Fuel pump and sealing arrangement

Abstract

A high-pressure fuel pump comprising a pump housing or body which defines a pumping chamber, a fuel inlet which allows low-pressure fuel into said pumping chamber, a fuel outlet which allows high-pressure fuel out of said pumping chamber, and a plunger bore which extends along an axis and opens into said pumping chamber The fuel pump further comprises a pumping plunger which reciprocates within said plunger bore along said axis such that reciprocation of said pumping plunger within said plunger bore increases and decreases a volume of said pumping chamber, wherein the pump housing has a sleeve member which defines the plunger bore at least in part. The fuel pump further comprises a plunger sealing ring arrangement for providing a seal between an outer surface of the plunger and the sleeve member. The plunger sealing ring arrangement comprises a sealing ring groove provided in the sleeve member and a sealing ring accommodated in the sealing ring groove. One benefit of this arrangement is that the sealing ring remains stationary with respect to the plunger bore during operation. This means that any fuel that moves past the sealing ring to a lower region of the bore is not 'pumped' by the reciprocating action of an alternative configuration having a sealing ring that is provided in the plunger itself.

Description

[0001] FUEL PUMP AND SEALING ARRANGEMENT

[0002] Technical Field

[0003] This disclosure relates generally to a fuel pump, more particularly to a high-pressure fuel pump which provides fuel at high-pressure for injection directly into a combustion chamber of an internal combustion engine. The fuel pump is of a type having a pumping plunger which reciprocates within a plunger bore of a pump housing to pressurize fuel within a pumping chamber defined in the pump housing.

[0004] Background

[0005] Modern gasoline-powered internal combustion engines typically use either a port fuel injection (PFI) arrangement or a gasoline direct injection (GDI) arrangement. In a PFI arrangement, fuel is injected into an air intake manifold of the engine at a relatively low pressure (typically below about 500kPa) and subsequently the fuel-air mixture flows into the combustion chambers via associated inlet valves whereas in a GDI engine fuel is injected directly into combustion chambers at a relative high pressure (typically above 14Mpa).

[0006] Due to the high-pressure requirements, GDI systems use high pressure fuel pumps (usually engine-driven) to boost the pressure of fuel compared to the pressure which can typically be achieved by electrically-driven fuel pumps.

[0007] In order to elevate the fuel pressure to the magnitude needed for direct injection, it known to use a piston- or plunger-type high-pressure fuel pump which is driven by a camshaft of the internal combustion engine. A known high pressure fuel pump is exemplified in W02018009390A1. In overview, such a fuel pump includes a pumping plunger that is movable within a plunger bore defined by a pump housing. Movement of the pumping plunger is driven by a camshaft of the internal combustion engine such that each cycle of the pumping plunger increases and decreases the volume of a pumping chamber. Suitable valving is provided to admit low pressure fuel into the pumping chamber and to permit high pressure fuel to be discharged from the pumping chamber where it can then be delivered to the combustion chambers of the engine.

[0008] In such a fuel pump, it is known to include a ring-shaped seal carried by the pumping plunger and which seals against the plunger bore to minimise leakage of fuel through the tight clearance between the plunger and the plunger bore. In W02018009390A1 , a ring-shaped seal having a generally rectangular cross section is used.

[0009] It is with a view to enhancing the functionality of the plunger sealing arrangement that the examples of the invention have been devised.

[0010] Summary of the Invention

[0011] Against this background, the invention provides a high-pressure fuel pump comprising a pump housing or body which defines a pumping chamber, a fuel inlet which allows low-pressure fuel into said pumping chamber, a fuel outlet which allows high-pressure fuel out of said pumping chamber, and a plunger bore which extends along an axis and opens into said pumping chamber. The fuel pump further comprises a pumping plunger which reciprocates within said plunger bore along said axis such that reciprocation of said pumping plunger within said plunger bore increases and decreases a volume of said pumping chamber, wherein the pump housing has a sleeve member which defines the plunger bore at least in part. The fuel pump further comprises a plunger sealing ring arrangement for providing a seal between an outer surface of the plunger and the sleeve member. The plunger sealing ring arrangement comprises a sealing ring groove provided in the sleeve member and a sealing ring accommodated in the sealing ring groove.

[0012] One benefit of this arrangement is that the sealing ring remains stationary with respect to the plunger bore during operation. This means that any fuel that moves past the sealing ring to a lower region of the bore is not ‘pumped’ by the reciprocating action of an alternative configuration having a sealing ring that is provided in the plunger itself. It is believed that this pumping effect can cause dramatic pressure variations in the volume of fuel that leaks to a lower region of the pump housing which can lead to cavitation in the volume of trapped fuel which may contribute to degradation of the sealing ring in configurations where it is carried by the plunger. Configuring the sealing arrangement so that the sealing ring is carried instead by the sleeve member is believed to avoid this issue.

[0013] The sealing ring and the sealing ring groove may be configured in various ways. For example, in one example the sealing ring groove is annular in form and extends around the entre circumference of an internal surface of the sleeve member which provided a portion of the plunger bore.

[0014] The circular shape of the sealing ring groove may lie in a place that is perpendicular to a major axis of the plunger. In principle the sealing ring groove may instead be formed such that it lies in a plane that is not perpendicular to the plunger axis, i.e. tilted or slanted with respect thereto.

[0015] In principle, the sealing ring groove may be formed of more than one groove portion. Each groove portion may extend part way about the circumference of the internal surface of the sleeve member. Each groove portion may accommodate a corresponding part of the sealing ring, being composed of several sealing ring portions.

[0016] The sealing ring may be configured in different ways. For example, the sealing ring could have a circular cross section. That cross section could be uniform the entire way about the annular length of the sealing ring. That cross section may be elliptical or rectilinear, for example rectangular. The cross section geometry may change from circular / elliptical to rectilinear at different points around the sealing ring.

[0017] In one example, the cross section of the sealing ring may be rectangular. The geometry of the cross section may substantially match the cross section geometry of the sealing ring groove so the sealing ring fits closely within the sealing ring groove. In other examples, the cross section geometry of the sealing ring may be configured to that it fits relatively loosely within the sealing ring groove. This may be such that the sealing ring can move in the axial direction slightly within the sealing ring groove.

[0018] In one example, particularly relevant to the version of the sealing ring having a rectilinear cross section, the part of the sealing ring (i.e. the radially outer surface) that faces the opposing surface of the sleeve member (i.e. the radially inner surface of the plunger bore) may be shaped in various ways. For example, the radially outer surface may be designed with different profiles. For example, in the case of a sealing ring having a rectangular cross section, the radially outer surface of the sealing ring would be flat when considered in a plane parallel to the axis of the plunger. That same surface would be curved when considered in a direction perpendicular to the plunger axis. However, other radial surface profiles are envisaged, such as a knife edge seal or a crenelated surface.

[0019] The sealing ring groove has an upper surface, a lower surface and a base surface extending between the upper surface and the lower surface. In one example, the upper, lower, and base surfaces are provided all by the insert member. However, in another example at least one of the upper surface, the lower surface and the base surface is provided by another component of the fuel pump. That other component may be the pump housing of the fuel pump. In other examples, the other component may be a retention member configured to retain the sealing ring within the sealing ring groove. For example, where the sealing ring groove is formed on a lower end of the pump housing (that is, distal from a pumping chamber of the pump housing), the retention member may serve to hold the sealing ring within the sealing ring groove. The retention member therefore provides the lower surface of the sealing ring groove in this instance. The retention member may be an annular member. The annular member may be configured to completely encircle the pumping plunger and to define a central aperture through which the pumping plunger may pass.

[0020] The pump housing may provide one of the side surfaces of the sealing ring groove (i.e. one of the upper and lower surfaces. This may be the case where the sealing ring groove is provided at an upper end of the insert member.

[0021] The sealing ring, and therefore also the sealing ring groove, may be located towards an end of the insert member. For example, the sealing ring may be located at a distance from one end of the insert member that is less than 40% of the total axial length of the insert member. In other examples, the sealing ring may be located at a distance that is less than 30%, or 20% or 10% of the total axial length of the insert member. The sealing ring and, thus, the sealing ring groove, may be located nearer to the upper end of the insert member and further away from the lower end of the sealing ring member. Conversely, the sealing ring may be located closer to the lower end of the inert member. In such a case, the position of the sealing ring towards the lower end of the insert member may mean that there is a greater degree of pressure drop along the clearance between the insert member and the pumping plunger which reduces pressure on the sealing ring and improves longevity.

[0022] In one example, the sealing ring arrangement may comprise a single sealing ring. However, in other examples the sealing ring arrangement may comprise at least a first sealing ring element and a second sealing ring element. The sealing ring elements may be configured so that they are position side by side to one another. However, in other examples, the sealing ring elements may be configured so that at least a portion of the first sealing ring element is nested within the second sealing ring element.

[0023] The first sealing ring element may comprise an upper surface, a lower surface, and a first outer peripheral surface which engages the plunger bore, and the second sealing ring element may comprise an upper surface, a lower surface and an outer peripheral surface which engages the plunger bore. Therefore, both of the sealing ring element may provide surfaces that engage the plunger bore. The nested arrangement of the sealing ring elements may provide improved contact force between the sealing ring arrangement and the plunger bore.

[0024] In an example configuration, the first sealing ring element may further comprise an inner peripheral surface which engages the base surface of the sealing ring groove and a second outer peripheral surface that is shaped so as not to engage the plunger bore. The second sealing ring element may further comprise an inner peripheral surface that is shaped to oppose the second outer peripheral surface of the first sealing ring element. In this sense, the inner peripheral surface of the second sealing ring element may be shaped to correspond to the second outer peripheral surface of the first sealing ring element. Those mating surfaces may be frustoconical in form.

[0025] In the case where there are first and second sealing ring elements, at least one of those sealing ring elements may have a discontinuity or split in its circumferential length, so as to provide a split ring. Where both sealing ring elements are provided with circumferential splits, they may be offset from one another in the radial direction.

[0026] The two sealing ring elements may be made of the same or different materials. For example the first sealing ring may be based on a thermoplastic polymer, optionally PTFE, and may contain a filler composite, such as carbon fibre, glass fibre, or similar. Other suitable materials for the first and / or second sealing ring elements may be a PEEK based material.

[0027] Brief Description of the Drawings

[0028] Figure 1 is a schematic view of a fuel system including a high-pressure fuel pump in which examples of the invention may be incorporated,

[0029] Figure 2 is a more detailed view of the fuel pump in Figure 1 shown a portion of a pumping plunger within a respective plunger bore of a pump housing, the pumping plunger incorporating a known example of a sealing ring arrangement,

[0030] Figure 3 is a view of a portion of a fuel pump, similar to that in Figure 2, but which shows an example of a sealing ring arrangement incorporating an example of the invention; Figure 4 is another example of a portion of a fuel pump, similar to that of Figure 3 but having some configurational differences;

[0031] Figure 5 is another example of a portion of a fuel pump, similar to that of Figure 3 but having some configurational differences;

[0032] Figures 6a to 6c, and Figure 7, show example cross section forms of sealing rings that may be used in the fuel pump;

[0033] Figure 8 shows a further aspect of the fuel pump and associated pumping plunger and components.

[0034] Detailed description

[0035] With reference to FIG. 1 , a fuel system 10 for an internal combustion engine 12 is shown in which aspects of the examples of the invention may be incorporated. It should be noted that FIG. 1 shows the fuel system 10 in schematic form so the various components described here and shown in the Figure may not correspond to actual manufactured components, as the skilled person would appreciate.

[0036] Fuel system 10 generally includes a fuel tank 14 which holds a volume of fuel to be supplied to internal combustion engine 12 for operation thereof; a plurality of high-pressure fuel injectors 16 which inject fuel directly into respective combustion chambers (not shown) of internal combustion engine 12; a low-pressure fuel pump 20; and a high-pressure fuel pump 22 where the low-pressure fuel pump 20 draws fuel from fuel tank 14 and elevates the pressure of the fuel for delivery to high-pressure fuel pump 22 where high-pressure fuel pump 22 further elevates the pressure of the fuel for delivery to high-pressure fuel injectors 16.

[0037] As an example, the low-pressure fuel pump 20 may elevate the pressure of the fuel to about 500 kPa or less and high-pressure fuel pump 22 may elevate the pressure of the fuel to above about 14 MPa where pressures on the order of 40 MPa and above are envisaged to be realistic in practice.

[0038] While four high-pressure fuel injectors 16 have been illustrated, it should be understood that more or fewer fuel injectors may be provided as is consistent with known configurations of multi-cylinder engines. As shown, the low-pressure fuel pump 20 may be provided within fuel tank 14. However, the low-pressure fuel pump 20 may alternatively be provided outside of fuel tank 14. Low-pressure fuel pump 20 may be an electric fuel pump. A low-pressure fuel supply passage 24 provides fluid communication from low-pressure fuel pump 20 to high-pressure fuel pump 22. High- pressure fuel pump 22 will be described in greater detail in the paragraphs that follow.

[0039] High-pressure fuel pump 22 includes a pump housing, or body, 30 which defines a pumping chamber 32 and a plunger bore 34 which opens into pumping chamber 32 such that plunger bore 34 extends along an axis 36. Pump housing 30 also includes a fuel inlet 38 in fluid communication with low-pressure fuel supply passage 24 such that fuel inlet 38 selectively allows low-pressure fuel from low-pressure fuel pump 20 to enter pumping chamber 32 as will be described in greater detail later. Pump housing 30 also defines a fuel outlet 40 which selectively allows high-pressure fuel to exit pumping chamber 32 as will be described in greater detail later. While pump housing 30 has been illustrated schematically as single-piece construction, it should be understood that pump housing 30 may comprise two or more pieces which are joined together to provide the features described herein, by way of non-limiting example only, a tubular insert may be provided within pump housing 30 such that the tubular insert defines plunger bore 34 or fuel inlet 38 may be provided as a feature of a pulsation damper cup (not shown) which houses a pulsation damper (also not show) for minimizing pressure pulsation in the fuel generated during operation.

[0040] High-pressure fuel pump 22 also includes a pumping plunger 42 located within plunger bore 34 such that pumping plunger 42 is able to reciprocate within plunger bore 34 along axis 36. Pumping plunger 42 is reciprocated within plunger bore 34, by way of non-limiting example only, by a camshaft 44 of internal combustion engine 12. Pumping plunger 42 is attached to (in contact with) a cam follower 46 which follows the profile of camshaft 44. Cam follower 46 is axially guided within a cam follower bore 48 of pump housing 30 such that a return spring 50 is compressed axially between pump housing 30 and cam follower 46 to maintain cam follower 46 in contact with camshaft 44 as camshaft 44 rotates. While cam follower 46 has been embodied as being guided within cam follower bore 48 of pump housing 30, it should now be understood that cam follower 46 may alternatively be guided within a bore of internal combustion engine 12 that is not within pump housing 30. When camshaft 44, cam follower 46, and return spring 50 cause pumping plunger 42 to move downward as viewed in the figures, the volume of pumping chamber 32 is increased, thereby resulting in an inlet stroke. Conversely, when camshaft 44 and cam follower 46 cause pumping plunger 42 to move upward as viewed in the figures, the volume of pumping chamber 32 is decreased, thereby resulting in a pressure stroke. While not shown, it should be understood that a low-pressure seal may be provided to prevent fuel that has leaked past the clearance between pumping plunger 42 and plunger bore 34 from mixing with oil that lubricates internal combustion engine 12.

[0041] High-pressure fuel pump 22 also includes an inlet valve 52 which selectively opens to permit fuel to enter pumping chamber 32 from low-pressure fuel supply passage 24. Inlet valve 52 may be, by way of non-limiting example only, a solenoid operated valve which is controlled by a controller 54. Controller 54 may receive input from a pressure sensor 56 which supplies a signal indicative of the pressure of the fuel being supplied to high-pressure fuel injectors 16. As illustrated, a pressure sensor 56 may arranged to read the fuel pressure within a high- pressure fuel rail 58 which receives high-pressure fuel from fuel outlet 40 through a high- pressure fuel supply passage 60 such that high-pressure fuel rail 58 distributes high-pressure fuel to each of high-pressure fuel injectors 16. However, it should be understood that pressure sensor 56 may be positioned at other locations that are indicative of the pressure of the fuel being supplied to high-pressure fuel injectors 16. Controller 54 sends signals to inlet valve 52 to open and close inlet valve 52 as necessary to achieve a desired fuel pressure at pressure sensor 56 as may be determined by current and anticipated engine operating demands. When inlet valve 52 is opened while pumping plunger 42 is moving to increase the volume of pumping chamber 32, i.e. when inlet valve 52 is moving downward as viewed in the figures, fuel from low-pressure fuel supply passage 24 is allowed to flow into pumping chamber 32 through fuel inlet 38.

[0042] High-pressure fuel pump 22 also includes an outlet valve 62 which selectively opens to permit fuel to exit pumping chamber 32 to high-pressure fuel supply passage 60. Outlet valve 62 may be a spring-biased valve which opens when the pressure differential between pumping chamber 32 and high-pressure fuel supply passage 60 is greater than a predetermined threshold. Consequently, when camshaft 44 and cam follower 46 cause pumping plunger 42 to decrease the volume of pumping chamber 32, the fuel within pumping chamber 32 is pressurized. Furthermore, when the pressure within pumping chamber 32 is sufficiently high, outlet valve 62 is urged open by the fuel pressure, thereby causing pressurized fuel to be supplied to high-pressure fuel injectors 16 through fuel outlet 40, high-pressure fuel supply passage 60, and high-pressure fuel rail 58. Additional reference will now be made to FIG. 2 which shows an enlarged portion of FIG. 1 , more particularly, an enlarged portion showing portions of pump housing 30 and pumping plunger 42. It should be noted that the general configuration of pump housing 30 and pumping plunger 42 are known.

[0043] In order to improve efficiency, particularly at low rotational speeds of camshaft 44 caused by low operating speeds of internal combustion engine 12, and to permit greater annular clearance between pumping plunger 42 and plunger bore 34, pumping plunger 42, which is cylindrical, is provided with a sealing ring groove 64 within which is located a sealing ring 66. It should be noted at this point that the sealing ring 66 is a known arrangement and is described here for context. The discussion will focus on a novel sealing ring arrangement later.

[0044] Pumping plunger 42 extends along axis 36 from a first end 42a, which is proximal to pumping chamber 32, to a second end 42b, which is distal from pumping chamber 32. Sealing ring groove 64 is annular in shape and concentric with pumping plunger 42 and plunger bore 34 such that sealing ring groove 64 extends radially inward from the outer periphery of pumping plunger 42 and such that sealing ring groove 64 is located between first end 42a and second end 42b. Sealing ring groove 64 extends along axis 36 from an upper shoulder 64a, which is proximal to first end 42a, to a lower shoulder 64b, which is distal from first end 42a such that upper shoulder 64a and lower shoulder 64b are separated from each other by a first distance 68 in a direction parallel to axis 36. Upper shoulder 64a and lower shoulder 64b are both transverse to axis 36 and may be perpendicular to axis 36 as illustrated in the figures. It should be noted that a chamfer or radius may join upper shoulder 64a with the outer periphery of pumping plunger 42 where this chamfer or radius is considered to be a portion of sealing ring groove 64. Similarly, a chamfer or radius may join lower shoulder 64b with the outer periphery of pumping plunger 42 where this chamfer or radius is considered to be a portion of sealing ring groove 64. A base 64c of the sealing ring groove 64 connects the two shoulders 64a, 64b

[0045] A diametric clearance 69 between pumping plunger 42 and plunger bore 34 (i.e. diameter of plunger bore 34 minus diameter of pumping plunger 42) is greater than 12 microns and less than 30 microns such that a portion of diametric clearance 69 is located between sealing ring groove 64 and first end 42a and extends for a second distance 70. In the illustrated example, the second distance 70 extends from first or upper surface 30a of the pump housing 30 to where the sealing ring groove 64 begins, that is upper shoulder 64a. Note that the first surface 30a surrounds the plunger bore 34 opening in the pump housing 30. In the illustrated example, the second distance 70 is at least four times first distance 68, and preferably at least eight times first distance 68, and such that another portion of diametric clearance 69 is located between sealing ring groove 64 and second end 42b and extends for a third distance 72 which is at least two times first distance 68 and is preferably at least four times first distance 68. In the illustrated example, the third distance 72 extends from second or lower surface 30b of the pump housing 30 to the sealing ring groove 64, i.e. the lower shoulder 64b of the sealing ring groove 64. Note that the second surface 30b surrounds the plunger bore 34 opening in the pump housing 30.

[0046] As illustrated in the figures, the portion of diametric clearance 69 that is located between sealing ring groove 64 and first end 42a may be continuous, however, may alternatively be discontinuous. By the term continuous, it will be appreciated that the adjacent portions of the plunger 42 and the bore 34 are uniformly cylindrical such that their diameters do not vary substantially along the axial direction such that the diametric clearance stays substantially the same along that portion, that is, continuous. Moreover, it will be noted that the exterior surface of the plunger is a plain cylinder between the sealing groove 64 and the first end 42a of the plunger. Thus, there are no other features between the sealing ring groove 64 and the plunger end 42a, such as pressure relief grooves and the like. Also, it is notable that the plunger end 42 a is circular and does not include spill features such as notches or flutes and the like.

[0047] Notably, in the illustrated example the plunger bore 34 is defined by a part of the pump housing 30. However, it is also envisaged that the bore 34 may be defined by an insert member, as mentioned above, that is a separate component to the pump housing 30. Such a configuration may provide for more convenient manufacture and assembly of the pump housing and better control of tolerances. An exemplary location for such an insert member is shown in Figure 2 as reference 71 , the insert member 71 being shown in dashed lines.

[0048] In the above discussion, the sealing ring 66 is captive in the sealing ring groove 64 and provides an interference fit within the plunger bore 34. This arrangement therefore provides an effective high-pressure seal against the pressure of fuel that may pass along the tight diametric clearance 69 between the pumping plunger 42 and the plunger bore 34. The sealing ring 66 may be made from any appropriate material, such as an engineering plastic like PTFE (polytetrafluoroethylene) due to low friction and fuel resistant properties or PEEK (polyether ether ketone).

[0049] Observations have been made that one or more surfaces and / or edges of the sealing ring 66 may degrade in use. For example, the low-pressure side of the sealing ring, i.e. the lower end surface of the sealing ring 66 as seen in the orientation of Figure 2, can show signs of accelerated wear which affects the volumetric efficiency of the fuel pump. One possible cause for this is that the sealing ring 66 must be deformed elastically in order to dilate its inner diameter to that it may be received over the pumping plunger 42 whereupon it can contract into the sealing ring groove 64 when in position. It is believed that the elastic deformation of the sealing ring 66 may affect the material characteristics detrimentally which reduces the long-term robustness of the sealing ring 66. It is also considered possible that lower quality fuels may also be a factor in premature wear of the sealing ring 66. A further possibility is that the high-pressure difference between upstream and downstream edges of the sealing ring 66 can cause what may be known as an “extrusion problem” which causes high stress to be exerted on the downstream edge against the lower surface of the sealing ring groove which, over time, can cause degradation of that edge. In addition, the movement of the plunger can in some circumstances generate strong depressurization on the low pressure side of the plunger which can lead to degradation of the seal due to cavitation.

[0050] FIGS. 3 to 8 illustrate example implementations of a sealing ring arrangement 100 which may address some or all of the challenges discussed above. It should be noted that the sealing ring arrangement 100 shown in FIGS. 3 to 8 is suitable to be used in the high-pressure fuel pump 22 in place of the sealing ring 66 that has been described in respect to FIGS.1 and 2. A such, a full discussion of component parts of the fuel pump 22 will not be described here, and any references to fuel pump components that are described above are considered also to apply to the sealing ring arrangement 100 and the inventive concept as defined by the claims. In the discussion that follows, the same reference numerals will be used to refer to relevant component parts of the fuel pump 22 as appropriate, as they apply to the sealing ring arrangement 100.

[0051] The fuel pump 22 shown in Figure 3 comprises an insert member 71 that forms part of an assembly with the pump housing 30.

[0052] The insert member 71 is in the form of a sleeve in this example and so has a generally cylindrical form. The insert member 71 extends from a lower region of the pump housing 30 towards an upper region of the pump housing 30. In this respect, it will be appreciated that the insert member 71 is accommodated within a correspondingly shaped socket or barrel 101 defined by the fuel pump housing 30. In this way, an upper portion 30a of the pump housing 30 is shaped to define a shoulder 30b against which an upper surface 71 a of the insert member 71 faces against when the insert member 71 is in position within the socket 102. The pump housing 30 and the insert member 71 together define the plunger bore 34. The plunger bore 34 therefore includes a first plunger bore portion 34a which is provided by an internal surface of the pump housing 30 and a second plunger bore portion 34b that is provided by an internal surface of the insert member 71.

[0053] The first plunger bore portion 34a and the second plunger bore portion 34b are cylindrical surfaces in this example. As can be seen in Figure 3, the first plunger bore portion 34a and the second plunger bore portion 34b have the same internal diameter so as to provide a continuous bore surface for the sliding plunger 42. It is envisaged, therefore, that the plunger bore 34 has a substantially uniform diameter along its length.

[0054] In terms of the fit of the plunger 42 within the plunger bore 34, it is envisaged that the plunger bore 34 and the plunger 42 may be configured so that there is a diametric clearance between 5 and 30 pm, as discussed above. In some examples however, the diametric clearance may be less than this, for example between 8 pm and 12 pm, and particularly 11 pm.

[0055] The provision of a separate insert member 71 affords several benefits. Firstly, the insert member 71 acts as a sacrificial wear component, allowing the sliding interface with the plunger to be maintained with high precision even after prolonged use. Secondly, because the insert member 71 is a discrete component, it may be manufactured from materials that have superior wear resistance and can undergo surface treatments or work hardening processes that would be impractical or uneconomical if applied to the entire pump body. Thirdly, the removable nature of the insert member 71 allows for field replacement, minimizing maintenance costs and downtime.

[0056] The insert member 71 may be formed from a range of metallic materials selected for their wear resistance, strength, and compatibility with the working environment of the high-pressure gasoline engine. Suitable materials include, but are not limited to hardenable steels, such as martensitic stainless steels (e.g., AISI 440C), tool steels (e.g., D2), or carburizing steels, which can be case hardened, work-hardening alloys, such as austenitic stainless steels (e.g., AISI 304 or 316), which may be cold-worked to increase surface hardness without compromising toughness, and surface-hardened alloys, such as nitrided steels or steels treated with carburizing, carbonitriding, or other diffusion processes to create a hard, wear-resistant surface layer while retaining a tough core.

[0057] The insert member 71 may also be coated with hard, low-friction materials, such as chromium or diamond-like carbon (DLC) coatings, to further enhance durability. The insert member 71 is particularly advantageous in that it can be subjected to work hardening independently of the pump body. Work hardening may be achieved through cold rolling, shot peening, or other mechanical deformation processes, which locally increase the hardness and wear resistance of the inner surface of the insert member 71 without affecting the structural integrity of the entire pump assembly. The pump housing 30, in contrast, is typically manufactured from a material selected primarily for its machinability, cost-effectiveness, and ability to withstand the structural loads of the fuel injector pump. For example, the pump housing 30 may be formed from cast iron, cast steel, or a lower-grade stainless steel. These materials may not be amenable to significant work hardening, or applying such processes to the entire body may be economically prohibitive. In some embodiments, the sleeve and the pump housing 30 may be made from similar base materials (e.g., both may be stainless steels) to ensure thermal compatibility and reduce the risk of galvanic corrosion. However, the sleeve may have a different heat treatment or surface treatment to provide enhanced hardness and wear resistance relative to the body. Alternatively, the sleeve may be made from a distinct material with inherently superior wear properties (such as a tool steel or work-hardened alloy), while the pump housing 30 uses a more conventional structural alloy.

[0058] While metallic materials are conventional for high-pressure fuel injector components, certain advanced polymeric materials may also be suitable for the insert member 71 , particularly where low friction, chemical resistance, and ease of manufacture are desired. The insert member 71 must withstand elevated temperatures, high contact stresses from the plunger, and continuous exposure to gasoline and combustion by-products. Accordingly, high- performance engineering polymers or polymer composites would be appropriate, such as Polyether ether ketone (PEEK) Polyimides (e.g., Vespel®) and PTFE-based Composites.

[0059] In the example of Figure 3, it will be noticed that there is no ring seal provided in the plunger 42 itself. Instead, the plunger seal arrangement 100 is embodied as a sealing ring 102 that is accommodated by the insert member 71.

[0060] As such, the insert member 71 is provided with an annular groove 104. The annular groove 104 is recessed from the bore surface of the insert member 71. The annular groove 104 in this example has first and second side surfaces 104a, b and a base surface 104c. The base surface 104c extends between the first and second side surfaces 104a,b.

[0061] The sealing ring 102 is received within the annular groove 104. As can be seen in Figure 3, the cross section form of the annular groove 104 corresponds or matches the cross section form of the sealing ring 102 so that the sealing ring 102 fits within the annular groove 104. Geometrical differences may be configured so that the sealing ring 102 fits within the annular groove 104 in a loose fit so that there is a slight gap between the side surfaces 104a,b of the annular groove 104 and the facing surfaces of the sealing ring 102, such that some movement (vertical movement in the orientation of Figure 3) is permitted.

[0062] In other examples, the comparative geometry of the sealing ring 102 and the annular groove 104 may be such that the sealing ring 102 is received in a close fit within the groove 104. In all other respects than the groove 64, the bore 34 and the plunger 42 define plain cylindrical surfaces with a tight diametric clearance as previously defined.

[0063] To insert the sealing ring 102 into the annular grove 104 within the insert member 71 , it is possible for the sealing ring to be compressed or reduced in diameter in some way in order to fit within the open internal diameter of the insert member 71 and then pushed into position. As an alternative, it is believed that one option is that the insert member 71 may be formed of two parts, each part defining part of the annular groove 104. The sealing ring 102 is then able to be captured within the annular groove 104 by bringing the two parts of the insert member 71 together and joining them in some way, for example by way of a suitable adhesive, or by friction welding.

[0064] In the example of Figure 3, it will be noted that the location of the sealing ring 102 and, therefore, also of the annular groove 104, is approximately in the middle of the length of the insert member 71 when considered in the direction along its major axis, i.e. in the longitudinal direction. However, it is also envisaged that the annular groove 104 may be positioned towards one of the ends of the insert member 71. For example, the annular groove 104 and, therefore, also the annular sealing ring 102 may be located a predetermined distance from the upper surface 71a of the insert member 71. That predetermined distance may be within 10% of the total axial length of the insert member 71 , or within 20%, or within 30%, or within 40%. It is believed that locating the annular groove 104 and, thus, the sealing ring 102 towards the upper surface 71a of the insert member 71 may be beneficial since may limit the extent to which pressurized fuel can leak down the diametric clearance between the insert member 71 and the plunger 42 which may help to reduce cavitation effects within that volume. In this respect, a surface of the pump housing (30), or a surface connected to the pump housing (30) may provide the upper surface of the annular groove 104.

[0065] Conversely, there may be benefits associated with locating the annular groove 104 and, thus, the sealing ring 102 towards the lower end of the insert member 71. That is, at a position that is located at a predetermined distance from a lower end surface 71b of the insert member 71. That predetermined distance from the lower end surface 71b may be within 10% of the total axial length of the insert member 71 , or within 20%, or within 30%, or within 40%. It is believed that locating the annular groove 104 and, thus, the sealing ring 102 towards the lower surface 71a of the insert member 71 may be beneficial since it may provide some support to the plunger 42 against the torque imposed by the camshaft 44 on the drive end of the plunger 42.

[0066] Furthermore, it will be appreciated that the axial length of the sealing ring groove 104, and, therefore, the axial length of the sealing ring 102, is relatively short when compared to the total length of the insert member 71. For example, it is envisaged that the axial length of the sealing ring groove 104, and therefore also of the sealing ring 102, should be less than 20%, and preferably less than 15%, of the length of the axial length of the insert member 71. Expressed another way, it is envisaged that the axial length of the sealing ring 102 is between 10-20%, and preferably between 10-15% of the axial length of the insert member 71 .

[0067] Similarly, the radial dimension of the sealing ring 102, that is the thickness of the groove in a dimension perpendicular to the axial length, is envisaged to be approximately 5-15% of the axial length of the insert member 71.

[0068] Figure 4 illustrates an alternative example which is similar to that shown in Figure 3. However, the example of Figure 4 features a sealing ring 102 that is provided in a different location on the insert member 71. In this example, the sealing ring 102 is more easily positioned inside or on the insert member 71.

[0069] In the following discussion of Figure 4 the same reference numerals will be used to refer to parts in common with the example of Figure 3. Moreover, a full discussion of the fuel pump 22 shown in Figure 4 will not be provided here for the sake of brevity. Instead, the discussion will focus on the differences between the examples of Figure 4 compared to Figure 3.

[0070] In the example of Figure 4, it will be noted that the sealing ring 102 is provided at an end of the insert member 71. In this case, the sealing ring 102 is provided at an upper end of the insert member 71 , when considered in the orientation of the drawings.

[0071] The otherwise cylindrical insert member 71 therefore is provided with an open- topped annular groove 104 which in effect provides an abutment shoulder onto which the sealing ring 104 is received. The annular groove 104 in Figure 4 therefore has a lower side surface 104b and a base surface 104c. The lower side surface 104b therefore provides the abutment shoulder. In contrast to the design in Figure 3, here the groove 104 is provided by a base surface 104c and the lower side surface 104b, but it does not have an upper side surface as does the design in Figure 3. It can also be appreciated that the upper surface 71a of the sleeve member 71 is adjacent to the base surface 104c of the groove 104.

[0072] It will be appreciated that this configuration is useful because the sealing ring 102 can be inserted onto the insert member 71 easily and does not have to be contracted in diameter in order to fit into a sealing ring groove that is placed in a mid-point of the insert member 71 , or for the insert member 71 to be formed of multiple parts to capture the sealing ring 102.

[0073] A further example is provided in Figure 5. In contrast to the example depicted in Figure 4, in which the annular groove 104 and, thus, the sealing ring 102 are located toward or at the upper end 71a of the insert member 71 , in Figure 5 the annular groove 104 and, thus, the sealing ring 102 are located at or near to the lower end surface 71 b of the insert member 71.

[0074] It will be noted that as the groove 104 is located at the lower end 71 b of the insert member 71 , it can be considered to be an open ended groove 104 that is defined by a base surface 104a, and a base surface 104c. Notably, the annular groove 104 does not have a lower side surface. Since the annular groove 104 is ‘open topped’, being bounded by two perpendicular surfaces, this configuration permits a sealing ring 102 to be inserted onto the end of the insert member 71. The end surface of the sealing ring 102 is aligned in a longitudinal direction with the lower end surface 71b of the insert member 71.

[0075] It will be noted that in the example of Figure 4, the upper portion 30a of the pump housing 30 held the sealing ring 102 captive on the end of the insert member 71 , despite the open groove 104. In this example of Figure 5, where the sealing ring 102 is provided on the lower end of the insert member 71 , a sealing ring retention arrangement 105 is provided.

[0076] The sealing ring retention arrangement 105 in the illustrated example comprises a retaining member 106 in the form of an annular plate. The annular plate may be made from any suitable material, for example a metal such as steel or an engineering plastics such as Nylon.

[0077] The retaining member 106 is configured to extend in a radial direction so as to span a lower end surface of the pump housing 30 and a lower end surface 71b of the insert member 71. The retaining member 106 has a central aperture that accommodates the pumping plunger 42 through it. The radial inner extent of the retention member 106 is such that it extends or overlaps over at least a part of the insert member 71 and the sealing ring 102. The retention member 106 therefore holds the sealing ring 102 in position on the insert member 71 and prevents the insert member 71 from shifting axially within the pump housing 30.

[0078] In some embodiments, the retention member 106 may be configured so that it provides support only to the sealing ring 102. The insert member 71 may be press fitted within the pump housing 30 so that axial support is not required for the insert member 71 to remain in position.

[0079] The retention member 106 may be coupled to the pump housing 30 in any suitable way. As shown in the illustrated example, the retention member 106 is secured to the underside of the pump housing 30 by a set of mechanical fasteners 107, which can be embodied by bolts or screws for example. Other approaches would be apparent to the skilled person. For example, magnetic coupling is believed to be a viable alternative, or bonding by an appropriate compound.

[0080] Without wishing to be bound by theory, it is believed that one benefit of the arrangements of Figure 3 to 5 is that the sealing ring 102 remains stationary with respect to the plunger bore 34 during operation. This means that any fuel that moves past the sealing ring 102 to a lower region of the bore 34 is not ‘pumped’ by the reciprocating action of a sealing ring that is provided in the plunger itself. It is believed that this pumping effect can cause dramatic pressure variations in the volume of fuel that leaks to a lower region of the pump housing. During a return stroke of the plunger, the trapped fuel is pressurized by the movement of the sealing ring captive on the plunger, and then the trapped fuel is depressurized rapidly during a pumping stroke of the plunger. This action can cause cavitation in the volume of trapped fuel which may contribute to degradation of the sealing ring in configurations where it is carried by the plunger. Configuring the sealing arrangement 100 so that the sealing ring 102 is carried instead by the insert member 71 is believed to avoid this issue.

[0081] In terms of fitments of the insert member 71 inside the pump housing 30, the insert member 71 carrying the seal member 102 are force fitted as an assembly inside the pump body 30. The pumping plunger 42 may then be machined appropriately to match the internal dimensions of the insert member 71. This is sometimes referred to as match honing.

[0082] In the examples of Figures 3 to 5, it will be noted that the sealing ring 102 has a rectilinear profile in cross section, and more specifically rectangular profile. As such, the radially outer face of the cross section profile of the sealing ring is flat, when considered in a plane that is parallel to the long axis of the plunger 42. Notably, the radially outer surface of the sealing ring 102 is curved with the same radius of curvature as the inner surface of the insert member 71 , when considered in a plane that is perpendicular to the long axis of the plunger 42. Although this is one possible form of sealing surface of the sealing ring 102, it is envisaged that other forms are acceptable. Figures 6a-6c show three examples.

[0083] Figure 6a illustrates an example of a cross section through a plane parallel to and passing through the long axis of the plunger 42 and shows the sealing surface 102a, being a radially inner peripheral surface, as providing a knife edge seal formation. As such, the sealing surface 102 has an apex between two sloping surfaces. The apex is shown here approximately in the middle of the axial length of the sealing ring 102, but it may be defined at other points along the axial length.

[0084] Figure 6b shows another example where the sealing ring 102 has a sealing surface 102a has an outwardly curved ‘nose’ profile which defines its inner peripheral surface.

[0085] Figure 6c shows a further example where the sealing ring 102 has a sealing surface 102a which has groove and ridge like features extending radially inwards. In this example therefore, the sealing ring 102 has more than one sealing line. The sealing lines could be knife edge features, or other features such as round- or nose-ended ridges.

[0086] A further alternative arrangement of sealing ring is shown in Figure 7. Here, the sealing ring arrangement 100 has a two-part nested structure and, as such, comprises a first sealing ring element 110 and a second sealing ring element 112. Both the first sealing ring element 110 and the second sealing ring element 112 are annular in form. More specifically, in this example both the sealing ring elements 110,112 have a circular outer diameter in plan, as is consistent with their role in sealing against the plunger 42.

[0087] The second sealing ring element 112 is configured and proportioned so that at least a portion of it is nested within a radially inner area defined by the first sealing ring element 110. That is to say, the second sealing ring element 112 has at least a portion that has an outer diameter sized so that it is smaller than a portion of the first sealing ring element 110 that has a larger inner diameter. As such, a portion of the second sealing ring element 112 is able to be received within the inner open circular area formed by the annular shape of the first sealing ring element 110. Expressed another way, at least a part of the second sealing ring element 112 fits inside an open annular portion A of the first sealing ring element 110. Notably, the axial length of the second sealing ring element 112 fits inside the axial length of the first sealing ring element 110. Therefore, the combination of the first and second sealing ring elements 110,112, when assembled, does not exceed the axial length of the first sealing ring element 110. In more detail, the first sealing ring element 110 extends in a direction along the axis 36 and as such defines a radial outer peripheral surface 110a and a radial inner surface 110b, an axially upper surface 110c and an axially lower surface 110d. The radial outer surface 110a is engaged with the base surface 104c of the sealing ring groove 104 in use. The first sealing ring element 110 therefore extends radially between the sealing ring groove 104 and the plunger 42. During a pumping event, high-pressure fuel is applied on the radial inner surface 110b.

[0088] It should be appreciated that terms such as ‘upper’ and ‘lower’ should be taken to be in relation to the orientation of the drawings and should not be considered to confer a particular orientation.

[0089] The first sealing ring element 110 is shaped to define first and second annular portions 116,118 which are part of the same integral whole. The second annular portion 118 has a reduced annular dimension as compared to the first annular portion 116. The first annular portion 116 is axially above the second annular portion 118. The first annular portion 116 provides the radial outer surface 110a and part of the radial inner surface 110b. The second annular portion 118 also provides a part of the radial inner surface 110b. The radially inner surface 110b is aligned in respect of its parts formed by each of the first and second annular portions 116,118.

[0090] The second annular portion 118 also provides a second radial inner peripheral surface 110e. The second radial inner surface 110e is radially offset from the radial inner surface 110b, which will now be referred to as the ‘first’ radial inner surface 110b, and has a reduced diameter compared to it. The first radial inner surface 110b and the second radial inner surface 110e are separated by a shoulder 11 Of. It should be noted that the second radial inner peripheral surface 110e does not engage with the plunger 42.

[0091] A chamfer 110g may be provided between the axially upper surface 110c and the radial inner surface 110b. The chamfer 110g is not essential but may reduce the risk of stress concentrations at a sharp corner, and therefore may avoid or reduce unnecessary wear in this region.

[0092] In this example, the second radial inner surface 110e is frustoconical in form to provide an inwardly tapering portion of the first sealing ring element 110. The tapering form is not essential, however, and as such it should be noted that the second radial inner surface 102e may be substantially vertical. A tapering surface, as shown, is believed to ease the process of assembly of the two sealing ring elements 110,112.

[0093] The second sealing ring element 112 has a less complex configuration compared to the first sealing ring element 110. The second sealing ring element 112 extends in a direction along the axis 36 and as such defines a radial outer peripheral surface 112a and a radial inner surface 112b, an axial upper surface 112c and an axial lower surface 112d.

[0094] It will be noticed that the radial outer surface 112a will be engaged with the base surface 104c of the sealing ring groove 104 whilst the axial lower surface 104d opposes the lower side surface 104b of the plunger sealing groove 104. The radial outer surface 112a of the second sealing ring element 112 is therefore engaged with the second radial inner surface 110e of the first sealing ring element 110.

[0095] In one example, the sealing ring arrangement 100 may be sized and shaped such that the two sealing ring elements 110,112, when assembled onto one another, fit within the sealing ring groove 104 in a tight fit. During use, therefore, the two sealing ring elements 110,110 will be compressed into the sealing ring groove 104 during a pumping event as fluid pressure acts on the surfaces of the sealing ring arrangement 100.

[0096] In another example, the sealing ring arrangement 100 may be sized and shaped so that a clearance is defined between the upper and lower surfaces of the sealing ring arrangement 100 and the opposing surfaces of the sealing ring groove 104. The clearance or gap in the axial dimension or ‘height’ of the sealing ring groove 104 and the axial dimension of the sealing ring arrangement 100 may be between 3% and 15% of the axial dimension of the sealing ring arrangement 100, and more preferably between 4% and 12%, and nominally around 8%. In terms of absolute dimensions, the gap may be between 0.1. and 0.3mm for a sealing ring groove dimension of about 2.5mm, provided by way of example only. The benefit of the gap is believed to be that it permits high pressure fuel to apply a compressive force on the sealing ring arrangement 100 from its upper surface 102c and also the radial inner surface 102b which on turn causes the first sealing ring element 110 to be urged into engagement with the plunger 42.

[0097] The geometry of the first sealing ring element 110 relative to the second sealing ring element 112 is clearly apparent in FIG.7. As will be appreciated, the geometry of the first sealing ring 110 is such that it defines an open central area A. The geometry of the open central area A is configured such that the second sealing ring element 112 fits within it. In particular, when the second sealing ring element 112 is received within the open central area A, it will be noted that the frustoconical surface 110e of the first sealing ring element 110 rests against or engages the radially inner surface 112a of the second sealing ring element 112. In this example, the radially inner surface 112a of the second sealing ring element 112 is also frustoconical. Here, the angle of inclination that the radial inner surface 112a of the second sealing ring element 112 makes with the axis 36 is substantially the same as the angle of inclination of the frustoconical surface 110e of the first sealing ring element 110.

[0098] The position of the second sealing ring element 112 when it is engaged with the first sealing ring element 110 is shown in FIG. 7 is dotted lines and marked as ‘B’. In this position, it can be seen that the axial lower surface 110d of the first sealing ring element 110 is axially aligned with the axial lower surface 112d of the second sealing ring element 112. Moreover, the radial inward surfaces of both the first and second sealing ring elements 110,112 define the same internal diameter and are cylindrical surfaces.

[0099] A benefit of providing the sealing ring arrangement 100 in two parts is that the second sealing ring element 112 may be formed from a different material as compared to the first sealing ring element 112. This provides the opportunity to form the second sealing ring element 112 from a stronger material which may be more resilient to mechanical and / or chemical wear in use. For example, it is believed there are benefits from forming the second sealing ring element from PEEK (polyether ether Ketone) whereas the first sealing ring element 112 is formed from PTFE. It is believed that forming the second sealing ring element 112 from a ‘stronger’ material such as PEEK may guard against extrusion of the first sealing ring element 112 that may be formed from a material that is softer than the material of the second sealing ring element 112, such as PTFE, whilst the sealing ring arrangement 100 is being pushed to the lower surface of the sealing ring groove 104 during a pumping event. However, the material of the first sealing ring element 102 is more suitable for sealing against the plunger 42. Furthermore, another benefit may be that the two-part form of the sealing ring arrangement 100 permits high-pressure fuel to penetrate between the first and second sealing ring elements 110,112 and force expansion thereof which may increase the pressure with which the second sealing ring element 112 forms with the plunger 42. The sealing effect may be improved by this mechanism.

[0100] Beneficially, PEEK is considered to be a harder material than PTFE and so advantages are achieved by forming the second sealing ring element 104 from PEEK, or a material with comparable characteristics suitable to the task, to resist the possibility of an extrusion effect. More specifically, when compared on the Shore D hardness scale (test method ASTM D2240), PEEK is considered to have a hardness rating between about 83 to 87, more particularly around 85, whereas PTFE is considered to have a hardness rating in the range of 58 to 68 depending on the specific type of PTFE (virgin PTFE, glass filled and so on). What is more, tensile strength of PTFE is considered typically to be around 24-35Mpa, compared to around 90-1 OOMpa for PEEK, whilst compressive strength is around 30-40Mpa for PTFE as compared to around 130Mpa to 150Mpa for PEEK, and flexural modulus is typically around 495Mpa for PTFE as compared to around 3900 for PEEK. On this basis, although both PEEK and PTFE are considered to be robust engineering plastics materials, the enhanced strength of PEEK makes it more suitable for the second sealing ring element 104 for its ‘anti-extrusion’ properties, thereby providing protection on the axial lower edge of the sealing ring arrangement 100. In contrast, the material of PTFE for the first sealing ring 102 also has beneficial strength characteristics (although somewhat less than that of PEEK), but is particularly beneficial for its low coefficient of friction, which is about 0.03-0.05, as compared to 0.35-0.45 for PEEK. Moreover the flexural modulus of PTFE is higher, at about 3900Mpa. Therefore, these characteristics make PTFE a suitable material for the first sealing ring element 102 which acts as a sliding sealing interface with the plunger bore, but which also is required to dilate under pressure.

[0101] Therefore, the skilled person will understand that materials other than PTFE and PEEK may be suitable for the first sealing ring element 110 and the second sealing ring element 110 respectively, based on the above discussion of suitable characteristics required for each of the sealing ring elements.

[0102] Figure 8 illustrates the sealing arrangement 100 in the context of a fuel pump 22 like that shown in Figure 1. Note that only a portion of the pump is shown in Figure 8. For ease of understanding, the same reference numbers that have been used above to refer to parts of the fuel pump 22 in Figures 1 to 5 will be used to refer to the same or comparable parts in Figure 8.

[0103] As will be appreciated, the fuel pump 22 includes a pump housing or body 30 which defines a pumping chamber 32 and a plunger bore 34 (partly defined by pump housing 30 and also by insert member 71), within which the pumping plunger 42 is slidably received. The pump housing 30 includes fuel inlet (not shown in Figure 8 but feature is common with Figure 1) which permits fuel at low pressure to be admitted into the pumping chamber 32 during a plunger return stroke. Pump housing 30 is also provided with a fuel outlet (also not shown in Figure 8) which permits high pressure fuel to exit pumping chamber 32. A full discussion of this mechanism will not be provided as it is well known and has been outlined above in the discussion of Figure 1 , so that discussion also applies here.

[0104] As is shown in Figure 8, the pumping plunger 42 is coupled to a return spring 50 that is compressed axially between the pump housing 30 and a spring retainer 46 which may also act as a cam follower. The spring retainer 46 in this example is a cap-like component with a central opening that is fitted on the lower end of the plunger 42. The lower end of the plunger may be driven by other means than a cam, however. For example, the plunger may be electrically driven by a suitable electromagnetic actuator.

[0105] The return spring 50 is coupled to the pump housing 30 by way of a spring abutment cap 120. The spring abutment cap 120 is a generally cup-shaped component that provided an annular recess 122 that receives an end of the return spring 50 (upper end as shown in Fig 8). A central wall 124 of the abutment cap 120 extends axially and closes around the plunger 42. A plunger seal 126 is provided between the plunger 42 and the spring abutment cap 120. The plunger seal 126 establishes a trapped volume 128 for fuel between the spring abutment cap 120 and the pump housing 30 and the insert member 71. Fuel that is able to leak past the sleeve member 71 is retained in the trapped volume 128 by the plunger seal 126. The plunger seal 126 also prevents oil contamination into the trapped volume 128. The plunger seal 126 may take different forms, for example anO-ring. As shown, the plunger seal 126 has some radial deformability as its cross section provided is V-shaped and double-ended in form.

[0106] The plunger seal 126 is held in place within the spring abutment cap 120 by a stopper 127. The stopped is annular in form and includes a protruding central portion that fits inside a correspondingly protruding part of the spring abutment cap 120. The stopped 127 may be press fit inside the spring abutment cap 120. By this means, the stopper 127 retains the plunger seal 126 within an end region of the spring abutment cap 120.

[0107] In use, the plunger 42 reciprocates within the insert member 71. lt will be appreciated from the above discussion that the seal member 102 is stationary with respect to the plunger and do not therefore move with it during reciprocating motion of the plunger 42. This means that the trapped volume 128 does not change significantly during reciprocating movement of the plunger 42. This can be compared to the known example shown in Figure 2 in which the sealing ring 66 is carried on the plunger 42. Since the sealing ring 66 in Figure 2 forms a seal against the plunger bore 34 and moves to and fro along the bore 34 during reciprocating movement of the plunger 42, this has the effect of changing the pressure of fuel within the trapped volume 128. The pressure change can be significant, and it is believed that in some circumstances the change in pressure can cause cavitation of the fuel in the trapped volume 128 which may cause slow degradation of the material of the sealing ring 66. It will therefore be appreciated that housing the sealing ring 102 in the wall of the plunger bore, that is, within the insert member 71 , can guard against this observed phenomenon.

[0108] A further feature of the fuel pump 22 shown in Figure 8 is the profile of the pumping plunger 42. As can be seen, the plunger 42 has an outer diameter that is substantially constant over a significant part of its length. Notably, the diameter of the plunger 42 is substantially constant between the sealing ring 102 and the plunger seal 126 provided on the spring abutment cap 120 throughout the range of motion of the plunger 42. By “substantially constant”, it is means that the plunger 42 is machined so as to have a constant diameter, although some small changes are to be expected within the limits of manufacturing capability. Where the plunger 42 extends out of the annular central aperture of the spring abutment cap 120, the plunger 42 is shown as having a region of reduced diameter 131 on its end which feature fits inside the spring retainer 46.

[0109] The substantially uniform diameter of the plunger 42 between the sealing ring 102 and the cap seal 126 means that the plunger 42 does not create any pumping effects within the trapped volume 128, which may further guard against cavitation within the trapped volume 128.

[0110] The skilled person will appreciate that various modifications may be made to the illustrated examples that have been discussed above without departing from the inventive concept as defined by the claims.

Claims

CLAIMS1. A high-pressure fuel pump comprising: a pump housing (30) which defines a pumping chamber (32), a fuel inlet (38) which allows low-pressure fuel into said pumping chamber, a fuel outlet (40) which allows high-pressure fuel out of said pumping chamber, and a plunger bore (34) which extends along an axis and opens into said pumping chamber; a pumping plunger (42) which reciprocates within said plunger bore (34) along said axis such that reciprocation of said pumping plunger within said plunger bore increases and decreases a volume of said pumping chamber, wherein the pump housing (30) has a sleeve member (71) which defines the plunger bore (34) at least in part, further comprising a plunger sealing ring arrangement (100) for providing a seal between an outer surface of the plunger and the sleeve member, the plunger sealing ring arrangement comprising: a sealing ring groove (104) provided in the sleeve member (71); and a sealing ring (102) accommodated in the sealing ring groove (104).

2. The fuel pump of Claim 1, wherein the sealing ring groove (104) has an upper surface (104a), a lower surface (104b) and a base surface (104c) extending between the upper surface and the lower surface.

3. The fuel pump of Claim 2, wherein the upper surface (104a) of the sealing ring groove (104) is defined by a surface of the pump housing (30).

4. The fuel pump of Claim 2, wherein the lower surface (104b) of the sealing ring groove (104) is defined by a retention member (105).

5. The fuel pump of Claim 4, wherein the retention member (105) is fixed to a portion of the pump housing (30).

6. The fuel pump of Claim 5, wherein the portion of the pump housing (30) is a lower end of the pump housing (30).

7. The fuel pump of any of Claims 4 to 6, wherein the retention member (105) is in the form of a plate.

8. The fuel pump of any of Claims 4 to 7, wherein the retention member has a central aperture through which passes the pumping plunger (42).

9. The fuel pump of any one of Claims 1 to 8, wherein the sealing ring (102) has a substantially rectangular cross section.

10. The fuel pump of Claim 9, wherein a sealing surface (102a) of the sealing ring is shaped to define one or more sealing lines.

11. The fuel pump of Claim 10, wherein the one or more sealing lines provided by the sealing surface (102) are provided by at least one of the following formations: a knife edge sealing surface, an outwardly curved sealing surface, a grooved or crenelated sealing surface.

12. The fuel pump of any one of the preceding claims, wherein the sealing ring is formed from a first sealing ring element and a second sealing ring element.

13. The fuel pump of Claim 12, wherein at least a part of the second sealing ring element is nested within a part of the first sealing ring element.

14. The fuel pump of Claim 13, wherein the first sealing ring element (110) comprises a radial inner surface (110b) which engages the plunger (42) and a second radial inner surface (110e) that is shaped so as not to engage the plunger (42).

15. The fuel pump of Claim 14, wherein the first sealing ring element (110) further comprises a radial outer surface (110a) which engages a base surface (104c) of the sealing ring groove (104).

16. The fuel pump of Claims 13 or 14, wherein the second sealing ring element (112) comprises a radial outer surface (112a) that is shaped to oppose the second radial inner surface (110e) of the first sealing ring element (110).

17. The fuel pump of Claim 16, wherein the radial outer surface (112a) of the second sealing ring element (112) is shaped to correspond to the second inner peripheral surface (110e) of the first sealing ring element (110).

18. The fuel pump of Claim 17, wherein the radial outer surface (112a) of the second sealing ring element (112) and the second inner peripheral surface (110e) of the first sealing ring element (110) are frustoconical in form.

19. The fuel pump of Claims 12 to 18, wherein the first sealing ring element is formed of a first material and the second sealing ring element is formed of a second material, which is different from the first material.

20. The fuel pump of Claim 19, wherein the first material includes a thermoplastic polymer, optionally PTFE, and wherein the second material includes a thermoplastic polymer, optionally PEEK.T1

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