Drive arrangement for a pump

Abstract

 A drive arrangement for a pumping plunger (24) of a pump assembly comprises a drive member (30) that is firstly co-operable with the pumping plunger (24) and secondly co-operable with a cam rider (20) so as to impart axial drive to the plunger (24) to perform a plunger pumping stroke whilst permitting lateral sliding movement of the rider (20) relative to the drive member (30). The drive member (30) and the cam rider (20) are co-operably shaped to define (i) an increased volume (44) for lubricating fluid which is variable throughout the pumping cycle and (ii) restricted flow means through which fluid within said volume (44) is dispelled at a relatively low rate as the plunger (24) is driven throughout the pumping stroke. This has the effect of prolonging transient fluid pressure within the volume (44) through that period of the pumping stroke for which return loading of the drive member (30) is a maximum and, hence, provides the benefit that wear of the drive member (30) due to scuffing is reduced.

Description

[0001] The invention relates to a drive arrangement for use in pump of the type suitable for use in a common rail fuel injection system of an internal combustion engine. In particular, the invention relates to a drive arrangement for a pump having at least one pumping plunger that is driven by means of a drive member co-operating with a cam rider mounted upon the engine cam shaft.

[0002] In a known common rail fuel pump of radial pump design, for example as described in EP 1 184 568A, three pumping plungers are arranged at equi-angularly spaced locations around an engine driven cam. Each plunger is mounted within a respective plunger bore provided in a pump housing and, as the cam is driven, each of the plungers is caused to reciprocate. As the plungers reciprocate, each causes pressurisation of fuel within an associated pump chamber. The delivery of fuel from the pump chambers to a common high pressure supply line is controlled by means of respective delivery valves associated with each of the pumps. The high pressure line supplies fuel to a common rail, or other accumulator volume, for delivery to the downstream injectors of the common rail fuel system.

[0003] In one known fuel pump of the aforementioned type, each of the plungers is coupled to a respective drive member in the form of a tappet. The cam carries a cam ring or cam rider that travels over the surface of the cam as it is driven by the engine. Each tappet is located within a tappet bore provided in a main pump housing and is arranged so that, as the cam is driven, each tappet is caused to reciprocate within its respective bore, resulting in reciprocating motion to the plungers.

[0004] As the rider rides over the cam surface to impart drive to the tappet in an axial direction, a base surface of the tappet is caused to translate laterally over a co-operating region of the rider surface. As the tappet is driven radially outward from the shaft, its respective plunger is driven to reduce the volume of the pump chamber. This part of the pumping cycle is referred to as the pumping stroke of the plunger, during which fuel within the associated pumping chamber is pressurised to a relatively high level.

[0005] As the tappet is driven outwardly from the shaft and the tappet base slides over the surface of the cam rider, a frictional force is generated between the two surfaces. This gives rise to a local increase in the surface temperature of the tappet, resulting in adhesive wear or "scuffing". This is undesirable and, in the worst case, can lead to pump failure.

[0006] It is known to provide a lubrication means between the sliding surfaces of the tappet base and the cam rider to reduce these disadvantageous effects. Typically, this is achieved by providing a relatively thin fluid film between the two surfaces to generate a transient fluid pressure between them which supports loading of the tappet and improves lubrication. This solution, however, is unsatisfactory in meeting the high expectations of evolving fuel pumps of the aforementioned type, particularly of the type intended for use in common rail diesel fuel engines.

[0007] It is one object of the present invention to overcome or alleviate the aforementioned problem.

[0008] According to the present invention, there is provided a drive arrangement for a pumping plunger of a pump assembly, the drive arrangement comprising; a drive member that is firstly co-operable with the pumping plunger and secondly co-operable with a cam rider so as to impart axial drive to the plunger to perform a plunger pumping stroke whilst permitting lateral sliding movement of the rider relative to the drive member, wherein the drive member and the cam rider are co-operably shaped to define

(i) an increased volume for lubricating fluid which is variable throughout the pumping cycle, and

(ii) restricted flow means through which fluid within said volume is dispelled at a relatively low rate as the plunger is driven through the pumping stroke so as to prolong transient fluid pressure within the volume through that period of the pumping stroke for which return loading of the drive member is a maximum.

[0009] It will be understood from the following description that variable return loading of the drive member arises due to the hydraulic load exerted on the drive member by fuel within the pump chamber, the pressure of which increases and decreases throughout a pumping cycle, and that the maximum return load applied to the drive member occurs part way between BDC and TDC when fuel within the pump chamber is pressurised to its maximum value, just prior to associated outlet or delivery valve means of the pump chamber being opened to permit high pressure fuel delivery.

[0010] The invention provides the advantage that lubrication between the drive member and the cam rider is improved during the plunger pumping stroke. The "squeeze film effect", which is provided as fluid within the variable volume is dispelled through said restricted flow means, is prolonged, to ensure a transient fluid pressure condition exists to support return loading of the drive member during that part of the pumping cycle when it is a maximum. Transient fluid pressure within the variable volume therefore supports return loading of the drive member for a longer period of duration than is provided by known drive arrangements of similar type.

[0011] Typically, the transient fluid pressure condition occurs part way between bottom-dead-centre (BDC) and top-dead-centre (TDC) of the pumping stroke. This has the beneficial effect that return loading of the drive member is supported during the most critical point in the pumping cycle (i.e. when the return loading is a maximum) and friction between the co-operating surfaces of the cam rider and the drive member is reduced. The effects of wear due to scuffing are therefore limited.

[0012] The drive arrangement may be incorporated within a pump assembly of the type having three plungers, wherein the plungers are radially spaced around a cam rider which is common to all three plungers, this being a so-called radial fuel pump.

[0013] In one embodiment, at least one of the drive member and the rider is shaped to define a recessed surface to define, together with a surface of the other of the drive member and the rider, said variable fluid volume.

[0014] For example, the surface of the drive member may be shaped so as to be substantially concave.

[0015] In this case the cam rider may include a substantially flattened surface which defines, together with the concave surface of the drive member, the variable fluid volume.

[0016] Alternatively, or in addition, the cam rider may include a substantially concave surface which defines, together with the surface of the drive member, the variable fluid volume.

[0017] In one embodiment the drive member may be shaped to include a drive member side wall of annular form defining an annular surface that is co-operable with the surface of the rider to define the restricted flow means. For example, the drive member may be provided with a recessed surface of substantially U-shaped cross section.

[0018] In any of the embodiments of the invention, the drive member may be shaped to define a radiussed surface to define the restricted flow means with the surface of the rider. This provides the benefit that lubricating fluid is encouraged to flow into the variable fluid volume during the return stroke of the drive member, and also in some configurations provides the benefit that the surface contact area between the drive member and the cam rider is increased, thereby reducing contact stresses.

[0019] According to a second aspect of the present invention, a drive arrangement for a pumping plunger of a pump assembly comprises;
a drive member that, in use, is firstly co-operable with the pumping plunger and secondly co-operable with a cam rider so as to impart drive to the plunger to perform a plunger pumping stroke during which fuel within a pump chamber is pressurised to a high level,
whereby, in use, the rider moves laterally relative to the drive member, and wherein respective surfaces of the drive member and the cam rider are co-operably shaped to define a variable volume for lubricating fluid throughout the pumping cycle, and to provide a transient pressure condition between said surfaces during a stage of the pumping stroke for which relative velocity between lateral movement of the drive member and the rider is substantially zero.

[0020] According to a third aspect of the present invention, there is provided a pump assembly including;
a plunger, and
a drive arrangement for the plunger as claimed in the accompanying claim set.

[0021] The preferred and/or optional features of the first aspect of the invention may therefore be provided, alone or in appropriate combination, in either the second or the third aspect of the invention also.

[0022] In a particularly preferred embodiment of each of the first, second and third aspects of the invention, the drive member takes the form of a tappet, for example a bucket tappet of substantially U-shaped cross-section.

[0023] The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a sectional view of a pump assembly of the type in which the drive arrangement of the present invention may be employed,

Figure 2 is an exaggerated view of a tappet and cam rider surface forming part of a first embodiment of the drive arrangement of the present invention,

Figure 3 is a diagram to show the relative velocity between the tappet and the cam rider surface throughout a 360° pumping cycle,

Figure 4 is a diagram to show the displacement of the tappet, with time, throughout the pumping cycle, with the position of the tappet relative to the cam rider surface also indicated,

Figures 5(a) to (c) show views of the tappet during first, second and third stages of a pumping stroke of the pumping cycle,

Figures 6, 7 and 8 are exaggerated views, similar to Figure 2, of alternative tappet and cam rider surface configurations for use in the pump assembly of Figure 1.

[0024] The present invention relates to drive arrangement for a pump assembly, generally of the type shown in Figure 1. The pump assembly 10 includes a first housing part 12 in the form of a main pump housing provided with an axially extending opening through which a cam drive shaft extends when the assembly 10 is installed within the engine. In the section shown in Figure 1, the central axis 16 of the drive shaft is identified, although the drive shaft itself is not visible. The drive shaft co-operates with a drive arrangement which includes an eccentrically mounted cam 18 carrying cam ring or rider 20 having a generally circular-like cross section.

[0025] Mounted around the cam 18 are first, second and third pump heads or units, generally referred to as 22a, 22b, 22c. Each pump unit is identical and so only one will be described in detail.

[0026] The first pump head 22a includes a plunger 24 which is reciprocal within a plunger bore 26 to cause pressurisation of fuel within a pump chamber 28 defined at a blind end of the bore 26. Fuel at relatively low pressure is supplied to the pump chamber 28, in use, and is pressurised to a high level suitable for injection as the plunger 24 is driven to perform a pumping stroke, that is between bottom-dead-centre (BDC) and top-dead-centre (TDC).

[0027] Figure 2 shows a first embodiment of a drive arrangement for the pump assembly in Figure 1. The plunger has an associated a drive member 30 in the form of a tappet is co-operable with the plunger 24. The tappet 30 may be a bucket tappet, of generally U-shaped or channelled cross section, and includes a base 32 and first and second side walls 34. The upper surface of the tappet base 32 may be provided with recess (not shown) for locating one end of a plunger return spring (item 36 - Figure 1), mounted concentrically with the plunger 24, which serves to drive a plunger return stroke between TDC and BDC. A circlip (not shown) couples the return spring 36 to the plunger 24 at its lower end. Although the tappet 30 and the plunger 24 are not physically coupled to one another, so that relative axial movement is permitted between these parts 24, 30, the spring 36 tends to maintain tappet and plunger contact during movement.

[0028] Examples of how the tappet and the plunger may be coupled together, if required, are described in our co-pending UK patent application GB 0229367.8.

[0029] A lower surface 37 of the tappet base 32 is co-operable with a flattened surface region 38, or flat, of the rider 20. The generally circular cam rider 20 is provided with three flattened surface regions 38 in total, equi-angularly spaced around the rider 20 so that each is co-operable with a respective one of the three tappets. The rider 20 may therefore be considered to be of generally prismatic-type form. The lower surface 37 of the tappet base 32 defines a surface edge 37a and the flattened surface 38 of the rider 20 defines a surface edge 38a. The surface edge 37a of the tappet is of annular form and, effectively, defines a 'surface line'.

[0030] In known fuel pumps of the type including a tappet driving a plunger, the facing co-operable surfaces of the tappet and the rider are flat and aligned in parallel to define a very small clearance between them which supports a thin film of lubricating fluid. As the tappet is driven through the pumping cycle, the thin fluid film between these two surfaces serves to reduce friction between the sliding surfaces, and as fluid it dispelled between the surfaces transient fluid pressure supports return loading of the tappet. This so-called "squeeze film" effect is well known, and mechanisms relying on this are known to exhibit reduced friction. It has been found, however, that this squeeze film effect does not reduce friction between the tappet and the rider to a sufficient extent, so that an unsatisfactory level of tappet wear occurs.

[0031] It is a particular feature of the present invention that the surface 37 of the tappet base 32 and the facing flattened surface 38 of the cam rider 20 are co-operably shaped to provide an increased volume between them for lubricating fluid. In Figure 2, for example, the lower surface of the tappet base 32 is provided with a recess to define a substantially concave surface 37, rather than being flat as is known in conventional tappet drive arrangements. This relatively large fluid volume 44 is variable throughout the pumping cycle and provides a prolonged transient fluid pressure condition which serves to reduce friction between the surfaces 37, 38 as they translate or slide relative to one another, in use. The reason for this is described in further detail below. It should be noted that the extent to which the surface 37 of the tappet base 32 is concave is exaggerated greatly in Figure 2.

[0032] In use, as the cam rider 20 is caused to ride over the surface of the cam 18 upon rotation of the drive shaft, an axial drive force is imparted to the tappet 30, and in turn to the plunger 24, causing the plunger 24 to reciprocate within its bore 26. The tappet 30 and the plunger 24 are thus driven together to perform a pumping cycle including a pumping stroke and a return stroke. During the pumping stroke the tappet 30 and the plunger 24 are driven radially outward from the shaft (i.e. vertically upwards in Figure 1) to reduce the volume of the pump chamber 28. During the plunger return stroke, effected by means of the return spring 36, the tappet 30 and the plunger 24 are urged in a radially inward direction (i.e. vertically downwards in Figure 1) to increase the volume of the pump chamber 28. As the tappet 30 is driven in a radially outward direction, to impart drive to the plunger 24 in an axial direction, a degree of lateral or sliding movement of the tappet 30 across the flattened rider surface 38 occurs, in a back and forth manner. The tappet slides across the flattened rider surface 38 in a similar manner during the return stroke.

[0033] The pump assembly is provided with an appropriate inlet metering valve (not shown) with appropriate inlet and outlet valves (also not shown) being provided for each of the three pump chambers. Pressurisation of fuel within the pump chamber 28 occurs during the pumping stroke of the plunger 24, during a period for which both the inlet and outlet valves are closed. When fuel is pressurised to a level that is sufficient to open the outlet valve, pressurised fuel is supplied through a delivery passage to the common rail. Typically, the pressure of fuel supplied through the outlet valve is in the range of between 1500 and 2000 bar. During the return stroke of the plunger 24, fuel pressure downstream of the pump chamber 28 is higher than that within the pump chamber 28 and the outlet valve is urged closed. During the period of the return stroke for which the inlet valve is urged open, fuel at relatively low pressure is supplied to the pump chamber 28 to fill the chamber 28 ready for commencement of the following pumping stroke.

[0034] As the tappet 30 and the plunger 24 are driven through the pumping cycle, the surface 37 of the rider 20 moves laterally, back and forth, relative to the surface 37 of the tappet 30. The relative velocity between the sliding surfaces 37, 38 varies through the pumping cycle, as shown in Figure 3 (it should be appreciated particularly that the vertical axis in Figure 3 represents relative velocity and not tappet displacement). As the surfaces 37, 38 are displaced laterally, relative to one another, the volume 44 defined between them fills with, and dispels, lubricating fluid, in a cyclic manner, as described below with reference to Figures 4 and 5.

[0035] For the purpose of the following description it should be noted in particular that, in practice, the tappet 30 is constrained laterally and so it is the rider 20 which moves relative to the tappet 30 to provide relative movement between their respective surfaces 37, 38. However, to aid the clarity of the following description Figure 4 shows relative displacement between the tappet 30 and the rider 20, with the tappet 30 being illustrated, relative to the moving rider 20, at different relative tappet positions.

[0036] Figure 5(a) shows the tappet 30 and the plunger 24 at the start of the pumping stroke, at or just after BDC (a first stage of the pumping stroke), when the relative velocity between the sliding surfaces 37, 38 is, approximately, at its maximum value. In Figure 4, this point in the pumping cycle is identified at 50 and at this point fuel pressure in the pump chamber 28 is relatively low so that only a relatively low return load is exerted on the plunger 24 and the tappet 30 due to fuel pressure in the chamber 28. The volume 44 of lubricating fluid between the surfaces 37, 38 is large at this stage due to the concavity of the tappet base 32, which volume 44 includes a small clearance defined between the surfaces 37, 38 in the region of the tappet edge 37a at the surface line. It is this large volume 44 of fluid between the surfaces 37, 38 which supports the hydraulic return loading of the tappet 30 due to fuel pressure in the pump chamber 28.

[0037] Figure 5(b) illustrates the tappet 30 and the plunger 24 at a point further through the pumping stroke, a part of the way between BDC and TDC, at which the relative velocity between the flattened rider surface 38 and the tappet surface 37 has decreased, progressively, to a minimum (a second stage of the pumping stroke). The return load on the plunger 24 and tappet 30 is increasing at this stage, as fuel pressure in the pump chamber 28 is increasing. The tappet base 32 has a degree of compliance so that, as the return load increases the base 32 is caused to be depressed slightly, thereby reducing the volume 44 between the surfaces 37, 38. As the volume 44 is reduced, lubricating fluid is dispelled from the volume 44 at a relatively low rate, as determined by the size of the gap or clearance between the tappet edge 37a at the surface line and the flattened surface 38. The dispelling of fluid from the volume 44 provides a squeeze film effect, which serves to reduce friction between the surfaces 37, 38.

[0038] Partly due to the large volume of lubricating fluid between the surfaces 37, 38 which is dispelled from the volume 44, and partly due to the restricted clearance between the surfaces at the tappet edges 37a, transient fluid pressure between the surfaces 37, 38 is prolonged such that, at the point at which the return load on the plunger 24 and tappet 30 is at a maximum and friction between the surfaces 37, 38 is most significant, transient fluid pressure between the surfaces 37, 38 is sufficient to support return loading of the tappet 30. This critical point in the pumping cycle occurs just prior to the outlet valve opening to deliver pressurised fuel within the pump chamber 38 to the rail, as it is at this point that fuel pressure in the chamber 28 is at a maximum.

[0039] Continuing through the pumping stroke, the volume 44 defined between the tappet and rider surfaces 37, 38 is reduced further still, with fluid continuing to be dispelled between the surfaces 37, 38, through the restricted clearance at a low rate until. This is the second stage of the pumping stroke, as shown in Figure 5(c).

[0040] Eventually at TDC (point 52 in Figure 4), the surfaces 37, 38 are, effectively, in contact so that substantially all fluid has been dispelled from the now collapsed volume, hence no fluid exists between them. This is the third stage of the pumping stroke, as shown in Figure 5(c)).

[0041] Between the second and third stages of the pumping stroke, progressive edge surface contact between the surfaces 37, 38 eventually increases until the surfaces contact. It will therefore be appreciated that it is only for part of the pumping stroke that fluid is dispelled from the reducing volume 44. Compared to known arrangements making use of the squeeze film effect, however, the period for which transient fluid pressure supports return loading of the tappet is significantly prolonged.
It will be appreciated especially from Figure 4 that, for all stages of the pumping stroke, as the surfaces 37, 38 move laterally relative to one another, back and forth, the surfaces 37, 38 are nonetheless substantially aligned. The rate at which fluid is dispelled from the volume 44, between the surfaces at the tappet edge 37a, is therefore maintained relatively low. It is an important feature of the invention that the flow area through which fuel is dispelled from the volume 44 is small so as to sustain transient fluid pressure within the volume 44 for a significant period of time, and particularly during that part of the pumping stroke when loading of the tappet is at a maximum (part way between BDC and TDC). This is achieved by shaping the tappet base 32 and the cam rider 20 to provide a restricted flow means between the tappet surface edge 37a and the flattened surface 38 of the rider 20. Any increased areas available for fluid flow from the volume 44 will serve to reduce the time for which transient fluid pressure supports return loading of the tappet 30, which is undesirable. In this embodiment, for example, it is therefore important that the surface 37 of the tappet is made accurately concave to sustain the restricted fluid flow between the surfaces 37, 38 from the volume 44 at all stages of the pumping stroke.

[0042] After the tappet has reached TDC and subsequently starts its return stroke, a cavity is drawn between the two edge-contacting surfaces 37, 38 as the plunger 24 is withdrawn from the pump chamber 28 and, thus, the volume 44 between the surfaces 37, 38 starts to increase. Eventually, when loading of the retracting plunger is reduced sufficiently, the seal between the surfaces 37, 38 is broken until, part way through the return stroke, filling of the volume 44 commences at the point in the stroke when the tappet 30 is displaced relative to the rider surface, in a positive direction, by a sufficient amount for the edge 37a of the tappet surface 37 to extend beyond the edge 38a of the flattened surface 38 of the rider 20. The period for which the volume 44 is expanding and filling is identified by the shaded region 46 in Figure 4 (two shaded regions 46 are identified for subsequent pumping cycles). During the initial stage of the return stroke, lubricating fluid is drawn into the volume 44 through the clearance gap between the edges 37a, 38a of the surfaces 37, 38. Part way through the return stroke the direction of motion of the tappet 30 reverses and, subsequently, filling of the volume 44 stops at the point in the cycle, just prior to BDC, when the edge 37a of the tappet surface 37 is again re-aligned with the edge 38a of the flattened rider surface 38 to close the clearance gap.

[0043] As described previously, during the following pumping stroke the tappet and the rider surfaces 37, 38 remain aligned, and transient fluid pressure within the volume supports the return loading of the tappet for a prolonged period due to the relatively large volume 44 of fluid between the surfaces 37, 38 at the tappet edge 37a being dispelled at a very low rate.

[0044] Figure 6 shows an alternative embodiment to that shown in Figures 2 and 5, in which the surface 137 of the tappet base 32 is not made concave but instead is provided with a recess, of generally U-shaped cross section, to define an annular outer wall 48. A lower annular surface 137a of the outer wall 48 is substantially flat and defines, together with the surface 38 of the cam rider 20, a restricted flow means for permitting fluid within the volume 44 to be dispelled at a relatively low rate as the tappet 30 performs the pumping stroke. It is one advantage of this embodiment that the contact area between the two surfaces 137a, 38 is increased during the final stages of the pumping stroke, and this has the effect of reducing surface contact stress.

[0045] Operation of this embodiment is similar to that described previously with reference to Figures 2 to 5, with the exception that the restricted flow means is defined between an annular surface 137a of the outer wall 48, rather than being defined by a surface edge such as 37a in Figures 2 to 5. As before, during the initial stages of the pumping stroke the volume 44 is gradually reduced as the load on the tappet 30 increases and the base 32 of the tappet 30 is depressed slightly to dispel fluid from the volume 44. During the final stage of the pumping stroke, just prior to TDC, the compliance of the tappet base 32 causes its lower recessed surface 137 to substantially flatten, with surface contact between the annular surface 137a of the tappet outer wall 48 and the rider surface 38 eventually providing a seal.

[0046] It is a further feature of the embodiment of Figure 6 that the tappet base 32 cannot distort as much as for the first embodiment due to the shaping of the recessed surface 137, so that the volume 44 between the surfaces 137, 38 does not collapse totally at the third stage of the pumping stroke.

[0047] In a further alternative embodiment, as shown in Figure 7, the surface 37 of the tappet base 32 and the surface 138 of the cam rider 20 are both shaped to be concave so as to further increase the volume 44 available for lubricating fluid. In this case it is important that both surfaces 37, 138 are shaped with a high degree of accuracy so as to ensure a sufficiently restricted flow area for fluid is maintained at all times through the pumping stroke in the region of their surface contact.

[0048] Once again, it should be noted that the extent to which the surface 137 of the tappet 30 is shown to be recessed in Figure 6, and the extent to which the surfaces 37, 138 of the tappet 30 and the rider 20 are shown to be concave in Figure 7, is greatly exaggerated.

[0049] Figure 8 shows a further alternative embodiment in which the tappet 30 is shaped in a similar manner to that shown in Figures 2 to 5, with the tappet base 32 being provided with a substantially recessed lower surface 237, but with its edge surface 237a being radiussed or 'rolled'. Radiussing of the edge surface 237a provides a first advantage that, during the return stroke of the plunger and tappet when the volume 44 is being filled with lubricating fluid through the clearance gap between the edges 237a, 38a, the radiussed outermost edge encourages fluid to be drawn between the surfaces 237a, 38 into the volume 44. A second advantage is obtained in that the contact area between the two surfaces 237a, 38 is increased during the final stages of the pumping stroke, thereby reducing surface contact stress.

[0050] In other variations the tappet and rider arrangements having the general constructions shown in Figures 6 and 8 may also be configured such that the surface edge of the tappet, which co-operates with the surface of the rider 20 to define the restricted flow means, is radiussed or rolled.

[0051] In any of the aforementioned embodiments, it may be further desirable to provide the recessed surface 37, 137, 237 of the tappet 30 with a plurality of small indentations or pockets to further enhance the available volume 44 for lubricating fluid. This may be achieved, for example, by forming laser pockets over the recessed tappet surface 37, 137, 237, or by rough grinding the recessed surface followed by super finishing.

[0052] In a three-plunger radial pump it will be appreciated that each of the three flattened surfaces of the rider 20, and the respective co-operable surfaces of the three tappets, may be shaped in the same manner as described for any of the aforementioned embodiments, or in an otherwise co-operably shaped manner to provide the functional benefit of the drive arrangement set out in the accompanying claims.

[0053] It will be appreciated that the drive arrangement of the present invention may or may not be manufactured to include the cam 18 and/or the plunger 24. It will also be appreciated that drive arrangement of the present invention may be employed in other types of pump assembly, not necessarily radial pump assemblies and not necessarily pump assemblies of the type having three plungers.

Claims

1. A drive arrangement for a pumping plunger (24) of a pump assembly, the drive arrangement comprising;
a drive member (30) that is firstly co-operable with the pumping plunger (24) and secondly co-operable with a cam rider (20) so as to impart axial drive to the plunger (24) to perform a plunger pumping stroke whilst permitting lateral sliding movement of the rider (20) relative to the drive member (30),
wherein the drive member (30) and the cam rider (20) are co-operably shaped to define (i) an increased volume (44) for lubricating fluid which is variable throughout the pumping cycle and (ii) restricted flow means through which fluid within said volume (44) is dispelled at a relatively low rate as the plunger (24) is driven throughout the pumping stroke so as to prolong transient fluid pressure within the volume (44) through that period of the pumping stroke for which return loading of the drive member (30) is a maximum.

2. The drive arrangement as claimed in claim 1, wherein at least one of the drive member (30) and the rider (20) is shaped to define a recessed surface (37, 38; 137, 38; 37, 138; 237, 38) which defines, together with a surface of the other of the drive member (30) and the rider (20), said variable fluid volume (44).

3. The drive arrangement as claimed in claim 2, wherein the recessed surface (37) of the drive member (30) is substantially concave.

4. The drive arrangement as claimed in claim 2 or claim 3, wherein the cam rider (20) includes a substantially flattened surface (38) which defines, together with the concave surface (37) of the drive member (30), the variable fluid volume (44).

5. The drive arrangement as claimed in claim 2 or claim 3, wherein the cam rider (20) includes a substantially concave surface (138) which defines, together with the surface (37) of the drive member (30), the variable fluid volume (44).

6. The drive arrangement as claimed in any one of claims 3 to 5, wherein the restricted flow means is defined by a surface edge (37a) of the recessed surface (37) of the drive member (30) and the surface (38) of the rider (20).

7. The drive arrangement as claimed in claim 2, wherein the drive member (30) is provided with a substantially U-shaped recess to define the recessed surface (137).

8. The drive arrangement as claimed in claim 7, wherein the drive member (30) is shaped to define a drive member side wall (48) of annular form defining an annular surface (137a) that is co-operable with the surface of the rider (20) to define the restricted flow means.

9. The drive arrangement as claimed in any one of claims 6 to 8, wherein the restricted flow means is defined by a radiussed surface (237a) of the drive member (30) and the surface (38) of the rider (20).

10. The drive arrangement as claimed in any one of claims 1 to 9, wherein the drive member is a tappet (30).

11. A drive arrangement for a pumping plunger (24) of a pump assembly, the drive arrangement comprising;
a drive member (30) that, in use, is firstly co-operable with the pumping plunger (24) and secondly co-operable with a cam rider (20) so as to impart drive to the plunger (24) to perform a plunger pumping stroke,
whereby, in use, the rider (20) moves laterally relative to the drive member (30), and wherein respective surfaces (37, 38; 137, 38; 37, 138; 237, 38) of the drive member (30) and the cam rider (20) are co-operably shaped to define a variable volume (44) for lubricating fluid throughout the pumping cycle, and to provide a transient pressure condition between said surfaces during a stage of the pumping stroke for which relative velocity between lateral movement of the drive member (30) and the rider (20) is substantially zero.

Drawing