Abstract:
A pump has a housing defining at least one pumping chamber, and a plunger slidably disposed within the at least one pumping chamber. The plunger is movable between a first and second spaced apart end positions to pressurize a fluid. The pump also has a driver operatively engaged with the plunger to move the plunger between the first end position and the second end position. The pump further has a high-pressure outlet in fluid communication with the at least one pumping chamber. The high pressure outlet passes pressurized fluid during movement of the plunger between the first end position and the second end position. The passing of pressurized fluid through the high-pressure outlet terminates before the plunger completes movement from the first end position to the second end position.

Description:
TECHNICAL FIELD  
       [0001]     The present disclosure relates generally to a fuel pump, and more particularly to a variable discharge fuel pump.  
       BACKGROUND  
       [0002]     A variable discharge fuel pump is utilized to maintain a pressurized fuel supply for a plurality of fuel injectors in a common rail fuel system. For example, U.S. Pat. No. 5,094,216 (the &#39;216 patent) to Miyaki et al. teaches a variable discharge high-pressure pump for use in a common rail fuel injection system. In such common rail systems, the pump supplies fuel to the common rail, which in turn supplies the fuel to the injectors when the injectors are energized. The pump serves to maintain the common rail at a desired pressure and does so by controllably displacing fuel from the pump to either a high-pressure common rail or toward a low-pressure reservoir with each pumping stroke of each pump piston. This is accomplished by associating an electronically controlled spill valve with each pump chamber. When the pump piston is undergoing its pumping stroke, the fuel displaced is initially pumped into a low-pressure reservoir past a spill control valve. When the spill control valve is energized, it closes the spill passageway causing fuel in the pumping chamber to quickly rise in pressure. The fuel in the pumping chamber is then pumped past a check valve into a high-pressure line connected to the common rail, and fuel is discharged into the fuel rail until the end of the pumping stroke.  
         [0003]     However, because the pump of the &#39;216 patent continues to discharge fuel into the fuel rail until the end of the pumping stroke, the pressure of the fuel discharged into the fuel rail may fluctuate undesirably. This fluctuation may occur due to, for example, the check valve remaining open during a portion of the downward motion of the plunger during an intake stroke, after completing the pumping stroke.  
         [0004]     The disclosed fuel pump is directed to overcoming one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0005]     In one aspect, the present disclosure is directed to a pump that includes a housing defining at least one pumping chamber and a plunger slidably disposed within the at least one pumping chamber. The plunger is movable between a first and second spaced apart end positions to pressurize a fluid. The pump also includes a driver operatively engaged with the plunger to move the plunger between the first end position and the second end position. The pump also has a high-pressure outlet in fluid communication with the at least one pumping chamber. The high-pressure outlet passes pressurized fluid during movement of the plunger between the first end position and second end position. The passing of pressurized fluid through the high-pressure outlet terminates before the plunger completes movement from the first end position to the second end position.  
         [0006]     In another aspect, the present disclosure is directed to a method of operating a pump. The method includes moving a plunger from a second end position to a first end position to draw a fluid into the pumping chamber. The method also includes moving the plunger from the first end position to the second end position to pump the fluid through a spill passageway. The method additionally includes blocking the spill passageway to build pressure within the pumping chamber and passing the pressurized fluid through a high-pressure outlet during movement between the first end position and the second end position. The passing of pressurized fluid through the high-pressure outlet terminates before the plunger reaches the second end position.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a schematic illustration of a common rail fuel system according to an exemplary embodiment of the present disclosure;  
         [0008]      FIG. 2  is an enlarged cross-sectional view of a fill and spill portion of the pump of the system of  FIG. 1 ; and  
         [0009]      FIG. 3 . is a graph showing solenoid actuation, spill valve actuation and outlet valve actuation relative to pump plunger movement according to the present disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0010]     Referring to  FIG. 1 , a fuel system  10  includes a fuel transfer pump  12  that may transfer fuel from a low pressure reservoir  14  to a high-pressure pump  16  via a fluid passageway  17 . High-pressure pump  16  may pressurize the fuel and direct the pressurized fuel through fluid passageway  18  to a fuel rail  20  that is in fluid communication with a plurality of fuel injectors  22  via fluid passageways  24 . Fuel injectors  22  may be fluidly connected to reservoir  14  via a leak return passageway  26 . An electronic control module  28  may be in communication with an actuator  30  connected to high-pressure pump  16  via a control communication line  32 , and with individual fuel injectors  22  via additional communication lines (not shown).  
         [0011]     High-pressure pump  16  may include a housing  34  defining a first and second barrel  36 ,  38 . High-pressure pump  16  may also include a first plunger  40  slidably disposed within first barrel  36 . First barrel  36  and first plunger  40  together may define a first pumping chamber  42 . High-pressure pump  16  may also include a second plunger  44  slidably disposed within second barrel  38 . Second barrel  38  and second plunger  44  together may define a second pumping chamber  46 .  
         [0012]     A first and second driver  48 ,  50  may be operably connected to first and second plungers  40 ,  44 , respectively. First and second drivers  48 ,  50  may include any means for driving first and second plungers  40 ,  44  such as, for example, a cam, a solenoid actuator, a piezo actuator, a hydraulic actuator, a motor, or any other driving means known in the art. A rotation of first driver  48  may result in a corresponding reciprocation of first plunger  40  and a rotation of second driver  50  may result in a corresponding reciprocation of second plunger  44 . First and second drivers  48 ,  50  may be positioned relative to each other such that first and second plungers  40 ,  44  are caused to reciprocate out of phase with one another. First and second drivers  48 ,  50  may each include three lobes such that one rotation of a pump shaft (not shown) connected to first and second drivers  48 ,  50  may result in six pumping strokes. Alternately, first and second drivers  48 ,  50  may include a different number of lobes rotated at a rate such that pumping activity is synchronized to fuel injection activity.  
         [0013]     High-pressure pump  16  may include an inlet  52  fluidly connecting high-pressure pump  16  to fluid passageway  17 . High-pressure pump  16  may also include a low-pressure gallery  60  in fluid communication with inlet  52  and in selective communication with first and second pumping chambers  42 ,  46 . A first inlet check valve  58  may be disposed between low-pressure gallery  60  and first pumping chamber  42  and may be configured to allow a flow of low-pressure fluid from low-pressure gallery  60  to first pumping chamber  42 . A second inlet check valve  62  may be disposed between low-pressure gallery  60  and second pumping chamber  46  and may be configured to allow a flow of low-pressure fluid from low-pressure gallery  60  to second pumping chamber  46 .  
         [0014]     High-pressure pump  16  may also include an outlet  54 , fluidly connecting high-pressure pump  16  to fluid passageway  18 . High-pressure pump  16  may include a high-pressure gallery  68  in selective fluid communication with first and second pumping chambers  42 ,  46  and outlet  54 . A first outlet check valve  70  may be disposed between first pumping chamber  42  and high-pressure gallery  68  and may be configured to allow a flow of fluid from first pumping chamber  42  to high-pressure gallery  68 . A second outlet check valve  74  may be disposed between second pumping chamber  46  and high pressure gallery  68  and may be configured to allow a flow of fluid from second pumping chamber  46  to high-pressure gallery  68 .  
         [0015]     High-pressure pump  16  may also includes a first spill passageway  64  selectively fluidly connecting first pumping chamber  42  to low-pressure gallery  60  and a second spill passageway  72  selectively fluidly connecting second pumping chamber  46  to low-pressure gallery  60 . A spill control valve  66  may be disposed between first and second pumping chambers  42 ,  46  and low-pressure gallery  60  and may be configured to selectively allow a flow of fluid from first and second pumping chambers  42 ,  46  to low-pressure gallery  60 .  
         [0016]     Only one of first and second pumping chambers  42 ,  46  may be fluidly connected to low pressure gallery  60  at a time. As illustrated in  FIG. 2 , the fluid connection between pumping chambers  42 ,  46  and low pressure gallery  60  may be established by a shuttle valve member  76  that includes a first hydraulic surface  78  exposed to fluid pressure in first pumping chamber  42 , and a second hydraulic surface  80 , which is oriented in opposition to first hydraulic surface  78  and exposed to fluid pressure in second pumping chamber  46 . Because first and second plungers  40 ,  44  may move out of phase relative to one another, one pumping chamber may be at high-pressure (pumping stroke) when the other pumping chamber is at low-pressure (intake stroke), and vice versa. This action may be exploited to move shuttle valve member  76  back and forth to fluidly connect either first spill passageway  64  to spill control valve  66 , or second spill passageway  72  to spill control valve  66 . Thus, first and second pumping chambers  42 ,  46  share a common spill control valve  66 .  
         [0017]     For example, when first plunger  40  moves through a pumping stroke and second plunger  44  moves through an intake stroke, shuttle valve member  76  may be in the position illustrated in  FIG. 2 , in which first pumping chamber  42  is fluidly connected to spill control valve  66 . The fluid connection between first pumping chamber  42  and spill control valve  66  is created when fluid, pressurized by first pumping chamber  42  acting on first hydraulic surface  78 , pushes shuttle valve member  76  to close second spill passageway  72  from spill control valve  66 . In similar fashion, as second plunger  44  moves through the pumping stroke and first plunger  40  moves through the intake stroke, shuttle valve member  76  may move to connect second spill passageway  72  to spill control valve  66 , while low-pressure fuel is drawn into first pumping chamber  42  past first inlet check valve  58 .  
         [0018]     Spill control valve  66  may include a spill valve member  82  having a hydraulic surface  84  that produces a latching affect when spill valve member  82  is in contact with a valve seat  86 . Spill valve member  82  is normally biased towards a first position where fluid is allowed to flow past spill valve member  82 , as shown in  FIG. 2 , via a biasing spring  88 . Spill valve member  82  may also be moved to a second position where fluid is blocked from flowing past to spill valve member  82  by energizing actuator  30 . Actuator  30  may include a solenoid  31  configured to attract an armature  90  coupled to spill valve member  82  when solenoid  31  is energized, thereby closing spill valve member  82 . One skilled in the art will recognize that actuator  30  may be any type of actuator known in the art such as for example, a piezo and/or piezo bender actuator.  
         [0019]     Control signals generated by electronic control module  28  directed to high-pressure pump  16  via communication line  32  may determine when and how much fuel is pumped into fuel rail  20 . Control signals generated by electronic control module  28  directed to fuel injectors  22  may determine the actuation timing and actuation duration of fuel injectors  22 .  
         [0020]     Electronic control module  28  may include all the components required to perform the required system control such as, for example, a memory, a secondary storage device, and a processor, such as a central processing unit. One skilled in the art will appreciate that electronic control module  28  can contain additional or different components. Associated with electronic control module  28  may be various other known circuits such as, for example, power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others.  
         [0021]      FIG. 3  illustrates the relative operation of solenoid  31 , spill control valve  66 , and first and second outlet check valves  70 ,  74  relative to the motion of first and second plungers  40 ,  44 . The operation of high-pressure pump  16 , with respect to  FIG. 3 , will be described in the following section.  
       INDUSTRIAL APPLICABILITY  
       [0022]     The disclosed pump finds potential application in any fluid system where it is desirous to control discharge from a pump. The disclosed pump finds particular applicability in fuel injection systems, especially common rail fuel injection systems. One skilled in the art will recognize that the disclosed pump could be utilized in relation to other fluid systems that may or may not be associated with an internal combustion engine. For example, the disclosed pump could be utilized in relation to fluid systems for internal combustion engines that use a hydraulic medium, such as engine lubricating oil. The fluid systems may be used to actuate various sub-systems such as, for example, hydraulically actuated fuel injectors or gas exchange valves used for engine braking. A pump according to the present disclosure could also be substituted for a pair of unit pumps in other fuel systems, including those that do not include a common rail.  
         [0023]     Referring to  FIG. 1 , when fuel system  10  is in operation, first and second drivers  48 ,  50  rotate causing first and second plungers  40 ,  44  to reciprocate within respective first and second barrels  36 ,  38 , out of phase with one another. When first plunger  40  moves through the intake stroke, second plunger  44  moves through the pumping stroke.  
         [0024]     During the intake stroke of first plunger  40 , fluid is drawn into first pumping chamber  42  via first inlet check valve  58 . As first plunger  40  begins the pumping stroke, fluid pressure causes shuttle valve member  76  to allow displaced fluid to flow from first pumping chamber  42  through spill control valve  66  to low-pressure gallery  60 . When it is desirous to output high-pressure fluid from high-pressure pump  16 , solenoid  31  of actuator  30  may be energized to move spill valve member  82  toward solenoid  31  and close spill control valve  66 .  
         [0025]     As illustrated in  FIG. 3 , closing spill control valve  66  causes an immediate build up of pressure within first pumping chamber  42 . After the pressure increases beyond a minimum threshold, solenoid  31  may be de-energized and the force generated by the build up of pressure against hydraulic surface  84  firmly holds spill control valve  66  in a closed position. As the pressure continues to increase within first pumping chamber  42 , a pressure differential across first outlet check valve  70  produces an opening force on outlet check valve  70  that exceeds a spring closing force of outlet check valve  70 . When the spring closing force of first outlet check valve  70  has been surpassed, first outlet check valve  70  opens and high-pressure fluid from within first pumping chamber  42  flows through first outlet check valve  70  into high-pressure gallery  68  and then into fuel rail  20  by way of fluid passageway  18 .  
         [0026]     One skilled in the art will appreciate that the timing at which actuator  30  is energized determines what fraction of the amount of fluid displaced by the first plunger  40  is pumped into the high-pressure gallery  68  and what is pumped back to low-pressure gallery  60 . This operation serves as a means by which pressure can be maintained and controlled in fuel rail  20 . As noted in the previous section, control of the energizing of actuator  30  is provided by signals received from electronic control module  28  over communication line  32 .  
         [0027]     Towards the end of the pumping stroke, as the angle of the portion of first driver  48  causing first plunger  40  to move decreases, the reciprocating speed of first plunger  40  proportionally decreases. As the reciprocating speed of plunger  40  decreases, the opening force caused by the pressure differential across first outlet check valve  70  nears and then falls below the spring force of first outlet check valve  70 . First outlet check valve  70  moves to the closed position to block fluid through first outlet check valve  70  when the opening force caused by the pressure differential across first outlet check valve  70  falls below the spring force of first outlet check valve  70 . The spring included in outlet check valve  70  has a spring constant selected to ensure that first outlet check valve  70  moves to block fluid from flowing through first outlet check valve  70  before the end of the pumping stroke. Because outlet check valve  70  moves to block fluid from flowing through outlet check valve  70  before the end of the pumping stroke, outlet check valve  70  will not be open during an intake stroke, thereby reducing the likelihood of pressure fluctuations within common rail  20 . After outlet check valve  70  closes, first plunger  40  continues pressurizing the fluid within first pumping chamber  42  until the end of the pumping stroke. Pressure build up within first pumping chamber  42  after outlet check valve  70  closes may be accommodated by leakage from first pumping chamber  42  between first plunger  40  and first barrel  36 , via compressibility of the fluid within first pumping chamber  42 , and/or via mechanical strain within first pumping chamber  42 .  
         [0028]     After first plunger  40  completes the pumping stroke and begins moving in the opposite direction during the intake stroke, the pressure of the fluid within first pumping chamber  42  creates a force caused by the pressure differential across spill valve member  82  that nears and then falls below the force exerted by biasing spring  88 . As the pressure differential across spill valve member  82  becomes less than the spring force of biasing spring  88 , biasing spring  88  moves spill valve member  82  from solenoid  31  to the open position.  
         [0029]     As second plunger  44  switches modes from filling to pumping (and first plunger  40  switches from pumping to filling), shuttle valve member  76  moves to the other side of its cavity blocking fluid flow from first pumping chamber  42  opening the path between pumping chamber  46  and spill control valve  66 , thereby allowing spill control valve  66  to control the discharge of second pumping chamber  46 . Second plunger  44  then completes a pumping stroke similar to that described above with respect to first plunger  40 .  
         [0030]     Several advantages are realized because the opening pressure of first and second outlet check valves  70 ,  74  is greater than the pressure required to hold spill valve member  82  in place. Spill valve member  82  may be held in place by fluid pressure while first and second outlet check valves  70 ,  74  are in the open position to allow fluid to flow through first and second outlet check valves  70 ,  74 . Build-up of pressure within first and second pumping chambers  42 ,  46  is immediate, which allows for solenoid  31  of actuator  30  to be quickly de-energized, thereby reducing energy consumption and improving efficiency of the engine. In addition, the immediate build-up of pressure also facilitates hot-starting when the viscosity of the fluid is at a minimum. Further, because the discharge of pressure through first and second outlet check valves  70 ,  74  will stop before the end of the pumping stroke, pressure fluctuations in common rail  20  caused by pumping to the end of the stroke may be reduced and/or eliminated.  
         [0031]     It will be apparent to those skilled in the art that various modifications and variations can be made to the pump of the present disclosure. Other embodiments of the pump will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.