
     Significant improvements in energy efficiency have been obtained with pump  100 , compared to a comparable prior art pump  20 , due to the provision of discharge recess  152 . 
     As will be apparent to those of skill in the art, the cross section of discharge recess  152  need not be constant, but it is preferred than any substantial restrictions of the flow of working fluid through discharge recess  152  be avoided. Further, while in the embodiment of pump  100  discussed above, discharge recess  152  is formed in both the upper and lower surface of control ring  116 , it is also contemplated that in some circumstances it may be desired to only form discharge recess  152  in one of the upper or lower surfaces of control ring  116 . 
       FIG. 7  shows another variable displacement vane pump  200  in accordance with the present invention. In pump  200 , components which are substantially similar to components of pump  100  are indicated with like reference numerals. 
     In pump  200 , and unlike the case with pump  100 , pivot  120  need not be moved radially outward from the rotational center of rotor  108 . Instead, pump  200  includes a passage  204 , which connects discharge port  140  to pump outlet  144 , wherein the mouth of passage  204  surrounds pivot  120 . Control ring  208  features a discharge recess  212  which also surrounds pivot  120 . In this manner, discharge port  140  and discharge recess  212  combine to serve as an enhanced discharge port. 
     To provide the necessary sealing to inhibit the migration of pressurized working fluid from the effective discharge port to cavity  112  outside control ring  208 , a seal  216  is provided on control ring  208  and seal  216  engages a sealing surface  220  in cavity  112 . 
     As indicated in  FIG. 8 , the width and length of discharge recess  212  provides a relatively large volume in which the pressurized working fluid can reverse direction and enter passage  204  and thus undesired areas of high pressure are avoided, reducing back torque on rotor  108  and increasing the energy efficiency of pump  200 . 
       FIG. 9  shows another variable displacement vane pump  300  in accordance with the present invention. In pump  300 , components which are substantially similar to components of pump  100  are indicated with like reference numerals. 
     In pump  300 , control ring  304  is formed with a discharge recess  308  which overlies a second discharge port  312  formed in cavity  112 . Second discharge port  312  is in fluid communication with passage  148  via one or more secondary passages  316  formed in pump housing  104 . The upper and lower instances of discharge recess  308  on control ring  304  are interconnected by another bore (coaxial with second discharge port  312  in the position of control ring  304  shown in  FIG. 9 ) such that working fluid in each discharge recess  308  can enter second discharge port  312 . Alternatively, a second discharge port  312  can be provided in pump housing  104  for the lower instance of discharge recess  308  and another second discharge port (not shown) can be provided in the pump cover for the upper instance of discharge recess  308 . 
     In the illustrated embodiment, secondary passages  316  have been bored through pump housing  104  but, as will be understood by those of skill in the art, secondary passages can be formed in a suitable manner and can be formed in pump housing  104  or the pump cover (not shown). 
     Pressurized working fluid entering discharge recess  308  can exit discharge recess  308  via second discharge port  312  to passage  148 , via secondary passages  316 , to inhibit the formation of high pressure areas adjacent the downstream end  156  of discharge port  140 . Discharge recess  308  and second discharge port  312 , in combination with discharge port  140 , form an enhanced discharge port and, as with pumps  100  and  200 , this enhanced discharge port reduces back torque on rotor  108  and increases the energy efficiency of pump  300 . 
     As shown in  FIG. 10 , pressurized working fluid from discharge port  140  can enter second discharge port  312  and travel through secondary passages  316  to passage  148  and then to pump outlet  144 . 
     The present invention provides a variable displacement vane pump which includes an enhanced discharge port which reduces areas of high pressure in the discharge port which would otherwise occur as the pressurized working fluid reverses its direction of flow to enter the discharge port. By reducing the areas of high pressure, the back torque on the pump rotor is reduced and the energy efficiency of the pump is enhanced. In one embodiment, the pivot for the pump control ring is located radially outwardly from a conventional location, to allow for a discharge recess to be formed in the control ring, adjacent the discharge port, and extending past the pivot to the pump outlet. In a second embodiment, the discharge recess is formed in the control ring around the pivot and a seal is provided on the control ring to inhibit leakage of pressurized working fluid past the control ring. In a third embodiment, a secondary discharge port is provided adjacent the discharge recess formed in the control ring and pressurized working fluid in the discharge recess can exit the discharge recess through the secondary discharge port which is in fluid communication with the pump outlet. 
     The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.