Pump assembly for a fuel injection system

Abstract

A fuel pump assembly 200 for an internal combustion engine comprising a pump housing 8 and a plunger 10. The assembly comprises a roller tappet assembly 18 housed within a tappet bore 13 and comprises

Description

Field of the Invention This invention relates to a pump assembly for a fuel injection system. In particular, but not exclusively, the invention relates to a pump assembly for supplying pressurised fuel to a fuel injection system for delivering fuel to an internal combustion engine. The invention is concerned with methods of reducing leakage in a pump assembly for a fuel injection system. Background of the Invention Fuel injection systems are used to introduce high pressure fuel into the combustion chambers of an internal combustion engine, such as a diesel engine. In a popular arrangement, the fuel injection system delivers fuel to the engine via a set of fuel injectors that are supplied with fuel from a pressurised accumulator, known as a common rail. The fuel in the common rail is typically pressurised by a high pressure reciprocating pump, which includes a plunger that is driven in a reciprocating linear motion inside a plunger bore, repeating successive pumping and filling strokes. The reciprocating motion of the plunger is driven by the rotation of a camshaft that features a suitably shaped cam for contacting a roller tappet assembly fixed to the plunger and displacing the plunger in a reciprocating motion as the camshaft rotates. As the cam rotates, a roller of the roller tappet assembly is in rolling contact with the outer surface of the cam. When the camshaft rotates, the roller tappet travels along the outer surface of the cam from portions closer to the centre of the cam to portions further from the centre of the cam. Advantageously, the roller allows the roller tappet to travel more smoothly over the outer surface of the cam, thus providing smoother reciprocal motion. In such systems, it is known to provide the roller, cam, and camshaft with lubricant, e.g. motor oil. However, a problem exists in that the lubricant can leak through the gap between the tappet and the bore. It is against this background that the invention has been devised. Summary of the Invention According to a first aspect of the invention, there is provided a fuel pump for pressurising fuel in a fuel system of an internal combustion engine. The fuel pump comprises a pump housing, a plunger configured for reciprocal motion within a plunger bore, and a roller tappet assembly configured for reciprocal motion within a tappet bore. The plunger comprises a first end and a second end. The roller tappet assembly comprises a roller and a tappet and is disposed at the first end of the plunger. A sleeve is disposed between an inner surface of the tappet bore and the tappet. The tappet bore is provided with a fluid inlet and a fluid outlet and the sleeve comprises a groove configured to provide a fluid flow path between the fluid inlet and the fluid outlet such that the fluid flow cools the sleeve. During use of the fuel pump, some components, namely the tappet bore and the tappet, will undergo thermal expansion during which a gap may form between the tappet and the tappet bore. In the case where the gap between the sleeve and the tappet is too large, a leakage of lubricating oil therebetween may exceed limits imposed by engine manufacturers. The fuel pump is advantageous at least in that, by reducing the temperature of the sleeve by the cooling flow, the gap formed between the tappet and the sleeve due to thermal expansion is reduced. The sleeve may comprise a groove to define, at least in part, the heat transfer portion. The groove may also be configured to define a fluid flow path between the fluid inlet and the fluid outlet. The groove may be an annular groove formed in the circumference of the sleeve. The tappet bore may comprise a first axial groove in fluid communication with the fluid inlet and a second axial groove in fluid communication with the fluid outlet. The first and second axial grooves may also communicate with the heat transfer portion. The sleeve may comprise a plurality of annular grooves, which may each be configured to provide a series of fluid flow paths between the fluid inlet and the fluid outlet. The tappet bore may be a stepped bore such that it comprises a sleeve bore portion configured to receive the sleeve. The sleeve bore portion may comprise a reduced diameter portion of the stepped bore. The sleeve may comprise an upper interface surface and a lower interface surface to define a first interference fit region with the sleeve bore portion (i.e. the upper and lower interface surfaces both contribute to the first interference fit region). The upper and lower interface surfaces may be separated by the heat transfer portion. Each of the plurality of annular grooves may be spaced apart by a respective interface portion which collectively define a second interference fit region with the sleeve bore portion (i.e. the interface portions collectively contribute to the second interference fit region). The heat transfer portion may comprise a plurality of radially projecting fins between the upper and lower interface surfaces. The pump housing and the sleeve may be formed of the same material. Optionally, the pump housing and the sleeve may be formed from aluminium and the tappet may be formed from steel or another hard metal. According to a second aspect of the invention, a pump system comprises at least two fuel pump assemblies of the aforementioned aspect of the invention, and a common fluid supply line which delivers fluid to the fluid inlet of each of the pump assemblies and a common fluid outlet line to which fluid, which has passed to and over a respective one of the heat transfer portions of the fuel pump assemblies, is delivered once the respective sleeve has been cooled by the fluid flow. It will be appreciated that preferred and / or optional features of the first aspect of the invention may be included in the second aspect of the invention also. Brief Description of the Drawings In order that the present invention may be more readily understood, embodiments will now be described, by way of non-limiting example, with reference to the following figures, in which: Figure 1 is a schematic view of a known pump assembly of a fuel system of an internal combustion engine; Figure 2 is a first schematic cross-sectional view of a pump assembly in accordance with a first embodiment; Figure 3 is a second schematic cross-sectional view of a pump assembly in accordance with the first embodiment shown in a different plane to that shown in Figure 2; Figure 4 is a perspective view of a sleeve for use in the pump assembly of Figures 2 and 3 in accordance with another embodiment; Figure 5 is a cross-sectional perspective view of the sleeve shown in Figure 4; Figure 6 is a perspective view of a sleeve for use in the pump assembly of Figures 2 and 3 in accordance with another embodiment; Figure 7 is a cross-sectional perspective view of the sleeve shown in Figure 6; and Figure 8 is a schematic diagram of a system comprising multiple pump assemblies in accordance with the embodiment shown in any of Figures 2 to 7. Detailed Description of Embodiments of the Invention To provide context for the invention, Figure 1 shows a portion of a pump assembly 2 for a fuel system in a simplified schematic form. The pump assembly 2 is configured to deliver a supply of pressurised fuel to an accumulator of the fuel system, such as a common fuel rail (not shown). Typically, the fuel system delivers pressurised fuel to the engine cylinders of a compression ignition internal combustion engine via fuel injection equipment (not shown), which receives pressurised fuel from the common rail. The pump assembly 2 is operated by the rotation of a camshaft 4, which may be driven by cooperation with an engine driveshaft (not shown), for example. The pump assembly 2 comprises an elongate compression chamber 6 formed within a pump housing 8 of the pump assembly 2 and a correspondingly shaped plunger 10 configured to move within the compression chamber 6 in a reciprocating linear motion. The plunger 10 reciprocates within a plunger bore 12 defined within the pump housing 8, with the compression chamber 6 being defined at one end of the plunger bore 12. Accordingly, the compression chamber 6 is configured to receive the plunger 10 via the plunger bore 12 in the pump housing 8, the plunger bore 12 extending from the compression chamber 6 to a cavity 16 in which the rotating camshaft 4 resides. When the pump 2 is assembled, the plunger 10 extends from the abutting camshaft 4, through the plunger bore 12, and into the compression chamber 6. The plunger 10 comprises a first end proximal to the cavity 16 and a second end proximal to the compression chamber 6. For the purpose of achieving reciprocating motion, the plunger 10 comprises an intermediate drive member 18 in the form of a roller-tappet assembly, also known as a lifter, at the first end for interfacing with the rotating camshaft 4. The roller tappet assembly 18 comprises both a roller 22 and a tappet 24 and is configured to ride a cam member 20 of the camshaft 4 as the camshaft 4 rotates about its longitudinal axis in the manner shown by arrow A. In this manner, the rotational motion of the camshaft 4 is converted into reciprocating linear motion of the plunger 10, wherein the plunger 10 is urged in alternating first and second opposed directions, out of and into, the compression chamber 6 via the bore 12, respectively. In other embodiments, an intermediate drive member 18 of alternative form may be used, for example including a shoe instead of the tappet 24. In use, fuel at relatively low pressure is supplied to the compression chamber 6 for pressurisation as the plunger 10 reciprocates. The fuel is supplied to the compression chamber 6 from a low pressure fuel source (not shown). Typically, the fuel is supplied through an inlet supply line 26 provided in the pump housing 8, wherein an inlet valve 28 is fitted to the supply line 26. The inlet valve 28 may take the form of an inlet metering valve which may be used to control the volume of fuel that is supplied to the compression chamber 6 for pressurisation in a given pump cycle. Once fuel is pressurised to a relatively high level within the compression chamber 6, it is supplied through an outlet supply line 31, provided in the pump housing 8, to the downstream parts of the fuel system and the common rail via an outlet valve 30. In accordance with known arrangements, the plunger 10 is shaped and dimensioned to achieve a close tolerance clearance fit within the plunger bore 12 and, correspondingly, the compression chamber 6. While most of the fuel in the compression chamber 6 is pushed through the outlet valve 30 during a pumping stroke, some fuel typically leaks between the plunger bore 12 and the plunger 10. To avoid a build-up of fuel in this region, a drain or return line 34 is provided which is configured to guide any leaked fuel out of the compression chamber 6 for recirculation to the low pressure source or fuel tank. The return line 34 opens into the plunger bore 12 at an axial location sufficiently far from the inlet supply line 26 that the plunger 12 covers the opening and substantially prevents fluid from flowing between the compression chamber 6 and the return line 34 throughout the full pumping cycle. A seal assembly may be mounted within the plunger bore 12 through which the plunger extends. The seal assembly takes the form of an annular seal assembly and includes a first annular seal 36 provided in the plunger bore 12. The first annular seal 36 is configured to prevent fuel from leaking out of the compression chamber 6, through the plunger bore 12, and into the cavity 16. In the example shown in Figure 1, the seal assembly also includes a second annular seal 38 provided in the bore 12, disposed axially below the first annular seal 36. The second annular seal 38 is configured to prevent lubricating oil applied to the camshaft 4 and the roller tappet assembly 18 from leaking into the compression chamber 6 via the plunger bore 12. Accordingly, each annular seal 36, 38 extends fully around the outer surface of the plunger 10 so as to fill a gap between the plunger 10 and the plunger bore 12. As such, each seal 36, 38 may be annular depending on the shape of the plunger 10 and the plunger bore 12. In some embodiments, the first annular seal 36 and the second annular seal 38 may be formed together to form one elongate seal. The pump assembly 2 further comprises an anti-rotation pin 25 and the tappet 24 may comprise an axial groove configured to receive the anti-rotation pin 25 such that, as the tappet 24 undergoes reciprocal axial motion within the sleeve 40, the orientation of the tappet remains constant. It is noted that, given recent developments in internal combustion engine design, modern pump housings, and therefore the tappet bores, may be manufactured from aluminium in order to reduce the mass of the engine. In these more advanced engines, the roller tappet assembly continues to be made out of steel given the preferable durability of steel. During the pump cycle, the plunger 10, the roller tappet assembly 18, and the pump housing 8 increase in temperature and undergo thermal expansion. During the thermal expansion, the tappet bore 13 and the tappet 24 increase in diameter. However, given that the thermal expansion coefficient of steel is approximately half of the thermal expansion coefficient of aluminium, a gap is formed between the tappet and the tappet bore, which may lead to lubricating oil leakage. Moreover, in some circumstances, the pump housing is not necessarily manufactured by the same manufacturer as the tappet. Therefore, it may be advantageous to be able to provide one tappet suitable for use in both aluminium and steel bores. Embodiments of the present invention provide a fuel pump assembly 200 designed such that it may be used in both an aluminium and / or a steel pump housings 8 and reduce the leakage of oil past the roller tappet assembly 18. Figure 2 shows a cross-sectional view of a pump assembly 200 according to a first embodiment in which a sleeve 40 is disposed between the tappet bore 13 in the pump housing 8 and the tappet 24 of the roller tappet assembly 18. The housing 8 may be formed from aluminium and so too is the sleeve 40. The tappet 24 may be made from steel. Here, the tappet bore 13 comprises a sleeve bore portion 130, which is of reduced diameter compared with an upper portion 132 of the tappet bore of relatively large diameter. The upper tappet bore portion 132 and the sleeve bore portion 130 together define a step 134 in the tappet bore 13. The sleeve 40 is in an interference fit configuration with an inner surface 130a of the sleeve bore portion 130 to prevent lubricating oil from leaking from the cavity 16 into the compression chamber 6 via the tappet bore 13, in use, and extends from the cavity 16 at its lower end to the step 134 at its upper end. Moreover, the pump housing 8 can be seen to comprise a tappet oil feed line 50. The tappet oil feed line 50 is configured to provide lubricating fluid, e.g. oil, to an outer surface of the tappet 24. It will be understood that, by having the sleeve 40 in an interference fit configuration with the inner surface 130a of the sleeve bore portion 130, the lubricating fluid provided to the outer surface of the tappet 24 is prevented from leaking past the step 134. The sleeve 40 comprises an annular flange 46 at its upper end. The annular flange 46 comprises a lower radial surface 46b which engages with the step 134 to locate the sleeve 40 within the sleeve bore portion 130. The sleeve 40 further comprises a sliding interface surface 40a, a radially extending lower surface 40b, which defines the bottom of the sleeve 40, and a radially extending upper surface 40c which defines the top of the sleeve 40. The sliding interface surface 40a of the sleeve 40 achieves a sliding fit with the tappet 24 and therefore defines a sliding interface surface of the sleeve 40. The tappet 24 is a close sliding fit within the sleeve 40 and is configured for reciprocal axial motion within the sleeve 40. In this respect, the interface between the sleeve 40 and the tappet 24 is the same as in a conventional arrangement where the tappet 24 is sliding directly within the tappet bore 13. The sleeve 40 may comprise a hole 41 therethrough configured such that the anti-rotation pin 25 extends through the hole 41 and into the axial groove of the tappet 24. Advantageously, in this embodiment the orientation of both the roller tappet assembly 18 and the sleeve 40 are maintained constant throughout the reciprocal axial motion of the tappet 24 through cooperation between the anti-rotation 25 pin and the axial groove of the tappet 24. Moreover, the anti-rotation pin 25 extending through the hole 41 in the sleeve 40 prevents the sleeve 40 from moving axially in the sleeve bore portion 130 during axial motion of the roller tappet assembly 18. At this point, it is noted that other alternative arrangements configured for preventing axial motion of the sleeve 40 and maintaining constant sleeve 40 and roller tappet assembly 18 orientations are envisaged and the above example is not intended to limit the scope of the appended claims. The sleeve 40 also comprises a heat transfer portion 43 defined by an axially-extending annular groove 42 formed in the sleeve 40. The annular groove 42 in the sleeve 40 divides the axial outer surface of the sleeve 40 into an upper interface surface 40d and a lower interface surface 40e wherein each of the upper and lower interface surfaces 40d, 40e are in an interference fit with a respective region of the sleeve bore portion 130 and the upper and lower interface surfaces 40d, 40e are separated by the heat transfer portion 43. The annular groove 42 of the sleeve 40 defines an annular groove volume 44 between the sleeve 40 and the first plunger bore portion 120 which extends axially from the bottom of the upper interface surface 40d to the top of the lower interface surface 40e. In the cross section of Figure 3 specifically, it can be seen that the pump housing 8 comprises a fluid inlet 52 and a fluid outlet 54. The annular groove 42 in the sleeve 40 is configured such that the fluid inlet 52 and the fluid outlet 54 are in fluid communication with one another via the annular groove 42. The sleeve bore portion 130 comprises a first axial groove 48a which is in fluid communication with the fluid inlet 52 and a second axial groove 48b which is in fluid communication with the fluid outlet 54. The first and second axial grooves 48a, 48b have respective axial lengths which are greater than the axial length of the annular groove 42 in the sleeve 40 such that the first and second axial grooves 48a, 48b extend axially both above and below the annular groove 42. In other words, the pump assembly 200 comprises a fluid flow path wherein fluid enters the sleeve bore portion 130 through the fluid inlet 52, flows into the annular groove 42 of the sleeve 40 through the first axial groove 48a in the sleeve bore portion 130, and exits the sleeve bore portion 130 through the fluid outlet 54 via the second axial groove 48 in the sleeve bore portion 130. The upper and lower interface surfaces 40d, 40e of the sleeve 40, and their cooperation with the sleeve bore portion 130, substantially prevent any fluid from leaking out of the flow path defined by the annular groove 42 of the sleeve 40, past the sleeve 40 and into either the cavity 16 or the compression chamber 6. Advantageously, the fluid provided to the groove 42 via the fluid inlet 52 provides a cooling flow over and around the full circumference of the sleeve 40. In one embodiment, the fluid may be fuel which enters the sleeve bore portion 130 at a lower temperature and exits the sleeve bore portion 130 at a higher temperature, having reduced the temperature of the sleeve 40 as it passes over and around the sleeve 40. Advantageously, reducing the temperature of the sleeve 40 will reduce the gap formed between the sleeve 40 and the tappet 24 during any thermal expansion of the sleeve 40, the sleeve bore portion 130 of the tappet bore 13, and the tappet 24, in use. As described in relation to Figures 2 and 3, embodiments of the pump assembly 2 reduce the leakage of oil from the tappet bore 13 into the cavity 16 by providing a sleeve 40 between the tappet bore 13 and the tappet 24 and providing a fluid flow to cool that sleeve 40. Figures 4 to 7 show embodiments of the sleeve 40 configured to increase the surface area of the heat transfer portion 43 of the sleeve 40 in order to increase the rate at which the sleeve 40 is cooled by the fluid flow. Figures 4 and 5 show an embodiment of the sleeve 40 wherein the heat transfer portion 43 comprises a plurality of annular grooves 42, rather than the single annular groove 42 of Figures 2 and 3. Each of the plurality of grooves 42 is configured to provide an annular groove volume 44 between the sleeve 40 and the sleeve bore portion 130 of the tappet bore 13. Between each of the annular grooves 42 the diameter of the sleeve 40 is equal to the diameter of each of the upper and lower interface surfaces 40d, 40e In other words, between each of the annular grooves 42 the sleeve 40 comprises a radially projecting region which defines an intermediate interface surface 40f (only one of which is identified) which is in an interference fit with the adjacent region of the sleeve bore portion 130, i.e. each of the plurality of annular grooves 42 is spaced apart by an interface portion which define, collectively, a second interference fit region with the sleeve bore portion 130, increasing the overall interference length of the sleeve 40 compared to the embodiment in Figures 2 and 3. Each of the plurality of annular grooves 42, provides a distinct, separate flow path between the first and second axial grooves 48a, 48b of the sleeve bore portion 130 as fluid flows between the inlet 52 and the outlet 54. Fluid enters the sleeve bore portion 130 from the inlet 52 and, via the first axial groove 48a of the sleeve bore portion 130, flows through each distinct flow path defined by the annular grooves 42 into the second axial groove 48b of the sleeve bore portion 130, and on to the outlet 54. Each of the grooves may be shaped to define a generally V-shaped groove having tapered side walls. The heat transfer portion 43 of the sleeve 40 extends axially between the upper interface surface 40d to the lower interface surface 40e. It will be appreciated that the heat transfer portion 43 may extend axially along a larger or smaller portion of the axial length of the sleeve 40. For example, the heat transfer portion 43 may extend over 50%, 80%, or any other suitable portion of the axial length of the sleeve 40. Moreover, in Figures 4 and 5, the heat transfer portion 43 is shown to comprise 11 annular grooves 42. However, it will be appreciated that the heat transfer portion 43 may comprise more or less than 11 annular grooves 42; for example, the heat transfer portion 43 may include 1, 4, 7, or any other suitable number of annular grooves 42. It will also be appreciated that the number of annular grooves 42 may depend on the axial length of the heat transfer portion 43. Adjusting the number of annular grooves 42 and the axial length of the heat transfer portion 43 may change the cooling of the sleeve 40 and the extent of cooling which can be achieved. For example, having the heat transfer portion 43 extend axially over a larger portion of the sleeve 40 may increase the rate of heat transfer but reduce the rigidity of the sleeve 40. Therefore, the number of annular grooves 42 and the axial length of the heat transfer portion 43 may be implementation dependent and determined through an optimisation analysis of the cooling properties required for each implementation. Figures 6 and 7 show another embodiment of the sleeve 40. As described previously regarding Figures 2 and 3, the sleeve 40 comprises an upper interface surface 40d, a lower interface surface 40e, and a heat transfer portion 43 defined axially therebetween comprising a single annular groove 42 defining a groove volume 44. However, in Figures 6 and 7, the heat transfer portion 43 also comprises a plurality of radially projecting fins 56 disposed within the groove volume 44 in the sleeve bore portion 130. Advantageously, the inclusion of fins 56 in the groove volume 44 increases the surface area of the heat transfer portion 43 of the sleeve 40. Increasing the surface area of the heat transfer portion 43 of the sleeve 40 will increase the rate at which the sleeve 40 is cooled by the fluid flow between the inlet 52 and the outlet 54. It will be appreciated that the heat transfer portion 43 may extend axially along larger or smaller portions of the axial length of the sleeve 40 and comprise any suitable number of fins 56. For example, the heat transfer portion 43 may extend over 50%, 80%, or any other suitable portion of the axial length of the sleeve 40. Additionally, the number of fins 56 disposed in the groove volume 44 may depend on the axial length of the groove 40. Adjusting the axial length of the heat transfer portion 43 or the number of fins 56 may change the extent of cooling of the sleeve 40. For example, having the heat transfer portion 43 extend axially over a larger portion of the sleeve 40 may increase the rate of heat transfer but reduce the rigidity of the sleeve 40. Therefore, the number of fins 56 and the axial length of the heat transfer portion 43 may be implementation dependent and determined through an optimisation analysis of the properties required for each implementation. In any embodiment, whether described or otherwise, an advantage is provided by the provision of the cooled sleeve 40 in that differences in thermal expansion between the tappet 24 and the tappet bore 13, especially when these are formed from different materials, can be reduced. Without the use of the sleeve 40 and the cooling flow, the different thermal expansivity of the tappet 24 and the tappet bore 13 can otherwise lead to oil leakage problems around the tappet 24 increasing as the temperature increases in operation. Figure 8 shows a schematic diagram of a system 800 comprising multiple pump assemblies 200. In this embodiment, fuel flows into the annular groove 42 from the fluid inlet 52 via the first axial groove 48a. The fuel then flows from the first axial groove 48a to the second axial groove 48b via the annular groove 42. It is noted that the fuel may flow in any direction, e.g. clockwise or anticlockwise as shown in Figure 8, through the annular groove 42. When the fuel enters the annular groove 42, it is at a lower temperature than the sleeve 40. As the fuel flows through the annular groove 42, it will reduce the temperature of the sleeve 40 and, in turn, the fuel will increase in temperature. The fuel, now at a higher temperature, flows out of the annular groove 42 through fluid outlet 54 via the second axial groove 48b. As the sleeve 40 reduces in temperature, its inner diameter, defined by the sliding interface surface 40a, will decrease and the difference between the inner diameter of the sleeve 40 and the outer diameter of the tappet 24 will be reduced. The pump system 800 is shown to comprise three pump assemblies 200, however, it will 5 be appreciated that the system 800 may comprise any suitable number of pump assemblies 200. In this embodiment, the three pump assemblies 200 are supplied with a fuel flow via a common fuel supply line 82, which provides the fuel for cooling the sleeve 40 to the fuel inlet 52. Moreover, the fluid outlets 54 of the three pump assemblies 200 communicate with a common fuel outlet line 84. After fuel has flowed out from the groove 10 42 through the fuel outlet 54, the fuel then flows through the common fuel outlet line 84. The common fuel inlet and outlet lines 82, 84 therefore form a cooling flow path which circulates the cooling fluid for all three of the fuel pump assemblies. It will be appreciated that various modifications may be made to the aforementioned 15 embodiments without departing from the scope of the invention as set out in the accompanying claims.

Claims

1. A fuel pump assembly (200) for pressurising fuel in a fuel system of an internal combustion engine, the fuel pump assembly (200) comprising:a pump housing (8);a plunger (10) configured for reciprocal motion within a plunger bore (12), the plunger (10) comprising a first end and a second end, anda roller tappet assembly (18) configured for reciprocal motion within a tappet bore (13), comprising a roller (22) and a tappet (24), disposed at the first end of the plunger (10); anda sleeve (40) disposed between an inner surface (13a) of the tappet bore (13) and the tappet (24) so as to define a sliding interface surface for the tappet (24), the sleeve (40) further defining a heat transfer portion (43) which serves to aid the transfer of heat away from the sliding interface surface (40a); and wherein the tappet bore (13) is provided with a fluid inlet (52) and a fluid outlet (54) for allowing fuel to be delivered to and flow over the heat transfer portion (43) to cool the sleeve (40) in use.

2. The fuel pump assembly (200) as claimed in claim 1, the sleeve (40) comprising a groove (42) to define the heat transfer portion (43), the groove (42) being configured to define a fluid flow path between the fluid inlet (52) and the fluid outlet (58).

3. A fuel pump assembly (200) according to claim 2, wherein the groove (42) is an annular groove (42) formed in the circumference of the sleeve (40).

4. A fuel pump assembly (200) according to any of claims 1 to 3, wherein the tappet bore (13) comprises a first axial groove (48a) in fluid communication with the fluid inlet (52) and a second axial groove (48b) in fluid communication with the fluid outlet (54), and wherein the first and second axial grooves (48a, 48b) communicate with the heat transfer portion (43).

5. A fuel pump assembly (200) according to any of claims 1 to 4, wherein the sleeve (40) comprises a plurality of annular grooves (42) configured to provide a plurality of fluid flow paths between the fluid inlet (52) and the fluid outlet (54).

6. A fuel pump (200) according to any of claims 1 to 5, wherein the tappet bore (13) is a stepped bore such that it comprises a sleeve bore portion (130) of reduced diameter compared to an upper portion (132) of the tappet bore (13) of larger diameter.

7. A fuel pump assembly (200) according to claim 6, wherein the sleeve (40) comprises an upper interface surface (40d) and a lower interface surface (40e) to define a first interference fit with the sleeve bore portion (130), and wherein the upper and lower interface surfaces (40d, 40e) are separated by the heat transfer portion (43).

8. A fuel pump assembly (200) according to claim 7 when dependent on claim 5, wherein each of the plurality of annular grooves is spaced apart by an interface portion which collectively define a second interference fit region with the sleeve bore portion (130).

9. A fuel pump assembly (200) according to claim 7, wherein the heat transfer portion (43) comprises a plurality of radially projecting fins (56) between the upper and lower interface surfaces (40d, 40e).

10. A fuel pump assembly (200) according to any of claims 1 to 9, wherein the pump housing (8) and the sleeve (40) are formed from the same material.

11. A fuel pump assembly (200) according to claim 10, wherein the pump housing (8) and the sleeve (40) are formed from aluminium and the tappet (24) is formed from steel.

12. A pump system (800) comprising at least two fuel pump assemblies (200) according to any of claims 1 to 11, comprising a common fluid supply line (82) which delivers fluid to the fluid inlet of each of the pump assemblies and a common fluid outlet line (84) to which fluid, which has passed to and over a respective one of the heat transfer portions of the fuel pump assemblies, is delivered once the respective sleeve has been cooled by the fluid flow.IntellectualPropertyOfficeApplication GB2418350.1Search report under Section 17 of the Patents Act 1977Date search completed: 14 May 2025Claims searched: 1-12International classificationSubclass and subgroup Valid from F02M59 / 10 01 / 01 / 2006 F02M59 / 44 01 / 01 / 2006 F16H53 / 06 01 / 01 / 2006Field of searchWorldwide search of patent documents classified in the following areas of the IPC:F02M, F16H, F04BDatabases used in the preparation of this search report:SEARCH-PATENTDocuments considered to be relevantPatent literatureCategory Relevant Document of relevanceclaimsA - CN 117404223 A (CHERY AUTOMOBILE CO LTD), Please see abstract and figures 1 and 3 in particular, taking note of tappet 2, inlet 13 and discharge hole 14. A - DE 102018214200A1 (BOSCH GMBH ROBERT), Please see abstract and figure 3, taking note of tappet 48, sleeve 42 and fluid passages 45,13,11 and 25. A - US 2007 / 0128058 A1 (KITAMURA), Please see figure 3 and paragraph [0073] in particular, taking note of lifter 38, lifter guide 27 and though holes 44,45. A - WO 2019 / 151038 A1 (ISUZU MOTORS LTD), Please see abstract and figure 8, taking note of tappet 52, cylinder portion 31 and oil passage 70.Non-patent literatureCategory Relevant claims Document of relevanceCategoriesLetter or DescriptionsymbolDocument indicating lack of novelty or inventive step.Letter or symbol Description Y Document indicating lack of inventive step, if combined with another document of the same category. & Member of the same patent family. A Document indicating technological background. P Document published on or after the priority date but before the fling date of the present application. E Earlier application published on or after the filing date of the present application.

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