Abstract:
A traditional variable-displacement vane pump is designed to operate at an equilibrium pressure which meets the worst case scenario. Thus, at lower speeds energy will be wasted as the pump will supply working fluid at a greater pressure than is required. A variable capacity vane pump ( 20 ) is provided which has a pump control ring ( 40 ) which is moveable to alter the volumetric displacement of the pump ( 20 ). The pump ring ( 40 ) is moved by at least first and second control chambers ( 76, 80 ), which act on the pump control ring ( 40 ) when pressurized working fluid is supplied to them to move the pump control ring ( 40 ) to alter the volumetric capacity of the pump ( 20 ). When pressurized fluid is supplied to only the first control chamber ( 76 ), the pump operates at a first equilibrium pressure and when pressurized fluid is also supplied to the second chamber ( 80 ), the pump operates at a second equilibrium pressure. If desired, pressurized fluid can also be supplied only to the second control chamber ( 80 ) to operate the pump ( 20 ) at a third equilibrium pressure and/or additional control chambers can be provided if required.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to variable displacement vane pumps. More specifically, the present invention relates to variable displacement vane pumps in which at least two different equilibrium pressures can be selected between by supplying working fluid to two or more control chambers which act against the control ring. 
       BACKGROUND OF THE INVENTION 
       [0002]    Variable displacement vane pumps are well known and can include a displacement adjusting element, in the form of a pump control ring that can be pivoted or moved to alter the rotor eccentricity of the pump and hence alter the volumetric displacement 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 displacement volume of the pump is equivalent to changing the pressure produced by the pump. 
         [0003]    Having the ability to alter the volumetric displacement 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 where the pressure of the working fluid is used to generate a force, either directly or via a moveable piston, to move the control ring, typically against a biasing force from a return spring, to alter the displacement of the pump. 
         [0004]    When the pressure at the output of the pump increases, such as when the operating speed of the pump increases, the increased pressure in the control chamber is applied to the control ring, either directly or via a piston, to overcome the bias of the return spring and to move the control ring to reduce the displacement of the pump, thus reducing the output volume and hence the pressure at the output of the pump. 
         [0005]    Conversely, as the pressure at the output of the pump drops, such as when the operating speed of the pump decreases, the decreased pressure supplied to the control chamber allows the bias of the return spring to move the control ring to increase the displacement 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. 
         [0006]    The equilibrium pressure is determined by the area of the control ring, or piston, 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. 
         [0007]    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, supplying a greater pressure of working fluid than required for those speeds, wasting energy pumping the surplus, unnecessary, working fluid. 
         [0008]    It is desired to have variable displacement vane pumps which can provide at least two selectable equilibrium pressures in a reasonably compact pump housing. 
       SUMMARY OF THE INVENTION 
       [0009]    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. 
         [0010]    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 housing having a rotor chamber therein; a vane pump rotor rotatably mounted in the rotor chamber; a pump control ring enclosing the vane pump rotor within said rotor chamber, the pump control ring being moveable within the rotor chamber to alter the volumetric displacement of the pump; a first control chamber between the pump housing 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 displacement of the pump; a second control chamber operable to receive pressurized fluid to create a force to move the pump control ring to alter the volumetric displacement of the pump; and a biasing spring acting between pump control ring and the pump housing to bias the pump control ring towards a position of maximum volumetric displacement, the biasing spring acting against the force of at least the first control chamber 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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
           [0012]      FIG. 1  is a front view of a variable capacity vane pump in accordance with the present invention; 
           [0013]      FIG. 2  is a front view of another embodiment of a variable capacity vane pump in accordance with the present invention; and 
           [0014]      FIG. 3  is a front view of another embodiment of a variable capacity vane pump in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    A variable capacity vane pump in accordance with an embodiment of the present invention is indicated generally at  20  in  FIG. 1 . Pump  20  includes a pump housing  24  which is sealed with a pump cover (not shown). 
         [0016]    Pump  20  includes a pump rotor  28  rotatably mounted within a rotor chamber  32  and rotor  28  is turned with a drive shaft  34 . A series of slidable pump vanes  36  rotate with rotor  28 , the radially outer end of each vane  36  engaging the inner surface of a pump control ring  40  to divide the volume about rotor  28  into a series of pumping chambers  44 , defined by the inner surface of pump control ring  40 , pump rotor  28  and vanes  36 . 
         [0017]    In the illustrated embodiment, pump control ring  40  is mounted within housing  24  via a pivot pin  48  mounted in housing  24 . It is also contemplated that pump control ring  40  can be pivotally mounted within housing  24  via any other suitable method as will occur to those of skill in the art. 
         [0018]    The pivoting of pump control ring  40  allows the center of pump control ring  40  to be moved relative to the center of rotor  28 . As the center of pump control ring  40  is located eccentrically with respect to the center of pump rotor  28  and each of the interior of pump control ring  40  and pump rotor  28  are circular in shape, the volume of pumping chambers  44  changes as pumping chambers  44  rotate around rotor chamber  32 , with their volume becoming larger at the low pressure side (the left hand side of rotor chamber  32  in  FIG. 1 ) of pump  20  and smaller at the high pressure side (the right hand side of rotor chamber  32  in  FIG. 1 ) of pump  20 . 
         [0019]    This change in volume of pumping chambers  44  generates the pumping action of pump  20 , drawing working fluid from an inlet port (schematically shown) at the low pressure side and pressurizing and delivering the working fluid to an outlet port (schematically shown) at the high pressure side. 
         [0020]    By moving pump control ring  40  about pivot surfaces  48  and  52 , the amount of eccentricity, relative to pump rotor  28 , can be changed to vary the amount by which the volume of pumping chambers  44  changes from the low pressure side of pump  20  to the high pressure side of pump  20 , thus changing the volumetric capacity/displacement of pump  20 . 
         [0021]    Control ring  40  includes a control structure  56  opposite pivot surface  48  from rotor  32 . Control structure  56  includes a spring surface  60  and a biasing spring  64  acts between spring surface  60  and pump housing  24  to bias control ring  40  toward the position of maximum eccentricity/maximum displacement for pump  20 . 
         [0022]    Control structure  56  further includes first and second reaction surfaces,  68  and  72  respectively which, in conjunction with pump housing  24  and resilient seals  52 , form first and second control chambers,  76  and  80  respectively. 
         [0023]    Each of first and second control chambers  76  and  80  can be supplied with pressurized working fluid from pump  20 , either directly from the outlet port of pump  20 , or via a pump control system  21  which is being supplied with pressurized working fluid from pump  20 . Pump control system  21  is a series of valves that can be operated mechanically or electronically in response to input signals, such as engine speed and oil temperature. 
         [0024]    Pressurized working fluid in first control chamber  76  exerts a force on first reaction surface  68  and this force acts against the biasing force of biasing spring  64  to move control ring  40  towards a position wherein the volumetric displacement of pump  20  is reduced. 
         [0025]    Similarly, pressurized working fluid in second control chamber  80  exerts a force on second reaction surface  72  and this force acts against the biasing force of biasing spring  64  to move control ring  40  towards a position wherein the volumetric displacement of pump  20  is reduced. 
         [0026]    As will be apparent to those of skill on the art, the areas of first reaction surface  68  and second reaction surface  72  can differ, such that the same pressure of working fluid in first control chamber  76  can produce a different force on pump control ring  40  than the pressurized working fluid in second control chamber  80 . 
         [0027]    Similarly, first and second reaction surfaces  68  and  72  can be located at different radial distances from the point at which control ring  40  pivots, thus applying the forces generated in first and second control chambers  76  and  80  with different mechanical advantages. In the illustrated embodiment, first reaction surface  68  is radially closer to pivot surfaces  48  and  52  than second reaction surface  72  and thus, if reaction surfaces  68  and  72  are the same size and first and second control chambers  76  and  80  are supplied with the same pressure of working fluid, second reaction surface  72  will counter the biasing force of biasing spring  64  to a greater extent than will first reaction surface  68 . 
         [0028]    As will be apparent to those of skill in the art, if it is desired that each of first and second control chambers  76  and  80  contribute the same amount of movement to control ring  40  for a given pressure, the sizes of first and second reaction surfaces  68  and  72  can be varied from each other to counteract the effects of their different radial distances from the pivot point of control ring  40 . 
         [0029]    In one embodiment, it is contemplated that one of first control chamber  76  and second control chamber  80  will be supplied with pressurized working fluid, through pump control system  21 , from pump  20  while the other of first control chamber  76  and second control chamber  80  will be selectively supplied with pressurized working fluid directly from pump  20 . For the purposes of illustration, second control chamber  80  can be selectively supplied with pressurized working fluid. In such a case, pump  20  is operated with the supply of pressurized working fluid to second control chamber  80  removed, pump  20  operates in a substantially conventional manner with a single equilibrium pressure with the force created on control ring  40  by the pressure of the working fluid in first control chamber  76  acting against the biasing force of biasing spring  64 . 
         [0030]    However, when pressurized working fluid is also supplied to second control chamber  80 , via pump control system  21 , pump  20  will operate at a second, different, equilibrium operating pressure with the force created on control ring  40  by the pressure of the working fluid in second control chamber  76  adding to the force created by the pressurized working fluid in first control chamber  76  and the sum of these forces act against the biasing force of biasing spring  64 . 
         [0031]    It is also contemplated that the supply of pressurized working fluid can be selectively supplied to both of first reaction chamber  76  and second reaction chamber  80 , as illustrated in broken lines to and from pump control system  21 . In such a case, provided that first and second control chambers  76  and  80  produce different forces on control pump ring  40  due to different areas of reaction surfaces  68  and  72  and/or their different radial distances from the pivot point of control ring  40 , pump  20  can be operated through pump control system  21  at a selected one of three different equilibrium pressures by selectively providing pressurized working to fluid to: (i) first control chamber  76 ; (ii) second control chamber  80 ; and (iii) both of first control chamber  76  and second control chamber  80 . 
         [0032]      FIG. 2  shows pump  100  which is another embodiment of the present invention wherein similar components to those of pump  20  of  FIG. 1  are indicated with like reference numerals. Unlike pump  20 , in pump  100  control structure  56  only includes one reaction surface  68  which is part of first control chamber  76 . A second control chamber  104  is provided in pump  100 , but control chamber  104  is formed between the inner surface of pump housing  24  and the portion of pump control ring  40  between pivot pin  48  and a slider  108 . One or both of control chambers  76  and  104  can be selectively supplied, directly or indirectly, with pressurized working fluid from pump  100  to operate pump  100  at any of two, or three, equilibrium operating pressures. 
         [0033]    In the embodiment illustrated in  FIG. 2 , a resilient seal  112  is used to seal one end of control chamber  104  and resilient seal  52  seals the other, as well of one side of control chamber  76 , the other side of which is sealed by a resilient seal  116 . As will be apparent to those of skill in the art, the use of such seals is not required but such seals can provide a manufacturing cost advantage in that relatively expensive machining steps, which would otherwise be required to ensure adequate sealing of control chambers  76  and  104 , can be avoided. 
         [0034]      FIG. 3  shows a pump  200  which is another embodiment of the present invention wherein similar components to those of pump  20  of  FIG. 1  are indicated with like reference numerals. Unlike pump  20 , pump  200  employs a sliding control ring  204  instead of a pivoting control ring. As shown, control ring  204  includes reaction surface  60  and a biasing spring  64  acts between pump housing  24  and reaction surface  60  to bias control ring  204  to the maximum eccentricity/maximum displacement position. Control ring  204  further includes two reaction surfaces  68  and  72  which serve as a moveable portion of control chambers  76  and  80  respectively. 
         [0035]    As illustrated, control ring  204  is sealed with resilient seals  212 . As mentioned above, the use of such seals is not required but such seals can provide a manufacturing cost advantage in that relatively expensive machining steps, which would otherwise be required to ensure adequate sealing of control ring  204  with respect to control chambers  76  and  80 , etc. can be avoided. 
         [0036]    In operation, one or both of control chambers  76  and  80  can be selectively supplied, directly or indirectly, with pressurized working fluid from pump  200  to operate pump  200  at any of two, or three, equilibrium operating pressures. The method of selectively supplying pressurized working fluid from pump  200  to control chambers  76  and  80  is not particularly limited and can comprise a mechanical or solenoid operated valve etc. If it is desired to operate at pump  200  at a selectable one of two equilibrium pressures, it is contemplated that one of control chambers  76  or  80  can be always connected, directly or indirectly, to the outlet of pump  200  while the other of control chambers  76  and  80  will selectively be supplied with pressurized working fluid. When the other of control chambers  76  and  80  is selectively supplied with pressurized working fluid, the force created on the respective reaction surface in that control chamber adds to the force created on the reaction surface of the other control chamber to further slide control ring  204  towards biasing spring  64 , further reducing the displacement of pump  200 . 
         [0037]    As will be apparent to those of skill in the art, the sizes and locations of reaction surfaces  60 ,  68  and  72  and control chambers  76  and  80  can be altered, as required, to meet a particular requirement for pump  200 . For example, control chambers  76  and/or  80  can be repositioned to better counter and/or reduce reaction forces exerted on pump control ring  204  during operation of pump  200 . Further, additional resilient seals can be employed, as necessary, to provide additional sealing. 
         [0038]    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.