Transfer pump

Abstract

 A transfer pump for use with a high pressure pump having a rotary drive member (10) and a stationary part (16), comprises a plurality of pumping elements (26) reciprocable within bores (24) provided in the drive member (10), the bores (24) extending generally parallel to the axis of rotation of the drive member (10), the pumping elements (26) being reciprocable under the influence of a cam surface (28) defined by a surface of the stationary part (16) of the high pressure pump, the pumping elements (26) being biased towards the cam surface (28), and valve means associated with the bores (24) controlling the flow of the fuel to and from the bores (24).

Description

[0001] This invention relates to a transfer pump for use in supplying fuel under relatively low pressure to a high pressure pump, and to a high pressure pump incorporating such a low pressure transfer pump.

[0002] Where a high pressure pump is used to charge, for example, a common rail or accumulator with diesel fuel it is known to use, as the high pressure pump, a fuel pump of the type in which a plurality of pumping plungers are reciprocable within respective bores under the influence of a cam surface. The pumping plungers are not spring biased, and in order to charge such a pump with fuel, a separate low pressure transfer pump is used. It is known to locate low pressure pumps in, for example, the fuel tank, or to incorporate such pumps within or adjacent the high pressure pump, but the provision of such low pressure pumps results in the fuel system being costly, unnecessarily complex or bulky.

[0003] A known transfer pump comprises a vane pump mounted around the high pressure pump drive shaft. As the drive shaft extends through the vane pump, the vane pump is of relatively large diameter. In order to avoid leakage and in order to reduce wear, it has been found that a wear-resistant port plate is required, and a pressure regulation valve is required in order to compensate for excess output. Another type of transfer pump is a radial piston pump. Such a pump is disadvantageous in that it extends beyond the profile of the high pressure pump and requires the provision of an additional cam surface. Such a pump also has the disadvantages that, during filling, cavitation within the inlet line is difficult to avoid, and as its output is not continuous, filling of the high pressure pump at the desired instant may not be possible.

[0004] According to the present invention there is provided a transfer pump for use with a high pressure pump having a rotary drive member and a stationary part, the transfer pump comprising a plurality of pumping elements reciprocable within bores provided in the drive member, the bores extending generally parallel to the axis of rotation of the drive member, the pumping elements being reciprocable under the influence of a cam surface defined by a surface of the stationary part of the high pressure pump, the pumping elements being biased towards the cam surface, and valve means associated with the bores controlling the flow of the fuel to and from the bores.

[0005] The cam surface conveniently takes the form of a flat surface angled relative to the axis of rotation of the drive member. The valve means may take the form of a plate defining first and second arcuate chambers, the first arcuate chamber communicating with the bores, the pumping elements of which are moving under the influence of the cam surface to expel fuel from the bores, the second arcuate chamber communicating with the bores, the pumping element of which are moving to draw fuel into the bores. As the drive member rotates, it will be appreciated that each bore fills with fuel whilst in communication with the second chamber, the bores subsequently moving into communication with the first chamber, shortly after which the pumping elements move to expel fuel from the bores to the first chamber.

[0006] It will be appreciated that, as the pumping element are located within the drive member, the dimensions of the high pressure pump are not significantly increased.

[0007] The invention also relates to a high pressure pump incorporating such a transfer pump. The high pressure pump is conveniently of the type comprising a plurality of pumping plungers reciprocable within bores formed in a hydraulic head under the influence of a cam surface forming part of or carried by the drive member, a surface of the hydraulic head defining the cam surface of the transfer pump.

[0008] The invention will further be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a view, partly in section, illustrating a high pressure pump incorporating a transfer pump in accordance with an embodiment of the invention;

Figure 2 is a view of the feed plate of the transfer pump of Figure 1 illustrating the porting arrangement; and

Figure 3 is a view illustrating a modification to the arrangement of Figure 1.

[0009] Figure 1 illustrates part of a high pressure pump arrangement incorporating a transfer pump in accordance with an embodiment of the invention. The high pressure pump comprises a rotary drive member 10 including a region of enlarged diameter which is rotatable within a housing 12.

[0010] Appropriate bearings 14 are provided to support the drive member 10, the bearings permitting rotary motion of the drive member 10 but substantially preventing axial movement of the drive member 10 relative to the housing 12. The enlarged diameter region of the drive member 10 forms a cup, the inner surface of which defines a cam surface. A hydraulic head 16 of the high pressure pump extends within the cup defined by the end of the drive member 10. The hydraulic head 16 is provided with a through bore 18 within which a pair of plungers 20 are reciprocable. The outer end of each plunger 20 engages the shoe of a respective shoe and roller arrangement 22, the roller of which is engageable with the cam surface such that as the drive member 10 rotates relative to the housing 12, the rollers of the shoe and roller arrangements 22 ride over the cam surface causing reciprocating motion of the plungers 20 within the bore 18.

[0011] The part of the drive member 10 forming the base of the cup is further provided with a plurality of through bores which extend in a direction parallel to the axis of rotation of the drive member 10, each through bore 24 housing a spherical pumping element 26, the pumping elements 26 being engageable with a cam surface 28 defined by an angled end wall of the hydraulic head 16.

[0012] An annular port plate 30 is secured to the rotary drive member 10 to close the ends of the bores 24 remote from the hydraulic head 16, the port plate 30 being secured in position by bolts 32. Coil springs 34 are trapped between the port plate 30 and the pumping elements 26 to bias the pumping elements 26 into engagement with the cam surface 28. The port plate 30 is provided with a plurality of openings 36, each opening 36 aligning with a respective one of the bores 24.

[0013] An annular valve plate 38 is keyed to the housing 12 by pegs 39, the valve plate 38 engaging the port plate 30 to form a substantially fluid tight seal therewith. As illustrated in Figure 2, the valve plate 38 is provided with a pair of arcuate grooves or channels 40, 42, the channels 40, 42 being located so as to communicate with the openings 36 provided in the port plate 30.

[0014] The housing 12 is provided with an inlet drilling 44 which communicates through inlet ports 46 with the chamber defined by the first arcuate channel 40. The chamber defined by the second arcuate channel 42 communicates through ports 48 with a drilling (not shown) which communicates with a passage 50 whereby fuel is supplied to a metering valve 52 controlling the supply of fuel to the through bore 18 of the high pressure pump. As illustrated in Figure 1, O-ring seals 54 are located between the housing 12 and the valve plate 38 in order to provide a substantially fluid tight seal around each of the ports 46, 48. In the arrangement illustrated a pair of inlet ports 46 and a pair of outlet ports 48 are provided. As a result, the valve plate 38 is supported evenly and the load forcing the valve plate 38 into contact with the port plate 30 is increased. It will be appreciated, however, that other numbers of inlet and outlet ports 46, 48 could be provided.

[0015] In use, as the drive member 10 rotates, each of the pumping elements 26 reciprocates within its bore 24 under the influence of the cam surface 28. When the volume of each bore 24 available for occupation by fuel is at its minimum, the opening 36 associated with that bore registers with the chamber defined by the first arcuate channel 40 thus permitting fuel to be supplied to that bore 24. As rotation of the drive member 10 continues, the pumping element 26 is permitted to move under the influence of the spring 34 to increase the volume available for occupation by fuel, the movement of the pumping element 26 drawing further fuel into the bore 24. As the pumping element 26 reaches its outermost position, the opening 36 associated with that bore 24 moves out of communication with the chamber defined by the first arcuate channel 40 and into communication with the chamber defined by the second arcuate channel 42. Continued rotation of the drive member 10 causes the pumping element 26 to be pushed further into the bore 24 under the influence of the cam surface 28, thus expelling fuel from the bore 24 through the chamber defined by the second arcuate channel 42 to the metering valve 52.

[0016] In the position illustrated in Figure 1, the pumping plungers 20 occupy substantially their innermost positions. As the drive member 10 rotates away from this position, the rollers rise over the cam lobes of the cam surface defined by the cup region of the drive member 10 thus permitting the plungers 20 to move outward under the influence of the fuel under pressure supplied to the bore 16 from the transfer pump arrangement. Subsequently, the plungers 20 will reach their outermost positions, and thereafter the plungers 20 will be forced inward due to the engagement of the rollers with subsequent cam lobes of the cam surface. Such movement of the plungers 20 will cause fuel to be displaced from the bore 18 to charge a common rail 56 or accumulator to an appropriate pressure. Appropriate valve arrangements are provided in order to ensure that the fuel displaced by the pumping plungers 20 is not returned to the metering valve 52 and transfer pump.

[0017] If required, a regulator arrangement may be provided between the inlet and outlet of the transfer pump arrangement in order to control the pressure of fuel supplied to the inlet metering valve 52. In an alternative arrangement, the regulator may be omitted, the valve plate 38 being arranged to move out of sealing engagement with the port plate 30 upon the pressure within the chamber defined by the second arcuate channel 42 exceeding a predetermined pressure to relieve the fuel pressure therein, such movement of the valve plate 38 being opposed by the resilience of the O-rings 54.

[0018] During manufacture, it is thought that the bores 24 may be machined to a slightly smaller diameter than is required, in use, and the spherical valve elements 26 forced therethrough to expand the bores 24 to the desired diameter, such an arrangement avoiding the time-consuming process of honing and matching the bores 24 and spherical pumping elements 26 to one another, whilst maintaining a sufficiently close contact to maintain leakage at an acceptable level. It will be appreciated that the fuel pressure within the transfer pump arrangement is relatively low, thus the level of leakage can be maintained at an acceptable level relatively easily.

[0019] Figure 3 illustrates a modification to the arrangement of Figure 1 in which the spherical pumping elements 26 are replaced by dome ended plunger elements 26a. Although the arrangement of Figure 3 is more complex than that of Figure 1, it has the advantages that the plunger elements 26a act to locate and guide the springs 34, and also that the leakage paths between the pumping elements 26a and walls of the bores 24 are of increased length, thus further reducing leakage, or permitting an increased clearance between the pumping elements 26a and bore walls whilst constraining leakage at an acceptable level. As the pumping elements 26 are hollow, the inertia thereof is relatively small. Further, a lower rate of spring may be used, if desired.

[0020] In a further modification, the plunger elements may be of substantially cylindrical form, each plunger element holding captive a spherical load transmitting member arranged to cooperate with the cam surface 28. Each plunger element may be of hollow form to locate the associated spring.

[0021] Although in the arrangements described hereinbefore, the rotary drive member 10 is provided with ten bores 24 and associated pumping elements, it will be appreciated that it is possible to provide fewer or a greater number of such bores and pumping elements. The diameters of the bores may also be altered. Further, the bores 24 may be provided in a component separate from the rotary drive member, but arranged to be rotated therewith.

[0022] Where the transfer pump is to supply fuel at very low pressure, it may be possible to mould the pumping elements from a suitable plastics material which, if desired, can be designed to be a light interference fit within the bores, lightly engaging the walls of the bores to minimise leakage.

[0023] In a further modification, a plurality of separate inlet and outlet valves may be provided to control the supply of fuel to and from the bores 24.

[0024] The transfer pump arrangement described hereinbefore is suitable for use with high pressure pumps other than that described hereinbefore, and it will be appreciated that the invention should not be limited to the use of the transfer pump arrangement with the particular type of high pressure pump described hereinbefore.

Claims

1. A transfer pump for use with a high pressure pump having a rotary drive member (10) and a stationary part (16), the transfer pump comprising a plurality of pumping elements (26) reciprocable within bores (24) provided in the drive member (10), the bores (24) extending generally parallel to the axis of rotation of the drive member (10), the pumping elements (26) being reciprocable under the influence of a cam surface (28) defined by a surface of the stationary part (16) of the high pressure pump, the pumping elements (26) being biased towards the cam surface (28), and valve means associated with the bores (24) controlling the flow of the fuel to and from the bores (24).

2. A transfer pump as claimed in Claim 1, wherein the cam surface (28) comprises a flat surface which is angled relative to the axis of rotation of the drive member (10).

3. A transfer pump as claimed in Claim 1 or Claim 2, wherein the surface of each pumping element (26) which cooperates with the cam surface (28) is of part spherical form.

4. A transfer pump as claimed in any one of Claims 1 to 3, wherein the valve means takes the form of a plate (38) defining first and second arcuate chambers (40, 42), the second arcuate chamber (42) communicating with the bores, the pumping elements of which are moving under the influence of the cam surface (28) to expel fuel from the bores, the first arcuate chamber (40) communicating with the bores, the pumping elements of which are moving to draw fuel into the bores.

5. A high pressure fuel pump assembly comprising a high pressure fuel pump including a rotary drive member (10) and a stationary part (16), and a transfer pump as claimed in any one of the preceding claims mounted upon the high pressure fuel pump.

6. A high pressure fuel pump assembly as claimed in Claim 5, wherein the high pressure fuel pump comprises a plurality of pumping plungers (20) reciprocable within bores formed in a hydraulic head (16) under the influence of a cam surface forming part of or carried by the drive member (10), a surface of the hydraulic head (16) defining the cam surface of the transfer pump.

Drawing