Fuel injector

Abstract

A fuel injector installation comprising an engine housing component 30 defining a pocket, and a fuel injector 110 received within the pocket. The injector has an electromagnetic actuator comprising a

Description

FIELD OF THE INVENTION This invention relates to a fuel injector for gaseous fuel. In particular, but not exclusively, the invention relates to a fuel injector for use in a fuel system of an internal combustion engine for a gaseous fuel such as hydrogen. BACKGROUND Gaseous fuels such as hydrogen are promising alternative fuels to gasoline and diesel due to their potential for low or zero emissions and there has been considerable interest in developing traditional internal combustion engines to run on ecologically produced hydrogen. High pressure injection of gaseous fuels into the combustion chamber of an internal combustion engine offers benefits, including reduced compression work, reduced susceptibility to uncontrolled auto-ignition, and greater flexibility in combustion strategies resulting in improved efficiency. A relatively low flow fuel injector for hydrogen fuel is already known, particularly for use with internal combustion engines, but there remains a need fora relatively high flow injector to satisfy the demands of engines with fuel cells. Injectors that can deliver the requisite high flows typically include a large flow area that require a significant magnetic force from an electromagnetic actuator to open an inwardly opening injector valve needle. The injector must open against a large gaseous fuel pressure difference between the injector inlet and the injector outlet. In order to generate the necessary force from the electromagnetic actuator, it is necessary to apply a large electrical current to the solenoid of the actuator, which can consequently lead to a high increase in temperature within the solenoid and the surrounding components. In some injector applications it is sufficient to rely on the injector off time to allow the dissipation of thermal energy. It is also known to manage the thermal energy within the injector using active cooling means, including the use of a fuel flow through the injector during injection. It is also known to provide a thermal conductive path for thermal energy from the injector to the fuel rail or the engine. One of the problems with fuel cell applications, however, is that the duration of injection is much longer than in internal combustion engine applications, which means the associated thermal loading is higher. Such injectors also tend to be side feed injectors so that fuel enters the injector much lower along the axial length of the injector and cannot easily be routed past the solenoid for cooling purposes. The mounting of an injector in a fuel cell engine also requires the mounting on an O-ring, and so thermal dissipation does not provide adequate cooling. It is against this background that the invention has been devised. SUMMARY OF THE INVENTION According to the invention, there is provided a fuel injector installation for a gaseous fuel system, the fuel injector installation comprising an engine housing component defining a pocket; a fuel injector, received within the pocket, for delivering gaseous fuel to the internal combustion engine; the fuel injector comprising an electromagnetic actuator to which a current is applied, in use, to activate the electromagnetic actuator; the electromagnetic actuator comprising a solenoid assembly comprising a solenoid tube housing a solenoid coil. The installation comprises a thermally conductive member comprising a first portion that extends axially along the fuel injector and is in connection with the solenoid assembly and a second portion that extends radially from the first portion and is configured for thermal connection with the engine housing component, so that the thermally conductive member provides at least a part of a heat transfer path between the solenoid assembly and the engine housing component for heat dissipation from the solenoid assembly. The provision of the thermally conductive member is advantageous because it allows heat within the solenoid assembly to dissipate to the engine housing component, thereby cooling the solenoid and other components of the fuel injector. The thermal load path is achieved through a convenient bracket component that may provide a direct thermal connection between the solenoid assembly and the engine housing component. The pocket may define an opening into which the fuel injector is received, and the second portion of the thermally conductive member may extend radially from an end of the first portion remote from the opening. In embodiments, the second portion of the thermally conductive member may define an engagement surface that faces away from the first portion. The fuel injector installation may further comprise a washer that is received within the pocket to engage between the engagement surface and the engine housing component to form a part of the thermal connection between the solenoid assembly and the engine housing component. In embodiments, the pocket may define an internal step, the washer being in engagement with the internal step. The washer not only provides a part of the thermal connection between the solenoid assembly and the engine housing component, but may be formed of a compliant material that takes up unwanted movement within the injector. The pocket may define an opening into which the fuel injector is installed, and the second portion of the thermally conductive member may extend radially from an end of the first portion proximal to the opening. For example, the second portion of the thermally conductive member may define an engagement surface for the engine housing component that faces towards the axially extending portion of the thermally conductive member. Alternatively, the second portion of the thermally conductive member may define an engagement surface for the engine housing component that faces away from the axially extending portion of the thermally conductive member. The fuel injector installation may comprise an overmould applied to an upper portion of the fuel injector, including at least a part of the axially extending portion of the thermally conductive member. The engagement surface may engage directly with a surface of the engine housing component to define the thermal connection to the engine housing component. The first portion of the thermally conductive member may be welded to the solenoid tube. The engine housing component may be formed from aluminium. The second portion of the thermally conductive member may comprise a plate that extends perpendicular to the injector axis. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a mounting portion of a known fuel injector installation for a fuel injector for gaseous fuel; Figure 2 is a cross section of a mounting portion of a fuel injector installation of a first embodiment; Figure 3 is a cross section of a mounting portion of a fuel injector installation of a second embodiment; Figure 4 is a perspective view of the fuel injector installation of either Figure 2 or Figure 3; Figure 5 is a cross section of a mounting portion of a fuel injector installation of a third embodiment; and Figure 6 is a perspective view of the fuel injector installation of Figure 5. Throughout this description, terms such as ‘upper’ and ‘lower’, and other directional references, are used with reference to the orientation of the injector as shown in the accompanying drawings. However, it will be appreciated that such references are not limiting and that injectors according to the invention can be used in any orientation. DETAILED DESCRIPTION OF THE INVENTION By way of background to the invention, an upper portion of a known fuel injector 10 is shown in Figure 1, to be installed within an engine housing component (not shown). Internally the injector 10 comprises an injection nozzle having an injector valve needle (not visible) that is inwardly-opening within the injection nozzle and is controlled by means of a servo valve mechanism, referred to generally as 12. Externally, the injector 10 can be seen to include several housing parts, including an actuator housing 14 and a main injector housing 16 for the valve needle. The fuel injector 10 is arranged to inject gaseous fuel in a gaseous fuel system comprising, for example, a combustion chamber of an internal combustion engine or a fuel cell by moving the valve needle towards and away from a valve needle seating to control the gaseous fuel flow through one or more injector outlets (not shown in Figure 1). An electromagnetic actuator (not shown in Figure 1) is positioned towards the upper end of the injector within the actuator housing 14. The electromagnetic actuator comprises a solenoid coil to which a current is supplied through an electrical connector (not shown) to generate an electromagnetic force that acts on the valve needle, directly or indirectly. The electrical connector is housed in a protrusion 18 of the actuator housing 14. Operation of the actuator therefore controls movement of the valve needle to control the injection of gaseous fuel. Gaseous fuel is introduced to the injector 10 via inlet ports 19 in the injector housing 16. The actuator housing 14 is formed from an overmould that is typically formed from plastic. The injector 10 is clamped to the fuel rail (or engine) through the plastic overmould. Also, being positioned on multiple O-rings, 22, 24, 26, there is no direct metal-to-metal contact between the injector and the fuel rail or engine to which it is mounted. Heating of the solenoid through operation presents a problem for the injector, as has been described previously. Without the ability to dissipate heat away from the solenoid, thermal damage may occur to the solenoid and / or the temperature increase can cause an increase in the resistance of the solenoid. If resistance increases too much, a threshold may be reached at which the voltage applied to the solenoid coil is unable to reach the target, preventing the injector from operating as desired. Any temperature increase may also lead to problems with a reduction in gaseous fuel flow due to the expansion of an elastomer damper (not shown) within the injector that affects needle lift. The invention addresses this problem by equipping the injector installation with a direct heat transfer path between the actuator and an external receptacle for the injector to allow heat to dissipate from the solenoid. Referring to Figure 2, an injector 110 is installed within an engine housing component 30 defining an opening or pocket 32 into which the injector 110 is received at the open end 33 thereof. The injector 110 comprises an actuator, referred to generally as 80, comprising a solenoid assembly having a solenoid coil 42 that is wound on a bobbin or holder 44. The solenoid assembly further comprises a solenoid tube 46, on which the solenoid coil 42 is wound, and a movable armature (not visible in Figure 2) that extends through the wound solenoid coil 42. As in the prior art of Figure 1, the armature is coupled to an injector valve needle (not shown) so that the electromagnetic force generated by applying a current to the solenoid coil 42 acts on the armature to control movement of the injector valve needle, along a main axis A-A of the injector 110, towards and away from a valve needle seating (not shown). Movement of the valve needle along the injector axis A-A controls injection through one or more gaseous fuel outlets. A main injector housing, also referred to as a fuel tube 50, extends through the wound solenoid coil 42 and the armature of the actuator resides within the fuel tube 50. The fuel tube 50 comprises several different sections of varying diameter including an upper portion of relatively narrower diameter, referred to generally as 52, and a lower region of relatively large diameter, referred to generally as 54. A step 56 between the upper and lower fuel tube regions 52, 54 defines a support surface for the holder 44 for the coil 42. Inlet ports 60 to the fuel tube 50 allow gaseous fuel to be delivered to the area of the valve needle seating, in use. The lower region 54 of the fuel tube 50 is received within the pocket 32 in the engine housing component 30, whilst the upper region 52 of the fuel tube 50 projects through the open upper end 33 of the pocket 32. Typically, the engine housing component 30 may be formed from aluminium to minimise engine weight. A radially projecting annular extension 62 on the lower region 54 of the fuel tube 50 defines a groove for housing an O-ring 64 that seals against the pocket 32. A lower end of the solenoid tube 46 is in abutment with the lower region of the fuel tube 50 on a radially outer surface 66. A thermally conductive member 70 is attached, by mean of welding or press-fitting, to a radially outer surface 72 of a generally lower portion of the solenoid tube 46 so that the solenoid tube 46 resides between the thermally conductive member 70 and the wound solenoid coil 42. The thermally conductive member 70 may take the form of a bracket and comprises an axially extending portion 70a, that aligns with the main axis A-A of the injector 110, and a radially extending portion 70b that projects tangentially from the upper end of the axially extending portion 70a. In other words, the radially extending portion 70b extends from the axially extending portion 70a at the end proximal to the pocket 32 in the engine housing component 30 and the axially extending portion 70a is contained within the pocket 32 of the engine housing component 30. The axial length of the axially extending portion 70a is greater than the radial length of the radially extending portion 70b and extends at least half of the way along the axial length of the wound solenoid coil 42. An upper portion of the solenoid tube 46 extends above the radially extending portion 70b of the bracket 70. The radially extending portion 70b of the bracket 70 defines a lower engagement surface 76 that engages with an upper surface 79 of the engine housing component 30 at the open end 33 of the pocket 32. The lower engagement surface 76 of the bracket 70 faces towards the axially extending portion 70a and is in direct contact with the upper surface 79 of the engine housing component 30 so that there is no other component between the bracket 70 and the engine housing component 30. This means there is a direct heat transfer path from the solenoid coil 42, via the solenoid tube 46 and the bracket 70, to the engine housing component 30. An overmould 80 is applied to the upper components of the injector 110 that projects beyond the open end 33 of the pocket 32 in the engine housing component 30. This means that the upper portion of the solenoid tube 46 is contained within the overmould 80. A lower surface of the overmould 80 abuts against an upper surface 82 of the radially extending portion 70b of the bracket 70. A small end section of the radially extending portion 70b of the bracket 70 extends downwardly beyond the extent of the overmould 80. An O-ring seal 84 is retained within the overmould 80 to abut the upper surface 82 of the radially extending portion 70b. If the overmould 80 does not entirely seal against the upper surface 82 of the bracket 70, this ensures the required seal is created between the surfaces 80, 82. An end cap 86 covers the upper portion 52 of the injector 110 and defines an internal abutment surface for a valve needle spring 88 (just visible in Figure 2). The end cap 86 and the overmould 80 together provide an upper enclosure for the components of the injector 110 that extend beyond the pocket 32 in the engine housing component 30. It is an important feature of the arrangement that the bracket 70 provides a direct connection between the solenoid tube 46 and the engine housing component 30 and, hence, provides a direct thermally conductive path between the solenoid coil 42 and the engine housing component 30. This means that heat that is generated in the solenoid coil 42, when a current is supplied to the coil 42, is able to dissipate through the thermally conductive component 70 to the engine component housing 30 so as to control the temperature of the solenoid coil 42 and surrounding injector components. A further benefit is provided due to the electrically conductive path between the injector 110 and the engine housing component 30, via the coil 42 and the bracket 70, to ensure that no differential voltage exists across the components. In order to assemble the injector 110 in Figure 2, the following assembly steps are followed. Initially the internal components of the injector 110, including the valve needle and the armature, are assembled within the fuel tube 50. The electromagnetic actuator is essentially a unitary assembly, which may be manufactured separately. The solenoid coil 42 and the solenoid tube 46 of the actuator are then assembled onto the external surface of the fuel tube 50. The cap 86 is applied to the upper end of the injector 110 and the overmould 80 is applied over the fuel tube 50 and the solenoid tube 46. The bracket 70 is then welded, via its axially extending portion 70a, onto the radially external surface 72 of the solenoid tube 46 and the O-ring 64 is installed. For installation, the assembly is then slotted into the pocket 32 in the engine housing component 30 so that the lower surface 76 of the bracket 70 rests against the upper surface 79 of the engine housing component 30. Figure 3 shows an alternative embodiment to that shown in Figure 2, in which the thermally conductive member 170 of the injector 110 is configured differently. Like parts to those shown in Figure 2 are denoted with like reference numbers and will not be described in further detail. In this embodiment the bracket 170 is oriented such that the axially extending portion 170a extends upwardly from the radially extending portion 170b, with the axially extending portion 170a attached through welding to a generally upper portion of the solenoid tube 46. A lower engagement surface 176 of the radially extending portion 170b of the bracket 170 abuts the upper surface 79 of the engine housing component 30, in direct contact therewith, with the lower engagement surface 176 facing away from the axially extending portion 170a. The axially extending portion 170a therefore extends out of the open end 33 of the pocket 32, together with a portion of the solenoid tube 46, and is contained within the overmould 80. This contrasts the embodiment of Figure 2 where no portion of the bracket 70 is contained within the overmould. The lower engagement surface 176 of the bracket 170 in Figure 3 is, as in Figure 2, proximal to the open end 33 of the pocket 32. In this embodiment, no O-ring seal 84 is provided between the overmould 80 and the radially extending portion 170b of the bracket 70, this component being optional. In order to assemble the injector 110 in Figure 3, initially the internal components of the injector 110, including the valve needle and the armature, are assembled within the fuel tube 50 as for Figure 2. The solenoid coil 42 and the solenoid tube 46 are then assembled onto the external surface of the fuel tube 50. The bracket 170 is then attached to the solenoid tube 46 by welding. The end cap 86 is inserted over the top of the injector 110 and the overmould 80 is applied over the assembled injector 110, including the fuel tube 50, the solenoid tube 46 and the thermally conductive bracket 170. In a variation, it may be possible to assemble the solenoid coil 42 and the solenoid tube 46 of the actuator together with the bracket 170, and then to assemble all of these pre-assembled components onto the fuel tube 50. In an alternative assembly method for Figure 3, the step of welding the bracket 170 to the solenoid tube 46 may be removed and instead the overmould 80 may be relied on to the secure the parts together. Figure 4 shows a perspective view of the upper portion of the fuel injector 110, with the bracket 70 or 170 extending in a plane perpendicular to the injector axis A-A. The bracket 70 or 170 may be configured as in Figure 2 or Figure 3 and takes the form of a generally square-shaped plate. The overmould 80 abuts an upper face of the bracket 70 or 170 and extends on one side to form an overmould projection 90 that houses the electrical connector (not shown) for the actuator. Drillings 92 are providing through diametrically opposite corners of the bracket 70 or 170 to accommodate bolts for securing the injector 110 to the engine housing component 30. The inlet ports 60 can be seen on the fuel tube 50 together with the O-ring seal 64 which resides above the inlet ports 60 (in the orientation shown). A further O-ring seal 94 resides below the inlet ports 60. Figures 5 and 6 show an alternative embodiment in which bracket 270 does not make direct contact with the engine housing component 30 but instead couples thermally to the engine housing component 30 via a washer 100. Similar parts of the injector 110 to those shown in Figures 2 and 3 are denoted with the same reference numbers and will not be described in further detail. The washer 100 may be what is known as a “wavy washer” having a resilience that serves to bias the bracket 270 upwardly. The washer 100 also defines a part of the heat transfer path between the solenoid coil 42 and the engine housing component 30, via the bracket 270. The bracket 270 is oriented such that the radially extending portion 270b of the bracket 270 extends from the base of the axially extending portion 270a of the bracket 270, being that end remote from the open end 33 of the pocket 32. The axially extending portion 270a is longer than the radially extending portion 270b and is welded to the solenoid tube 46, as in Figure 2. The washer 100 abuts an internal step 102 formed within the pocket 32 of the engine housing component 30 and is sandwiched between the step 102 and the lower surface 276 of the bracket 270. A closure plate 104 abuts the upper surface 79 of the engine housing component 30 at the open end 33 of the pocket 32. As seen in Figure 6, the bracket 270 defines a flange of generally circular form and extends in a plane perpendicular to the main injector axis A-A. The overmould 80 is formed over the top of the injector 110 and the overmould projection 90 defines a housing for an electric connector (not shown) for the solenoid coil 42. In order to assemble the injector 110 in Figures 5 and 6, the bracket 270 is installed on the solenoid assembly and welded to the radially outer surface 72 of the solenoid tube 46, and then the overmould 80 is applied over the top of the injector 110. The washer 100 is inserted into the pocket 32 of the engine component 30 and the injector 110 is inserted into the pocket 32, resting on the washer 100. The bracket 270 is then applied on top of the engine housing component 30 to clamp all parts together. In use, the high pressures within the combustion chamber can cause the injector 110 to move upwardly; however, the presence of the washer 100 and the bracket 270 limit any such movement, which is advantageous. The washer 100 is compliant and takes up some of the unwanted injector movement, urging the bracket 270 and the injector 110 to which it is welded upwardly against the closure plate 104. In any embodiment of the invention, a benefit is achieved in that the thermally conductive member 70, 170, 270 allows a direct thermal heat path between the solenoid coil 42, which can tend to overheat, and the engine housing component 30, typically formed from aluminium, to tend to cool the solenoid coil 42. The thermally conductive member 70, 170, 270 is easy to manufacture and assemble and provides little extra cost to solve the heating problem.

Claims

1. A fuel injector installation for a gaseous fuel system, the fuel injector installation comprising:an engine housing component (30) defining a pocket (32);a fuel injector (110), received within the pocket (32; the fuel injector (110) comprising an electromagnetic actuator; the electromagnetic actuator comprising a solenoid assembly comprising a solenoid tube (46) that houses a solenoid coil (42);a thermally conductive member (70; 170; 270) comprising a first portion (70a; 170a; 270a) that extends axially along the fuel injector (110) and is in connection with the solenoid assembly (42, 46) and a second portion (70b; 170b; 270b) that extends radially from the first portion (70a; 170a; 270a) and is configured for thermal connection with the engine housing component (30), so that the thermally conductive member provides at least a part of a heat transfer path between the solenoid assembly (42, 46) and the engine housing component (30) for heat dissipation.

2. The fuel injector installation as claimed in claim 1, wherein the pocket (32) defines an open end (33) into which the fuel injector (110) is received, and wherein the second portion (270b) of the thermally conductive member (270) extends radially from an end of the first portion (270a) remote from the open end (33).

3. The fuel injector installation as claimed in claim 2, wherein the second portion (270b) of the thermally conductive member (270) defines an engagement surface (276) that faces away from the first portion (270a).

4. The fuel injector installation as claimed in claim 3, further comprising a washer (100) that is received within the pocket (32) to engage betweenthe engagement surface (276) and the engine housing component (30) to form a part of the thermal connection between the solenoid assembly (42, 46) and the engine housing component (30).

5. The fuel injector installation as claimed in claim 4, wherein the pocket (32) defines an internal step (102), the washer (100) being in engagement with the internal step (102).

6. The fuel injector installation as claimed in claim 1, wherein the pocket (32) defines an opening (33) into which the fuel injector (110) is installed, and wherein the second portion (70b; 170b) of the thermally conductive member (70; 170) extends radially from an end of the first portion (70a, 170a) proximal to the opening (33).

7. The fuel injector installation as claimed in claim 6, wherein the second portion (70b) of the thermally conductive member (70) defines an engagement surface (76) for the engine housing component (30) that faces towards the axially extending portion (70a) of the thermally conductive member (70).

8. The fuel injector installation as claimed in claim 6, wherein the second portion (170b) of the thermally conductive member (170) defines an engagement surface (176) for the engine housing component (30) that faces away from the axially extending portion (170a) of the thermally conductive member (70).

9. The fuel injector installation as claimed in claim 8, comprising an overmould (80) applied to an upper portion (52) of the fuel injector (110), including at least a part of the axially extending portion (170a) of the thermally conductive member (170).

10. The fuel injector installation as claimed in any of claims 6 to claim 9, wherein the engagement surface (76; 176) engages directly with an upper surface (79) of the engine housing component (30) to define the thermal connection to the engine housing component (30).

11. The fuel injector installation as claimed in any of claims 1 to 10, wherein the first portion (70a; 170a; 270a) of the thermally conductive member (70; 170; 270) is welded to the solenoid tube (46).5 12. The fuel injector installation as claimed in any of claims 1 to 11, whereinthe engine housing component (30) is formed from aluminium.

13. The fuel injector installation as claimed in any of claims 1 to 12, whereinthe second portion of the thermally conductive member (70; 170; 270) 10 comprises a plate that extends perpendicular to the injector axis (A-A).15