GB2234289A - A nozzle for a two-stage lift fuel injector - Google Patents

Abstract

A sleeve 21, lining an upstream section of the nozzle housing wall, has one or more holes 22 in fluid communication with the fuel inlet 12. A part 25 of the valve member overlaps the hole or holes so as to block the fuel inlet to an extent related to the axial position of the valve member in the bore, and thereby effects control over the flow of fuel from the outlet 13 at least at the end of the first stage of valve lift. The hole 22 may take various forms (Fig. 2). <IMAGE>

Description

A NOZZLE FOR A TWO-STAGE LIFT FUEL INJECTOR This invention relates to a fuel injector for a vehicle engine and particularly to a nozzle for a two-stage lift fuel injector.

There is an increasing demand for vehicle engines, especially diesel engines, which run quietly when they are idling, and to that end so-called two-stage lift fuel injectors have been developed.

A fuel injector of this kind is fitted with a nozzle which can regulate the discharge of fuel. Typically, the nozzle comprises a generally tubular housing having a fuel inlet and a fuel outlet. A needle-like valve member, which can move axially within a bore of the housing, is resiliently biassed towards a closed position in which an end of the valve member bears against the housing adjacent the fuel outlet to prevent the discharge of fuel.

When the engine is running, the pressure of fuel in the injector displaces the valve member in the axial direction opposing the biassing force and thereby lifts the end of the valve member away from the housing allowing fuel to pass through the outlet for combustion.

During an initial lift stage, the valve member undergoes only a slight axial displacement away from the housing, to a first set position. In this position, the gap between the end of the valve member and the housing provides a restricted passage for fuel to the outlet and maintains the fuel flow rate at a relatively low level.

For normal running, the valve member undergoes a further, much larger displacement, to a second set position. In this position the end of the valve member and the housing provide a much larger passage for fuel to the outlet and so a higher fuel flow rate is achieved.

The axial displacement required for the initial lift stage is so small that the nozzle is difficult to embody in an economical manner. The manufacturing tolerances required to attain such a small axial displacement tend to be prohibitive. Furthermore, the effect of wear on the component parts, and of so-called lacquer deposits which accumulate on the co-operating portions of the valve member and the housing, are also of significance and can have an adverse effect on the desired operation of a nozzle.

It is an object of the present invention to provide a nozzle for a fuel injector which at least alleviates the afore-mentioned problems associated with known nozzle constructions.

According to a first aspect of the invention there is provided a nozzle for a two-stage lift fuel injector comprising a housing having a passage therethrough for the flow of fuel from an inlet to an outlet, said passage including a bore within which a valve member is displaceable between a position in which an end of the valve member adjacent the outlet co-operates with the housing to close the passage and first and second set positions in which a flow of fuel to the outlet is permitted, and control means being provided in the passage upstream of the end of the valve member for controlling the flow of fuel to the outlet to an idling level when the valve means is in said first set position.

The control means, provided at said position upstream of the end of the valve member, enables the valve member to undergo a relatively large axial displacement during the initial lift stage to the first set position (because the valve member is not controlling the fuel flow) and yet still attain a comparatively low fuel flow rate required for quieter idling.

The control means may regulate the rate at which fuel is admitted to the bore of the housing and, in an embodiment, the control means may comprise a part of the valve member capable of restricting the flow of fuel into the bore to an extent related to the axial position of the valve member in the bore.

The passage may include a part connecting the inlet to the bore, and said part of the valve member may progressively uncover an outlet of said part of the passage, to an extent related to the axial position of the valve member in the bore, to control the flow of fuel into the bore.

The valve member may be axially displaceable relative to a sleeve in the bore, lining an upstream section of the housing wall. The sleeve may have one or more holes in fluid communication with the inlet and said part of the valve member may overlap the hole or holes in the sleeve to an extent which is related to the axial position of the valve member in the bore, thereby to effect the restriction.

The sleeve may have a single hole whose transverse dimension decreases in the longitudinal direction thereof approaching the outlet.

Alternatively, the sleeve may have two or more holes, disposed at successive positions along the length thereof, and successive holes, in the direction approaching the fuel outlet, may be of decreasing size.

Accordingly, by appropriately shaping and/or dimensioning the hole or holes in the sleeve, it is possible to attain a relatively low fuel flow rate, required for quieter idling, even though: the valve member undergoes a relatively large initial axial displacement.

The housing wall may have an annular recess for providing fluid communication between said hole or holes in the sleeve and the inlet.

The outlet may comprise a perforate wall defining a cavity in the housing wall, and said end of the valve member may comprise a tapered tip which, in the closed position of the valve member, bears against a valve seat around the mouth of the cavity.

According to a further aspect of the invention there is provided a two-stage lift fuel injector for a vehicle engine incorporating a nozzle in accordance with the first aspect of the invention.

A nozzle embodying the present invention is now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a longitudinal sectional view through the nozzle; and Figures 2a to 2d show a side elevation view of an end portion of a sleeve shown in Figure 1 and illustrate different configurations of hole formed in that portion of the sleeve.

Referring to Figure 1, the nozzle 10 comprises a generally tubular housing 11 having a passage therethrough for the flow of fuel from an inlet 12 to an outlet 13. The passage has a longitudinal bore 14 containing a needle-like valve member 15 which can assume a closed position (as shown in the drawing) and can be displaced axially (in the direction of arrow A) allowing fuel to be discharged from the outlet.

The nozzle is intended to form part of a two-stage lift fuel injector and, in use, would be clamped, in known manner, to a conventional injector assembly (not shown), with a flat end surface 16 of the nozzle housing being disposed in abutting relationship with a surface of the injector assembly. As is conventional in two-stage lift fuel injectors, the valve member 15 is acted upon by a pair of springs (not shown) which form part of the injector assembly and urge the valve member towards the shown, closed position.

In operation of the nozzle, the valve member undergoes an initial displacement, from the closed position to a first set position, in order to set the relatively low fuel flow rate required for idling, followed by a further axial displacement, to a second set position, in order to set a higher fuel flow rate appropriate for normal running.

With the nozzie configurations shown in the drawings, it is possible to set the relatively low flow rate, to achieve the desired reduction in engine noise during idling, even though the valve member undergoes a much larger initial axial displacement than has hitherto been possible using known nozzle constructions.

Referring again to Figure 1, the fuel outlet 13 comprises a perforate, domed wall 17 defining a hemispherical cavity 18 at the outlet end of the housing. A valve head 19 at the outlet end of the valve member is in the form of a tapered tip which, in the closed position of the valve member, bears against a valve seat 20 formed in the housing 11 around the mouth of the cavity, blocking a flow of fuel from the outlet. When, in response to fuel pressure, the valve member is displaced in the direction of arrow A, the valve head is lifted away from the valve seat enabling fuel to be discharged.

The valve member is supported centrally in the housing by sleeve 21 which lines an upstream section of the housing wall and is provided with one or more transverse holes 22.

The passage has an inclined portion 23 and an annular recess 24 affording fluid communication between the portion 23 and the hole or holes 22 in the sleeve 21.

An upstream part 25 of the valve member overlaps the hole or holes in the sleeve and so restricts the flow of fuel into the bore. The extent of this restriction depends partly on the relative axial positions of the valve member and the sleeve and partly on the shape, size and position of the hole or holes 22.

The holes may be formed in the sleeve wall with high precision using any convenient technique such as E.D.M., ultrasonic machining etc. Figures 2a to 2d show a selection of alternative hole configurations. In Figure 2a, the sleeve has two holes at different longitudinal positions, the upstream hole 22' having a larger diameter than the downstream hole 22". In Figures 2b to 2d the sleeve has a single hole whose transverse dimension (d) increases in the direction of axial displacement (represented by arrow A).

In the closed position of the valve member, the upstream part 25 overlaps the hole or holes 22 to the maximum extent, and as the valve member is displaced (in the direction of arrow A) an increasing proportion of the total hole area becomes exposed, allowing a greater flow of fuel.

Accordingly, by appropriately shaping and/or dimensioning the hole or holes 22, the valve member may undergo a relatively large initial axial displacement (greater than 0.05 mm used in hitherto known constructions) and yet still attain the comparatively low fuel rates required for quieter idling, because the flow of fuel for idling is no longer controlled by the valve head 19.

Consequently, the manufacturing tolerances associated with the described valve constructions are much less exacting than for hitherto known constructions, and the effect of wear on the component parts, and of lacquer deposits on the valve head and valve seat, tend to be of less significance.

The hole configurations shown in Figures 2a to 2d are given by way of example only, and clearly other hole configurations could be used.

When the nozzle is fitted to the injector assembly the sleeve 21 is clamped between a spring washer 26 and an annular shim 27. Accordingly, the axial position of the sleeve (and of the hole or holes 22) can be set with precision by choosing the thickness of the shim appropriately. If desired, the sleeve can be fixed in position using a suitable adhesive.

In summary, the described nozzle enables attainment of relatively low fuel fow rates required for quieter idling, and yet requires less exacting manufacturing tolerances and is relatively independent of the effects of wear and lacquer deposits than are nozzles of hitherto known construction.

Claims (16)

1. A nozzle for a two-stage lift fuel injector comprising a housing having a passage therethrough for the flow of fuel from an inlet to an outlet, said passage including a bore within which a valve member is displaceable between a position in which an end of the valve member adjacent the outlet co-operates with the housing to close the passage and first and second set positions in which a flow of fuel to the outlet is permitted, and control means being provided in the passage upstream of the end of the valve member for controlling the flow of fuel to the outlet to an idling level when the valve means is in said first set position.

2. A nozzle as claimed in claim 1, wherein the control means regulates the rate at which fuel is admitted to the bore of the housing.

3. A nozzle as claimed in claim 2, wherein the control means comprises part of the valve member capable of restricting the flow of fuel into the bore to an extent related to the axial position of the valve member in the bore.

4. A nozzle as claimed in any one of claims 1 to 3, wherein the passage includes a part connecting the inlet to the bore.

5. A nozzle as claimed in claim 4, wherein said part of the valve member progressively uncovers an outlet of said part of the passage to an extent related to the axial position of the valve member in the bore, to control the flow of fuel in the bore.

6. A nozzle as claimed in any one of claims 1 to 5, wherein the valve member is axially displaceable relative to a sleeve in the bore lining an upstream section of the housing wall.

7. A nozzle as claimed in claim 6, wherein the sleeve has one or more holes in fluid communication with the inlet.

8. A nozzle as claimed in claim 7, wherein said part of the valve member overlaps the hole or holes in the sleeve to an extent related to the axial position of the valve member in the bore.

9. A nozzle as claimed in claim 7 or claim 8, wherein the sleeve has a single hole whose transverse dimension decreases in the longitudinal direction approaching the outlet.

10. A nozzle as claimed in claim 7 or claim 8, wherein the sleeve has two or more holes disposed at successive positions along the length thereof.

11. A nozzle as claimed in claim 10, wherein successive holes are of decreasing size in the direction approaching the fuel outlet.

12. A nozzle as claimed in any one of claims 7 to 11, wherein the housing wall has an annular recess for providing fluid communication between said hole or holes in the sleeve and the inlet.

13. A nozzle as claimed in any one of claims 1 to 12, wherein the outlet comprises a perforate wall defining a cavity in the housing wall.

14. A nozzle as claimed in claim 13, wherein said end of the valve member comprises a tapered tip which, in the closed position of the valve member, bears against a valve seat around the mouth of the cavity.

15. A two-stage lift fuel injector for a vehicle engine incorporating a nozzle according to any one of claims 1 to 14.

16. A nozzle for a two-stage lift fuel injector substantially as herein described with reference to the accompanying drawings.