EP2299114A1

EP2299114A1 - Pump assembly

Info

Publication number: EP2299114A1
Application number: EP09169972A
Authority: EP
Inventors: Aissa Djema; Paul Garland
Original assignee: Delphi Technologies Holding SARL
Current assignee: Delphi Technologies Operations Luxembourg SARL
Priority date: 2009-09-10
Filing date: 2009-09-10
Publication date: 2011-03-23
Anticipated expiration: 2029-09-10
Also published as: WO2011029649A1; EP2299114B1; ATE556221T1

Abstract

A pump assembly for an internal combustion engine comprising a pump housing (40), at least one pumping arrangement having a pumping plunger (56, 58) for pressurising fluid within a pump chamber; a drive shaft (46) carrying a cam (48) and a cam rider (50) which cooperates with the pumping arrangement to drive plunger movement along a plunger axis; and a plate (74; 174; 274; 374) coupled, on one side (74b), to the cam rider (50) and, on its other side (74a), to the housing (40) by coupling means (84, 86, 80, 82; 84, 180; 280, 286; 380, 480).The coupling means is arranged to constrain movement of the plate (74; 174; 274; 374) relative to the housing (40) in a first linear direction and to constrain movement of the cam rider (50) relative to the plate in a second linear direction, and to prevent angular movement of the cam rider (50) about its axis. Wear of the plunger, or of any intermediate component between the cam rider and the plunger, can be reduced as the cam rider is unable to tilt about its axis.

Description

TECHNICAL FIELD

The invention relates to a pump assembly suitable for use in an internal combustion engine. In particular, but not exclusively, the invention relates to a pump assembly for a common rail compression-ignition (diesel) internal combustion engine.

BACKGROUND TO THE INVENTION

Referring to Figure 1, a known common rail pump assembly for use in a common rail diesel engine includes a main pump housing 10 provided with a pair of opposed bores 12, 14 within which an associated tappet 16, 18 reciprocates, in use, under the influence of a drive arrangement. Each tappet has an associated plunger (not shown) which is driven by the reciprocal motion of the respective tappet 16, 18 to cause pressurisation of fuel within an associated pump chamber (not shown). Each pump chamber is defined within an associated pump head 20, 22 which is secured to the main pump housing 10 by means of screws (not shown).
The pump chambers are connected to a common fuel volume, referred to as the common rail, via an associated outlet valve. Fuel is pressurised within the pump chamber as its tappet and plunger reciprocate together. Once pressurised fuel within the pump chamber reaches a predetermined level, it is delivered through the outlet valve to the common rail.
The drive arrangement for the pump assembly includes a cam 24 carried on an engine-driven shaft, the axis of which is identified at 26. The cam 24 carries a cam rider 28 which extends co-axially with the cam and is provided with two flats 30, 32, one for each of the tappets 16, 18. Each tappet 16, 18 co-operates with its associated flat 30, 32 on the cam rider 28 and couples to the plunger so that, as the tappet 16, 18 is driven upon rotation of the cam 24, drive is imparted to the plunger. As the cam 24 is rotated by the drive shaft, the cam rider 28 is caused to ride over the cam surface. Each of the flats 30, 32 on the surface of the cam rider 28 co-operates with the face of the associated tappet 16, 18 with the result that the tappet is driven axially within its bore, radially outward from the cam shaft, whilst a degree of relative sliding movement between the rider flat 30, 32 and the tappet face occurs in a lateral direction (as the cam rider is able to slide relative to the tappet). Tappet movement is guided by the bore 12, 14 within which it reciprocates and each tappet is therefore confined to move axially within its bore.
Upon axial movement of the tappet 16, 18, each plunger is driven to perform a pumping stroke in which fuel within the associated pump chamber is pressurised to a high level for delivery to the common rail, after which the plunger performs a return stroke, to complete the pumping cycle, under the force of an associated plunger return spring 34, 36.
Other pump configurations are known in which three plungers are arranged around the drive shaft, rather than two, with the cam rider having three flats, one for each tappet. Single-plunger pump assemblies are also known.
Ideally, in any of the aforementioned pump assemblies, the cam rider 28 is prevented from turning on its own axis by forces applied through the plungers as a result of fuel pressure within the pump chamber acting on the end of the associated plunger and the force due to the springs. However, it has been found under certain conditions that these forces are inadequate to retain the cam rider 28 to translate along an exact circular path and it is able to turn angularly, to a degree, about its own axis. If the cam rider 28 is able to turn on its own axis then a number of problems can occur, depending on the severity of angular movement of the cam rider. If angular movement between the cam rider 28 and the tappet 16, 18 is only small, then contact between the flat 30, 32 on the rider and the tappet face may be locally concentrated at the periphery of the tappet face, and this may lead to accelerated wear of the tappet. If angular rotation of the cam rider 28 is larger, then the end of the flat on the cam rider may engage with the tappet face and may cause further damage. Finally, as illustrated in Figure 2, if angular movement between the cam rider 28 and the tappet 16, 18 is very large, catastrophic failure of the pump assembly may occur as the plunger has insufficient clearance at the top of its pumping stroke to accommodate the additional lift. In this case the force applied to the pump head 20, 22 by the plunger may be sufficient to break the fixing screws for the pump head, and the high stresses induced may cause the tappet and/or plunger to fracture.
By way of background to the invention, US 6446604 describes a pump assembly in which the problem of angular tilt of the cam rider is addressed by means of a guide device in the form of a pin which projects into an annular indentation to constrain the cam rider to move circumferentially within the indentation and to prevent angular tilt relative to the cam rider axis. However, a potential problem with this arrangement is that the pin may become jammed within the indentation, particularly when the cam rider is urged to tilt by only a small amount.
It is an object of the present invention to provide a pump assembly in which the aforementioned problems are alleviated or overcome.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a pump assembly for an internal combustion engine comprising a pump housing, at least one pumping arrangement having a plunger which is driven along a plunger axis to pressurise fluid within a pump chamber; a drive shaft carrying a cam and a cam rider which cooperates with the pumping arrangement; and a plate coupled, on one side, to the cam rider and, on its other side, to the housing by coupling means arranged to constrain movement of the plate relative to the housing in a first linear direction and to constrain movement of the cam rider relative to the plate in a second linear direction, and to prevent angular movement of the cam rider about its axis.
The benefit of the invention is that the cam rider is unable to tilt about its axis as it is constrained to move along a pair of linear paths and therefore translates along an exact circular path. The effects of wear of the cam rider as it engages with the plunger (or an intermediate component, such as a tappet, between the cam rider and the plunger) are therefore minimised or avoided altogether. In addition, the problem of the guide device jamming, which is associated with the prior art in US 6446604 , is avoided.
The coupling plate of the invention has similarities with an Oldham-style coupling that is traditionally used in rotary drive applications to tolerate misalignments in drive trains and to transmit drive from one shaft to another. In the invention, however, the concept is modified by using the Oldham-style coupling plate to "lock" the angular movement between non-rotating elements (the housing and the cam rider), whilst allowing the cam rider to follow a circular path of translation (i.e. to move back and forth in a linear direction relative to the plate).
In one embodiment, the plate is of annular form and therefore the drive shaft can extend through the plate. For example, the annular plate may have a central opening for receiving the drive shaft. In another embodiment the plate need not be annular, for example if the drive shaft is supported by a bearing and does not need to extend through the plate.
Preferably, the coupling means may include at least one engaging formation on one of the plate and the housing which cooperates in a sliding manner with at least one receiving formation on the other of the plate and the housing to constrain movement of the plate relative to the housing in the first linear direction. For example, the coupling means may comprise a pair of engaging formations on one of the plate and the housing which cooperates in a sliding manner with a pair of receiving formations on the other of the plate and the housing.
Preferably, the coupling means further includes at least one engaging on one of the plate and the cam rider which cooperates in a sliding manner with at least one receiving formation on the other of the plate and the cam rider to constrain movement of the cam rider relative to the plate in the second linear direction. For example, the coupling means may comprise a pair of engaging formations on one of the plate and the cam rider which cooperates in a sliding manner with a pair of receiving formations on the other of the plate and the cam rider.
In one embodiment, the plate may be provided with at least one through-slot connecting the opposed sides of the plate, thereby to provide a passage for fluid through the plate. This has the benefit of reducing the weight of the plate, and also allows fuel pressure on either side of the plate to equalise.
In one embodiment, the first linear direction is axially aligned with the axis of plunger movement.
In another embodiment, the first linear direction is at an oblique angle relative to the axis of plunger movement.
In one embodiment, the first and second linear directions are substantially perpendicular to one another. This provides the advantage that displacement of the plate is minimised and so the size of the housing can be kept as small as possible.
The cam rider may cooperate with the plunger directly or, alternatively, the cam rider may drive the plunger via an intermediate component such as a tappet.
In one particular embodiment, the pump assembly may further comprise a second coupling plate, wherein one coupling plate is coupled to the cam rider on one side of the cam rider and the second coupling plate is coupled to the other side of the cam rider.

BRIEF DESCRIPTION OF THE DRAWINGS

The background to the present invention has already been described with reference to Figures 1 and 2, in which:

Figure 1 is a cross-section of a part of a known pump assembly including two opposed tappets and a cam rider carried by an engine-driven cam which serves to drive movement of the tappets, in use; and
Figure 2 is a cross-section of the pump assembly parts in Figure 1, to illustrate the undesirable effect of angular movement of the cam rider about its axis.

The present invention will now be described, by way of example only, with reference to the following figures in which:

Figure 3 is a section view of a two-plunger pump assembly in accordance with a first embodiment of the present invention, including a coupling plate between the pump housing and a cam rider of the assembly;
Figure 4 is an exploded view of the two-plunger pump assembly in Figure 3;
Figure 5 is a perspective view of the cam rider and the coupling plate in Figure 3, in isolation;
Figures 6(a) to 6(c) are perspective views of the plate in Figure 5, from various orientations, to illustrate perpendicular formations on the front and rear sides of the plate;
Figure 7 is a perspective view of an alternative coupling plate for use in the invention, in which the formations on the front and rear sides of the plate are not perpendicular;
Figure 8 is a section view of a two-plunger pump assembly of a further alternative embodiment of the invention; and
Figures 9(a) to 9(c) are views, from three different perspectives, of a further alternative coupling plate for use in the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figures 3 and 4 show a first embodiment of the pump assembly of the present invention for use in delivering pressurised fuel to a common rail of a compression ignition internal combustion engine.
The pump assembly includes a main pump housing 40 provided with a cavity 42 for receiving low pressure fuel and an opening 44 through which an engine-drive shaft 46 extends into the cavity 42. The drive shaft 46 has a drive shaft axis 47 carries a cam 48 (only visible in Figure 4) which, in turn, carries a cam rider 50. The cam rider 50 is a generally tubular element having two opposed flattened regions (or flats) 52, 54 on its outer surface.
Each of the flats 52, 54 on the cam rider 50 is cooperable with the base of a respective one of first and second footed-plungers (only a first one of the plungers 56 is clearly visible in Figure 3, whereas only the foot 58 of the second plunger is visible). It should be noted that the plungers in Figures 3 and 4 differ from those shown in Figures 1 and 2 in that they are provided with a plunger foot, which cooperates with the cam rider 50, whereas in the prior art in Figures 1 and 2 an intermediate tappet component 16, 18 is provided between the cam rider 50 and the plunger. The present invention is equally applicable to either type of plunger arrangement (i.e. with or without an intermediate component between the cam rider 50 and the plunger).
Opposed bores 60, 62 are provided through the pump housing 40, with each of the plungers being received within a respective one of the bores 60, 62 and extending into an associated pump head 64, 66 which is secured to the main pump housing 40. Within each pump head 64, 66 a pump chamber is defined (not visible in the figures) which is filled, in use, with fuel at relatively low pressure.
As the shaft rotates, in use, the plungers 56, 58 are caused to reciprocate within their respective bores 60, 62, causing fuel within the pump chambers to be pressurised during a plunger pumping stroke in which the plunger is driven between bottom-dead-centre and top-dead-centre. A plunger return spring 68, 70 is provided for each plunger 56, 58, respectively, in a known manner, to effect a plunger return stroke between top-dead-centre and bottom-dead-centre.
Considering the first plunger 56, as the drive shaft 46 rotates the cam rider 50 is caused to ride over the surface of the cam 48 and an axial drive force is imparted to the plunger 56 causing it to perform its pumping stroke, during which it is driven radially outward from the shaft (i.e. vertically upwards in Figure 3) to reduce the volume of the associated pump chamber. During the plunger return stroke, effected by means of the return spring 68, the plunger 56 is urged in a radially inward direction (i.e. vertically downwards in Figure 3) to increase the volume of the associated pump chamber. During the plunger pumping stroke, pressurised fuel is delivered from the pump chamber to the downstream common rail (not shown) via an outlet valve (also not shown). During the plunger return stroke, the pump chamber is filled with fuel at relatively low pressure, via an inlet valve (not shown), ready for the next plunger pumping stroke on the next rotation of the drive shaft 46.
As the plunger 56 is driven in a radially outward direction, a degree of lateral or sliding movement of the foot of the plunger 56 across the flat 52 on the rider 50 occurs, in a back and forth manner. The plunger 56 slides across the flat 52 on the rider 50 in a similar manner during the return stroke.
The other plunger 58 is driven in a similar manner through cooperation with the other flat 54 on the rider 50, with motion of the plungers being 180° out-of-phase with one another.
Referring also to Figures 5 and 6(a) to (c), the cam rider 50 can be considered to have a front side 50a, facing towards the driven end of the shaft (i.e. the front of the pump assembly), and an opposed rear side 50b which abuts a rear thrust bearing 72 on the drive shaft 46. A movable coupling plate 74 is mounted on an internal surface of the pump housing 40, inside the cavity 42. The plate 74 is of annular form, including a central opening 76 through which the drive shaft 46 is received. A front face 74a of the coupling plate 74 is coupled to the housing 40 so that the plate 74 is constrained to move relative to the housing only in a vertical direction (up-down), but so that there is no component of movement of the plate in a horizontal direction. The rear face 74b of the coupling plate is coupled to the front face 50a of the cam rider so that the cam rider is constrained to move only laterally (side to side) relative to the coupling plate 74 (i.e. in a direction perpendicular to the direction of motion between the plate 74 and the housing 40), but so that there is no component of movement of the cam rider 50 in a vertical direction relative to the plate.
The coupling plate 74, the housing 40 and the cam rider 50 are provided with respective pairs of engaging/receiving formations which are cooperable with one another to guide movement of the plate 74, and of the cam rider 50, in the aforementioned manner. The rear face 74b of the coupling plate 74 is provided with first and second horizontal projections 80 in alignment with one another on either side of the central opening 76 in the plate 74. Each of the first and second horizontal projections 80 is cooperable, in a sliding manner, with a respective one of first and second horizontal slots 82 provided on the front face 50a of the cam rider 50. The coupling between the horizontal slots 82 on the front face 50a of the cam rider 50 and the horizontal projections 80 on the rear face 74b of the plate 74 constrains movement of the cam rider 50 relative to the plate 74 in a first, linear direction.
The front face 74a of the coupling plate 74 is provided with first and second vertical projections 84 in alignment with one another on either side of the central opening 76 in the plate 74. These first and second vertical projections 84 are cooperable with a respective one of first and second vertical slots 86 provided in the internal surface of the housing 40. By means of the coupling between the vertical slots 86 on the housing 40 and the projections 84 on the front face 74a of the plate 74, the plate is constrained to follow a linear path, in a second direction, relative to the housing 40. The second direction of motion of the plate 74 is perpendicular to the first direction of motion of the cam rider 50 described above by virtue of the pairs of projections 80, 84 on opposed sides of the plate being perpendicular to one another.
The cam rider 50 is therefore constrained to follow a pair of linear paths only (i.e. horizontally and vertically), and to follow a circular path of translation, but is unable to move angularly, or "tilt", about its axis: the clearances between the pairs of projections 80, 84 in their slots 82, 86 ensure that substantially no tilting of the cam rider 50 can occur. In other words, the cam rider 50 moves in such a way that the flats 52, 54 remain perpendicular to the plunger bores 60, 62 for all angular positions of the drive shaft 46. The invention therefore avoids the problems encountered in prior art pump assemblies, where tilting of the cam rider about its axis can lead to plunger or tappet wear or, at worst, complete pump failure due to insufficient clearance at the top of the plunger pumping stroke to accommodate the additional lift caused by cam rider tilt.
In the embodiment of Figures 3 to 6, the cam rider 50 is constrained to move, relative to the plate 74, in a direction that is perpendicular to the direction in which the coupling plate 74 is constrained to move relative to the housing 40 (i.e. the plate 74 translates vertically, and the cam rider 50 translates horizontally relative to the plate 74). In an alternative embodiment, as shown in Figure 7, the plate 174 may be provided with front-and rear-facing projections 184, 180 that are not perpendicular, so that motion of the cam rider 50 relative to the plate 174 is not perpendicular to motion of the plate 174 relative to the housing 40. In this example, the plate 174 is provided with vertical projections 184 on its front face 174a that align with vertical slots 86 in the internal surface of the housing 40, as in Figure 5, but the rear face 74b of the plate 174 is provided with projections 180 that are arranged at an oblique angle to the front-face vertical projections 184. The projections 180 on the rear face 174b cooperate with corresponding slots on the cam rider 50, which takes the same form as that shown in Figure 5.
In this embodiment the coupling plate 174 is mounted to the housing such that the plate 174 moves at an oblique angle to the vertical direction, in a linear direction, whilst the cam rider is still constrained to move horizontally, relative to the plate 174, by virtue of the coupling between the rear-face projections 180 on the plate 174 and the front-face slots on the cam rider 50. Orienting the plate 174 so that it moves in a direction that is oblique to the horizontal movement of the cam rider means that the displacement of the plate 174 is greater, relative to an embodiment in which movement of the plate 174 is perpendicular to movement of the cam rider. In this case the pump assembly would therefore necessarily be larger. In this embodiment the slots on the cam rider can be arranged at any angle to the slots on the housing, and at any angle relative to the plunger bores, providing there is sufficient stroke in two oblique directions to accommodate the full range of motion of the cam rider.
A further alternative embodiment of the invention is shown in Figure 8, in which the projections on the front- and rear-faces of the coupling plate are again perpendicular to one another, as in Figures 3 to 6, but in which the plate 274 is oriented relative to the pump housing 40 so that the projections that it carries are at an oblique angle to the axes of plunger movement (i.e. vertically in the orientation shown in Figure 8). The plate 274 is provided with projections (not shown) on its rear face which cooperate with slots 286 on the housing 40 that are arranged at an oblique angle to the plunger axes. The plate is also provided with projections (only one of which, 280, is visible) on its front face that are cooperable with corresponding receiving slots (not visible) on the rear face of the cam rider 50. The cam rider 50 is therefore constrained to move parallel to the projections 280 on the plate 274, whilst the plate 274 is able to move in a linear direction at an oblique angle to the plunger axes. As before, the cam rider 50 is therefore constrained to translate along an exact circular path and does not move angularly about it axis.
In a still further alternative embodiment (not shown), the coupling plate may be provided with multiple pairs of projections on each face to reduce the effects of wear on the projections, in use. For example, referring to Figures 9(a) to (c), the coupling plate 374 may be provided with first and second pairs of horizontal projections 380, 480 on its rear face 374b to cooperate with corresponding pairs of receiving formations on the front face of the cam rider (not shown in Figure 9). Each projection in a pair 380, 480 is arranged in parallel with the other projection in the pair so that motion of the cam rider 50 relative to the plate 374 is constrained to move in a linear direction only.
In other embodiments, it is envisaged that the coupling plate may be provided with the slots, whereas the cam rider and the housing may be provided with the projections which cooperate with respective ones of the slots in the plate. Alternatively, the plate may be provided with slots on one side and projections on the other, to match appropriately shaped engaging/receiving formations on the cooperable parts. However, it is envisaged that a plate provided with projections is the most practical solution as the plate is a relatively thin component and removal of additional material from the plate to create slots may reduce its strength undesirably.
The invention is equally applicable to a pump assembly having a greater or lesser number of plungers than a twin-plunger pump, with the cam rider being shaped with a corresponding number of flats to cooperate with a respective one of the plungers.
Typically, the pump housing and plate components may be formed from steel. However, if it is preferable to form the pump housing and plate components from aluminium, which is relatively light, the parts may have insufficient strength or hardness to withstand the forces acting on the projections and slots. In this case the projections and/or slots may be provided with a hardened insert or coating, such as diamond-like-carbon (DLC). It may also be desirable to apply a low friction coating to the projections and/or slots to improve durability at high pumping loads.
In any of the aforementioned embodiments, a further improvement may be achieved by providing one or more additional slots or grooves through the plate 74, from the front face 74a to the rear face 74b, to allow fuel pressure on either side of the plate to equalise and to reduce wear on the sliding surfaces between the slots/projections by means of the improved circulation of lubricant. Slots or grooves may also be provided through the plate for the purpose of minimising the weight of the plate.
In another embodiment (not shown), a second coupling plate may be coupled to the rear face of the cam rider 50 having the same configuration as the first coupling plate coupled to the front face of the cam rider 50 to further enhance the guiding movement of the cam rider. It is also possible to "stack" multiple coupling plates on one side of the cam rider.
In any of the aforementioned embodiments it will be appreciated that the central opening 76 in the plate is not necessary, and so the plate need not be of annular form (e.g. if the drive shaft is supported by a bearing and does not need to pass through the plate).

Claims

A pump assembly for an internal combustion engine comprising:
a pump housing (40),

at least one pumping arrangement having a pumping plunger (56, 58) for pressurising fuel within a pump chamber;

a drive shaft (46) carrying a cam (48) and a cam rider (50) which cooperates with the pumping arrangement to drive plunger movement along a plunger axis; and

a plate (74; 174; 274; 374) coupled, on one side (74b), to the cam rider (50) and, on its other side (74a), to the housing (40) by coupling means (84, 86, 80, 82; 184, 180; 280, 286; 380, 480) arranged to constrain movement of the plate (74; 174; 274; 374) relative to the housing (40) in a first linear direction and to constrain movement of the cam rider (50) relative to the plate in a second linear direction, and thereby to prevent angular movement of the cam rider (50) about its axis.
A pump assembly as claimed in claim 1, wherein the plate (74; 174; 274; 374) is of annular form.
A pump assembly as claimed in claim 2, wherein the annular plate (74; 174; 274; 374) has a central opening for receiving the drive shaft.
A pump assembly as claimed in any one of claims 1 to 3, wherein the first and second linear directions are substantially perpendicular to one another.
A pump assembly as claimed in any one of claims 1 to 4, wherein the coupling means includes at least one engaging formation (80, 84; 180, 184; 380, 480) on one of the plate (74, 174, 274, 374) and the housing (40) which cooperates in a sliding manner with at least one receiving formation (86; 286) on the other of the plate and the housing to constrain movement of the plate relative to the housing in the first linear direction.
A pump assembly as claimed in claim 5, wherein the coupling means comprises a pair of engaging formations (80, 84; 180, 184; 380, 480) on one of the plate (74, 174, 274, 374) and the housing (40) which cooperates in a sliding manner with a pair of receiving formations (86; 286) on the other of the plate and the housing.
A pump assembly as claim in any one of claims 1 to 6, wherein the coupling means includes at least one engaging formation (80; 180; 280; 380, 480) on one of the plate and the cam rider which cooperates in a sliding manner with at least one receiving formation (82) on the other of the plate and the cam rider to constrain movement of the cam rider relative to the plate in the second linear direction.
A pump assembly as claimed in claim 7, wherein the coupling means comprises a pair of engaging formations (80; 180; 280; 380, 480) on one of the plate and the cam rider which cooperates in a sliding manner with a pair of receiving formations (82) on the other of the plate and the cam rider.
A pump assembly as claimed in any one of claims 1 to 8, wherein the plate (74, 174, 274, 374) is provided with at least one through-slot connecting the opposed sides of the plate, thereby to provide a passage for fluid through the plate.
A pump assembly as claimed in any one of claims 1 to 9, wherein the first linear direction is axially aligned with the axis of plunger movement.
A pump assembly as claimed in any one of claims 1 to 9, wherein the first linear direction is at an oblique angle relative to the axis of plunger movement.
A pump assembly as claimed in any one of claims 1 to 11, wherein the cam rider (50) cooperates with the plunger (56, 58) directly.
A pump assembly as claimed in any one of claims 1 to 11, wherein the pumping arrangement further comprises an intermediate member between the cam rider and the plunger, such that the cam rider cooperates with intermediate member which serves to drive the plunger.
A pump assembly as claimed in any one of claims 1 to 13, further comprising a second coupling plate, wherein one coupling plate is coupled to the cam rider on one side of the cam rider and the second coupling plate is coupled to the other side of the cam rider.