Integrated Outlet Check Valve and Pressure Relief Valve

Abstract

The disclosed integrated outlet check valve and pressure relief valve are used in a high pressure fuel pump including a pumping chamber and an outlet fitting defining an outlet passage to a common rail. The pressure relief valve comprises a movable pressure relief valve shuttle including a pressure relief valve surface configured to mate with a pressure relief valve seat in a closed position. The pressure relief valve shuttle moves from the closed position to an open position when pressure in the common rail exerts a force greater than the bias of a pressure relief valve spring. The pressure relief valve shuttle also includes an outlet check valve seat configured to mate with an outlet check valve ball in a closed position. The outlet valve ball moves from the closed position to an open position when pressure in the outlet passage is less than pressure in the pumping chamber.

Claims

1. An integrated outlet check valve and pressure relief valve for a high pressure fuel pump, said high pressure fuel pump having a pumping chamber where a pumping plunger reciprocates between a pumping phase and a charging phase and an outlet fitting defining an outlet passage to a common rail, said integrated outlet check valve and pressure relief valve comprising: a pressure relief valve shuttle movable between a closed position and an open position, said pressure relief valve shuttle having a pressure relief valve surface configured to mate with a pressure relief valve seat and an outlet check valve seat configured to mate with an outlet check valve ball; a pressure relief valve cup arranged concentrically about at least a portion of said pressure relief valve shuttle; a pressure relief valve spring comprising a conical disc spring arranged between said pressure relief valve shuttle and said pressure relief valve cup, said pressure relief valve spring biasing said pressure relief valve shuttle toward said closed position; a pressure relief valve support defining an outlet flow path and including said pressure relief valve seat; said outlet check valve ball movable between a closed position and an open position, said outlet check valve ball biased toward said closed position by an outlet check valve spring; a pressure relief passage defined between said pressure relief valve seat and said complimentary pressure relief valve surface of said pressure relief valve shuttle; and wherein, said outlet check valve ball mates with said outlet check valve seat in said closed position preventing fluid communication through said outlet flow path, said outlet check valve ball moves from said closed position to said open position permitting fluid communication through said outlet flow path when pressure in said outlet passage is less than pressure in said pumping chamber, said pressure relief valve surface mates with said pressure relief valve seat in said closed position preventing fluid communication through said pressure relief passage, and said pressure relief valve shuttle moves from said closed position to said open position permitting fluid communication through said pressure relief passage when pressure in said common rail exerts a force greater than the bias of said pressure relief valve spring.

2. The integrated outlet check valve and pressure relief valve of claim 1, wherein said pressure relief valve cup has an interference fit within said pump outlet fitting and traps said pressure relief valve shuttle, said pressure relief valve spring, said check valve ball, said check valve spring, and said pressure relief valve seat within the pump outlet fitting.

3. The integrated outlet check valve and pressure relief valve of claim 1, wherein said pressure relief valve seat includes an annular, conical surface configured to mate with said pressure relief valve surface.

4. The integrated outlet check valve and pressure relief valve of claim 1, wherein said pressure relief valve surface and said pressure relief valve seat form a conical surface together in said closed position of said pressure relief valve shuttle.

5. The integrated outlet check valve and pressure relief valve of claim 1, wherein said pressure relief valve seat is arranged radially inward of said pressure relive valve surface.

6. The integrated outlet check valve and pressure relief valve of claim 1, wherein said outlet check valve support defines sides of said outlet check valve.

7. The integrated outlet check valve and pressure relief valve of claim 1, wherein said pressure relief valve seat contacts said pressure relief valve shuttle radially outward of said outlet check valve ball.

8. A method of controlling pressure and discharge of fuel through an outlet passage of a high pressure fuel pump, said high pressure fuel pump having a pumping chamber where a pumping plunger reciprocates between a pumping phase and a charging phase, said method comprising: providing an outlet check valve ball; providing a pressure relief valve support defining an outlet flow path and having a pressure relief valve seat, said pressure relief valve seat having an annular surface; providing a pressure relief valve shuttle having a pressure relief valve surface configured to mate with said annular surface of said pressure relief valve seat and an outlet check valve seat configured to mate with said outlet check valve ball, said pressure relief valve surface arranged radially outward of said pressure relief valve seat, said outlet check valve seat arranged radially outward of said outlet check valve ball, said outlet check valve shuttle and said outlet check valve ball exposed to pressure in said outlet passage; biasing said pressure relief valve shuttle toward said pressure relief valve seat with a pressure relief valve spring comprising a conical disc spring, said pressure relief valve spring compressing in response to pressure in said outlet passage; biasing said outlet check valve ball toward said outlet check valve seat; defining a pressure relief passage between said pressure relief valve seat and said pressure relief valve surface; moving said pressure relief valve shuttle between a closed position mated with said pressure relief valve surface and preventing fluid communication through said pressure relief passage and an open position permitting fluid communication through said pressure relief passage, said pressure relief valve shuttle moving from said closed position to said open position when pressure in said outlet passage exerts a force greater than the bias of said pressure relief valve spring; and moving said outlet check valve ball between a closed position mated with said outlet check valve seat and preventing fluid communication through said outlet flow path and an open position permitting fluid communication through said outlet flow path, said outlet check valve ball moving from said closed position to said open opposition when pressure in said outlet passage is less than pressure in said pumping chamber.

9. The method of claim 8, wherein said step of providing a pressure relief valve cup includes said pressure relief valve cup trapping said pressure relief valve shuttle, said pressure relief valve spring, said check valve ball, said check valve spring, and said pressure relief valve seat within said high pressure fuel pump.

10. The method of claim 8, wherein said step of providing a pressure relief valve seat includes said pressure relief valve seat having an annular, conical surface configured to mate with said pressure relief valve surface.

11. The method of claim 8, wherein said step of providing a pressure relief valve shuttle includes said pressure relief valve surface and said pressure relief valve seat forming a conical surface together in said closed position of said pressure relief valve shuttle.

12. The method of claim 8, further comprising a step of providing an outlet check valve support, said pressure relief valve seat being arranged on said outlet check valve support.

13. The method of claim 8, wherein said step of providing a pressure relief valve shuttle includes said pressure relief valve shuttle contacting said pressure relief valve seat in said closed position radially outward of said check valve ball.

14. The method of claim 8, further comprising a step of calibrating an opening pressure of the pressure relief valve by setting a position of a pressure relief valve cup concentrically about at least a portion of said pressure relief valve shuttle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Aspects of a disclosed embodiment will be described in reference to the drawings, where like numerals reflect like elements:

[0013] FIG. 1 is a sectional view of a high pressure fuel pump incorporating valves according to aspects of the disclosure;

[0014] FIGS. 2-8 are schematic diagrams of a fuel injection system incorporating the disclosed high pressure fuel pump showing valve position and fuel flow in different operating states of the fuel injection system;

[0015] FIGS. 9-16 are enlarged sectional views of a portion of the high pressure fuel pump of FIG. 1, showing the structure and operation of valves in different operating states of the high pressure fuel pump.

DETAILED DESCRIPTION

[0016] FIG. 1 is a sectional view of a high pressure fuel pump (HPP) 10 incorporating illustrative examples of an inlet control valve (ICV) 12, pressure relief valve (PRV) 14, and discharge check valve (DCV) 16 according to aspects of the disclosure. As will be discussed in greater detail below, the PRV 14 and DCV 16 are integrated with each other and situated in a pump outlet fitting 18 according to aspects of the disclosure. FIG. 2 is a schematic diagram showing the functional elements and relationships in a fuel injection system incorporating the disclosed HPP 10. With reference to FIG. 2, a low pressure pump (LPP) 20 supplies fuel to the HPP 10, via an inlet fitting 22. High pressure fuel leaves the HPP 10 through a discharge fitting 18 that communicates with a rail feed passage 24 and the common rail 26. In the fuel injection system of FIG. 2, engine control unit (ECU) 28 uses information from a crankshaft position sensor 30 and other inputs to operate fuel injectors 32 connected to the common rail 26. A pressure sensor 34 detects the pressure in the common rail 26 and provides this information to the ECU 28. The ECU 28 operates the fuel injectors 32 so that fuel is injected into each combustion chamber at the time and in the quantity demanded by the engine (not shown) according to the engine's operational condition, i.e., accelerating under load, idling, descending a long grade, etc. The ECU 28 and fuel injectors 32 are configured for substantially constant pressure in the common rail 26, which is maintained by the HPP 10 under control of the ECU 28.

[0017] The HPP 10 is illustrated in the form of a single plunger pump driven by a cam 36. A pumping plunger 38 reciprocates in a pump bore 40 to alternately expand the pumping chamber 42 to draw fuel into the pumping chamber and then pressurize the pumping chamber 42 to pump fuel to the common rail 26 via the outlet fitting 18 and rail feed passage 24. A cam follower 44 is biased toward the profile 46 of the cam 36 and is connected to the pumping plunger 38 to translate the shape of the cam profile 46 into reciprocal movement of the pumping plunger 38. The cam 36 has a four-sided profile 46 that will generate four charge/pump cycles of the pumping plunger 38 for each 360 rotation of the cam 36. The cam may have any number of lobes, with most having three or four lobes. The durations of the charging and pumping cycles are a function of the cam profile 46 and rotational speed of the cam 36. The cam 36 in FIG. 2 is shown at a top dead center (TDC) of the cam profile, which defines the end of a pumping cycle and the beginning of a charging cycle. In the symmetrical cam profile used to illustrate this application, the mid-point of each side of the cam profile 46 corresponds to the lowest point and is the bottom dead center (BDC) of the cam profile 46, which defines the end of a charging cycle and the beginning of a pumping cycle. In a cam profile having asymmetrical shape, the lowest point of the cam profile corresponding to BDC may not be at the mid-point between lobes. The total stroke of the pumping plunger is defined by the radial distance from the cam's TDC and BDC positions. Each lobe of the cam profile 46 may be asymmetric such that the angular displacement from BDC to TDC may be different from TDC to BDC. The shape of all lobes of the cam 36 is typically the same, but this is not required.

[0018] As shown in FIG. 1 a pump body 48 is the primary structural component of the disclosed HPP 10, and provides locations for receiving and mounting the components of the HPP 10. In addition to conventional fasteners, components of the HPP 10 may be secured to the pump body 48 by threaded, interference fit, or welded connections. Other methods of assembly and connection will occur to those skilled in the art, and the disclosed HPP 10 is not limited by exemplary methods discussed in this application. Stepped bores can be employed to trap internal components within the pump body 48. The inlet fitting 22 may include an inlet filter 50 and communicates with a volume defined by an accumulator cover 52 secured to the pump body 48. The accumulator cover 52 surrounds a volume containing an accumulator 54 configured to damp pressure fluctuations generated by the HPP 10 during operation. The accumulator 54 includes gas filled metal bellows supported within the accumulator cover 52 by an accumulator support and accumulator spacers, so that the accumulator 54 can change shape to absorb pressure pulses generated by the HPP 10. A control valve feed passage 56 defined by the pump body 48 leads from the accumulator 54 to the ICV 12.

[0019] An embodiment of an ICV 12 according to aspects of the disclosure is illustrated in FIG. 1 and FIGS. 9-16. As will be described in greater detail below, the disclosed ICV 12 functions as both a pump inlet check valve and an inlet metering valve to control both the timing and quantity of fuel flow through the ICV 12 to the pumping chamber 42. Elimination of a dedicated pump inlet check valve reduces the part count of the disclosed HPP 10, and also reduces the trapped volume of the pump by eliminating volume that would be associated with a dedicated pump inlet check valve. The illustrated ICV 12 is a two port, two position, normally open, directly solenoid actuated flow control valve. A control valve seat 58 is received in a stepped bore defined by the pump body 48 and defines a fluid flow passage connecting the control valve feed passage 56 with part of the pumping chamber 42 defined by a stop pin support 60. As best seen in FIGS. 9-16, the inlet valve 62 includes a disc shaped valve member 64 integrally connected to a valve stem 66 that passes through the inlet valve seat 58. The stop pin support 60 supports a stop pin 68 and defines part of the pumping chamber 42 in communication with the valve seat 58 and high pressure discharge from the pumping chamber 42 to the outlet fitting 18. The valve stem 66 is coupled to an inlet valve armature 70 by an armature retaining ring 71. The inlet valve armature 70 and inlet valve 64 are biased toward an open position (shown in FIGS. 1 and 9) by an inlet valve spring 72.

[0020] A control valve solenoid 74 includes a coil that generates a magnetic field in a control valve pole 76 aligned with and adjacent to the inlet valve armature 70. When the control valve solenoid 74 is energized under control of the ECU 28, the magnetic field generated by the solenoid coil attracts the inlet valve armature 70 and the inlet valve 62 is moved to a closed position (shown in FIG. 10) against the bias of the inlet valve spring 72. In a closed position, the valve member 64 is in contact with the inlet valve seat 58, separating the control valve feed passage 56 from the pumping chamber 42. Closure of the inlet valve 62 during a pumping cycle allows fuel in the pumping chamber 42 to be pressurized and pumped through the DCV 16, outlet fitting 18 and high pressure passage 24 to the common rail 26. The timing of closure of the ICV 12 is set by the ECU 28 in response to inputs including the pressure of the common rail 26 detected by pressure sensor 34 and the camshaft position reported by the camshaft position sensor 30. Once the inlet valve 62 is closed, the inlet valve spring 72 cannot open the inlet valve 62 until the pressure of the pumping chamber falls to a minimum. This allows the control valve solenoid 74 to be de-energized before completion of a pumping cycle to reduce electrical power consumption and reduce heat added to the system.

[0021] The disclosed ICV configuration reduces the number of impacts between components to two impacts per actuation cycle, specifically impact of the inlet valve 62 and valve seat 58 and impact of the inlet valve 62 and stop pin 68. These impacts occur near the center of the HPP 10, and far from the extremities of the HPP 10 where noise is more easily radiated. Further noise reduction can be attained by selection of the material from which the stop pin 68 is constructed, such that the impact would generate less energetic vibrations. The surface of the valve member 64 that contacts the stop pin may include material such as engineered plastic, for example PEEK, to reduce noise generated by impact of the inlet valve 62 with the stop pin. The stop pin support 60 may be configured to reduce the transmission of impact vibrations from the stop pin to surrounding structures. In the disclosed HPP 10, the end of the stop pin 68 opposite the inlet valve 62 is exposed to a fluid volume leading to the DCV 16 and outlet fitting 18, which may reduce noise radiated from the stop pin 68.

[0022] The pumping plunger 38 reciprocates in the pumping bore 40 defined by a plunger sleeve 78. The plunger sleeve 78 is secured to the pump body 48 by a pilot tube 80 received in a shallow bore defined by the pump body 48. The plunger sleeve 78 is biased toward the pump body 48 by a load ring 82 compressed between an internal shoulder 84 of the pilot ring 80 and the lower end of the plunger sleeve 78. A neck portion 86 of the pilot tube 80 supports a plunger seal 88 that seals against a lower portion of the pumping plunger 38. A plunger return spring seat 90 is secured to the lower end of the pumping plunger 38 and a plunger return spring 92 is biased between the plunger return spring seat 90 and an external shoulder 94 of the pilot tube 80. A plunger retaining ring 96 is received in a groove defined at the lower end of the pumping bore 40 to prevent the pumping plunger 38 from being pulled out of the pumping bore 40 by the plunger return spring 92. As shown in FIG. 2, a cam follower 44 is situated between the pumping plunger 38 and the cam 36 and is arranged to follow the cam profile 46, exerting reciprocal motion on the pumping plunger 38.

[0023] Some leakage will occur between the pumping plunger 38 and pumping bore 40 during pump operation. The disclosed HPP 10 defines a pump drain 98 from the pilot tube 80 to the control valve feed 56 via passages in the control valve seat 58, allowing leakage flow back to the low pressure inlet of the HPP 10. A pumping plunger 38 having a pumping end with a greater diameter than the driven end as shown in FIG. 1, will tend to pump leakage flow during the charging cycle, and this pumped leakage flow is also directed to the pump drain 98.

[0024] With reference to FIGS. 1, 9 and 10, the ICV 12 includes the control valve solenoid 74 with control valve pole 76, inlet valve 62, control valve seat 58, inlet valve armature 70 and inlet valve spring 72. The inlet valve 62 includes a valve stem 66 integrally connected to a valve member 64 configured to mate with an annular surface on the valve seat 58 when moved to the closed position. The valve stem 66 reciprocates in a bore defined by the valve seat 58, guiding movement of the inlet valve 62 between the open position (FIG. 9) and the closed position (FIG. 10). The inlet valve 62 is biased toward an open position by the inlet valve spring 72, which acts on the inlet valve armature 70 and inlet valve 62. The open position of the inlet valve 62 is determined by contact between the valve member 64 and the stop pin 68 as shown in FIG. 9. When the inlet valve 62 is in the open position, there is an air gap between the inlet valve armature 70 and the control valve pole 76. As shown in FIG. 10, when the solenoid 74 is energized, the inlet valve armature 70 and inlet valve are attracted to the control valve pole 76, compressing the inlet valve spring 72 and closing the valve member 64 against the valve seat 58.

[0025] Movement of the inlet valve 62 between contact with the stop pin 68 and contact with the valve seat 58 defines the ICV stroke as shown in FIG. 10. According to aspects of the disclosure, the ICV stroke is less than the air gap between the control valve pole 76 and the inlet valve armature 70 when the inlet valve 62 is in the open position, leaving an armature gap between the control valve pole 76 and the inlet valve armature 70 when the inlet valve is in the closed position. The length of the valve stem 66 and the shape of the inlet valve armature 70 are selected to ensure the inlet valve armature 70 does not contact the control valve pole 76 when the inlet valve 62 is in the closed position. As shown in FIG. 10, an armature gap remains between the inlet valve armature 70 and the control valve pole 76 when the inlet valve 62 is in the closed position. The armature gap eliminates one point of contact between moving components in the disclosed ICV 12.

[0026] FIGS. 1 and 9-16 illustrate a discharge/outlet check valve (DCV) 16 and pressure relief valve (PRV) 14 integrated into a pump outlet fitting 18 according to aspects of the disclosure. With specific reference to FIGS. 1 and 9, the pump outlet fitting 18 defines a stepped bore 100 communicating at one end with the pumping chamber 42 (or a passage fluidly connected to the pumping chamber) and at the other end with the high pressure passage 24 to the common rail 26. A PRV seat 102 defines an outlet flow path 103 through bores disposed around a discharge check valve spring seat (DCV spring seat) 104 arranged on an axis A of the outlet fitting 18. The discharge check valve ball (DCV ball) 106 is biased by the DCV spring 108 toward a discharge check valve seat (DCV seat) 110 on a pressure relief valve shuttle (PRV shuttle) 112. The PRV seat 102 includes an annular, conical surface 114 that mates with a complementary surface 116 (surrounding the DCV seat 110) on the PRV shuttle 112. The PRV seat 102 is in a fixed position defined by the stepped bore 100, and the PRV shuttle 112 is biased against the PRV seat 102 by a PRV spring 118.

[0027] According to aspects of the disclosure, the PRV spring 118 is a stack of conical disc springs compressed between a pressure relief valve cup (PRV cup) 120 and the PRV shuttle 112 to bias the PRV shuttle 112 toward a closed position illustrated in FIGS. 1 and 9. The stacked conical disc springs generate the high force necessary to maintain the PRV 14 in the closed position against operating pressures in the common rail 26 of 350 bar (35 MPa) or more, in a very compact configuration. Little or no space is left between the stacked conical disc springs, and the stroke of the PRV shuttle 112 is very short, meaning very little trapped volume is associated with the disclosed PRV 14. The PRV cup 120 has an interference fit within the stepped bore 100 of the pump outlet fitting 18, and traps the PRV shuttle 112, PRV spring 118, DCV ball 106, DCV spring 108, and PRV seat 102 within the pump outlet fitting 18. The position of the PRV cup 120 in the stepped bore 100 is set during assembly to calibrate the opening pressure of the PRV 14. The opening pressure of the PRV 14 can be calibrated before assembly of the outlet fitting 18 to the pump body 48. The PRV cup 120 and PRV shuttle 112 are configured to occupy most of the space within the stepped bore 100 between the DCV ball 106 and the pumping chamber 42, further reducing the trapped volume of the HPP 10 attributable to the PRV 14.

[0028] The outlet fitting 18 including an integrated PRV 14 and DCV 16 minimize the trapped volume of the HPP 10 to which the outlet fitting 18 is attached, provide high flow capacity through the PRV 14, and the short stroke of the PRV shuttle 112 results in fast actuation and closure of the PRV 14 while the HPP 10 is operating. The DCV ball 106 opens only when the pressure in the high pressure passage 24 leading to the common rail 26 is less than the pressure in the pumping chamber 42 or passage leading from the pumping chamber to the pump outlet fitting 18 as shown in FIGS. 10, 13, and 16. This condition occurs during a pumping cycle when the pressure of the pump outlet passage 24 and common rail 26 are below maximum pressure.

[0029] FIGS. 3 and 11 illustrate fuel flow in the disclosed HPP 10 during a charging cycle of the pump, i.e., during retraction of the pumping plunger 38. Fuel pumped by the LPP 20 enters the inlet fitting 22 and passes through the inlet filter 50 (if present). The inlet fitting 22 is in fluid communication with the accumulator 54, and fuel may be routed through the accumulator 54 as shown in FIG. 1. The ICV 12 is in its normally open state, and allows fuel to flow into the pumping chamber 42 as the pumping plunger 38 is retracted. The DCV 16 is held closed by pressure behind the DCV ball 106, which is exposed to the pressure of the common rail 26. In the disclosed HPP 10, the pumping chamber 42 is completely filled with fuel by the end of the charging cycle. When the cam follower 44 reaches the center of a side of the cam profile 46 the plunger stops retracting, ending the charging cycle. As the cam 36 rotates further, the cam follower 44 begins pushing the pumping plunger 38 into the pumping bore, beginning a pumping cycle.

[0030] FIGS. 4 and 12 illustrate an initial portion of a pumping cycle, during which the ICV 12 remains open. When the pumping plunger 38 is being driven into the pumping bore 40, the volume of the pumping chamber 42 is reduced, pushing fuel out of the pumping chamber 42. With the ICV 12 open, fuel is spilled from the pumping chamber back toward the low pressure inlet. When the ICV 12 is closed by the ECU 28 energizing the control valve solenoid 74, fuel in the pumping chamber 42 begins to be pressurized by the pumping plunger 38. When the pressure in the pumping chamber 42 exceeds the pressure of the common rail 26, the DCV 16 opens and fuel is pumped to the common rail 26. The timing of ICV 12 closure determines the quantity of fuel pumped to the common rail 26, because fuel pressurization cannot begin until the ICV 21 is closed. In this manner, the ICV 12 meters the quantity of fuel pumped to the common rail 26 under control of the ECU 28.

[0031] FIGS. 5 and 13 illustrate the position of the ICV 12 and DCV 16 during fuel delivery to the common rail 26. The control valve solenoid 74 is energized, the ICV 12 is closed, and fuel in the pumping chamber 42 has reached a pressure greater than the pressure of the common rail 26, opening the DCV 16. Any fuel that leaks between the pumping plunger 38 and the pumping bore 40 is directed by the pump drain 98 back to the low pressure inlet of the HPP 10. Pressure in the pumping chamber 42 acts on the valve member 64 to hold the inlet valve 62 in the closed position. The inlet valve spring 72 cannot open the inlet valve 62 until the pressure of the pumping chamber 42 drops to a minimum. This permits intentionally de-energizing the control valve solenoid 74 before the completion of a pumping cycle to reduce electrical power consumption and reduce heat added to the system.

[0032] FIGS. 6 and 14 illustrate actuation of the PRV 14 in response to a heat soak condition where the pressure of the common rail 26 is greater than maximum pressure. The PRV shuttle 112 and closed DCV ball 106 are exposed to the pressure of the common rail 26 through the high pressure passage 24 connected to the pump outlet fitting 18. The PRV shuttle 112 is moved away from the PRV seat 102 against the bias of the PRV spring 118 and allows excess pressure to pass between valve surfaces 114, 116, through the pumping chamber 42, the open ICV 12, and control valve feed passage 56 to the low pressure inlet. In a heat soak condition, the PRV shuttle 112 will move (open) a small amount because the volume of fluid being relieved is small and the rate of fluid flow is low.

[0033] FIGS. 7 and 15 illustrate actuation of the PRV 14 during pump operation, which is exactly the same as PRV 14 actuation in response to a heat soak, except the PRV shuttle 112 will open further due to the larger volume of fluid to be relieved and the high rate of fluid flow required to relieve pressure during a charging cycle of the pump. As shown in FIG. 15, the inlet valve 62 is held closed by high pressure fuel being relieved from the common rail through the PRV 14. Fuel being relieved from the common rail 26 fills the pumping chamber 42 as the pumping plunger 38 is retracted during a charging cycle of the pump.

[0034] FIGS. 8 and 16 illustrate fuel flow through the ICV 12, pumping chamber 42 and DCV 16 during a limp home scenario where the HPP 10 is not operational. In this scenario, the high pressure passage 24 and common rail 26 are no longer being supplied with high pressure fuel. The DCV valve spring 108 is selected with a light bias that will open when exposed to feed pressure generated by the LPP 20 that has passed through the open ICV 12 and the pumping chamber 42. With no pressure behind it, the DCV ball 106 opens when exposed to feed pressure and allows low pressure fuel to fill the common rail 26. Common rail pressure corresponding to feed pressure from the LPP 20 is sufficient to allow the fuel injectors 32 and engine to operate at reduced power. Engine operation will be sub-optimal, but sufficient to provide minimum driving capabilities towards a safe environment or maintenance facility.

[0035] While the embodiment of the disclosed integrated outlet check valve 16 and pressure relief valve 14 has been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit of the disclosure and the scope of the claimed coverage.