GB2220984A

GB2220984A - Fuel injection nozzle

Info

Publication number: GB2220984A
Application number: GB8817268A
Authority: GB
Inventors: Robert Henry Scott
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1988-07-20
Filing date: 1988-07-20
Publication date: 1990-01-24
Also published as: GB8817268D0

Abstract

The valve stem 3 is cut away to form flats 8, 9, 10 and 11, one pair of flats 8, 10 being at right angles to the other 9, 11. Because of the shape of the flats, incoming fuel can only enter chambers 13, 15 formed by one pair of flats 9, 11 and can only be discharged from chambers 12, 14 formed by the other pair 8, 10. To pass from one pair of chambers to the other, the fuel must traverse a restricted area between the stem 3 and the bore 2 which acts as an edge filter to trap entrained material which might clog the discharge holes in the end 7 of the nozzle. <IMAGE>

Description

FUEL INJECTION NOZZLES This invention relates to fuel injection nozzles particularly, but not exclusively, for internal combustion engines of the compression ignition type.

Such nozzles are normally supplied with measured quantities of fuel under pressure at regular intervals by a pump, the delivery pressure of which is sufficient to cause a spring-loaded valve stem to be axially displaced in a bore in the nozzle body to open a valve and permit fuel to be discharged from the nozzle via holes therein.

These valves are conventionally of the high-- precision needle type and it is of the utmost importance to prevent any foreign matter entrained by the fuel from interfering with the movement of the needle valve stem or blocking any of the holes in the nozzle. It is usual to prevent such material from entering the pump itself by providing, upstream thereof, a fine filter of, for example, fhe roLLed paper type. This does not, however, prevent all possible- deleterious material from entering the nozzle since such material may result, for example, from deterioration or degradation of the pressure hose or other connecting means from the pump to the nozzle.

In order to deal with this problem, it is known to insert a further filter, preferably of the edge type, either in an inlet adaptor for the nozzle or in the fuel inlet drilling of the. nozzle body itseLf. In either case, this involves extra parts, additional manufacturing steps and an inevitable increase in cost.

In order to overcome these disadvantages, there is provided in accordance with the invention in its broadest aspect a fuel injector nozzle comprising a valve of which the valve stem is configured to serve as an integral edge filter.

More specifically, the invention provides a fuel injector nozzle having a valve comprising a valve stem axially-displaceable in a bore in the nozzle body to open the valve and permit fuel to be discharged from the nozzle via one or more holes therein, the stem being configured to provide, upstream of the valve, a fuel path having at least one area of restricted dimensions forming an integral edge filter capable of allowing the free passage of fuel but only of such material entrained therein as will easily pass through the holes in the nozzle.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a section through a fuel injection nozzle in accordance with a first embodiment, Figure 2 is a section on the line II-II of Figure 1, Figure 3 is a section on the line III-III of Figure 1, Figure 4 is a section on the line IV-IV of Figure 1, Figure 5 is a section through a fuel injection nozzle in accordance with a second embodiment, and Figure 6 is a section on the line VI-VI- of Figure 5, Figure 7 is a section on the line V11 - V11 of Figure 5, Figure 8 is a section on the Line V111 -# if Figure 5, and Figure 9 is a section on the line 1X - 1X of Figure 5.

Referring to Figures 1 to 4, the injection nozzle has a body 1 provided with a longitudinal blind bore 2 to receive the stem 3 of a needle valve formed between the pointed lower end 4 of the stem and an inwardly-tapering surface at the blind lower end of the bore 2.

In accordance with known practice, the lower end of the stem is provided with conically-formed surfaces at different angles, the convex junction between these surfaces defining a precise valve seat 5 on the conical surface at the lower end of the bore 2. A compression spring (not shown) normally maintains the needle end 4 of the stem in contact with the seat 5 so that the valve remains closed.

As is well known, a fuel injection pump (not shown) supplies measured quantities of fuel under pressure at regular intervals to the nozzle via a passage 6 whose lower end communicates with the bore 2. The pump delivery pressure is such as to displace the stem 3 upwards and open the valve 4,5 so that fuel can pass along the lower part of the stem to discharge holes (not visible) in the domed end 7 of the nozzle.

In accordance with this embodiment, the external surface of the lower portion of the stem 3 is cut away to form flats 8,9,10 and 11. Flats 8 and 10 are disposed at 180 degrees to each other and flats 9 and 11 are disposed at 180 degrees to each other, the two pairs of opposed flats being at right angles to each other as shown most clearly in Figure 3.

The flats are each inclined to the axis of the stem and taper from a maximum width at one end (the Lower end of 8 and 10, the upper end of 9 and 11), where the stem is most cut away, to a minimum width at the other end where the stem is least cut away.

The effect of the flats 8,9,tO and li is that they provide respective chambers 12,13,14 and 15 between the stem 3 and the internal surface of the bore 2.

These chambers allow free flow for the fuel and any extraneous material entrained therein along most of the lower part of the stem.

At their upper ends, the flats 9 and 11 provide maximum clearance between the stem 3 and the bore 2, thus constituting openings through which fuel can flow into chambers 13 and 15. At their lower ends, flats 8 and 10 similarly form openings through which fuel can flow out of chambers 12 and 14. It will be appreciated that the openings at the two ends are mutually offset.

Between the flats, the stem has four areas of restricted dimensions or very limited clearance from the bore as shown at 16 in Figures 3 and 4 in the case of the area between flats 8 and 11. This clearance is less than the diameter of the holes in the nozzle end 7.

Fuel entering the chambers 13 and 15 via the openings at the upper ends thereof can only reach the chambers 12 and 14 and leave via the openings at the lower ends thereof by traversing the areas of restricted dimensions such as shown at 16. These areas therefore fulfil the function of an integral edge filter, providing a suitably large flow area so as not to produce a restriction to fluid flow but preventing the passing to the discharge holes of any entrained material other than that which is so small that it can easily pass through those holes.

The bore between the openings from the chambers 12 and 14 and the valve 4,5 is relieved as shown at 17 (Figure 1) to present an unrestricted fuel path.

The embodiment shown in Figures 5 to 9 differs from that shown in Figures 1 to 4 only by the fact that the flats 18 to 21 on the stem 3 are parallel to the axis thereof.

It is to be understood that many modifications can be made to the form of the edge filter provided by the invention. For example, the filter could take the form of a labyrinth such as that provided by intersecting screw threads of opposite hands.

Moreover the invention is applicable to a wide variety of fuel injector nozzles including those of the pintle-type.

Apart from the advantages of the invention already mentioned, it will be appreciated that there is a further advantage over previously known arrangements in that the edge filter is located as close as possible to the valve and the discharge holes in the nozzle.

Claims

CLAIMS:

1. A fuel injection nozzle comprising a valve of which the valve stem is configured to serve as an integral edge filter.

2. A fuel injection nozzle having a valve comprising a valve stem axially-displaceable in a bore in the nozzle body to open the valve and permit fuel to be discharged from the nozzle via one or more holes therein, the stem being configured to provide, upstream of the valve, a fuel path having at least one area of restricted dimensions forming an integral edge filter capable of allowing the free passage of fuel but only of such material entrained therein as will easily pass through the holes in the nozzle.

3. A fuel injection nozzle as claimed in claim 2 in which the fuel path includes at least two separate chambers formed between the body of the stem and the surface of the bore, and at least two openings formed between the body of the stem and the surface of the bore and disposed at opposite ends of the chambers, each opening communicating with a respective chamber and the two openings being mutually offset whereby fuel can only flow from one opening to the other by traversing the area of restricted dimensions formed between the surface of the bore and a portion of the stem between the two chambers.

4. A fuel injection nozzle as claimed in claim 3 in which the chambers are formed by flats on the stem which are inclined to the axis thereof and taper from a maximum width adjacent the respective opening at one end to a minimum width as they join the surface of the stem at the other.

5. A fuel injection nozzle as claimed in claim 3 in which the chambers are formed by flats on the stem which are parallel to the axis thereof.

6. A fuel injection nozzle substantially as described with reference to the accompanying drawings.