Abstract:
A valve ( 100 ) comprises a barrel ( 104 ) having a central bore ( 110 ), an inlet ( 112 ), and an outlet ( 114, 116 ), and a spool ( 120 ) disposed for motion within the central bore, including a ball tip ( 128 ), a metering edge ( 130 ), and a bore ( 132 ). The spool is moveable between a closed position, wherein the ball tip engages a seat ( 142 ) to prevent fluid flow through the inlet and the metering edge is disposed in a lower chamber ( 148 ) of the central bore to prevent the fluid flow through the outlet, and an opened position, wherein the tip is spaced apart from the seat to permit fluid flow through the inlet and the spool bore into an upper chamber ( 154 ) of the central bore to equalize pressure on the spool, and the metering edge is disposed in a flow path of the outlet to permit fluid flow through the outlet.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates in general to high pressure pump systems, and, in particular, to a system and method for metering fluid to one or more high pressure pumping chambers. 
       BACKGROUND 
       [0002]    Government imposed requirements for fuel economy and emissions reduction are one reason fuel systems manufacturers seek to provide precise control over the amount of fuel that is injected during injection events of a combustion cycle. More specifically, a goal of many high pressure fuel injection systems is to provide increased control of the amount of fuel injected by the fuel injectors of an internal combustion engine. 
         [0003]    As shown in  FIG. 1 , a typical high pressure fuel pump system  10  generally includes a fuel supply  12  which supplies fuel to a hydro mechanical actuator such as an inlet metering valve  14 . Metering valve  14 , which is controlled by an electronic control module (“ECM”)  15 , is configured to control the amount of fuel provided to a plurality of high pressure pumping chambers  16 . Pumping chambers  16  then disperse the fuel to a receptacle such as a common rail fuel apparatus or accumulator  18 . 
         [0004]    In many such systems, metering valve  14  includes a variable area orifice operated by a solenoid. In certain embodiments, the linear position of a spool inside metering valve  14  controls the amount of fuel to be supplied to pumping chambers  16 . As such, metering valve  14  may be configured to prevent fuel from passing to chambers  16  when metering valve  14  is fully closed. However, in many systems, the mechanical configuration of metering valve  14  is insufficient to completely prevent fuel flow, and some leakage occurs. Moreover, in some systems the pressure of the fuel supply  12  to metering valve  14  requires significant counter-force by valve  14  when valve  14  is moved to a partially opened position to maintain valve  14  in its desired position. Generally, this counter-force is provided by a high performance solenoid controlled by ECM  15 . Finally, in order to deliver the fuel economy and emission reduction desired, it is desirable to provide a highly accurate mechanism for metering fuel to chambers  16  when valve  14  is opened. 
       SUMMARY 
       [0005]    According to one embodiment of the disclosure, a metering valve is provided comprising a barrel having a central bore, at least one inlet in flow communication with the central bore, and at least one outlet in flow communication with the central bore, and a spool disposed for reciprocal motion within the central bore of the barrel. In such an embodiment, the spool includes a ball tip, a metering edge, and at least one bore extending from a first orifice to a second orifice. The spool is moveable between a closed position, wherein the ball tip engages a conical seat formed in a wall of the barrel to prevent fluid flow between the at least one inlet and a lower chamber of the central bore and the metering edge is disposed in the lower chamber to prevent fluid flow between the lower chamber and the at least one outlet, and an opened position, wherein the ball tip is spaced apart from the conical seat to permit fluid flow between the inlet and the lower chamber and through the at least one bore of the spool into an upper chamber of the central bore to thereby equalize pressure of the fluid on the spool, and the metering edge is disposed in a flow path of the at least one outlet to permit fluid flow between the lower chamber and the at least one outlet. In one aspect of this embodiment, the valve further comprises a spring disposed in the lower chamber to bias the spool toward the opened position. In a variant of this aspect, the valve further comprises a solenoid for generating a magnetic flux as a function of input current, the magnetic flux causing a plunger in contact with the spool to move the spool toward the closed position against the biasing force of the spring. In another aspect of this embodiment, the valve further comprises a spring disposed in the valve to bias the spool toward the closed position, and a solenoid for generating a magnetic flus as a function of input current, the magnetic flux causing a plunger connected to the spool to move the spool toward the opened position against the biasing force of the spring. In another aspect, the barrel includes multiple outlets. In yet another aspect, the valve further comprises a plunger in contact with the spool, the plunger being positioned within a housing of the valve for guided movement as the spool is moved between the closed position and the opened position. In another aspect, the at least one bore extends substantially diagonally through a body of the spool from a side wall of the body to an upper surface of the body. In a variant of this aspect, fluid flow through the at least one bore causes rotation of the spool about a longitudinal axis of the spool. In still another aspect of this embodiment, when the spool is in a fully opened position, a plunger in contact with the spool engages a portion of a housing of the valve. 
         [0006]    In another embodiment of the present disclosure, a system for metering fuel to at least one fuel pumping chamber is provided, comprising a fuel supply, an inlet metering valve having a first opening in flow communication with the fuel supply and a second opening in flow communication with the at least one pumping chamber, the valve further including a solenoid and a spool mounted within a housing for reciprocal movement between a plurality of opened positions, wherein fuel flows through the valve from the fuel supply to the at least one pumping chamber, and a closed position, wherein fuel is substantially prevented from flowing through the valve, and an ECM configured to provide signals to the solenoid to position the spool into the plurality of opened positions and the closed position. In this embodiment, the spool includes a ball tip at one end that engages a seating surface to prevent fuel flow when the spool is in the closed position, a metering edge disposed on an outer surface of the spool that cooperates with the second opening when the armature is in the plurality of opened positions to meter the quantity of fuel flowing through the valve, and the valve includes a flow path between a first chamber disposed between the first opening and the second opening and a second chamber disposed adjacent another end of the spool, the flow path permitting fuel flow between the first chamber and the second chamber to substantially equalize pressure exerted by the fuel on each end of the spool. According to one aspect of this embodiment, the valve includes a barrel having a central bore defining the first chamber adjacent the one end of the spool and the second chamber adjacent the other end of the spool. In a variant of this aspect, the barrel further defines the first opening and the second opening. In another variant, the barrel defines a plurality of outlets. Another aspect of this embodiment further comprises a spring disposed in the first chamber to bias the spool toward the plurality of opened positions. In a variant of this aspect, the solenoid generates a magnetic flux as a function of an input current from the ECM, the magnetic flux urging the spool to move toward the closed position against the biasing force of the spring. Another aspect further comprises a spring disposed within the valve to bias the spool toward the closed position, wherein the solenoid generates a magnetic flux as a function of an input current from the ECM, the magnetic flux urging the spool to move toward the plurality of opened positions against the biasing force of the spring. In yet another aspect, the valve further includes a plunger in contact with the spool, the plunger being positioned within the housing of the valve for guided movement as the spool is moved between the closed position and the plurality of opened positions. In still another aspect, the flow path includes at least one bore extending through the spool from a first orifice disposed in the first chamber to a second orifice disposed in the second chamber, the at least one bore permitting fuel flow between the first chamber and the second chamber to substantially equalize pressure exerted by the fuel on each end of the spool. In a variant of this aspect, the at least one bore extends substantially diagonally through a body of the spool from the first orifice to the second orifice such that fuel flow through the at least one bore causes rotation of the spool about a longitudinal axis of the spool. In another aspect of this embodiment, the flow path includes at least one groove extending from the first chamber to the second chamber. In a variant of this aspect, the at least one groove is formed in a side wall of a body of the spool. In still another aspect, the flow path includes at least one flat formed in a side wall of a body of the spool and extending from the first chamber to the second chamber. In yet another aspect, when the spool is in a fully opened position, a plunger in contact with the spool engages a portion of the housing of the valve to limit further movement of the spool away from the closed position. 
         [0007]    In yet another embodiment of the present disclosure, a method of metering fuel to a fuel pumping chamber is provided, comprising supplying fuel to a metering valve, supplying a signal to the metering valve that activates a solenoid which moves a spool of the metering valve against a biasing force of a spring, and controlling the signal supplied to the metering valve to cause movement of the metering valve between a closed position, wherein a ball tip of the spool engages a conical seat at one opening of the valve to substantially prevent fuel from flowing through the valve, and a plurality of opened positions, wherein a metering edge of the spool is disposed within a flow path of another opening of the valve to permit a metered quantity of fuel to flow to the pumping chamber, and a bore extending through the spool distributes pressure exerted on the spool by the fuel to an upper surface of the spool. In one aspect of this embodiment, the valve includes a barrel having a central bore that receives the spool, the central bore defining a first chamber adjacent one end of the spool and a second chamber adjacent the upper surface of the spool. In a variant of this aspect, the barrel further defines the openings of the valve. In another variant, the spring is disposed in the first chamber to bias the spool toward the plurality of opened positions. In another aspect of this embodiment, the spring is disposed in the valve to bias the spool toward the closed position. In another aspect, supplying a signal includes generating a magnetic flux as a function of an input current supplied by an ECM, the magnetic flux urging the spool to move toward the closed position against the biasing force of the spring. In still another aspect, supplying a signal includes generating a magnetic flux as a function of an input current supplied by an ECM, the magnetic flux urging the spool to move out of the closed position against the biasing force of the spring. Another aspect of this embodiment further includes limiting movement of the spool away from the closed position by causing a plunger in contact with the spool to engage a portion of a housing of the valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The embodiments will be more readily understood in view of the following description when accompanied by the below figures and wherein like reference numerals represent like elements, wherein: 
           [0009]      FIG. 1  is a conceptual block diagram of components of a high pressure fuel pump system; 
           [0010]      FIG. 2  is a cross-sectional view of one embodiment of an inlet metering valve according to the present disclosure in an opened position; 
           [0011]      FIG. 3  is a cross-sectional view of the inlet metering valve of  FIG. 2  in a closed position; 
           [0012]      FIG. 4  is an enlarged view of portion A of  FIG. 2 ; and 
           [0013]      FIG. 5  is an enlarged view of portion A of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0014]    The embodiments disclosed herein are not intended to be exhaustive or limit the invention to the precise form disclosed in the following detailed description. Rather, the embodiments were chosen and described so that others skilled in the art may utilize their teachings. 
         [0015]    Embodiments of an inlet metering valve according to the present disclosure are described herein in the context of a work machine having a high pressure fuel pump system  10  as depicted in  FIG. 1 . It should be understood that a work machine may be any type of fixed or mobile machine that performs some type of operation required by a particular application. Non-limiting examples of work machines may include commercial machines, such as cranes, earth moving machines, other material handling equipment, farming equipment, marine vessels, aircraft, vehicles of any type and power-generation equipment. In particular applications, the present metering valve is used in conjunction with a diesel engine that forms part of such a working machine. 
         [0016]    Referring now to  FIGS. 2 and 4 , one embodiment of an inlet metering valve according to the present disclosure is shown. Valve  100  generally includes a housing  102  which at least partially contains a valve barrel  104 , a solenoid  106 , a plunger  118  and a spool  120 . Barrel  104  includes a central bore  110 , an inlet  112  in flow communication with central bore  110 , and outlets  114 ,  116  in flow communication with central bore  110 . In this embodiment, two additional outlets (not shown) are formed in barrel  104  in perpendicular relationship to outlets  114 ,  116 . It should be understood, however, that more or fewer outlets may be used according to the principles described herein. 
         [0017]    In the embodiment described herein, inlet  112  receives fuel from fuel supply  12  depicted in  FIG. 1  and outlets  114 ,  116  provide metered fuel (in the manner described below) to pumping chambers  16  depicted in  FIG. 1 . It should be understood, however, that the valve according to the present disclosure can meter fluid or any type (i.e., not just fuel) and that the direction of flow of the fluid may opposite to that described herein. In other words, fluid may flow into the valve through the openings labeled outlets  114 ,  116  in the drawings, and out of the valve through the opening labeled inlet  112  in the drawings. 
         [0018]    In one embodiment, plunger  118  is formed as an elongated rod having an upper end  122  and a lower end  124  which contacts spool  120 . In one embodiment, spool  120  includes a substantially cylindrical body  126  sized to fit within central bore  110  of barrel  104  with low clearance and for reciprocating movement in the manner described below. Spool  120  further includes a ball tip  128  at an end distal to lower end  124  of plunger  118 , a circumferential metering edge  130 , and bore  132  extending through body  126 . More specifically, in one embodiment bore  132  extends from a lower orifice  134  disposed in a side wall  136  adjacent ball tip  128  and below metering edge  130  to an upper orifice  138  disposed in an upper surface  140  of body  126 . 
         [0019]    Barrel  104  further includes a conical seat  142  formed at the inner end of inlet  112  in lower wall  144  of barrel  104 . Additionally, a spring  146  is disposed within a lower chamber  148  of central bore  110  between lower wall  144  of barrel  104  and metering edge  130 . As is further described below, in one embodiment spring  146  biases spool  120  upwardly such that valve  100  is biased toward the opened position shown in  FIGS. 2 and 4 . Movement of plunger  118  is guided by upper guide  150  and lower guide  152 . As will be apparent to one skilled in the art, valve  100  may instead be configured such that spool  120  is biased toward the closed position shown in  FIGS. 3 and 5 . In such an embodiment, spring  146  may be positioned in upper chamber  154  of barrel  104  to exert a downward biasing force onto upper surface  140  of spool body  126 . Alternatively, spring  146  may have a normally compressed shape and be disposed in lower chamber  148  with one end connected to wall  144  and another end connected to body  126 . In any such “normally closed” embodiment of valve  100 , lower end  124  of plunger  118  is connected to spool  120  and solenoid  106 , when powered, causes plunger  118  to move upwardly thereby moving spool  120  out of its normally closed position. 
         [0020]    While not shown in the drawings, solenoid  106  of valve  100  is coupled to ECM  15  ( FIG. 1 ) to receive control current from ECM  15 . In one embodiment, the amount of current supplied to solenoid  106  by ECM  15  determines the strength of the magnetic flux generated by solenoid  106 . In general, the strength of the magnetic flux generated by solenoid  106 , which in one embodiment imparts a downward force on armature  108 , determines the linear position of spool  120  against the upward biasing force of spring  146 . When valve  100  is in the opened position as shown in  FIGS. 2 and 4 , insufficient current is supplied to solenoid  106  by ECM  15  to overcome the upward biasing force of spring  146  and cause downward movement of spool  120 . As such, plunger  118  is in its uppermost position with its upper end  150  engaged against housing  102 , which thereby limits upward movement of plunger  118  and spool  120 . In this fully opened position, valve  100  permits maximum flow of fluid through barrel  104 . More specifically, in the embodiment shown fluid flows into inlet  112 , between conical seat  142  and ball tip  128 , into lower chamber  148 , and out of barrel  104  through the spaces formed between metering edge  130  and outlets  114 ,  116 . 
         [0021]    Referring now to  FIGS. 3 and 5 , when valve  100  is in the closed position, sufficient current is supplied to solenoid  106  by ECM  15  to overcome the upward biasing force of spring  146 . As such, spool  120  is in its lowermost position such that ball tip  128  engages conical seat  142  and metering edge  130  is disposed below outlets  114 ,  116  rather than in the flow path of outlets  114 ,  116  as shown in  FIGS. 2 and 4 . Consequently, fluid is prevented from flowing through valve  100  by two mechanisms. First, the seal between ball tip  128  and conical seat  142  prevents fluid from entering lower chamber  148  of barrel  104 . Second, the position of metering edge  130  below outlets  114 ,  116  and tight fit between body  126  of spool  120  and central bore  110  of barrel  104  prevents fluid from flowing from lower chamber  148  through outlets  114 ,  116 . 
         [0022]    Valve  100  is moved from its closed position ( FIGS. 3 and 5 ) to its opened position ( FIGS. 2 and 4 ) by reducing the current supplied to solenoid  106 . As the current is reduced, the downward magnetic flux force exerted by solenoid  106  on plunger  118  begins to be overcome by the upward force of spring  146  on spool  120 . Consequently, plunger  118  and spool  120  begin to move upwardly. As this occurs, ball tip  128  separates from conical seat  142  and permits fluid to enter into lower chamber  148 . It should be understood that other near zero leak mating surfaces (i.e., other than ball tip  128  and conical seat  142 ) may be used to prevent fluid flow into lower chamber  148  until spool  120  is permitted to move upwardly by solenoid  106 . For example, various combinations of ball, conical, flat or crowned spool tip surfaces may be used with conical, flat or crowned seating surfaces. 
         [0023]    As the fluid fills lower chamber  148 , it flows into lower orifice  134  of bore  132 . The fluid further flows out of upper orifice  138  and fills upper chamber  154 . With the pressure balance drilling provided by bore  132  in this manner, the pneumatic pressure placed on spool  120  by the fluid is substantially equalized between lower chamber  148  and upper chamber  154 . As such, solenoid  106  does not need to be sized to overcome the upward biasing force of spring  146  in addition to the upward force applied to spool  120  by the fuel flowing into inlet  112 . 
         [0024]    When valve  100  is moved to an opened position such that metering edge  130  is positioned within the flow path of outlets  114 ,  116 , fluid not only flows from lower chamber  148  through outlets  114 ,  116 , fluid also flows through diagonal bore  132 , into upper chamber  154 , and from upper chamber  154 , between spool  120  and the inner surface of central bore  110 , through outlets  114 ,  116 . The diagonal orientation of diagonal bore  132  and the fluid flow through bore  132  causes spool  120  to rotate or spin about its longitudinal axis. This rotation occurs each time valve  100  is moved to an opened position, and provides for distributed wear on the surfaces of spool  120 . 
         [0025]    While a diagonal bore  132  is shown in the drawings for providing the above-described pressure balancing, it should be understood that many different balancing configurations that provide a flow path between lower chamber  148  and upper chamber  154  may be employed. For example, grooves or flats may be formed in the outer surface of side wall  136  of spool  120 , a plurality of ports may be formed through body  126 , grooves may be formed on the inner surface of central bore  110 , etc. In still other embodiments, the clearance between side wall  136  of spool  120  and the inner surface of central bore  110  may be adjusted such that fluid may flow around spool  120  between lower chamber  148  and upper chamber  154  to balance pressure exerted on spool  126 . 
         [0026]    As the current supplied to solenoid  106  is further reduced, plunger  118  moves upwardly within upper guide  150  and lower guide  152 , and spool  120  moves further upwardly within central bore  110 . Eventually, metering edge  130  is disposed in the flow path of outlets  114 ,  116  such that lower chamber  148  is in flow communication with outlets  114 ,  116 . The knife edge formed by metering edge  130  not only functions to prevent fluid flow out of lower chamber  148  when metering edge  130  is positioned below outlets  114 ,  116 , it also provides highly precise flow characteristics when metering edge is positioned in the flow path of outlets  114 ,  116 . More specifically, the knife edge results in a very precise flow vs. solenoid  106  current curve. 
         [0027]    The foregoing description has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the exemplary embodiments disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the invention be limited not by this detailed description of examples, but rather by the claims appended hereto.