GB2146068A

GB2146068A - Fuel injection nozzle

Info

Publication number: GB2146068A
Application number: GB08420503A
Authority: GB
Inventors: Godfrey Greeves; Keith Richard Browne; David Eric Draper
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-09-03
Filing date: 1984-08-13
Publication date: 1985-04-11
Also published as: GB8323678D0; GB8420503D0

Abstract

The valve head 14 is urged into contact with a seating 15 by a spring and in the closed position of the valve head a clearance of between zero and five microns exists between the cylindrical portion 29 of the valve head and the wall of the bore 28 to minimise the formation of carbon deposit. <IMAGE>

Description

SPECIFICATION Fuel injection nozzle This invention relates to a fuel injection nozzle of the so-called outwardly opening type comprising a nozzle body, a bore formed in the body and a seating defined therein adjacent one end of the body, a valve member having a head shaped for co-operation with said seating, resilient means for biasing the valve head into contact with the seating, said bore downstream of said seating being of enlarged diameter, the wall of said enlarged diameter portion of the bore and said valve head defining an outlet through which fuel can flow when the head is lifted from the seating.

Such nozzles are also known in the art as "poppet" nozzles and the outer peripheral surface of the valve head and/or said enlarged portion of the bore may be carefully contoured so as to obtain a nozzle, the effective area of the outlet of which varies as the valve head is moved away from the seating.

A problem with this form of nozzle is that in use carbon deposits form on the valve head and the aforesaid wall and such carbon deposits impair the performance of the nozzle and lead to modification of the flow characteristics of the nozzle which may impair the operation of an associated engine. Various ways have been tried to minimize the build up of carbon deposits for example, British Specification 2099505A discloses a nozzle in which the fuel flow past the valve head is turbulent thereby tending to wash away any carbon deposit. In addition, precautions are taken to minimise the volume of fuel downstream of the seating which will be subject to the heat of combustion and also to minimize transfer of heat to the fuel from the exposed portion of the valve head.

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

According to the invention in a fuel injection nozzle of the kind specified the diametral clearance in the closed position of the valve head, between the peripheral surface of the valve head and the wall of the enlarged portion of the bore is between zero and five microns.

An example of a fuel injection nozzle in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional side elevation of the nozzle; and Figure 2 is a view to an enlarged scale of a portion of the nozzle seen in Figure 1.

Referring to Figure 1 of the drawings, the nozzle includes a valve assembly generally indicated at 10 and which includes a flanged body part 11 in which is formed a bore 12 within which is slidable a valve member 13. The valve member Includes a head 14 which can engage with a seating 15 to prevent flow of fuel from the bore 12 through an outlet defined by a slightly enlarged portion of the bore downstream of the seating.

The valve member 13 includes a fluted portion 16 which guides the valve member for movement within the bore, and a plain cylindrical portion 17 which is partly located within the bore but which extends therefrom. The portion of the valve member between the fluted portion and the cylindrical portion is of reduced diameter so as to define an annular clearance with which communicates a pair of ports 19 formed in the body portion 11.

The portion 17 of the valve member which projects from the bore 12 mounts a spring abutment 20 between which and the flanged portion of the body part 11 is located a coiled compression spring 21. The spring abutment is retained in position on the valve member by means of a retainer 22.

The valve assembly is located within a chamber 23 which is defined in part by an integral skirt portion 24 of a holder 25. The holder includes a fuel supply passage 26 which communicates with a fuel inlet of the nozzle and which in use, is connected to the outlet of a fuel injection pump. The valve assembly is secured to the holder by means of a cap nut 27, the connection between the cap nut and the holder being obtained by complementary screw threads. In the particular example the cap nut 27 is provided with screw threads on its external peripheral surface whereby the nozzle can be secured within a complementary bore in the cylinder head of an engine.

When fuel under pressure is supplied to the chamber 23 the fuel pressure acts upon the valve member to move the valve member against the action of the spring 21 in the outward direction. As the valve head 14 is lifted from the seating 15, fuel can flow through the annular opening defined between the valve head 14 and the enlarged portion of the bore. When the flow of fuel to the chamber ceases, the valve member is moved to the closed position under the action of the spring.

Referring now to Figure 2, it will be seen that the enlarged portion of the bore has a right cylindrical wall 28 and the valve head 14 is contoured to provide an annular clearance between the wall 28 and the valve head, which varies as the valve head moves away from the seating. At its outer end the valve head 14 is provided with a right cylindrical portion 29. In the closed position of the valve member, the right cylindrical portion 29 enters into the enlarged portion of the bore and the dimensions of the wall 28 and the portion 29 are chosen so that the clearance therebetween in the closed position of the valve member is substantially zero.

In practice a diametral clearance of up to 5 microns can be provided. The small clearance between the valve head and the wall 28 in the closed position of the valve member protects the fuel which is contained within the annular space about the valve head when the valve head is in the closed position, from the hot combustion gases within the combustion chamber of the associated engine. The possibility therefore of the fuel becoming heated and therefore carbonising, is minimized.

Tests have shown that where the diametral clearance is equal to or less than 5 microns, carbon deposition on the surface of the valve head and on the wall 28, is substantially reduced.

Claims

1. A fuel injection nozzle of the kind specified in which the diametral clearance in the closed position of the valve head, between the peripheral surface of the valve head and the wall of the enlarged portion of the bore is between zero and five microns.

2. A fuel injection nozzle according to Claim 2 in which the portion of the valve head remote from the seating is of right cylindrical form.

3. A fuel injection nozzle of the so-called outwardly opening type substantially as hereinbefore described with reference to the accompanying drawings.