Fuel injector assembly

Abstract

A gaseous fuel injector assembly (fig.2,10) comprising an inlet (fig.3,34) and an outlet 50. The injector has an injector unit (fig.1,20) comprising an injector housing (fig.1,22) and a valve assembly

Description

FIELD OF THE INVENTION This invention belongs to the field of fuel injector assemblies, particularly gaseous fuel injector assemblies. TECHNICAL BACKGROUND Fuel injector assemblies are well known components of combustion engine systems. Historically, most combustion engines have utilised liquid fuels, such as petrol / gasoline or diesel. However, in light of the relatively recent trend in the automotive industry towards cleaner fuels, gaseous fuels, especially hydrogen, have been investigated as a way to reduce the carbon footprint of vehicles such as cars and trucks while still making use of the decades of progress made in combustion engine technology. Nevertheless, the move towards gaseous fuels does present a need to adapt certain aspects of existing fuel system architectures due to certain features of gaseous fuels. It is against this background that the invention has been devised. SUMMARY OF THE INVENTION In a first aspect, the invention provides a gaseous fuel injector assembly comprising: an inlet; an outlet; an injector unit comprising an injector housing and a valve assembly configured to control the flow of fuel between the inlet and the outlet; and a seating member. The seating member comprises: a seat body; a valve seat; and at least one foraminous filter region disposed between the inlet and the outlet, wherein the at least one foraminous filter region is integral with the seat body. The assembly may further comprise a first circumferential seal and a second circumferential seal that seals the seating member to the injector housing. The first circumferential seal and the second circumferential may together define an axially-extending annular sealed space between said seals, and an axial span of the at least one foraminous filter region may be wholly defined within the axially-extending annular sealed space. The first circumferential seal may comprise a first circumferential weld joint between the seating member and the injector housing. The second circumferential seal may comprise a second circumferential weld joint between the seating member and the injector housing. Alternatively, or additionally, the second circumferential seal may comprise an elastomeric sealing member engaged between the seating member and the injector housing. The at least one foraminous filter region may have a reduced radial thickness compared to the seat body. The seating member may comprise a plurality of foraminous filter regions equi-angularly spaced around the circumference of the seating member, wherein neighbouring filter regions are separated by axially extending struts defined in the seat body. In a second aspect, the invention provides a method of manufacturing a seating member for a gaseous fuel injector assembly. The method comprises: injection moulding a seat body; and integrally forming a foraminous filter region within the seat body. The step of forming the foraminous filter region within the seat body may comprise injection moulding the foraminous filter region together with the seat body. Alternatively, the step of forming the foraminous filter region within the seat body may comprise laser drilling perforations in the seat body. In a third aspect, the invention provides a method of assembling a gaseous fuel injector assembly. The method comprises: providing an injector unit comprising an injector housing and a valve assembly; providing a seating member comprising a seat body and at least one foraminous filter region integral with the seat body; engaging the injector unit with a valve seat of the seating member such that the valve assembly is received within the valve seat; and sealing the injector unit to the seating member. The step of sealing the injector unit to the seating member may comprise: making a first circumferential seal between the seating member and the injector housing; and making a second circumferential seal between the seating member and the injector housing, wherein the first circumferential seal and the second circumferential seal together define an axially-extending annular sealed space between said seals. An axial span of the at least one foraminous filter region may be wholly defined within the axially-extending annular sealed space. The step of making the first circumferential seal may comprise welding a first circumferential weld joint between the seating member and the injector housing. The step of making the second circumferential seal may comprise welding a second circumferential weld joint between the seating member and the injector housing. Alternatively, or additionally, the step of making the second circumferential seal may comprise engaging an elastomeric sealing member between the seating member and the injector housing. Different elements of the different aspects of the invention may be combined where appropriate. BRIEF DESCRIPTION OF THE DRAWINGS So that it may be more easily understood, the invention will now be described with reference to the following drawings, in which: Figure 1 shows a cross-sectional view of a gaseous fuel injector assembly; Figure 2 shows a cross-sectional view of an interface between an injector unit and a seating member in a gaseous fuel injector assembly; Figure 3 shows a three-dimensional view of the interface and the seating member shown in Figure 2; Figure 4 shows a perspective cut-away view of the seating member shown in Figures 2 and 3; and Figure 5 shows a cross-sectional view of an alternative embodiment of the injector assembly, to show an interface between an injector unit and a seating member. DETAILED DESCRIPTION Fuel injector assemblies control the delivery of fuel into an internal combustion engine. Figure 1 shows a fuel injector assembly 10 for gaseous fuels. As is typical, the fuel injector assembly 10 comprises an injector unit 20. The injector unit 20 comprises an injector housing 22, within which a valve assembly 24 is received. The valve assembly 24 comprises a valve needle 26, which is biased against a valve seat 42, defined by a seat body 40, by the action of a spring 28 to hold the injector assembly 10 in a closed position. The valve needle 26 can be moved away from the valve seat 42 against the biasing action of the spring 28 under the action of an actuator. In Figure 1, the actuator takes the form of a solenoid actuator including a coil 30 that generates an electromagnetic field that causes an armature 32 to move upwardly away from the valve seat, against the biasing spring force. The armature 32 is engaged with the valve needle 26 and so the movement of the actuator 32 lifts the valve needle 26 away from the valve seat 42. With the valve needle 26 lifted away from the valve seat 42, the injector assembly 10 is considered to be in an open position. The injector housing 22 comprises at least one inlet 34. The inlet 34 shown in Figure 1 is a side feed inlet. A filter 44 is disposed between the seat body 40 and the injector housing 22. The filter 44 comprises a cylindrical filter body 46 that supports a plurality of foraminous, or perforated, filter regions 48, designed to remove any solid impurities from fuel as it flows through the filter 44. By foraminous, it is meant that the filter regions 48 comprise a plurality of small holes extending through each filter region 48 to allow fuel to flow therethrough. The cylindrical shape of the filter 44 is a consequence of the side-feed architecture of the injector assembly 10. The filter body 46 may typically be made from a plastic material or may also be made from metal. Fuel enters the fuel injector assembly 10 via the inlet or inlets 34 in the injector housing 22. From there, it passes through the foraminous filter regions 48 and into a chamber defined by the interior of the filter body 46. Further passage of the fuel through the injector assembly 10 is prevented by the bearing of the valve needle 26 against the valve seat 42 until the valve needle 26 is lifted away from the valve seat 42 by the action of the coil 30 and armature 32. With the injector assembly 10 in an open position, fuel flows through an opening 50 defined by the valve seat 42 and into the engine. The opening 50 therefore acts as an outlet for the injector assembly 10. Figures 2 and 3 show close up views of the region around the valve seat 42 for an injector assembly 10 of an embodiment of the invention. Figure 2 is a cross-sectional view, while Figure 3 shows a perspective view. Figures 2 and 3 show the inlet or inlets 34, the injector housing 22 and the valve needle 26. In contrast to the injector assembly 10 shown in Figure 1, the injector assembly 10 shown in Figures 2 and 3 comprises a seating member 52 that incorporates both a valve seat 42 and foraminous filter regions 48. Therefore, the seating member 52 shown in Figures 2 and 3 incorporates the functionality of both the valve seat 42 and the filter 44 of the injector assembly 10 shown in Figure 1. The seating member 52 is shown in isolation in Figure 4 in cut-away view. The seating member 52 comprises a generally cylindrical seat body 40. The seat body 40 comprises an inner platform 58. The platform 58 separates the seating member 52 into an upper region 60 and a lower region 62, with the upper region 60 being disposed closer to the valve assembly 24 than the lower region 62 when the seating member 52 is received in place in the injector assembly 10. Throughout this description, terms such as ‘upper’ and ‘lower’, and other directional references, are used with reference to the orientation of the fuel injector as shown in the accompanying drawings. However, it will be appreciated that such references are not limiting and that fuel injectors according to the invention can be used in any orientation. The valve seat 42 is defined on the platform 58. The valve seat 42 shown in Figures 2 to 5 takes the form of a petaloid arrangement of raised protuberances. Each protuberance 42 defines an opening 50 in the form of a radially-oriented slot through the platform 58. However, the skilled person will be aware of other ways in which the valve seat 42 and opening, or openings, 50 may be realised. For example, the valve seat 42 and opening 50 may both be defined by a central bore through the platform 58, within which the valve needle 26 is received and which is sized such that the valve needle 26 prevents fluid flow through the bore when received therein. The filter regions 48 are defined in the cylindrical walls of the seat body 40 in the upper region 60, and are formed integrally with the walls of the seat body 40. As such, the seating member 52 acts as an integrated seat and filter (i.e. the valve seat 42 and the filter region(s) 48 are integrally formed within the seat body 40 of the seating member 52). In Figures 3 and 4, a plurality of filter regions 48 are shown, equi-angularly spaced around the circumference of the seating member 52 and separated by axially extending struts 64 defined by the seat body 40. The struts 64 provide mechanical support to the filter regions 48 when the seating member 52 is pressed into place in the injector assembly 10. However, the skilled person will appreciate that the number of individual filter regions 48 is not of central importance and, provided the filter region 48 is strong enough to withstand installation, one continuous filter region 48 may be present that extends around the entire circumference of the seat body 40. It will also be apparent that the filter regions 48 in Figure 4 have a reduced radial thickness compared to the rest of the seat body 40, including the struts 64. The reduced radial thickness of the filter regions 48 results in the creation of arcuate relief channels 68 around the filter regions 48 when the seating member 52 is received in place in the injector housing 22. This allows fuel to flow around the outside of the filter regions 48 such that the whole area of each filter region 48 is accessible to the gaseous fuel. The struts 64, being of the same radial thickness as the seat body 40, delimit the circumferential extent of each arcuate relief channel 68. Although there is the possibility of very limited fluid flow across a strut 64 and between neighbouring relief channels 68, this does not occur at sufficient rate for neighbouring relief channels to be considered to be in fluid communication in a functionally substantive way. As such, each filter region 48 (and corresponding relief channel 68) must be in fluid communication with at least one inlet 34. Depending on the angular circumferential extent of a filter region 48, a plurality of inlets 34 may be present. However, it is still desirable for the area of each filter region 48 to be greater than the area of the inlet, or inlets, 34 feeding that filter region 48. This helps to ensure that the pressure drop as fuel flows across the filter regions 48 does not impede flow of the fuel too greatly. An equi-angular distribution of the filter regions 48 and the inlets 34 is preferred to ensure even fuel flow around the valve needle and through the opening 50. To manufacture the seating member 52, the seat body 40, including the inner platform 58 and the valve seat 42, is formed by injection moulding. The foraminous filter region, or regions, 48 are formed in the seat body 40, either as part of the injection moulding process, or by way of laser drilling the perforations in the seat body 40 after the seat body 40 has been moulded. Laser drilling, in particular, offers an opportunity for very fine control of the size and distribution of the perforations to define the filter regions 48. As can be seen in Figures 2 and 3, the seating member 52 is received within the injector housing 22. The seating member 52 is press fit into the injector housing 22 and sealed thereto to prevent the leaking of fuel therearound. This prevents fuel from bypassing the filter regions 48. Specifically, the injector assembly 10 comprises a first circumferential seal 54 and a second circumferential seal 56, with each of the seals 54, 56 acting between the seat body 40 of the seating member 52 and the injector housing 22. The first and second circumferential seals 54, 56 are axially separated along the cylindrical axis of the seating member 52 such that an axially-extending annular sealed space 66 is defined in the axial span between the two seals 54, 56. The first circumferential seal 54 is axially disposed on a lower side of the seating member 52 with respect to the filter regions 48 and the opening of the inlet or inlets 34, while the second circumferential seal 56 is axially disposed on an upper side of the seating member 52 with respect to the filter regions 48 and the opening of the inlet or inlets 34. As a result of the disposition of the first and second circumferential seals 54, 56 either side of the filter regions 48 and the opening of the inlet or inlets 34, the axial spans of the filter regions 48, the arcuate relief channels 68 and the opening of each inlet 34 are wholly contained within the axial span of the sealed space 66. Viewed another way, a radially outward side, or inlet side, of each filter region 48 is wholly contained within the annular sealed space 66, as is the opening of each inlet 34. Beneficially, this arrangement ensures that all fuel flowing through the inlet 34 passes through the filter regions 48. The arcuate relief channels 68 may therefore be considered sub-regions of the annular sealed space 66. In Figures 2 and 3, both the first and second circumferential seals 54, 56 are formed by circumferential weld joints between the seat body 40 of the seating member 52 and the injector housing 22 of the injector unit 20. The circumferential weld joints are formed in respective welding grooves in the injector housing 22, as best shown in Figure 3. However, the skilled person will be aware of other ways in which the sealing capability may be achieved in order to prevent fuel bypassing the filter regions 48. For example, Figure 5 shows an alternative embodiment of the injector assembly 10 to that shown in Figures 2 and 3 in which the second circumferential seal 56 is formed by the engagement of an elastomeric sealing member, such as an O-ring in between the seating member 52 and the injector housing 22. In current injector assemblies, stack-up issues can occur as a result of the valve seat 42 and filter regions 48 being defined by a separate seat body 40 and filter 44, especially when considering manufacturing tolerances of the two components. This can lead to vertical movement of the filter 44 during the lifetime of the injector assembly 10. This poses a risk of the sealing of the filter 44 to other components in the injector assembly failing, allowing the bypass of contaminants past the filter and into the cylinders of the engine. In contrast, by integrating the filter regions 48 and the valve seat 42 into the seating member 52, these stack-up issues can be avoided, and the integral formation of the filter regions 48 within the seat body 40 prevents any migration of the filter regions 48 relative 5 to the valve seat 42, enabling more effective filtration of contaminants across the lifetime of the injector assembly 10. The integrated nature of the seating member 52 is particularly beneficial in the context of a high-flow gaseous fuel injector, as gaseous fuels are more prone to finding leak paths (such as between the seat body 40 and filter 44 of Figure 1) in the system architecture, especially when the flow of fuel through the system is high. 10 It will be appreciated that modifications may be made to the seating member 52 and the injector assembly 10 while still falling within the scope of the appended claims.

Claims

1. A gaseous fuel injector assembly (10) comprising:an inlet (34);an outlet (50);an injector unit (20) comprising an injector housing (22) and a valve assembly (24) configured to control the flow of fuel between the inlet (34) and the outlet (50); and a seating member (52), wherein the seating member (52) comprises:a seat body (40);a valve seat (42); andat least one foraminous filter region (48) disposed between the inlet (34) and the outlet (50), wherein the at least one foraminous filter region (48) is integral with the seat body (40).

2. The gaseous fuel injector assembly (10) of Claim 1, further comprising a first circumferential seal (54) and a second circumferential seal (56) sealing the seating member (52) to the injector housing (22), wherein the first circumferential seal (54) and the second circumferential seal (56) together define an axially-extending annular sealed space (66) between said seals (54, 56), and wherein an axial span of the at least one foraminous filter region (48) is wholly defined within the axially-extending annular sealed space (66).

3. The gaseous fuel injector assembly (10) of Claim 2, wherein the first circumferential seal (54) comprises a first circumferential weld joint between the seating member (52) and the injector housing (22).

4. The gaseous fuel injector assembly (10) of Claim 2 or Claim 3, wherein the second circumferential seal (56) comprises a second circumferential weld joint between the seating member (52) and the injector housing (22).

5. The gaseous fuel injector assembly of Claim 2 or Claim 3, wherein the second circumferential seal (56) comprises an elastomeric sealing member engaged between the seating member (52) and the injector housing (22).

6. The gaseous fuel injector assembly of any preceding claim, wherein the at least one foraminous filter region (48) has a reduced radial thickness compared to the seat body (40).

7. The gaseous fuel assembly (10) of any preceding claim, wherein the seating member (52) comprises a plurality of foraminous filter regions (48) equi-angularly spaced around the circumference of the seating member (52), wherein neighbouring filter regions (48) are separated by axially extending struts (64) defined in the seat body (40).

8. A method of manufacturing a seating member (52) for a gaseous fuel injector assembly (10), comprising:injection moulding a seat body (40); andintegrally forming a foraminous filter region (48) within the seat body (40).

9. The method of Claim 8, wherein the step of forming the foraminous filter region (48) within the seat body (40) comprises injection moulding the foraminous filter region (48) together with the seat body (40).

10. The method of Claim 8, wherein the step of forming the foraminous filter region (48) within the seat body (40) comprises laser drilling perforations in the seat body (40).

11. A method of assembling a gaseous fuel injector assembly (10), comprising:providing an injector unit (20) comprising an injector housing (22) and a valve assembly (24);providing a cylindrical seating member (52) comprising a seat body (40) and at least one foraminous filter region (48) integral with the seat body (40);engaging the injector unit (20) with a valve seat (42) of the seating member (52) such that the valve assembly (24) is received within the valve seat (42); and sealing the injector unit (20) to the seating member (52).

12. The method of Claim 11, wherein the step of sealing the injector unit (20) to the seating member (52) comprises:making a first circumferential seal (54) between the seating member (52) and the injector housing (22);making a second circumferential seal (56) between the seating member (52) and the injector housing (22),wherein the first circumferential seal (54) and the second circumferential seal (56) together define an axially-extending annular sealed space (66) between said seals (54, 56), and wherein an axial span of the at least one foraminous filter region (48) is wholly defined within the axially-extending annular sealed space (66).

513. The method of Claim 12, wherein the step of making the first circumferential seal (54) comprises welding a first circumferential weld joint between the seating member (52) and the injector housing (22).10 14. The method of Claim 12 or Claim 13, wherein the step of making the secondcircumferential seal (56) comprises welding a second circumferential weld joint between the seating member (52) and the injector housing (22).

15. The method of Claim 12 or Claim 13, wherein the step of making the second 15 circumferential seal (56) comprises engaging an elastomeric sealing member between the seating member and the injector housing (22).

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