GB2389390A

GB2389390A - Fuel injection nozzle with inclined grooves formed in the valve needle

Info

Publication number: GB2389390A
Application number: GB0213005A
Authority: GB
Inventors: Godfrey Greeves; Simon Tullis
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2002-06-06
Filing date: 2002-06-06
Publication date: 2003-12-10
Also published as: GB0213005D0

Abstract

An fuel injection nozzle for an internal combustion engine comprises a nozzle body (10) with a blind bore (14) within which a valve needle (16) is movable along a valve needle axis (17). The valve needle (16) is engageable with a seating surface (14a) to control fuel flow between a delivery chamber (20) and an injection nozzle outlet (12). A first fuel flow path (27) is defined between the outer surface of needle (16) and bore (14) when needle (16) is lifted from its seating. Additionally, at least one of the needle (16) and bore (14) has a surface provided with a groove (24; 124) having a groove axis (26; 126) inclined to the valve needle axis (17) which defines, together with a surface of the other of needle (16) and bore (14), an additional flow path for fuel between delivery chamber (20) and outlet (12). The groove (24; 124) is shaped such that the cross sectional flow area of the additional flow path relative to the cross sectional area of the first flow path (27) varies as the needle (16) moves from the seated to fully lifted position, thereby to permit a fuel spray of variable spray angle to be injected into the combustion space as needle(16) moves through its range of travel. Also disclosed is an injection nozzle where upstream of a valve needle seating there is a first region of the valve needle with an angle of beta between the first region of the valve needle and an adjacent region of the nozzle bore.

Description

. INJECTION NOZZLE

The invention relates to an injection nozzle of a fuel injector for supplying fuel to a compression ignition internal combustion engine. In particular, the invention relates to an injection nozzle for injecting a fuel spray of variable spray angle into an engine cylinder or other combustion space.

Injection nozzles for direct injection diesel engines are known which have nozzle tips such as that shown in Figure 1 in which a nozzle body 10 of the tip is provided with one or more outlets or spray holes 12. The nozzle body 10 is provided with a blind bore 14 within which a valve needle 16 is movable, the valve needle 16 having a seating line 18 which is engageable with a valve seating surface 14_ defined by the bore 14 to form a seal with the nozzle body 10 when the valve needle 16 adopts its innermost position within the bore 14.

The nozzle is a so-called VCO (Valve Covered Orifice) type nozzle, in which a surface of the valve needle is cooperable with an inlet end 13 of the outlet 12 to control fuel delivery through the outlet.

An outer surface of the valve needle 16 defines, together with the bore 14, a delivery chamber 20 to which high pressure fuel is delivered, in use. When the valve needle 16 is seated against the valve seating surface 14a, high pressure fuel supplied to the delivery chamber 20 is unable to flow past the valve seating surface 14a to the outlet 12. When the valve needle 16 is lifted through a distance, H. into the position shown in Figure 1, fuel is able to flow past the valve seating surface 14a to the outlet 12 and forms a fuel spray jet 22 in the combustion chamber of the engine.

- 2 The fuel spray jet 22 emerging from the outlet 12 defines an included angle a, which determines the initial interaction of the fuel spray jet with the air charge in the combustion chamber. For most conditions it is desirable to have a relatively small spray jet angle, a (as shown in Figure 1), at the beginning of injection as this ensures a penetrating fuel spray jet with good utilization of the air available in the cylinder and minimum formation and emission of soot, especially at high engine load conditions.

Under certain operating conditions, however, it is desirable to have a wider initial spray jet angle, or. For example, for conventional direct injection diesel engines it is desirable to have a small quantity of fuel injected with a wider spray jet angle at the beginning of fuel injection as this gives rise to a more rapid formation of a suitable fuel-air mixture for compression ignition. The effect is to shorten the ignition delay period and reduce the amount of pre-

mixed fuel which burns very rapidly immediately after compression ignition.

As a result, the maximum rate of cylinder pressure rise is reduced and, thus, the combustion noise emission from the engine is reduced. For the subsequent and main part of the fuel injection, however, it is desirable for the spray jet angle to be relatively narrow to provide good spray penetration, good air utilisation and low soot emission.

For so-called Homogeneous Charge Compression Ignition (HCCI) engine combustion operation it is also desirable to produce a wider initial fuel spray jet angle, a, when injecting fuel early in the compression stroke of the engine under part load conditions. This is required in order to prevent over penetration of the fuel spray jets and liquid fuel impingement on the cylinder walls. At high loads it is desirable to revert to normal diesel combustion operation with relatively narrow initial spray jet angles.

- 3 It is an object of the present invention to provide an injection nozzle which enables a variable fuel spray angle to be achieved.

According to a first aspect of the present invention, an injection nozzle for supplying a fuel spray, having a spray angle, to a combustion space of an internal combustion engine, comprises: a nozzle body provided with a blind bore within which a valve needle is movable along a valve needle axis, the valve needle being engageable with a seating surface to control fuel flow between a delivery chamber and an injection nozzle outlet, wherein a surface of the bore and the outer surface of the valve needle define a first flow path through which fuel flows from the delivery chamber to the outlet when the valve needle is lifted from the seating surface, and an additional flow path for said flow defined by a groove provided in one of the outer surface of the valve needle and the bore' and a surface of the other of the valve needle and the bore, wherein the groove has a groove axis inclined to the valve needle axis and is shaped such that the cross sectional flow area of the additional flow path relative to the cross sectional area of the first flow path varies as the valve needle moves through a range of travel from the seated position to a fully lifted position, thereby to permit a fuel spray having a variable spray angle to be injected into the combustion space as the valve needle moves through the range of travel.

In one embodiment, the groove is shaped such that the additional flow path has a converging cross sectional area from a larger cross sectional area upstream end to a relatively smaller cross sectional area downstream end.

The groove may preferably be shaped such that the additional flow path has a substantially uniform taper between the upstream and downstream ends thereof. When the valve needle is moved through the range of travel by a relatively small amount (i.e. relatively small needle lift) the cross sectional area of the additional flow path is relatively large compared with the cross sectional area of the first flow path (i.e. the cross sectional area of the path between the ungrooved remainder of the valve surface and the bore). For low values of needle lift, the additional flow path therefore presents a significant flow area to fuel flowing to the outlet compared with the first flow path, and flow through the additional flow path is accelerated to impart a rotational component of velocity to the flow and therefore to give rise to a fuel spray through the outlet having a relatively wide spray angle. When the valve needle is moved further through the range of travel by a larger amount (i. e. relatively large needle lift) the cross sectional area of the additional flow path, relative to that of the first flow path, is less significant and the rotational velocity component imparted to the flow is less than for small values of lift. For higher values of needle lift, a narrower fuel spray is therefore injected through the outlet.

When the cross sectional area of the flow path is large compared to the cross sectional area of the outlet (i.e. for relatively large amounts of needle lift), fuel flow through Me flow path will have a relatively low velocity compared to that through the outlet. As a result, the flow entering the outlet is relatively

-5 undisturbed and the rotational component of fuel flow velocity about the axis of the outlet is minimised. This results in a relatively narrow fuel spray emerging from the outlet. Conversely, if the cross sectional area of the flow path between the delivery chamber and the outlet is small compared to the cross sectional area of the outlet (i.e. for relatively small amounts of needle lift), fuel flow through the flow path will have a relatively high velocity compared to that through the outlet. As a result, the flow entering the outlet has a high rotational component of fuel flow velocity about the axis of the outlet, resulting in a fuel spray from the outlet having a relatively large spray angle.

The spray angle therefore varies throughout the range of Gavel of the valve needle, from an initial, wider spray angle for small needle lift to a narrower spray angle for larger needle lift.

In an alternative embodiment, the groove is shaped such that the first flow path has a diverging cross sectional area from a smaller cross sectional area upstream end to a relatively larger cross sectional area upstream end.

The valve needle is shaped to define a valve needle seating which is engageable with a seating surface defined by the bore to control fuel delivery through the outlet, the valve needle including a first region upstream of the valve needle seating and a second region downstream of the valve needle seating. The injection nozzle may be of the so-called ''VCO'' type (Valve Covered Orifice), in which a surface of the valve needle is cooperable with an inlet end of the outlet to control fuel delivery through the outlet.

Alternatively, the nozzle may be a sac-type nozzle in which the valve needle is engageable with the seating surface to control fuel flow from the delivery chamber to a sac volume defined by a blind end of the bore, and wherein an inlet end of the outlet communicates with the sac volume.

The groove may be provided on an outer surface of the valve needle.

In one embodiment, the groove may be provided in the first region of the valve needle upstream of the valve needle seating. Alternatively, the groove may be provided in the second region of the valve needle downstream of the valve needle seating.

As a further alternative, the groove may be provided in an internal surface of He bore in the nozzle body.

For example, the bore includes a first bore region upstream of the valve needle seating when the valve needle is in a seated position and a second bore region downstream of the valve needle seating when the valve needle is in a seated position, and wherein the groove is provided in the first bore region.

Alternatively, the groove may be provided in the second bore region.

In a further preferred embodiment, the valve needle is provided with a circumferential groove having an upstream edge defining an upper valve seating line and a downstream edge defining a lower valve seating line.

If the groove is provided in the bore, the groove may be located such that it intersects the lower valve needle seating line when the valve needle is seated.

Alternatively if the groove is provided in the needle, the groove may be located to intersect the lower valve needle seating line.

Preferably, the groove axis and the axis of the valve needle define an angle, 0, of between 10 and 70 degrees.

Preferably, the first region of the valve needle and the adjacent region of the bore together define a first differential angle, it, therebetween of less than 3 degrees, thereby to provide a hydraulically selfcentralising force to an end of the valve needle adjacent to the outlet.

If two or more outlets are provided in the nozzle body, the provision of a very small first differential angle, it, of preferably between 0.5 and 3 degrees, provides the advantage that the fuel flow distribution through each outlet is substantially uniform due to the hydraulically selfcentralising force which acts on the valve needle.

In one embodiment, at least one of the valve needle and the bore is provided with more than one inclined groove, each of which defines, together with a surface of the other of the valve needle and the bore, an additional flow path for fuel between the delivery chamber and the outlet, wherein each inclined groove is shaped such that the cross sectional flow area of the respective additional flow path relative to the cross sectional area of the first flow path varies as the valve needle moves through the range of travel.

- 8 According to a second aspect of the invention, an injection nozzle for supplying a fuel spray jet to a combustion space of an internal combustion engine comprises; a nozzle body provided win a blind bore within which a valve needle is movable along a valve needle axis, a delivery chamber, defined by the bore and an outer surface of the valve needle for delivering high pressure fuel to an injection nozzle outlet, wherein the valve needle is shaped to define a valve needle seating which is engageable with a seating surface defined by the bore to control fuel delivery through the outlet, the valve needle including a first region upstream of the valve needle seating and a second region downstream of the valve needle seating, and wherein the first region of the valve needle and an adjacent region of the bore together define a first differential angle, it, therebetween of less than 3 degrees, thereby to provide a hydraulically self-centralising force to an end of the valve needle adjacent to the outlet.

Preferably, the first differential angle is between 0.5 and 3 degrees.

It will be appreciated that the second aspect of the invention may also include one or more of the preferred or alternative features of the first aspect of the invention. The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

- 9 - Figure 1 is a sectional view of conventional VCO-type injection nozzle, Figure 2(a) is a sectional view of a first embodiment of an injection nozzle of the present invention of the VCO-type, Figure 2(b) is a sectional view, along line A-A in Figure 1, of a part of the valve needle of the injection nozzle in Figure 1 to show a groove in the surface of the valve needle, Figure 3 is a sectional view of alternative VCO-type injection nozzle of the present invention, Figure 4 is a sectional view of a further alternative embodiment of the invention, wherein the nozzle is a sac-type nozzle, Figures 5 and 6 are sectional views of further alternative embodiments of VCO-type nozzles, Figure 7 is a sectional view of an alternative sac-type nozzle, and Figure 8 is a sectional view of a further alternative VCO-type nozzle.

The injection nozzle in Figure 2(a) is of the VCO-type and includes a nozzle body 10 provided with an outlet 12 having an outlet axis 22 and through which fuel is injected, in use, into a cylinder (not shown) of an associated engine. As described previously with reference to Figure 1, the nozzle body 10 is provided with a blind bore 14 within which a valve needle 16 is movable along a valve needle axis 17. The valve needle includes a first region 16_ upstream of a

- 10 seating, a so-called "valve needle seating line" 18, and a second region 16b downstream of the valve needle seating linelS. The bore 14 is shaped to define an annular seating surface 143 against which the seating line 18 of the valve needle is seated when it is required to prevent fuel delivery through the outlet 12 to the engine. The second region 16b of the valve needle 16 terminates in a tip portion 16c which extends into a sac volume 19 defined by the blind end of the bore 14.

An outer surface of the valve needle 16 and a region of the bore 14 upstream of the seating surface 14a together define a delivery chamber 20 to which high pressure fuel is delivered, in use, through a high pressure supply passage (not shown) provided partly within the nozzle body 10. An outer surface of the second region 16b of the valve needle 16 is cooperable with an inlet end 13 of the outlet 12 to control fuel delivery through the outlet 12, in use. When the valve needle 16 is in a closed position, in which the seating linelB of the valve needle 16 is in engagement with the seating surface 14a of the bore 14, the outer surface of the second region 16_ covers the inlet end 13 of the outlet 12 to prevent fuel injection into the engine. When the valve needle 16 is moved outwardly from the bore 14 away from the seating surface 14a, the outer surface of the second region 1 6b uncovers the inlet end 13 of the outlet 12 to permit fuel flow past the seating surface 14a. A fuel spray 21 is therefore injected through the outlet 12 and into the engine cylinder.

Movement of the valve needle 16 within the bore 14 may be controlled by an actuator arrangement (not shown), for example an electro-magnetic actuator including an energisable winding. Alternatively, the actuator may be a piezoelectric actuator including a stack of one or more piezoelectric elements, for example as described in EP0995901A1. In a further alternative

- 11 embodiment, valve needle movement may be effected simply in response to hydraulic pressure within the delivery chamber 20 acting on thrust surfaces of the valve needle, in which case no additional actuation means is provided.

The nozzle in Figure 2(a) differs from that shown in Figure 1 in that the outer surface of the valve needle 16 is provided with an inclined groove or recess 24 having a groove axis 26. The groove 24 is shaped such that the groove axis 26 is inclined to the valve needle axis 17 at an angle, 0, which typically has a range of values between 10 and 70 degrees. For the purpose of the specification, the angle, 0, shall be referred to as the "groove inclination

angle". The groove 24 is provided on a surface of the first region 1 6a of the valve needle 16 such that it is located upstream of the valve needle seating line 18, and is shaped so as to guide fuel flow towards the outlet 12 and to impart a rotational component of velocity to the flow.

When the valve needle 16 is spaced away from the seating surface 14a, the groove 24 and the surface of the bore 14 together define a flow path for fuel between the delivery chamber 20 and the outlet 12, in which position fuel delivered to the delivery chamber 20 is able to flow past the seating surface 14_ and through the outlet 12, both through the flow path defined by the groove 24 and through an annular flow path defined between the outer surface of the valve needle 16 and the unrecessed surface of the bore 14. The groove 24 therefore defines an additional flow area for fuel, further to the annular flow area which exists in an ungrooved needle. When the valve needle 16 is seated against the seating surface 14a, such flow of fuel from the delivery chamber 20 past the seating surface 14_ through the flow path or past the remainder of the valve surface is prevented.

- 12 The groove 24 is shaped such that the additional flow path is of converging cross-sectional flow area from a greater cross sectional area upstream end to a relatively smaller cross sectional area downstream end. The groove 24 has a width, W. at the surface of the valve needle 16 along an axis substantially perpendicular to the groove inclination axis 26. As can be seen most clearly in Figure 2(b), a base surface 28 of the groove 24 has a depth, D, relative to the outer surface of the valve needle. The base surface of the groove 24 is shown by a dashed line 28a in Figure 2(a) to illustrate a view of the groove 24 rotated about the valve needle axis 17 by substantially 90 . A "groove angle", 6, is also shown in Figure 2(a) and is a measure of the extent of inclination of the conical groove in the surface of the valve needle along the groove axis 26.

The valve needle 16 is shaped such that the first region 16a defines, together with a surface of the bore 14 downstream of the delivery chamber 20, a first differential angle, y and He second region 16b defines, together with a further downstream surface of the bore 14, a second differential angle, e. In the embodiment shown in Figure 2(a), the profile calf the second region lob of the valve needle 16 below the seating line 18 is shaped such that the second differential angle, c, is substantially constant between the valve needle seating line 18 and the tip portion 1 6c of the needle 16. This produces a VCO-type effect for zero needle lift, H. so as to minimise HC emissions arising from residual fuel remaining in the sac volume 19 after an injection.

In use, when the valve needle is lifted from the seating surface 14a, fuel is able to flow from the delivery chamber 20 through a first flow path 27 defined between the outer surface of the valve needle 1 (i and the inner surface and the bore 14 (i.e. He flow path defined by the ungrooved portion of the valve needle surface). The groove 24 defines an additional flow path for fuel flow between

- 13 the delivery chamber 20 and the outlet 12 and, for small values of lift (i.e. needle lift, H. is relatively low), this additional flow path has a relatively large cross sectional flow area compared with that of the first flow path 27. The groove 24 therefore provides a significant flow area for fuel, compared with that through the flow path 27, and causes a rotational component of velocity to be imparted to the flow through the groove 24. As the valve needle moves further from the seating towards higher values of lift, the flow area through the additional flow path becomes less significant compared to the flow area through the first flow path, and the rotational component of velocity is much reduced. It is this effect that gives rise to the variable spray angle during injection. If the valve needle 16 is only lifted away from the seating surface 14a by a relatively small amount, the cross-sectional flow area for fuel flow through the additional flow path is small compared with the cross-sectional flow area for fuel flowing through the outlet 12. Flow through the additional flow path therefore has a relatively high velocity and there is an increased rotational component of fuel flow velocity about the valve needle axis 17. This gives rise to a greater rotational component of velocity at an upstream end of the inlet 13 compared with that at the downstream end of the inlet 13 such that the rotational flow velocity component about the axis 22 of the outlet 12 is relatively high. The fuel spray 21 emerging from the outlet 22 therefore has a relatively large spray angle, Al.

As the valve needle 16 moves a further distance through its range of travel, the cross-sectional area of the additional flow path is less significant to the total flow area, which is large compared with the flow area through the outlet 12.

The fuel flow velocity through the additional flow path is therefore relatively

- 14 low such that an undisturbed flow enters the inlet end 13 of the outlet 12, thereby minimising the rotational component of fuel flow velocity about the outlet axis 22. As a result, the fuel spray 21 through the outlet 12 has a relatively narrow spray angle, oc2. The fuel spray characteristic therefore varies with the extent of movement of the valve needle 16 away from the seating surface 14a to give a relatively wide fuel spray angle during initial movement of the valve needle 16 followed by a narrower fuel spray angle for larger values of needle lift.

The fuel flow velocities through the flow path defined by the groove 24 can be increased further for relatively small amounts of needle lift by shaping the first region 16_ of the valve needle 16 and the adjacent region of the bore 14 so as to minimise the angle, y, typically to angles in the range of 0.5 and 3 degrees.

The provision of the groove 24 on the surface of the valve needle 16 in combination with a relatively small angle, it, provides a means of producing a significant rotational component of fuel flow velocity about the valve needle axis 17 in the flow path above the seating surface 14_ for relatively small values of needle lift, H. In turn this provides a significant rotational component of fuel flow velocity through the outlet 12 about the outlet axis 22.

The magnitude of the rotational component of fuel flow velocity about the outlet axis 22 compared with the axial component through the outlet 12, and hence the spray jet angle, a, can be selected by design. In particular, the magnitude of the rotational flow velocity will be governed by the groove inclination angle,,B, the groove angle, o, the depth, D, and width, W. of the groove 24 and the first differential angle, . In an alternative embodiment to that shown in Figure 2(a), the valve needle 16 may be provided with two or more inclined grooves 24. The number of grooves will also have an effect on

- 15 the rotational component of fuel flow velocity about the outlet axis 22 compared with the axial velocity component through the outlet 12 and, hence, the variation of fuel spray angle, a, with needle lift, H. Referring to Figure 3, in an alternative embodiment of the invention the valve needle 16 is provided with a circumferential groove 30 between the first and second regions 16_, 16_. The upstream edge of We groove 30 defines an upper valve needle seating line 1 8a and the lower edge of the groove 30 defines a lower valve seating line 1 8b which forms a boundary with a downstream seating surface defined by the second region 16b of the valve needle 16. In practice, the valve needle seats against the upper valve seating line 18_ when in the non-injecting state, and may also seat against the lower seating line 1 8b.

During the service life of the injector, the seating line 1 8a becomes worn but the presence of the groove 30 ensures the effective seat diameter does not migrate to lower values (i.e. whereupon the effective seat diameter is defined lower down the needle in the orientation shown). The nozzle opening pressure at which needle lift occurs is therefore substantially unaffected by valve needle and/or seat wear. A so-called "grooved tip" nozzle such as that shown in Figure 3 is described further in US 5 890 660.

Figure 4 shows a further alternative embodiment in which the nozzle is a so-

called "sac type" nozzle. In the nozzle of Figure 4, the sac volume 19 at the blind end of the bore 14 communicates with the inlet end 13 of the outlet 12.

When the valve needle 16 is in a position in which the seating line 18 is seated against the seating surface 14b, fuel within the delivery chamber 20 is unable to flow past the seating surface 14a, neither through the flow path defined by the groove 24 nor past the remainder of the outer surface of the valve needle 16.

Fuel injection through the outlet 12 does not therefore take place. As described

- 16 previously with reference to Figure 2, when the valve needle 16 is lifted through a relatively small amount away from the seating surface 14t, the fuel: within the delivery chamber 20 is able to flow through the flow path, into the sac volume 19 and, hence, out through the outlet 12. For initial, low values of needle lift, H. the cross-sectional flow area through the flow path is relatively low such that fuel flow through the flow path has a high flow velocity compared to that through the outlet 12 and, hence, there is a relatively high rotational component of flow velocity about the axis 22 of the outlet 12. For i small amounts of needle lift, H. the fuel spray 21 therefore has a relatively wide spray angle, al. For higher values of needle lift, H. the cross-sectional flow I area through the flow path defined by the groove 24 and the surface of the bore 14 is increased, thereby giving rise to a lower fuel flow velocity through the flow path than that through the outlet 12. The rotational component of flow velocity about the outlet axis 22 is therefore minimised and a fuel spray of narrower spray angle, a2, is injected through the outlet 12.

Again, it is preferable to minimise the differential angle, A, to a value between about 0.5 and 3 degrees to further increase the fuel flow velocity through the flow path for low values of needle lift, H. thereby giving rise to a wider fuel spray angle, a2, at initiation of injection. Additionally, by selecting the differential angle to fall within this range, a hydraulic self-centralising force i acts on the end of the valve needle 16 adjacent to the outlet 12. If two or more outlets are provided, self-centralisation of the valve needle ensures there is a substantially uniform fuel distribution through each outlet 12.

The embodiments described in Figures 2 to 4 enable a variable fuel spray angle to be achieved by providing an inclined groove 24, or a plurality of grooves, on the surface of the valve needle 16. In a further alternative embodiment, the

- 17 variable spray angle characteristic is achieved by providing an inclined groove on the surface of the bore 14.

Figure 5 shows a VCO-type injection nozzle for which the nozzle body 10 has a nozzle body axis 117 which is substantially aligned with the valve needle axis 17 in Figures 2 to 4. An inclined groove 124 is provided on an internal surface of the bore 14 above the seating surfacel4b, wherein thegroove 124 has a groove axis 126 inclined at an angle,,B, to the nozzle body axis 117 (and i hence to the valve needle axis). The groove 124 is also shown as a dashed line for the nozzle body 10 rotated by substantially 90 about the nozzle body axis I 117. The valve needle of the nozzle in Figure 5 does not include a circumferential groove 30, but this may be provided, if desired.

The injection nozzle in Figure 6 is an alternative VCO-type nozzle in which the valve needle 16 is provided with a circumferential groove 30, as described previously with reference to Figure 3, but in which the groove 24 is provided in a surface of the valve needle 16 below the lower seating line 1 8b. Due to the method by which the groove 24 is machined, and the requirement to avoid impacting the seating line 1 8b during machining of the groove 24, it is most likely that the groove 24 will be shaped so as to define a flow path of diverging cross-sectional flow area (i.e. a flow path having a smaller cross sectional area i upstream end and a relatively larger cross sectional area downstream end). It is an important feature of the invention that the groove 24 is shaped to define a flow path through which the flow of fuel is accelerated relative to the flow between the remainder of the surface of the valve needle 16 and the bore, so as to impart a rotational component of velocity to the flow.

- 18 Hence, as described previously, for initial, low values of needle lift, H. the cross-sectional flow area through the flow path is relatively low such that fuel: flow through the flow path has a high flow velocity compared to that through the outlet 12 and, hence, there is a relatively high rotational component of flow velocity about the axis 22 of the outlet 12. For small amounts of needle lift, H. the fuel spray 21 therefore has a relatively wide spray angle, al. For higher values of needle lift, H. the cross-sectional flow area through the flow path defined by the groove 124 and the surface of the bore 14 is increased, thereby i giving rise to a lower fuel flow velocity through the flow path than that through the outlet 12. The rotational component of flow velocity about the outlet axis I 22 is therefore rninimised and a fuel spray of narrower spray angle, a2, is injected through the outlet 12 for higher values of needle lift.

In a further alternative embodiment shown in Figure 7, the nozzle is a sac-type nozzle in which the inclined groove 124 is positioned below the seating surface 14b in the bore 14 of the nozzle body 10. If desired, the valve needle 16 in Figure 7 may also be provided with a circumferential groove (not shown) to alleviate the effects of wear of the nozzle during its operational life.

In a variation of the sac-type nozzle shown in Figure 7 (not illustrated), the inclined groove 124 may be positioned below the seating line 18 on the outer i surface of the valve needle 16.

Figure 8 is a further alternative embodiment of a VCO-type nozzle in which the valve needle is provided with a circumferential groove 30 defining an upstream valve needle seating line 1 8a and a downstream valve needle seating line 1 8b, and wherein the valve needle 16 is provided with an inclined groove 24 which intersects the downstream valve needle seating line 1 8b.

- 1 9 For each of the embodiments of the invention described in Figures 2 to 8, the bore 14 is preferably shaped to include a guide region (not shown) at its end remote from the outlet 12 which cooperates with an adjacent region of the valve needle 16 to guide movement of the valve needle 16 as it lifts away from the seating surface 14b. A clearance is defined between the guide region and the valve needle 16 which, throughout the service life of the nozzle, can cause the first and second regions 16_, 16b of the needle 16 to become eccentric relative to the nozzle body 10. As a result, fuel flow through the flow path defined by the inclined groove(s) 24, 124, whether the groove is provided on the valve needle or in the bore of the nozzle body, can vary around the valve needle axis. For nozzles in which the nozzle body 10 is provided with more than one outlet 12, the effect of such fuel flow variation about the valve needle axis is to cause an unequal distribution of fuel flow to the different outlets. This is undesirable and is particularly noticeable for low values of needle lift, H. However, by shaping the valve needle 16 and/or the nozzle body 10 such that the differential angle, A, is between about 0.5 and 3 degrees, it has been found that a hydraulically self- centralising force is applied to the lower end of the needle 16, therefore giving rise to a more equal fuel flow distribution to the outlets 12.

It has been found that the VCO-type nozzle shown in Figure 6, having a circumferential groove 30 on the valve needle 16, one or more inclined grooves 124 below the downstream edge 18b of the groove 30 and first and second differential angles, it, E, both less than 3 degrees, provides a particularly advantageous fuel spray characteristic, having a wider fuel spray angle, oil, at low values of needle lift, a narrower fuel spray angle, 2, for higher values of needle lift, substantially equal fuel flow distribution to the outlets and good

- 20 coverage of the inlet ends 13 of the outlets 12 for zero needle lift. This particular nozzle achieves a combination of low combustion noise and low emission of soot and HC from the engine exhaust.

Claims

- 21 CLAIMS

1. An injection nozzle for supplying a fuel spray, having a spray angle, to a combustion space of an internal combustion engine, the injection nozzle comprising; a nozzle body provided with a blind bore within which a valve needle is movable along a valve needle axis, the valve needle being engageable with a seating surface to control fuel flow between a delivery chamber and an injection nozzle outlet, wherein a surface of the bore and the outer surface of the valve needle define a first flow path through which fuel flows from the delivery chamber to the outlet when the valve needle is lifted from the seating surface, and an additional flow path for said flow defined by a groove provided in one of the outer surface of the valve needle and the bore, and a surface of the other of the valve needle and the bore, wherein the groove has a groove axis inclined to the valve needle axis and is shaped such that the cross sectional flow area of the additional flow path relative to the cross sectional area of the first flow path varies as the valve needle moves through a range of travel from the seated position to a fully lifted position, thereby to permit a fuel spray having a variable spray angle to be injected into the combustion space as the valve needle moves through the range of travel.

- 22 2. An injection nozzle as claimed in Claim 1, wherein the groove is shaped

such that the first flow path has a converging cross sectional area from a larger cross sectional area upstream end to a relatively smaller cross sectional area downstream end.

3. An injection nozzle as claimed in Claim 1, wherein the groove is shaped such that the first flow path has a diverging cross sectional area from a smaller cross sectional area upstream end to a relatively larger cross sectional area upstream end.

4. An injection nozzle as claimed in any of Claims 1 to 3, wherein a surface of the valve needle is cooperable with an inlet end of the outlet to control fuel delivery through the outlet.

5. An injection nozzle as claimed in any of Claims 1 to 3, wherein the valve needle defines a valve needle seating which is engageable with the seating surface to control fuel flow from the delivery chamber to a sac volume defined by a blind end of the bore, and wherein an inlet end of the outlet communicates with the sac volume.

6. An injection nozzle as claimed in any of Claims 1 to 5, wherein the groove is provided on an outer surface of the valve needle.

7. An injection nozzle as claimed in Claim 6, wherein the outer surface of the valve needle defines a valve needle seating which is engageable with the seating surface, and wherein the valve needle includes a first region upstream of the valve needle seating and a second region downstream of the valve needle

- 23 seating, the groove being provided in the first region of the valve needle upstream of the valve needle seating.

8. An injection nozzle as claimed in Claim 6, wherein the outer surface of the valve needle defines a valve needle seating which is engageable with the seating surface, and wherein the valve needle includes a first region upstream of the valve needle seating and a second region downstream of the valve needle seating, the groove being provided in the second region of the valve needle downstream of the valve needle seating.

10. An injection nozzle as claimed in any of Claims 1 to 57 wherein the groove is provided in an internal surface of the bore in the nozzle body.

11. An injection nozzle as claimed in Claim 10, wherein the bore includes a first bore region upstream of the valve needle seating when the valve needle is in a seated position and a second bore region downstream of the valve needle seating when the valve needle is in a seated position, and wherein the groove is provided in the first bore region.

12. An injection nozzle as claimed in Claim 10, wherein the bore includes a first bore region upstream of the valve needle seating when the valve needle is in a seated position and a second bore region downstream of the valve needle seating when the valve needle is in a seated position, and wherein the groove is provided in the second bore region.

- 24 13. An injection nozzle as claimed in any of Claims 1 to 12, wherein the valve needle is provided with a circumferential groove having an upstream edge defining an upper valve seating line and a downstream edge defining a lower valve seating line.

14. An injection nozzle as claimed in Claim 13 when dependent on Claim 10, wherein the groove intersects the lower valve needle seating line when the valve needle is seated.

15. An injection nozzle as claimed in Claim 13 when dependent on Claim 6, wherein the groove intersects the lower valve needle seating line.

16. An injection nozzle as claimed in any of Claims l to IS, wherein the groove axis and the axis of the valve needle define an angle,,B, of between 10 and 70 degrees.

17. An injection nozzle as claimed in any of Claims 7 to 16, wherein the first region of the valve needle and the adjacent region of the bore together define a first differential angle, it, therebetween of less than 3 degrees, thereby to provide a hydraulically self-centralising force to an end of the valve needle adjacent to the outlet.

18. An injection nozzle as claimed in Claim 17, wherein the first differential angle, is between O.S and 3 degrees.

19. -- An injection nozzle as claimed in any of Claims 7 to 18 wherein the second region of the valve needle and the adjacent region of the bore together define a differential angle, c, therebetween of less than 3 degrees.

- 25 20. An injection nozzle as claimed in any of Claims 1 to 19, wherein at least one of the valve needle and the bore is provided with more than one inclined groove, each of which defines, together with a surface of the other of the valve needle and the bore, an additional flow path for fuel between the delivery chamber and the outlet, wherein each inclined groove is shaped such that the cross sectional flow area of the respective additional flow path relative to the cross sectional area of the first flow path varies as the valve needle moves through the range of travel.

21. An injection nozzle for supplying a fuel spray jet to a combustion space of an internal combustion engine, the injection nozzle comprising; a nozzle body provided with a blind bore within which a valve needle is movable along a valve needle axis, a delivery chamber, defined by the bore and an outer surface of the valve needle for delivering high pressure fuel to an injection nozzle outlet, wherein the valve needle is shaped to define a valve needle seating which is engageable with a seating surface defined by the bore to control fuel delivery through the outlet, the valve needle including a first region upstream of the valve needle seating and a second region downstream of the valve needle seating, and wherein the first region of the valve needle and an adjacent region of the bore together define a first differential angle, it, therebetween of less than 3 degrees, thereby to provide a hydraulically self- centralising force to an end of the valve needle adjacent to the outlet.

- 26 22. An injection nozzle as claimed in Claim 21, wherein the first differential angle is between 0.5 and 3 degrees.

23. An injection nozzle substantially as herein described with reference to the accompanying Figures 2 to 8.