GB2125894A

GB2125894A - I.C. engine fuel injection nozzle

Info

Publication number: GB2125894A
Application number: GB08320778A
Authority: GB
Inventors: Paul Lakra
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-08-26
Filing date: 1983-08-02
Publication date: 1984-03-14
Also published as: GB2125894B; GB8320778D0

Abstract

A valve member 16 slidable in a bore 15 formed in a nozzle body 13, is shaped to co-operate with a seating in the body with which in the closed position it makes an electrical connection. In the open position the valve member is insulated from the wall of the bore by a layer of electric insulating material 30 such as a ceramic which is contained within a groove 16A in the valve member or a groove in the bore wall. <IMAGE>

Description

SPECIFICATION Fuel injection nozzles This invention relates to fuel injection nozzles for supplying fuel to a combustion chamber of an intermittent combustion engine, the nozzle being of the kind comprising a fuel pressure actuated valve member slidable within a bore in a body, resilient means for urging the valve member into contact with a seating, the valve member being lifted from the seating by fuel under pressure supplied to a fuel inlet of the nozzle to allow fuel flow through an outlet.

For the purpose of accurate control of the timing of delivery of fuel to the combustion chamber when the nozzle is in use, it is desirable to be able to detect when the valve member is lifted from the seating. Several methods are known whereby a signal indicative of the lifting of the valve member from the seating can be provided and one such method is described in the specification of British Patent No. 1 586254. In the nozzle described therein reliance is placed upon the electrical insulating property of the film of fuel between the valve member and bore to electrically insulate the valve member from the wall of the bore.The resilient means is in the form of a coiled spring which is insulated from the body and the valve member and seating constitute a switch which is connected into an electrical circuit It has been found that the fuel film does not always provide the required degree of insulation with the result that the signals supplied to an associated control system may cause malfunction of the control system.

The object of the present invention is to provide a fuel injection nozzle of the kind specified in a simple and convenient form.

According to the invention a fuel injection nozzle for supplying fuel to a combustion chamber of an intermittent combustion engine comprises a fuel pressure actuated valve member slidable within a bore in a body, resilient means for urging the valve member into contact with a seating, the valve member being lifted from the seating by fuel under pressure supplied to a fuel inlet of the nozzle to allow fuel flow through an outlet, an elongated circumferential groove formed in the valve member or in the wall of the bore, a layer of electric insulating material in the groove, said layer acting to insulate the valve member from the wall of the bore, said valve member making an electrical connection with the body through the seating when the valve member is in the closed position, the nozzle including terminal means electrically connected to the valve member.

One example of a fuel injection nozzle in accordance with the invention will now be described with reference to the accompanying drawings: In the drawings: Figure 1 is a sectional side elevation of the nozzle; Figure 2 is an enlarged view of a portion of the nozzle seen in Figure 1; Figure 3 is an enlarged sectional view of a further portion of the nozzle of Figure 1, and Figures 4 and 5 show modifications of the nozzle.

Referring to Figure 1 of the drawings, the injection nozzle comprises a main body 10 which is of generally cylindrical form and which has a lateral extension 11 having a threaded aperture formed therein which in use, receives a pipe union 1 2 which constitutes the fuel inlet for the nozzle.

At one end there is secured to the main body 10, a nozzle body 13, this being of stepped cylindrical form. The narrower end portion of the body 13 projects, in use, through the wall of a combustion space of an engine, and the body 13 is retained relative to the main body 10 by a cupshaped retaining member 14, having an aperture in its base wall through which the narrower portion of the body 13 extends.

Formed with the nozzle body 13 is a bore 1 5.

The bore 1 5 extends to adjacent the end of the narrow portion of the body and defines a seating for a valve member 1 6 which is slidable within the bore. The valve member is shaped to cooperate with the seating to prevent flow of fuel through outlet orifices which communicate with the blind end of the bore. The valve member 16 is of stepped form, the narrower portion of the valve member lying generally within the portion of the bore 1 5 which is formed in the narrower portion of the nozzle body. In the general region of the steps on the body and valve member, there is formed in the bore an enlargement 1 SA which is connected by co-operating passages 17, 1 8 in the nozzle body and the main body respectively with the aforementioned fuel inlet.

Formed in the main body 10 is a further axially extending bore which accommodates a push-rod 19. The push-rod is engaged about an axial projection on the valve member 1 6 and at its other end opens into an enlarged chamber 20.

The end of the push-rod in the chamber is provided with an abutment 21 for resilient means in the form of a coiled compression spring 22. The other end of the coiled compression spring is engaged about a further abutment 23 which in turn engages a cup-shaped member 24 which is in screw-thread engagement with the wall of the chamber 20. The cup-shaped member 24 is prevented from rotating in the main body by a locknut and the aperture 29 is provided in the member 24 to allow fuel to leak from the chamber 20.

In operation, when fuel under pressure is admitted to the enlargement 1 so, the fuel under pressure acts on the valve member and the valve member is moved against the action of the coiled compression spring to permit fuel flow through the aforesaid outlets. When the supply of fuel under pressure ceases the valve member is returned into contact with its seating by the action of the coiled compression spring. Any fuel which leaks between the valve member and the wall of the bore 1 5 can flow into the chamber 20 and the fuel accumulating in the chamber 20 can flow through the aperture 29 to a drain.

As will be seen from Figure 3, a layer of electrical insulating material is provided between the valve member and the wall of the bore. The layer is in the form of a coating 30 which has an axial length such that only the coating can engage the wall of the bore in the event that the fuel film between the coating and the wall of the bore is broken.

In order to provide an indication of the movement of the valve member towards and away from the seating, use is made of the variation in the electrical resistance which occurs during such movement, between the valve member 1 6 and the nozzle body 13. The nozzle body is of course electrically connected to the main body 10 and the valve member is connected to terminal means through the push-rod 19, the spring 22 and the abutment 23. The push-rod 19 is spaced from the wall of the bore in which it is mounted as also is the abutment 21 and the spring 22. The abutment 23 as shown in Figure 2, is insulated from the cup-shaped member 24 by means of an electrically insulating disc 28 so that the only direct electrical connection between the valve member and the nozzle body occurs when the valve member is in contact with the seating.

The abutment 23 as more clearly shown in Figure 2, has secured thereto an electrical conductor 27 which passes through an insulating collar 25 located within an aperture in the base wall of the cup-shaped member and is connected to an electrical connector 26.

The electrical resistance offered by the unit is measured between the connector 26 and the main body 10. When the valve member is in the closed position there is substantially no electrical resistance between the valve member and the nozzle body. There is, however, a sharp increase in the resistance when the valve member lifts from the seating.

The coating 30 is formed from a hard wearing material such for example as a ceramic which is deposited within an elongated circumferential groove 1 6A formed in the valve member.

Conveniently the material is deposited into the groove before the valve member is ground to the required size. The end walls of the groove act to support the coating so as to prevent crumbling of the material forming the coating. Following the grinding operation, the valve member must be lapped with the wall of the bore in the usual manner and also the valve member must be lapped with the seating.

Ceramic material has been mentioned above as being suitable material to form the coating.

Such material can be applied using plasma spraying or ion deposition techniques.

Other materials can be used to form the coating providing they have the following general properties: 1. Good electrical insulation.

2. High wear resistance.

3. Good machinability.

4. The ability to be deposited without affecting the heat treatment of the valve member or body.

5. Good resistance to chipping.

6. High bond strength.

7. Low porosity.

8. Similar thermal properties to steel, and 9. A high yield stress.

The nozzles described are of the so-called inwardly opening types. Another form of nozzle is Df the outwardly opening type. It is possible to provide for insulation of the valve member of this type of nozzle in a similar manner to that described. However, it is more difficult with this type of nozzle to provide an electrical connection to the exterior of the nozzle. This is because in this type of nozzle the chamber which contains the spring also in use contains fuel at high pressure.

The groove 1 6A and the layer 30 shown in Figure 3 have a length such that at all positions of the valve member in the bore, the valve member is insulated from the wall of the bore. This means that even when the valve member is fully open a small portion of the layer is exposed to the fuel within the enlargement 1 so. During the delivery of fuel, the fuel in the enlargement is in a highly turbulent state with the result that the exposed portion of the layer can be eroded. In order to minimise the possibility of erosion taking place and as shown in Figure 4, the end of the groove 1 6A adjacent the enlargement is stepped back so that it no longer lies beyond the end of the bore.

In order to maintain the electrical insulation, the valve member and a portion of the layer 30 are relieved by machining a step in order to establish a clearance indicated at 31, between the wall of the bore and the valve member. The clearance is very small being sufficient to provide the required electrical insulation and also to act to damp out pressure fluctuations which would tend to cause erosion. It will be understood that the drawing is exaggerated and that the step which appears in the layer 30 is very small.

Figure 5 shows a modification in which the valve member is provided with a taper 32, the taper including the end portion of the layer 30.

Claims

1. A fuel injection nozzle for supplying fuel to a combustion chamber of an intermittent combustion engine comprising a fuel pressure actuated valve member slidable within a bore in a body, resilient means for urging the valve member into contact with a seating, the valve member being lifted from the seating by fuel under pressure supplied to a fuel inlet of the nozzle to allow fuel flow through an outlet, an elongated circumferential groove formed in the valve member or in the wall of the bore, a layer of electric insulating material in the groove, said layer acting to insulate the valve member from the wall of the bore, said valve member making an electrical connection with the body through the seating when the valve member is in the closed position, the nozzle including terminal means electrically connected to the valve member.

2. A nozzle according to Claim 1 in which said groove is formed in the valve member, the groove having a length such that it extends beyond the ends of the bore.

3. A nozzle according to Claim 1 in which one end of the bore in which the valve member is mounted is subjected in use to fuel which is in a state of turbulence, the groove being formed in the valve member and the end of the groove terminating short of said end of the bore, said valve member and the layer of insulating material being relieved to ensure electrical insulation.

4. A nozzle according to Claim 3 in which said valve member and layer are relieved by machining a step thereon, the clearance between the relieved portion of the valve member and layer and the bore acting to damp out pressure fluctuations so as to maintain damage to the material forming the layer.

5. A nozzle according to Claim 3 in which the valve member is provided with a taper, the taper including the end portion of the insulating layer.

6. A nozzle according to any one of the preceding claims in which the layer is formed from ceramic material.

7. A fuel injection for supplying fuel to a combustion chamber of an intermittent combustion engine substantially as hereinbefore described with reference to Figures 1-3 of the accompanying drawings.

8. A fuel injection for supplying fuel to a combustion chamber of an intermittent combustion engine substantially as hereinbefore described with reference to Figures 1-3 as modified by Figure 4 of the accompanying drawings.

9. A fuel injection for supplying fuel to a combustion chamber of an intermittent combustion engine substantially as hereinbefore described with reference to Figures 1-3 as modified by Figure 5 of the accompanying drawings.