GB2598598A

GB2598598A - Fuel pump

Info

Publication number: GB2598598A
Application number: GB2013884.8A
Authority: GB
Inventors: J Maclane Stephen
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2020-09-03
Filing date: 2020-09-03
Publication date: 2022-03-09
Also published as: GB202013884D0

Abstract

A fuel pump 10 for a vehicle, comprising: a plunger 42 arranged to reciprocate along a plunger axis 38 within a pump body 24; a drive cam 18 arranged to rotate about a drive cam axis 21 to drive movement of the plunger in a first direction along the plunger axis; A return lever 46 arranged to pivot about a return lever axis 48 to drive plunger movement in a second direction along the plunger axis that opposes the first direction; Wherein the drive cam and return lever define a desmodromic mechanism that drives plunger movement. A corresponding method is disclosed. The drive cam may engage the lever, the lever acting to maintain continuous engagement between the plunger and drive cam or drive lever. The return lever may be driven by the drive cam, or by a separate return cam. The return and drive cams may be coaxial.

Description

FUEL PUMP

Field of the invention

This invention relates to an automotive fuel pump, and in particular to a fuel pump configured for high speed use.

Background to the Invention

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 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 plunger is typically held in contact with its driving cam during filling strokes by a return spring. This arrangement inherently limits the speed at which the system can run effectively, since there will be a threshold pump speed above which the force provided by the return spring becomes insufficient to generate the zo required acceleration in the plunger to hold the plunger in continuous contact with the cam. If the engine speed were to rise above the threshold level, the plunger would lose contact with the cam during the filling stroke and then forcibly reengage the cam subsequently in a somewhat unpredictable manner. In the worst case, this could cause catastrophic damage to the pump. Accordingly, the engine speed must be limited to avoid this situation from arising.

While this problem can be mitigated to some extent by increasing the return spring force by providing larger, stronger springs, or multiple springs, doing so increases the space required to accommodate the springs and so impacts the overall packaging space required for the pump. Even with larger springs a threshold pumping speed will remain, albeit at a higher level, which dictates a corresponding maximum engine speed for any vehicle in which the pump is used. It is against this background that the present invention has been devised.

Summary of the Invention

An aspect of the invention provides a fuel pump for a vehicle. The fuel pump comprises: a plunger arranged for reciprocating movement along a plunger axis within a body of the pump; a drive cam arranged to rotate about a drive cam axis to drive movement of the plunger in a first direction along the plunger axis; and a return lever arranged to pivot about a return lever axis to drive movement of the plunger in a second direction along the plunger axis that is opposed to the first direction. The drive cam and the return lever together define a desmodromic mechanism that drives movement of the plunger.

By virtue of the desmodromic mechanism provided by the drive cam and the return lever, separation of the plunger from the driving element can be prevented at any pumping speed. This avoids the above-mentioned problem associated with pumps that use return springs, which must be speed-limited to avoid separation of the plunger and the driving element and the associated risk of damage to the pump components.

The drive cam may engage the plunger to drive movement of the plunger in the first direction, in which case the return lever acts to maintain continuous engagement between the plunger and the drive cam. Engagement between the drive cam and the plunger may be indirect, for example through a cam follower arrangement.

The drive cam may drive movement of the plunger in the first direction through a drive lever, in which case the return lever acts to maintain continuous engagement between the plunger and the drive lever.

Accordingly, whether the driving element is the drive cam or a drive lever driven by the drive cam, the desmodromic arrangement ensures continuous engagement between the plunger and the driving element.

In some embodiments, the return lever is driven by the drive cam, creating an elegant arrangement with relatively few components. In such embodiments, the return lever and the plunger may engage the drive cam at respective orthogonal angular positions relative to the drive cam axis.

Alternatively, the pump may comprise a return cam configured to drive the return lever. The return cam may be orthogonal to the drive cam, and may be coaxial with the drive cam. This may be particularly useful where packaging constraints make it difficult to position the drive cam in line with the plunger.

The drive cam axis and the return lever axis are optionally parallel and mutually spaced.

The return lever may be substantially straight. Alternatively, the return lever may be bent at the return lever axis.

The plunger axis may intersect the drive cam axis. Alternatively, the plunger axis may be laterally offset from the drive cam axis.

Another aspect of the invention provides a method of moving a fuel pump plunger. The method comprises: rotating a drive cam to drive movement of the plunger in a first direction along a plunger axis; and subsequently, pivoting a return lever to drive movement of the plunger in a second direction along the plunger axis, the second direction being opposed to the first direction.

It will be appreciated that preferred and/or optional features of each aspect of the invention may be incorporated alone or in appropriate combination in the other aspects of the invention also.

Brief Description of the Drawings

In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which like features are assigned like reference numbers, and in which: Figure 1 shows in perspective view a fuel pump according to an embodiment of the invention; Figure 2 shows the fuel pump of Figure 1 with a pump housing removed to reveal interior features of the pump; Figure 3 shows the fuel pump of Figure 1 in transverse cross-section in a first operating position; Figure 4 corresponds to Figure 3 but shows a different operating position; and Figure 5 shows in schematic form an alternative mechanism to that of the pump of Figures 1 to 4 for driving movement of a fuel pump plunger.

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 pumps of embodiments of the invention may be oriented differently to the manner depicted in the drawings in practice.

Detailed Description of Embodiments of the Invention In general terms, embodiments of the invention provide fuel pumps in which desmodromic arrangements are used to hold a plunger in contact with a cam throughout a pumping cycle, instead of a conventional return spring. This arrangement prevents separation of the plunger from the cam at high pumping speeds and the associated potential for damage to the pump, allowing the pump to run at higher speeds than conventional counterparts.

This ability for the pump to run at higher speeds finds particular benefit in direct injection arrangements, such as gasoline direct injection (GDI) or diesel direct injection (DDI) systems, where higher pumping speeds are often required; although in general terms embodiments of the invention are applicable to all vehicle and engine types.

Referring generally to Figures 1 to 4, a fuel pump 10 according to an embodiment of the invention is shown. The fuel pump 10 includes a pump housing 12 that supports a pair of pumping heads 14 arranged in axial succession along a longitudinally-extending camshaft 16. It is noted that other embodiments may involve a different number of pumping heads.

As best seen in Figure 2, in which the pump housing 12 is hidden to reveal internal features of the pump 10, the camshaft 16 carries a pair of cams 18 arranged in axial series on the camshaft 16, so that each cam 18 aligns axially with a respective one of the pumping heads 14.

As is most clear in Figures 3 and 4, the cams 18 are identical, being oval in shape to define a pair of opposed lobes 20. Each cam 18 has two transversely-extending, orthogonal planes of symmetry that intersect along a central axis of the respective cam 18. The central axes of the cams 18 are aligned with each other and with a central axis 21 of the camshaft 16, which therefore defines an axis of rotation for each cam 18.

In this embodiment, the cams 18 are arranged orthogonally to one another on the camshaft 16, in that the respective pairs of lobes 20 of the cams 18 extend in orthogonal directions. Accordingly, when the camshaft 16 rotates, in use, the cams 18 are 90° out-of-phase with one another.

Each pumping head 14 is generally conventional and so shall not be described in detail.

Briefly, each pumping head 14 is composed of a valve assembly 22 and 30 a pumping head body 24.

The valve assembly 22 comprises a cylindrical valve assembly body 26 having a central bore 28 of varying diameter, an enlarged upper end of the central bore 28 accommodating an inlet valve assembly 30 that protrudes outwardly from the valve assembly body 26 to define a pump inlet 32 for the pumping head 14. A tubular protrusion of the valve assembly body 26 extends at an inclination to the central bore 28 to define an outlet 33 for the pumping head 14, the outlet 33 containing a secondary bore 34 housing an outlet valve assembly 35 through which pressurised fuel exits the pump 10. The skilled reader will appreciate that various other valve configurations are known, any of which may be employed in embodiments of the invention.

In this example, the pumping head body 24 is arranged directly beneath the valve assembly 22 in end-to-end engagement with the valve assembly body 26. The pumping head body 24 is generally tubular and has a central through-bore defining a main bore 36, the main bore 36 having a longitudinal axis 38 that aligns with the corresponding axis of the central bore 28 of the valve assembly body 26.

A lower portion of the pumping head body 24 is of reduced diameter to define a turret 40 of the pumping head body 24.

Each pumping head 14 is disposed radially outboard of the camshaft 16 to align axially with a respective one of the cams 18, the pumping head 14 being oriented such that the longitudinal axis 38 of the main bore 36 extends in a rotational plane of the cam 18, so that the longitudinal axis 38 is orthogonal to and intersects the central axis of the respective cam 18.

An elongate cylindrical rod defining a plunger 42 is received in the main bore 36 of the pumping head body 24 for reciprocating movement along the longitudinal axis 38 of the main bore 36, which therefore defines a plunger axis.

The plunger 42 extends telescopically from the turret 40 to engage the respective cam 18 through a cam roller assembly 44 that is fixed to a lower end of the plunger 42.

The skilled reader will appreciate that the plunger 42 would ordinarily be biased into contact with the cam 18, via the cam roller assembly 44, by a return spring. The spring would typically fit around the turret 40, for example. However, in this embodiment of the invention the return spring is replaced with a lever 46 that performs this function, to ensure that the plunger 42 and the cam roller assembly 44 remain engaged at all times. Accordingly, in combination the cam 18 and the lever 46 form a desmodromic mechanism that drives movement of the plunger 42, as explained in more detail below.

As for known pumps employing return springs, keeping the plunger 42 engaged with the cam 18 means that rotation of the camshaft 16 is translated into reciprocating linear motion of the plunger 42 along the plunger axis 38, so that the plunger 42 moves into and outwardly from the pumping head 14. In the orientation of the pump 10 shown in Figure 3, upward movement of the plunger 42 corresponds to a 'pumping stroke', in which fuel is pressurised and driven out from the pump outlet 33, and downward movement of the plunger 42 corresponds to a 'filling stroke', in which fuel is drawn into the pumping head 14 through the pump inlet 32.

Since the two cams 18 of the pump 10 are arranged with orthogonal orientations, a filling stroke of one pumping head 14 coincides with a pumping stroke of the other pumping head 14, so that one of the pumping heads 14 delivers pressurised fuel at any given time for a substantially continuous output from the pump 10.

As shown in Figure 3, as the cam 18 turns in use the plunger 42 reaches an upper position within the pumping head 14, corresponding to the end of a pumping stroke, when the cam roller assembly 44 aligns with the widest region of the cam 18. Continued rotation of the cam 18 causes the plunger 42 to sink in a filling stroke until the plunger 42 occupies a lower position, which is shown in Figure 4, once the cam 18 has rotated through a right angle so that the cam roller assembly 44 aligns with the narrowest region of the cam 18.

As noted above, in this embodiment the above described plunger movement is controlled in part by the lever 46. The lever 46 is rigid, for example being of steel, and is pivotably mounted to a lever shaft 48 to allow the lever 46 to rotate in a plane in which the respective cam 18 also rotates. The lever shaft 48 therefore defines a lever axis that is parallel to and mutually spaced from the central axis 21 of the camshaft 16. In this respect, the lever shaft 48 extends parallel to the camshaft 16 and is fixed within the pump housing 12 in a position that, in the orientation shown in Figure 3, is laterally offset to the left of the cam roller assembly 44. In this embodiment, a sintered bush is used as a pivot bearing at the interface between the lever 46 and the lever shaft 48.

As is clear from Figure 3, the pump housing 12 includes an enlarged cuboid cavity on its left side to accommodate the lever 46. Aside from this, the pump housing 12 is substantially identical to that of an equivalent conventional pump. Accordingly, the increased packaging requirements dictated by the addition of the lever 46 are minimal, and are expected to be significantly lower than the increase in packaging size that would be incurred to provide a larger return spring configured for similar pumping speeds.

It is noted that each pumping head 14 comprises a respective lever 46, those levers 46 being identical. The levers 46 of both pumping heads 14 each attach to the lever shaft 48, which therefore defines a common pivot axis for the respective levers 46.

Each lever 46 is bent at its point of attachment to the lever shaft 48, dividing the lever 46 into an upper lever portion 46a above the lever shaft 48 and a lower lever portion 46b below the lever shaft 48. The bend in the lever 46 accommodates the position of the cam 18 directly below the plunger 42, as shall become clear from the description that follows. It is noted that the lever 46 can be shaped and positioned differently to accommodate different cam positions relative to the plunger 42, to allow for the packaging requirements of each application. The upper lever portion 46a extends generally circumferentially towards the plunger 42 and is shaped and dimensioned to engage an upper surface of the cam roller assembly 44. Accordingly, upward movement of the cam roller assembly 44 during a pumping stroke -namely, from the position shown in Figure 4 to the position shown in Figure 3 -drives corresponding upward movement of the engaged end of the upper lever portion 46a, causing the lever 46 to rotate anticlockwise in the orientation shown in Figures 3 and 4, as is evident from the relative positions of the plunger 42 and the lever 46 in Figures 3 and 4.

A comparison of Figures 3 and 4 also reveals that the engaged end of the upper lever portion 46a slides across the upper surface of the cam roller assembly 44 during the pumping stroke to accommodate the change in relative positions of the lever 46 and the plunger 42. The engaged end of the upper lever portion 46a is curved where it makes contact with the cam roller assembly 44, thereby facilitating the sliding movement. Thus, the engagement between the lever 46 and the cam roller assembly 44 is passive.

It is noted that while Figure 3 shows a section taken through the longitudinal axis 38 of the main bore 36, Figure 4 shows a section taken through a plane slightly offset from the longitudinal axis and hence shows slightly different features to Figure 3.

The lower lever portion 46b extends generally downwardly, and therefore at an inclination that is close to a right angle with the upper lever portion 46a, to terminate in a bushed roller 50 that engages the cam 18. Accordingly, rotation of the cam 18 during a filling stroke -namely, from the position shown in Figure 3 to the position shown in Figure 4 -drives corresponding outward movement of the engaged end of the lower lever portion 46b, causing the lever 46 to rotate clockwise, as viewed in Figure 3 and 4. In turn, the clockwise rotation of the lever causes the engaged end of the upper lever portion 46a to move downwardly, thereby driving the plunger 42 downwards during the filling stroke and so holding the plunger 42 in contact with the cam roller assembly 44.

Relative to the central axis of the cam 18, the bushed roller 50 and the cam roller assembly 44 engage the cam 18 at positions that are at 900 to each other so that, for example, when the cam roller assembly 44 is aligned with the widest part of the cam 18, the bushed roller 50 engages the cam 18 at its narrowest point.

Accordingly, movement of the lever 46 is precisely 90° out-of-phase with the rotation of the cam 18, meaning that the lever 46 oscillates in a manner that is perfectly complementary to the rotation of the cam 18. In this way, the movement of the cam roller assembly 44 is controlled at all times for any pumping speed.

It is noted the cam 18 and the lever 46 drive the plunger 42 in a reciprocal manner, so that only one of the cam 18 and the lever 46 exerts a force on the plunger 42 at any given time. For example, during a pumping stroke the cam 18 applies a force to the plunger 42 via the cam roller assembly 44, while the lever 46 is turned passively by the cam roller assembly 44. Correspondingly, as soon as the cam 18 moves past the orientation corresponding to the upper position of the plunger 42 shown in Figure 3 to commence a filling stroke, the cam 18 no longer drives the plunger 42 but instead immediately urges the lever 46 outwardly, and the resultant pivoting of the lever 46 drives the plunger 42 downwardly to remain in contact with the cam roller assembly 44.

Accordingly, unlike known pumps having return springs, by virtue of the rigidity of the lever 46 and its continuous engagement with the cam roller assembly 44, the desmodromic mechanism of the pump 10 of this embodiment is not susceptible to separation of the plunger 42 and the cam roller assembly 44. The performance of the pump 10 is therefore not sensitive to the pumping speed, allowing the pump 10 to operate at higher speeds than an equivalent pump employing a return spring, thus avoiding the need to limit the operating speed of an engine with which the pump 10 is used.

It should be appreciated that the desmodromic arrangement shown in Figures 1 to 4 is only an example, and many variations are possible to suit the requirements of each application. For example, while a benefit of the pump 10 of Figures 1 to 4 is that it requires only one cam for each pumping head, in other arrangements a pair of cams may be used with each pumping head, each cam of the pair driving movement of the plunger in a respective direction.

Figure 5 shows in schematic form a possible desmodromic mechanism of this kind. Figure 5 shows a plunger 42 and a cam roller assembly 44 that may correspond to those of Figures 1 to 4. All other features of the fuel pump that are not shown in Figure 5 can be assumed to be generally identical to those of the pump 10 of Figures 1 to 4, aside from the pump housing, which will be altered to accommodate the different relative component positions.

Figure 5 also shows a pair of cams 180, each being associated with a respective lever 460. Each lever 460 is generally straight and rigid, and is pivotably mounted to a respective lever shaft 480 at a point slightly offset from a midpoint of the lever 460 to rotate in a common plane with its respective cam 180.

As for the previous embodiment, the cams 180 are mounted to a camshaft (not visible in Figure 5) so that the cams are coaxial with the camshaft, whilst being orthogonal to each other. The lever shafts 480 extend parallel to the camshaft, both lever shafts being disposed inwardly of the camshaft to lie between the camshaft and the plunger 42.

A first one of the cams 180, shown oriented such that its lobes 20 are spaced horizontally from each other in Figure 5, is responsible for driving upward movement of the plunger 42 during pumping strokes and so defines a drive cam 180a. It follows that the lever associated with the drive cam 180a, which is the lowermost lever in Figure 5, defines a drive lever 460a. The lever shaft 480 supporting the drive lever 460a is disposed at a higher level than the central axis of the drive cam 460a. The drive cam 180a engages an end of the drive lever 460a at a point directly below the central axis of the drive cam 180a, for example through a bushed roller as in the pump 10 of Figures 1 to 4. The opposed end of the drive lever 460a is pivotably fixed to the underside of the cam roller assembly 44. Correspondingly, the second one of the cams 180 is responsible for driving downward movement of the plunger 42 during filling strokes and so defines a return cam 180b. It follows that the lever associated with the return cam 180b defines a return lever 460b. The lever shaft 480 supporting the return lever 460b is disposed at a lower level than the central axis of the return cam 180b. The return cam 180b engages an end of the return lever 460b at a point directly above the central axis of the drive cam 180a, again through a bushed roller as in the pump 10 of Figures 1 to 4. The opposed end of the return lever 460b is pivotably fixed to the plunger 42 at a point above the cam roller assembly 44.

As the camshaft rotates in the anticlockwise direction indicated by the arrow in Figure 5, the cams 460 reach the position shown in Figure 5, in which the lobes of the return cam 180b are spaced vertically. While approaching this position, the return lever 460b progressively engages the widest part of the return cam 180b and is therefore forced upwardly such that the return lever 460b turns anticlockwise. In turn, this anticlockwise rotation of the return lever 460b drives the plunger 42 downwardly.

Subsequently, as the camshaft rotates further and passes the position shown in Figure 5 the return cam 180b ceases exerting a force on return lever 460b, and instead the drive cam 180a begins to apply a force to the drive lever 460a to move the end of the drive lever 460a that engages the drive cam 180a downwardly. This forces clockwise rotation of the drive lever 460a, which in turn drives the plunger 42 upwardly.

This cycle repeats continuously, so that the plunger 42 is driven through reciprocating movement in a similar manner to the plunger 42 of the pump 10 of Figures 1 to 4. Accordingly, the drive cam 180a, the drive lever 460a, the return cam 180b and the return lever 460b combine to form a desmodromic mechanism that drives all stages of movement of the plunger 42.

The desmodromic arrangement shown in Figure 5 shares the ability of the pump of Figures 1 to 4 to run at any pumping speed without risking disengagement of the plunger 42 from the driving element, which in this case is the drive lever 460a. The different positions of the cams 180 and other components in Figure 5 relative to the pump 10 of Figures 1 to 4, namely to the side of the plunger 42 instead of below the plunger 42, may be beneficial for certain applications having specific packaging requirements.

It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms to that described herein, without departing from the scope of the appended claims.

References used: 10-pump 12-pump housing 14-pumping head 16 -camshaft 18-cam -cam lobe 21 -central axis of the camshaft 22 -valve assembly 24 -pumping head body 26 -valve assembly body L1 28 -central bore (of the valve assembly body) 30 -inlet valve assembly 32 -pump inlet 33 -pump outlet 34 -secondary bore -outlet valve assembly 36 -main bore (of the pumping head body) 38 -longitudinal axis of the main bore 40 -turret 42 -plunger 44 -cam roller assembly 46 -lever 48 -lever shaft -bushed roller 180a -drive cam 180b -return cam 460a -drive lever 460b -return lever 480 -lever shaft

Claims

Claims: 1. A fuel pump (10) for a vehicle, the fuel pump (10) comprising: a plunger (42) arranged for reciprocating movement along a plunger axis (38) within a body (24) of the pump (10); a drive cam (18, 180a) arranged to rotate about a drive cam axis (21) to drive movement of the plunger (42) in a first direction along the plunger axis (38); and a return lever (46, 460b) arranged to pivot about a return lever axis to drive movement of the plunger (42) in a second direction along the plunger axis (38) that is opposed to the first direction; wherein the drive cam (18, 180a) and the return lever (46, 460b) together define a desmodromic mechanism that drives movement of the plunger (42).
2. The pump of claim 1, wherein the drive cam (18, 180a) engages the plunger (42) to drive movement of the plunger (42) in the first direction, and wherein the return lever (46, 460b) acts to maintain continuous engagement between the plunger (42) and the drive cam (18, 180a).
3. The pump of claim 1, wherein the drive cam (18, 180a) drives movement of the plunger (42) in the first direction through a drive lever (460a), and wherein the return lever (46, 460b) acts to maintain continuous engagement between the plunger (42) and the drive lever (460a).
4. The pump of any preceding claim, wherein the return lever (46, 460b) is driven by the drive cam (18, 180a).
5. The pump of claim 4, wherein the return lever (46, 460b) and the plunger (42) engage the drive cam (18, 180a) at respective orthogonal angular positions relative to the drive cam axis (21).
6. The pump of any of claims 1 to 3, comprising a return cam (180b) configured to drive the return lever (46, 460b).
7. The pump of claim 6, wherein the return cam (180b) is orthogonal to the drive cam (18, 180a).
8. The pump of claim 6 or claim 7, wherein the return cam (180b) is coaxial with the drive cam (18, 180a).
9. The pump of any preceding claim, wherein the drive cam axis (21) and the return lever axis are parallel and mutually spaced.
10. The pump of any preceding claim, wherein the return lever (46, 460b) is substantially straight.
11. The pump of any of claims 1 to 9, wherein the return lever (46, 460b) is bent at the return lever axis
12. The pump of any preceding claim, wherein the plunger axis (38) intersects the drive cam axis (21).
13. The pump of any of claims 1 to 11, wherein the plunger axis (38) is laterally offset from the drive cam axis (21).
14. A method of moving a fuel pump plunger (42), the method comprising: rotating a drive cam (18, 180a) to drive movement of the plunger (42) in a first direction along a plunger axis (38); and subsequently, pivoting a return lever (46, 460b) to drive movement of the plunger (42) in a second direction along the plunger axis (38), the second direction being opposed to the first direction.