Fuel pump and combination outlet and pressure relief valve thereof

Abstract

An outlet and pressure relief valve assembly for a fuel pump includes a housing which extends along an axis from an inner end to an outer end. The housing has a bore which extends thereinto along the axis from the inner end. A valve seat is located within the bore and has an end wall which is transverse to the axis and also has a sidewall which is annular in shape and extends away from the end wall. An outlet flow passage extends through the end wall such that the outlet flow passage is centered about the axis. A pressure relief flow passage extends through the end wall such that the pressure relief flow passage is laterally spaced from the outlet flow passage. An outlet valve member is located within the valve seat sidewall and a pressure relief valve member is located between the valve seat and the inner end.

Claims

1. A fuel pump comprising: a fuel pump housing with a pumping chamber defined therein, said fuel pump housing having an outlet valve bore, said outlet valve bore extending along, and being centered about, an outlet valve bore axis; a pumping plunger which reciprocates within a plunger bore along a plunger bore axis such that an intake stroke of said pumping plunger increases volume of said pumping chamber and a compression stroke of said pumping plunger decreases volume of said pumping chamber; and an outlet and pressure relief valve assembly comprising: a valve housing which extends along said outlet valve bore axis from an inner end, which is proximal to said pumping chamber, to an outer end which is outside of said fuel pump housing, said valve housing having a valve housing bore which extends into said valve housing along said outlet valve bore axis from said inner end, said valve housing also having an outlet passage which is in fluid communication with said valve housing bore and extending to said outer end; a valve seat located within said valve housing bore, said valve seat having a valve seat end wall which is transverse to said outlet valve bore axis and also having a valve seat sidewall which is annular in shape and extends away from said valve seat end wall, wherein an outlet flow passage extends through said valve seat end wall such that said outlet flow passage is centered about said outlet valve bore axis and wherein a pressure relief flow passage extends through said valve seat end wall such that said pressure relief flow passage is laterally spaced from said outlet flow passage relative to said outlet valve bore axis; an outlet valve member which is located within said valve seat sidewall such that said outlet valve member is moveable between 1) a seated position which prevents flow through said valve housing in a first direction from said outer end to said inner end and 2) an unseated position which allows flow through said valve housing in a second direction from said inner end to said outer end; and a pressure relief valve member which is located between said valve seat and said inner end such that said pressure relief valve member is moveable between 1) a seated position which prevents flow through said valve housing in said second direction and 2) an unseated position which allows flow through said valve housing in said first direction; wherein said outlet valve member and said pressure relief valve member are both located entirely within said fuel pump housing; and wherein said plunger bore axis is transverse to said outlet valve bore axis and said valve housing is aligned with said pumping plunger in a direction parallel to said plunger bore axis.

2. The fuel pump as in claim 1, wherein: said valve housing bore extends into said valve housing along said outlet valve bore axis from said inner end to a shoulder which is transverse to said outlet valve bore axis and which faces toward said inner end; and said valve seat is positioned within said valve housing bore either directly or indirectly by said shoulder.

3. The fuel pump as in claim 2, wherein said valve seat sidewall spaces said valve seat end wall away from said shoulder.

4. The fuel pump as in claim 1, wherein said outlet and pressure relief valve assembly further comprises an outlet valve spring which biases said outlet valve member toward said seated position, said outlet valve spring being located within said valve seat sidewall.

5. The fuel pump as in claim 4, wherein: said valve housing bore extends into said valve housing along said outlet valve bore axis from said inner end to a shoulder which is transverse to said outlet valve bore axis and which faces toward said inner end; said outlet valve assembly further comprises an outlet valve spring seat which is captured axially between said valve seat and said shoulder such that said outlet valve spring seat engages both said valve seat and said shoulder; and said outlet valve spring is grounded to said valve housing through said outlet valve spring seat.

6. The fuel pump as in claim 5, wherein said outlet valve spring is located entirely within said valve seat sidewall.

7. The fuel pump as in claim 1, wherein said outlet and pressure relief valve assembly further comprises a pressure relief valve spring which biases said pressure relief valve member toward said seated position, said pressure relief valve spring being surrounded directly by said valve housing.

8. The fuel pump as in claim 1, wherein an unobstructed passage is provided, in a direction parallel to said outlet valve bore axis, from said inner end to said outlet valve member.

9. An outlet and pressure relief valve assembly for a fuel pump, said outlet and pressure relief valve assembly comprising: a valve housing which extends along an axis from an inner end to an outer end, said valve housing having a valve housing bore which extends into said valve housing along said axis from said inner end, said valve housing also having an outlet passage which is in fluid communication with said valve housing bore and extending to said outer end; a valve seat located within said valve housing bore, said valve seat having a valve seat end wall which is transverse to said axis and also having a valve seat sidewall which is annular in shape and extends away from said valve seat end wall such that a volume is formed radially inward from said valve seat sidewall, wherein an outlet flow passage extends through said valve seat end wall such that said outlet flow passage is centered about said axis and wherein a pressure relief flow passage extends through said valve seat end wall such that said pressure relief flow passage is laterally spaced from said outlet flow passage relative to said axis and such that said pressure relief flow passage opens into said volume; an outlet valve member which is located within said valve seat sidewall and within said volume such that said outlet valve member is moveable between 1) a seated position which prevents flow through said valve housing in a first direction from said outer end to said inner end and 2) an unseated position which allows flow through said valve housing via said volume in a second direction from said inner end to said outer end; and a pressure relief valve member which is located between said valve seat and said inner end such that said pressure relief valve member is moveable between 1) a seated position which prevents flow through said valve housing in said second direction and 2) an unseated position which allows flow through said valve housing via said volume in said first direction.

10. The outlet and pressure relief valve assembly as in claim 9, wherein: said valve housing bore extends into said valve housing along said axis from said inner end to a shoulder which is transverse to said axis and which faces toward said inner end; and said valve seat is positioned within said valve housing bore either directly or indirectly by said shoulder.

11. The outlet and pressure relief valve assembly as in claim 10, wherein said valve seat sidewall spaces said valve seat end wall away from said shoulder.

12. The outlet and pressure relief valve assembly as in claim 9, wherein said outlet and pressure relief valve assembly further comprises an outlet valve spring which biases said outlet valve member toward said seated position, said outlet valve spring being located within said valve seat sidewall.

13. The outlet and pressure relief valve assembly as in claim 12, wherein: said valve housing bore extends into said valve housing along said axis from said inner end to a shoulder which is transverse to said axis and which faces toward said inner end; said outlet valve assembly further comprises an outlet valve spring seat which is captured axially between said valve seat and said shoulder such that said outlet valve spring seat engages both said valve seat and said shoulder; and said outlet valve spring is grounded to said valve housing through said outlet valve spring seat.

14. The outlet and pressure relief valve assembly as in claim 13, wherein said outlet valve spring is located entirely within said valve seat sidewall.

15. The outlet and pressure relief valve assembly as in claim 9, wherein said outlet and pressure relief valve assembly further comprises a pressure relief valve spring which biases said pressure relief valve member toward said seated position, said pressure relief valve spring being surrounded directly by said valve housing.

16. The outlet and pressure relief valve assembly as in claim 9, wherein an unobstructed passage is provided, in a direction parallel to said axis, from said inner end to said outlet valve member.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) This disclosure will be further described with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic view of a fuel system including a fuel pump in accordance with the present disclosure;

(3) FIG. 2 is an enlarged cross-sectional view of the fuel pump of FIG. 1;

(4) FIG. 3 is a cross-sectional view of an outlet and pressure relief valve assembly of the fuel pump of FIG. 1;

(5) FIGS. 4 and 5 are exploded isometric views of the outlet and pressure relief valve assembly of FIG. 3 taken from different perspectives;

(6) FIG. 6 is the cross-sectional view of FIG. 3 shown with an outlet valve member in an unseated position and arrows to show the path of fuel flow; and

(7) FIG. 7 is the cross-sectional view of FIG. 3 shown with a pressure relief valve member in an unseated position and arrows to show the path of fuel flow.

DETAILED DESCRIPTION OF INVENTION

(8) In accordance with a preferred embodiment of this disclosure and referring initially to FIG. 1, a fuel system 10 for an internal combustion engine 12 is shown in schematic form. Fuel system 10 generally includes a fuel tank 14 which holds a volume of fuel to be supplied to internal combustion engine 12 for operation thereof; a plurality of fuel injectors 16 which inject fuel directly into respective combustion chambers (not shown) of internal combustion engine 12; a low-pressure fuel pump 18; and a high-pressure fuel pump 20 where the low-pressure fuel pump 18 draws fuel from fuel tank 14 and elevates the pressure of the fuel for delivery to high-pressure fuel pump 20 where the high-pressure fuel pump 20 further elevates the pressure of the fuel for delivery to fuel injectors 16. By way of non-limiting example only, low-pressure fuel pump 18 may elevate the pressure of the fuel to about 500 kPa or less and high-pressure fuel pump 20 may elevate the pressure of the fuel to above about 14 MPa and may be about 35 MPa depending on the operational needs of internal combustion engine 12. While four fuel injectors 16 have been illustrated, it should be understood that a lesser or greater number of fuel injectors 16 may be provided.

(9) As shown, low-pressure fuel pump 18 may be provided within fuel tank 14, however low-pressure fuel pump 18 may alternatively be provided outside of fuel tank 14. Low-pressure fuel pump 18 may be an electric fuel pump as are well known to a practitioner of ordinary skill in the art. A low-pressure fuel supply passage 22 provides fluid communication from low-pressure fuel pump 18 to high-pressure fuel pump 20. A fuel pressure regulator 24 may be provided such that fuel pressure regulator 24 maintains a substantially uniform pressure within low-pressure fuel supply passage 22 by returning a portion of the fuel supplied by low-pressure fuel pump 18 to fuel tank 14 through a fuel return passage 26. While fuel pressure regulator 24 has been illustrated in low-pressure fuel supply passage 22 outside of fuel tank 14, it should be understood that fuel pressure regulator 24 may be located within fuel tank 14 and may be integrated with low-pressure fuel pump 18.

(10) Now with additional reference to FIG. 2, high-pressure fuel pump 20 includes a fuel pump housing 28 which includes a plunger bore 30 which extends along, and is centered about, a plunger bore axis 32. As shown, plunger bore 30 may be defined by a combination of an insert and directly by fuel pump housing 28 but may alternatively be formed only, and directly by, fuel pump housing 28. High-pressure fuel pump 20 also includes a pumping plunger 34 which is located within plunger bore 30 and reciprocates within plunger bore 30 along plunger bore axis 32 based on input from a rotating camshaft 36 of internal combustion engine 12 (shown only in FIG. 1). A pumping chamber 38 is defined within fuel pump housing 28. An inlet valve assembly 40 of high-pressure fuel pump 20 is located within a pump housing inlet passage 41 of fuel pump housing 28 and selectively allows fuel from low-pressure fuel pump 18 to enter pumping chamber 38 while an outlet and pressure relief valve assembly 42 is located within an outlet valve bore 43 of fuel pump housing 28 and selectively allows fuel to be communicated from pumping chamber 38 to fuel injectors 16 via a fuel rail 44 to which each fuel injector 16 is in fluid communication. Outlet and pressure relief valve assembly 42 also provides a fluid path back to pumping chamber 38 if the pressure downstream of outlet and pressure relief valve assembly 42, i.e. between outlet and pressure relief valve assembly 42 and fuel injectors 16, reaches a predetermined limit which may pose an unsafe operating condition if left unmitigated. Outlet valve bore 43 is centered about, and extends along, an outlet valve bore axis 43a. In operation, reciprocation of pumping plunger 34 causes the volume of pumping chamber 38 to increase during an intake stroke of pumping plunger 34 (downward as oriented in FIG. 2) in which a plunger return spring 46 causes pumping plunger 34 to move downward, and conversely, the volume of pumping chamber 38 decreases during a compression stroke (upward as oriented in FIG. 2) in which camshaft 36 causes pumping plunger 34 to move upward against the force of plunger return spring 46. In this way, fuel is drawn into pumping chamber 38 during the intake stroke, and conversely, fuel is pressurized within pumping chamber 38 by pumping plunger 34 during the compression stroke, depending on the state of operation of inlet valve assembly 40 as will be described in greater detail later, and discharged through outlet and pressure relief valve assembly 42 under pressure to fuel rail 44 and fuel injectors 16. For clarity, a portion of pumping plunger 34 is shown in phantom lines in FIG. 2 to represent the intake stroke at a bottom dead center position (volume of pumping chamber 38 is maximized) and pumping plunger 34 is shown in solid lines in FIG. 2 to represent the compression stroke at a top dead center position (volume of pumping chamber 38 is minimized) such that pumping plunger 34 reciprocates between the bottom dead center position and the top dead center position.

(11) Outlet and pressure relief valve assembly 42 will now be discussed with continued reference to FIGS. 1 and 2 and additionally with particular reference to FIGS. 3-7. Outlet and pressure relief valve assembly 42 generally includes a valve housing 48 which is tubular and extends along outlet valve bore axis 43a from an inner end 48a, which is proximal to pumping chamber 38, to an outer end 48b, which is distal from pumping chamber 38 and outside of fuel pump housing 28. A valve housing bore 48c extends into valve housing 48 from inner end 48a along outlet valve bore axis 43a such that valve housing bore 48c is centered about outlet valve bore axis 43a. Valve housing bore 48c extends from inner end 48a to a shoulder 48d which is transverse to outlet valve bore axis 43a and which faces toward inner end 48a. A valve housing outlet passage 48e extends from shoulder 48d to outer end 48b such that valve housing outlet passage 48e provides fluid communication from valve housing bore 48c to outer end 48b. The inner periphery of valve housing bore 48c and valve housing outlet passage 48e are each surfaces of revolution centered about outlet valve bore axis 43a. Similarly, the outer periphery of valve housing 48 is a surface of revolution centered about outlet valve bore axis 43a. Furthermore, the outer periphery of valve housing 48 includes an external shoulder 48f which is annular in shape and which is transverse to outlet valve bore axis 43a such that external shoulder 48f engages a complementary internal shoulder 43b of outlet valve bore 43, thereby providing a stop to establish a position of outlet and pressure relief valve assembly 42 within outlet valve bore 43.

(12) Outlet and pressure relief valve assembly 42 also includes a valve seat 50 which is located within valve housing bore 48c and is positioned either directly or indirectly by shoulder 48d. As illustrated herein, shoulder 48d indirectly positions valve seat 50 because an intermediate element, which will be described later, is disposed between valve seat 50 and shoulder 48d such that the intermediate member acts as an extension of shoulder 48d to provide a positive stop for valve seat 50, however, it is anticipated that valve seat 50 could alternatively directly contact shoulder 48d. Valve seat 50 includes a valve seat end wall 50a which is transverse to outlet valve bore axis 43a. Valve seat 50 also includes a valve seat sidewall 50b which is annular in shape and which extends away from valve seat end wall 50a such that valve seat sidewall 50b spaces valve seat end wall 50a away from shoulder 48d. An outlet flow passage 50c extends through valve seat end wall 50a such that outlet flow passage 50c is centered about outlet valve bore axis 43a and such that outlet flow passage 50c provides a path for fuel through valve seat end wall 50a when fuel flows from inner end 48a to outer end 48b in order to communicate pressurized fuel from pumping chamber 38 to fuel injectors 16. Furthermore, one or more pressure relief flow passages 50d extend through valve seat end wall 50a such that each pressure relief flow passage 50d is laterally spaced from outlet flow passage 50c relative to outlet valve bore axis 43a. In this way, pressure relief flow passages 50d are arranged in a polar array which is centered about outlet valve bore axis 43a. Pressure relief flow passages 50d provide a path for fuel through valve seat end wall 50a when fuel flows from outer end 48b to inner end 48a during an over-pressure condition downstream of outlet and pressure relief valve assembly 42. While two pressure relief flow passages 50d have been illustrated in the figures, it should be understood that different quantities may be used. The inner periphery of valve seat sidewall 50b includes a plurality of circumferentially alternating flow channels 50e and valve guides 50f such that flow channels 50e provide a path for fuel to flow therethrough. Valve seat 50 is sealed to valve housing 48 such that flow is prevented radially between the outer periphery of valve seat 50 and the inner periphery of valve housing bore 48c. For example, the outer periphery of valve seat 50 may engage the inner periphery of valve housing bore 48c in an interference fit.

(13) Outlet and pressure relief valve assembly 42 also includes an outlet valve member 52 which is located within valve seat sidewall 50b and which is moveable between 1) a seated position, shown in FIGS. 3 and 7, against said valve seat end wall 50a which prevents flow through valve housing 48 by way of outlet flow passage 50c in a first direction from outer end 48b to inner end 48a and 2) an unseated position, shown in FIG. 6, spaced apart from valve seat end wall 50a which allows flow through valve housing 48 by way of outlet flow passage 50c in a second direction from inner end 48a to outer end 48b. Movement of outlet valve member 52 in a direction laterally relative to outlet valve bore axis 43a is limited by valve guides 50f while flow channels 50e provide a path to flow around outlet valve member 52 when outlet valve member 52 is unseated. As illustrated herein, outlet valve member 52 is spherical. While outlet valve member 52 may be illustrated herein as a full sphere, spherical as used herein includes a portion of a sphere, such as a frustum of a sphere, a spherical cap, or a spherical segment. Alternatively, outlet valve member 52 may be conical or frustoconical. Outlet valve member 52 is biased toward valve seat end wall 50a by an outlet valve spring 54 which is grounded to valve housing 48 through an outlet valve spring seat 56 and which is located entirely within valve seat sidewall 50b. Outlet valve spring 54 is a coil compression spring and outlet valve spring seat 56 is a disk with one or more outlet valve spring seat apertures 56a extending therethrough to allow passage of fuel. Outlet valve spring seat apertures 56a are arranged in a polar array centered about outlet valve bore axis 43a, thereby allow the central portion of outlet valve spring seat 56 to remain solid to provide a surface for outlet valve spring 54 to engage. While five outlet valve spring seat apertures 56a have been illustrated in the figures, it should be understood that different quantities may be used. The outer edge of outlet valve spring seat 56 is captured axially between valve seat sidewall 50b and shoulder 48d such that outlet valve spring seat 56 engages both valve seat sidewall 50b and shoulder 48d. Since the outer edge of outlet valve spring seat 56 is captured axially between valve seat sidewall 50b and shoulder 48d such that outlet valve spring seat 56 engages both valve seat sidewall 50b and shoulder 48d, shoulder 48d indirectly positions valve seat 50 within valve housing bore 48c. In this way, valve seat 50 is pressed into place during assembly of outlet and pressure relief valve assembly 42 until it is stopped by shoulder 48d and outlet valve spring seat 56.

(14) Outlet and pressure relief valve assembly 42 also includes a pressure relief valve member 58 located within valve housing bore 48c between valve seat 50 and inner end 48a such that pressure relief valve member 58 is moveable between 1) a seated position, shown in FIGS. 3 and 6, against valve seat end wall 50a which prevents flow through valve housing 48 in the second direction from inner end 48a to outer end 48b by way of pressure relief flow passages 50d and 2) an unseated position, shown in FIG. 7, spaced apart from valve seat end wall 50a which allows flow through valve housing 48 in the first direction from outer end 48b to inner end 48a by way of pressure relief flow passages 50d. Pressure relief valve member 58 is centered about outlet valve bore axis 43a such that pressure relief valve member 58 extends along outlet valve bore axis 43a from a pressure relief valve member inner end 58a, which is proximal to inner end 48a, to a pressure relief valve member outer end 58b, which is distal from inner end 48a. A pressure relief valve member outlet flow passage 58c extends axially through pressure relief valve member 58 from pressure relief valve member inner end 58a to pressure relief valve member outer end 58b such that pressure relief valve member outlet flow passage 58c provides a path for fuel to flow when outlet valve member 52 is unseated. Pressure relief valve member outlet flow passage 58c is centered about outlet valve bore axis 43a. The outer periphery of pressure relief valve member 58 is a surface of revolution about outlet valve bore axis 43a such that the outer periphery is stepped in diameter, thereby forming a pressure relief valve spring seat 58d which is annular in shape and which is transverse to outlet valve bore axis 43a, and is preferably perpendicular to outlet valve bore axis 43a. Pressure relief valve member outer end 58b is annular in shape, is planar, and projects over the entirety of pressure relief flow passages 50d such that pressure relief valve member 58 prevents fluid communication through pressure relief flow passages 50d when pressure relief valve member 58 is in the seated position.

(15) Outlet and pressure relief valve assembly 42 also includes a pressure relief valve spring 60 which is located within valve housing bore 48c. It should be noted that pressure relief valve spring 60 is surrounded directly by valve seat sidewall 50b, i.e. there are no intermediate elements located radially between pressure relief valve spring 60 and valve seat sidewall 50b, thereby allowing any radial shift of pressure relief valve spring 60 to be controlled directly by valve housing 48. Pressure relief valve spring 60 is a coil compression spring which is held in pression by pressure relief valve spring seat 58d and a pressure relief valve spring retainer 62. Pressure relief valve spring retainer 62 is located within valve housing bore 48c and is annular in shape such that a pressure relief valve spring retainer outlet passage 62a extends axially, i.e. along outlet valve bore axis 43a, through pressure relief valve spring retainer 62, thereby providing a path for fuel to flow when outlet valve member 52 is unseated. Pressure relief valve spring retainer outlet passage 62a is centered about outlet valve bore axis 43a. The outer periphery of pressure relief valve spring retainer 62 is engaged with the inner periphery of valve housing bore 48c and during assembly of outlet and pressure relief valve assembly 42, pressure relief valve spring retainer 62 is pressed into valve housing bore 48c until a predetermined compression force, within an acceptable tolerance range, of pressure relief valve spring 60 is achieved. In this way, pressure relief valve member 58 is unseated from valve seat 50 when a predetermined pressure downstream of outlet and pressure relief valve assembly 42 occurs.

(16) Inlet valve assembly 40 will now be described with particular reference to FIG. 2. Inlet valve assembly 40 generally includes an inlet valve member 40a, an inlet valve seat 40b, and a solenoid assembly 40c. Inlet valve member 40a and inlet valve seat 40b act together as a check valve which normally allows fuel to flow into pumping chamber 38 from pump housing inlet passage 41 when pumping plunger 34 is moving to expand the volume of pumping chamber 38, i.e. moving downward as oriented in the figures during the intake stroke, but prevents fuel from flowing from pumping chamber 38 to pump housing inlet passage 41 when pumping plunger 34 is moving to decrease the volume of pumping chamber 38, i.e. upward as oriented during the compression stroke. However, an electronic control unit 64 may be used to time the supply of an electric current to solenoid assembly 40c during the compression stroke, thereby varying the proportion of fuel from the compression stroke that is supplied to fuel injectors 16 and the proportion of fuel from the compression stroke that is spilled back to pump housing inlet passage 41. When an electric current is supplied to solenoid assembly 40c, inlet valve member 40a and inlet valve seat 40b act together as a check valve, i.e. fuel can flow into pumping chamber 38 through inlet valve assembly 40 but fuel cannot flow out of pumping chamber 38 through inlet valve assembly 40. Conversely, when no electric current is supplied to solenoid assembly 40c, inlet valve member 40a is held open, thereby allowing fuel to flow back to pump housing inlet passage 41 during a portion of the compression stroke, thereby allowing for the appropriate pressure and volume of fuel to be provided to fuel injectors 16. Inlet valve assembly 40 will not be describe further herein, however, further details may be found in United States Patent Application Publication No. US 2020/0011279 A1 to Dauer et al., the disclosure of which is hereby incorporated by reference in its entirety.

(17) In operation, and with particular reference to FIGS. 2 and 6, when inlet valve assembly 40 is closed and pumping plunger 34 is in the compression stroke, pressure within pumping chamber 38 is elevated, thereby resulting in a force sufficient to cause outlet valve member 52 to unseat from valve seat end wall 50a. Consequently, outlet flow passage 50c is opened, thereby allowing fuel to flow from pumping chamber 38 to fuel injectors 16. It should be noted that the coaxial nature of pressure relief valve spring retainer outlet passage 62a, pressure relief valve member outlet flow passage 58c, and outlet flow passage 50c provides an unobstructed passage, in a direction parallel to outlet valve bore axis 43a, from inner end 48a to outlet valve member 52. As a result, the fuel passing through pressure relief valve assembly 42 from pumping chamber 38 to fuel injectors 16 departs from linear flow to flow around outlet valve member 52, however, the spherical nature of outlet valve member 52 provides for a smooth transition, thereby minimizing restriction to the outlet flow of fuel. It should also be noted that outlet valve member 52 is located entirely within fuel pump housing 28 which minimizes transmission of audible noise which may otherwise be transmitted to an operator of a motor vehicle containing internal combustion engine 12. Furthermore, valve housing 48 extends into pumping chamber 38 such that a portion of valve housing 48 is aligned with pumping plunger 34 in a direction parallel to plunger bore axis 32. This relationship minimizes the volume of pumping chamber 38 which is formed larger than necessary in order to accommodate installation of inlet valve seat 40b. If pumping chamber 38 is too large in volume, pumping efficiency can be reduced.

(18) In operation, and with particular reference to FIGS. 2 and 7, if the pressure downstream of pressure relief valve assembly 42 exceeds a predetermined threshold, the force of pressure relief valve spring 60 is overcome, thereby allowing pressure relief valve member 58 to unseat from valve seat end wall 50a. Consequently, pressure relief flow passages 50d are opened, thereby allowing fuel pressure to be relieved back to pumping chamber 38, thereby mitigating the over-pressure condition downstream of pressure relief valve assembly 42. While pressure relief valve member 58 should rarely, if ever, open during the life of high-pressure fuel pump 20, it should be noted that pressure relief valve member 58 is located entirely within fuel pump housing 28 which minimizes transmission of audible noise which may otherwise be transmitted to an operator of a motor vehicle containing internal combustion engine 12. It should also be noted that the planar mating nature of pressure relief valve assembly 42 and valve seat end wall 50a, which may be more likely to produce noise, is more easily tolerated applied to the pressure relief function because of its low use over its lifetime.

(19) High-pressure fuel pump 20 and outlet and pressure relief valve assembly 42 as described herein provides for ease of manufacturing and low cost of manufacturing. For example, only pressure relief valve spring retainer 62 needs to be set specific to each assembly and all other components are assembled to a hard stop. As another example, all passages, i.e. outlet flow passage 50c, pressure relief flow passages 50d, pressure relief valve member outlet flow passage 58c, and pressure relief valve spring retainer outlet passage 62a are formed parallel to outlet valve bore axis 43a, thereby eliminated the need for forming angled passages which can increase manufacturing complexity. Furthermore, outlet fuel flow is optimized due to only needing to flow around outlet valve member 52. Even furthermore, noise during operation is minimized since outlet valve member 52, which cycles rapidly, does not mate with valve seat 50 in a planar interface.

(20) While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.