FUEL PUMP

Abstract

 The present disclosure relates to a fuel pump (10) having a head member (12) provided with a blind bore (14) in which a piston (26) is adapted to perform a pumping cycle by reciprocating along the main axis (X1) of the bore (14) between a top dead center (TDC) position and a bottom dead center (BDC) position. Fuel is pressurized during the cycle in a compression chamber (30) defined between the top extremity (28) of the piston and the blind end of the bore (14). The piston (26) reciprocates under the influence of a rotating cam (36) cooperating with a follower assembly (34) combined to the piston (26). The pump (10) also includes a spring (46) compressed between the head member (12) and the follower assembly (34) in order to bias the follower assembly (34) toward the cam (36). An end cap (48) is mounted to the piston (26) for engaging the follower assembly (34). The end cap (48) may locate a spring seat member (44) or may form a spring seat member (44).

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to a fuel pump having a piston reciprocating in a bore under the influence of a cam follower. The invention particularly focuses on the interface between the piston and the cam follower assembly.

BACKGROUND

[0002] Fuel injection equipment comprise high pressure pump aiming at pressurizing fuel at several thousands of bars prior to flow said fuel to injectors that spray the fuel in combustion chambers of an internal combustion engine. Well known pumps comprise a pump head member provided with an inlet and an outlet both opening in a compression chamber that is near the blind end of a bore in which a piston slidably reciprocates along the pumping axis of the bore. The piston performs a pumping cycle between a Top Dead Centre (TDC) position around which fuel in the compression chamber is compressed and released toward the injectors and, a Bottom Dead Centre (BDC) position around which fuel is aspired in the chamber. The piston reciprocates under the influence of a cam rotating about a cam axis perpendicular to the pumping axis. The cam is followed by a follower assembly combined to an external extremity of the piston, said follower assembly typically having a cup-like body member in which a roller is free to rotate about a rolling axis perpendicular to the piston axis and parallel to the cam axis.

[0003] A spring is compressed between the pump head member and the follower assembly in order to permanently bias the follower assembly against the cam. The spring pulls the piston down as it travels from the Top Dead Centre (TDC) position to the Bottom Dead Centre (BDC) position. This function is important for filling efficiency of the pump and transfer of the spring load to the follower assembly in order to maintain contact with the cam. In known arrangements, a spring seat member is provided for receiving the spring. One approach is to mount the spring seat member to an outer diameter of the piston by pressing. The spring seat member may be fixedly mounted to the piston such that relative movement is inhibited. Alternatively, a mounting collar may be fixedly mounted to an outer diameter of the piston to support the spring seat member, for example by press fitting. In this arrangement, the spring seat member may be movable relative to the piston, but is operatively biased against the collar by the action of the spring. A further alternative is to form a keyed interface for mounting the spring seat member to the piston. The keyed interface may not require a press fit arrangement, but machining is required to form the keyed interface on the piston and/or the spring seat member.

[0004] Increased pumping loads place additional demands on the fuel pump. For example, higher pumping loads may lead to high contact stresses between the plunger and the cam follower assembly. The contact area between the piston and the cam follower assembly is determined by the outer diameter of the piston in known arrangements. In order to deliver higher pumping pressures, the piston must be capable of sustaining higher operating loads to avoid contact stress problems. Furthermore, increased engine speeds places higher loads on the spring to inhibit separation between the cam and the cam follower assembly. To reduce the loads on the spring, the inventor(s) has recognised that it would be desirable to reduce the mass of moving components in the fuel pump.

SUMMARY OF THE INVENTION

[0005] Aspects of the present invention relate to a fuel pump of an injection system.

[0006] According to a further aspect of the present invention there is provided a fuel pump having a head member provided with a blind bore in which a piston is adapted to perform a pumping cycle by reciprocating along the main axis of the bore between a top dead center position and a bottom dead center position, fuel being pressurized during the cycle in a compression chamber defined between the top extremity of the piston and the blind end of the bore, the piston reciprocating under the influence of a rotating cam cooperating with a follower assembly, the pump further comprising a spring compressed between the head member and the follower assembly in order to bias the follower assembly toward the cam, characterized in that an end cap is mounted to the piston for engaging the follower assembly. The end cap defines a contact surface for engaging the follower assembly. The end cap may be configured to reduce the contact stresses applied to the piston. The contact surface may provide a larger contact area which is suitable for reducing contact stresses and may withstand higher pumping loads.

[0007] The term "blind bore" is used herein to refer to a bore which is closed at one end to form the compression chamber. The bore may be an open bore having an inlet valve, such as an inlet poppet valve. The inlet valve may selectively close the bore to form the compression chamber.

[0008] The end cap may be configured to locate a spring seat member on the piston. The spring seat member may be biased against the end cap by said spring.

[0009] The end cap may comprise a head. The head may be formed integrally with said end cap. The head may have a diameter which is substantially equal to or less than the diameter of the piston. Alternatively, the head may have a diameter which is larger than the piston.

[0010] In certain embodiments, the head may be suitable for cooperating with said spring seat member. The head may define a shoulder for locating the spring seat member. The spring may bias the spring seat member against the end cap.

[0011] In alternate embodiments, the head may form a spring seat member. The spring seat member may be formed integrally with the end cap.

[0012] The head may comprise a contact surface for engaging the follower assembly. The contact surface may be a convex contact surface. The contact surface may be part-spherical or part-spheroidal. Alternatively, the contact surface may be substantially planar.

[0013] The head may comprise a circumferential flange which forms a radially outer portion of the contact surface. The circumferential flange may be deformable elastically under load. One or more aperture may be formed in an outer sidewall of the head to form said circumferential flange. Each aperture may be in the form of a groove or channel. More particularly, a circumferential groove may be formed in an outer sidewall of the head to form said circumferential flange.

[0014] The piston may comprise a longitudinal bore. The longitudinal bore may extend along a central axis of the piston. The longitudinal bore may reduce the mass of the piston. The end cap may close the longitudinal bore. The end cap may seal the longitudinal bore. The end cap may have a projection disposed in said longitudinal bore to mount the end cap. The projection may be a press fit in said longitudinal bore. The end cap may form a plug which closes the longitudinal bore. In an alternate embodiment, the end cap may comprise a bore for receiving a projection formed on the piston. Other types of connectors are also contemplated for mounting the end cap.

[0015] The end cap may be formed from the same material as the piston or a different material.

[0016] According to a further aspect of the present invention there is provided a fuel pump having a head member provided with a blind bore in which a piston is adapted to perform a pumping cycle by reciprocating along the main axis of the bore between a top dead center position and a bottom dead center position, fuel being pressurized during the cycle in a compression chamber defined between the top extremity of the piston and the blind end of the bore, the piston reciprocating under the influence of a rotating cam cooperating with a follower assembly, the pump further comprising a spring compressed between the head member and the follower assembly in order to bias the follower assembly toward the cam, the piston having a contact surface for engaging the follower assembly;

characterized in that the piston comprises a circumferential flange forming a radially outer portion of the contact surface, the circumferential flange being deformable elastically under load. The elastic deformation of the circumferential flange may help to avoid edge contact and/or to reduce contact stress at the edges of the piston.

[0017] The circumferential flange may be formed by a separate component mounted to an end of the piston. Alternatively, the circumferential flange may be formed integrally with the piston. For example, the piston may be machined to form the circumferential flange.

[0018] One or more aperture may be formed in an outer sidewall of the piston to form said circumferential flange. Each aperture may be in the form of a groove or channel. More particularly, one or more circumferential groove may be formed in an outer sidewall of the piston to form said circumferential flange. The one or more circumferential groove may be offset from the contact surface along a longitudinal axis of the piston.

[0019] The contact surface may be substantially planar. At least in certain embodiments, the circumferential groove can be used as an alternative to machining a convex profile on the contact surface of the piston. Thus, the contact surface may be substantially planar.

[0020] The circumferential flange may have an outer diameter which is substantially the same as, less than or greater than the outer diameter of the piston.

[0021] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a fuel pump incorporating an end cap in accordance with a first embodiment of the present invention;

Figure 2 shows an enlarged view of the end cap mounted to the piston in the fuel pump shown in Figure 1;

Figure 3 shows a fuel pump incorporating an end cap in accordance with a second embodiment of the present invention;

Figure 4 shows an enlarged view of the end cap mounted to the piston in the fuel pump shown in Figure 3;

Figure 5 shows a fuel pump incorporating a piston having a circumferential flange in accordance with a third embodiment of the present invention; and

Figure 6 shows an enlarged view of the circumferential flange shown in Figure 5.

DETAILED DESCRIPTION

[0023] In reference to Figures 1 and 2 is represented a high pressure fuel unit pump 10 of fuel injection equipment. The unit pump 10 comprises a head member 12 provided with a blind bore 14 axially extending along a main axis X1 and opening centrally in an under face 16 of a turret projection 18 that downwardly protrudes from the underside 20 of the head member 12. An inlet poppet valve 22, arranged at the top of the bore 14 controls a fuel inlet orifice 24 opening into the bore 14.

[0024] For clarity purposes this description utilizes the arbitrary orientation of the figures and words and expressions such as "top, bottom, under, over..." may be utilized without any intention to limit the scope of the invention. Also, the bore 14 is identified as a "blind" bore even if it is open on its very top where is arranged the fuel inlet orifice 24 controlled by the inlet poppet valve 22. Indeed, in operation the inlet poppet valve 22 sealingly closes the fuel inlet orifice 24, the bore 14 actually being blind. In alternative embodiments of the pump said inlet valve may be radially arranged relative to the bore while an outlet check valve is arranged on the very top of the bore. A truly permanently blind bore can also be considered.

[0025] A shaft-like piston 26 slidably arranged in the bore 14 is inside the head member 12, where its top extremity 28 defines with the blind end of the bore a compression chamber 30 and also, partially extending outside the bore 14, downwardly protruding from the turret projection 18 toward a lower end 32. A follower assembly 34 is combined to the lower end 32, the follower assembly 34 cooperating with a rotating cam 36 which rotates about a cam axis X2 to actuate the piston 26 in reciprocal axial displacements inside the bore 14.

[0026] The follower assembly 34 comprises a cup-like body 38 provided with aligned bearing means 40 for a roller 42 to freely rotate about a roller axis X3 perpendicular to the main axis X1 and parallel to the cam axis X2. Inside the cup-like body 38 is arranged a spring seat member 44 for receiving a coil spring 46 axially arranged around the piston 26 and compressed between said spring seat member 44 and the underside 20 of the head member 12. The final upper spirals of the spring 46 are engaged around the turret 18 for the compression spring to be guided and to generate an upward force on the pump head member 12 and an opposite downward force on the follower assembly 34.

[0027] In operation the piston 26 reciprocally translates between a top dead center (TDC) position, represented in figure 1, and, after a 90° rotation of the cam a bottom dead center (BDC) position (not shown), the stroke of the piston 26 depending on the profile of the cam 36. The angle of rotation, here 90°, depends on the cam profile which here has two lobes. Alternative cam design having just one lobe, or three, or four or more lobes enable to reach BDC after an angle rotation of 180° or 60° or 45°.

[0028] An end cap 48 is disposed on the low pressure side of the piston 26. In particular, the end cap 48 is fixedly mounted to the piston 26 and arranged to engage the follower assembly 34. The end cap 48 comprises a projection 50 and a head 52. The piston 26 has a longitudinal bore 54 for receiving the projection 50 to mount the end cap 48. The longitudinal bore 54 is a blind bore extending partway along the length of the piston 26. The projection 50 has a cylindrical profile and is a press fit in the longitudinal bore 54. The end cap 48 plugs the longitudinal bore 54.

[0029] The head 52 of the end cap 48 has a diameter which is larger than that of the piston 26. The head 52 projects radially outwardly from the piston 26 and forms an annular shoulder 56 for locating the spring seat member 44. The spring 46 biases the spring seat member 44 against the annular shoulder 56. The head 52 has a contact surface 58 for engaging the follower assembly 34. The contact surface 58 has a convex profile. In the present embodiment, the contact surface 58 is part-spherical or part-spheroidal. This can help to avoid edge contact which would otherwise cause a high stress concentration under load. By avoiding edge contact, stress concentration in the middle of the contact surface 58 may increase but stresses at the edges of the head 52 may be decreased.

[0030] In an alternative arrangement, a circumferential groove 60 is formed in an outer sidewall 62 of the head 52 proximal to the contact surface 58. The circumferential groove 60 is offset from the contact surface 58 along the main axis X1 such that a circumferential flange 64 is formed at a lower end of the head 52. The circumferential flange 64 forms a radially outer portion of the contact surface 58 and is adapted to undergo elastic deformation under load. The elastic deformation of the circumferential flange 64 may help to avoid edge contact and/or to reduce contact stress at the edges of the end cap 48. The contact surface 58 in this arrangement may be substantially planar. In use, the circumferential flange 64 deforms under load, thereby reducing operating stresses. The circumferential flange 64 can be used as an alternative to machining the contact surface 58 to form the aforementioned convex profile.

[0031] In use, the end cap 48 is disposed between the piston 26 and the follower assembly 34. The spring 46 biases the spring seat member 44 against the end cap 48. The annular shoulder 56 formed by the head 52 retains the spring seat member 44. The contact surface 58 engages the follower assembly 34 and causes the piston 26 to reciprocally translate between the top dead center (TDC) position and the bottom dead center (BDC) position as the cam 36 rotates. The contact surface 58 provides a larger contact area suitable for reducing contact stresses and at least in certain embodiments may withstand higher pumping loads. The longitudinal bore 54 reduces the mass of the piston 26.

[0032] A second embodiment of the high pressure fuel pump 10 is shown in Figures 3 and 4. The second embodiment is similar to the first embodiment and the description herein focuses on the differences. Like references are used for like components.

[0033] The fuel pump 10 according to the second embodiment is modified such that the spring seat member 44 is formed integrally with the end cap 48. In particular, the end cap 48 comprises a support flange 66 for engaging the lower end of the spring 46. The support flange 66 has an annular profile and extends radially outwardly from an upper end of the head 52. The contact surface 58 of the end cap 48 comprises a part-spherical surface for engaging the follower assembly 34. The circumferential groove 60 is formed in the outer sidewall 62 of the head 52 proximal to the contact surface 58. The mounting arrangement of the end cap 48 in the piston 26 is unchanged from the first embodiment.

[0034] It will be understood that the operation of the fuel pump 10 according to the second embodiment is unchanged from the first embodiment.

[0035] A third embodiment of the high pressure fuel pump 10 is shown in Figures 5 and 6. The third embodiment is a modification of the second embodiment and the description herein focuses on the differences. Like references are used for like components.

[0036] The piston 26 has an outer sidewall 68 and a longitudinal axis arranged coaxially with the main axis X1. A contact surface 70 for engaging the follower assembly 34 is defined at a lower extremity 72 of the piston 26. The end cap 48 is omitted from the high pressure fuel pump 10 in the third embodiment. Instead, the contact surface 70 of the piston 26 engages the follower assembly 34. An aperture in the form of a circumferential groove 74 is formed in the sidewall 68 of the piston 26. The circumferential groove 74 is offset from the contact surface 70 such that a circumferential flange 76 is formed at the lower extremity 72 of the piston 26. The circumferential flange 76 is adapted to undergo elastic deformation under load. It will be appreciated that the circumferential flange 76 defines a radially outer portion of the contact surface 70. Thus, in use, the radially outer portion of the contact surface 70 can undergo elastic deformation. At least in certain embodiments, this elastic deformation of the circumferential flange 76 may help to avoid edge contact and/or to reduce contact stress at the edges of the piston 26. The contact surface 70 of the piston 26 is substantially planar. At least in certain embodiments, the circumferential groove 74 can be used as an alternative to machining a convex profile on the contact surface 70 of the piston 26.

[0037] The spring seat member 44 is mounted to the sidewall 68 of the piston 26 above the circumferential groove 74. The spring seat member 44 in the present embodiment is a press fit on the piston 26. It will be appreciated that other mounting or fastening arrangements may be used to locate the spring seat member 44.

[0038] It will be appreciated that various changes and modification may be made to the apparatus described herein without departing from the scope of the present invention. For example, the longitudinal bore 54 could be extended to reduce further the mass of the piston 26.

[0039] The first and second embodiments comprise an end cap 48 having a projection 50 which is a press fit in the longitudinal bore 54 in the piston 26. In an alternate arrangement, the end cap 48 could comprise a longitudinal bore for receiving a projection formed at the end of the piston 26. It will be appreciated that other types of cooperating male and female connectors may be employed to mount the end cap 48.

Claims

1. Fuel pump (10) having a head member (12) provided with a blind bore (14) in which a piston (26) is adapted to perform a pumping cycle by reciprocating along the main axis (X1) of the bore (14) between a top dead center (TDC) position and a bottom dead center (BDC) position, fuel being pressurized during the cycle in a compression chamber (30) defined between the top extremity (28) of the piston and the blind end of the bore (14), the piston (26) reciprocating under the influence of a rotating cam (36) cooperating with a follower assembly (34), the pump (10) further comprising a spring (46) compressed between the head member (12) and the follower assembly (34) in order to bias the follower assembly (34) toward the cam (36),
characterized in that an end cap (48) is mounted to the piston (26) for engaging the follower assembly (34),
wherein the end cap (48) is configured to locate a spring seat member (44) on the piston (26),
wherein the end cap (48) comprises a head (52) for cooperating with said spring seat member (44), wherein the head (52) comprises a contact surface (58) for engaging the follower assembly (34),
wherein the head (52) comprises a circumferential flange (64) forming a radially outer portion of the contact surface (58), the circumferential flange (64) being deformable elastically under load.

2. Fuel pump (10) as claimed in claim 1, wherein the spring seat member (44) is biased against the end cap (48) by said spring (46).

3. Fuel pump (10) as claimed in claim 1, wherein the end cap (48) comprises a head (52).

4. Fuel pump (10) as claimed in claim 3, wherein the head (52) forms a spring seat member (44).

5. Fuel pump (10) as claimed in any one of claims 1, 3 or 4, wherein the head (52) has a larger diameter than the piston (26).

6. Fuel pump (10) as claimed in claim 1, wherein a circumferential groove (60) is formed in an outer sidewall (62) of the head (52) to form said circumferential flange (64).

7. Fuel pump (10) as claimed in any one of the preceding claims, wherein the piston (26) comprises a longitudinal bore (54).

8. Fuel pump (10) as claimed in claim 7, wherein the end cap (48) closes the longitudinal bore (54) formed in the piston (26).

9. Fuel pump (10) as claimed in claim 7 or claim 8, wherein the end cap (48) comprises a projection (50) disposed in said longitudinal bore (54) to mount the end cap (48).

10. Fuel pump (10) as claimed in claim 9, wherein the projection (50) is a press fit in said longitudinal bore (54).

11. Fuel pump (10) having a head member (12) provided with a blind bore (14) in which a piston (26) is adapted to perform a pumping cycle by reciprocating along the main axis (X1) of the bore (14) between a top dead center (TDC) position and a bottom dead center (BDC) position, fuel being pressurized during the cycle in a compression chamber (30) defined between the top extremity (28) of the piston (26) and the blind end of the bore (14), the piston (26) reciprocating under the influence of a rotating cam (36) cooperating with a follower assembly (34), the pump (10) further comprising a spring (46) compressed between the head member (12) and the follower assembly (34) in order to bias the follower assembly (34) toward the cam (36), the piston (26) having a contact surface (70) for engaging the follower assembly (34);
characterized in that the piston (26) comprises a circumferential flange (76) forming a radially outer portion of the contact surface (70), the circumferential flange (76) being deformable elastically under load.

12. Fuel pump (10) as claimed in claim 11, wherein one or more circumferential groove (74) is formed in an outer sidewall (68) of the piston (26) to form said circumferential flange (76).

13. Fuel pump (10) as claimed in claim 12, wherein the one or more circumferential groove (74) is offset from the contact surface (70) along a longitudinal axis (X1) of the piston (26).

14. Fuel pump (10) as claimed in any one of claims 11, 12 or 13, wherein the contact surface (70) is substantially planar.

Drawing