GB2630618A

GB2630618A - Fuel pump drive arrangement

Info

Publication number: GB2630618A
Application number: GB2308159.9A
Authority: GB
Inventors: Richard Jones David
Original assignee: Phinia Delphi Luxembourg SARL
Current assignee: Phinia Delphi Luxembourg SARL
Priority date: 2023-05-31
Filing date: 2023-05-31
Publication date: 2024-12-04
Also published as: GB202308159D0; CN121219492A; WO2024246331A1

Abstract

A drive arrangement (12, Fig. 1) for a fuel pump 10 for a vehicle, comprising: a drive cam 26 configured to rotate about a rotational axis 28, in use; and a cam rider member 20 configured for reciprocating movement on the drive cam 26 along the rotational axis 28 as the drive cam 26 rotates; An eccentricity of the drive cam 26 relative to the rotational axis 28 varies along the rotational axis 28; the drive cam axis 36 may be inclined relative to the rotational axis 28; the cam rider member 20 may comprise an opening 38 in which the drive cam 26 is received, the opening 38 being shaped to conform to an outer surface (34, Fig. 4) of the drive cam 26.

Description

Fuel pump drive arrangement

FIELD OF THE INVENTION

This invention relates to a fuel pump. In particular, but not exclusively, the invention relates to a fuel pump of a compression-ignition internal combustion engine.

BACKGROUND

Combustion-based automotive vehicles typically use a high-pressure fuel pump to pressurise fuel flowing to an engine of the vehicle through a fuel line, often via an intermediate accumulator such as a fuel rail. A conventional pump has one or more cam-driven plungers that reciprocate through pumping cycles comprising pumping and filling strokes, to pressurise fuel. In turn, the driving cams are driven by the vehicle engine and so the pumping speed is directly related to the engine speed.

A drive cam is typically mounted to a driveshaft of the pump, which may be operably coupled to a crankshaft of the engine, for example, such that rotation of the crankshaft as the engine operates drives corresponding rotation of the pump driveshaft. In some implementations the pump driveshaft rotates at the same speed as the crankshaft, although in other implementations a speed ratio may be provided between the crankshaft and the pump driveshaft, for example using a gearbox or belt drive arrangement.

At an interface between the cam and the pumping plunger, a drive force may be transferred from the cam to the plunger using a slipper-tappet arrangement or a roller-shoe arrangement, for example.

Slipper-tappet arrangements tend to provide relatively large contact areas between the drivetrain components, namely the cam, a rider and a tappet, which promotes high durability. However, such arrangements are typically restricted to a single pumping event per revolution of the driveshaft for each pumping head. Accordingly, if a higher pump output is desired, a speed ratio or gearing ratio may be required between the engine and the pump to increase the pumping speed. Alternatively, the pump may be arranged with multiple pumping heads to increase the number of pumping events for each driveshaft revolution, but with the increased cost associated with each additional pumping head.

Alternatively, in pumps employing a roller-shoe arrangement, higher outputs may be achieved using a multi-lobed cam, so that each revolution of the driveshaft causes multiple pumping events for the same pumping head. However, roller-shoe arrangements tend to have relatively low durability due to the line contact between the respective curved surfaces of the cam and the roller, which can lead to Hertzian Stress concerns at higher pressures. This low durability may be exacerbated by adding lobes to the cam.

It is against this background that the invention has been devised.

STATEMENTS OF INVENTION

According to an aspect of the present invention, there is provided a drive arrangement for a fuel pump for a vehicle. The drive arrangement comprises a drive cam configured to rotate about a rotational axis, in use. An eccentricity of the drive cam relative to the rotational axis varies along the rotational axis. The drive arrangement further comprises a cam rider member configured for reciprocating movement on the drive cam along the rotational axis as the drive cam rotates.

By providing a drive cam with a variable eccentricity and a cam rider member that can move axially along the drive cam to exploit that variation in eccentricity, the drive arrangement can be arranged to effect multiple pumping events for each full revolution of the drive cam. This, in turn, enables the output of the pump in which the drive arrangement is used to be increased without adding pumping heads.

Thus, the pump output can be increased without greatly increasing the size of the pump and without having to provide, or increase, a speed ratio between the pump and a prime mover that drives operation of the pump, for example an engine of the vehicle in which the pump resides.

The drive arrangement may define, comprise or be embodied as a drivetrain.

An outer surface of the drive cam may be inclined relative to the rotational axis.

In some embodiments, the drive cam extends along a drive cam axis that is inclined relative to the rotational axis. The drive cam axis may intersect the rotational axis midway between axial ends of the drive cam. The cam rider member may move parallel to the drive cam axis while moving along the rotational axis.

The drive cam may have a parallelogram profile in a plane containing the rotational axis. In another plane containing the rotational axis, for example a plane orthogonal to a plane in which the profile is a parallelogram, the profile of the drive cam may include two sides that are parallel to the rotational axis. The drive cam may have end faces that extend in mutually parallel planes. The drive cam may have the general form of an inclined cylinder.

The cam rider member may comprise an opening in which the drive cam is received, the opening being shaped to conform to an outer surface of the drive cam. The cam rider member may have a cylindrical outer surface.

The drive arrangement may comprise a second rider member that engages the cam rider member, so that the cam rider member is disposed between the drive cam and the second rider member. The second rider member may have a fixed orientation in a plane orthogonal to the rotational axis. The second rider member may be in engagement, directly or indirectly, with a tappet associated with a plunger of the pump. The second rider member may substantially envelop or otherwise receive the cam rider member.

The drive arrangement optionally comprises a guide arrangement configured to guide movement of the cam rider member along the rotational axis. The guide arrangement may comprise a guide groove formed in one of the cam rider member and the second rider member, and a guide member that is received in the guide groove. The guide groove may follow an elliptical path, which path may extend around a surface of the cam rider member or second rider member.

The drive arrangement may comprise a driveshaft arranged to rotate about a driveshaft axis defining the rotational axis, the drive cam being located on the driveshaft. The drive cam may be mounted on the driveshaft, for example. It is also possible for the drive cam to be integral with the driveshaft.

The invention also extends to a fuel pump comprising the drive arrangement of the above aspect.

Another aspect of the invention provides a fuel pump for a vehicle, the fuel pump comprising: a drive cam configured to rotate about a rotational axis, in use; and a cam rider member configured for reciprocating movement on the drive cam along the rotational axis as the drive cam rotates. An eccentricity of the drive cam relative to the rotational axis varies along the rotational axis.

The pump of either of the above aspects may comprise a plunger arranged for reciprocating movement along a plunger axis within a body of the pump, the drive cam being arranged to drive movement of the plunger along the plunger axis. The pump may be configured so that a single revolution of the drive cam drives multiple pumping cycles of the plunger.

The invention also extends to a vehicle comprising the drive arrangement or the fuel pump of the above aspects.

Another aspect of the invention provides a method of operating a drive arrangement of a fuel pump for a vehicle. The drive arrangement comprises a drive cam having a rotational axis and an eccentricity relative to the rotational axis that varies along the rotational axis. The method comprises rotating the drive cam about the rotational axis to cause a cam rider member to move on the drive cam, along the rotational axis.

It will be appreciated that the various features of each aspect of the invention are equally applicable to, alone or in appropriate combination, the other aspects of the invention also.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the invention will now be described, by way of example only, with reference to the accompanying figures, in which like features are assigned like reference numbers, and in which: Figure 1 is a perspective view of a drivetrain of a fuel pump according to an embodiment of the invention; Figure 2 shows the drivetrain of Figure 1 in side view; Figure 3 shows the drivetrain of Figure 1 in axial cross-section; Figure 4 shows a driveshaft of the drivetrain of Figure 1 in isolation; Figure 5 shows a main rider member of the drivetrain of Figure 1 in isolation; Figures 6a-6c show the drivetrain of Figure 1 in perspective, front and axial cross-sectional views respectively, in a configuration corresponding to a first bottom-dead-centre position for an associated pumping head; Figures 7a-7c correspond to Figures 6a-6c respectively, but show the drivetrain in a first top-dead-centre position; Figures 8a-8c correspond to Figures 6a-6c respectively, but show the drivetrain in a second bottom-dead-centre position; Figures 9a-9c correspond to Figures 6a-6c respectively, but show the drivetrain in a second top-dead-centre position; Figure 10 shows a front view of the drivetrain of Figure 1 in a configuration corresponding to a 45° offset from a bottom-dead-centre position for an associated pumping head; and Figure 11 shows a front view of the drivetrain of Figure 1 in a configuration corresponding to a 45° offset from a top-dead-centre position for an associated pumping head.

In the following description, directional or relative references such as 'upper', 'lower', 'above' and 'below', relate to the orientation of the features as illustrated in the drawings, but such references are not to be considered limiting. The skilled reader will appreciate that drive arrangements and pumps of embodiments of the invention may be oriented differently to the manner depicted in the drawings in practice.

SPECIFIC DESCRIPTION

In general terms, embodiments of the invention provide drive arrangements for fuel pumps that are configured such that a single revolution of a drive cam of the drive arrangement causes multiple pumping events in an associated pumping head, whilst avoiding the use of a roller-shoe interface between the cam and a plunger of the pumping head. In this way, the output of the pump can be increased for a given driveshaft speed, whilst maintaining high durability. A 'drive arrangement' may mean a drivetrain, for example.

In some embodiments, an increased pump output is achieved by using a cam that is inclined relative to the driveshaft such that the eccentricity of the cam with respect to an axis of the driveshaft varies along that driveshaft axis. In this respect, the eccentricity of the cam with respect to the driveshaft axis at a given point along the driveshaft axis may be defined by the offset between the driveshaft axis and the centre of a cross-section of the drive cam taken in a plane orthogonal to the driveshaft axis.

A double rider arrangement involving a pair of rider members may be used to convert the rotary motion of the cam into linear back-and-forth movement of the associated pumping plunger. The rider arrangement may include a first, intermediate rider member having a complementary configuration to the cam, which is received on, and shuttles back and forth along, the cam and thus acts as a cam rider member. The rider arrangement may further include a second, main rider member, which receives or otherwise engages the intermediate rider member and transfers drive force to the plunger. Accordingly, unlike existing slipper-tappet interfaces, the rider arrangement introduces axial movement of a rider member with respect to the driveshaft. Although the axial package of the pump may increase slightly to accommodate this axial movement, the overall package of the pump reduces by removing the need for additional pumping heads.

Figures 1 to 3 show, in greatly simplified and schematic form, a portion of a fuel pump 10 according to an embodiment of the invention. Specifically, Figures 1 to 3 show a drive arrangement 12 of the pump 10, the drive arrangement hereafter being referred to as a drivetrain 12. The drivetrain 12 is configured to deliver a drive force to a plunger 13 of a pumping head of the pump 10 to cause reciprocating pumping movement of the plunger 13 along a plunger axis 15 through pumping and filling strokes to pressurise fuel, in operation. Specifically, the drivetrain 12 drives pumping strokes of the plunger 13, while a return spring 17 acts to bias the plunger 13 towards the drivetrain 12 and thus effects filling strokes.

The pump 10 has a pump body 14, or housing, that supports a driveshaft 16 for rotation. A representative portion of the pump body 14 is visible in Figures 1 to 3.

A rider arrangement is arranged around the driveshaft 16, the rider arrangement comprising a generally cuboid main rider 18 and a generally annular intermediate rider 20 accommodated within the main rider 18. The intermediate rider 20 and the main rider 18 are each solid members, which may be of steel or another suitable material for example.

A planar lower end face of a generally cylindrical tappet 22 rests on an upper exterior surface of the main rider 18. The main rider 18 supports the tappet 22 in a direction parallel to a central axis 23 of the tappet 22, such that a component of movement of the main rider 18 in a direction parallel to the tappet axis 23 drives corresponding linear movement of the tappet 22 along its axis 23. Conversely, relative sliding is permitted between the engaged faces of the main rider 18 and the tappet 22, which accommodates lateral movement of the main rider 18 relative to the tappet 22, in use, as shall become clear from the description that follows.

The tappet 22 is in turn coupled to the plunger 13 of the pump 10, so that movement of the tappet 22 effects corresponding movement of the plunger 13. The tappet 22 is therefore constrained to move only along the tappet axis 23, which is coaxial with the plunger axis 15.

The driveshaft 16 is shown more clearly in Figure 4, which reveals that the driveshaft 16 comprises a cylindrical core shaft 24 and an eccentric drive cam 26 mounted centrally on the core shaft 24. The core shaft 24 is longer than the drive cam 26, such that the core shaft 24 protrudes axially from each end of the drive cam 26. A central longitudinal axis of the core shaft 24 defines a driveshaft axis 28. The driveshaft axis 28 is perpendicular to the plunger axis 15.

In this embodiment, the core shaft 24 and the drive cam 26 are formed as separate components that are assembled to create the driveshaft 16, for example by press-fitting the drive cam 26 onto the core shaft 24. In this respect, as Figure 3 makes clear one end of the core shaft 24 is radially enlarged, defining a shoulder 30 that acts to locate the drive cam 26 on the core shaft 24 during assembly. Other assembly methods are possible, and it is also possible for the driveshaft to be fabricated as a single piece so that the drive cam 26 is integral with the core shaft 24.

The protruding ends of the core shaft 24 serve as journal members that are received in corresponding respective bearings of the pump 10 that support rotation of the driveshaft 16 about the driveshaft axis 28. Accordingly, the driveshaft axis 28 defines a rotational axis for the driveshaft 16 and the drive cam 26.

The drive cam 26 forms part of a drive arrangement or interface, namely the drivetrain 12, which converts the rotary motion of the driveshaft 16 into linear motion of the plunger 13. In this respect, in operation a drive force is transferred from the driveshaft 16 to the plunger 13 via the drive cam 26, the intermediate rider 20, the main rider 18 and the tappet 22, which therefore collectively form the drivetrain 12. The components of the drivetrain 12 are each solid members, which may be of steel or another suitable material for example.

The drive cam 26 has the general form of an inclined cylinder with circular, planar end faces 32 that are mutually parallel but radially offset from one another.

Accordingly, as Figure 3 shows, the drive cam 26 has a parallelogram profile in side view. Conversely, the longitudinal sides of the drive cam 26 appear parallel to the driveshaft axis 28 when viewed from above, in the orientation shown in Figures 1 to 3.

Figure 3 also shows that the drive cam 26 is arranged with its end faces 32 oriented orthogonally to the driveshaft axis 28, while a curved outer surface 34 of the drive cam 26 is inclined relative to the driveshaft axis 28. The inclined cylinder defining the drive cam 26 is elongate, in that it has an axial length exceeding its diameter.

A drive cam axis 36 extends centrally through the drive cam 26 and intersects the centre of each end face 32 of the drive cam 26. The drive cam axis 36 is inclined relative to the driveshaft axis 28. In this example, the inclination of the drive cam axis 36 relative to the driveshaft axis 28 is approximately 25°, but this angle may vary in other examples. As the cross-sectional view of Figure 3 reveals, the driveshaft axis 28 intersects the drive cam axis 36 at a midpoint of the drive cam 26, and therefore midway between the end faces 32 of the drive cam 26.

The drive cam 26 is configured with a uniform cross section along its length, that cross section being circular when taken in a plane orthogonal to the driveshaft axis 28 at any point along the drive cam axis 36.

The circular end faces 32 of the drive cam 26 are mutually offset radially with respect to the driveshaft axis 28, the respective centres of the end faces 32 being on opposed sides of the driveshaft axis 28, each end face 32 being spaced radially from the driveshaft axis 28 to the same extent, but in opposed radial directions.

Accordingly, the protruding portions of the core shaft 24 at each end of the drive cam 26 are at different positions relative to the respective adjacent end faces 32 of the drive cam 26. In this respect, at one end of the drive cam 26, shown to the left in Figure 4, the protruding portion of the core shaft 24 is positioned close to an upper region of a circular edge of the associated end face 32 of the drive cam 26, while the portion of the core shaft 24 protruding from the opposite end of the drive cam 26 is close to the lower region of the edge of the corresponding end face 32 of the drive cam 26.

The figures show a reference mark on the end face 32 of the drive cam 26, positioned at the bottom of the end face 32 visible in Figure 4, to indicate the angle of the drive cam 26. It should be appreciated that this reference mark is for illustrative purposes and does not necessarily represent a physical feature of the drive cam 26.

It follows from the above that the eccentricity of the drive cam 26, with respect to the driveshaft axis 28 and the core shaft 24, varies along the driveshaft axis 28. The opposed ends of the drive cam 26 have mutually opposite eccentricity, in that the centre of the end face 32 at one end of the drive cam 26 is directly above the driveshaft axis 28, whereas the centre of the end face 32 at the other end of the drive cam 26 is directly below the driveshaft axis 28. The eccentricity of the drive cam 26 transitions steadily from one end of the drive cam 26 to the other due to the inclined nature of the drive cam 26. It should be appreciated that the eccentricities shown in Figure 4 will effectively reverse if the driveshaft 16 turns through 180°.

Returning to Figure 3, the intermediate rider 20 is generally annular in form, having a cylindrical outer surface and a central opening 38. The central opening 38 is defined by an angled bore, such that the wall of the central opening 38 is shaped to conform to the shape of the exterior curved surface of the drive cam 26. The intermediate rider 20 is received onto the drive cam 26 in the manner of a sleeve or collar, with the central opening 38 of the intermediate rider 20 being a close sliding fit with the exterior of the drive cam 26. The intermediate rider 20 has an axial length corresponding to half of the axial length of the drive cam 26 with respect to the driveshaft axis 28.

In use, as the drive cam 26 turns the intermediate rider 20 slides back and forth along the driveshaft axis 28, from the position shown in Figure 3 in which a left planar end face of the intermediate rider 20 is aligned with an end face 32 of the drive cam 26 to the left of the image, to a position in which a right planar end face of the intermediate rider 20 aligns with an end face 32 of the drive cam 26 shown to the right. Accordingly, the intermediate rider 20 is always fully received on the drive cam 26, and shuttles between the ends of the drive cam 26 as the driveshaft 16 rotates, as described more fully below. The intermediate rider 20 may therefore be regarded as a cam rider member. In this example, the intermediate rider 20 moves parallel to the drive cam axis 36, and thus moves both radially and axially with respect to the driveshaft axis 28 while moving along the driveshaft axis 28, due to the inclination of the drive cam axis 36 relative to the driveshaft axis 28.

To assemble the drivetrain 12, in this embodiment the intermediate rider 20 is fitted onto the drive cam 26 before the core shaft 24 is inserted into the drive cam 26, since the core shaft 24 may otherwise occlude the intermediate rider 20 from being fitted due to the angle of its central opening 38 and that of the drive cam 26. In other embodiments it may be possible to assemble or fabricate the driveshaft first and then fit the intermediate rider 20 onto the drive cam 26, however.

The cylindrical exterior of the intermediate rider 20 includes a radially-extending bore 40 that accommodates a spring-loaded guide member 42, which is visible in the lower portion of the intermediate rider 20 in Figure 3. The guide member 42 cooperates with a guide groove 44 formed in an interior wall of the main rider 18 to form a guide arrangement that guides movement of the intermediate rider 20. The guide member 42 is biased into the guide groove 44 by a spring 46 that acts between the guide member 42 and a closed end of the bore 40.

Spring loading the guide member 42 aids assembly of the rider arrangement, in that the spring 46 enables the guide member 42 to be retracted into the bore 40 as the intermediate rider 20 is inserted into the main rider 18, and then urges the guide member 42 into the guide groove 44 once the two come into alignment.

In this embodiment, the guide member 42 takes the form of a ball bearing that is able to roll in the guide groove 44, the guide member 42 being supported by a cup 48 to form a knuckle joint that provides an interface between the ball bearing and the spring 46. Other forms of guide member 42 may be used in other embodiments, however.

The main rider 18 is shown in more detail in Figure 5, which reveals that it has a cylindrical through-bore having a diameter corresponding to the outer diameter of the intermediate rider 20. The through-bore defines a chamber 50 in which the intermediate rider 20 is housed. The main rider 18 has a depth corresponding to a length of the drive cam 26 with respect to the driveshaft axis 28, such that the chamber 50 also fully accommodates the drive cam 26. When assembled, the end faces 32 of the drive cam 26 are coplanar with end faces of the main rider 18.

The main rider 18 is restrained against movement in the direction of the driveshaft axis 28, for example using guide features of the pump body 14, to maintain alignment between the end faces of the main rider 18 and the drive cam 26. The main rider 18 is also restrained against rotation around the driveshaft axis 28 and so has a fixed orientation in a plane orthogonal to the driveshaft axis 28. The intermediate rider 20 and the drive cam 26 therefore both rotate within, and relative to, the main rider 18.

The guide groove 44 of the main rider 18 is visible in Figure 5, which makes clear that the groove forms a closed loop that follows a generally elliptical path around a central axis of the chamber 50.

When the drive cam 26 rotates, the geometry of the interfacing surfaces of the drive cam 26 and the intermediate rider 20 entail that the intermediate rider 20 tends to rotate with the drive cam 26, noting also that the orientation of the intermediate rider 20 is maintained by the main rider 18. However, such rotation could occur without axial movement of the intermediate rider 20 along the drive cam 26, which would cause the main rider to reciprocate in a vertical direction in a similar manner to a conventional slipper-tappet arrangement. To avoid this, the guide arrangement formed by the guide member 42 and the guide groove 44 ads to draw the intermediate rider 20 along the drive cam 26 in response to rotation of the drive cam 26, whilst also ensuring that the intermediate rider 20 rotates with the drive cam 26. The precise shape of the guide groove 44 is determined to account for the axial movement of the intermediate rider 20 as the drive cam 26 turns, so that the intermediate rider 20 traverses the length of the drive cam 26 over one half turn of the drive cam 26. It is noted, however, that the guide arrangement primarily acts as a guide in this example, and the force acting to move the intermediate rider 20 along the drive cam 26 predominantly arises from the drive cam 26 itself, by virtue of its varying eccentricity.

Similarly to existing slipper-tappet drivetrains, hydrodynamic bearings may be used to accommodate relative movement between the drive cam 26, the intermediate rider 20 and the main rider 18. It is also possible to use a bearing on the exterior of the intermediate rider 20 to reduce the length of bearing bush required and thereby reduce or eliminate disruption to the bearing by the guide groove 44, which may beneficially entail that only one component of the drivetrain 12 requires bearings.

The movement of the drivetrain components is illustrated in the sequence illustrated in Figures 6a to 9c, which show the drivetrain configuration over a series of 90° intervals in the angular position of the drive cam 26, and so collectively illustrate the movement of the drivetrain components during one complete revolution of the driveshaft 16.

Figures 6a and 6b show perspective and front views respectively of the drivetrain 12 when the tappet 22 is in a first bottom-dead-centre (BDC) position, corresponding to a BDC position for the plunger 13 when the plunger 13 is at the end of a filling stroke and about to commence a pumping stroke.

Reference marks shown on the visible end faces 32 of the drive cam 26 and the intermediate rider 20 indicate the respective angles of these components, these reference marks being aligned in Figures 6a and 6b, and remaining aligned in the subsequent stages of movement shown in Figures 7a to 9c. It is reiterated that these reference marks are illustrative and so do not necessarily denote physical features.

Figure 6c provides an axial cross-section of the arrangement, which shows that the intermediate rider 20 is aligned with the end of the drive cam 26 that is furthest from the pump body 14 in this position.

As the drive cam 26 initially turns from the position shown in Figures 6a to 6c, the intermediate rider 20 is moved upwardly due to the eccentricity of the portion of the drive cam 26 with which the intermediate rider 20 is aligned at that stage. This, in turn, causes the main rider 18 to move upwardly, which in turn presses the tappet 22 and the plunger 13 upwardly to effect a pumping stroke of the plunger 13.

This continues until the tappet 22 and plunger 13 reach a first top-dead-centre (TDC) position, which occurs when the drive cam 26 has turned by 90°. This position is illustrated in Figures 7a to 7c, as indicated by the reference marks on the drive cam 26.

The guide arrangement acts to translate the rotation of the drive cam 26 into sliding of the intermediate rider 20 in the direction of the driveshaft axis 28 towards the pump body 14. Figure 7c shows that the intermediate rider 20 has reached a central position, such that the respective axial midpoints of the intermediate rider 20 and the drive cam 26 are aligned.

With continued rotation of the drive cam 26, the intermediate rider 20 continues its progress towards the opposite end of the drive cam 26 and the pump body 14. However, due to the rotation of the drive cam 26 and its variable eccentricity, beyond the midpoint of the drive cam 26 the intermediate rider 20 starts to fall, in turn causing the plunger 13 to fall and therefore undergo a filling stroke.

This downward movement of the plunger 13 continues until the drive cam 26 has rotated by 180° relative to the initial position shown in Figures 6a to 6c, which is shown in Figures 8a to 8c. At this stage, the effect of the variable eccentricity and the rotation of the drive cam 26 is that the portion of the drive cam 26 nearest the pump body now has an eccentricity corresponding to the BDC position and, as Figure 8c shows, the intermediate rider 20 is now located on this portion. Accordingly, the configuration shown in Figures 8a to 8c defines a second BDC position.

As the driveshaft 16 continues to turn, the direction of travel of the intermediate rider 20 reverses so that the intermediate rider 20 is drawn back towards the midpoint of the drive cam 26, such that the stages of movement shown in Figures 6a to 8c are repeated in the opposite direction. Accordingly, the main rider 18 is initially driven upwards once more, causing a second pumping stroke of the plunger 13. Once the driveshaft 16 has turned by 270° relative to the initial position of Figures 6a to 6c, the intermediate rider 20 once again aligns with the midpoint of the drive cam 26, and so resumes the position shown in Figure 7c. This position is shown in Figures 9a to 9c and defines a second TDC position for the drivetrain 12 and the plunger 13.

From this position, as the drive cam 26 completes its revolution the drivetrain 12 returns to the configuration shown in Figures 6a to 6c and thus reaches a BDC configuration. This sequence then repeats continuously as the driveshaft 16 rotates.

It follows from the above that a single revolution of the driveshaft 16 causes two pumping strokes of the plunger 13, and thus effects two pumping events. Meanwhile, the drive cam 26, the intermediate rider 20 and the main rider 18 share significant contact areas and so offer higher durability than a roller-shoe arrangement. It also follows from the above that the intermediate rider 20 reciprocates on the drive cam 26, along the driveshaft axis 28, at the same frequency as the cyclical frequency of the driveshaft 16.

It is noted that the main rider 18 moves in a circle around the driveshaft axis 28 as the drive cam 26 rotates, similarly to the rider of a conventional slipper-tappet arrangement, and thus moves both vertically and laterally. Although the main rider 18 is in the same lateral position in each of the stages shown in Figures 6a to 9c, Figures 10 and 11 illustrate the lateral movement of the main rider 18.

In this respect, Figure 10 shows the drivetrain 12 once the drive cam 26 has turned by 45° relative to the BDC position shown in Figures 6a to 6c, and thus shows an intermediate position between the BDC position of Figures 6a to 6c and the TDC position of Figures 7a to 7c. When the drive cam 26 is at this angle, a left edge of the main rider 18, as viewed in Figure 10, is offset slightly to the right of an illustrative reference mark in an upper left corner of the pump body 14.

Figure 11 shows the drivetrain 12 once the drive cam 26 has turned through a further 90°, and is thus offset by 45° from the TDC position shown in Figures 7a to 7c. In this position, the left edge of the main rider 18 is slightly to the left of the reference mark. Thus, a comparison between Figures 10 and 11 reveals the extent of lateral movement that the main rider 18 undergoes.

It will be appreciated that various other embodiments of the invention are also envisaged without departing from the scope of the appended claims.

For example, the guide arrangement could be reversed relative to the example above, so that the guide groove is formed in the exterior of the intermediate rider and a guide member is held in the main rider.

Also, the main rider need not necessarily house and fully envelop the intermediate rider as in the above example, but may instead be a smaller element that provides an interface between the intermediate rider and the tappet. Such a main rider may still have a fixed orientation as in the above example. A smaller main rider may offer the benefit of reducing the reciprocating mass of the pump.

The shaft positions could be reversed relative to the example described above, so that BDC positions occur when the intermediate rider is in the centre of the drive cam and TDC positions arise when the intermediate rider is at either end of the drive cam. This could be achieved, for example, by altering the angle of the guide groove by 90°.

List of parts -fuel pump 12 -drivetrain 13 -plunger 14 -pump body -plunger axis 16 -driveshaft 17 -plunger return spring 18 -main rider -intermediate rider 22 -tappet 23 -tappet axis 24 -core shaft 26 -drive cam 28 -driveshaft axis -shoulder (of the core shaft) 32 -end faces (of the drive cam) 34 -outer surface of the drive cam 36 -drive cam axis 38 -central opening of the intermediate rider -bore of the guide arrangement 42 -guide member 44 -guide groove 46 -spring 48 -cup of guide arrangement 50 -chamber of main rider

Claims

CLAIMS1. A drive arrangement (12) for a fuel pump (10) for a vehicle, the drive arrangement (12) comprising: a drive cam (26) configured to rotate about a rotational axis (28), in use, wherein an eccentricity of the drive cam (26) relative to the rotational axis (28) varies along the rotational axis (28); and a cam rider member (20) configured for reciprocating movement on the drive cam (26) along the rotational axis (28) as the drive cam (26) rotates.
The drive arrangement (12) of claim 1, wherein an outer surface (34) of the drive cam (26) is inclined relative to the rotational axis (28).
The drive arrangement (12) of claim 1 or claim 2, wherein the drive cam (26) extends along a drive cam axis (36) that is inclined relative to the rotational axis (28).
4. The drive arrangement (12) of claim 3, wherein the drive cam axis (36) intersects the rotational axis (28) midway between axial ends of the drive cam (26).
5. The drive arrangement (12) of any preceding claim, wherein the drive cam (26) has a parallelogram profile in a plane containing the rotational axis.
6. The drive arrangement (12) of any preceding claim, wherein the cam rider member (20) comprises an opening (38) in which the drive cam (26) is received, the opening (38) being shaped to conform to an outer surface (34) of the drive cam (26).
7. The drive arrangement (12) of any preceding claim, comprising a second rider member (18) that engages the cam rider member (20), so that the cam rider member (20) is disposed between the drive cam (26) and the second rider member (18).
The drive arrangement (12) of claim 7, wherein the second rider member (18) has a fixed orientation in a plane orthogonal to the rotational axis (28).
9. The drive arrangement (12) of claim 7 or claim 8, wherein the second rider member (18) is in engagement with a tappet (22) associated with a plunger (13) of the pump (10).
10. The drive arrangement (12) of any preceding claim, comprising a guide arrangement configured to guide movement of the cam rider member (20) along the rotational axis (28).
11. The drive arrangement (12) of claim 10 when dependent on claim 7, wherein the guide arrangement comprises a guide groove (44) formed in one of the cam rider member (20) and the second rider member (18), and a guide member (42) that is received in the guide groove (44).
12. A fuel pump (10) comprising the drive arrangement (12) of any preceding claim.
13. The pump (10) of claim 12, comprising a plunger (13) arranged for reciprocating movement along a plunger axis (15) within a body of the pump (10), wherein the drive cam (26) is arranged to drive movement of the plunger (13) along the plunger axis (15).
14. The pump (10) of claim 13, configured so that a single revolution of the drive cam (26) drives multiple pumping cycles of the plunger (13).
15. A method of operating a drive arrangement (12) of a fuel pump (10) for a vehicle, the drive arrangement (12) comprising a drive cam (26) having a rotational axis (28) and an eccentricity relative to the rotational axis (28) that varies along the rotational axis (28), the method comprising rotating the drive cam (26) about the rotational axis (28) to cause a cam rider member (20) to move on the drive cam (26), along the rotational axis (28).