GB2178483A

GB2178483A - Fuel injector for I.C. engines

Info

Publication number: GB2178483A
Application number: GB08617305A
Authority: GB
Inventors: John Herbert Kenning
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1985-07-31
Filing date: 1986-07-16
Publication date: 1987-02-11
Also published as: GB8519251D0; GB8617305D0

Abstract

A fuel injector includes a valve plate 28 which is biased into contact with an annular seat element 23 to prevent flow of fuel through an outlet orifice 22. The valve plate is lifted from the seat element by energising a solenoid having a central pole piece 13 and a surrounding annular pole piece 18. The valve plate or the pole piece 18 is constructed so that the initial movement of the plate is a tilting movement and this is achieved by arranging that the attraction forces acting on the valve plate are unbalanced. The apertures 29 are larger than apertures 24A and the lower surface of the valve plate 28 may be relieved at 30 to ensure that the left side of the valve plate lifts first. Tilting upon de-energisation of the solenoid is promoted by relieving the surface of the valve plate at 31 or by castellation of the adjacent portion of spacer element 27. <IMAGE>

Description

SPECIFICATION Fuel injector This invention relates to a fuel injector for supplying fuel to an internal combustion engine more particularly a petrol injector for supplying fuel to an air inlet manifold of a spark ignition engine, the injector comprising a valve seat member having an orifice formed therein and through which fuel can flow from a fuel inlet, an annular seat element defined on the seat member about said orifice, a valve plate biased into contact with said seat element to prevent fuel flow through said orifice and a solenoid which can be energised to lift said valve plate away from said seat element thereby to allow fuel flow through the orifice.

An injector of the aforesaid type is shown in British Published Specification 2147949A.

Tests with this form of injector have shown that the operating characteristics vary and it is believed that this is due to variations in the way in which the valve plate is lifted away from the seat element by the action of the magnetic forces developed by the solenoid.

The valve plate may tilt as it moves under the influence of the magnetic force and the tilt may be initiated at any point around the plate.

Alternatively the plate as it lifts may remain parallel to the seat member. These variations in the mode of movement cause the operating characteristics of the injector to vary.

The object of the invention is to provide an injector of the kind specified in an improved form.

According to the invention the injector is constructed so that upon energisation of the solenoid the magnetic forces acting upon the valve plate will be unbalanced whereby the initial movement of the valve plate away from said seat element will be a tilting movement.

An example of a fuel injector 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 a known example of petrol injector, Figure 2 is a view to an enlarged scale of part of the injector shown in Figure 1, Figure 3 is a view similar to Figure 2 showing the modification to the injector in accordance with the present invention, and Figure 4 is a plan view of part of the injector of Figure 3, Figure 5 is a view similar to Figure 4 showing a further modification, and Figure 6 is a section on the line A-A of Figure 5.

Referring to Figures 1 and 2 of the drawings, the injector comprises a hollow generally cylindrical outer body 11 formed from magnetic material. Within the body there extends a magnetic hollow flanged core 13 through which extends a passage 14 which connects an inlet 12 with an outlet 15 of the body.

Surrounding the core 13 within the body is a former 16 which is formed from synthetic resin material and upon which is wound a solenoid winding 17. The outlet which is in the form of a sleeve retained within the body, projects in use into the air inlet manifold of a spark ignition engine.

Adjacent the outlet 15 the body 11 defines an integral radially inwardly extending annular shoulder 18 against which a Steel annulus 19 is trapped by a steel valve sqat member 21.

The seat member is in the form of a disc the diameter of which is equal to the internal diameter of the body 11, the disc having a cen tral outlet orifice 22 formed therein. The orifice extends from the surface of the valve seat member remote from the outlet and it is surrounded by a pair of annular spaced seat elements 23, 23A which project above the general level of the aforesaid surface.

Located within the steel annulus 19 is a valve plate 24 which is formed from magnetic material. The valve plate is in the form of a disc slidably received within the annulus 19, the peripheral edges of the disc being rounded as shown in Figure 2. Formed in the valve plate is a plurality of circumferentially spaced apertures 24A, the apertures 24A being aligned with the seat element 23A. The valve plate is biased into contact with the seat elements 23, 23A by means of a coiled compression spring 26 which is housed within the passage 14.

The shoulder 18 and the end face of the core 13 form pole pieces of a solenoid which includes the winding and when the winding is energised the pole pieces assume opposite magnetic polarity. The internal diameter of the shoulder 18 is less than the diameter of the annulus 19 and the shoulder therefore overlies the outer peripheral portion of the valve plate.

When the winding is energised the valve plate is attracted towards the shoulder and the end of the core 13, the thickness of the valve plate being less than the thickness of the annulus by a predetermined amount to permit the valve plate 24 to move by said predetermined amount. The movement of the valve plate is arrested by the shoulder and when in this position, fuel can flow through the passage 14, through the apertures 24A to the outlet orifice 22. When the solenoid winding is de-energised the spring 26 returns the valve plate into engagement with the seat elements.

It is the inner seat element 23 which with the valve plate 24, forms the valve which controls fuel flow through the orifice 22. The outer seat element 23A is provided to minimise tilt ing of the valve plate when the solenoid is de energised so as to assure complete cut-off in the supply of fuel through the orifice 22. In order to minimise the risk of the valve plate magnetically "sticking" in the open position, it is prevented from actual contact with the shoulder 18 by a thin spacer element 27 formed from non-magnetic material and this assures a small gap in the magnetic circuit so as to improve the closing characteristic of the valve.Although the valve plate and the associated components of the magnetic circuit are formed in a symmetrical fashion, this does not always guarantee that the valve plate moves away from the seat member in so-called parallel fashion that is to sa maintaining a parallel relationship with the seat member. Sometimes this may occur but at other times it appears that the valve plate can tilt and again it appears that the tilt occurs in a random fashion.

As a result it has been found that the operating characteristics of a given injector can vary.

In order to provide consistent operating characteristics the valve plate can be modified as shown in Figure 3. The first modification is to ensure that the magnetic pull on the valve plate 28 when the solenoid is energised, is unbalanced. This is achieved by, in the particular example, enlarging the diameters of two of the apertures 29 formed in the valve plate and lying to one side of a diameter of the valve plate.As will be seen from Figure 3 the apertures 29 are enlarged to the extent that they overlap the core member 13 and hence the magnetic pull on this portion of the valve plate will be reduced so that there will be a tendency for the left hand portion of the valve plate, as shown in Figure 3, to lift first because of the increased force As a result the valve member is caused to tilt but will eventually assume its fully open position with it being disposed generally parallel to but spaced from the seat member 21.

The tilting effect of the valve plate following energisation of the solenoid is enhanced by relieving the surface of the valve plate presented to the seat member on the opposite side of said dimater and opposite the enlarged apertures 29. This relief of the valve plate indicated at 30 in Figure 3, ensures that there is a reduced tendency for the valve plate to stick to the seat element 23A.

It is desired to promote a similar tilting action when the solenoid is de-energised and this is achieved by relieving the surface of the valve plate which is presented to the shoulder 18 in the region of the enlarged ports 29. The relief is indicated at 31 and it has the effect of further reducing the attraction force between the valve plate and the shoulder 18 so that as the flux decreases upon de-energisation of the solenoid, the valve plate will again tend to tilt in its movement away from the shoulder under the action of the spring.

Figure 4 shows a plan view of the valve plate and it shows the relieved portions 31 associated with the apertures 29, and the relieved portion 30.

The production of the valve plate shown in Figures 3 and 4 can present practial difficulties and a modified version of the valve plate is shown in Figures 5 and 6.

As will be seen from Figures 5 and 6 the two apertures 29 are of enlarged diameter and this when the solenoid is energised causes the valve plate to tilt as it moves away from the seat member and it also causes tilting of the valve plate as it moves to the closed position. The sticking of the valve plate to the seat element 23A is reduced by countersinking the apertures 4A on the face of the valve plate presented fo the seat member. It will be noted that the countersink of the two apertures 24A opposite the apertures 29 is deeper and this is to provide the same effect as the relieved portion 30 in the valve plate of Figures 3 and 4. It should be noted that a short bridge portion 32 remains between the countersinks, this acting to stabilize the final movement of the valve plate to the closed position.

The relieved portions 31 are not provided however, in order to minimise the retention of the valve plate when the solenoid is deenergised the spacer element 27 over that portion which will be engaged by the valve plate is castellated i.e. the inner portion of the spacer element is toothed possibly up to a 50/50 mark/space ration in the case of a non-magnetic metallic spacer element.

In an alternative construction (not shown) the valve plate is of wedge section so that the air gap between the shoulder 18 and the end of the core 13 varies across the valve plate. This again will have the effect of causing an unbalance in the magnetic pull applied to the valve plate when the solenoid is energised.

The modifications to the valve plate as described above, cause the valve plate to tilt as the solenoid is energised and since the modification is carried out on the valve plate the latter will always tilt in the same manner so far as its own axes are concerned even though it may during prolonged operation of the injector, move angularly about the axis of the injector.

Unbalanced magnetic forces can be applied to the valve plate by modifying the face of the shoulder 18 presented to the valve plate, in one region. With this arrangement however there may still be variations in the operating characteristics of the injector although to a lesser extent, because the valve plate can move angularly within the injector body.

Claims

1. A fuel injection for supplying fuel to an internal combustion engine more particularly a petrol injector for supplying fuel to an air inlet manifold of a spark ignition engine comprises a valve seat member having an orifice formed therein and through which fuel can flow from a fuel inlet, an annular seat element defined on the seat member about said orifice, a valve plate biased into contact with said seat ele ment to prevent fuel flow through said orifice and a solenoid which can be energised to lift said valve plate away from said seat element thereby to allow fuel flow through the orifice, the injector being constructed so that upon energisation of the solenoid the magnetic forces acting upon the valve plate will be unbalanced whereby the initial movement of the valve plate away from the seat element will be a tilting movement.

2. An injector according to Claim 1 in which said solenoid includes a central pole piece and an annular pole piece presented to the valve plate.

3. An injector according to Claim 2 in which said valve plate is of wedge section whereby the air gap between the pole pieces and the valve plate in the closed position of the valve plate varies across the valve plate.

4. An injector according to Claim 2 in which a portion of the face of the valve plate presented to the pole pieces and lying on one side of a transverse axis of the valve plate is cut away to reduce the attraction force experienced by said one side of the valve plate.

5. An injector according to Claim 4 in which the valve plate is provided with a series of apertures disposed in a circle, the apertures lying outside the portion of the valve plate which contacts said seat element, one of the apertures lying on said one side of the transverse axis being of enlarged diameter.

6. An injector according to Claim 5 in which the face of the valve plate presented to the pole pieces is relieved over an area extending from said one aperture to the periphery of the valve plate.

7. An injector according to Claims 4, 5 and 6 including a further annular seet element defined on the seat member and which surrounds the first mentioned seat element in spaced relationship, a portion of the face of the valve plate presented to the further seating element and lying on the opposite side of said transverse axis is relieved.

8. An injector according to Claim 7 in which said relief is obtained by countersinking the apertures.

9. A fuel injector for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings as modified by Figures 3 and 4.

10. A fuel injector for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings as modified by Figures 5 and 6.