GB2144201A

GB2144201A - Fuel injector valve seat

Info

Publication number: GB2144201A
Application number: GB08415516A
Authority: GB
Inventors: Stuart Michael Barlow; John Herbert Kenning
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-07-28
Filing date: 1984-06-18
Publication date: 1985-02-27
Also published as: GB8415516D0; GB2144201B

Abstract

A fuel injector includes a plate type valve member 34 formed from magnetizable material which is movable away from a valve seat member 30 to allow flow of fuel through the injector. The movement is effected by energising a solenoid. The valve seat member 30 is formed from a plastics material to avoid magnetic disturbance, to facilitate manufacture and to minimise cavitation damage. <IMAGE>

Description

SPECIFICATION Fuel injector This invention relates to a petrol injector for supplying fuel to an air inlet manifold of an internal combustion engine, the injector being of the kind comprising a hollow body, a valve seat member supported at one end of the body, the seat member having formed therein an outlet orifice, a plate valve member movable into engagement with the seat member to prevent flow of fuel through the outlet orifice, said plate valve member being formed from magnetizeable material and a solenoid housed within the body said solenoid having a pair of pole faces disposed adjacent the valve member and which assume opposite magnetic polarity when a solenoid winding is energised thereby to create a magnetic force to lift the valve member away from the valve seat member.

It has been the practice to form the valve seat member from steel but it has been found that the seat member influences the movement of the valve member due partly to the fact that eddy currents due to the changing magnetic field, flow in the seat member. Moreover, the seat member being formed from heaty treated steel, can become permanently magnetized. In addition it is necessary to machine the seat member to a high degree of accuracy in order to ensure a fuel tight seal with the valve member. Also in use, cavitation of the fuel can take place on the surface of the seat member which can cause erosion of the surface.

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

According to the invention a petrol injector of the kind specified is characterised in that the valve seat member is formed from a plastics material.

The accompanying drawing is a sectional side elevation of one example of a petrol injector in accordance with the invention.

With reference to the drawing the injector comprises a body part which is formed in two parts 10, 11. The part 10 of the body is of cup shaped form having a side wall 13 and a base wall 14. The body part 10 is formed from magnetizeable material and has a groove formed in its outer peripheral surface in which is located a sealing ring 15 which in use forms a fuel tight seal with the wall of a bore formed in the inlet manifold of the associated engine.

In the base wall 14 of the body part 10 is formed an aperture 16 and extending within the aperture is a hollow stem 17 formed from magnetizeable material. The stem is provided with a collar 18 which is a snug fit within the open end of the body part 10 and is secured therein by welding. Surrounding the stem 17 is a former 19 conveniently formed from plastics material, about which is wound a winding 20. The ends of the winding are connected to a pair of terminal posts 21 which are moulded into the former and which extend through apertures in the collar 18. The winding 20 is sealed against the fuel by a first sealing ring 22 located between the former and the base wall 14 and a second sealing ring 23 located between the former and the stem adjacent the collar.

The stem 17 extends beyond the collar and within the stem is a plug 24 which forms an abutment for one end of a coiled compression spring 25 which extends within the stem. The plug 24 is a push fit within the stem and forms a fuel tight seal with the wall thereof.

The body part 11 is also of cup shaped form but has a shorter side wall 26 than that of the body part 10. In its base wall 27 is formed a diverging outlet 28 and about a reduced portion of the base wall is located a sealing ring 29 which co-operates with the wall of the bore in the manifold in which the injector is located. The bore intermediate the sealings rings 15 and 29 defines a fuel inlet passage connected to a source of fuel under pressure.

Located against the base wall of the body part 11 is a valve seat member 30 in which is formed an outlet orifice 31. A sealing ring 32 is located in a groove in the base wall so as to establish a fuel tight seal between the base wall and the seat member 30. Located against the inner face of the valve seat member is an annular guide member 33 which guides the movement of a disc like valve member 34 formed from magnetizeable material.

The valve member is biased towards the seat member by the aforesaid spring, the valve member being provided with a recess to locate the end of the spring. The seat member on its face presented to the valve member defines a pair of annular ribs, the inner rib 35 forms a seating for the valve member and the outer rib 36 acts to minimize the risk of the valve member tilting as it moves into contact with the seating formed by the inner rib. The guide member 33 is preferably formed from stainless steel.

The valve member is provided with a plurality of through holes 37 which lie outside the inner rib 35 and these holes in the particular example allow fuel flow from a space 38 through the outlet orifice when the valve member is lifted away from the inner rib 35.

The body part 11 is secured to the body part 10 by welding indicated at 39 and to provide accurate location of the body parts a tongue and groove connection is provided. In the example the body part 10 is provided with an annular groove 39A and the body part 11 with an annular tongue or rib 40. Moreover, before the parts are secured together a non magnetic washer 41 is positioned between the guide member 33 and the adjacent surface of the base wall 14.

Fuel is communicated to the space 38 from the exterior of the body by way of a pair or more slots 42 which are formed in the base wall 14 and the fuel entering the slots is filtered by an annular filter 43 which conveniently is formed from plastics material and which is engaged about the body. The filter has openings which are covered by a filter net.

In operation, when the winding is supplied with electric current, the base wall 14 and the stem are polarized to opposite magnetic polarity and the valve member 34 is lifted against the action of the spring 25 away from the rib 35 to permit fuel flow through the outlet orifice 31, the fuel passing through the holes 37 in the valve member. When the solenoid winding is de-energised the valve member returns into contact with the rib to halt the flow of fuel under the action of the spring, the washer 41 acting to minimize the possibility of the valve member "sticking" due to remanent magnetic flux.

The valve seat member 30 may be formed from steel but it is more conveneint to form it from nonmagnetic material such as a plastics. This has a number of advantages so far as performance and also manufacture are concerned.

If the valve seat member is formed from steel since it is connected to the base wall 14 of the body part 10 it does become magnetized when the solenoid winding is energized. The fluctuating magnetic field induces eddy currents in the valve seat member thereby reducing the performance of the solenoid. Moreover, it is found that a heat treated steel seat member tends to become permanently magnetized in use.

The plastics seat member can be formed by a moulding operation with no finishing required. In the case of the steel seat expensive machining and heat treatment are required. Moreover, although the plastics may be hard it is nevertheless slightly flexible and it can withstand cavitation of the fuel which will erode a metal surface.

Examples of plastics which can be used to form the seat member are acetal, polyimide, polyether sulphone, polycarbonate and phenolics. These may be filled or unfilled. One particular form of plastics which has been used in the manufacture of the valve seat member is that sold under the trade name "Vespel" by the DuPont Corporation, this being a thermosetting polyimide.

Claims

1. A petrol injector for supplying fuel to an air inlet manifold of an internal combustion engine, the injector being of the kind comprising a hollow body, a valve seat member supported at one end of the body, the seat member having formed therein an outlet orifice, a plate valve member movable into engagement with the seat member to prevent flow of fuel through the outlet orifice, said plate valve member being formed from magnetizeable material and a solenoid housed within the body said solenoid having a pair of pole faces disposed adjacent the valve member and which assume opposite magnetic polarity when a solenoid winding is energised thereby to create a magnetic force to lift the valve member away from the valve seat member, characterized in that the valve seat member is formed from a plastics material.

2. A petrol injector according to Claim 1 in which the valve seat member is formed by a moulding operation.

3. A petrol injector according to Claim 2 in which the material forming the valve seat member is a thermosetting polyimide.

4. A petrol injector comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.