Abstract:
A vane pump ( 20 ) is provided which has an output pressure hat can be selected from a continuous range of pressures, independent of the operating speed of the pump. The pump has first ( 68 ) and second ( 72 ) control chambers which create opposed forces on the pump control ring ( 40 ) to selectively move the pump control ring ( 40 ) between maximum displacement and minimum displacement positions. In one embodiment, the control chamber ( 68 ) which urges the ump control ring to the minimum displacement position is continually supplied with pressurized working fluid during operation of the ump while the control chamber ( 72 ) which urges the pump control ring to the maximum displacement position can selectively be supplied with pressurized working fluid, isolated, or can be relieved of pressurized working fluid to alter the displacement of the pump.

Description:
FIELD OF THE INVENTION 
     The present invention relates to variable displacement vane pumps. More specifically, the present invention relates to a variable displacement vane pump and system whose output pressure is continuously variable and which can be selected independent of the operating speed of the pump. 
     BACKGROUND OF THE INVENTION 
     Mechanical systems, such as internal combustion engines and automatic transmissions, typically include a lubrication pump to provide lubricating oil, under pressure, to many of the moving components and/or subsystems of the mechanical systems. In most cases, the lubrication pump is driven by a mechanical linkage to the mechanical system and thus the operating speed, and output, of the pump varies with the operating speed of the mechanical system. While the lubrication requirements of the mechanical system also vary with the operating speed of the mechanical system, unfortunately the relationship between the variation in the output of the pump and the variation of the lubrication requirements of the mechanical system is generally nonlinear. The difference in these requirements is further exacerbated when temperature related variations in the viscosity and other characteristics of the lubricating oil and mechanical system are factored in. 
     To deal with these differences, prior art fixed displacement lubricating pumps were generally designed to operate safely and effectively at high, or maximum, oil temperatures, resulting in an oversupply of lubricating oil at most mechanical system operating conditions and a waste, or pressure relief, valve was provided to “waste” the surplus lubricating oil back into the pump inlet or oil sump to avoid over pressure conditions in the mechanical system. In some operating conditions such as low oil temperatures, the overproduction of pressurized lubricating oil can be 500% of the mechanical system&#39;s needs so, while such systems work reasonably well, they do result in a significant energy loss as energy is used to pressurize the unneeded lubricating oil which is then “wasted” through the relief valve. 
     More recently, variable displacement vane pumps have been employed as lubrication oil pumps. Such pumps generally include a control ring, or other mechanism, which can be operated to alter the volumetric displacement of the pump and thus its output at an operating speed. Typically, a feedback mechanism, in the form of a piston in a control chamber or a control chamber acting directly upon the control ring, is supplied with pressurized lubricating oil from the output of the pump, either directly or via an oil gallery in the mechanical system, alters the displacement of the pump to operate the pump to avoid over pressure situations in the engine throughout the expected range of operating conditions of the mechanical system. An example of such a variable displacement pump is shown in U.S. Pat. No. 4,342,545 to Schuster. 
     While such variable displacement pumps provide some improvements in energy efficiency over fixed displacement pumps, they still result in a significant energy loss as their displacement is controlled, directly or indirectly, by the output pressure of the pump which changes with the operating speed of the mechanical system, rather than with the changing requirements of the lubrication system. Accordingly, such variable displacement pumps must still be designed to provide oil pressures which meet the highest expected mechanical system requirements, despite operating temperatures and other variables, even when the mechanical system operating conditions normally do not necessitate such high requirements. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel vane pump with continuously variable pressure control 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 vane pump with continuously variable output pressure, comprising: a variable displacement vane pump having a pump control ring which is moveable to alter the displacement of the pump; a first control chamber operable to create a force on the pump control ring to urge the pump control ring towards the position of minimum displacement, the force resulting from pressurized working fluid in the first control chamber; a second control chamber operable to create a force on the pump control ring to urge the pump control ring towards the position of maximum displacement, the force resulting from pressurized working fluid in the second control chamber; a control means operable to vary supply of pressurized working fluid to at least one of the first and second control chambers to vary the displacement of the pump during operation of the pump to achieve an output pressure selected from a continuously variable range of output pressures from the pump which are independent from the operating speed of the pump. 
     According to another aspect of the present invention, there is provided a vane pump to supply pressurized working fluid to a mechanical system, the output pressure being selected from a continuously variable range of output pressures from the pump which are independent of the operating speed of the pump, comprising: a variable displacement vane pump having a pump control ring which is moveable to alter the displacement of the pump; a first control chamber operable to receive working fluid pressurized by the pump to create a force to urge the pump control ring towards the position of minimum displacement; a biasing spring to urge the pump control ring towards the maximum displacement position; a second control chamber operable to receive working fluid pressurized by the pump to create a force to urge the pump control ring towards the position of maximum displacement; a control means operable to vary the supply of pressurized working fluid to at least one of the first and second control chambers to vary the displacement of the pump during operation of the pump to achieve an output pressure selected from a continuously variable range of output pressures from the pump which are independent from the operating speed of the pump; and a third control chamber operable to continuously receive working fluid pressurized by the operation of the pump to create a force on the pump control ring to oppose the force of the biasing spring, the third control chamber and the biasing spring providing a failsafe function should a failure occur in the control means, the first control chamber or the second control chamber. 
     The present invention provides a vane pump whose output pressure can be selected from a continuous range of pressures, independent of the operating speed of the pump. The pump includes at least first and second control chambers which create opposed forces on the pump control ring to selectively move the pump control ring between maximum displacement and minimum displacement positions. In one embodiment, the control chamber which urges the pump control ring to the minimum displacement position is continually supplied with pressurized working fluid during operation of the pump while the control chamber which urges the pump control ring to the maximum displacement position can selectively be supplied with pressurized working fluid, isolated or can be relieved of pressurized working fluid to alter the displacement of the pump as desired. In another embodiment, each control chamber can be selectively supplied with pressurized working fluid, isolated or can be relieved of pressurized working fluid to alter the displacement of the pump as desired. In another embodiment, three control chambers are employed, the third control chamber being continuously supplied with working fluid pressurized during operation of the pump, the third control chamber acting against the force of the biasing spring to provide a failsafe function should a failure occur in the first or second control chambers or with the selective supply, isolation or relief of the first or second control chambers. Both pivoting pump control ring and sliding pump control ring embodiments are disclosed. 
    
    
     
       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 an example of a plot of the oil pressure demand of a mechanical system versus the output of a prior art lubricating pump; 
         FIG. 2  shows a plot of the oil pressure demand of a mechanical system versus the output of a variable displacement vane pump system with two equilibrium pressure operating points; 
         FIG. 3  shows a vane pump whose output pressure is selectable from a continuous range of pressures in accordance with the present invention; 
         FIG. 4  shows a vane pump whose output pressure is selectable from a continuous range of pressures with a failsafe function in accordance with the present invention; 
         FIG. 5  shows a plot of the oil pressure demand of a mechanical system versus the output of the continuously variable displacement vane pump and system of  FIG. 4 ; 
         FIG. 6  shows another embodiment of a vane pump whose output pressure is selectable from a continuous range of pressures in accordance with the present invention; and 
         FIG. 7  shows another embodiment of a vane pump whose output pressure is selectable from a continuous range of pressures in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a typical plot of the lubricating oil pressure requirement (shown in solid line) of a mechanical system, such as a typical internal combustion engine, versus the output (shown in dashed line) of a prior art variable displacement pump, such as the pump taught in the above-mentioned Schuster patent. The corner on the output (dashed line) results from the movement of the control slide by the control piston to reduce the displacement of the pump as the output of the pump reaches a preset value. The shaded area between the engine demand curve and the pump output curve represents the engine operating conditions wherein energy is lost as the pump pressure output exceeds engine demand. 
     More recently, a variable displacement vane pump has been developed, as described in co-pending U.S. Provisional Patent Application 60/763,720, entitled, “Variable Displacement Variable Pressure Vane Pump System”, filed Jan. 31, 2006 and assigned to the assignee of the present invention, in which a two step adjustment of the output pressure of the pump can be obtained to reduce the energy loss in the pump by more closely matching the output pressure of the pump to the requirements of the mechanical system.  FIG. 2  shows a plot, similar to that of  FIG. 1 , illustrating an improvement obtained with that Variable Displacement Variable Pressure Vane Pump System invention. 
     However, as is still apparent from  FIG. 2 , energy is still wasted pumping working fluid that is not required by the mechanical system, as represented by the shaded area of the plot. 
       FIG. 3  shows a pump system and vane pump  20  in accordance with the present invention and pump  20  has a continuously variable pressure control system. 
     Specifically, pump  20  includes a pump housing  24  and a pump rotor  28  rotatably mounted within a rotor chamber  32  in housing  24 . Rotor  28  is turned, clockwise in the illustrated embodiment, with a drive shaft  34  and 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 . 
     In the illustrated embodiment, pump control ring  40  is mounted within housing  24  via a pivot pin  48 . It is also contemplated that pump control ring  40  can be pivotally mounted within housing  24  via a pivot surface (not shown) or via any other suitable means as will occur to those of skill in the art. 
     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. 3 ) of pump  20  and smaller at the high pressure side (the right hand side of rotor chamber  32  in  FIG. 3 ) of pump  20 . 
     This change in volume of pumping chambers  44  generates the pumping action of pump  20 , drawing working fluid from an inlet port  54  at the low pressure side and pressurizing and delivering the working fluid to an outlet port  56  at the high pressure side. 
     By moving pump control ring  40  about pivot pin  48 , 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 . 
     Control ring  40  includes a control structure  60 , opposite pivot pin  48  from rotor  32 , which is received in a recess  64 , formed in pump housing  24 . 
     Control structure  60  divides recess  64  into two opposed control chambers  68  and  72  which can selectively be: connected to a source  76  of pressurized working fluid; a return line  80  to a working fluid sump  84 ; or isolated to maintain the pressurized working fluid in control chambers  68  and  72 . 
     In the illustrated embodiment, source  76  of pressurized working fluid is a gallery in the mechanical system  88  being supplied with pressurized working fluid from pump outlet  56  but, it will be apparent to those of skill in the art that source  76  can be any direct or indirect connection to outlet  56  of pump  20 . 
     Pump control ring  40  further includes a reaction surface  92  and a biasing spring  96  which acts between pump housing  24  and reaction surface  92  to bias pump control ring  40  to the maximum displacement position. Unlike conventional variable displacement vane pumps, in the illustrated embodiment of pump  20  biasing spring  96  is only intended to provide sufficient biasing force on pump control ring  40  to return pump control ring  40  to the maximum displacement position for start up of pump  20  and regulation of the displacement of pump  20  during operation is achieved with opposed control chambers  68  and  72 , as described below. The forces generated on pump control ring  40  by control chamber  68  during operation of pump  20  are significantly larger than the biasing force generated by biasing spring  96 . It is contemplated that biasing spring  96  can be omitted, if desired, and pump control ring  40  moved to the maximum displacement position at start up of pump  20  solely by the force created in control chamber  72  by pressurized working fluid, although it is presently preferred that biasing spring  96  be included to improve the start up performance of pump  20 . 
     As mentioned above, opposed control chambers  68  and  72  can selectively be isolated or one of control chambers  68  and  72  can be selectively connected to source  76  while the other of control chambers  68  and  72  is connected to return line  80 . The isolation and connection of control chambers  68  and  72  to source  76  and/or return line  80  is achieved by a switching modulator  100 . As described further below, switching modulator  100  can be operated in a variety of manners to control the pressure of the working fluid in control chambers  68  and  72 . 
     As should now be apparent to those of skill in the art, by applying pressurized working fluid to control chamber  68  and connecting control chamber  72  to return line  80 , pump control ring  40  will be moved towards the minimum displacement position. Similarly, by applying pressurized working fluid to control chamber  72  and connecting control chamber  68  to return line  80 , pump control ring  40  will be moved towards the maximum displacement position. 
     Further, by isolating both of control chambers  68  and  72  from both supply  76  and return line  80 , a hydraulic lock can be achieved for a period of time, to maintain pump control ring  40  at any desired position between the maximum and minimum displacement positions. If the hydraulic lock degrades, or is lost, over some period of time while pump  20  is operating, due to leaking, seepage, etc., the hydraulic lock can be re-established by connecting either or both of control chambers  68  and  72 , via switching modulator  100 , to supply  76  as necessary. 
     By operating switching modulator  100  accordingly, the volumetric displacement of pump  20  can be adjusted to very closely match the output of pump  20  to the specific requirements for the mechanical system  88  supplied by pump  20  or to any other performance profile which may be desired. 
     In one embodiment of the present invention, switching modulator  100  is electrically operated and a microcontroller, such as the Engine Control Module (not shown) of an internal combustion engine provides the necessary control signals to switching modulator  100 . In such a case, the Engine Control Module (ECM) can monitor the pressure of the working fluid supplied by pump  20  and can compare that pressure to a desired value of pressure for the corresponding engine operating conditions (RPM, coolant temperature, etc.) of the engine. 
     If the pressure of the working fluid is greater than the required operating pressure, the ECM will operate switching modulator  100  to supply pressurized fluid to control chamber  68  and to connect control chamber  72  to return line  80  such that pump control ring  40  is moved to reduce the volumetric displacement of pump  20 . Once the ECM determines that the output pressure has been reduced to be substantially at the required operating pressure, the ECM will control switching modulator  100  configure both of chambers  68  and  76  to establish a hydraulic lock to maintain pump control ring  40  in the desired position. 
     Conversely, if the pressure of the working fluid is less than the required operating pressure, the ECM will operate switching modulator  100  to supply pressurized fluid to control chamber  72  and to connect control chamber  68  to return line  80  such that pump control ring  40  is moved to increase the volumetric displacement of pump  20 . Once the ECM determines that the output pressure has been increased to be substantially at the required operating pressure, the ECM will control switching modulator  100  to again isolate both of control chambers  68  and  72 , effectively locking pump control ring  40  in the desired position. 
     As will be apparent to those of skill in the art, the ECM, or other control system, can compare the actual pressure of working fluid from pump  20  to a determined required pressure at regular intervals and make adjustments to the pressure of the working fluid in control chambers  68  and  72 , and hence the position of pump control ring  40 , as appropriate. While it is presently preferred that a microcontroller-based control system be used with switching modulator  100 , it is contemplated that other control modalities can also be employed if desired, including control systems employing mechanical or hydraulic control mechanisms. 
       FIG. 4  shows another embodiment of a pump system and vane pump  150  in accordance with the present invention wherein similar components to those of pump  20  are indicated with like reference numerals. In pump  150 , a third control chamber  154  is provided and is connected, either directly or indirectly, to source  76  of pressurized working fluid. As should be apparent to those of skill in the art, third control chamber  154  and biasing spring  96  which, unlike in pump  20  must be present in pump  150 , mimic conventional variable displacement pumps which operate with single equilibrium pressure points and thus provide a failsafe function should a failure occur in switching modulator  100 , control chambers  68  or  72 , etc. 
     The area of third control chamber  154  over which the pressurized working fluid acts and the spring force of biasing spring  96  are selected to provide a conventional equilibrium operating pressure curve, such as that illustrated in  FIG. 5  when the pump is operating in failsafe mode. In this manner, a failure of the continuously variable displacement components, such as switching modulator  100  or chambers  68  or  72 , will result in pump  150  operating in failsafe mode wherein it operates as a conventional pump with a single equilibrium operating pressure, thus avoiding potential damage to mechanical system  88 . 
     When switching modulator  100  and control chambers  68  and  72  are functioning normally, pressurized working fluid can be supplied to control chamber  72  to add to the force of biasing spring  96  and counter the force produced in control chamber  154 . Alternatively, pressurized working fluid can be supplied to control chamber  68  to add to the force produced in control chamber  154  and to counter the force of biasing spring  96 . When pump  150  is operating with pump control ring  40  positioned to achieve a desired displacement, pressurized working fluid can be supplied to each of chambers  68  and  72 , or chambers  68  and  72  can be isolated from each of supply  76  and return line  80 , to substantially lock pump control ring  40  in that position until it is desired to change the displacement of pump  150 . 
       FIG. 5  shows a plot of the operation of pump  150  versus the working fluid pressure requirements of a mechanical system  88 . Curve  156  represents the output of pump  150  in failsafe mode, curve  160  represents the working fluid requirements of mechanical system  88  and curve  164  represents the actual output pressure of pump  150  when operating in non-failsafe mode. The shaded portion between curves  160  and  164  represents the energy “wasted” in the system and can be larger or smaller depending upon the sensitivity of the control system employed to control switching modulator  100  and/or the responsiveness of switching modulator  100 . The stippled area between curve  156  and curve  164  represents the energy saved by pump  150  compared to a conventional variable displacement pump with a single equilibrium operating point. As will be apparent to those of skill in the art, if desired, pump  150  can be operated at conditions corresponding to any location within the stippled area, if desired, by altering the control of switching modulator  100 . 
       FIG. 6  shows another embodiment of a pump system and vane pump  200  in accordance with the present invention wherein similar components to those of pump  20  are indicated with like reference numerals. In pump  200 , pump control ring  204  slides, rather than pivots, to alter the rotor eccentricity and hence the volumetric displacement of pump  200 . As was the case with pump  20 , biasing spring  96  can be provided to bias control ring  204  to the maximum displacement position for start up of pump  200 . In pump  200 , control chambers  68  and  72  are located on opposite sides of pump control ring  204  and pressurized working fluid in control chamber  68  will urge pump control ring  204  towards the minimum displacement position while pressurized working fluid in control chamber  72  will urge pump control ring  204  to the maximum displacement position. 
     While pump  200  can be connected to a similar switching modulator  100  as pump  20 , in the illustrated embodiment, pump  200  is controlled via a simplified control valve  208 . As shown, control chamber  68  is connected to outlet port  56  of pump  200  and, in the particular illustrated embodiment, this is an indirect connection  212  through a gallery or similar feature of mechanical system  88 . Thus, control chamber  68  is continually supplied with pressurized working fluid from pump outlet  56  when pump  200  is operating. 
     In contrast, control chamber  72  can be selectively supplied with pressurized working fluid from pump outlet  56  or can be isolated to maintain the pressure on chamber  72  or can be connected to return line  80  to relieve the pressure in chamber  72 . 
     As will now be apparent, the volumetric displacement of pump  200 , and hence the pressure of the working fluid it supplies to mechanical system  88 , can be altered as required during operation of pump  200  by selectively applying and relieving pressurized working fluid in control chamber  72  via control valve  208 , or can be maintained, during unchanging operating conditions, by isolated chamber  72  from supply  76  and return line  80 . 
     As the supply of pressurized working fluid is always applied to control chamber  68 , it is preferred that the pressurized working fluid in control chamber  72  act over a larger area than the area of control chamber  68  to ensure that sufficient force can be developed in control chamber  72  to move pump control ring  204  against the force created in control chamber  68 , especially if biasing spring  96  is omitted. 
     While pump  200  has been shown with simplified control valve  208  and with control chamber  68  continually supplied with pressurized working fluid, it should be apparent to those of skill in the art that pumps in accordance with the present invention which employ sliding pump control rings can also be controlled with switching modulator  100  or the like and, in such a case, each of control chambers  68  and  72  can be selectively supplied, isolated or relieved of pressurized working fluid. 
     Further, while pump  20  has been shown with switching modulator  100  and with each of control chambers  68  and  72  selectively supplied, isolated or relieved of pressurized working fluid, it should be apparent to those of skill in the art that pumps in accordance with the present invention which employ pivoting pump control rings can also be controlled with a simplified control valve  208  and switching modulator  100  or the like and, in such a case, control chamber  68  can be continually supplied with pressurized working fluid. 
       FIG. 7  shows another embodiment of a pump system and vane pump  250  in accordance with the present invention wherein similar components to those of pump  200  are indicated with like reference numerals. In pump  250 , a third control chamber  254  is provided and, like control chamber  72 , control chamber  254  can selectively be connected to supply  76 , return line  80  or isolated from both to either supply third chamber  254  with pressurized working fluid, relieve chamber  254  of pressurized working fluid or isolate chamber  254  from both supply  76  or return line  80 . 
     In operation, chamber  68  and biasing spring  96  provide a failsafe operation for pump  254  similar to that discussed above with respect to pump  150 . In non-failsafe operating conditions, chambers  72  and  254  operate, under the control of switching modulator  258 , to alter the displacement of pump  250  as desired and as described previously above. 
     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.