Fuel pump

Abstract

 A fuel pump comprises a plurality of pumping plungers (32) reciprocable within bores (14) formed in a pump body (10). The plungers (32) are reciprocable under the influence of an eccentric cam arrangement (50, 56) including a cam surface which encircles the part of the pump body (10) within which the bores (14) are provided. The cam arrangement (50, 56) may be driven by a drive member (56) supported by bearings (60) located in generally the same plane as and radially outward of the bores (14) and plungers (32).

Description

[0001] This invention relates to a fuel pump, and in particular to a fuel pump suitable for use in supplying fuel under pressure to charge an accumulator or common rail of a common rail fuel injection system to permit the delivery of fuel under pressure to the cylinders of a compression ignition internal combustion engine.

[0002] It is desirable to drive such a high pressure fuel pump directly from the cam shaft of the associated engine. Clearly, such location of the fuel pump increases the overall dimensions of the engine, such an increase being undesirable especially where the engine is to be mounted transversely in a vehicle engine compartment. It is also desirable to minimise additional loads on the cam shaft, and to avoid the generation of excessive pressure fluctuations in the common rail or accumulator out of phase with the operation of the injectors.

[0003] EP-A-0809023 describes a fuel pump for use in charging a common rail, the pump comprising a plurality of pumping plungers driven by an eccentric cam arrangement mounted upon a drive shaft. The supply of fuel by one or more of the pumping plungers may be terminated, in use, in order to control the quantity of fuel delivered by the pump at any particular operating speed without applying excessive torque fluctuations to the drive shaft.

[0004] According to the present invention there is provided a fuel pump comprising a plurality of pumping plungers reciprocable within bores provided in a pump body under the influence of an eccentric cam arrangement having an eccentric cam surface, wherein the eccentric cam surface encircles the part of the pump body within which the bores are provided, and bearings for supporting the eccentric cam arrangement whilst permitting rotation thereof, the bearings being located radially outward of the eccentric cam surface in a plane generally aligned with the pumping plungers.

[0005] The eccentric cam arrangement may form part of or be carried by a drive member which is conveniently driven from the cam shaft of an associated engine. Such an arrangement is advantageous in that the axial length of the fuel pump can be reduced as the drive member bearings are located in the same plane as the pumping plungers. Further, the application of side loads to the drive member and cam shaft is reduced.

[0006] Conveniently, the bores communicate with a common inlet passage located adjacent an inner end of each of the bores. Inlet and outlet valves are associated with each bore, the inlet valves conveniently being located within each respective bore. Such an arrangement permits a reduction in the dead volume.

[0007] The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a fuel pump in accordance with an embodiment of the invention; and

Figure 2 is a sectional view along the line 2-2 of Figure 1.

[0008] The fuel pump illustrated in the accompanying drawings comprises a pump body 10 which comprises a region 10a of generally triangular cross-section which is integral with a region 10b defining a generally circular flange. The region 10a is provided with three upstanding projections 12, blind bores 14 extending through the projections 12, along the axes thereof, and extending into the main part of the region 10a. An axially extending inlet passage 16 extends from the face of the region 10a remote from the flange 10b, the passage 16 terminating adjacent the inner ends of the bores 14. Drillings 18 of diameter smaller than the diameter of the bores 14 interconnect the bores 14 with the passage 16. The end of the passage 16 remote from the flange 10b is closed by a plug 20. The passage 16 communicates through a radially extending drilling 22, the outer end of which is closed by a plug 24, with a drilling 26 which extends in a direction parallel to the axis of the pump body 10. A plug 28 closes the end of the drilling 26 remote from the flange 10b. The drilling 26 communicates with an inlet port 30 provided in the flange 10b.

[0009] A pumping plunger 32 is reciprocable within each of the bores 14. An inlet valve arrangement controls the supply of fuel to each bore 14 from the passage 16, the inlet valves each taking the form of a valve member 34 which is engageable with a seating defined by the step at the interconnection between each bore 14 and the associated drilling 18. The valve members 34 take the form of generally circular members of diameter smaller than the diameter of the bores 14 each member including three equi-angularly spaced, radially extending arms of length sufficient to ensure that the valve member 34 remains generally coaxial with the bore 14, the arms spacing the circular part of the valve member 34 from the wall of the bore 14 to define a flow path permitting fuel to flow between the valve member 34 and wall of the bore 14 when the valve member 34 is lifted from its seating. A low rate coil spring 36 is engaged between the pumping plunger 32 and the valve member 34 to bias the valve member 34 towards its seating. As illustrated, the coil springs 36 are conveniently located within axially extending blind drillings provided in the plungers 32.

[0010] The flange 10b is provided with a relatively large diameter, blind bore within which a plug 38 is located, the plug 38 and bore together defining an annular chamber 40 which communicates with an outlet passage and outlet port 42. Drillings 44 provide flow paths between each bore 14 and the annular chamber 40, the drillings 44 defining valve seats against which spherical valve elements 46 are engageable to permit fuel to flow from the bores 14 to the outlet port 42, but substantially prevent flow in the reverse direction. The plug 38 acts as a stop to limit movement of the spherical valve elements 46 away from the seatings.

[0011] The outer end of each plunger 32 engages a pad 48 which in turn engages an inner surface of a load transmitting member 50. As illustrated in Figure 2, the load transmitting member 50 comprises a tubular member having a generally circular outer periphery, the central passage of the tubular member being of generally hexagonal cross-section. The pads 48 are biased into engagement with the load transmitting member 50 by coil springs 54 which are engaged between the part 10a of the pump body and clip members 52 which are located within grooves provided against the outer ends of the plungers 32, the clip members 52 being shaped to engage the surface of the pads 48 remote from the load transmitting member 50.

[0012] The load transmitting member 50 is located within a large diameter bore formed in a rotary drive member 56 which is arranged to be driven from the cam shaft of an associated engine through an Oldham coupling arrangement 58. The rotary drive member 56 is supported for rotary movement by bearings 60, 62 within a pump housing 64. The pump housing 64 is arranged to be bolted or otherwise secured to the engine adjacent the cam shaft thereof. As illustrated in the drawings, the bore provided in the rotary drive member 56 is offset from the axis of rotation of the rotary drive member 56. The wall of the bore defines an eccentric cam surface which engages the load transmitting member 50 and, as a result, as the drive member 56 rotates about its axis, the load transmitting member 50 follows a generally circular path, the load transmitting member remaining in the orientation illustrated due to the engagement of the pads 48 therewith, thus it will be appreciated that sliding movement occurs between the eccentric cam surface of the rotary drive member 56 and the load transmitting member 50.

[0013] In use, starting from the position illustrated in the accompanying drawings, the uppermost one of the pumping plungers 32 occupies its innermost position. As the rotary drive member 56 rotates away from this position, the movement of the eccentric cam surface defined by the bore formed in the rotary drive member 56 allows the uppermost pumping plunger 32 to move under the influence of the spring 54 drawing fuel into the bore 14 from the inlet passage 16 through the inlet valve. It will be appreciated that the movement of the load transmitting member 50 results in sliding movement of the pad 48 on the inner surface of the load transmitting member 50. The outward movement of the uppermost plunger continues until the rotary drive member 56 has rotated through an angle of 180°.

[0014] Once this position has been achieved, the uppermost pumping plunger 32 occupies its outermost position. Continued rotation of the rotary drive member 56 causes the uppermost pumping plunger 32 to be pushed inwards, pressurizing the fuel within the bore 14 to a sufficient extent to cause the valve member 46 of the outlet valve to lift from its seating, thus permitting the supply of fuel under pressure to the outlet port 42. It will be appreciated that during the inward movement of the plunger 32, the fuel pressure within the bore 14 assists the spring 36 in ensuring that the inlet valve remains closed. The other two plungers move in a like manner, but out of phase with each other and the uppermost plunger.

[0015] As, in the arrangement illustrated in Figures 1 and 2, the pumping plungers 32 are arranged to be withdrawn from the bores 14 under the action of the springs 56, it will be appreciated that the provision of a separate, low pressure transfer pump may be avoided.

[0016] As the bearings 60 are located radially outward of the eccentric cam surface, and in generally the same plane as that containing the bores 14 and pumping plungers 32, it will be appreciated that a fuel pump of relatively short axial length can be provided. Further, the forces applied to the pumping plungers 32 to cause inward movement thereof, in use, are transmitted through the bearings 60 to the housing 64 without applying a significant side load to the rotary drive member 56 or cam shaft.

[0017] The arrangement may be modified by replacing the pads 48 with bucket tappet arrangements which ride on the outer surfaces of the projections 12 thus avoiding the application of side loads to the pumping plungers 32. In such an arrangement, the springs 54 are located radially outward of the skirts of the bucket tappet arrangements. If the fuel pump is used in conjunction with a fuel metering arrangement, then in order to permit partial filling of the bores 14, and hence movement of the plungers 32 outward to a limited extent whilst ensuring that the bucket tappet arrangements remain in permanent contact with the load transmitting member 50, the clips 52 must be omitted.

[0018] The arrangement may further be modified by replacing the springs 36 with spring arrangements which engage in grooves provided in the walls of the bores 14 rather than in drillings formed in the pumping plungers 32.

[0019] If desired, the rotary drive member 56 may be rigidly secured to and carried by the cam shaft, in which case the provision of the bearings 60, 62 may be omitted. In a further alternative, a conventional taper drive arrangement may be used between the cam shaft and the rotary drive member 56. Clearly, where the provision of bearings 60, 62 can be avoided, then the outer diameter of the pump may be reduced.

[0020] As an alternative to using a metering arrangement controlling the supply of fuel to the pump, the outward movement of the plungers 32 may be controlled by appropriately controlling the fuel or fluid pressure within the housing 64.

[0021] Where the arrangement includes an Oldham coupling 58, the Oldham coupling arrangement 58 and the bearing 62 may be lubricated advantageously using engine oil, fuel being used to lubricate the bearing 60, and an appropriate seal 66 being used to contain the fuel.

[0022] Conveniently, an opening 68 is provided between the seal 66 and the bearing 62 to permit monitoring of whether either seal is leaking.

[0023] The bearing 62 is an interference fit with both the housing 64 and the drive member 56. The bearing 62 incorporates a dynamic seal between its races. The seal of the bearing 62 and the seal 66, separated from one another by a region which is vented to the atmosphere through the opening 68, reliably isolate the engine oil from the fuel. The use of a dynamic seal rather than an additional seal separate from the bearing 62 saves space.

[0024] In order to accommodate thermal expansion, the bearing 60 is conveniently free to slide relative to the housing 64, the bearing 62 serving to locate the drive member 56 axially. Alternatively, the bearing 60 could take the form of a cylindrical roller bearing arrangement. In a further alternative, the bearing 60 could be fixed relative to the housing 64, the bearing 62 being free to slide to accommodate such expansion. In such an arrangement, an additional seal may be required.

Claims

1. A fuel pump comprising a plurality of pumping plungers (32) reciprocable within bores (14) provided in a pump body (10) under the influence of an eccentric cam arrangement (56) having an eccentric cam surface, wherein the eccentric cam surface encircles the part of the pump body (10) within which the bores (14) are provided, and bearings (60) for supporting the eccentric cam arrangement (56) whilst permitting rotation thereof, the bearings (60) being located radially outward of the eccentric cam surface in a plane generally aligned with the pumping plungers (32).

2. A fuel pump as claimed in Claim 1, wherein the eccentric cam arrangement (56) forms part of or is carried by a drive member.

3. A fuel pump as claimed in Claim 2, wherein the drive member is arranged to be driven from the cam shaft of an associated engine.

4. A fuel pump as claimed in any one of the preceding claims, wherein the bores (14) communicate with a common inlet passage (16) located adjacent the inner ends of the bores (14).

5. A fuel pump as claimed in Claim 4, further comprising inlet and outlet valves associated with each bore (14) controlling the flow of fuel to and from each bore (14).

6. A fuel pump as claimed in Claim 5, wherein each inlet valve (34) is located within a respective bore (14).

Drawing