GB2229495A

GB2229495A - Fuel injector

Info

Publication number: GB2229495A
Application number: GB8906679A
Authority: GB
Inventors: David John Gaskell
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1989-03-22
Filing date: 1989-03-22
Publication date: 1990-09-26
Also published as: GB8906679D0

Abstract

The injector has a flow control annulus constituted by the space between an annular projection 22 on either the valve 12 or the seating 16 and the immediately confronting surface on the seating or the valve. The valve in initially closing to its seated position deforms this projection by predetermined amount. When the valve next lifts, for a given amount of lift the control annulus has a predetermined cross sectional area. Any lacquer which has become deposited in this area is subjected to compression or displacement by closure of the needle valve, and hence the control annulus cross sectional area is maintained at a substantially constant value even if lacquer has been deposited during the valve-open part of the cycle. The projection may be formed by a copper or silver insert (42, Fig. 5). <IMAGE>

Description

FUEL INJECTOR This invention relates to a fuel injector particularly although not exclusively for compression ignition oil engines.

The performance of a modern high speed oil engine is highly dependent on its fuel injection system. When employing a single or multi-hole fuel injector the fuel flow is controlled by a needle valve which cooperates with a conical seating surface. The initial rate of flow of fuel is determined by the crosssectional area of the annulus between needle valve and seating. It has been found that a so-called lacquer, comprising for example of the solid products of combustion, tends to builcl up on the seating surface or sometimes on the needle valve conical surface and these deposits limit the cross-sectional area of the flow path when the needle valve lifts. Consequently the initial fuel flow in practice fails to cnnform to the designed fuel flow so that the engine starting or idling is unsatisfactory.

It is an aim of the invention to solve or reduce this problem.

According to the invention, a fuel injector including a needle valve and a cooperating seating surface has a control annulus constituted by the space between an annular projection on either the valve or the seating and the immediately confronting surface on the seating or the valve as the case may be.

With such an arrangement, the needle valve in closing to its seated position deforms This projection by predetermined amount. When the needle valve next lifts, for a given amount of lift the control annulus has a predetermined cross sectional area. Any lacquer which has become deposited in this area is subjected to compression or displacement by closure of the needle valve, and hence the control annulus cross sectional area is maintained at a substantially constant value even if lacquer has been deposited during the valve-open part of the cycle.

The annular projection may be provided in various ways. A control ring of soft material, e.g. lead, may be included in the valve seat surface spaced somewhat downstream from the valve seat, or it Inay be included on a conical surface of the needle valve. Alternatively a formed ridge may be provided at the junction of the "sac" and the valve seating surface. This formed ridge may be made by an ironing procedure using a tool such as a carbide mandrel.

The invention will be better understood from the following non-limiting description of examples thereof given with reference to the accompanying drawings in which: Figures 1 and 2 illustrate conventional multi-hole injectors, Figure 2 showing a long-stem type; Figures 3, 4 and 5 respectively show, on an enlarged scale, the nozzle ends of respective injectors of the type shown in Figure 2 and incorporating respective first, second and third embodiments of the invention.

In the drawings, like parts are denoted by like reference numerals.

Referring firstly to Figure 1, a fuel injector has a body 10 and a needle valve 12 (also called a nozzle valve) which is accurately lapped into the nozzle body 10 to the closest possible fit, within which it will work freely. Fuel fed under pressure via a gallery 11 and a bore 13 causes a lifting of the needle valve 12 following which fuel is forced out under pressure from the fuel exit holes 20.

The operation of a long stem type of injector as seen in Figure 2 is similar. In both types of injector, upward movement of the needle valve 12 is resisted by a biassing means such as a strong spring.

The lower part of the needle valve 12 has two different conical tapers thereon which merge to provide a line contact valve seat 14 at their junction.

The valve seat 14 cooperates with a part-conical seating surface 16 provided in the lower part of the valve body. The lowest part of the valve body 10 defines a charnber or "sac" 18 which receives fuel under pressure when the needle valve 12 lifts and through which the fuel passes prior to exiting into the engine combustion chamber via the fuel exit holes 20. The zcne of the interior wall of the valve body at and around the junction between the sac and the part conical surface 16 is often subject to build up of lacquer or other products of combustion. The effect of this build up is to limit the available cross sectional area through which the fuel flows as it passes to the sac, and, as stated, an aim of the present invention is to alleviate the consequences of this.For this purpose, the material of the injector body 10 is worked to form a ridge or projection 22 which extends towards the conical surface 15 of the needle valve 12. This projection 22 is of such a size that it is deformed when the needle valve 12 is fully closed, the needle valve 12 being made, as is conventional, of a particularly hard material. This deformation of the projection 22 has the result that for a predetermined lift of the needle valve 12, the fuel path annulus thereby created has a predetermined size, thereby providing a controlled area restriction in the fuel path. Each closing operation of the valve effects a similar deformation of any material that has built up in that region, and hence after each closing operation of the valve the cross sectional area of the fuel path annular restriction is restored to its predeterrnined desired area.The formed projection 22 seen in Figure 3 may be obtained by working the material of the nozzle body by ironing a cone 24 in a finally machined and assembled nozzle using a suitable tool such as 8 carbide mandrel.

A similar effect may be achieved in other ways. For example, referring to Figure 4, there is an annular projection 32 formed on the conical surface 15 of the needle valve 12. In this embodiment the conical surface 16 joins with a substantially cylindrical portion 34 of the surface defining the sac 18. The projection 32 may be formed in a similar way to the projection 22 of Figure 3.

Another alternative construction in accordance with the invention embodies the insertion of a separate control ring of soft material such as copper or silver. This control ring is shown at 42 in Figure 5, it being inserted in a recess 44 provided in the injector body 10. In another embodiment,' not illustrated, a control ring similar to the ring 42 may be disposed in an annular recess in the surface 15 of the needle valve 12.

Initially, in one particular embodiment in accordance with the invention, the smallest cross sectional area of the flow path for the fuel is at the top of the seat i.e. at the seating line. Depending on the differential angle the minimum restriction moves to the bottom of the seat at about 17xm needle lift. This position then remains the throttling area until as the lift increases it equals the total area of the spray holes. With a normal single stage lift nozzle it is normal to aim for a flow area ratio of 1:1.25 to ensure maximum pressure drop across the spray holes. With 2 stage lift the pre-lift position is controlled (about Stm lift) to achieve throttling across the seat sac interse tion. This controls the initial rate of fuel injection and therefore the noise from combustion.The formation of a deposit in this region affects the cross sectional area and therefore the initial rate of fuel injection. Apart from affecting the noise it can affect the idling stability.

It will be seen that there have been disclosed and illustrated arrangements for overcoming or greatly reducing problems of improper fuel metering to an engine which arise when there is lacquer build up or build up of other combustion products at certain sensitive zones in the fuel path. While particular embodiments of the invention have been illustrated and particularly described, other variations may occur to a man of average skill in the art. The present invention may be applied in connection with pintle-type fuel injections or with needle valves having a shape different from the shapes illustrated in Figures 3-5 and is not considered to be limited to the specific details described and illustrated herein. In particular, the present invention can be applied- to injectors having needle vales with three cone angles or needle valves having extensions on the needle tip. Such extensions are sornetimes included to reduce the sac volume.

Claims

1. A fuel injector including a needle valve and a cooperating seating surface has a control annulus constituted by the space between an annular projection on either the valve or the seating and the immediately confronting surface on the seating or the valve as the case may be.

2. A fuel injector according to claim 1 in which the annular projection is provided by a control ring of soft material, e.g. leadwhich is included in the valve seat surface spaced somewhat downstream from the valve seat.

3. A fuel injector according to claim 2 modified in that the control ring is included on a conical surface of the needle valve.

4. A fuel injector substantially as herein described and illustrated in the accompanying drawings.