GB2227282A

GB2227282A - C.i. engine fuel injection nozzle

Info

Publication number: GB2227282A
Application number: GB8901335A
Authority: GB
Inventors: David John Gaskell
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1989-01-21
Filing date: 1989-01-21
Publication date: 1990-07-25
Also published as: GB8901335D0

Abstract

A fuel pressure actuated valve member (14, Fig. 3) is urged into contact with an annular seating (12) by the action of two springs 23, 25 which are connected in series. The spring 23 is a low rate spring and a stop 29 is provided to limit its deflection as the valve member moves to the open position. The spring 25 is a high rate spring. The valve member and the seating are constructed so that the additional area of the valve member which is exposed to fuel pressure when the valve member is lifted from the seating is minimised. The springs may be arranged one within the other (Fig. 2). <IMAGE>

Description

FUEL INJECTION NOZZLE This invention relates to fuel injection nozzles for supplying fuel to a compression ignition engine and of the kind comprising a fuel pressure operable valve member having one end shaped for co-operation with a seating, the valve member being resiliently biased into engagement with the seating to prevent flow of fuel through an outlet from an inlet, the valve member defining a surface against which fuel under pressure from the inlet can act to lift the valve member from the seating to allow fuel flow through the outlet.

The conventional form of nozzle has a single spring and the valve member defines an annular step which defines an annular surface which is always exposed to the fuel pressure at the inlet. In addition, the area of the end of the valve member which lies outside the seating is exposed to the pressure at the inlet and it is the sum of these two areas together with the force exerted by the spring when the valve member is in contact with the seating, which determines the pressure of fuel which is required to lift the valve member from the seating. As soon as the valve member is lifted from the seating the whole of the end area of the valve member is exposed to fuel under pressure and an increased force is applied to the valve member which will have the effect of further lifting the valve member from the seating.

In the past this effect was considered to be advantageous. However, modern engines in the interests of increased efficiency and reduced engine noise have a higher fuel injection pressure but at the same time require the initial quantity of fuel to be delivered at a restricted and carefully regulated rate.

One way of adapting the conventional nozzle is to increase the rating of the spring. A problem which follows from this step is the variation of the pressure required to lift the valve member from the seating which occurs in the use of the nozzle. Such variation can be due to wear of the valve member and the seating and slight relaxation of the spring. Since the spring has a high rate any variation in the effective spring length will result in a substantial variation in the force exerted by the spring and therefore a substantial variation of the nozzle opening pressure.

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

According to the invention a fuel injection nozzle of the kind specified comprises a pair of springs connected in series and acting on the valve member to urge it into contact with the seating, one of said springs having a high rate and the other a low rate, means for limiting the extent of deflection of the low rate spring and the end of the valve member which cooperates with the seating and the seating, being designed so that the increase of the area of the valve member exposed to the fuel pressure when the valve member is lifted from the seating, is minimised.

Examples of fuel injection nozzle in accordance with the invention will now be described with reference to the accompanying drawings in which: Figures 1 and 2 show part sectional side elevations of parts of two examples of nozzle in accordance with the invention, and Figure 3 is a similar view showing the remaining part of the nozzle.

Referring to Figures 1 and 3 of the drawings, the fuel injection nozzle comprises a nozzle body 10 in which is defined a bore 11. At one end of the bore there is defined a seating 12 which is of an annular form and surrounds an outlet orifice 13. Slidable within the bore is a valve member 14 which at one end is shaped for cooperation with the seating 12, the relative angles of the end of the valve member and the seating being such that the line of contact between the end of the valve member and the seating lies close to the outlet. The valve member is of stepped form and an annular space 15 is defined between the narrower portion of the valve member and the bore 11, the space communicating with one end of a passage 16 which extends to the wider and flanged end of the body 10.

The valve member is provided with an extension 17 of reduced diameter which extends from the bore.

The nozzle body is mounted at one end of a cylindrical elongated holder 18, the body being retained relative to the holder by the usual form of cap nut not shown. The extension 17 of the valve member extends into the chamber 19 defined in the holder and the passage 16 communicates with a passage 20 formed in the holder and opening to a fuel inlet 21 formed in the side wall thereof. In use, the inlet 21 is connected to an outlet of a fuel injection pump.

Within the chamber 19 there is located a spring abutment 22 which is mounted upon the extension 17 and engaged with the abutment is one end of a low rate coiled compression spring 23. The other end of the spring engages one face of an intermediate plate 24 against the other face of which is engaged one end of a high rate spring 25. The other end of the spring 25 is engaged with an adjustable plug 26 which is in screw threaded engagement with the wall of the chamber 19. A lock nut 27 is provided to secure the plug 26 once adjustment as will be explained, has been effected.

The intermediate plate 24 mounts an axially adjustable rod 29 the free end of which extends to adjacent the abutment 22.

The two springs are effectively connected in series and assuming as shown, that in the closed position of the valve member there is a clearance between the rod 29 and the spring abutment 22, when fuel under pressure is supplied to the inlet the fuel pressure will act upon the area of the step which forms an end wall of the space 15 and also upon the end area of the valve member which lies outside the zone of contact between the valve member and the seating. A force will therefore be developed upon the valve member which will be opposed by the force exerted by the springs. When the fuel pressure is sufficiently high the valve member will be lifted from its seating and fuel will flow through the outlet orifice 18.The increase in the area of the valve member exposed to the fuel pressure will be very small and therefore there will only be a small increase in the force acting on the valve member. Moreover, the movement of the valve member will cause deflection of both springs but primarily the low rate spring 23. The extent of deflection of the low rate spring is limited by the engagement of the spring abutment 22 with the rod 29 and further movement of the valve member as the pressure of fuel supplied to the inlet increases, will be against the action of the high rate spring 25.

The nozzle opening pressure that is to say the fuel pressure which is required to lift the valve member from its seating, is adjusted by means of the plug 26 and the extent of deflection of the low rate spring 23 is adjusted by adjustment of the rod 29 relative to the intermediate plate 24.

As wear takes place the gap between the spring abutment and the rod 29 in the closed position of the valve member will increase, however, since the spring 23 is a low rate spring there will be only a small reduction in the force exerted upon the valve member to maintain it in the closed position. As a result the nozzle opening pressure will not be lowered by any significant extent. If the high rate spring 25 relaxes then this will also tend to increase the aforesaid gap but again due to the presence of the low rate spring, the force acting upon the valve member will not be reduced by any significant amount.

Figure 2 shows a modification to the arrangement shown in Figure 1 and essentially the two springs are located one within the other. The low rate spring engages the spring abutment 30, this being mounted upon the extension 17 of the valve member. The opposite end of the low rate spring 23 engages a member 31 which is adjustably mounted in the base wall of a stirrup 32 which has an outwardly extending flange 33 which is engaged by one end of the high rate spring 25. The opposite end of this spring engages an adjustable plug 26 and the operation of the nozzle is exactly the same as described with reference to Figure 1 except that the spring abutment 30 engages with the flange 33 of the stirrup to limit the deflection of the low rate spring 23. The adjustment of the member 31 relative to the stirrup determines the extent of the clearance between the flange 33 and the abutment 13 once the nozzle opening pressure has been set by adjustment of the plug 26.

The gap in the aforesaid examples could be such as to provide a two stage lift injector nozzle but in the case as described it is preferable that the gap be kept to a minimum.

Claims

1. A fuel injection nozzle for supplying fuel to a compression ignition engine comprising a fuel pressure operable valve member having one end shaped for cooperation with a seating, resilient means biasing the valve member into engagement with the seating to prevent flow of fuel through an outlet from an inlet, the valve member defining a surface against which fuel under pressure from the inlet can act to lift the valve member from the seating to allow fuel flow through the outlet, said resilient means comprising a pair of springs connected in series, one of said springs having a high rate and the other a low rate, means for limiting the extent of deflection of the lower rate spring and the end of the valve member which co-operates with the seating and the seating, being arranged so that the increase in area of the valve member which is exposed to the fuel under pressure as the valve member is lifted from the seating is minimized.

2. A nozzle according to Claim 1 in which one end of the lower rate spring is carried by a spring abutment mounted on the valve member and the other end of the lower rate spring engages an intermediate plate member engaged by one end of the higher rate spring, said plate member mounting an adjustable stop engageable with said abutment to limit the deflection of the lower rate spring.

3. A nozzle according to Claim 1 in which one end of the lower rate spring is carried by a spring abutment mounted on the valve member, a stirrup member which surrounds the lower rate spring and has an outwardly extending flange engaged by one end of the higher rate spring, said stirrup member mounting an adjustable abutment member engaged by the other end of the lower rate spring, said spring abutment being engageable with said stirrup member to limit the deflection of the lower rate spring.

4. A fuel injection nozzle for supplying fuel to a compression ignition engine substantially as hereinbefore described with reference to Figures 1 and 3 of the accompanying drawings.

5. A fuel injection nozzle for supplying fuel to a compression ignition engine substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.