WO2004081365A1

WO2004081365A1 - Fuel injector

Info

Publication number: WO2004081365A1
Application number: PCT/GB2004/000998
Authority: WO
Inventors: Andrew Male
Original assignee: Delphi Technologies, Inc.
Priority date: 2003-03-11
Filing date: 2004-03-11
Publication date: 2004-09-23
Also published as: GB0305557D0

Abstract

A fuel injector has an injector control valve (44) including a control valve member (48) which is movable within a bore (50; 50a, 50b) provided in a control valve housing (46; 86, 88). A valve needle (10; 80) of the injector is movable relative to a valve needle seating to control fuel injection through one or more injector outlets and a fuel inlet (66) of the injector receives a supply of fuel at high pressure. An annular flow path (51) is provided for delivering a flow of fuel from the fuel inlet (66) to an injector delivery chamber (16; 38), from where fuel is delivered to the or each outlet. The annular flow path (51) is defined between the bore (50; 50a, 50b) in the control valve housing (46; 86, 88) and an outer surface of the injector control valve, although said flow of fuel is not controlled by means of the injector control valve (44). It is a benefit of the invention, therefore, that the fuel supply path for high pressure fuel utilises the bore (50; 50a, 50b) for the control valve member (48) to define a part of the flow, rather than relying on a separate drilling through the control valve housing (46, 86).

Description

FUEL INJECTOR

The invention relates to a fuel injector of the type suitable for use in a fuel injection system of a compression ignition internal combustion engine. In particular, the invention relates to a fuel injector for use in a common rail fuel injection system or a unit pump injection system. The invention also relates to a fuel injector mounting for use particularly in a fuel injection system of the common rail or unit pump type.

It is well known in common rail fuel injection systems to provide one fuel injector for each engine cylinder, and to mount each injector within a pocket provided within an engine cylinder head. In unit pumps the injector may be mounted in the engine in a similar manner. In a common rail system a high pressure pump supplies fuel at high pressure to an accumulator volumeror common rail, from where fuel is delivered to all of the injectors. In a unit pump a dedicated pump element is provided for each injector to pressurise fuel within an pump chamber associated with the injector, with the pump chamber delivering high pressure fuel only to its associated injector.

Typically, in both common rail and unit pump type injection systems, each injector includes a nozzle having a valve needle that is engageable with a valve needle seating to control fuel injection to the associated cylinder through outlet openings provided in an injector nozzle body. In one known injector type for use in common rail or unit injection systems, the valve needle is co-operable with a valve needle balance piston that engages or is otherwise coupled to the valve needle at the end of the valve needle remote from the outlets. A spring acts on the balance piston, and hence on the valve needle, and serves to urge the valve needle into engagement with its seating, and in which seated position no injection takes place through the outlets. The end of the balance piston remote from the valve needle is exposed to fuel pressure within a control chamber, fuel pressure within the control chamber being controlled by means of what is commonly referred to as a "nozzle control valve" or "needle control valve".

Typically, the nozzle control valve includes a nozzle control valve member that is movable by means of an electromagnetic actuator. The actuator includes an armature that is coupled to the nozzle control valve member, and energisation and de-energisation of an actuator winding causes movement of the armature and, hence, the nozzle control valve member. The nozzle control valve member is movable between two different states, one in which the control chamber communicates with a low pressure drain and one in which the control chamber communicates with a supply of high pressure fuel. In this way the movement of the nozzle control valve member between its two different states provides a means for varying fuel pressure within the control chamber.

The injector is mounted or is received within an injector pocket provided in a cylinder head of the associated engine cylinder. A lower region of the injector nozzle projects into the engine cylinder and an upper region of the injector extends through the injector pocket, with the uppermost end of the injector projecting through the open end of the pocket. The control chamber is defined within a housing at the uppermost end of the injector, and is located externally to the injector pocket. Likewise the housing for the nozzle control valve is located outside the injector pocket. The actuator for the nozzle control valve is of relatively large size, and the accommodation space required for the actuator makes it necessary to locate the actuator outside the injector pocket. In use, a supply of high pressure fuel from the common rail or the unit pump chamber is delivered to a high pressure fuel inlet of the injector. The fuel inlet is arranged outside the injector pocket, and delivers fuel to a high pressure supply line defined by one or more drillings provided in the nozzle body and various other housing parts of the injector. It is also necessary for one or more further drillings to be provided within the injector housings so as to permit a supply of high pressure fuel into the control chamber, depending on the state of the nozzle control valve.

It is one object of the invention to provide a fuel injector which requires a reduced accommodation space within the engine. There is a requirement to improve the response or responsiveness of injectors generally of the aforementioned type, in particular so as to permit injection of small fuel quantities, and it is a further object of the present invention to provide a fuel injector which achieves this.

According to a first aspect of the present invention, there is provided a fuel injector having an injector control valve including a control valve member which is movable within a bore provided in a valve housing, a valve needle movable relative to a valve needle seating to control fuel injection through one or more injector outlets, a fuel inlet for receiving a supply of fuel at high pressure, and an annular flow path for delivering a flow of fuel from the fuel inlet to an injector delivery chamber from where fuel is delivered to the or each outlet, wherein the annular flow path is defined between the bore in the valve housing and an outer surface of the injector control valve, but wherein said flow of fuel is not controlled by means of the injector control valve. "The flow of high pressure fuel from the injector fuel inlet flows through the valve housing bore and around the injector control valve member on its path to the injector delivery chamber. The injector can therefore be made of relatively compact design as the functionality of the high pressure supply path (i.e. between the inlet and the delivery chamber) and the injector control valve are provided by the same component parts. The flow of high pressure fuel to the delivery chamber is achieved conveniently through the bore provided for the control valve member, rather than there being a requirement for an additional drilling or drillings to be provided in the valve housing and other housings. As a consequence at least a portion of the high pressure supply path may be located at a higher axial position along the injector axis than the pressure control chamber.

In one type of injector the control valve may take the form of a so-called nozzle control valve for controlling fuel pressure within a pressure control chamber. In one embodiment a surface associated with the valve needle is exposed to fuel pressure within the pressure control chamber.

In another embodiment the valve needle is co-operable with an intermediate member, wherein a surface of the intermediate member is exposed to fuel pressure within the pressure control chamber. In this embodiment the nozzle control valve therefore controls movement of the intermediate member and the valve needle by controlling fuel pressure within the pressure control chamber.

Typically, the intermediate member may be referred to as a "balance piston", which may be engaged or otherwise coupled to the injector valve needle such that movement of the balance piston as a result of controlling fuel pressure within the pressure control chamber causes accompanying movement of the valve needle. Alternatively, if he intermediate member is not provided a manufacturing advantage is ac eved n thaTfhe valve needle element can^'b fofme in a single piece, providing a greater dynamic advantage, in use.

In this embodiment, it is preferable to arrange for respective upper and lower ends of the control valve to be guided for movement within first and second bores provided in respective adjacently mounted housings, and which bores preferably define a part of the annular flow path.

In an alternative embodiment to that mentioned previously, the injector control valve need not be a nozzle control valve but may, for example, be a spill valve for controlling communication between a pump chamber for supplying fuel to the injector delivery chamber and a low pressure drain. The spill valve may be movable within the valve housing bore. For example, the injector may form part of a unit pump having a dedicated pump element and pump chamber for delivering fuel to the inlet of the injector, and to no other injector inlet, and wherein the spill valve is arranged to control communication between the pump chamber and the low pressure drain.

It will be appreciated from the following description that the injector control valve, whether for example a spill valve or a nozzle control valve, is a separate and distinct component from the injector valve needle.

If, however, a nozzle control valve is provided it may include a nozzle control valve member that is movable within a housing bore of a valve housing. More preferably, the nozzle control valve member is substantially co-axially aligned with the axis of the injector. Alternatively the nozzle control valve member may be arranged parallel to, but axially offset from, the axis of the injector. The annular flow patlT or fuel is convementl} leτϊhed^"b>y a diametricarclearance between the control valve member and the valve housing bore.

In a further preferred embodiment the fuel inlet is arranged, in use, to receive fuel through a fuel supply passage that extends approximately laterally from the axis of the injector.

It is preferable for the fuel supply passage to be defined, at least in part, within a cylinder head of the engine cylinder with which the injector is associated.

It is preferable for the point or region of fluid communication between the fuel inlet and the annular flow path to be approximately in alignment, in a lateral direction to the injector axis, with an open delivery end of the fuel supply passage.

In a further preferred embodiment, the fuel inlet includes a drilling or passage, and the open, delivery end of the fuel supply passage communicates with the annular flow path by means of said drilling or passage.

For the annular flow path to permit a flow of high pressure fuel around the control valve member, it is convenient to provide a nozzle control valve member of relatively long length compared to that in known injector designs. In an injector incorporating an intermediate member, this enables the intermediate member to have a relatively short axial length. Typically, for example, the axial length of the intermediate member is approximately equal to, or at least is no greater than, the axial length of the nozzle control valve member. Α further advantage is therefore obtained m that the response of the valve ήeeά e7mleπnediate member combination is imprόved,^"as me cόhibi tion is of reduced axial length. The combined valve needle/intermediate member component may therefore be of reduced mass and thus may have an increased axial stiffness. This provides a particular benefit when it is required to deliver small fuel quantities, such as in post or pilot injections of fuel, when it is required to open and close the valve needle quickly.

Preferably, the control valve includes an actuator for controlling movement of an armature coupled to the valve member of the control valve.

The injector may also include an electrical connector for connection to the actuator.

It is a still further advantage of the present invention that due to the reduced length of the intermediate member, and due to the provision of the annular flow path, the actuator of the control valve can be located within an injector housing that, preferably, is received almost entirely within an injector pocket of the associated engine cylinder head. Typically, therefore, only the electrical connector for the actuator needs to be located outside the injector pocket, thus reducing the overall accommodation space required for the injector within the engine. This advantage is also achieved if no intermediate member is provided.

According to a third aspect of the invention, there is provided a fuel injector mounting including a fuel injector of the first aspect of the invention, and including an engine cylinder head provided with an injector pocket for receiving the injector, wherein the engine cylinder head is further provided with a fuel supply passage having an open delivery end and extending in an approximately lateral direction to the axis of the injector when the injector is received within the ocket and^" wherein the ϊuel^~supply passage rs^"_u a ged to communicate witlTJEe annular flow path at a fluid communication region that is approximately aligned, in a direction lateral to the injector axis, with the open delivery end of the fuel supply passage.

In a preferred embodiment the injector is received within the pocket such that a control valve housing is located within the pocket. In a further preferred embodiment an actuator for a control valve of the injector is also located within the pocket.

Preferably, the fluid communication region is defined by one end of a drilling which communicates with a housing bore in a nozzle control valve housing, the other end of the drilling opening into the open delivery end of the fuel supply passage.

According to a fourth aspect of the present invention, there is provided a fuel injector having a fuel inlet and fuel delivery means for delivering high pressure fuel from the fuel inlet to an injector delivery chamber, a valve needle co- operable with an intermediate member, a surface associated with the intermediate member being exposed to fuel pressure within a control chamber, and a control valve having an elongate control valve member for controlling fuel pressure within the control chamber thereby to control movement of the intermediate member and the valve needle, wherein the intermediate member has a relatively short length compared to the valve needle and the nozzle control valve member has a relatively long length compared to the valve needle, thereby to improve the response of the intermediate member. In one embodiment the intermediate member, typically in the form of a balance piston, has approximately

By utilising a balance piston of relatively short length compared to known injector designs, the mass of the coupled balance piston/valve needle combination is reduced and, hence, the axial stiffness is increased. A benefit is therefore obtained as the injector responds more quickly to pressure variations within the pressure control chamber, and in addition a more linear response is achieved.

It will be appreciated that the preferred and/or optional features of the first and second aspects of the invention may be incorporated in the other of the first and second aspects of the invention, and in the third and fourth aspects of the invention also, alone or in appropriate combination.

The invention will be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is one sectional view of a fuel injector of a first embodiment of the invention,

Figure 2 is an enlarged view of a nozzle control valve part of the fuel injector in Figure 1,

Figure 3 is another sectional view to show the fuel injector of Figure 1 when mounted within an engine cylinder head pocket, and

Figure 4 is a sectional view of a fuel injector of a second embodiment of the invention. Referring to Figures 1 to "5, one embodiment of a fuel injector in accordance with a first aspect of the present invention includes a valve needle 10 that is engageable with a valve needle seating to control fuel delivery into an associated engine cylinder or other combustion space through one or more injector outlets (not shown) provided in an injection nozzle body 12. In this embodiment of the invention the fuel injector is incorporated within a common rail fuel injection system, in which an accumulator volume or common rail for high pressure fuel supplies fuel to the one or more injectors of the system.

The injection nozzle body 12 is provided with a blind bore 14 within which the valve needle 10 is movable between a seated position, in which the valve needle 10 is engaged with the valve needle seating so that fuel injection does not take place through the outlets, and a lifted position in which the valve needle is moved away from its seating to permit fuel injection.

An upper end of the bore 14 in the nozzle body 12 includes a region of enlarged diameter that defines an injector delivery chamber 16 for receiving fuel at high pressure. The delivery chamber 16 communicates with, and is supplied with fuel from, a fuel delivery means in the form of a high pressure supply passage 18 defined, in part, by a drilling provided in the nozzle body 12 and partially by drillings or bores provided in various other injector housings, as described in further detail hereinafter. The valve needle 10 itself is provided with grooves or flutes on its outer surface that permit fuel that is delivered to the delivery chamber 16 to flow towards the blind end of the bore 14 and, hence, to the injector outlets.

The uppermost end of the valve needle 10 is in engagement or is otherwise coupled to an intermediate member, or balance piston 22, respective lower and upper regions 22a, 22b of which are located within first and second bores 24, 26^" provided in first and second injector housings 28, 30 respectively. The first bore 24 opens into a spring chamber 32 housing a compression spring 34 through which the lower region 22a of the balance piston 22 extends. The lower region 22a of the balance piston 22 is also provided with a collar 36, a surface of which defines a seat for one end of the spring 34.

The spring chamber 32 communicates with a recess 38 provided in a lower surface of the second housing 30, and an appropriate spacer or shim 40 is located within the recess 38 to provide a seat for the other end of the spring 34. The spring 34 therefore serves to apply a closing force to the balance piston 22, and hence to the valve needle 10, which serves to urge the valve needle 10 into engagement with the valve needle seating. The spacer 40 therefore provides a means for varying the pre-load of the spring 34 to alter the injection characteristics, as in a known manner. The first and second housings 28, 30 are provided with first and second drillings respectively to define parts of the high pressure flow passage 18 through which fuel is delivered to the injector delivery chamber 16.

The bore 26 in the second housing 30 has a blind end that defines, together with a surface of the upper region 22b of the balance piston 22, a pressure control chamber 42 for receiving fuel at high pressure. The pressure of fuel within the control chamber 42 is controlled by means of a nozzle control valve, referred to generally as 44, having a valve housing 46 that abuts the second housing 30. The nozzle control valve 44 includes a nozzle control valve member 48 of substantially cylindrical and elongate form that is slideable within a valve housing bore 50 provided in the valve housing 46 under the control of an electromagnetic actuator 52. The valve housing bore 50, and hence the nozzle control valve member 48, is substantially co-axially aligned with the major axis of the injector. The valve housing bore 50 is of slightly enlarged diameter along a substantial part of its length so that a diametrical clearance between the valve housing bore 50 and the nozzle control valve member 48 defines a generally annular flow path 51 for fuel around the outer cylindrical surface of the nozzle control valve member 48. An electrical connector 53 (as shown in Figure 3) for the actuator 52 is mounted on the uppermost end of the valve housing 46 to permit appropriate control signals to be supplied to the actuator 52, in use.

The electromagnetic actuator 52 includes a winding 43 (visible only in the section shown in Figure 3) that is energiseable to cause movement of an armature 57 coupled or attached to the nozzle control valve member 48. In response to energisation and de-energisation of the winding 43, the nozzle control valve member 48 is movable between first and second positions. When in its first position, the nozzle control valve member 48 is seated against a first valve seating 54 defined by an upper end face of the second housing 30. This is the position shown in Figure 3. It cannot be seen from the scale shown in Figure 3, but when the nozzle control valve member 48 is in the first position it is spaced away from the second seating 56. When in its second position the nozzle control valve member 48 is spaced from the first valve seating 54. This is the position shown in Figures 1 and 2. When in the second position, an enlarged diameter region of the nozzle control valve member 48 is engaged with a second valve seating 56 defined by an internal surface of the valve housing bore 50.

The second housing 30 is provided, at its upper end face, with a recess or drilling 58 which communicates with a passage 59 to a low pressure fuel drain or reservoir (not shown). An additional drilling 60 is also provided in the upper end face of the second housing 30 which, in co-operation with a further drilling 62 provided m the valve housing 46, defines a passage tor fuel flow between the valve housing bore 50 and the control chamber 42 when the nozzle control valve member 48 is spaced away from the second seating 56. Thus, by moving the nozzle control valve member 48 between its first and second positions the control chamber 42 is either in communication with the valve housing bore 50 (in which case communication to drain is broken), or the control chamber 42 is in communication with the low pressure drain (in which case communication with the valve housing bore 50 is broken).

The valve housing 46 is provided with a fuel inlet 66 terminating in an inlet drilling 64 that extends substantially laterally to the axis of the injector. One end of the fuel inlet 66 (at the innermost end of the drilling 64) is in communication with the annular flow path 51 towards an upper end thereof, and the other end of the fuel inlet 66 defines an opening at the outer surface of the valve housing 46. The end of the inlet drilling 64 at the annular flow path 51 therefore defines a region or point of communication between the fuel inlet 66 and the valve housing bore 50, from where fuel is delivered to the injector delivery chamber 16.

The injector nozzle body 12, the first and second housing parts 28, 30 and a lower end of the valve housing 46 are all received within an outer housing member, typically in the form of a cap nut 68. As can be seen most clearly in Figure 3, the complete injector unit, including the cap nut 68, is then received within a pocket or opening 70 provided in an engine cylinder head 72 that is associated with the engine cylinder to which the injector delivers fuel. An 0-ring or other seal member 74 is provided to seal the injector unit within the injector pocket 70. It is a particular feature of the present invention that a significant portion of the valve housing 46 for the nozzle control valve 44, including its actuator 52, is received ^"within the injector pocket 70, leaving only a relatively small portion of the valve housing 46 extending from the upper open end of the pocket 70.

A fuel supply passage 76 is defined within the engine cylinder head 72 and includes an open, delivery end 76a that communicates with the fuel inlet 66 at the surface of the valve housing 46. The end of the fuel supply passage 76 remote from the open delivery end communicates with the common rail. Thus, a supply of high pressure fuel is delivered from the common rail, to the fuel supply passage 76, through the fuel inlet 66 and the drilling 64 and thus to the annular flow path 51 defined by the valve housing bore 50. The annular flow path 51 defines a passage for fuel flow between the fuel inlet 66 and a still further drilling 78 in the valve housing 46, which drilling 78 forms part of d e high pressure supply passage 18. It will therefore be appreciated that the valve housing bore 50 itself forms part of the fuel delivery means for permitting a flow of high pressure fuel from the fuel inlet 66 of the injector delivery chamber 16 and, hence, to the outlet openings for injection to the engine cylinder.

By virtue of the location of the nozzle control valve 44, including its actuator 52, within the injector pocket 70 in the cylinder head 72, and as the valve housing bore 50 defines a part of the high pressure supply passage to the injector delivery chamber 16, it is convenient to provide the engine cylinder head with the fuel supply passage 76 (as shown in Figure 2) as the fuel inlet 66 of the injector aligns conveniently with the valve housing bore 50, along a direction lateral to the injector axis. It is of considerable benefit to locate the actuator for the nozzle control valve 44 within the injector pocket, as the overall "height" of the arrangement is reduced, there being a requirement to mount only the electrical connector 53 externally to the pocket 70. As can be seen most clearly in Figure 3, the point or region of fluid communication between the fuel inlet 66 of the injector (i.e. at one of the inlet drilling 64) and the annular flow path 51 is located approximately in alignment, in a lateral direction to the injector axis, with the open delivery end 76a of the inlet passage 76 in the cylinder head 72. One benefit of utilising the valve housing bore 50 to define a part of the high pressure supply passage is that the whole injector assembly can be made relatively compact. In particular, the balance piston 22 is of much reduced axial length compared to the same feature in known injectors of this type. As can be seen in Figures 1 and 2, the balance piston 22 is approximately the same axial length as the nozzle control valve member 48, whereas in known injectors typically the nozzle control valve member 48 may be several times shorter than the balance piston 22. By utilising a balance piston 22 of reduced axial length, the overall responsiveness of the coupled balance piston valve needle arrangement 22, 10 can be improved, and this has considerable advantages when injecting small fuel delivery quantities, such as in pilot or post injections of fuel. To aid the reader's understanding of how this benefit is achieved, the method of operation of the injector illustrated in Figures 1 and 2 will now be described in greater detail.

In use, high pressure fuel from a common rail (not shown) or other fuel accumulator or store is supplied to the supply passage 76 in the cylinder head 72 and, hence, is delivered to the fuel inlet 66, 64 of the injector. Fuel at high pressure is delivered through the fuel inlet 66, 64, into the valve housing bore 50 and flows through the annular flow path 51 around the cylindrical outer surface of the nozzle control valve member 48 itself. From the annular flow path 51 fuel is able to flow into the high pressure supply passage 18 to the delivery chamber 16. If the valve needle 10 is seated against the valve needle seating, high pressure fuel that is supplied to the dehvery chamber 16 is unable to flow through the injector outlets and so fuel injection does not take place.

If, with a supply of high pressure fuel flowing through the annular flow path 51, the nozzle control valve member 48 is seated against its first seating 54 (i.e. spaced away from its second seating 56), high pressure fuel that flows through the annular flow path 51 will also be able to flow through the drillings 62, 60 and, hence, into the control chamber 42. With the nozzle control valve member 48 in this position, a relatively high force therefore acts on the end of the balance piston 22 due to high fuel pressure within the control chamber 42. This hydraulic force acts in combination with the force due to the spring 34 and serves to urge the valve needle 10 against its seating.

If the nozzle control valve 44 is energised or actuated such that the nozzle control valve member 48 is lifted away from its first seating 54 into engagement with it second seating 56, communication between the annular flow path 51 (and hence the flow of high pressure fuel) and the drillings 62, 60 to the control chamber 42 is broken. In addition, due to the nozzle control valve member 48 being lifted from the first seating 54, the drillings 62, 60, and hence the control chamber 42, are brought into communication with the low pressure drain passage 59 by virtue of the drilling 58 at the upper end of the second housing 30. As a result, fuel pressure within the control chamber 42 is reduced and the force acting on the balance piston 22, and hence on the valve needle 10, will be reduced sufficiently to permit the valve needle 10 to lift from its seating to commence injection. Flow of fuel to the injector delivery chamber 16 is not, however, disturbed or otherwise affected by movement of the nozzle control valve member 48 away from the first seating 54 (i.e. the valve function) as the flow is at all times able to flow through the annular flow path 51, between the valve member 48 and the valve housing bore 50.

In order to re-seat the valve needle 10 so as to terminate injection, the nozzle control valve 44 is de-energised or de-actuated so as to move the nozzle control valve member 48 back into engagement with the first seating 54, thereby breaking communication between the control chamber 42 and the low pressure drain passage 59 and again allowing high pressure fuel to flow into the control chamber 42. High fuel pressure is therefore re-established within the control chamber 42 and the high force acting on the balance piston 22 acts in combination with the spring 34 to seat the valve needle 10, thus terminating injection.

It will be appreciated therefore that initiation and termination of injection is controlled by moving the nozzle control valve member 48 between its first and second seatings 54, 56 to control fuel pressure within the control chamber 42.

However, operation of the nozzle control valve member 48 does not at any stage affect the supply of high pressure fuel between the fuel inlet 66 and the delivery chamber 16. The flow of high pressure fuel through the annular flow path 51 to the high pressure supply passage 18 is a unidirectional flow between the inlet 66 and the delivery chamber 16, and this flow is not affected, or 'controlled', by operation of the nozzle control valve 44.

The speed at which the balance piston 22 and the valve needle 10 can react to varying fuel pressure within the control chamber 42 is determined, in part, by their size (i.e. mass), and so the reduced length of the balance piston 22 compared to that in known arrangements provides a response benefit. When it is required to inject only a small quantity of fuel, such as a pilot injection of fuel preceding a mam injection or a post injection of fuel following a mam injection, it is important to be able to "open" and "close" the valve needle quickly. The present invention enables this to be achieved effectively.

It will be appreciated that although in the embodiment described previously the fuel dehvery means for enabling high pressure fuel to be delivered from the injector fuel inlet 66, 64 to the dehvery chamber 16 is defined by the bore 50 within the valve housing 46, in practice advantages are also realised if the fuel delivery means is defined, in part, by a separate drilling provided in the valve housing 46 approximately adjacent to the nozzle control valve member 48. In this arrangement, the point or region of fluid communication between the injector fuel inlet 66 and an inlet portion of the fuel delivery means (e.g. a separate drilling provided in the valve housing 46) may also be defined at a position that is approximately aligned, in a lateral direction to the injector axis, with the open end 76a of the supply passage 76. This configuration would also enable the majority of the injector assembly to be received within the injector pocket 70 in the cylinder head 72, and again a balance piston 22 of relatively short length (and hence a nozzle control valve of relatively long length) may be utilised. A possible disadvantage of this arrangement compared to that shown in Figures 1 to 3 is that there is a requirement for an additional drilling to define that part of the fuel delivery means within the valve housing 46.

An alternative embodiment of the present invention to that shown in Figures 1 to 3 is shown in Figure 4. Where the injector of Figure 4 includes similar parts to those in Figures 1 to 3 these have been identified with like reference numerals and will not be described in further detail. A difference between the embodiment of Figures 1 to 3 and that of Figure 4 is that the intermediate member component is not present. In other words, the valve needle and the intermediate member elements are effectively combined to form a single, integral part, identified as item 80. This provides a manufacturing advantage over the previous embodiment as there is only a requirement to provide a single component.

The valve needle 80 is provided with a spring 34 arranged within a spring chamber 38 which is defined within the nozzle body 12. The upper end of the valve needle 80 extends through an open upper end of the bore 14 in the nozzle body 12 and is received within a further bore 82 provided in a control chamber housing part 84 mounted adjacent to the nozzle body 12. The pressure control chamber 42 for the valve needle 80 is defined within this housing part 84 and is supplied with high pressure fuel through drillings 60, 62 (equivalent to drillings 60, 62 shown in Figures 1 and 2) when the nozzle control valve member 48 is moved to a position in which the control chamber 42 is brought into communication with the supply passage 18. It will be appreciated that a further difference between the injector in Figure 4 and that in Figure 3 is that the injector delivery chamber in the Figure 4 embodiment is the chamber 38 for the valve needle spring 34, so that the high pressure supply passage 18 communicates with the nozzle outlets via the spring chamber 38. As described previously, the fuel delivery means for delivering high pressure fuel from the fuel inlet 66 to the injector delivery chamber (chamber 38) includes the annular flow path 51 around the nozzle control valve member 48.

It is a further feature of the injector of Figure 4 that the nozzle control valve member 48, being of relatively long length, includes an upper valve member region 48a and a lower valve member region 48b, with movement of the upper region 48a being guided within a first bore region 50a of the bore 50 and movement of the lower region 48b being guided within a second bore region 50b of the bore 50. The first bore region 50a is provided in a first, upper valve housing 86 and the second bore region 50b is provided in a second, lower valve housing 88 mounted between the upper valve housing 86 and the control chamber housing part 84. The flow of fuel through the annular flow path 51 and around the nozzle control valve member 48 therefore traverses a join between the valve housings 86, 88.

The embodiment of Figure 4 provides similar advantages to those described previously, with the response of the valve needle being improved by its relatively short axial length, and hence mass, and its improved axial stiffness. In this case it can be seen that the valve needle 80 is generally of similar axial length to the nozzle control valve member 48.

In a further alternative embodiment, the injector may form part of a unit pump, in which a dedicated pump chamber supplies fuel directly to the injector, and usually to no other injector of the system, through the fuel supply passage 76. As before, the injector may be provided with the fuel delivery means for permitting a flow of fuel adjacent to the nozzle control valve of the injector, in a generally annular flow path 51 around with nozzle control valve member 48.

The invention is also applicable to other injector designs, in which no electromagnetic or other actuator is provided for controlling the control chamber pressure at the back of the needle. In injectors of this type, injection is initiated and terminated hydraulically and, thus, there is no need to provide a nozzle control valve. Injection is initiated as a result of the pressure of fuel delivered to the injector delivery chamber exceeding a predetermined level that is sufficient to overcome the closing force of the spring (e.g. equivalent to spring 34), and any residual high pressure fuel at the back of the valve needle.

In a well known unit pump of this type a spill valve is arranged to control communication between an associated injector pump chamber (in communication with a passage equivalent to supply passage 18) and a low pressure drain. When it is required to initiate injection the spill valve is closed to cause fuel pressure within the pump chamber to be increased during a pumping stroke of a plunger of the pump. When fuel pressure reaches a predetermined level sufficient to cause the valve needle to lift from its seating, injection is commenced. To terminate injection the spill valve is opened to relieve fuel pressure in the pump chamber, thereby causing the pressure of fuel that is delivered to the injector delivery chamber to be reduced and thus allowing the valve needle to seat under the closing spring force. In an alternative embodiment of the present invention, therefore, the flow delivery means for dehvering high pressure fuel between an inlet to the injector and the injector delivery chamber may be defined, at least in part, by an annular flow path around the spill valve in a unit pump generally of the aforementioned type.

Claims

1. A fuel injector having:

an injector control valve (44) including a control valve member (48) which is movable within a bore (50; 50a, 50b) provided in a control valve housing (46; 86, 88),

a valve needle (10; 80) movable relative to a valve needle seating to control fuel injection through one or more injector outlets,

a fuel inlet (66) for receiving a supply of fuel at high pressure, and

an annular flow path (51) for delivering a flow of fuel from the fuel inlet (66) to an injector delivery chamber (16; 38), from where fuel is delivered to the or each outlet,

characterised in that the annular flow path (51) is defined between the bore (50; 50a, 50b) in the control valve housing (46; 86, 88) and an outer surface of the injector control valve, but wherein said flow of fuel is not controlled by means of the injector control valve (44).

2. A fuel injector as claimed in Claim 1, wherein the valve needle (10) is co- operable with an intermediate member (22), an associated surface of said intermediate member (22) being exposed to fuel pressure within a pressure control chamber (42).

3. A fuel injector as claimed in Claim 2, wherein the intermediate member (22) is a l^'anc TpisTon whicTTis engaged or^" otherwise coupled to the valve needle (10) such that movement of the balance piston, as a result of controlling fuel pressure within the pressure control chamber (42), results in accompanying movement of the valve needle (10).

4. A fuel injector as claimed in Claim 2 or Claim 3, wherein the intermediate member (22) has a relatively short axial length.

5. A fuel injector as claimed in Claim 4, wherein the axial length of the intermediate member (22) is approximately equal to, or at least is no greater than, the axial length of the control valve member (48).

6. A fuel injector as claimed in Claim 1, wherein a surface of the valve needle (80) is exposed to fuel pressure within a pressure control chamber (42).

7. A fuel injector as claimed in Claim 6, wherein respective upper (48a) and lower (48b) ends of the control valve member (48) are guided for movement within first and second bores (50a, 50b) provided in respective adjacently mounted housings (86, 88) such that the first and second bores (50a, 50b) define the annular flow path (51 ) .

8. A fuel injector as claimed in any one of Claims 1 to 7, wherein the injector control valve is a spill valve for controlling fuel flow to a low pressure drain.

9. A fuel injector as claimed in any one of Claims 1 to 7, wherein the injector control valve is a nozzle control valve (44), including a nozzle control valve member (48) for controlling fuel pressure within the pressure control chamber (42).

TθL Tfuel injector as claimedln Claim 9, wherem the nozzle control valve member (48) is substantially co-axially aligned with the axis of the injector.

11. A fuel injector as claimed in any one of Claims 1 to 10, wherein the fuel inlet (66) is arranged, in use, to receive fuel through a fuel supply passage (76) that extends approximately laterally from the axis of the injector.

12. A fuel injector as claimed in Claim 11, wherein a point or region of fluid communication between the fuel inlet (66) and the annular flow path (51) is approximately in alignment, in a lateral direction to the injector axis, with an open delivery end (76a) of the fuel supply passage (76).

13. A fuel injector as claimed in Claim 12, wherein the fuel inlet (66) includes a drilling (64) in the control valve housing (46; 86), and wherein the open delivery end (76a) of the fuel supply passage (76) is arranged to communicate with the annular flow path (51) by means of said drilling (64).

14. A fuel injector as claimed in any one of Claims 1 to 13, including an actuator (52) for controlling movement of an armature coupled to the control valve member (48), and wherein the actuator (52) is located within an injector housing (46; 86) that is to be received substantially within an injector pocket (70) of the associated engine cylinder head, in use.

15. A fuel injector mounting including a fuel injector as claimed in any one of Claims 1 to 14, and including an engine cylinder head (72) provided with an injector pocket (70) for receiving the injector, wherein the engine cylinder head (72) is further provided with a fuel supply passage (76) having an open delivery end (76a) and extending in an approximately lateral direction to the axis of the in^ctor vheh the^' tnj cto is^" supply passage (76) is arranged to communicate with the annular flow path (51) of the injector at a fluid communication region that is approximately aligned, in a direction lateral to the injector axis, with the open dehvery end (76a) of the fuel supply passage (76).

16. A fuel injector as claimed in Claim 15, wherein the injector is received within the pocket (70) such that the control valve housing (46; 86) is located substantially entirely within the pocket (70).

17. A fuel injector as claimed in Claim 15 or Claim 16, wherein a fluid communication region between the fuel supply passage (76) and the annular flow path (51) is defined at one end of a drilling (64), said one end of the drilling (64) being arranged to communicate with the annular flow path (51) and the other end of the drilling (64) opening into the open delivery end (76a) of the fuel supply passage (76).

18. A fuel injector mounting as claimed in any one of Claims 15 to 17, wherein an actuator (52) for the injector control valve (44) is located within the pocket (70).

19. A fuel injector having a fuel inlet (66) and a flow delivery means (18, 51) for delivering high pressure fuel from the fuel inlet (66) to an injector delivery chamber (16), a valve needle (10) co-operable with an intermediate member (22) that is exposed to fuel pressure within a pressure control chamber (42), and a nozzle control valve (44) having an elongate nozzle control valve member (48) for controlling fuel pressure within the control chamber (42), thereby to control movement of the intermediate member (22) and the valve needle (10), wherein the intermediate member (22) has a relatively short length compared to the valve needle (10) and the nozzle control valve member (48) has a relatively long length compared to the valve needle, thereby to improve the response of the valve needle (10).

20. A fuel injector as claimed in Claim 19, wherein the intermediate member (22) has approximately the same length as the nozzle control valve member (48).