Fuel Injector

This invention relates to a fuel injector for supplying liquid fuel to an air inlet duct of a spark ignition engine and of the kind comprising a valve seat member in which is formed a discharge orifice and about which on one side of the seat member is formed an annular seating element, a circular plate-like valve member which is urged into engagement with said seating element by means of a spring to prevent flow of fuel through said discharge orifice, an electromagnet which when energized attracts the valve member away from the seating element to allow fuel flow through the orifice and an annular spacer member which surrounds the valve member.

An example of such a fuel injector is seen in European Patent Application Publication No. EP-A-0328277 wherein spring is of the coiled compression type and is located within a bore formed in a central core member of the electromagnet. The bore also serves to convey fuel from an inlet of the injector to adjacent the valve member so that when the latter is lifted from the seating element, fuel can flow through the outlet orifice. The end of the spring adjacent the valve member is located within a recess formed in the adjacent face of the valve member. The base wall of the recess in a practical example of the injector is made parallel to the surface of the valve member which engages the seating element and the rim of the valve member is rounded. A small clearance exists between the rim and the internal surface of the spacer member.

In the use of the injectors it is found that the performance of some injectors is not consistent with the flow of fuel through the injector for a given fuel pressure at the inlet and for a given length of energizing pulse, varying throughout the life of the injector. The variation of fuel delivery is undesirable.

The object of the present invention is to provide an injector of the type specified above, but having a more consistent performance than heretofor knows.

According to the invention in a fuel injector of the type specified the face of the valve member remote from the seating element is provided with a centrally disposed recess and the base wall of the recess or the corresponding wall of an insert located within the recess, and which is engaged by the end of the spring, is inclined to the surface of the valve member which is presented to the seating element, the inclination of the wall resulting in a lateral force being applied to the valve member so as to urge the rim of the valve member into engagement with the internal surface of the spacer member.

An example of an injector in accordance with the invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is an axial cross sectional view of the injector;

FIG. 2 is a view an an enlarged scale of part of the injector seen in FIG. 1; and

FIG. 3 is an enlarged cross-sectional view of part of the injector as seen in FIG. 2 showing a different embodiment of the valve member.

Referring to 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 member 13 through which extends a passage 14 which at the flanged end of the core member is connected to an inlet 12. Surrounding the core member 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 ends of which are connected to terminals in a connector member 18.

The body 11 defines an inwardly extending annular shoulder 19 the face 20 of which remote from the solenoid defines a pole face against which is located a non-magnetic annular washer 21. The washer may be formed from stainless steel. Adjacent the washer there is located an annular non-magnetic spacer member 22 which is engaged by a seat member 23. The seat member is held in position by means of an annular generally tubular outlet member 24 which is secured within the outer body 11. In the example there is located within the outlet member an insert 25 which is provided with a central drilling 26 and an end wall which defines a pair of inclined through holes 27 which terminate in outlets 15.

Formed in the seating member is a central discharge orifice 28 and surrounding the orifice 28 and formed on the face of the seating member presented to the core member 13, is an annular seating element 29. A further annular element 30 is provided on the face of the seating member, the further element 30 surrounding and being spaced outwardly of the seating element 29.

Moveable in the space which is defined between the core member and the seating member is a circular plate-like valve member 31 which is formed from magnetic material. The diameter of the valve member is slightly smaller than that of the circular aperture in the spacer member. The rim of the valve member is rounded and formed in the valve member are a series of angularly spaced openings 32 which are positioned outwardly of the seating element 29. The face of the valve member remote from the core member is carefully machined so as to form a seal with the seating element 29 in the closed position of the valve member.

The valve member is biassed into engagement with the seating element 29 by means of a coiled compression spring 33 which is located in the bore 14. One end of the spring engages a sleeve-like element 34 which is an interference fit in the bore and the other end of the spring is located within a recess 35 which is formed in the face of the valve member 31 presented to the core member 13.

In use, the outlet member 24 is located in the wall of an air inlet duct of a spark ignition engine with the outlets 15 positioned to direct fuel into the individual air inlets of a pair of adjacent engine cylinders or into a pair of air inlets of a single cylinder. When the solenoid winding 17 is energized the central core member 13 and the flange 19 are polarized to opposite magnetic polarity and the valve member is lifted away from the seating element to allow fuel to flow through the orifice 28. The extent of movement of the valve member is limited by its engagement with the washer 21 and the thickness of this washer is so arranged that there is no contact between the core member and the valve member. In the example the fuel which flows through the orifice 28 is directed at the bridge defined between the inner ends of the drillings 27 and fuel sprays issue from the outlets 15 to mix with the air flowing to the combustion chambers. When the solenoid is de-energized the valve member moves under the action of the spring 33 to reestablish seating engagement with the seating element 29 so that fuel flow through the orifice 28 is prevented. Owing to the slight difference in the diameter of the valve member 31 and the aperture in the spacer member 22 a small gap exists therebetween and the rim of the valve member is curved so that there is minimum interference to the movement of the valve member when the solenoid is energized. In the past the base wall of the recess 35 has been made parallel to the surface of the valve member which engages the seating element 29. It has been found however that over the life of the injector the quantity of fuel which flows through the injector for a given length of energizing pulse and a given fuel pressure at the inlet, tends to increase. It has been found however that by inclining the base wall of the recess 35 relative to the surface of the valve member which engages the seating element 29, the aforesaid effect can be minimized.

The range of inclination of the base wall of the recess can lie between 6.degree. and 16.degree.. The effect of inclining the base wall of the recess is to cause the spring 33 to exert a side thrust on the valve member 31 so that at one point the rim of the valve member engages with the spacer member 22. Excessive side thrust has to be avoided and above the upper limit of inclination quoted there is a tendency for the valve member as it moves away from the seating element under the influence of the magnetic field, to lift in a series of jerks so that variation in the dynamic fuel flow can occur. With an inclination below the minimum quoted, there is no worthwhile improvement. The optimum value appears to be 12.degree. of inclination. As illustrated in FIG. 2, the base wall of the recess is inclined. However, there can be located between the spring and the base wall of the recess a wedge like insert 36, as shown in FIG. 3, having inclined surface 35' thereon to provide the required effective inclination. In the example the valve member has a diameter which lies between 8.95 mm and 8.925 mm and the internal diameter of the spacer member 22 lies between 9.0 mm and 8.975 mm. The thickness of the spacer member 22 is adjusted so that the movement of the valve member away from the seating element is between 35 and 75 microns depending on the fuel flow required.