Abstract:
A variable capacity vane pump includes a pump casing having a pump chamber with an inlet and an outlet port. A pump control ring is moveable within the pump chamber to alter the capacity of the pump. A vane pump rotor is rotatably mounted within the pump control ring and includes a plurality of slidably mounted vanes engaging the inside surface of the pump control ring. First and second control chambers between the pump casing and the pump control ring are operable to receive pressurized fluid to urge the pump control ring to reduce the volumetric capacity of the pump. A return spring biases the pump ring toward a position of maximum volumetric capacity against the force of the first and second control chambers to establish an equilibrium pressure. The supply of pressurized fluid to the second control chamber may be varied to change the equilibrium pressure of the pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/CA05/01946 which has an international filing date of Dec. 21, 2005, which designated the United States of America, which application claims the benefit of U.S. Provisional Application No. 60/639,185 filed on Dec. 22, 2004. The entire disclosure of each of the above applications is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a variable capacity vane pump. More specifically, the present invention relates to a variable capacity vane pump in which at least two different equilibrium pressures can be selected between by supplying working fluid to two or more control chambers adjacent the control ring. 
   BACKGROUND OF THE INVENTION 
   Variable capacity vane pumps are well known and can include a capacity adjusting element, in the form of a pump control ring that can be moved to alter the rotor eccentricity of the pump and hence alter the volumetric capacity of the pump. If the pump is supplying a system with a substantially constant orifice size, such as an automobile engine lubrication system, changing the output volume of the pump is equivalent to changing the pressure produced by the pump. 
   Having the ability to alter the volumetric capacity of the pump to maintain an equilibrium pressure is important in environments such as automotive lubrication pumps, wherein the pump will be operated over a range of operating speeds. In such environments, to maintain an equilibrium pressure it is known to employ a feedback supply of the working fluid (e.g. lubricating oil) from the output of the pump to a control chamber adjacent the pump control Ting, the pressure in the control chamber acting to move the control ring, typically against a biasing force from a return spring, to alter the capacity of the pump. 
   When the pressure at the output of the pump increases, such as when the operating speed of the pump increases, the increased pressure is applied to the control ring to overcome the bias of the return spring and to move the control ring to reduce the capacity of the pump, thus reducing the output volume and hence the pressure at the output of the pump. 
   Conversely, as the pressure at the output of the pump drops, such as when the operating speed of the pump decreases, the decreased pressure applied to the control chamber adjacent the control ring allows the bias of the return spring to move the control ring to increase the capacity of the pump, raising the output volume and hence pressure of the pump. In this manner, an equilibrium pressure is obtained at the output of the pump. 
   The equilibrium pressure is determined by the area of the control ring against which the working fluid in the control chamber acts, the pressure of the working fluid supplied to the chamber and the bias force generated by the return spring. 
   Conventionally, the equilibrium pressure is selected to be a pressure which is acceptable for the expected operating range of the engine and is thus somewhat of a compromise as, for example, the engine may be able to operate acceptably at lower operating speeds with a lower working fluid pressure than is required at higher engine operating speeds. In order to prevent undue wear or other damage to the engine, the engine designers will select an equilibrium pressure for the pump which meets the worst case (high operating speed) conditions. Thus, at lower speeds, the pump will be operating at a higher capacity than necessary for those speeds, wasting energy pumping the surplus, unnecessary, working fluid. 
   It is desired to have a variable capacity vane pump which can provide at least two selectable equilibrium pressures in a reasonably compact pump housing. It is also desired to have a variable capacity vane pump wherein reaction forces on the pivot pin for the pump control ring are reduced. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a novel variable capacity 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 capacity vane pump having a pump control ring which is moveable to alter the capacity of the pump, the pump being operable at least two selected equilibrium pressures, comprising: a pump casing having a pump chamber therein; a vane pump rotor rotatably mounted in the pump chamber; a pump control ring enclosing the vane pump rotor within said pump chamber, the control pump ring being moveable within the pump chamber to alter the capacity of the pump; a first control chamber between the pump casing and the pump control ring, the first control chamber operable to receive pressurized fluid to create a force to move the pump control ring to reduce the volumetric capacity of the pump; a second control chamber between the pump casing and the pump control ring, the second control chamber operable to receive pressurized fluid to create a force to move the pump control ring to reduce the volumetric capacity of the pump; and a return spring acting between pump ring and the casing to bias the pump ring towards a position of maximum volumetric capacity, the return spring acting against the force of the first and second control chambers to establish an equilibrium pressure and wherein the supply of pressurized fluid to the second control chamber can be applied or removed to change the equilibrium pressure of the pump. 
   According to a second aspect of the present invention, there is provided a variable capacity vane pump comprising: a pump casing having a pump chamber therein; a vane pump rotor rotatably mounted in the pump chamber; a pump control ring enclosing the vane pump rotor within said pump chamber, the control pump ring being moveable about a pivot pin within the pump chamber to alter the capacity of the pump; a control chamber defined between the pump casing, the pump control ring, the pivot pin and a resilient seal between the pump control ring and the pump casing, the control chamber being operable to receive pressurized fluid to create a force to move the pump control ring to reduce the volumetric capacity of the pump; and a return spring acting between pump ring and the casing to bias the pump ring towards a position of maximum volumetric capacity, the return spring acting against the force of the control chamber to establish an equilibrium pressure and wherein the pivot pin and the resilient seal are positioned to reduce the area of the pump control ring within the control chamber such that the resulting force on the pump control ring exerted by pressurized fluid in the control chamber is reduced. 
   Preferably, the return spring is oriented such that the biasing force it applies to the pump control ring farmer reduces the reaction forces on the pivot pin. Also preferably, the control chamber is positioned, with respect to the pivot pin, such that the resulting force reduces reaction forces on the pivot pin. 

   
     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  is a front view of a variable capacity vane pump in accordance with the present invention with the control ring positioned for maximum rotor eccentricity, 
       FIG. 2  is a front perspective view of the pump of  FIG. 1  with the control ring positioned for maximum rotor eccentricity; 
       FIG. 3  is the a front view of the pump of  FIG. 1  with the control ring position for minimum eccentricity and wherein the areas of the pump control chambers are in hatched line; 
       FIG. 4  shows a schematic representation of a prior art variable capacity vane pump; and 
       FIG. 5  shows a front view of the pump of  FIG. 1  wherein the rotor and vanes have been removed to illustrate the forces within the pump. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A variable capacity vane pump in accordance with an embodiment of the present invention is indicated generally at  20  in  FIGS. 1 ,  2  and  3 . 
   Referring now to  FIGS. 1 ,  2  and  3 , pump  20  includes a housing or casing  22  with a front face  24  which is sealed with a pump cover (not shown) and a suitable gasket, to an engine (not shown) or the like for which pump  20  is to supply pressurized working fluid. 
   Pump  20  includes a drive shaft  28  which is driven by any suitable means, such as the engine or other mechanism to which the pump is to supply working fluid, to operate pump  20 . As drive shaft  28  is rotated, a pump rotor  32  located within a pump chamber  36  is turned with drive shaft  28 . A series of slidable pump vanes  40  rotate with rotor  32 , the outer end of each vane  40  engaging the inner surface of a pump control ring  44 , which forms the outer wall of pump chamber  36 . Pump chamber  36  is divided into a series of working fluid chambers  48 , defined by the inner surface of pump control ring  44 , pump rotor  32  and vanes  40 . The pump rotor  32  has an axis of rotation that is eccentric from the center of the pump control ring  44 . 
   Pump control ring  44  is mounted within casing  22  via a pivot pin  52  which allows the center of pump control ring  44  to be moved relative to the center of rotor  32 . As the center of pump control ring  44  is located eccentrically with respect to the center of pump rotor  32  and each of the interior of pump control ring  44  and pump rotor  32  are circular in shape, the volume of working fluid chambers  48  changes as the chambers  48  rotate around pump chamber  36 , with their volume becoming larger at the low pressure side (the left hand side of pump chamber  36  in  FIG. 1 ) of pump  20  and smaller at the high pressure side (the right hand side of pump chamber  36  in  FIG. 1 ) of pump  20 . This change in volume of working fluid chambers  48  generates the pumping action of pump  20 , drawing working fluid from an inlet port  50  and pressurizing and delivering it to an outlet port  54 . 
   By moving pump control ring  44  about pivot pin  52  the amount of eccentricity, relative to pump rotor  32 , can be changed to vary the amount by which the volume of working fluid chambers  48  change from the low pressure side of pump  20  to the high pressure side of pump  20 , thus changing the volumetric capacity of the pump. A return spring  56  biases pump control ring  44  to the position, shown in  FIGS. 1 and 2 , wherein the pump has a maximum eccentricity. 
   As mentioned above, it is known to provide a control chamber adjacent a pump control ring and a return spring to move the pump ring of a variable capacity vane pump to establish an equilibrium output volume, and its related equilibrium pressure. 
   However, in accordance with the present invention, pump  20  includes two control chambers  60  and  64 , best seen in  FIG. 3 , to control pump ring  44 . Control chamber  60 , the rightmost hatched area in  FIG. 3 , is formed between pump casing  22 , pump control ring  44 , pivot pin  52  and a resilient seal  68 , mounted on pump control ring  44  and abutting casing  22 . In the illustrated embodiment, control chamber  60  is in direct fluid communication with pump outlet  54  such that pressurized working fluid from pump  20  which is supplied to pump outlet  54  also fills control chamber  60 . 
   As will be apparent to those of skill in the art, control chamber  60  need not be in direct fluid communication with pump outlet  54  and can instead be supplied from any suitable source of working fluid, such as from an oil gallery in an automotive engine being supplied by pump  20 . 
   Pressurized working fluid in control chamber  60  acts against pump control ring  44  and, when the force on pump control ring  44  resulting from the pressure of the pressurized working is sufficient to overcome the biasing force of return spring  56 , pump control ring  44  pivots about pivot pin  52 , as indicated by arrow  72  in  FIG. 3 , to reduce the eccentricity of pump  20 . When the pressure of the pressurized working is not sufficient to overcome the biasing force of return spring  56 , pump control ring  44  pivots about pivot pin  52 , in the direction opposite to that indicated by arrow  72 , to increase the eccentricity of pump  20 . 
   Pump  20  further includes a second control chamber  64 , the leftmost hatched area in  FIG. 3 , which is formed between pump casing  22 , pump control ring  44 , resilient seal  68  and a second resilient seal  76 , Resilient seal  76  abuts the wall of pump casing  22  to separate control chamber  64  from pump inlet  50  and resilient seal  68  separates chamber  64  from chamber  60 . Control chamber  60  extends circumferentially from pivot pin  52  to resilient seal  68  an amount identified as angle A in  FIG. 3 . Angle A is less than 90 degrees and substantially 80 degrees. Control chamber  64  extends from resilient seal  68  to second resilient seal  76 . An angle B depicts the total number of degrees swept by both control chamber  60  and control chamber  64 . Angle B is less than the 180 degree value of the prior art as shown in  FIGS. 3 and 4 . Angle B is substantially 135 degrees. 
   Control chamber  64  is supplied with pressurized working fluid through a control port  80 . Control port  80  can be supplied with pressurized working fluid from any suitable source, including pump outlet  54  or a working fluid gallery in the engine or other device supplied from pump  20 . A control mechanism  81  such as a solenoid operated valve or diverter mechanism is employed to selectively supply working fluid to chamber  64  through control port  80 , as discussed below. As was the case with control chamber  60 , pressurized working fluid supplied to control chamber  64  from control port  80  acts against pump control ring  44 . 
   As should now be apparent, pump  20  can operate in a conventional manner to achieve an equilibrium pressure as pressurized working fluid supplied to pump outlet  54  also fills control chamber  60 . When the pressure of the working fluid is greater than the equilibrium pressure, the force created by the pressure of the supplied working fluid over the portion of pump control ring  44  within chamber  60  will overcome the force of return spring  56  to move pump ring  44  to decrease the volumetric capacity of pump  20 . Conversely, when the pressure of the working fluid is less than the equilibrium pressure, the force of return spring  56  will exceed the force created by the pressure of the supplied working fluid over the portion of pump control ring  44  within chamber  60  and return spring  56  will to move pump ring  44  to increase the volumetric capacity of pump  20 . 
   However, unlike with conventional pumps, pump  20  can be operated at a second equilibrium pressure. Specifically, by selectively supplying pressurized working fluid to control chamber  64 , via control port  80 , a second equilibrium pressure can be selected. For example, a solenoid-operated valve controlled by an engine control system, can supply pressurized working fluid to control chamber  64 , via control port  80 , such that the force created by the pressurized working fluid on the relevant area of pump control ring  44  within chamber  64  is added to the force created by the pressurized working fluid in control chamber  60 , thus moving pump control ring  44  further than would otherwise be the case, to establish a new, lower, equilibrium pressure for pump  20 . 
   As an example, at low operating speeds of pump  20 , pressurized working fluid can be provided to both chambers  60  and  64  and pump ring  44  will be moved to a position wherein the capacity of the pump produces a first, lower, equilibrium pressure which is acceptable at low operating speeds. 
   When pump  20  is driven at higher speeds, the control mechanism can operate to remove the supply of pressurized working fluid to control chamber  64 , thus moving pump ring  44 , via return spring  56 , to establish a second equilibrium pressure for pump  20 , which second equilibrium pressure is higher than the first equilibrium pressure. 
   While in the illustrated embodiment chamber  60  is in fluid communication with pump outlet  54 , it will be apparent to those of skill in the art that it is a simple matter, if desired, to alter the design of control chamber  60  such that it is supplied with pressurized working fluid from a control port, similar to control port  80 , rather than from pump outlet  54 . In such a case, a control mechanism (not shown) such as a solenoid operated valve or a diverter mechanism can be employed to selectively supply working fluid to chamber  60  through the control port. As the area of control ring  44  within each of control chambers  60  and  64  differs, by selectively applying pressurized working fluid to control chamber  60 , to control chamber  64  or to both of control chambers  60  and  64  three different equilibrium pressures can be established, as desired. 
   As will also be apparent to those of skill in the art, should additional equilibrium pressures be desired, pump casing  22  and pump control ring  44  can be fabricated to form one or more additional control chambers, as necessary. 
   Pump  20  offers a further advantage over conventional vane pumps such as pump  200  shown in  FIG. 4 . In conventional vane pumps such as pump  200 , the low pressure fluid  204  in the pump chamber exerts a force on pump ring  216  as does the high pressure fluid  208  in the pump chamber. These forces result in a significant net force  212  on the pump control ring  216  and this force is largely carried by pivot pin  220  which is located at the point where force  212  acts. 
   Further, the high pressure fluid within the outlet port  224  (indicated in dashed line), acting over the area of pump ring  216  between pivot pin  220  and resilient seal  222 , also results in a significant force  228  on pump control ring  216 . While force  228  is somewhat offset by the force  232  of return spring  236 , the net of forces  228  less force  232  can still be significant and this net force is also largely carried by pivot pin  220 . 
   Thus pivot pin  220  carries large reaction forces  240  and  244 , to counter net forces  212  and  228  respectively, and these forces can result in undesirable wear of pivot pin  220  over time and/or “stiction” of pump control ring  216 , wherein it does not pivot smoothly about pivot pin  220 , making fine control of pump  200  more difficult to achieve. 
   As shown in  FIG. 5 , the low pressure side  300  and high pressure side  304  of pump  20  result in a net force  308  which is applied to pump control ring  44  almost directly upon pivot pin  52  and a corresponding reaction force, shown as a horizontal (with respect to the orientation shown in the Figure) force  312 , is produced on pivot pin  52 . Unlike conventional variable capacity vane pumps such as pump  200 , in pump  20  resilient seal  68  is located relatively closely to pivot pin  52  to reduce the area of pump control ring  44  upon which the pressurized working fluid in control chamber  60  acts and thus to significantly reduce the magnitude of the force  316  produced on pump control ring  44 . 
   Further, control chamber  60  is positioned such that force  316  includes a horizontal component, which acts to oppose force  308  and thus reduce reaction force  312  on pivot pin  52 . The vertical (with respect to the orientation shown in the Figure) component of force  316  does result in a vertical reaction force  320  on pivot pin  52  but, as mentioned above, force  316  is of less magnitude than would be the case with conventional pumps and the vertical reaction force  320  is also reduced by a vertical component of the biasing force  324  produced by return spring  56   
   Thus, the unique positioning of control chamber  60  and return spring  56 , with respect to pivot pin  52 , results in reduced reaction forces on pivot pin  52  and can improve the operating lifetime of pump  20  and can reduce “stiction” of pump control ring  44  to allow smoother control of pump  20 . As will be apparent to those of skill in the art, this unique positioning is not limited to use in variable capacity vane pumps with two or more equilibrium pressures and can be employed with variable capacity vane pumps with single equilibrium pressures. 
   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.