PUMP HEAD FOR A FUEL PUMP

Abstract

 A pump head for a fuel pump for use in a common rail fuel injection system is provided. The pump head (300) comprises a pump head housing (302), a pumping chamber (306) defined within the pump head housing (302), and an inlet valve arrangement (308) for controlling fuel flow into the pumping chamber (306), the inlet valve arrangement (308) including an inlet valve member (310) moveable between open and closed positions wherein, in use, movement of the inlet valve member (310) is damped by means of viscoelastic damping.

Description

Field of the Invention

[0001] The present invention relates to a pump head for a fuel pump and, in particular, to a pump head for a fuel pump for use in a common rail fuel injection system.

Background Art

[0002] High-pressure fuel pumps for common rail fuel injection systems typically comprise one or more hydraulic pump heads where fuel is pressurised in a pumping chamber of the pump head by the reciprocating movement of a plunger. Typically, low-pressure fuel is fed to the pump heads by a low-pressure lift pump in the fuel tank, or alternatively by a transfer pump built into the high-pressure fuel pump. Once pressurised, the high-pressure fuel is fed from the pumping chamber to the common rail.

[0003] A known pump head of a high-pressure fuel pump is described in International Patent Publication No. WO-A1-2010-007409. Figure 1 shows a pump head 1 of the kind described in WO-A1-2010-007409. Referring to Figure 1, the pump head 1 comprises a pump head housing 2. The pump head housing 2 has a plunger bore 4 in which a pumping plunger (not shown) is disposed for reciprocating movement therein. As described in WO-A1-2010-007409, a lower end of the pumping plunger includes a foot which is driven by a cam mounted on a drive shaft. As the drive shaft rotates, the cam imparts an axial force on the plunger foot, causing the pumping plunger to reciprocate within the plunger bore. The pump head housing 2 defines a pumping chamber 6 at an upper end of the plunger bore 4, such that fuel is pressurised within the pumping chamber 6 by the reciprocal motion of the pumping plunger within the plunger bore 4.

[0004] Low-pressure fuel is fed to the pumping chamber 6 by a low-pressure lift pump in a fuel tank (not shown in Figure 1), or alternatively by a transfer pump built into the high-pressure fuel pump. The pump head housing 2 includes an exit drilling (not shown in Figure 1) in fluid communication with the pumping chamber 6. In use, pressurised fuel is fed from the pumping chamber 6, along the exit drilling, and through an outlet valve to downstream components of a fuel injection system, such as a common rail.

[0005] The fuel pump head 1 includes an inlet valve arrangement 8 which comprises a moveable inlet valve member 10 for controlling fuel flow into the pumping chamber 6. The inlet valve member 10 has a conical body 12 and an elongate neck 14 and is moveable between open and closed positions in response to the fuel pressure in a gallery 16, which is machined in the pump head housing 2 above the pumping chamber 6, so as to surround a frustoconical lower end surface of the inlet valve member 10.

[0006] The conical body 12 is housed within the pump head housing 2, adjacent to the pumping chamber 6, whilst the neck 14 extends from the conical body 12, coaxially with the plunger bore 4, away from the pumping chamber 6. The neck 14 is slidable within a valve bore 18 defined by the pump head housing 2. Consequently, the inlet valve member 10 is guided by the pump head housing 2 at the lower end of the neck 14.

[0007] The neck 14 of the inlet valve member 10 extends beyond the valve bore 18, and out from an upper surface 20 of the pump head housing 2. The upper surface 20 of the pump head housing 2 is planar and substantially flat. A proximal end 22 of the neck 14 (adjacent to the conical body 12) remains within the pump head housing 2, whilst a distal end 24 of the neck 14 remains outside the pump head housing 2 and carries a spring seat 26. A valve return spring 28 is provided between the upper surface 20 of the pump head housing 2 and the spring seat 26 to urge the inlet valve member 10 closed against a valve seat 30 when fuel pressure within the gallery 16 drops below a predetermined level. A slight recess 32 is provided in the otherwise flat upper surface 20 of the pump head housing 2 to locate the lower end of the spring 28 therein.

[0008] A closure member in the form of a valve cap 34 is mounted on top of and, thus, externally to, the upper surface 20 of the pump head housing 2. The valve cap 34 is provided over the distal end 24 of the neck 14 of the inlet valve member 10 (i.e. the part of the inlet valve member 10 that is outside the pump head housing 2). The valve cap 34 comprises a dome 36 with an annular flange 38 extending radially outwards from the dome 36.

[0009] The pump head housing 2 includes a raised portion or projection 40 that is substantially circular, and projects into, and fits the footprint of, the dome 36 of the valve cap 34. The dome 36 may be fitted over the raised portion 40 such that the raised potion 40 protrudes into the dome 36 in a manner similar to a plug and socket arrangement.

[0010] The valve cap 34 defines an external chamber 42 within which the distal end 24 of the valve member 10 is housed. The external chamber 42 communicates with the gallery 16 defined in the pump head housing 2. An entry drilling 44 and a plurality of radial feed drillings 46 (only one of which is shown in Figure 1) are provided in the pump head housing 2. The entry drilling 44 extends to and opens at the upper surface 20 of the pump head housing 2, and so communicates with the external chamber 42. The radial feed drillings 46 also communicate with the external chamber 42, and extend between the gallery 16 and the upper surface 20 of the pump head housing 2, emerging at a position on the upper surface 20 of the pump head housing 2 which is outside the diameter of the spring 28. The radial feed drillings 46 are equally spaced about the circumference of the gallery 16. In use, low-pressure fuel is pumped along the entry drilling 44 and into the external chamber 42. The low-pressure fuel is then fed from the external chamber 42, through the radial feed drillings 46 in the pump head housing 2, and into the gallery 16. Once sufficient pressure is built in the gallery 16, the valve member 10 is urged away from its seat 30, against the spring force, to allow fuel into the pumping chamber 6.

[0011] The radial outer surface of the projection 40 faces, and engages, a radial inner surface of the valve cap 34. The external chamber 42 is therefore defined between the internal surface of the dome 36, and the upper surface of the raised portion 40. A low-pressure seal is provided between the radial internal surface of the dome 36 and the radial outer surface of the raised portion 40, for example by an O-ring 48 surrounding the raised portion 40. The O-ring 48 is located within an annular groove 50 provided in the radial outer surface of the raised portion 40 and serves to minimise the loss of fuel from the external chamber 42.

[0012] There is a problem with the fuel pump head 1 having the above described configuration in that, over its lifetime, the valve member 10 is subject to wear caused by the repeated opening and closing of the inlet valve arrangement 8. In particular, when the valve member 10 moves into the closed position, the conical body 12 impacts against the valve seat 30. This causes wear of the valve seat 30 and the conical body 12 which may result in a poor seal between the two, thereby reducing the efficiency of the pump, which is undesirable.

[0013] It is an aim of the present invention to provide an improved pump head for a fuel pump which substantially overcomes or mitigates the above-mentioned problem.

Summary of the Invention

[0014] According to a first aspect of the present invention, there is provided a pump head for a fuel pump for use in a common rail fuel injection system, the pump head comprising:

a pump head housing;

a pumping chamber defined within the pump head housing; and

an inlet valve arrangement for controlling fuel flow into the pumping chamber, the inlet valve arrangement including an inlet valve member moveable between open and closed positions wherein, in use, movement of the inlet valve member is damped by means of viscoelastic damping.

[0015] Advantageously, this viscoelastic damping mechanism reduces the velocity with which the inlet valve member comes to rest in the open and closed positions. This reduces wear of the inlet valve member over the lifetime of the pump thereby maintaining a good seal when the inlet valve member is in the closed position.

[0016] Preferably, the pump head comprises a damping volume which is defined, at least in part, by a surface associated with the inlet valve member such that, in use, the size of the damping volume varies in response to movement of the inlet valve member and, viscoelastic damping of the inlet valve member is effected by the restricted flow of fuel between the damping volume and a second volume. More preferably, the second volume is a chamber disposed externally to the pump head housing, the damping volume being in fluid communication with the external chamber.

[0017] Still more preferably, the inlet valve member opens and closes in response to fuel pressure within a gallery, wherein the gallery communicates with the external chamber, such that, in use, the gallery communicates with a source of low-pressure fuel via the external chamber.

[0018] Conveniently, the external chamber is defined by a closure member mounted externally to the pump head housing.

[0019] More preferably, the inlet valve member comprises an elongate neck which is guided within a valve bore in the pump head housing, the valve bore extending between an upper surface of the pump head housing and a valve seat;

wherein the external chamber is defined between the closure member and the upper surface of the pump head housing;

wherein a distal end of the neck, disposed away from the valve seat, projects above the upper surface of the pump head housing into the external chamber; and

wherein the damping volume is defined, at least in part, between a radial outer surface of the distal end of the neck and the radial inner surface of an annular shroud disposed around the distal end of the neck.

[0020] Advantageously, the annular shroud may be formed integrally with the pump head housing and projects upwardly from the upper surface thereof. Alternatively, the annular shroud may, conveniently, be formed integrally with the closure member and projects downwardly from the inner surface thereof.

[0021] Preferably, the pump head comprises a spring which acts on the inlet valve member to urge the inlet valve member into the closed position, the spring being disposed between the upper surface of the pump head housing and a spring seat disposed on the distal end of the neck and projecting radially outwards therefrom, wherein said surface associated with the inlet valve member is a surface of the spring seat which extends radially outward from the distal end of the neck.

[0022] More preferably, the damping volume communicates with the external chamber via a control clearance defined between an outer radial surface of the spring seat and an inner radial surface of the annular shroud.

[0023] The annular shroud may, conveniently, comprise one or more radial drillings to permit fluid communication between the damping volume and the external chamber. In this case, the pump head may comprise a sealing member disposed between the radial outer surface of the spring seat and the radial inner surface of the annular shroud, the sealing member being operable to prevent the flow of fuel therepast.

[0024] The valve bore may, conveniently, include an annular recess disposed between the upper surface of the pump head housing and the valve seat, the damping volume being defined, at least in part, between the annular recess and the inlet valve member.

[0025] Preferably, the valve bore comprises a guide region disposed between the gallery and the annular recess, and the inlet valve member comprises a guide portion which cooperates with the guide region to guide the movement of the inlet valve member within the valve bore, wherein the flow of fuel between the guide portion and guide region is substantially prevented; and

wherein said surface associated with the inlet valve member is a shoulder formed on the inlet valve member by a transition between the guide portion and a further portion above the guide portion, the further portion having a diameter less than that of the guide portion.

[0026] Preferably, the pump head housing comprises one or more drillings which provide fluid communication between the damping volume and the external chamber.

[0027] Preferably, the damping volume communicates with the external chamber via a control clearance defined between the inlet valve member and the valve bore, the control clearance being disposed between the annular recess and the upper surface of the pump head housing.

[0028] More preferably, the pump head housing comprises a sealing member disposed between the radial outer surface of inlet valve member and the radial inner surface of valve bore, the sealing member being disposed between the annular recess and the upper surface of the pump head housing.

[0029] According to a second aspect of the invention, there is provided a fuel pump for use in a common rail fuel injection system, comprising at least one pump head as described above.

[0030] It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination in the fuel pump of the second aspect.

Brief Description of the Drawings

[0031] Embodiments of the present invention will now be described, by way of example only, with reference to Figures 2 to 4 of the accompanying drawings, in which:

Figure 1 is a schematic cross-sectional view of a known pump head;

Figure 2 is a schematic cross-sectional view of a first embodiment of a pump head according to the present invention;

Figure 3 is a schematic cross-sectional view of a second embodiment of a pump head according to the present invention; and

Figure 4 is a schematic cross-sectional view of a third embodiment of a pump head according to the present invention.

Detailed Description of the Preferred Embodiments

[0032] Referring to Figure 2, a first embodiment of a pump head 100 according to the present invention comprises a pump head housing 102. The pump head housing 102 has a plunger bore 104 in which a pumping plunger 105 is disposed for reciprocating movement therein. As described previously with reference to the known fuel pump head of Figure 1, a lower end of the pumping plunger 105 includes a foot which is driven by a cam mounted on a drive shaft. As the drive shaft rotates, the cam imparts an axial force on the plunger foot, causing the pumping plunger 105 to reciprocate within the plunger bore 104. Alternatively, the pumping plunger 105 can also be driven by a tappet or roller/shoe arrangement. The pump head housing 102 defines a pumping chamber 106 at an upper end of the plunger bore 104, such that fuel is pressurised within the pumping chamber 106 by the reciprocal motion of the pumping plunger 105 within the plunger bore 104.

[0033] Low-pressure fuel is fed to the pumping chamber 106 by a low-pressure lift pump in a fuel tank (not shown in Figure 2), or alternatively by a transfer pump built into the high-pressure fuel pump. The pump head housing 102 includes an exit drilling (not shown in Figure 2) in fluid communication with the pumping chamber 106. In use, pressurised fuel is fed from the pumping chamber 106, along the exit drilling, and through an outlet valve to downstream components of a fuel injection system, such as a common rail.

[0034] The pump head 100 includes an inlet valve arrangement 108 which comprises a moveable inlet valve member 110 for controlling fuel flow into the pumping chamber 106. The inlet valve member 110 has a conical body 112 and an elongate neck 114 and is moveable between open and closed positions in response to the fuel pressure in a gallery 116, which is machined in the pump head housing 102 above the pumping chamber 106, so as to surround a frustoconical lower end surface of the inlet valve member 110.

[0035] The conical body 112 is housed within the pump head housing 102, adjacent to the pumping chamber 106, whilst the neck 114 extends from the conical body 112, coaxially with the plunger bore 104, away from the pumping chamber 106. The neck 114 is slidable within a valve bore 118 defined by the pump head housing 102. Consequently, the inlet valve member 110 is guided by the pump head housing 102 at the lower end of the neck 114.

[0036] The neck 114 of the inlet valve member 110 extends beyond the valve bore 118, and out from an upper surface 120 of the pump head housing 102. A proximal end 122 of the neck 114 (adjacent to the conical body 112) remains within the pump head housing 102, whilst a distal end 124 of the neck 114 remains outside the pump head housing 102 and carries a spring seat 126. A valve return spring 128 is provided between the upper surface 120 of the pump head housing 102 and the spring seat 126 to urge the inlet valve member 110 closed against a valve seat 130 when fuel pressure within the gallery 116 drops below a predetermined level. A slight recess 132 is provided in the upper surface 120 of the pump head housing 102 to locate the lower end of the spring 128 therein.

[0037] A closure member in the form of a valve cap 134 is mounted on top of and, thus, externally to, the upper surface 120 of the pump head housing 102. The valve cap 134 is provided over the distal end 124 of the neck 114 of the inlet valve member 110 (i.e. the part of the inlet valve member 110 that is outside the pump head housing 102). The valve cap 134 comprises a dome 136 with an annular flange 138 extending radially outwards from the dome 136.

[0038] The pump head housing 102 includes a raised portion or projection 140 that is substantially circular, and projects into, and fits the footprint of, the dome 136 of the valve cap 134. The dome 136 may be fitted over the raised portion 140 such that the raised potion 140 protrudes into the dome 136 in a manner similar to a plug and socket arrangement.

[0039] The valve cap 134 defines an external chamber 142 within which the distal end 124 of the valve member 110 is housed. The external chamber 142 communicates with the gallery 116 defined in the pump head housing 102. An entry drilling (not shown in Figure 2, but similar to the entry drilling 44 of Figure 1) and a plurality of radial feed drillings 146 (only one of which is shown in Figure 2) are provided in the pump head housing 102. The entry drilling extends to and opens at the upper surface 120 of the pump head housing 102, and so communicates with the external chamber 142. The radial feed drillings 146 also communicate with the external chamber 142, and extend between the gallery 116 and the upper surface 120 of the pump head housing 102, emerging at positions on the upper surface 120 of the pump head housing 102 which are outside the diameter of the spring 128. The radial feed drillings 146 are equally spaced about the circumference of the gallery 116. In use, low-pressure fuel is pumped along the entry drilling and into the external chamber 142. The low-pressure fuel is then fed from the external chamber 142, through the radial feed drillings 146 in the pump head housing 102, and into the gallery 116. Once sufficient pressure is built in the gallery 116, the valve member 110 is urged away from its seat 130, against the spring force, to allow fuel into the pumping chamber 106.

[0040] The radial outer surface of the projection 140 faces, and engages, a radial inner surface of the valve cap 134. The external chamber 142 is therefore defined between the internal surface of the dome 136, and the upper surface of the raised portion 140. A low-pressure seal is provided between the radial internal surface of the dome 136 and the radial outer surface of the raised portion 140, for example by an O-ring 148 surrounding the raised portion 140. The O-ring 148 is located within an annular groove 150 provided in the radial outer surface of the raised portion 140 and serves to minimise the loss of fuel from the external chamber 142.

[0041] The valve cap 134 also comprises an annular shroud 152 which projects from the inner surface of the dome 136. The annular shroud 152 has a generally hollow cylindrical form and is arranged such that, when the valve cap 134 is mounted on the pump head housing 102, it is coaxial with the valve bore 118 and the inlet valve member 110. Accordingly, with this configuration, the distal end 124 of the inlet valve member 110 and the spring seat 126 are received within the annular shroud 152.

[0042] A control clearance 154 is defined between the radial outer surface of the spring seat 126 and the inner surface of the annular shroud 152. The control clearance 154 defines a boundary between the external chamber 142 and a damping volume 156, the damping volume 156 generally comprising the region between the annular shroud 152 and the distal end 124 of the inlet valve member 110.

[0043] As mentioned previously, during operation, the external chamber 142 is filled with fuel via the entry drilling. The external chamber 142 therefore constitutes a second volume which is distinct from the damping volume 156. Fuel flows from the external chamber 142 into the gallery 116 along the radial drillings 146 and through the control clearance 154 into the damping volume 156. The inlet valve member 110 moves into the open position away from the valve seat 130 when the pressure of the fuel in the gallery 116 exceeds the closing force provided by a combination of the spring 128 and the force of the fluid pressure within the pumping chamber 106. This condition occurs during a filling stroke of the pumping plunger 105 when the pumping plunger 105 moves away from the inlet valve arrangement 108 thereby increasing the volume of the pumping chamber 106 and resulting in a corresponding drop in the fluid pressure therein.

[0044] As the inlet valve member 110 opens, the damping volume 156 increases in size and the pressure within it drops. In turn, this causes fuel from the external chamber 142 to flow into the damping volume 156. However, the flow of fuel into the damping volume 156 is restricted due to the fact that it must pass through the control clearance 154 between the spring seat 126 and the inner surface of the annular shroud 152. The result is that movement of the inlet valve member 110 from the closed position into the open position is damped. This improves the efficiency of the of the pump because it reduces the tendency for the inlet valve member 110 to oscillate when it is in the open position. Such oscillations are undesirable as they may cause variations in the amount of fuel pumped during each pumping stroke.

[0045] When the pumping plunger 105 commences a pumping stroke, it moves toward the inlet valve arrangement 108 reducing the volume of the pumping chamber 106 thereby increasing the fluid pressure therein. When the combination of the spring force and the pressure in the pumping chamber 106 exceeds the fuel pressure in the gallery 116, the inlet valve member 110 moves toward the closed position. Accordingly, the damping volume 156 is reduced as the inlet valve member 110 closes. Fuel in the damping volume 156 is forced out through the control clearance 154 and into the external chamber 142. Thus, the restriction in the flow of fuel from the damping volume 156 causes the motion of the inlet valve member 110 to be damped as it closes. Advantageously, this viscoelastic damping mechanism reduces the velocity with which the conical body 112 of the inlet valve member 110 impacts the valve seat 130 to close the inlet valve arrangement 108. This reduces wear of the valve seat 130 and the inlet valve member 110 over the lifetime of the pump thereby maintaining a good seal between the valve seat 130 and the inlet valve member 110 when the inlet valve member 110 is in the closed position.

[0046] Furthermore, with the above-described arrangement, the degree of damping of the inlet valve member 110 is determined by the characteristics of the control clearance 154, i.e. the width, length of the clearance, etc. Accordingly, the selection of an appropriate control clearance 154 provides a convenient way of tuning the dynamics of the inlet valve arrangement 108 so as to increase the efficiency of the inlet valve arrangement 108, which leads to better filling of the high pressure chamber 106 and therefore to better overall pump efficiency. This can be a contributor to save energy/reduce CO2 emissions on the low pressure circuit.

[0047] In a variation of the above-described embodiment, the annular shroud 152 may be provided with one or more radial drillings 157 (shown in dashed lines in Figure 2) which allow fuel to flow between the damping volume 156 and the external chamber 142 when the inlet valve member 110 moves between the open and closed positions. In this case, the degree of damping is determined by the combination of the control clearance 154 and the dimensions of the drillings 157 in the annular shroud 152.

[0048] Alternatively, in the case that the annular shroud 152 is provided with one or more drillings 157 as described above, there may be no control clearance between the spring seat 126 and the inner surface of the annular shroud 152. For example, the radial outer surface of the spring seat 126 may be provided with a sealing member, such as an O-ring, which prevents any fluid flow between the spring seat 126 and the annular shroud 152. In this case, the nature of the damping of the inlet valve member 110 is determined by the number and dimensions of the drillings 157 in the annular shroud 152.

[0049] Damping of the inlet valve member 110 is also beneficial in that the chances of seizure of the inlet valve member 110 are reduced because the inlet valve member 110 will accelerate and decelerate more gradually as it moves between the open and closed positions.

[0050] Referring to Figure 3, a second embodiment of a pump head 200 is similar to the embodiment shown in Figure 2 but comprises a pump head housing 202 having an annular shroud 252 which is formed integrally therewith. The annular shroud 252 projects from the upper surface 220 of the pump head housing 202 and, as before, has a hollow cylindrical form which is coaxial with the valve bore 218 and the inlet valve member 210 of an inlet valve arrangement 208. The valve bore 218 defines a gallery 216 from which fuel is fed to a pumping chamber 206.

[0051] A control clearance 254 is defined between the radial outer surface of the spring seat 226 and the inner surface of the annular shroud 252. In the embodiment shown in Figure 3, the damping volume 256 is between the spring seat 226 and the upper surface 220 of the pump head housing 202, i.e. the region surrounding the spring 228.

[0052] With this arrangement, movement of the inlet valve member 210 is damped as it moves into the open position by fuel being forced out of the damping volume 256 through the control clearance 254. Conversely, during closing of the inlet valve member 210, damping is caused due to a reduction in fluid pressure within the damping volume 256 as it expands and the fact that the flow of fuel back into the damping volume 256 is restricted by the control clearance 254.

[0053] In order to achieve the required damping, the annular shroud 252 may be provided with one or more radial drillings 257 (shown in dashed lines in Figure 3), to allow fuel to flow between the damping volume 256 and the external chamber 242 as the inlet valve member 210 opens and closes. In the case that additional drillings 257 are provided, the spring seat 226 may be provided with a sealing member, as described previously, so that there is no control clearance between the radial outer surface of the spring seat 226 and the inner surface of the annular shroud 252. In this case, the flow of fuel into and out of the damping chamber 256 occurs only through the one or more drillings 257.

[0054] Damping of the inlet valve member 210 is most beneficial when the inlet valve member 210 closes, as this reduces wear at the valve seat 230. Accordingly, the annular shroud 252 may be configured such that, when the valve cap 234 is attached to the pump head housing 202, a gap 258 between an upper end of the annular shroud 252 and the inner surface of the dome 236 of the valve cap 234 provides a further control clearance. In this case an additional damping volume 260 is defined at the distal end 224 of the neck 214 of the inlet valve member 210 in the region disposed between the gap 258 and the spring seat 226. Thus, when the inlet valve member 210 moves toward the closed position, damping is provided as fuel in the additional damping volume 260 is forced through the gap 258 into the external volume 242.

[0055] The embodiment shown in Figure 3 has a particular advantage in that it is possible to set the width of the control clearance 254 between the annular shroud 252 and the spring seat 226 with a high level of precision. This is because the position of the axis of the valve bore 218, and therefore that of the inlet valve member 210, is well known, and both the valve bore 218 and the annular shroud 252 are formed integrally in the pump head housing 202.

[0056] Referring to Figure 4, a third embodiment of a pump head 300 comprises a pump head housing 302 having a damping volume 356 formed integrally therein. The pump head housing 302 includes a valve bore 318 which extends from a valve seat 330 to the upper surface 320 of the pump head housing 302. As before, an inlet valve arrangement 308 comprises an inlet valve member 310 having a conical body 312 which seals against the valve seat 330 when the inlet valve member 310 is in the closed position, and an elongate neck 314 which extends through the valve bore 318 and projects from the upper surface 320 of the pump head housing 302.

[0057] A spring seat 326 is disposed at the distal end 324 of the neck 314, such that a spring 328 disposed between the spring seat 326 and a recess 332 in the upper surface 320 of the pump head housing 302 acts to bias the inlet valve member 310 toward the closed position. The valve bore 318 defines a gallery 316 disposed adjacent to a proximal end 322 of the neck 314 (adjacent to the conical body 312), from which fuel is fed to the pumping chamber 306 when the inlet valve member 310 opens. Above the gallery 318, the valve bore 318 comprises a guide region 362, having a uniform diameter along its axial length. The damping volume 356 is disposed above the guide region 362 and is defined between the inlet valve member 310 and an annular recess 364 within the valve bore 318.

[0058] The neck 314 of the inlet valve member 310 is provided with a guide portion 366 which is concentric and a close fit with the surface of the guide region 362 of the valve bore 318 so as to ensure that the inlet valve member 310 moves parallel to the axis of the valve bore 318, and to prevent the flow of fuel therebetween. At the upper end of the guide portion 366 a shoulder 368 defines a transition between the guide portion 366 of the neck 314 and a further portion having a reduced diameter 370. A control clearance 354 is defined between the surface of the valve bore 318 above the annular recess 364 and the surface of the reduced diameter portion 370 of the neck 314 of the inlet valve member 310.

[0059] With the above-described arrangement, the inlet valve member 310 is damped as it moves between the open and closed positions. In more detail, when the inlet valve member 310 moves away from the valve seat 330, the guide portion 366 of the neck 314 moves within the guide region 362 of the valve bore 318. This causes the damping volume 356 to increase in size as the shoulder 368 moves through the guide portion 366 of the valve bore 318 leaving a space where the reduced diameter portion 370 of the neck 314 is adjacent the guide region 362 of the valve bore 318.

[0060] The increase in the size of the damping volume 356 reduces the pressure therein, which causes fuel in the external chamber 342 (defined by the valve cap 334) to flow into the damping volume 356. The flow of fuel into damping volume 356 is restricted by the control clearance 354, which slows the movement of the inlet valve member 310 accordingly. Similarly, when the inlet valve member 310 moves toward the closed position, the shoulder 368 reduces the size of the damping volume 356 and fuel within the damping volume 356 is forced out into the external chamber 342 past the control clearance 354. Thus, the restriction in the flow of fuel past the control clearance 354 reduces the velocity of the inlet valve member 310 as it closes.

[0061] In a variation of the above-described embodiment, one or more radial drillings 357 (shown in dashed lines in Figure 3) may be provided in the pump heading housing 302 to allow fuel to flow between the damping volume 356 and the external chamber 342 when the inlet valve member 310 moves between the open and closed positions. In this case, the degree of damping is determined by the combination of the control clearance 354 and the dimensions of the drillings 357 in the pump head housing 302.

[0062] In addition to the various above-mentioned advantages associated with viscoelastic damping of the inlet valve member which are provided by the embodiments shown in Figures 2, 3 and 4, a further advantage is that each of the embodiments provides damping without the addition of any extra parts to the fuel pump head. Accordingly, assembly of the fuel pump head is not made more complicated or more time consuming by the inclusion of the damping volume. Also, there is a minimum increase in the cost of producing fuel pump head, since no additional parts are required.

Claims

1. A pump head for a fuel pump for use in a common rail fuel injection system, the pump head (100; 200; 300) comprising:

a pump head housing (102; 202; 302);

a pumping chamber (106; 206; 306) defined within the pump head housing (102; 202; 302); and

an inlet valve arrangement (108; 208; 308) for controlling fuel flow into the pumping chamber (106; 206; 306), the inlet valve arrangement (108; 208; 308) including an inlet valve member (110; 210; 310) moveable between open and closed positions characterized in that

the pump head is further provided with means of viscoelastic damping ensuring that, in use, movement of the inlet valve member (110; 210; 310) is damped when moving into the open position and also, when moving into the closed position,

the pump head further comprising a damping volume (156; 256; 356) which is defined, at least in part, by a surface associated with the inlet valve member (110; 210; 310) such that, in use, the size of the damping volume (156; 256; 356) varies in response to movement of the inlet valve member (110; 210; 310) and, viscoelastic damping of the inlet valve member (110; 210; 310) is effected by the restricted flow of fuel between the damping volume (156; 256; 356) and a second volume and

wherein, the second volume is a chamber (142; 242; 342) disposed externally to the pump head housing (102; 202; 302), the damping volume (156; 256; 356) being in fluid communication with the external chamber (142; 242; 342) and wherein,

the valve bore (318) includes an annular recess (364) disposed between the upper surface (320) of the pump head housing (302) and the valve seat (330), the damping volume (356) being defined, at least in part, between the annular recess (364) and the inlet valve member (310).

2. A pump head according to claim 1, wherein the inlet valve member (110; 210; 310) opens and closes in response to fuel pressure within a gallery (116; 216; 316), wherein the gallery communicates with the external chamber (142; 242; 342), such that, in use, the gallery (116; 216; 316) communicates with a source of low-pressure fuel via the external chamber (142; 242; 342).

3. A pump head according to claim 1 or claim 2, wherein the external chamber (142; 242; 342) is defined by a closure member (134; 234; 334) mounted externally to the pump head housing (102; 202; 302).

4. A pump head according to claim 1, wherein the valve bore (318) comprises a guide region (362) disposed between the gallery (316) and the annular recess (364), and the inlet valve member (310) comprises a guide portion (366) which cooperates with the guide region (362) to guide the movement of the inlet valve member (310) within the valve bore (318), wherein the flow of fuel between the guide portion (366) and guide region (362) is substantially prevented; and
wherein said surface associated with the inlet valve member (310) is a shoulder (368) formed on the inlet valve member (310) by a transition between the guide portion (366) and a further portion (370) above the guide portion (366), the further portion (370) having a diameter less than that of the guide portion (366).

5. A fuel pump for use in a common rail fuel injection system, comprising at least one pump head according to any one of claims 1 to 4.

Drawing