GB2341893A

GB2341893A - Two-stage electromagnetically actuated fuel injector for i.c. engines

Info

Publication number: GB2341893A
Application number: GB9920648A
Authority: GB
Inventors: Andrew John Hargreaves; Michael Peter Cooke; Paul Buckley
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1998-09-23
Filing date: 1999-09-02
Publication date: 2000-03-29
Also published as: GB9920648D0

Abstract

The fuel injector eg for use in a common rail system comprises, fig.1, a valve needle 10 slidable in a bore 12, the upper end of the needle 10 being exposed to pressure in a control chamber 30. The pressure in the control chamber 30 is relieved by valve 26, 28 to initiate injection. The valve member 26 is movable by a first electromagnetic actuator which comprises a first component 42 coupled to the valve member and a second component 44 which is movable by a second electromagnetic actuator 48, 50, 52. Thus injection can be made in two stages by energizing the actuator windings 46, 50 of the two actuators respectively. Alternatively, fig.8, the valve member 26 may be coupled to an armature 42 movable by a single electromagnetic actuator 114 having a winding 124 located between relatively movable stator components 116, 120 defining respective pole faces 118, 122 which are spaced from the armature 42 by different distances. The injection valve member may open inwardly or outwardly. The valve needle 10 may terminate in a blind bore in which an inner needle member (102, fig.8) slides so that injection occurs through first openings 20 or through both first and second openings 20, (106).

Description

FUEL INJECTOR This invention relates to a fuel injector for use in delivering fuel to a combustion space of a compression ignition internal combustion engine. In particular, the invention relates to an injector of the type including a valve needle which can occupy, in use, a closed position, a fully open position and at least one intermediate stable position. Such an injector is commonly known as a two-stage lift injector. The invention also relates to an actuator suitable for use in such an injector.

Two-stage lift injectors are beneficial in that they permit the delivery of fuel at a relatively low initial rate, the majority of the fuel injected during an injection cycle being delivered, subsequently, at a higher rate. It has been found that delivering fuel in this manner permits an improvement in the combustion quality and that levels of NO,, emissions and noise can be reduced.

It is known to provide a two-stage lift capability in an injector by biasing the injector needle towards a seating using two springs in parallel or series, the springs being arranged such that the application of fuel at a relatively low pressure to the needle causes movement of the needle to a first lift position against one of the springs, the application of fuel at a higher pressure causing the needle to move to a fully open position against the action of the other or both springs.

Such a two-stage lift arrangement is not suitable for use in a common rail type fuel system as, in use, the injectors are supplied constantly with fuel at

high pressure. It is an object of the invention to provide a two-stage lift injector suitable for use in a common rail fuel system.

According to the present invention there is provided a fuel injector comprising a valve needle slidable within a bore, a surface associated with the needle defining, in part, a control chamber, a valve member cooperable with a seating to control the fuel pressure within the control chamber, the valve member being moveable under the control of a first electromagnetic actuator including a first component which is coupled to the valve member and a second component which is moveable by a second electromagnetic actuator.

The seating may be defined by the surface associated with the valve needle.

The first component of the first actuator conveniently comprises an armature, the second component comprising a core associated with a winding. The winding may be moveable with the core or may remain fixed with respect to the remainder of the injector.

The valve member may be moveable between a first position, a second, intermediate, stable position, and a third stable position, wherein the movement of the valve member from its first position to its second position occurs under the control of the first actuator, movement of the valve member from its second position to its third position occurring under the control of the second actuator.

The valve member may be moveable relative to an armature of the first actuator such that, upon energization of the first actuator to move the valve

member to its second position, further movement of the valve member to its third position can occur without further movement of the armature of the first actuator occurring. The valve needle may be moveable outwardly to commence fuel injection, the fuel injector therefore being of the outwardly opening type.

The invention also relates to an electromagnetic actuator comprising a stator and an armature moveable under the magnetic field generated, in use, by the stator, the stator comprising a first stator component defining a first pole face, a second stator component moveable relative to the first stator component and defining a second pole face, and an actuator winding.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectional view illustrating part of an injector in accordance with an embodiment of the invention; Figure 2 is a view similar to Figure 1 illustrating a modification; Figure 3 is an alternative embodiment of the present invention; Figures 4 to 7 are views illustrating various modifications to the injector of Figure 3; Figure 8 is a schematic view of a fuel injector, including an electromagnetic actuator in accordance with a further aspect of the invention; and

Figure 9 is a schematic view illustrating another fuel injector incorporating the actuator in Figure 8.

The fuel injector illustrated, in part, in Figure 1 is intended for use in a fuel system of the common rail type, the injector comprising an injector needle 10 which is slidable within a blind bore 12 formed in a nozzle body 14. The needle 10 is of stepped form, including an upper region lOa of diameter substantially equal to that of the adjacent part of the bore 12, and a reduced diameter lower region lOb defining, with the bore 12, a delivery chamber 16 which is supplied with fuel under high pressure through a supply passage 18 from a common rail which is charged with fuel to a high pressure, in use, by an appropriate fuel pump. The needle 10 further defines thrust surfaces lOc which are exposed to the fuel pressure within the delivery chamber 16 and which are orientated such that the application of fuel under high pressure to the delivery chamber 16 applies a force to the needle 10 urging the needle 10 away from a seating defined adjacent the blind end of the bore 12.

Movement of the needle 10 away from the seating permits fuel to flow from the delivery chamber 16 to one or more outlet openings 20 located downstream of the seating, thus such movement of the needle 10 permits delivery of fuel through the injector to a combustion space of an associated engine. It will be appreciated that the distance through which the needle 10 moves away from the seating controls the rate at which fuel is able to flow to the outlet openings 20, thus the position of the needle 10 controls the rate at which fuel is injected. In the drawings, the outlet openings 20 are shown as being located at the same level. However, it is possible for the outlet openings 20 to be located at more than one level.

The upper end of the nozzle body 14 abuts a distance piece 22 which is provided with a through bore 24. The bore 24 includes a region of relatively small diameter through which a tubular valve member 26 extends, the lower end of the valve member 26 being cooperable with a seating member 28 carried by the upper end of the needle 10. The bore 24 further includes a region of relatively large diameter defining a control chamber 30, parts of the upper end surfaces of the needle 10 and the seating member 28 being exposed to the fuel pressure within the control chamber 30. A passage 32 including a restriction or orifice defines a restricted flow path between the supply passage 18 and the control chamber 30.

A helical compression spring 34 is located within the control chamber 30, the helical compression spring 34 acting upon the valve member 26, biasing the valve member 26 into engagement with the seating member 28, and urging the needle 10 into engagement with its seating.

The distance piece 22 abuts an actuator housing 36, the nozzle body 14 and distance piece 22 being secured to the actuator housing 36 by means of a screw-threaded cap nut 38. The actuator housing 36 defines a chamber 40 which communicates with the interior of the tubular valve member 26 such that, when the valve member 26 is lifted from the seating member 28, communication is permitted between the control chamber 30 and the chamber 40 through the passage extending along the axis of the tubular valve member 26. The chamber 40 communicates with an appropriate low pressure fuel reservoir or drain through passages 41. Located within the chamber 40 is a first electromagnetic actuator comprising a first component in the form of an armature 42 secured to the upper end of the valve member 26 and a second

component in the form of a core 44 carrying an actuator winding 46 which is electrically connected to an appropriate control arrangement.

The actuator housing 36 further defines a chamber housing a second electromagnetic actuator which includes a fixed component comprising a core 48 carrying an actuator winding 50, and a moveable component in the form of an armature 52. The armature 52 is coupled through a connecting rod 54 which extends through an opening formed in a wall of the actuator housing 36 separating the chamber 40 from the chamber housing the second actuator with the core 44 of the first electromagnetic actuator. A helical compression spring 56 is engaged between the actuator housing 36 and the core 44 and biases the armature 52 away from the core 48 of the second actuator. A shim 58 is provided to limit movement of the armature 52 away from the core 48, and stops 60 are carried by the core 48 to limit movement of the armature 52 towards the core 48. Similarly, stops 62 are provided on the core 44 of the first electromagnetic actuator to limit movement of the armature 42 towards the core 44.

In use, with the first and second electromagnetic actuators de-energized, and with fuel under high pressure supplied to the supply passage 18, injection of fuel does not take place, the fuel pressure within the control chamber 30 in conjunction with the action of the spring 34 being sufficient to ensure that the needle 10 engages its seating, thus ensuring that fuel is unable to flow from the delivery chamber 16 to the outlet openings 20.

When injection is to occur, the winding 46 of the first electromagnetic actuator is energized resulting in movement of the armature 42 towards the core 44. Such movement of the armature 42 results in movement of the valve

member 26 away from the seating member 28, and as a result fuel is able to escape from the control chamber 30 through the passage defined by the valve member 26 to the chamber 40 and low pressure reservoir. As fuel is only permitted to flow to the control chamber 30 at a restricted rate, the fuel pressure within the control chamber 30 falls, and as a result the magnitude of the force applied to the needle 10 urging the needle 10 towards its seating is reduced. The fuel pressure within the control chamber 30 will fall to a point at which the needle 10 is able to lift away from its seating due to the action of the fuel under pressure within the delivery chamber 16, the movement continuing until the flow between the valve member 26 and the seating member 28 matches that through the restricted passage 32, resulting in a slight lifting of the needle 10 away from its seating. Thus, the outlet openings 20 are only partly uncovered (or, in the case where they are disposed at more than one level, only some of the outlet openings 20 are uncovered). As a result, fuel is injected at a desired low initial flow rate.

However, as an alternative, it is possible to control the initial flow rate by changing the magnitude of the lift of the valve needle 10. This can be effected by choice of the size of shim 58 which determines the position of the core 44, and also by the dimensions of the stops 62. These dimensions are chosen to ensure that during this stage in the operating cycle of the injector, the valve needle 10 is lifted to an intermediate position in which fuel is injected at the desired low initial flow rate.

In order to allow injection at the full rate, the actuator winding 50 of the second electromagnetic actuator is energized resulting in movement of the armature 52 towards the core 48 until the armature 52 engages the stops 60.

The movement of the armature 52 results in movement of the core 44 of the first electromagnetic actuator, and a result, the armature 42 of the first

electromagnetic actuator and the valve member 26 are also moved. The movement of the valve member 26 once again lifts the valve member 26 from the seating member 28, thus permitting further fuel to flow from the control chamber 30 to the low pressure reservoir, and as described hereinbefore, the fuel pressure within the control chamber 30 will fall permitting further movement of the needle 10, the movement of the needle 10 continuing until the flow between the valve member 26 and seating member 28 matches that through the restricted passage 32. Once such a position has been reached, it will be appreciated that the valve needle 10 is in its fully lifted position and causes all of the outlet openings 20 to be fully exposed. In this position, fuel is injected at the higher rate.

In order to terminate injection, the first and second actuator windings 46,50 are de-energized, and as a result, the core 44 is returned to its initial position under the action of the spring 56 and the valve member 26 is returned to its initial position under the action of the spring 34, the movement of the valve member 26 to its initial position also causing movement of the needle 10 into engagement with its seating, thus terminating the delivery of fuel from the delivery chamber 16 to the outlet openings 20.

It will be appreciated that in addition to the needle 10 moving into engagement under the action of the spring 34, the movement of the needle 10 is assisted by the force applied to the needle 10 by the fuel pressure within the control chamber 30, the fuel pressure within the control chamber 30 rising once the valve member 26 has moved into engagement with the seating member 28 to terminate the flow of fuel from the control chamber 30 to the low pressure reservoir. Optionally, by providing a restriction within the supply passage 18, the fuel pressure within the delivery chamber 16 at this

point in the injection cycle is relatively low, thus the force urging the needle 10 away from its seating is of relatively low magnitude.

The cores 44,48 may take the form of E cores conveniently constructed using an appropriate laminating technique. Alternatively, the cores could take the form of pot cores. The winding 46 of the first actuator may be carried by and moveable with the core 44. Alternatively, the winding 46 may be held in a fixed position relative to the actuator housing 36, the core 44 being moveable relative to the winding 46.

Figure 2 illustrates a modification to the arrangement illustrated in Figure 1 in which an additional stop member 64 is carried by the core 44 of the first electromagnetic actuator, the stop member 64 being arranged to limit the maximum separation of the armature 42 from the core 44. As shown, when the actuators are not energised, the stop member 64 is spaced by a small distance from the armature 42, and so has no effect. In such an arrangement, it will be appreciated that the operating cycle of the injector may be as described hereinbefore, or alternatively the winding 50 of the second actuator may be energized prior to energization of the first actuator. In such a mode of operation, the energization of the winding 50 of the second actuator causes movement of the core 44 of the first actuator, such movement causing movement of the armature 42 due to the cooperation between the armature 42 and the stop member 64. The movement of the armature 42 continues until the armature 52 of the second actuator has reached its energized position. As described hereinbefore, the movement of the armature 42 of the first actuator will result in corresponding movement of the needle 10.

After energization of the second actuator, the first actuator may be energized resulting in further movement of the valve member 26, and hence in movement of the needle 10 to its fully lifted position.

By arranging for the armatures of the first and second actuators to move through different strokes, the arrangement of Figure 2 can be operated to permit the needle 10 to be held in either its closed position, a first intermediate position governed by the stroke of the first actuator, a second intermediate position governed by the stroke of the second actuator, and a fully lifted position governed by the combined strokes of the first and second actuators.

In both of the embodiments described hereinbefore, if desired the volume of the control chamber 30 may be reduced, and the spring 34 may be moved to a position in which it acts between the armature 42 or upper end of the valve member 26 and either a fixed stop member located within the chamber 40 or part of the core 44.

Figure 3 shows a fuel injector of the outwardly opening type in accordance with a further alternative embodiment of the invention, in which similar parts to those shown in Figures 1 and 2 are denoted by the same reference numerals. The needle valve 10 is provided with an axially extending blind drilling 70 which communicates through a radially extending drilling 72 with a delivery chamber 16 defined by the bore 12. The needle 10 is further provided with a plurality of outlet drillings 74 which communicate with the axially extending blind drilling 70, the outlet drillings 74 being located such that upon movement of the needle 10 to space an enlarged end region thereof from the nozzle body 14, the outlet drillings 74 move beyond the end of the

nozzle body 14, thus permitting fuel to flow from the delivery chamber 16 through the drilling 72 and the axially extending drilling 70 through the outlet drillings 74 to a combustion space of an associated engine. The outlet drillings 74 are located in positions axially spaced from one another such that the number of outlet drillings 74 uncovered when the needle 10 occupies a position in which the enlarged region thereof is spaced from the nozzle body 14 depends upon the distance through which the needle 10 is moved.

The needle 10 carries a tubular sleeve member 76 which is a piston-like fit within the adjacent part of the bore 12, the sleeve member 76 assisting in guiding the needle 10 for sliding movement within the bore 12. The sleeve member 76 is conveniently secured to the valve needle 10 by welding.

However, it will be appreciated that other techniques may be used to secure the sleeve member to the needle 10, and Figures 2 to 5 illustrate various alternative techniques for securing the sleeve member 76 to the needle 10. In the arrangements of Figures 4 and 5, a circlip 78 is used to secure the sleeve 76 to the needle 10, the circlip 78 either being arranged to be compressed (Figure 4) or expanded (Figure 5) during assembly. In the arrangement of Figure 6, the needle 10 is provided with outwardly extending projections around which the sleeve member 76 is deformed. In the arrangement of Figure 7, the sleeve member 76 is an interference fit upon the needle 10.

In each case, the sleeve member 76 includes, at its end remote from the enlarged diameter end region of the needle 10, an inwardly extending lip which carries a seating member 80. The sleeve member 76, needle 10 and seating member 80 together define a chamber which is supplied with fuel under pressure through the drilling 70. Where the sleeve member 76 is a relatively loose fit upon the needle 10, fuel may flow to the chamber at a

sufficient rate between the sleeve member 76 and the needle 10, in which case part of the drilling 70 may be omitted (see Figures 4 and 5).

A spring 82 is engaged between the sleeve member 76 and a step defined by part of the bore 12, the spring 82 biasing the needle 10 towards a position in which the enlarged diameter end region thereof is seated against the end of the nozzle body 14. The dimensions of the sleeve member 76 and the needle 10 are chosen to ensure that the application of fuel under pressure to the delivery chamber 16 applies a force to the needle 10 urging the enlarged diameter region thereof into engagement with the nozzle body 14.

The bore 12 of the nozzle body 14 is closed by a distance piece 84, and it will be appreciated that the distance piece 84, the nozzle body 14 and the tubular sleeve member 76 together define a control chamber 86. A passage 88 including a region of restricted diameter is provided in the distance piece 84 to provide a restricted flow path between the control chamber 86 and a low pressure fuel reservoir. The distance piece 84 is provided with an axially extending bore or drilling within which a valve member 90 is slidable, the valve member 90 including an end region 90a of enlarged diameter which is located within the chamber defined between the tubular sleeve member 76 and the needle 10, and is engageable with the seating member 80 to control communication between the chamber, and hence the delivery chamber 16, and the control chamber 86.

The distance piece 84 abuts the actuator housing 36, the distance piece 84 and the nozzle body 14 being secured to the actuator housing 36 by means of a screw-threaded cap nut 38. The actuator housing 36 is provided with an axially extending bore within which a control rod 92 is slidable, the control

rod 92 being arranged to engage the valve member 90. The control rod 92 is cooperable with an extension 94, the extension 94 carrying an armature 95 of a first electromagnetic actuator 97. A spring 96 cooperates with the armature 95 to apply a force to the valve member 90 acting in a downward direction in the orientation illustrated.

The control rod 92 carries a second armature 93 forming part of a second electromagnetic actuator 99. A spring 98 engages the second armature 93 to apply a force to the control rod 92 and valve member 90 urging the valve member 90 in an upward direction in the orientation illustrated. The spring force applied by the spring 98 is greater than that applied by the spring 96 with the result that, when the first and second actuators are de-energized, the valve member 90 occupies a first, upper position. Although not illustrated in detail in Figure 3, the control rod 92 and extension 94 are separable from one another. This may be achieved by guiding these components so that, in use, they are engageable with one another. Alternatively, a spring may be interposed between the control rod 92 and the extension 94 such that upon completion of movement of the extension 94, further movement of the control rod 92 may take place.

In use, starting from the position illustrated in which the first and second actuators 97,99 are de-energized, and in which fuel under high pressure is applied to the supply passage 18, the fuel pressure within the control chamber 86 is relatively low, and fuel is unable to flow to the control chamber from the delivery chamber 16. In this position, as the fuel pressure within the control chamber 86 is relatively low, the action of the fuel under pressure within the delivery chamber 16 is unable to move the needle 10 against the action of the spring 82, thus the needle 10 remains in the position illustrated

in which the enlarged end region thereof is seated against the nozzle body 14.

In this position, fuel is not delivered by the injector.

In order to commence injection, the first actuator 97 is energized.

Energization of the first actuator 97 results in the armature 95 being attracted towards the stator of the first actuator 97, the movement of the first armature 95 being limited by engagement of the first armature 95 with a stop member 97a forming part of the first actuator 97. The movement of the first armature 97 is transmitted through the extension 94 and control rod 92 to the valve member 90. The valve member 90 is moved to a second position in which the enlarged end 90a thereof is lifted from the seating member 80, thus permitting fuel from the delivery chamber 16 to flow to the control chamber 86. The flow of fuel to the control chamber 86 increases the fuel pressure therein, and a point will be reached beyond which the fuel pressure within the control chamber 86 is sufficient to move the needle 10 against the action of the spring 82 and the action of fuel under pressure within the delivery chamber 16, the movement of the needle 10 resulting in one or more of the outlet drillings 74 moving beyond the lower end of the nozzle body 14. Such movement permits fuel to be delivered through the exposed outlet drillings 74 to the combustion space with which the injector is associated. The movement of the needle 10 continues until the seating member 80 has moved to a position adjacent the enlarged end 90a of the valve member 90. In this position the rate of fuel flow between the valve member 90 and seating member 80 to the control chamber 86 is throttled to a level substantially equal to the rate of fuel flow through the drilling 88 from the control chamber 86 to the low pressure fuel reservoir.

After a predetermined time or after a predetermined quantity of fuel has been delivered, the second actuator 99 is energized, the energization of the second actuator 99 attracting the second armature 93 towards the stator of the second actuator 99, the movement of the second armature 93 being limited by engagement between the second armature 93 and stop members 99a forming part of the second actuator 99. The movement of the second armature 93 results in corresponding movement of the control rod 92 and the valve member 90 moving the valve member 90 to a third position. As a result, fuel is permitted to flow to the control chamber 86 at an increased rate thus increasing the fuel pressure within the control chamber 86 and moving the valve needle 10 through a further distance. As a result, fuel delivery is permitted through more of the outlet drillings 74, and hence delivery of fuel occurs at an increased rate.

The movement of the needle 10 continues until a position is reached in which the rate of fuel flow to the control chamber 86 is throttled to a level substantially equal to that at which fuel is escaping from the control chamber 86. It will be appreciated that the additional movement of the control rod 92 results in the control rod 92 separating from the extension 94, and hence that the movement of the second armature 93 following the energization of the second actuator 99 is not impaired by the first armature 95 having moved into engagement with the stop members 97a.

In order to terminate injection, the first and second actuators 97,99 are deenergized, and as a result the control rod 92 moves under the action of the spring 98. The valve member 90 moves under the action of the fuel pressure applied thereto, following the movement of the control rod 92, and as a result, the enlarged end 90a of the valve member 90 moves into engagement

with the seating member 80. The flow of fuel to the control chamber 86 ceases and as fuel is able to escape from the control chamber 86 to the low pressure fuel reservoir, the fuel pressure within the control chamber 86 falls.

The reduction in fuel pressure within the control chamber 86 will fall to a level beyond which the needle 10 is able to move under the action of the spring 82 and the fuel pressure within the delivery chamber 16 to return the enlarged diameter end region thereof into engagement with the nozzle body 14. It will be appreciated that such movement terminates the delivery of fuel to the combustion space.

As illustrated in Figure 3, the control rod 92 is shaped to include an angled thrust surface 92a which is exposed to the fuel pressure within the supply passage. The dimensions of the thrust surfaces 92a are chosen to ensure that the combination of the valve member 90 and the control rod 92 is substantially fuel pressure balanced. As a result, the actuator force which must be generated by the first and second actuators 97, 99, in use, can be reduced. Additionally, the diameter of the seating line formed between the end region 90a of the valve member 90 and the seating member 80 is conveniently equal to the diameter of the part of the valve member 90 extending through the control chamber 86 to ensure that changes in the control chamber pressure are not transmitted through the valve member 90 to the actuator or the springs associated therewith.

It will be appreciated that the response time of the injector (the time between energization/de-energization of the actuator(s) and completion of movement of the needle can be adjusted by modifying the size of the restriction to fuel flow through the passage 88.

Figure 8 shows a valve needle of inwardly opening type in which similar parts to those shown in Figures 1 to 7 are denoted with the same reference numerals. The fuel injector includes an electromagnetic actuator arrangement, referred to generally as 114, which has only a single winding 124.

The needle 10 is shaped to include a blind bore within which an inner needle member 102 is slidable, the inner needle member 102 being provided with an elongate slot through which a pin 104 carried by the needle 10 extends. In use, upon movement of the needle 10 away from its seating by a small distance, the pin 104 rides within the slot of the inner needle 102, and movement of the inner needle 102 does not occur. Movement of the needle 10 through a greater distance results in the pin 104 reaching an end of the slot, and in further movement of the needle 10 being transmitted through the pin 104 to the inner needle 102 with the result that the inner needle 102 is lifted from a respective seating, whereon fuel is permitted to flow to a second group of outlet openings 106. It will be appreciated that, in such an arrangement, the rate at which fuel is injected using the injector is dependent upon the distance moved by the needle 10. When the needle 10 is moved away from its seating by a small distance, injection occurs only through the first group of outlet openings 20, and thus occurs at a relatively low rate, movement of the needle 10 through a greater distance permitting injection to occur through both the first group of outlet openings 20 and the second group of outlet openings 106, thus fuel injection occurs at a higher rate.

The nozzle body 14 abuts a valve housing 108, the valve housing 108 and nozzle body 14 together defining a control chamber 110 which is supplied

with fuel under high pressure from the supply passage 18 through the small diameter drilling 32, as is the case in the fuel injectors in Figures 1 and 2.

The seating member 28 is positioned so as to be engageable by the valve member 26, the valve member 26 being of tubular form and being slidable in a piston-like manner within a through bore formed in the valve housing 108.

The valve member 26 defines a passage which communicates, in use, with a chamber 112 defined by recesses formed in the valve housing 108 and the actuator housing 36 arranged to abut the valve housing 108, the chamber 112 communicating through passages (not shown) with an appropriate low pressure fuel reservoir. It will be appreciated that when the valve member 26 engages the seating member 28, fuel is not permitted to escape from the control chamber 110 through the passage defined by the valve member 26 to the low pressure fuel reservoir, and that when the valve member 26 is lifted away from the seating member 28, communication between the control chamber 110 and the low pressure fuel reservoir is permitted. The valve member 26 is secured to the armature 42 forming part of the electromagnetic actuator such that energization of the actuator arrangement 114 to attract the armature 42 towards pole faces thereof results in axial movement of the valve member 26.

The actuator arrangement 114 includes a stator comprising a first, stationary stator component 116 which is mounted within the actuator housing 36 and which defines a first pole face 118, and a second stator component 120 which is slidable relative to the first stator component 116, and which defines a second pole face 122. The actuator winding 124 is located between the first and second stator components 116,120.

A spring 126 is provided between the actuator housing 36 and the second stator component 120 to bias the second stator component 120 in a downward direction in the orientation illustrated, a circlip 128 being mounted upon the second stator component 120 in order to limit movement of the second stator component 120 under the action of the spring 126. The second stator component is provided with an axially extending recess within which a spring 130 is located, the spring 130 being engaged between the second stator component 120 and the valve member 26 to bias the valve member 26 in a downward direction in the orientation illustrated.

Figure 8 illustrates the actuator arrangement 114 in its rest position. In this position, it will be appreciated that the armature 42 occupies a first position in which it is spaced from the second pole face 122 by a relatively small distance, and is spaced from the first pole face 118 by a greater distance.

In use, with the supply passage 18 communicating with a source of fuel under high pressure and with the actuator arrangement 114 in its de-energized condition, as described hereinbefore, the control chamber 110 is charged with fuel at a relatively high pressure, the action of the fuel under pressure within the control chamber 110 upon the end surface of the needle 10 being sufficient to ensure that the needle 10 remains in engagement with its seating, thus injection of fuel does not take place. In order to commence injection of fuel at a relatively low rate, the winding 124 of the actuator arrangement 114 is energized to a relatively low level. Such energization applies a relatively low magnitude attractive force to the armature 42, and the energization level of the winding 124 is chosen to be sufficient to cause the armature 42 to move against the action of the spring 130 towards the second pole face 122 to a second position. The attractive force is insufficient to cause compression of

the spring 126, thus the second stator component 120 does not move.

Movement of the valve member 26 is limited by appropriate stop members 120a associated with the second stator component 120.

The movement of the valve member 26 by a small distance to its second position as described hereinbefore permits the fuel pressure within the control

chamber 110 to be relieved, and as result, the magnitude of the force urging 9mg the needle 10 into engagement with its seating is reduced, and a point will be reached beyond which the fuel pressure acting upon the thrust surfaces lOc is sufficient to overcome the action of the fuel within the control chamber 110, and the needle 10 will lift away from its seating. The movement of the needle will continue until the seating member 28 has moved to a position in which it is adjacent the lower end of the valve member 26, the rate at which fuel is able to escape from the control chamber 110 through the passage defined by the valve member 26 to the low pressure fuel reservoir being substantially equal to the rate at which fuel is supplied through the small diameter drilling 32 in this position.

The distance through which the valve member 26 and hence the needle 10 moves during this part of the operating cycle of the injector is chosen to ensure that movement of the inner valve needle 102 does not occur, thus injection occurs only through the first group of outlet openings 20, fuel not being delivered through the second group of outlet openings 106, and as described hereinbefore, fuel injection therefore only occurs at a relatively low rate.

When fuel is to be injected at a higher rate, the winding 124 of the actuator arrangement 114 is energized to a second, higher level. The energization

level is chosen to apply a sufficiently large magnitude attractive force to the armature 42 to permit the armature 42 and the second stator component 120 to move against the action of the spring 126, the movement of the armature 42 being restricted by appropriate stop members (not shown) associated with the first stator component 116 defining a third stable position. The stop members may alternatively be associated with the valve member 26.

As described hereinbefore, the movement of the valve needle 10 again permits fuel to escape from the control chamber 110 at an increased rate, thus reducing the fuel pressure therein and permitting the needle 10 to move away from its seating by a further distance. The movement of the needle 10 is conveniently limited by the end surface thereof moving into engagement with a stop surface defined by part of the valve housing 108.

The additional movement of the needle 10 causes the pin 104 to move into engagement with the end of the slot of the inner valve needle 102, and hence the valve needle 10 is lifted from its seating permitting fuel to be injected through both the first group of outlet openings 20 and the second group of outlet openings 106. As a result, fuel injection occurs at a higher rate.

In order to terminate injection, the actuator winding 124 is de-energized and the valve member 26 returns into engagement with the seating member 28 under the action of the spring 126 and the spring 130. As a result, the fuel pressure within the control chamber 110 will rise, and a point will be reached beyond which the fuel pressure within the control chamber 110 is sufficient to overcome the action of the fuel upon the thrust surfaces lOc, and the needle 10 will move into engagement with its seating, terminating the flow of fuel to both groups of outlet openings 20,106.

The use of the actuator arrangement 114 described hereinbefore is advantageous in that the total separation between the pole faces and the armature is reduced compared to a conventional arrangement, and therefore the efficiency of the actuator can be improved.

Figure 9 illustrates an alternative application for the actuator arrangement.

The injector illustrated in Figure 9 is of the outwardly opening type, as is the fuel injector in Figure 3, and operates in a manner similar to that of the Figure 8 arrangement. The main distinction between the arrangement of Figure 8 and that of Figure 9 is that the control chamber 110 communicates through a drilling 132 of restricted diameter with a passage which communicates with a low pressure fuel reservoir, the valve member 26 which is moveable under the influence of the actuator arrangement 114 being engageable with a seating to control the rate at which fuel under high pressure is supplied to the control chamber 110. It will be noted that in this arrangement, energization of the electromagnetic actuator 114 results in movement of the valve member 26 in a downward direction in the orientation illustrated, such movement being followed by downward movement of the valve needle 10 to move one or more groups of outlet openings 74a, 74b beyond the lower end of the nozzle body 14 to permit fuel injection through those outlet openings. De-energization of the actuator winding 124 results in return movement of the armature 42 under the action of the springs 126,130.

In this embodiment, the valve member 26 is not directly coupled to the armature 42, and the return movement of the armature 42 is followed by movement of the valve member 26 due to the action of fuel under high pressure acting upon the lower end surface of the valve member 26.

It will be noted that in the arrangement of Figure 9, the needle is spring biased towards a closed position.

Although in the description hereinbefore, the actuator arrangement 114 is used in controlling the operation of fuel injectors of the type in which the valve needle is moveable between three stable positions, it will be appreciated that the actuator arrangement 114 is suitable for use in other applications, and that this invention should not be restricted to the use of the actuator arrangement in a fuel injector.

Claims

CLAIMS 1. A fuel injector comprising a valve needle slidable within a bore, a surface associated with the needle defining, in part, a control chamber, a valve member cooperable with a seating to control the fuel pressure within the control chamber, the valve member being moveable under the control of a first electromagnetic actuator including a first component which is coupled to the valve member and a second component which is moveable by a second electromagnetic actuator.
2. The fuel injector as claimed in Claim 1, wherein the seating is defined by the surface associated with the needle.
3. The fuel injector as claimed in Claim 1 or 2, wherein the first component of the first actuator comprises an armature, the second component comprising a core associated with a winding.
4. The fuel injector as claimed in Claim 3, wherein the winding is moveable with the core.
5. The fuel injector as claimed in Claim 1, wherein the valve member is moveable between a first position, a second, intermediate, stable position, and a third stable position, wherein the movement of the valve member from its first position to its second position occurs under the control of the first actuator, movement of the valve member from its second position to its third position occurring under the control of the second actuator.

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FUEL INJECTOR This invention relates to a fuel injector for use in delivering fuel to a combustion space of a compression ignition internal combustion engine. In particular, the invention relates to an injector of the type including a valve needle which can occupy, in use, a closed position, a fully open position and at least one intermediate stable position. Such an injector is commonly known as a two-stage lift injector. The invention also relates to an actuator suitable for use in such an injector.

Two-stage lift injectors are beneficial in that they permit the delivery of fuel at a relatively low initial rate, the majority of the fuel injected during an injection cycle being delivered, subsequently, at a higher rate. It has been found that delivering fuel in this manner permits an improvement in the combustion quality and that levels of NO,, emissions and noise can be reduced.

It is known to provide a two-stage lift capability in an injector by biasing the injector needle towards a seating using two springs in parallel or series, the springs being arranged such that the application of fuel at a relatively low pressure to the needle causes movement of the needle to a first lift position against one of the springs, the application of fuel at a higher pressure causing the needle to move to a fully open position against the action of the other or both springs.

Such a two-stage lift arrangement is not suitable for use in a common rail type fuel system as, in use, the injectors are supplied constantly with fuel at