GB2574863A

GB2574863A - Valve assembly for a fuel injector

Info

Publication number: GB2574863A
Application number: GB201810175A
Authority: GB
Inventors: A Meek George; Sullivan Kris; Braybrooke Tristan
Original assignee: Delphi Technologies IP Ltd
Current assignee: Borgwarner US Technologies LLC
Priority date: 2018-06-21
Filing date: 2018-06-21
Publication date: 2019-12-25
Anticipated expiration: 2038-06-21
Also published as: GB2574863B; GB201810175D0

Abstract

A valve assembly for a fuel injector (16, fig 1) for delivering fuel to an internal combustion engine comprises an armature assembly with an armature 62 movable within a fluid chamber (35, fig 8) of the fuel injector under the influence of an actuation force. The armature has a front surface 68 and a rear surface 69 and defines at least one flow path 82 to allow a flow of fluid through the armature between the front and rear surfaces, and at least one valve element (76, fig 7) mounted at the rear surface. The or each valve element is operable under the influence of fluid pressure to allow the flow of fluid through the at least one flow path and around the fluid chamber, thereby balancing fluid pressure at the front and rear surfaces to minimise fluctuations in movement. A fuel injector comprising the valve assembly has an electromagnetic actuator (34, fig 1) for applying an electromagnetic force to the armature.

Description

VALVE ASSEMBLY FOR A FUEL INJECTOR

TECHNICAL FIELD

The invention to a valve assembly for a fuel injector for the delivery of fuel to a combustion space of an internal combustion engine. The valve assembly is operable to control movement of an injector valve needle to control injection by the fuel injector.

BACKGROUND TO THE INVENTION

To optimize diesel engine combustion, it is necessary to have precise control over the quantities of fuel delivered by the fuel injectors. It is desirable to be able to inject small quantities of fuel across a wide range of fuel pressures and fuel injectors must be capable of delivering fuel in small quantities at very high fuel pressures. It is a particular requirement to be able to inject multiple pulses of fuel with good accuracy and repeatability.

Typically, a fuel injector includes an injection nozzle having a nozzle needle which is movable towards and away from a nozzle needle seating so as to control fuel injection into the engine. The nozzle needle is controlled by means of a nozzle control valve (NCV), which controls fuel pressure in a control chamber at the back of the nozzle needle. The nozzle control valve is controlled by means of an electromagnetic actuator including an electromagnetic winding which is energised to control movement of an armature towards and away from a stator. The armature of the electromagnetic actuator resides within an actuator chamber filled with fuel and is movable towards and away from the stator. An injector of the aforementioned-type is typically referred to as an ‘indirect-acting’ injector, because the nozzle needle is not actuated directly but is instead actuated by controlling the fuel pressure in a control chamber at the back of the nozzle needle. In contrast, a direct-acting injector is one in which the actuator controls movement of the nozzle needle through a direct mechanical coupling.

One problem with injectors of the aforementioned type is that the electromagnetic actuator is subject to fluid perturbations within the actuator chamber. This is largely due to the inertia of fuel moving within the actuator chamber and through a small air gap which remains between the stator and the armature when the armature is moved towards the stator. Such fluid perturbations within the actuator chamber give rise to variations in actuator control which ultimately affect the accuracy and repeatability with which the nozzle needle can be controlled, and which can especially give rise to inaccuracies in multi-pulse injections.

It is one object of the invention to alleviate or overcome at least the aforementioned problem.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a valve assembly for a fuel injector for use in delivering fuel to an internal combustion engine, the valve assembly comprising an armature assembly comprising an armature which is movable within a fluid chamber under the influence of an actuation force, wherein the armature includes front surface and a rear surface and defines at least one flow path to allow a flow of fluid through the armature between the front and rear surfaces; and at least one valve element mounted at the rear surface of the armature, the or each valve element being operable under the influence of fluid pressure to allow the flow of fluid through the at least one flow path of the armature and around the fluid chamber, thereby to balance fluid pressure at the front and rear surfaces of the armature so as to minimise fluctuations in movement thereof, in use.

It is a benefit of the invention that unwanted fluctuations in armature movement due to fluid pressure variations within the fluid chamber are damped or substantially avoided due to the flow path which is provided through the armature to allow fluid to flow between opposing faces of the armature. As a consequence, when implemented in a fuel injector as a nozzle control valve member, any fluctuations of the armature which may otherwise arise during injection due to the build-up of pressure beneath the armature assembly are substantially avoided, and accuracy of valve control is therefore improve. Accuracy of injector valve needle movement, and injection control, is therefore improved.

The armature assembly may further comprise a support plate for the or each valve element, the support plate being mounted to the rear surface of the armature.

In one embodiment, the valve assembly and the armature are arranged in a stack, with the valve assembly located between the armature and the support plate.

The support plate may be provided with at least one flow path, the or each flow path being associated with a respective one of the valve elements.

The or each valve element may take the form of a flexible valve element such as a reed valve.

For example, the or each flexible valve element may take the form of a disc which is movable to block a respective one of the flow paths.

In one embodiment, the rear surface of the armature is provided with one or more recess to accommodate movement of the one or more valve elements along an axis of the valve assembly.

The or each recess may be closed in a radial direction by an annular land defined around the periphery of the armature. For example, the support plate may be fixed to the armature via the annular land.

In another aspect of the invention a fuel injector is provided comprising a valve assembly of the previous aspect and further comprising an electromagnetic actuator for applying an electromagnetic force to the armature to effect movement thereof.

The fuel injector may be an indirect-acting fuel injector comprising which is operable under the influence of the valve assembly to control fluid pressure in a control chamber of the injector, thereby to control movement of a valve needle of the injector.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of a fuel injector of the type with which the present invention may be used;

Figures 2 to 5 illustrate an armature assembly forming part of a valve assembly in a known fuel injector, during various stages of injection, to illustrate a problem encountered in the prior art;

Figure 6 is a perspective, exploded view of an armature assembly of a valve assembly of the present invention to overcome the problems encountered with the armature assembly in Figures 2 to 5;

Figure 7 is a plan view of a reed valve forming part of the armature assembly in Figure 6;

Figures 8 to 11 illustrate the armature assembly in Figure 6 in various stages of operation to illustrate the benefits of the present invention; and

Figure 12 is a graph to illustrate a comparison between the performance of a fuel injector including a valve assembly of the invention and a known fuel injector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It should be understood that the terms ‘upper’ and ‘lower’ are used for convenience, and refer to the orientation of the injector as illustrated in the drawings. However, these terms are not intended to limit the scope of the invention or imply any limitations on the actual orientation of the injector in use. Likewise, the terms ‘downward’ and ‘upward’ relate only to the orientation of the injector as shown in the drawings and should not imply any limitation on the orientation of the injector in use.

Figure 1 is a schematic view of a part of a fuel injector 10 for use in delivering fuel to an engine cylinder or other combustion space of a compression ignition (diesel) internal combustion engine. The fuel injector 10 comprises an injector nozzle, referred to generally as 12, including a nozzle needle in the form of a valve needle 14, and a three-way nozzle control valve (NCV) assembly, referred to generally as 16.

The injector nozzle 12 includes an injector body (not identified) which is provided with a nozzle outlet 18 through which fuel 20 is injected into the combustion space. A lower part of the valve needle 14 terminates in a valve tip which is engageable with a needle seat so as to control fuel delivery through the nozzle outlet 18 into the combustion space. A plurality of outlets may be provided in some embodiments. A spring 22 may be provided in the injector nozzle 12 for biasing the valve needle 14 towards the valve needle seat.

As can be seen in Figure 1, an upper end of the valve needle remote from the nozzle outlet 18 is located within a control chamber 24 defined within the injector body.

In use, fuel under high pressure is delivered from a source 25 of fuel through a main fuel supply passage 26 to a nozzle chamber 28 defined within the injector body and within which the valve needle 14 is located. From the nozzle chamber 28, high pressure fuel is able to flow through the nozzle outlet 18 of the nozzle when the valve needle 14 is moved away from the valve needle seat.

The control chamber 24 at the upper end of the valve needle 14 communicates with the main fuel supply passage 26 through a restriction referred to as an inlet orifice 30, which restricts the flow of fuel into the control chamber 24. Fuel pressure within the control chamber 24 applies a force to the valve needle 14, which serves to urge the valve needle 14 in a downward direction and, hence, serves to urge the valve needle 14 against the valve needle seat to prevent fuel injection through the nozzle outlet 18. Controlling fuel pressure in the control chamber 24 allows movement of the valve needle 14 to be controlled towards and away from the valve needle seat, so as to control initiation and termination of fuel injection through the nozzle outlet 18.

The pressure of fuel within the control chamber 24 is controlled by means of the NCV assembly 16. The NCV assembly 16 includes a nozzle control valve 32 which is movable by means of an actuator assembly including an electromagnetic winding on a stator 34. The nozzle control valve 32 carries an armature 36 which is movable under the influence of a magnetic field generated by supplying a current to the winding. The armature 36 resides within an armature chamber 35 filled with fuel.

The lower portion of the nozzle control valve 32, referred to as the valve head 38, is located and slidable within a valve chamber 40 which communicates with a drain passage 42 which, in turn, communicates with a low pressure drain 44, depending on the position of the nozzle control valve 32. The valve chamber 40 also communicates with a branch passage 46 from the main fuel supply passage 26.

When the valve head 38 is engaged with a first, lower valve seat 48, communication between the valve chamber 40 and the drain passage 42 is broken and communication between the valve chamber 40 and the branch passage 46 from the main fuel supply passage 26 is open so that the valve chamber 40 receives high pressure fuel. Hence, high pressure fuel is supplied to the control chamber 24 at the back of the valve needle 14, via a restricted orifice 31 (spill orifice). This is a first position of the nozzle control valve 32.

When the nozzle control valve 32 is moved such that the valve head 38 moves away from the lower valve seat 48, an upper surface of the valve head 38 is caused to engage with a second, upper valve seat 50 in a second position of the nozzle control valve 32. In the second position of the nozzle control valve 32, the control chamber 24 communicates with the low pressure drain 44, via the drain passage 42, and communication between the control chamber 24 and the branch passage 46 for high pressure fuel is broken. Fuel within the control chamber 24 flows to the drain 44 through the spill orifice 31 at a restricted rate.

The nozzle control valve 32 is biased into the first valve position by means of a spring 52 and movement of the nozzle control valve 32 away from the first valve position, into the second valve position, is controlled by energising the winding 34 of the actuator assembly.

In use, when the nozzle control valve assembly is de-actuated, the nozzle control valve 32 is in its first valve position such that the valve head 40 is in engagement with the first valve seat 48 under the spring force. In this position, fuel at high pressure is able to flow from the branch passage 46 past the second valve seat 50 and into the valve chamber 40, from where it can flow into the control chamber 24 via the spill orifice 31. In such circumstances, the control chamber 24 is pressurised and the valve needle 14 is urged downwards so that injection through the nozzle outlet 18 does not occur. It will be appreciated that pressurising the control chamber24 ensures the upwards force acting on the thrust surface of the valve needle 14, in combination with any force due to combustion chamber pressure acting on the tip of the valve needle 14, is overcome sufficiently to seat the valve needle 14 against the valve needle seat.

When the nozzle control valve assembly is actuated, that is when the nozzle control valve 32 is moved away from the first valve seat 48 into engagement with the second valve seat

50, high pressure fuel within the branch passage 46 is no longer able to flow past the second valve seat 50 to the control chamber 24. Instead, fuel within the control chamber 24 is able to flow, via the spill orifice 31, past the first valve seat 48 into the drain passage 42 and to the low pressure drain 44. Fuel pressure within the control chamber 24 is therefore reduced and the control chamber 24 is depressurised. As a result, the valve needle 14 is urged upwards away from the valve needle seat due to the force of fuel pressure within the nozzle chamber 28 acting on the thrust surfaces of the valve needle 14.

It is a particular concern of the present invention how the armature 36 moves within the armature chamber 35 through an injection cycle, as will now be described.

Figures 2 to 5 illustrate a known armature assembly, generally of the aforementioned type, and are presented to show the movement of the armature 136 within the armature chamber 135 as it moves through an injection cycle between the position in which the nozzle control valve closes communication between the control chamber 24 (as shown in Figure 1) and the low pressure drain 44 (the first valve position) and the position in which communication between the control chamber 24 and the drain 44 is open (the second valve position).

A relatively small gap 54 exists between the upper surface of the armature 136 and the lower surface of the stator 134 when the actuator assembly is de-energised (i.e. the nozzle control valve is in its second valve position). The gap is often referred to as the “final air gap (FAG)” as it represents the space or gap that remains even after the armature 136 has been actuated to move the nozzle control valve 132 upwardly, out of the first valve position and against the spring force, to cause injection to occur.

The flow of fuel within the armature chamber 135 at this time is shown in Figure 3, where it can be seen that as the armature 136 is moved towards the lower surface of the stator 134, fuel is squeezed through the final air gap 54 and flows around the armature 136, around the armature chamber 135, and underneath the armature 136. The flow of fuel is indicated by arrow 140.

Figure 4 shows the situation where the force of the actuator is removed (i.e. when it is desired to terminate injection). In Figure 4 the effect of fuel flowing underneath the armature 136 is illustrated and it can be seen that a force (as indicated by arrows 142) is experienced by the armature 136 which may cause it to bounce or move within the armature chamber 135, despite the actuation force being stopped.

In Figure 5, the actuator is de-actuated and as the armature 136 is urged downwards under the force of the spring (not shown), fuel is caused to flow around the armature 136 and through the armature chamber 135 once again, towards the FAG 54, as indicated by the arrows 144.

Whether movement of the armature 136 is actuated, or whether de-actuated and under the force of the spring, fluid flowing around the armature 136 causes unwanted forces on the armature 136 which, in turn, influences the accuracy and repeatability with which the nozzle control valve 132 is controlled and, hence, the accuracy and repeatability with which fuel pressure in the control chamber 24 of the injection nozzle 12 can be controlled.

Figures 6 to 11 illustrate an armature assembly of a valve assembly of the present invention, which may be used with a fuel injector 10 of the type shown in Figure 1 to overcome the aforementioned problem.

It can be seen in Figure 6 that the armature assembly 60 comprises an upper armature plate 62 and a lower support plate 64, with a valve means in the form of a reed valve plate 66 being located or sandwiched between the upper and lower plates 62, 64. The upper and lower plates 62, 64 and the reed valve plate 66 are stacked along the central axis of the armature assembly. The upper armature plate 62 defines the upper surface 68 of the armature assembly which faces the lower surface of the stator (not shown in Figure 6). The upper surface 68 experiences the magnetic force due to the stator being energised, in use. The upper armature plate 62 has a rear surface 69.

Referring also to Figure 7, the reed valve plate 66 is of circular form and includes an outer rim portion 70 from which a plurality of flexible arms 72 extend inwardly. The outer rim portion 70 is affixed to the lower support plate 64 by welding. The flexible arms 72 are integrally formed with, and hence attached to, the outer rim portion 70 but are able to flex away from the lower support plate 64, in use. The arms flex completely from the point where the slender leg section of each arm joins the thick portion of metal near the outer rim portion 70. Each of the flexible arms, of which there are six terminates in a reed valve element 76 in the form of a disc which aligns with a respective one of a plurality of holes 80 provided in the lower support plate 64 so that each disc covers ones of the holes 80. In this way each of the reed valve elements 76 functions as a one-way valve, as will be described further below.

A plurality of holes 80 are provided in the lower support plate 64. The holes 80 are arranged in a regular array and extend fully through the lower support plate 64, from one side to the other, to define flow channels for fuel, in use. A central hole (not shown) also extends through the lower support plate 64. The upper plate 62 is also provided with a plurality of holes 82, arranged at regularly spaced locations around a circular path. A central hole 82a also extends through the upper plate 62, which is greater in diameter than the diameter of the holes 82. The reed valve plate 66 includes a central hole 75 which extends through the plate, from one side to the other. The central hole 82a in the upper plate 62, the central hole (not shown) in the lower plate 64 and the central hole 75 in the reed valve plate 66 are aligned along the axis of the actuator assembly to receive the nozzle control valve 32.

The holes 82 in the upper plate 62 extend fully through the plate, from one side to the other, and also define flow channels for fuel, in use (as will be described in further detail below). The holes 82 are equidistant on a common radius from the central axis of the upper plate 62, as are the holes 80 in the support plate 64. The holes 82, 80 in each plate are typically offset from one another by around 30° to ensure that when the reed valve elements 76 are open they do not cover the holes 82 in the upper plate 62 during flow.

Referring also to Figures 8 to 11, the lower surface of the upper plate 62 is provided with an annular recess 84, centred around the central hole 82a, which can accommodate some movement, along the axis of the armature assembly, of the reed valve elements 76 and the flexible arms 72 on the reed valve plate 66. The annular recess 84 is closed radially at the periphery of the upper armature plate 62 so as to leave an outer annular land 86 on lower surface of the plate to which the outer rim of the lower support plate 64 is fixed.

Operation of the fuel injector, and in particular the armature assembly, will now be described with reference to Figures 8 to 11, and also referring back to Figure 1.

Referring especially to Figure 8, prior to injection, the nozzle control valve assembly 16 is de-actuated and the valve needle 14 is seated against the valve seating under the force due to fuel pressure which has built up within the control chamber 24, due to the continuous supply of fuel from the main supply passage 26. In this operating configuration the nozzle control valve 32 is seated on its lower seat 48 so that fuel within the control chamber 24 cannot flow to the low pressure drain 44. In this situation the armature assembly is de-actuated (i.e. no current is supplied to the winding) and the armature assembly is urged downwardly, under the force of the spring 52, so that the nozzle control valve 32 is seated on the lower seat 48 in the first valve position. In such circumstances fuel pressure within the armature chamber 35 is substantially equal both above and below the armature assembly 60, and the reed valve elements 76 close the holes 80 in the lower plate 64. Thus, in these circumstances the reed valve elements block the flow through the holes 80 and there is no flow through the holes 80 within the armature assembly.

Referring to Figure 9, when it is desired to commence injection, the winding is energised to cause the armature assembly 60 to move upwards, against the armature spring force, moving the nozzle control valve 32 out of the first valve position into the second valve position and opening communication between the control chamber 24 and the low pressure drain 44. As fuel pressure in the control chamber 24 is reduced, the valve needle 14 is able to lift and injection through the nozzle outlet 18 commences.

As the armature assembly 60 moves upwards within the armature chamber to close the final air gap (FAG) 54, fuel within the FAG 54 is squeezed radially outwardly, through and around the armature chamber 35, as indicated by the arrow 92. Initially as the armature assembly 60 starts to move upwards there is a pressure drop underneath the armature assembly 60, but eventually fuel flows around the armature assembly 60 towards the lower pressure region. Eventually the armature assembly 60 reaches its uppermost position with the upper surface 68 of the upper armature plate 62 at or very close to the lower surface of the stator 34. In such circumstances, the nozzle control valve 32 is open (i.e. the second valve position) and the control chamber 24 communicates with the low pressure drain 44 so that the valve needle 14 remains lifted. The reed valve elements 76 remain closed against the associated holes in the lower support plate 64 during this period of operation.

Referring to Figure 10, as fuel is squeezed out through the FAG 54 and circulates within the armature chamber 35, pressure builds up beneath the lower support plate 64 and so that the reed valve elements 76 are caused to lift away from the lower support plate 64, under the influence of fuel pressure, to allow fuel to flow through the holes 80. The reed valve elements 76 lift upwardly slightly, such movement being accommodated by the recess 84 in the lower surface of the armature plate 62. With the reed valve elements 76 lifted, the flow through the holes 80 in the lower support plate 64 continues through the holes 82 in the upper armature plate 62 (as indicated by the arrows 94) so that flow circulates around the armature chamber 35 and through the holes 80, 82. The speed of movement of fuel flowing around the armature chamber 35 is high due to the restricted flow through the FAG 54. The result of this high momentum flow through the holes 80, 82 is that fuel pressure above and below the armature assembly 60 tends to balance quickly, and any unwanted movement of the armature assembly 60, which would otherwise arise due to the build-up of pressure beneath the armature assembly 60, is avoided.

Referring to Figure 11, because some of the fuel within the armature chamber 35 can flow through the holes 80 in the lower support plate 64 and the holes 82 within the armature plate 62, the amount of fuel experiencing high speeds, and hence high inertia, is reduced. Unwanted fluctuations in the position of the armature assembly 60 during injection, and hence any associated unwanted fluctuations in the position of the nozzle control valve 32, are therefore damped and/or substantially avoided. These benefits are achieved through the one way valve function provided by the reed valve plate 76.

When injection is to be terminated by de-energising the winding 34, the armature assembly 60 is caused to move downwards once again, under the spring force, so that the nozzle control valve moves back to the second valve position, closing communication between the control chamber 24 and the low pressure drain 44. As pressure builds up in the control chamber 24, the valve needle 14 is caused to be seated and injection ceases. The armature assembly 60 then reverts to the position shown in Figure 8, adopting its lowermost position within the armature chamber 35 and with the reed valve elements 76 closing the holes 80 in the lower support plate 64 once again.

In the present invention the reduction of unwanted fluctuations of the armature assembly 60 are achieved without compromising the magnetic performance of the actuator assembly 60. This is because the reed valve elements 76 are located remote from the magnetic surface (i.e. the upper surface 68) of the armature plate 62, and the recess 84 which accommodates movement of the reed valve elements 76 is provided in the lower surface of the armature plate 62, away from the source of magnetic force.

Figure 12 is a graphical representation to illustrate the benefit of the present invention. The graph illustrates nozzle control valve lift as a function of time. Line 100 is a conventional arrangement in which no reed valve component is provided, and where fluctuations in needle lift can be seen. Line 102 represents an embodiment of the present invention in which the reed valve feature 66, 76 is provided and the fluctuations in needle lift are well damped.

The present invention may be implemented in a common rail injector, in which a common supply (rail) delivers fuel to at least two injectors of the engine, or may be implemented in an electronic unit injector (EUI) in which each injector of the engine is provided with its own dedicated pump and, hence, high pressure fuel supply. The invention may also be implemented in a hybrid scheme, having dual common rail/EUI functionality. The injector need not be an indirect-acting injector, such as that shown in Figure 1, but may be a direct10 acting injector in which there is a direct connection between the actuator assembly and the valve needle.

It will be appreciated that various modifications may be made to the aforementioned embodiments without departing from the scope of the appended claims.

Claims

1. A valve assembly for a fuel injector (16) for use in delivering fuel to an internal combustion engine, the valve assembly comprising an armature assembly comprising an armature (62) which is movable within a fluid chamber (35) of the fuel injector (16) under the influence of an actuation force, wherein the armature (62) includes front surface (68) and a rear surface (69) and defines at least one flow path (82) to allow a flow of fluid through the armature (62) between the front and rear surfaces (68, 69); and at least one valve element (76) mounted at the rear surface (69) of the armature (62), the or each valve element (76) being operable under the influence of fluid pressure to allow the flow of fluid through the at least one flow path (82) of the armature (62) and around the fluid chamber (35), thereby to balance fluid pressure at the front and rear surfaces (68, 69) of the armature (62) so as to minimise fluctuations in movement thereof, in use.

2. The valve assembly as claimed in Claim 1, wherein the armature assembly further comprises a support plate (64) for the or each valve element (76), the support plate being mounted to the rear surface (69) of the armature (62).

3. The valve assembly as claimed in Claim 2, wherein the support plate (64), the valve assembly (66, 76) and the armature (62) are arranged in a stack, with the valve assembly (66, 76) located between the armature and the support plate.

4. The valve assembly as claimed in Claim 2 or Claim 3, wherein the support plate (64) is provided with at least one flow path (80), the or each flow path (80) being associated with a respective one of the valve elements (76).

5. The valve assembly as claimed in any of Claims 1 to 4, wherein the or each valve element takes the form of a flexible valve element (76).

6. The valve assembly as claimed in Claim 5, wherein the or each flexible valve element includes a disc (76) which is movable to block a respective one of the flow paths (80).

7. The valve assembly as claimed in any of Claims 1 to 6, wherein the rear surface (69) of the armature (62) is provided with one or more recess (84) to accommodate movement of the one or more valve elements (76) along an axis of the valve assembly.

8. The valve assembly as claimed in Claim 7, wherein the or each recess (84) is closed in a radial direction by an annular land (86) defined around the periphery of the armature (62).

9. The valve assembly as claimed in Claim 8, wherein the support plate (64) is fixed to the armature (62) via the annular land (86).

10. A fuel injector (16) comprising a valve assembly as claimed in any of Claims 1 to 9, further comprising an electromagnetic actuator (34) for applying an electromagnetic force to the armature (62) to effect movement thereof.

11. The fuel injector as claimed in any of Claims 1 to 10, wherein the fuel injector is an indirect-acting fuel injector comprising which is operable under the influence of the valve assembly to control fluid pressure in a control chamber (24) of the injector, thereby to control movement of a valve needle (14) of the injector.