In general the invention relates to a fuel injector. More specifically, the invention concerns a seal arrangement for an actuator for use in a fuel injector.

Background

Fuel injectors are used in internal combustion engines to deliver pressurised fuel to the combustion chambers of the engine. Fuel injectors may be positioned such that they inject pressurised fuel directly into the combustion chambers or, alternatively, they may be positioned so that fuel is injected upstream of the combustion chambers, for example into a throttle body, inlet manifold or, more usually, into air intake ports of each of the combustion chambers. Direct injection arrangements are used almost exclusively in diesel engines. Indirect injection arrangements are more typical in spark-ignition engines, although direct injection is becoming increasingly common. Contemporary fuel injectors make use of an electronically-switchable actuator arrangement, such as an electromagnetic actuator arrangement or piezoelectric actuator arrangement, to control the position of a valve needle which, in turn, controls the delivery of fuel from one or more injection holes defined in a nozzle at the tip of the injector. During termination of fuel delivery from an injector, pressurised fuel is discharged or 'spilt' from the actuator arrangement into a so-called backleak circuit which is routed back to the fuel tank of the vehicle. In some injectors, the actuator may form part of the backleak circuit such that the actuator itself is immersed in fuel. It is challenging to provide electrical power to the actuator arrangement whilst at the same time establishing a robust seal to prevent fuel from escaping the backleak circuit in order to avoid chemical attack of the electrical connection to the actuator arrangement. Sealing arrangements are provided for this purpose and provide a sealing interface to seal the 'fuel' side of an actuator arrangement from the 'electrical' side of the actuator arrangement.

It is against this background, that an improved seal arrangement in accordance with the invention has been devised. Statements of Invention

According to one aspect of the invention there is provided a seal arrangement configured to provide a seal for an actuator against an internal bore of a fuel injector. The seal arrangement comprises a seal member having a longitudinal axis and defining a high pressure side and a low pressure side, one or more terminal passages defined in the seal member for accommodating a respective one or more electrical terminals. The seal member includes an outer sealing profile configured such that contact pressure between the outer sealing profile and a mating surface of the bore increases in dependence on a pressure differential between the high pressure side and the low pressure side, in use.

Advantageously therefore the seal member responds to the pressure of fluid on the high pressure side of it, increasing the pressure with which it engages the bore in accordance with increasing fluid pressure. The position of the seal member is therefore not affected by rapid increases in fluid pressure on the high pressure side. This is particularly beneficial in low temperature conditions in which the material of the seal member may become hardened which may otherwise compromise the effectiveness of the seal.

In the embodiment disclosed, the outer sealing profile includes a first sealing region including a tapered section which defines a sealing line. The tapered section may extend along the longitudinal axis of the seal member between a first section and a second section, the second section having an outer dimension greater than that of the first section. Although the outwardly tapered section may be concave in form, for example, it is currently preferred that it is frustoconical.

To enhance its sealing properties, the seal arrangement may include dilation means that is configured to dilate the first sealing region when it is exposed to pressured fluid. This has the effect of further increasing the sealing pressure applied to the bore by the sealing region.

The dilation means may be configured in various ways. One option, currently preferred, is for an annular cavity to be defined in the high pressure side of the seal member which extends about the longitudinal axis of the seal member. Instead of a single annular cavity, however, a similar effect could be achieved by a series of cavities arranged about the longitudinal axis of the seal member. To further improve sealing effectiveness, the seal member may also include a second sealing region that is spaced from the first sealing region along the longitudinal axis of the seal member. The outer surface profile of the seal member may be contoured to define a relatively narrow region between the first and second regions. Beneficially, the relatively narrow region acts as a collection volume for any fluid that manages to leak past the first sealing region.

To enhance the robustness of the seal member the seal arrangement may further include a bearing member carried on its low pressure side. In the preferred form as disclosed the bearing member has a 'two-part' form comprising a body and an insert incorporated into the body, wherein the insert is formed from a material that is harder than the material of the body. Preferably the insert is metallic, for example steel, and the body is polymeric, for example a suitable engineering plastic as would be known to the skilled person.

In one embodiment, the insert provides an exposed hardened seating surface of the bearing member that is perpendicular to the longitudinal axis of the seal member. However, in an alternative configuration, the insert may define a frustoconical seating surface.

To enable the seal member to seal into a circular bore, the seal member preferably has a circular transverse cross sectional profile. However, the cross sectional profile may also be elliptical which may provide a more even distribution of pressure about the profile of the seal member when exposed to pressurised fluid.

Similarly, the one or more terminal passages passing through the seal member preferably have a circular hole profile, although an elliptical hole profile may improve the distribution of pressure on the terminals that are received through the passages when in situ.

The invention embraces an actuator arrangement for a fuel injector comprising an actuator having a working end and a connection end including one or more electrical terminals, wherein the connection end includes a seal arrangement as described above configured so that the one or more electrical terminals extend through a respective one of the one or more terminal passages defined in the seal arrangement. The invention also extends to a fuel injector fitted with the seal arrangement or the actuator arrangement.

Within the scope of this application the various aspects, embodiments, examples, features and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings maybe taken independently or in any combination thereof.

Brief Description of the Drawings

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a part sectional view of a known fuel injector arrangement;

Figure 2 is a perspective view of an actuator and an associated electrical connection for use in the fuel injector arrangement in Figure 1 ;

Figure 3 includes two comparative side views of the actuator in Figure 2;

Figure 4 is a side view, partly in section, of an actuator arrangement in accordance with an embodiment of the invention, and Figure 5 is an enlarged view of a seal arrangement of the actuator arrangement in Figure 4; Figure 6 is a section view of an alternative configuration of seal member for use with the actuator arrangement in Figure 4;

Figures 7 and 8 are views of a bearing member of the sealing arrangement of Figures 4 to 6; and

Figures 9 and 10 are views of alternative configurations of bearing members.

Detailed description of embodiments of the invention For the avoidance of doubt, throughout the description terms such as 'upper', 'lower', 'horizontal', 'vertical' and so on relate to the orientation of the components as shown in the accompanying drawings and it should be appreciated that this the terms are not to be interpreted as requiring a particular orientation.

An example of a known fuel injector 2 is shown in Figure 1 , and includes an elongate nozzle holder body 4, a valve housing 6 and a nozzle body 8. All three of these components are coupled together by cap nut 10 through which a tip portion 8a of the nozzle body 8 extends.

A lower end of the nozzle holder body 4 includes a socket 12 which houses an electromagnetic actuator arrangement 14 in the form of a solenoid, as would be known in the art. The actuator arrangement 14 includes an elongate electrical connection arrangement 16 that extends upwardly through a generally cylindrical barrel or bore 18 defined in the nozzle holder body 4. An opening 20 is defined in an upper end 4a of the nozzle holder body 4 into which a power plug 22 can be inserted in order to couple to the electrical connection arrangement 16 in the bore 18 so as to supply energy to the actuator arrangement 14.

The lower end of the nozzle older body 4 and, therefore, also the actuator 14, abut against the valve housing 6. The valve housing 6 accommodates a plate-like fluid control valve 24 the axial position of which is influenced by the energisation state of the actuator arrangement 14 and a return spring 25.

The axial position of the fluid control valve 24, also known as the 'nozzle control valve', determines the position of a valve needle 26 that is housed in the nozzle body 8. To this end the nozzle control valve 24 controls the pressure of fuel in a control chamber 28 that is positioned adjacent an upper end 26a of the valve needle 26.

Pressurised fuel is provided to the nozzle body 8 through a fuel delivery passage 30 that is defined in part by each of the nozzle older body 4, the valve housing 6 and the nozzle body 8. The fuel delivery passage 30 extends from a fuel connector block 32 at the upper end 4a of the nozzle holder body 4 to a delivery chamber 34 that is defined in the nozzle body 8 and extends about a waist-section of the valve needle 26. During energisation of the actuator, the nozzle control valve 24 is moved to an open position which causes pressurised fuel in the control chamber 28 to vent to a backleak circuit of the injector 2. In part, the backleak circuit is defined by the actuator socket 12 and so the actuator arrangement 14 is immersed in relatively low pressure fuel during operation. To prevent backleak fuel from leaking into the bore 18 in the nozzle holder body 4, the actuator arrangement 14 includes a seal arrangement 40 that is located between the bore 18 and the actuator socket 12. The seal arrangement 40 is shown generally in Figure 1 , but Figures 2 and 3 show the seal arrangement 40 in more detail.

The seal arrangement 40 comprises a polymeric grommet-like seal member 42 having a generally cylindrical midsection 44 which has an outer dimension comparable to that of the bore 18. The grommet 42 therefore fits tightly within the bore 18 and serves to prevent backleak fuel from flowing past the immersed actuator arrangement 14 into the bore 18 and so protects the electrical connection arrangement 16 from fuel contamination. As can be seen in Figure 3, the seal member 42 includes passages that allow a set of terminals 46 to pass through it so that the actuator 14 may be coupled to the electrical connection arrangement 16.

However, it has been observed that in some circumstances the seal arrangement 40 allows fuel leakage in which case the electrical connection arrangement 16 is vulnerable to failure. Such a failure may be more apparent when the injector is driven in such a way that the pressures within the backleak circuit are relatively high, or where there is prolonged cycling between low and high pressures.

Figures 4 and 5 show an embodiment of a seal arrangement 50 in accordance with the invention and which may be used instead of the seal arrangement 40 of the fuel injector 2 in Figure 1 . Therefore, in Figure 4 the seal arrangement 50 is shown in situ within the nozzle holder body 4 which is only shown partially. In the following description, parts in common with the fuel injector in Figure 1 will be referred to with the same reference numerals.

Referring firstly to Figure 4, the seal arrangement 50 is shown housed within the nozzle holder body 4 between the actuator arrangement 14 (hereinafter 'actuator') and the electrical connection arrangement 16.

The seal arrangement 50 includes a seal member 52 and a bearing or stop member 54 which bears against a step 56 in the bore 18 of the nozzle holder body. The bearing member 54 will be described in more detail later. The seal member 52 comprises a first end 60 that is adjacent the actuator 14, a second end 62 that contacts the step 56 by way of the bearing member 54 and a profiled sealing surface 61 that extends between the first and second ends 60,62. It is to be noted that the profiled sealing surface 61 is shown here in section form, but that the sealing surface 61 it defines the circular circumferential profile of the sealing member 52.

Since the actuator 14 is immersed in fuel at backleak pressure, the first end 60 of the seal member 52 can be considered to be the 'high pressure side'. Conversely, since the second end 62 of the seal member 52 is exposed to atmospheric pressure in the bore 18 of the nozzle holder body 4 it can be considered to be the 'low pressure side' of the seal member 52.

In this embodiment, the seal member 52 is generally cylindrical in form and so is rotationally symmetric about its longitudinal axis 'L' and is dimensioned to match the cylindrical dimension of the region of the bore 18 within which it is received.

The first end 60 of the seal member 52 is shaped to define a socket 64 into which is received a correspondingly shaped projection 66 at the back end of the actuator 14. The electrical terminals 46 of the actuator 14 extend from the projection 66 and pass through respective passages 68 provided longitudinally through the seal member 62. The seal member 62 therefore 'sits' on the projection 66 so that the seal member 52 is held in position prior to being assembled into the nozzle holder body 4. Although a pair of terminals 46 is shown here, it is also possible to provide a single terminal or more than two terminals, for example three or more terminals, depending on the electrical requirements of the actuator 14.

A biasing means 70 in the form of a spring plate sits on top of the actuator 14 and extends about the projection 66. The spring plate 70 engages a second step 72 in the bore 18 of the nozzle holder body 4 and biases the actuator 14 in a downwards direction. It should be appreciated that the spring plate 70 does not form part of the invention and so will not be described further.

The sealing profile 61 of the seal member 52 will now be described in more detail, with reference also to Figure 5. In general terms, the seal member 52 provides first and second sealing regions at spaced axial positions with respect to the longitudinal axis L. A first sealing region 80 is defined at the first end 60 of the seal member 52, that is to say at the high pressure side, and a second sealing region 82 is defined towards the second end 62 of the sealing member, that is to say near to the low pressure side. The diameter of the seal member 52 at the first and second sealing regions 80,82 is relatively large compared to a mid- region 84 having a reduced diameter.

The first sealing region 80 comprises a first section 88 and a second section 90 that define a sealing line 92 between them. As can be seen, the first section 88 is cylindrical and the second section 90 is frustoconical and contacts the bore 18 at the sealing line 92. Specifically, the sealing line 92 contacts the bore 18 at a frustoconical portion of it, as labelled with reference '91 ' in Figures 4 and 5. Although the second section 90 has been described here as frustoconical, it should be appreciated that this is not strictly necessary and instead it could take any outwardly tapered form, for example concave, extending from the relatively narrow mid-region 84 to the relatively wide second section 88 so as to define the seating line 92. However, a frustoconical profile is straightforward to manufacture using existing techniques. By way of example, it is envisaged that the second section 90 may define a cone angle of 50° and have a depth of approximately 2mm, although these values are not to be considered as limiting and other values may function acceptably. It should be noted that the cone angle is defined here as the vertex angle of an imaginary cone defined by the sloping sides of the frustonconical second section 90. Although not shown here, the diameter of the cylindrical section 88 is slightly larger than the bore 18 such that insertion of the seal member 52 into the bore 18 is achieved by a press fit which compresses the cylindrical section 88 slightly and establishes a seal.

The application of high pressure fluid on the high pressure side 60 of the seal member 52 applies a compressive force to the seal member 52 along its longitudinal axis L which acts to press the sealing line 92 against the frustoconical portion 91 of the bore 18. This therefore increases the force by which the sealing line 92 is pressed into contact with the bore 18. As a result, an extremely robust seal is achieved since the sealing force at the sealing line 92 increases as the pressure differential across the sealing region 80 is increased. The mid-region 84 of the seal member 52 is adjacent the first sealing region 80 and includes a plurality of cylindrical and frustoconical sections that serve to define an annular recess 94 between the outer circumferential surface of the mid-region 84 and the bore 18 and which then taper outwardly towards the seating line 92. More specifically, a tapering concave section 96 extends from the upper edge of the frustoconical section 90 of the first sealing region 80, which then blends into a relatively short cylindrical section 98 which, in turn, blends into two further tapering sections 100, 102 to a cylindrical section 104 of minimum diameter. This cylindrical section 104 sits below the second sealing region 82.

The second sealing region 82 has a diameter significantly larger than that of the mid- region 84 and slightly larger than the diameter of the bore 18 so as to define a press fit with it. This compresses the second sealing region 82 of the seal member 52 at this point which establishes an effective seal and also applies a compression of the terminals passages 68.

The second sealing region 82 is defined by a cylindrical section 106 that provides a flat contact surface. Upwards of the cylindrical section is provided a series of tapering sections that reduce the diameter of the sealing member 52. The second sealing region 82 therefore serves as a backup seal that is designed to trap any fluid that may have escaped past the first sealing region 80 and into the annular recess 94.

It is envisaged that an appropriate material for the seal member 52 is a high-performance engineering plastic such as a polytetrafluoroethylene (PTFE) or a polyimide such as Vespel®, although these are not to be considered as limiting and the skilled person would understand that other suitable materials could be used.

Beneficially, in the embodiment in Figures 4 and 5, the first sealing region 80 can be considered to be 'responsive' to the pressure differential between the high pressure side 60 and the low pressure side 62 of the seal member 52, and so an effective seal is provided to a guard against escape of fuel from the drain area to the electrical connection area in the bore 18 of the nozzle holder body 4. The force with which the first sealing region 80 seals against the bore 18 increases with fluid pressure on the high pressure side which improves the 'strength' of the seal even if the fluid pressure rises dramatically. A further advantage is that the seal member 52 is also provided with a backup seal in the event that some fuel escapes past the first sealing region 80. An alternative embodiment will now be described with reference to Figure 6 in which the same reference numerals will be used to refer to features in common with the previous embodiment.

In this embodiment, the seal member 52 is configured in substantially the same way as the seal member 52 in the embodiment of Figures 4 and 5. However, its sealing effectiveness is enhanced by means 74 to dilate the outer dimension of the sealing region when pressurised fluid is applied to the first end 60 of the seal member.

From Figure 7 it will be noted that the outer profile 61 of the seal member 52 corresponds to that in Figures 4 and 5. However, in this embodiment the seal member 52 is provided with an annular cavity 76 defined in the first end 60 of the seal member 52 and about the terminal passages 68. Here, the annular cavity 76 extends into the seal member 52 towards its mid-region 84 and tapers somewhat towards the base of the cavity 76 due to the thinner wall section of the seal member 52 in the region of the mid- region 84. It should be appreciated, however, that the cavity 76 may be shallower or deeper if desired. In circumstances where the first end 60 of the seal member 52 is exposed to pressurised fuel, the cavity 76 allows pressure to be applied to the inner wall surface 78 of the sealing region. Due to the relatively thin wall section, the pressure in the cavity 76 urges the wall radially outwards and, since outward movement is constrained by the bore 18, this will result in an increase in the sealing force between the first sealing region 80 and the bore 18.

Although the dilation means 74 has been described here as an annular cavity 76, it will be appreciated that a similar result could be achieved by other configurations. For example, a series of discrete bores or drillings arranged in a radial pattern in the first end 60 of the seal member 52 would approximate the configuration of the annular cavity 76 and so would have a similar affect.

In the above embodiments, the sealing arrangement 40 includes a bearing member 54 via which the seal member 52 bears against the step 56 in the bore 18 of the nozzle holder body 4. The bearing member 54 is configured to provide a robust seating for the seal member 52 against the internal surface of the nozzle holder body 4, without compromising the electrical isolation of the terminals 46 that extend through the seal member 52 and the bearing member 54.

To this end, the bearing member 54 has a two-part form comprising an electrically insulating body 1 10 that incorporates a relatively hard insert 1 12. In this embodiment the insert 1 12 is made from a material that is relatively hard in comparison to the material of the insulating body 1 10. It is envisaged that the insulating body 1 10 would be a polymeric material, for example an engineering plastic such as acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polyamides/polyimides, polyether ether ketone (PEEK) etc, although the skilled person will understand that other materials are possible.

Passages 1 1 1 are provided in the insulating body 1 10 to accommodate the terminals of the actuator.

In comparison to the insulating body 1 10, the insert 1 12 is selected to be relatively hard and so it is currently envisaged that the insert will be metallic, and preferably steel, although this is not to be considered limiting and other materials such as an engineering plastics, or even a ceramic material, may provide a suitable strength for the insert instead of metal.

As can be seen particularly clearly in Figure 7, the bearing member 54 is configured so that the insert 1 12 is incorporated or embedded in the insulating body 1 10. Such a construction may be achieved by overmoulding the insulating body 1 10 onto the insert 1 12 or by other means such as crimping or bonding. Here, the insert 1 12 is disk-like in form so as to be shaped like a circular washer. An edge region 1 14 around the periphery of the insert 1 12 is not embedded in the insulating body 1 10 and so defines a contact shoulder of the insert 1 12.

The bearing member 54 is sized so that the shoulder 1 14 of the insert 1 12 seats against the first step 56 in the bore 18 of the nozzle holder body 4. During operation of the injector, the seal member 52 applies a force to the bearing member 54 (as indicated by the arrows TV) due to the pressure of fluid on the high pressure side of the seal member 52 and the step 56 applies a reaction (indicated by the arrows 'R') on the shoulder 1 14. As also shown in Figure 8, the central area of the insert 1 12 includes an aperture 1 15 shaped to provide a suitable clearance to allow the terminals 46 to pass through the insert 1 12 surrounded by the insulating body 1 10. Further provided in the insert 1 12 are bonding features 1 13 in the form of shallow depressions or recesses which promote bonding between the insert 1 12 and the body 1 10 during the overmoulding fabrication process. Two such bonding features 1 13 are provided, although it should be appreciated that this is not intended to be limiting.

The dual material configuration of the bearing member 54 is advantageous in that the plastics material of the insulating body 1 10 provides an insulating path for the terminals 46 to pass through the low pressure end 62 of the seal member 52 without risk of electrical shorting, but the hardened insert 1 12 provides a strong, wear resistant seat for the bearing member 54 against the nozzle holder body 4. An alternative configuration of bearing member 54 is shown in Figure 9. In this embodiment the insulating body 1 10 is generally frustoconical in form and the disk-like insert 1 12 is embedded in the relatively wide lower region of the insulating body 1 10. Also, in this embodiment, the nozzle holder body 4 includes a frustoconical inner surface 1 18 and the insulating body 1 10 seats against the inner surface 1 18 in addition to the outer peripheral edge 120 of the insert 1 12 which also contacts the inner surface 1 18. The frustoconical form of the bearing member 54 in this embodiment may for make for easier fitment of the actuator 16 into the nozzle holder body 4.

A further alternative configuration of bearing member 54 is shown in Figure 10. In this embodiment the bearing member 54 is generally frustoconical in form, an outer frustoconical sealing surface 122 being defined by the insert 1 12.

Some variants of the specific embodiments have already been described above. However, the skilled person would be aware that further modifications may be made to the above embodiments without departing from the scope of the invention as defined by the claims.

In the above embodiments, the outer circumference of the seal member 52 has been described as being circular. However, it should be appreciated that this need not be the case and other forms are possible. For example, it is envisaged that the outer circumference of the seal member 52 may be elliptical in form which may improve the uniformity the contact pressure around the circumference of the seal member 52 when it is press fit into the bore 18 of the nozzle holder body 18. Alternatively, the seal member 52 may be circular and the bore 18 of the nozzle holder body 4 could be configured to have an elliptical hole profile, although manufacturing the bore 18 to be elliptical/oval may be more complex than moulding the seal member 52 to have an elliptical hole profile.

Furthermore, it has been described that the terminal passages 68 have a circular hole profile to conform to the circular profile of the terminals 46. However, the terminal passages 68 may instead be configured with an elliptical hole profile which may provide a more uniform distribution of contact pressure between the passages 68 and the terminals 46 when the sealing arrangement is press fit into the nozzle holder body 4.