Fuel pump and sealing arrangement therefor

Abstract

A high-pressure fuel pump comprising a pumping plunger reciprocable within a plunger bore of a pump housing along a plunger axis The pumping plunger includes a sealing ring groove that is annular in shape and extends about the pumping plunger so as to define an upper surface, a lower surface and a base surface extending between the upper surface and the lower surface. There is also provided a plunger sealing ring wherein the plunger sealing ring has a split ring form provided by way of a circumferential discontinuity. Furthermore the circumferential discontinuity split of the split ring form is planar and comprises a split plane which is parallel to and offset from the central axis. The sealing ring engages both the base surface of the sealing ring groove of the two-part pumping plunger and the plunger bore.

Description

[0001] FUEL PUMP AND SEALING ARRANGEMENT THEREFOR

[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 pressurise fuel within a pumping chamber defined in the pump housing. The pumping plunger includes an annular sealing ring groove and a sealing ring arrangement accommodated within the sealing ring groove which engages the plunger bore in an interference fit to minimize leakage of fuel between the interface of the pumping plunger and the plunger bore.

[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-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. 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.

[0008] It is with a view to enhancing the functionality of the plunger sealing arrangement that the examples of the invention have been devised.

[0009] Summary of the Invention

[0010] Against this background, the invention provides a high-pressure fuel pump comprising a pump housing 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. A pumping plunger 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. The pumping plunger includes a sealing ring groove that is annular in shape and extends about the pumping plunger so as to define an upper surface, a lower surface and a base surface extending between the upper surface and the lower surface. There is also provided at least one plunger sealing ring arrangement accommodated in the sealing ring groove wherein the at least one plunger sealing ring has a split ring form provided by way of a circumferential discontinuity. At least a portion of a split of the split ring form is planar and comprises a split plane which is parallel to the central axis.

[0011] Beneficially, providing a split in the sealing ring allows for simpler and less damaging assembly of the sealing ring to the pumping plunger.

[0012] Optional and or preferable features are set out in the dependent claims and discussed in the detailed description which now follows.

[0013] Brief Description of the Drawings

[0014] 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, 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,

[0015] 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 split sealing ring arrangement incorporating an example of the invention;

[0016] Figure 4 is the same as Figure 3, but which shows the pumping plunger and split sealing ring arrangement in cross section;

[0017] Figures 5A and 5B provide detailed views of an example of a split sealing ring arrangement shown in Figures 3 and 4 but isolated from the associated pumping plunger and plunger bore;

[0018] Figures 6A and 6B provide detailed views of an alternative example of a split sealing ring arrangement to that shown in Figures 5A and 5B; and

[0019] Figures 7A and 7B provide detailed views of another alternative example of a split sealing ring arrangement to that shown in Figures 5A, 5B, 6A and 6B.

[0020] Detailed description

[0021] With reference to FIG. 1 , a fuel system 10 for an internal combustion engine 12 is shown. 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.

[0022] The fuel system 10 generally includes a fuel tank 14 which holds a volume of fuel to be supplied to the 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 the 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 the fuel tank 14 and elevates the pressure of the fuel for delivery to the high-pressure fuel pump 22 where the high-pressure fuel pump 22 further elevates the pressure of the fuel for delivery to the high-pressure fuel injectors 16.

[0023] As an example, the low-pressure fuel pump 20 may elevate the pressure of the fuel to about 500 kPa or less and the high-pressure fuel pump 22 may elevate the pressure of the fuel to above about 14 MPa where pressures in the order of 40 MPa and above are envisaged to be realistic in practice.

[0024] 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.

[0025] As shown, the low-pressure fuel pump 20 may be provided within the fuel tank 14. However, the low-pressure fuel pump 20 may alternatively be provided outside of the fuel tank 14. The low-pressure fuel pump 20 may be an electric fuel pump. A low-pressure fuel supply passage 24 provides fluid communication from the low-pressure fuel pump 20 to the high-pressure fuel pump 22. The high-pressure fuel pump 22 will be described in greater detail in the paragraphs that follow.

[0026] The high-pressure fuel pump 22 includes a pump housing 30 which defines a pumping chamber 32 and a plunger bore 34 which opens into the pumping chamber 32 such that the plunger bore 34 extends along a central axis 36. The pump housing 30 also includes a fuel inlet 38 in fluid communication with the low-pressure fuel supply passage 24 such that the fuel inlet 38 selectively allows low-pressure fuel from the low-pressure fuel pump 20 to enter the pumping chamber 32 as will be described in greater detail later. The pump housing 30 also defines a fuel outlet 40 which selectively allows high-pressure fuel to exit the pumping chamber 32 as will be described in greater detail later. While the pump housing 30 has been illustrated schematically as single-piece construction, it should be understood that the 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 the pump housing 30 such that the tubular insert defines the plunger bore 34 or the fuel inlet 38 may be provided as a feature of a pulsation damper cup (not shown) which houses a pulsation damper (also not shown) for minimizing pressure pulsation in the fuel generated during operation. The high-pressure fuel pump 22 also includes a pumping plunger 42 located within the plunger bore 34 such that the pumping plunger 42 is able to reciprocate within the plunger bore 34 along the central axis 36. The pumping plunger 42 is reciprocated within the plunger bore 34, by way of non-limiting example only, by a camshaft 44 of the internal combustion engine 12. The pumping plunger 42 is attached to (in contact with) a cam follower 46 which follows the profile of the camshaft 44. The cam follower 46 is axially guided within a cam follower bore 48 of the pump housing 30 such that a return spring 50 is compressed axially between the pump housing 30 and the cam follower 46 to maintain cam follower 46 contact with the camshaft 44 as the camshaft 44 rotates. While the cam follower 46 has been embodied as being guided within the cam follower bore 48 of the pump housing 30, it should now be understood that the cam follower 46 may alternatively be guided within a bore of the internal combustion engine 12 that is not within the pump housing 30. When the camshaft 44, the cam follower 46, and the return spring 50 cause the 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.

[0027] Conversely, when the camshaft 44 and the cam follower 46 cause the pumping plunger 42 to move upward as viewed in the figures, the volume of the 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 the pumping plunger 42 and the plunger bore 34 from mixing with oil that lubricates the internal combustion engine 12.

[0028] The high-pressure fuel pump 22 also includes an inlet valve 52 which selectively opens to permit fuel to enter the pumping chamber 32 from the low-pressure fuel supply passage 24. The inlet valve 52 may be, by way of non-limiting example only, a solenoid operated valve which is controlled by a controller 54. The controller 54 may receive input from a pressure sensor 56 which supplies a signal indicative of the pressure of the fuel being supplied to the 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 the fuel outlet 40 through a high-pressure fuel supply passage 60 such that the high-pressure fuel rail 58 distributes high-pressure fuel to each of the high-pressure fuel injectors 16. However, it should be understood that the pressure sensor 56 may be positioned at other locations that are indicative of the pressure of the fuel being supplied to the high-pressure fuel injectors 16. The controller 54 sends signals to the inlet valve 52 to open and close the inlet valve 52 as necessary to achieve a desired fuel pressure at the pressure sensor 56 as may be determined by current and anticipated engine operating demands. When the inlet valve 52 is opened while the pumping plunger 42 is moving to increase the volume of the pumping chamber 32, i.e. when the inlet valve 52 is moving downward as viewed in the figures, fuel from the low- pressure fuel supply passage 24 is allowed to flow into the pumping chamber 32 through the fuel inlet 38.

[0029] The high-pressure fuel pump 22 also includes an outlet valve 62 which selectively opens to permit fuel to exit the pumping chamber 32 to the high-pressure fuel supply passage 60. The outlet valve 62 may be a spring-biased valve which opens when the pressure differential between the pumping chamber 32 and the high-pressure fuel supply passage 60 is greater than a predetermined threshold. Consequently, when the camshaft 44 and the cam follower 46 cause the pumping plunger 42 to decrease the volume of the pumping chamber 32, the fuel within the pumping chamber 32 is pressurised. Furthermore, when the pressure within the pumping chamber 32 is sufficiently high, the outlet valve 62 is urged open by the fuel pressure, thereby causing pressurised fuel to be supplied to the high-pressure fuel injectors 16 through the fuel outlet 40, the high-pressure fuel supply passage 60, and the high-pressure fuel rail 58.

[0030] 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 the pump housing 30 and the pumping plunger 42.

[0031] In order to improve efficiency, particularly at low rotational speeds of the camshaft 44 caused by low operating speeds of the internal combustion engine 12, and to permit greater annular clearance between the pumping plunger 42 and the plunger bore 34, the 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 sealing ring arrangement 100 later.

[0032] The pumping plunger 42 extends along the central axis 36 from a first end 42a, which is proximal to the pumping chamber 32, to a second end 42b, which is distal from the pumping chamber 32. The sealing ring groove 64 is annular in shape and substantially concentric with the pumping plunger 42 and the plunger bore 34 such that the sealing ring groove 64 extends radially inward from an outer periphery of the pumping plunger 42 and such that the sealing ring groove 64 is located between the first end 42a and the second end 42b. The sealing ring groove 64 extends along the central axis 36 from an upper shoulder 64a, which is proximal to the first end 42a, to a lower shoulder 64b, which is distal from the first end 42a such that the upper shoulder 64a and the lower shoulder 64b are separated from each other by a first distance 68 in a direction parallel to the central axis 36. The upper shoulder 64a and the lower shoulder 64b are both transverse to the central axis 36 and may be perpendicular to the central axis 36 as illustrated in the figures. It should be noted that a chamfer or radius may join upper the shoulder 64a with the outer periphery of the pumping plunger 42 where this chamfer or radius is considered to be a portion of the sealing ring groove 64. Similarly, a chamfer or radius may join the lower shoulder 64b with the outer periphery of the pumping plunger 42 where this chamfer or radius is considered to be a portion of the sealing ring groove 64. A base 64c of the sealing ring groove 64 connects the two shoulders 64a, 64b.

[0033] A diametric clearance 69 between the pumping plunger 42 and the plunger bore 34 (i.e. a diameter of the plunger bore 34 minus a diameter of the pumping plunger 42) is greater than 12 microns and less than 30 microns such that a portion of the diametric clearance 69 is located between the sealing ring groove 64 and the first end 42a and extends for a second distance 70. In the illustrated example, the second distance 70 extends from the first or upper surface 30a of the pump housing 30 to where the sealing ring groove 64 begins, that is the 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 the first distance 68, and preferably at least eight times the first distance 68, and such that another portion of the diametric clearance 69 is located between the sealing ring groove 64 and the second end 42b and extends for a third distance 72 which is at least two times the first distance 68 and is preferably at least four times the first distance 68. In the illustrated example, the third distance 72 extends from the 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.

[0034] As illustrated in the figures, the portion of the diametric clearance 69 that is located between the sealing ring groove 64 and the 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 42a is circular and does not include spill features such as notches or flutes and the like. 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 plunger 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 30 and better control of tolerances. An exemplary location for such an insert is shown in Figure 2 as reference 71 , the insert member 71 being shown in dashed lines.

[0035] Similarly, the portion of the diametric clearance 69 that is located between the sealing ring groove 64 and the second end 42b may be continuous, however, may alternatively be discontinuous.

[0036] By having the second distance 70 be at least four times the first distance 68 and preferably eight times the first distance 68, the portion of the diametric clearance 69 which extends over the second distance 70 provides a pressure drop to the fuel such that the sealing ring 66 is not subjected to the full pressure experienced within the pumping chamber 32, thereby increasing the service life of the sealing ring 66. Furthermore, by having the second distance 70 be at least four times the first distance 68, and preferably eight times the first distance 68, and by having the third distance 72 be at least two times the first distance 68, and preferably at least four times the first distance 68, tilting of the pumping plunger 42 is minimised which allows for a more reliable sealing contact between the sealing ring 66 and the plunger bore 34, thereby improving pumping efficiency and durability of the sealing ring 66.

[0037] Expressed another way, the second distance 70 may be between four times and eight times the first distance 68, or even greater than eight times the first distance 68, and the third distance 72 may be between two times and four times the first distance 68, or greater than four times the first distance 68. It will be appreciated from observing the Figures that the diametric clearance 69 is constant / continuous along the length of the plunger 42 whilst the plunger 42 is within the plunger bore 34, except for the location of the sealing ring groove 64.

[0038] In a further example, the second distance 70 may be between five times and six times the first distance 68.

[0039] In the above discussion, the location of the sealing ring groove 64 in the plunger 42 has been expressed in terms of the second distance 70 between the upper shoulder 64a of the sealing ring groove 64 and the upper surface 30a of the pump housing, that is to say that the second distance is the length of the plunger bore 34 in the plunger housing 30 that extends to the location of the sealing ring groove 64.

[0040] It should be noted that the second distance 70 is determinable at the ‘free length’ or ‘free position’ of the plunger 34, which can be considered to be when the pump is at rest, without its position being influenced by the camshaft 44. That is to say, the ’free position’ of the plunger 34 can be considered to be the position at which the plunger 34 rests when the pump 22 is not installed in an engine 12, so that the return spring 50 urges the plunger 34 into an outermost point of the pump stroke.

[0041] The location of the sealing ring groove 64 can also be expressed in terms of a distance from the end 42a of the plunger 42. As such, a fourth distance is illustrated in Figure 2 as reference 73. The fourth distance 73 may be at least five times the first distance 68, and preferably at least 12 times the first distance 69. In another example, the fourth distance 73 may be between five times and twelve times the first distance 68, and in a further example the fourth distance 73 may be between six times and nine times the first distance 68. In one example, the fourth distance 73 may be between six and seven times the first distance 68.

[0042] In a particular example, the second distance 70 is between five times and six times the first distance 68, and the fourth distance 73 is between six times and seven times the first distance 68.

[0043] 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 its low friction and fuel resistant properties or PEEK (polyether ether ketone).

[0044] Observations have been made that the 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 66, i.e. the lower end surface of the sealing ring 66 as seen in Figure 2, can show signs of accelerated wear which affects the volumetric efficiency of the fuel pump 22. One possible cause for this is that the basic sealing ring 66 must be deformed elastically in order to dilate its inner diameter so that it may be received over the pumping plunger 42 whereupon it can contract into the sealing ring groove 64 when in position. Without being bound by theory, it is believed that the elastic deformation of the sealing ring 66 as a result of imparting hoop stress on 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, overtime, can cause degradation of that edge.

[0045] FIGS. 3 to 6 illustrate a split sealing ring arrangement 100, or split ring, which may address some or all of the challenges discussed above. It should be noted that the split ring 100 shown in FIGS. 3 to 6 is apt 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. As 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 split ring 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 split ring 100.

[0046] At this point, it should be noted that FIGS 3 and 4 show the split ring 100 as it is located in the sealing ring groove 64 of the pumping plunger 42 of the fuel pump 22, wherein FIG. 4 shows the pumping plunger 42 and the split ring 100 also in section view. The split ring comprises a radially outer surface for interfacing, engaging, or otherwise contacting with the plunger bore 34 of the high-pressure fuel pump 22, and a radially inner surface for interfacing, engaging or contacting with a base 64c of the sealing ring groove 64 of the pumping plunger 42. Additionally, the split ring 100 comprises upper and lower surfaces which join the radially inner and outer surfaces.

[0047] Figures 5A and 5B illustrate the split ring 100. The split ring 100 has a split ring form provided by way of a circumferential discontinuity. A body 102 of the split ring remains substantially annular in form and comprises a singular split 104 to create the circumferential discontinuity. The split 104 comprises at least one split plane 106 that is parallel to the central axis 36. In effect, the discontinuity provides a planar cut through the thickness of the body 102 thereby creating two opposed ends. The split ring 100 is made discontinuous with the split 104 comprising a singular split plane 106. As the split 104 comprises just one split plane 106, this split arrangement will be known henceforth as a planar split. The split plane 106 intersects a secant line 108 of the split ring arrangement 100 that is radially offset from the central axis 36. An offset distance 110 of the secant line from the central axis 36 is also less than a length of an inner radius 112 of the split ring 100. The secant line 108 extends ad infinitum beyond the outer radius 114 of the split ring 100. The split plane 106 is also parallel to the central axis 36. In other words, the planar split 106 extends axially though the body 102 of the split ring 100. The split plane 106 therefore intersects the body 102 of the split ring 100 in two locations A, B, however, the planar split 104 is provided at either one of these intersection location A, B. If the split 104 was provided at both of these intersection location A, B, the split ring 100 would no longer be unitary.

[0048] Advantageously, providing the split 104 in the split ring 100 makes assembly of the split ring 100 onto the pumping plunger 42 more straightforward than assembling a conventional sealing ring 66 onto the same pumping plunger 42. For example, specialised tooling is required to expand the conventional sealing ring 66 to allow it to pass over the outer periphery of the pumping plunger 42 before being seated into the sealing ring groove 64. This radial expansion introduced hoop stress to the sealing ring 66 that is potentially irreversibly damaging to the material of the sealing ring 66. This may cause premature degradation of the sealing ring 66 and reduced pumping efficiency of the high-pressure fuel pump 22 over time. The split ring 100 can be assembled to the pumping plunger 42 manually, i.e., without the need for specialised tools. Furthermore, bending the material of the split ring 100 in order to ‘open’ the split ring 100 for assembly onto the pumping plunger 42 is not considered to impart any damage to the split ring 100 that will cause material degradation during service.

[0049] Figure 6A and 6B illustrate and alterative embodiment of the split ring 200. In this embodiment, the split ring 200 is made discontinuous with a split 204 comprising two split planes 206A, 206B. As the split 204 comprises two split planes 206A, 206B, this split arrangement will be henceforth known as a chevron split, as the split 204 appears chevron-shaped in plan view, that is through a plane perpendicular to the axis 36. Similar to the planar split 104, a first split plane 206A of the chevron split 204 intersects a secant line 208 of the split ring 200 that is radially offset from and parallel to the central axis 36. As before, an offset distance 210 of the secant line 208 from the central axis 36 is also less than a length of the inner radius 212 of the split ring 200. A second split plane 206B of the chevron split 204 is also parallel to the central axis 36. It should be noted that the second split plane 206B of the chevron split 204 can intersect or be offset from the central axis 36. The second split plane 206B is angularly offset from the first split plane 206A. An intersection axis 216 is formed where the first and second split planes 206A, 206B intersect.

[0050] A radial distance of the intersection axis 216 from the central axis 36 is greater than the length of the inner radius 212 of the split sealing ring arrangement 200 and less than the length of the outer radius 214 of the spit sealing ring arrangement 200. In other words, the position of the intersection axis 216 is within the body 202 of the split ring 200. The inclusion of the intersection axis 216 within a boundary of the body 202 of the split ring 200 provides the chevron split with its distinctive shape.

[0051] The skilled person will appreciate that a first split portion 204A formed on the first split plane 206A may be positioned radially inward of a tangent line 218 intersecting the intersection axis 216 of the split planes 206A, 206B. Correspondingly a second split portion 204B formed on the second split plane 206B would be positioned radially outward of the tangent line 218. This ensures that the chevron split 204 does not become a re-entrant feature, in other words, the split ring 200 would remain continuous. Alternatively, the positions of the first and second split portions 204A, 204B could be reversed, with the first split portion 204A being positioned radially outward of the tangent line 218 and the second split portion 204B being radially inward of the tangent line 218.

[0052] FIGs. 7A and 7B show an alternative embodiment of the split sealing ring arrangement 300 where the split sealing ring arrangement 300 has a two-part nested structure and, as such, comprises a first sealing ring element 302 and a second sealing ring element 304. Both the first sealing ring element 302 and the second sealing ring element 304 are annular in form. More specifically, in this example both the sealing ring elements 302, 304 have a circular outer diameter in plan, as is consistent with their role in sealing against a cylindrical plunger bore 34. The first sealing ring element 302 extends in a direction along the axis 36 and as such defines a radial outer surface 306 and a radial inner surface 308, an axially upper surface 310 and an axially lower surface 312. The radial inner surface 308 is engaged with the base 64c of the sealing ring groove 64 in a sealing fit. The radial outer surface 306 is engaged with the plunger bore 34 in a sealing fit.

[0053] The first sealing ring element 302 is configured and proportioned so that at least a portion of it is nested within a radially inner area defined by the second sealing ring element 304. That is to say, the first sealing ring element 302 has at least a portion that has an outer diameter sized so that it is smaller than a portion of the second sealing ring element 304 that has a larger inner diameter. As such, a portion of the first sealing ring element 302 is able to be received within the inner open circular area formed by the annular shape of the second sealing ring element 304. Expressed another way, at least a part of the first sealing ring element 302 fits inside an open annular portion of the second sealing ring element 304. Notably, the axial length of the second sealing ring element 304 fits inside the axial length of the first sealing ring element 302 (see Figure 7B). Therefore, the combination of the first and second sealing ring elements 302, 304, when assembled, does not exceed the axial length of the first sealing ring element 302.

[0054] In more detail, the first sealing ring element 302 extends in a direction along the axis 36 and as such defines a radial outer peripheral surface 306 and a radial inner surface 308, an axially upper surface 310 and an axially lower surface 312. The radial outer surface 306 is engaged with the plunger bore 34 in a sealing fit. The first sealing ring element 302 therefore extends radially between the sealing ring groove 64 and the plunger bore 34.

[0055] The first sealing ring element 302 is shaped to define first and second annular portions 314, 316 which are part of the same integral whole. The second annular portion 316 has a reduced annular dimension as compared to the first annular portion 314. The first annular portion 314 is axially above the second annular portion 316 in the Figures. The first annular portion 314 provides the radial outer surface 306 and part of the radial inner surface 308. The second annular portion 316 also provides a part of the radially inner surface 308. The second annular portion 316 also provides a second radial outer surface 318. The second radial outer surface 318 is radially offset from the radial outer surface 306, which will now be referred to as the ‘first’ radial outer surface 306, and has a reduced diameter compared to it. The first radial outer surface 306 and the second radial outer surface 318 are separated by a shoulder 320. It should be noted that the second radial outer surface 318 does not engage with the plunger bore 34.

[0056] A chamfer 330 may be provided between the axially upper surface 310 and the radial outer surface 306. The chamfer 330 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.

[0057] In this example, the second radial outer surface 318 is frustoconical in form to provide an inwardly tapering portion of the first split sealing ring element 302. The tapering form is not essential, however, and as such it should be noted that the second radial outer surface 318 may be substantially vertical. A tapering surface, as shown, is believed to ease the process of assembly of the two sealing ring elements 302, 304. The second sealing ring element 304 has a less complex configuration compared to the first sealing ring element 302. The second sealing ring element 304 extends in a direction along the central axis 36 and as such defines a radial outer surface 322 and a radial inner surface 324, an axial upper surface 326 and an axial lower surface 328.

[0058] It will be noticed that the radial outer surface 322 is engaged with the plunger bore 34, whilst the axial lower surface 328 opposes the lower side surface 64b of the plunger sealing groove 64. The radial inner surface 324 of the second split sealing ring element 304 is engaged with the second radial outer surface 318 of the first sealing ring element 302.

[0059] In one example, the sealing ring arrangement 300 may be sized and shaped such that the two sealing ring elements 302, 304, when assembled onto one another, fit within the sealing ring groove 64 in a tight fit. During use, therefore, the two sealing ring elements 302, 304 will be compressed into the sealing ring groove 64 during a pumping event as fluid pressure acts on the surfaces of the sealing ring arrangement 300.

[0060] In another example, the sealing ring arrangement 300 may be sized and shaped so that a clearance is defined between the upper and lower surfaces 310, 312, 328 of the sealing ring arrangement 300 and the opposing surfaces of the sealing ring groove 64. The clearance or gap in the axial dimension or ‘height’ of the sealing ring groove 64 and the axial dimension of the sealing ring arrangement 300 may be between 3% and 15% of the axial dimension of the sealing ring arrangement 300, 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 300 from its upper surface 310 and also the radial inner surface 308 which on turn causes the first sealing ring element 302 to be urged into engagement with the plunger bore 34.

[0061] It will be appreciated in the above discussion that the geometry of the second sealing ring element 304, and particularly the dimensions of the radial inner surface 324, defines an open central area of the second sealing ring element 304 within which a portion of the first sealing ring element 302, and more specifically the second annular portion 316 thereof, can be received. The first sealing ring element 302 therefore at least partially nests within the second sealing ring element 304. The geometry of the first sealing ring element 302 relative to the second sealing ring element 304 is clearly apparent in FIG. 7B. As will be appreciated, the geometry of the second sealing ring 304 is such that it defines an open central area X.

[0062] The geometry of the open central area X is configured such that the second annular portion 316 of the first sealing ring element 302 fits within it. In particular, when the second annular portion 316 of the first sealing ring element 302 is received within the open central area X, it will be noted that the frustoconical surface 318 of the first sealing ring element 302 rests against or engages the radially inner surface 324 of the second sealing ring element 304. In this example, the radially inner surface 324 of the second sealing ring element 304 is also frustoconical. Here, the angle of inclination that the radial inner surface 324 of the second sealing ring element 304 makes with the axis 36 is substantially the same as the angle of inclination of the frustoconical surface 318 of the first sealing ring element 302.

[0063] The position of the second sealing ring element 304 when it is engaged with the first sealing ring element 302 is shown in FIG. 7B is dotted lines and marked as ‘Y’. In this position, it was be seen that the axial lower surface 312 of the first sealing ring element 302 is axially aligned with the axial lower surface 328 of the second sealing ring element 304.

[0064] A benefit of providing the sealing ring arrangement 300 in two parts is that the second sealing ring element 304 may be formed from a different material as compared to the first sealing ring element 302. This provides the opportunity to form the second sealing ring element 304 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 302 is formed from PTFE. It is believed that forming the second sealing ring element 304 from a ‘stronger’ material such as PEEK may avoid any extrusion problem of the first sealing ring element 302 that is formed from a material that is softer than the material of the second sealing ring element 304, such as PTFE, whilst the sealing ring arrangement 300 is being pushed to the lower surface 64b of the sealing ring groove 64 during a pumping event. However, the material of the first sealing ring element 302 is more suitable for sealing against the plunger bore 34. Furthermore, another benefit may be that the two-part form of the sealing ring arrangement 300 permits high-pressure fuel to penetrate between the first and second sealing ring element 302, 304 and force expansion of the second sealing ring element 304 in a radially outward direction, increasing the pressure with which the second sealing ring element 304 forms with the plunger bore 34. The sealing effect may be improved by this mechanism. Beneficially, PEEK is considered to be a harder material than PTFE and so advantages are achieved by forming the second sealing ring element 304 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 304 for its ‘anti-extrusion’ properties, thereby providing protection on the axial lower edge of the sealing ring arrangement 300. In contrast, the material of PTFE for the first sealing ring 302 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 302 which acts as a sliding sealing interface with the plunger bore, but which also is required to dilate under pressure.

[0065] In this context, it will be appreciated there may be benefits in forming the sealing ring element that is further from the high-pressure side of the pumping plunger (e.g., the second sealing ring element 304, in this example) from a stronger material than the other sealing ring element 302. The term ‘strength’ may be constituted by the hardness of the material, so that the hardness rating (e.g. Shore D scale) of the second sealing ring element 304 may be more than the hardness rating of the first sealing ring element 302. The "strength” of the sealing ring elements may also be constituted by other suitable parameters, as discussed above. The hardness rating of the sealing ring element that is closer to the pumping end of the plunger 42 (in this case the first sealing ring element 302) may be selected so that it is less than the hardness rating of the sealing ring element that is further away from the pumping end of the plunger. Positioning the harder (or stronger) sealing ring element on the side of the other sealing ring element that is further away from the high-pressure side of the pumping plunger 42 is believed to guard against possible extrusion effects of that sealing ring element and provide an overall more robust sealing ring arrangement 100. Therefore, the skilled person will understand that materials other than PTFE and PEEK may be suitable for the first sealing ring element 302 and the second sealing ring element 304 respectively, based on the above discussion of suitable characteristics required for each of the sealing ring elements.

[0066] It will be appreciated by the reader that the first and second sealing ring elements 302, 304 can comprise either the planar split or the chevron split as described in the above embodiments. Furthermore, the first sealing ring element 302 could remain circumferentially continuous and the second sealing ring element 304 could comprise a circumferential discontinuity in the form of either the planar or chevron split as described above. Beneficially, providing the second sealing element comprising the harder and less elastic material with a split will aid assembly of the sealing ring arrangement 300 onto the pumping plunger 42.

[0067] 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 (22) 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 a central axis (36) and opens into said pumping chamber; a pumping plunger (42) which reciprocates within said plunger bore along the central axis such that reciprocation of said pumping plunger within said plunger bore increases and decreases a volume of said pumping chamber; wherein the pumping plunger includes a sealing ring groove (64) that is annular in shape and extends about the pumping plunger (42) so as to define an upper surface (64a), a lower surface (64b) and a base surface (64c) extending between the upper surface and the lower surface; further comprising a plunger sealing ring (100) accommodated in the sealing ring groove; wherein the plunger sealing ring has a split ring form provided by way of a circumferential discontinuity; wherein at least a portion of the circumferential discontinuity (104) of the split ring form is planar and comprises a split plane (106) which is parallel to and offset from the central axis.

2. The fuel pump (22) of Claim 1 , wherein the circumferential discontinuity (104) is planar.

3. The fuel pump (22) of Claim 1 , wherein the circumferential discontinuity (204) is biplanar or chevron shaped comprising two split planes (206A, 206B).

4. The fuel pump (22) of Claim 3, wherein both split planes (206A, 206B) are parallel to the central axis (36).

5. The fuel pump (22) of any preceding claim, wherein at least one split plane (106) is colinear with a secant line (108) of the sealing ring (100) that is offset from the central axis (36).

6. The fuel pump (22) of any one of the preceding claims, wherein an upper surface of the plunger sealing ring (100) engages the upper surface (64a) of the sealing ring groove (64).

7. The fuel pump (22) of any one of the preceding claims, wherein a lower surface of the plunger sealing ring (100) engages the lower surface (64b) of the sealing ring groove (64).

8. The fuel pump (22) of any one of the preceding claims, comprising the plunger sealing ring (302) as a first sealing ring, and further comprising a second sealing ring (304) that complements first sealing ring (302).

9. The fuel pump (22) of Claim 8, wherein the first sealing ring (302) comprises a first material and wherein the second sealing ring (304) comprises a second material, wherein the first material is different to the second material.

10. The fuel pump (22) of Claim 9, wherein the second material comprises a higher shore hardness value than that of the first material.

11. The fuel pump (22) of Claim 10, wherein the first sealing ring (302) is located in an axial position closer to a high-pressure side of the pumping plunger (42) compared to the axial position of the second sealing ring (304).

12. The fuel pump (22) of any one of Claims 8 to 11, wherein the second sealing ring (304) does not have a circumferential discontinuity.

13. The fuel pump (22) of any one of Claims 8 to 12, wherein at least a portion of the first sealing ring (302) is nested within the second sealing ring (304).

14. The fuel pump (22) of any of Claimsa 9 to 13, wherein the first material is a thermoplastic polymer, optionally PTFE.

15. The fuel pump (22) of any of Claims 9 to 14, wherein the second material is a thermoplastic polymer, optionally PEEK.

16. The fuel pump (22) of any one of the preceding claims, wherein a diametric clearance (69) is provided between the plunger bore (34) and the pumping plunger (42) which extends from the sealing ring groove (64) to an upper end of the plunger bore, wherein the diametric clearance is between 12 microns and 30 microns.

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