Patent Document

TECHNICAL FIELD  
         [0001]    This invention relates to engine lubrication systems and, more particularly, to variable displacement pumps for supplying engine oil to internal combustion engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known in the art relating to engine oil pumps to use positive displacement pumps to supply pressurized oil to lubrication and hydraulic systems of the engine. These pumps are typically fixed displacement pumps that rely on a pressure responsive valve to regulate maximum oil pressure, thus regulating engine oil flow. Automotive engines have used both external pinion gears, commonly referred to as spur gear pumps, and internal/external pinion gears, commonly referred to as gerotor, crescent, etc., gear pumps, to serve as the pumping elements. Because these are fixed displacement pumps, their output flow is directly proportional to their operational speed. Similarly, the torque required to drive these pumps is proportional to both the pressure rise across the pump and their theoretical displacement. As used in automotive engines that directly drive the pumps, the drive torque of these pumps increases directly with the engine operating speed.  
           [0003]    Use of fixed displacement pumps to supply a minimum oil pressure under hot idle conditions requires using a pump that is larger in displacement than is needed for providing adequate oil flow and pressure at other engine speeds where oil flow is increased and oil pressures are higher.  
           [0004]    Thus, at speeds other than idle, use of a fixed displacement pump creates a significant parasitic energy loss for the engine.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a variable displacement vane engine oil pump which is small in size, has excellent volumetric efficiency at low speeds and significantly reduces parasitic losses at speeds greater than idle.  
           [0006]    In a specific embodiment, a variable displacement vane pump includes a housing inside of which a slide ring is retained within the housing wall by a slide ring pivot. A rotor with slide vanes and a hex shaft drive of the rotor are located within the slide ring. Inlet and outlet ports allow fluid to enter and exit the pumping volume within the slide ring. A pick-up tube extends from the bottom of the pump and connects with the inlet port. A modular pressure relief valve assembly screws into a pump outlet passage.  
           [0007]    A flange extends from the slide ring on a side opposite the slide ring pivot. The flange acts as a slide stop, a slide seal support, and a slide spring tab. A slide seal is attached to the slide seal support and extends beyond the slide seal support to sealingly engage the housing wall. A pressure control chamber is formed in a space between the housing wall, the slide ring, the slide stop and the slide seal. A reaction spring is located between the housing wall and the slide spring tab and is opposite the pressure control chamber. The spring urges the slide ring toward a maximum displacement position of the rotor wall.  
           [0008]    A variable displacement vane pump in accordance with the invention may be driven by a camshaft through a cross-axis gear that turns the pump at a slower rate than the engine crankshaft speed. A ported pressure signal from a rear main bearing cap, to which the pump is mounted by a single bolt, acts on the pump&#39;s slide ring to cause it to pivot against the spring, thereby decreasing the pump&#39;s displacement. Use of the ported pressure signal provides a closed loop pressure control from the backside of the crankshaft rear main bearing, which prevents pressure sag in the engine lubrication system due to high component flow restriction or oil aeration.  
           [0009]    The slide is sealed on its end opposite the pivot and outside the slide stop, which biases the pressure required to initiate the slide ring movement. Once the slide ring moves off its stop, the pressure signal acts on a larger area of the slide ring to further move it until the force becomes balanced with a reaction spring. As a result, the pump is capable of producing a relatively flat oil pressure regulation curve. A modular pressure relief ball valve assembly attached to the pump outlet further limits pressure transients under cold engine conditions.  
           [0010]    Inlet and outlet ports of the pump are preferably on opposite sides of the vanes, which prevents the entrapment of gases in the pump chambers. The combination of the slide stop, the slide seal support and the slide spring tab into one component also aids in keeping the size of the pump small.  
           [0011]    These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a plan view of the vane engine oil pump of the invention with the top cover of the housing removed to show internal elements of the pump.  
         [0013]    [0013]FIG. 2 is a cross-sectional view of portions of an engine showing the pump mounting and drive connected in the engine oil lubrication system.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    Referring now to the drawings in detail, numeral  10  generally indicates a variable displacement vane engine oil pump in accordance with a specific embodiment of the present invention. As is more fully hereinafter described, the variable displacement vane pump  10  provides for more efficient pumping of engine oil and improved regulation of engine oil pressure.  
         [0015]    As illustrated in FIG. 1, variable displacement vane pump  10  includes a housing  12  having a wall  14 . A rotor  16  having a plurality of slide vanes  18  is rotatable in the housing on a fixed axis  19 . The slide vanes  18  internally engage a slide ring  20  to define pumping chambers  22  within the slide ring  20 . Vane rings (not shown) float in counterbores on opposite sides of the rotor  16  and engage inner edges of the slide vanes  18  to help them maintain contact with the slide ring  20 . An inlet port  24  is formed in an inlet side  25  of the housing  12  and an outlet port  26  (shown in phantom in FIG. 1) is formed in an outlet side or top cover  27  of the housing (shown in FIG. 2). The ports  24 ,  26  communicate with the pumping chambers  22  in the slide ring  20  on opposite bottom and top sides of the rotor  16 .  
         [0016]    An oil pick-up tube  28 , attached to the inlet side  25  of the housing  12 , connects to the inlet port  24  and extends below and away from the housing  12 . The rotor  16  is powered by a cross-axis hex shaft drive  30 . Rotation of the rotor  16  by the shaft drive  30  causes oil to be sucked into the pumping chambers  22  through the inlet port  24  and pushed out of the pumping chambers  22  through the outlet port  26 .  
         [0017]    The slide ring  20  is pivotally retained against the housing wall  14  by a slide ring pivot  32 . A flange  34  extends outward from the slide ring  20  at a location opposite from the slide ring pivot  32 . The flange  34  includes a slide spring tab  36 , a slide stop  38  and a slide seal support  40 . The slide seal support  40  is perpendicular to the slide spring tab  36  and the slide stop  38  while the slide spring tab  36  is on a side of the flange  34  opposite from the slide stop  38 . The slide stop  38  contacts a protrusion  42  on the housing wall  14  when the pump is operating at maximum displacement. The slide seal support  40  carries a slide seal  44  that extends radially beyond the slide stop  38  to engage the housing wall  14 .  
         [0018]    A pressure control chamber  46  is defined by the housing wall  14 , the slide ring pivot  32 , the slide ring  20 , the slide stop  38  and the slide seal  44 . An oil pressure signal port  48  is located in the housing  12  and communicates with the pressure control chamber  46 . A reaction spring  50  is disposed between the housing wall  14  and the slide spring tab  36 . A mounting bolt  52  on the outside of the housing  12  provides for attachment of the vane pump  10  to an engine body.  
         [0019]    In FIG. 2, the variable displacement vane engine oil pump  10  is shown integrated into an engine oil lubrication system  53  of an automotive internal combustion engine  54  having a cylinder block  55 . The vane pump  10  is attached to the bottom of a rear main bearing cap  56  by the mounting bolt  52 . The vane pump  10  is located below the bearing cap  56  within the engine oil pan  58 . The oil pick-up tube  28  extends close to the bottom of the oil pan  58  to draw in oil from the pump in a conventional manner.  
         [0020]    A modular pressure relief ball valve  60  is screwed into the top cover  27  and communicates with the outlet port  26 . The oil pressure signal port  48  connects the pressure control chamber  46  of the pump  10  through the rear main bearing cap  56  to the crankshaft oil feed on the backside of the rear main bearing  62 . The cross-axis hex shaft drive  30  extends from a driven gear  63  near the upper end of the engine cylinder block  55  and down into the vane pump  10  through the top cover  27  of the housing  12  and is powered by rotation of a camshaft drive gear  64  when the engine  54  is running.  
         [0021]    Referring now to both FIGS. 1 and 2, the vane pump  10  is integrated into the oil lubrication system  53  of the engine  54  to efficiently maintain engine oil pressure. During operation of the engine, the camshaft drive gear  64  turns the cross-axis hex shaft drive  30 , which in turn causes the rotor  16  inside the vane pump  10  to rotate on its axis  19 . The spinning of the rotor  16  causes oil to be drawn from the bottom of the oil pan  58  through the oil pick-up tube  28  into the pumping chambers  22  and forced out to the oil lubrication system  53  through the outlet port  26 . As the engine  54  and vane pump  10  operate, oil flow is generated by the vane pump  10  and an oil pressure signal (an indication of the relative system oil pressure) is sent from the rear main bearing cap  56  of the engine  54  through the oil pressure signal port  48  into the pressure control chamber  46  of the vane pump  10 , creating a closed loop pressure control system. Hence, the oil pressure in the pressure control chamber  46  varies with that in the oil lubrication system.  
         [0022]    During operation of the engine  54  at idle speed, engine oil pressure is low but must be kept above a certain minimum oil pressure. Since the oil pressure within the pressure control chamber  46  is equally low, the force of the reaction spring  50  against the flange  34  is greater than the force of the oil pressure in the pressure control chamber  46  acting against the slide ring  20 , so that the slide stop  38  is forced into contact with the protrusion  42 . In this orientation, the slide ring  20  is at its greatest eccentricity from the rotor axis  19  which results in maximum displacement of the vane pump  10 . This maintains the minimum required oil pressure in the engine  54  while rotational speeds of the engine  54  and the vane pump  10  are at their slowest.  
         [0023]    As engine speed is increased from idle, the relative speed of the vane pump  10  increases, thus increasing the pump outlet flow. This, in turn, increases the pressure in the engine oil system, including the pressure control chamber  46 . When the force of oil pressure in the pressure control chamber  46  acting on the slide ring  20  becomes greater than the counteracting force of the reaction spring  50 , the slide ring is pivoted about the slide ring pivot  32 , moving the slide stop  38  away from the housing wall  12 . The pivoting movement of the slide ring  20  about the slide ring pivot  32  reduces the eccentricity between the slide ring  20  and the rotor  16 . This alters the orientation of the slide vanes  18  and therefore decreases the unit displacement of the vane pump  10 .  
         [0024]    The unique design of the slide stop  38  and the slide seal  44  bias the pressure required to initiate this slide ring movement and cause the pressure signal to act on a larger area once the slide ring  20  begins to move. This results in a relatively flat oil pressure regulation curve. As the slide ring  20  moves and the unit displacement of the vane pump  10  decreases, the vane pump  10  pumps relatively less oil at each rotational cycle. Thus, a steady oil pressure is maintained while the torque required to drive the pump is proportionately reduced. When the oil pressure reaches a maximum, as may occur under cold engine oil conditions, the pressure relief valve  60  opens to control the maximum pressure by bypassing oil from the outlet of the vane pump  10  back into the oil pan  58 .  
         [0025]    Several additional features are included in the specific embodiment of variable displacement vane engine oil pump just described:  
         [0026]    To maximize the length of the pump extension below the rear main bearing cap, the slide vanes are made longer and narrower than is common in vane pump design. In particular, the vanes have an aspect ratio (length/width) of about 2:1, which differs from a usual 1:1 ratio. The high ratio allows the pump to maintain high volumetric efficiency without the use of a side face seal. Depending upon space available, the aspect ratio may be varied substantially in particular engine applications.  
         [0027]    Placement of the inlet and outlet ports in opposite sides of the pump vanes provides through oil flow in the pumping chambers which reduces the entrapment of gases in the chambers.  
         [0028]    The integration of the slide spring tab, slide stop and slide seal support into a single flange provides efficient packaging of the pump. It also provides the feature of biasing initial movement of the slide ring to increase the effect of pressure in the control chamber to reduce displacement of the pump rotor after movement of the slide stop  38  away from the housing protrusion  42 . The location of the slide stop  38  relative to the protrusion  42  can be adjusted to achieve the desired pressure biasing for a particular engine application.  
         [0029]    While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.

Technology Category: 2