GB2226078A

GB2226078A - C.i. engine fuel injection nozzle

Info

Publication number: GB2226078A
Application number: GB8826229A
Authority: GB
Inventors: David John Cunningham Law
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1988-11-09
Filing date: 1988-11-09
Publication date: 1990-06-20
Also published as: GB8826229D0

Abstract

A valve member 17 forms a pivot on the axis of movement of the valve member for a beam 23. A spring 25 acts on the beam at a position offset from the pivot and in the closed position of the valve member 17 one end of the beam adjacent the spring engages a first stop surface and the other end of the beam is clear of a second stop surface. The initial movement of the valve member away from the seating to allow restricted flow of fuel through an outlet, pivots the beam about its one end until its other end engages the second stop surface and with increasing fuel pressure the valve member moves to allow unrestricted flow of fuel during which the beam pivots about its other end. <IMAGE>

Description

FUEL INJECTION NOZZLES This invention relates to a fuel injection nozzle of the inwardly opening type, for supplying fuel to a compression ignition engine the nozzle being of the kind comprising a fuel pressure operable valve member which is slidable within a bore, a seating defined in the bore, the valve member being shaped for engagement with the seating and being resiliently biased into engagement therewith to prevent flow of fuel through an outlet from an inlet, the valve member being lifted from the seating to allow fuel flow through the outlet when the fuel pressure at the inlet rises to a predetermined value.

It is known that some engines benefit by having the initial flow of fuel to the combustion spaces of the engine taking place at a restricted rate. Various forms of nozzle are known to achieve this object. In one form the resilient means biasing the valve member comprises a pair of springs one of which is brought into action to restrain the movement of the valve member only after the latter has moved through a predetermined distance. The movement of the valve member through the predetermined distance allows fuel flow through the outlet at restricted rate. In another form of nozzle a single spring is utilised and the movement of the valve member through the predetermined distance is assisted by a piston the final movement of the valve member being under the action of fuel pressure acting on the valve member alone.In another form of nozzle a single spring is utilised and a piston is provided which is effective after the valve member has moved through the predetermined distance, to assist the spring in opposing further movement of the valve member.

The nozzle constructions outlined above are expensive either because of the additional spring and the extra space which must be found for the spring or because of the piston and cylinder which require accurate machining together with the additional space required therefore.

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

According to the invention a fuel injection nozzle of the kind specified comprises a beam pivotally mounted intermediate its ends, on the valve member, a spring acting on the beam at a position offset from the pivot point, a first stop surface engaged by one end of the beam when the valve is in the closed position and a second stop surface for engagement by the other end of the beam, the arrangement being such that when fuel under pressure is applied to the valve member the valve member will cause the beam to pivot about the point of engagement of the one end of the beam with said first stop surface until the other end of the beam engages said second stop surface said valve member moving through a predetermined distance to allow restricted flow of fuel through the outlet, and with an increase in pressure the valve member moving further to cause the beam to pivot about the point of engagement of the other end of the beam with said second stop surface, the further movement of the valve member allowing substantially unrestricted flow of fuel through the outlet.

In the accompanying drawings: Figure 1 is a part sectional side elevation showing part of a fuel injection in accordance with the invention.

Figure 2 is a view similar to Figure 1 showing a modified form of nozzle, Figure 3 is a sectional plan view of the nozzle seen in Figure 1, Figures 4 and 5 show alternative forms for part of the nozzle, and Figure 6 in the three views illustrates the nozzle of Figure 1 with the valve member in the closed position, in the partly open position and in the fully open position.

Referring to Figure 1 of the drawings the nozzle comprises a nozzle body 10 which is secured to a nozzle holder 11 in any convenient manner for example by means of the usual form of cap nut. Interposed between the nozzle body and the nozzle holder is a beam housing 12 and as will be seen from Figure 3, the beam housing is provided with a generally rectangular opening 13 therethrough.

Formed in the nozzle body is a bore 14 which has an enlargement 15 intermediate its ends and at its end removed from the beam housing there is defined a seating 16 about an outlet orifice (not shown).

Slidable in the bore 14 is a valve member 17 which at its end remote from the seating is provided with an extension 18 of reduced diameter and having a generally part-spherical surface. The portion of the valve member intermediate the enlargement and the seating is of reduced diameter as compared with the adjacent portion of the bore and the enlargement 15 is in communication with a passage 19 which extends to the face of the nozzle body presented to the beam housing.

The beam housing is provided with a connecting passage 20 which forms a connection between the passage 19 and a fuel inlet passage 21 in the holder. The passage 21 in use, is connected to the outlet of a high pressure fuel injection pump driven by the associated engine.

As shown in Figure 3, the beam housing is provided with through apertures 22 which serve to accommodate dowels (not shown) extending between the nozzle body and the holder.

Located within the opening 13 in the beam housing is a pivotal beam 23, the beam being pivotally located intermediate its ends, upon the spherical surface of the extension 18. On the face of the beam remote from the nozzle body and at a position offset from the pivotal axis of the beam, there is provided a location 24 about which is located one end of a coiled compression spring 25 which is accommodated within a longitudinal recess 26 formed in the holder and offset relative to the axis thereof.

The operation of the nozzle thus far described will now be explained with reference to Figure 6.

Figure 6A shows the nozzle with the valve member in the closed position and corresponds with Figure 1. It will be noted that one end of the beam is in engagement with the end surface of the nozzle body which will hereinafter be referred to as the first stop surface 27.

The other end of the beam is spaced by a small distance, from the end surface of the holder which will hereinafter be referred to as the second stop surface 28. When fuel under pressure is supplied to the enlargement a force acts upon the valve member tending to lift the valve member away from the seating. This force is opposed by the spring 25 and when the force developed by the fuel pressure acting on the valve member becomes high enough, the force exerted by the spring is overcome and the valve member is lifted from the seating. During the movement of the valve member away from the seating the beam pivots about its point of engagement with the stop surface 27 and the movement of the valve member continues until as shown in Figure 6B, the other end of the lever contacts the stop surface 28.In this position both the one end and the other end of the beam are in engagement with the respective stop surfaces and the movement of the valve member away from the seating is sufficient to allow fuel flow to the engine at a restricted rate. It will be noted that during this movement the valve member has a higher lever ratio than the spring.

As the pressure of fuel delivered by the injection pump increases, the valve member will exert an increased force against the beam and eventually the force will be sufficient to cause movement of the beam against the action of the spring to the fully open position of the valve member as seen in Figure 6C.

During this phase of movement the lever pivots about its point of engagement with the second stop surface 28 and the movement of the valve member is limited when the one end of the lever engages the stop surface 28.

It will be understood that during the second phase of movement the spring has the higher lever ratio and therefore there will have to be a substantial increase in the fuel pressure before the valve member can move to its fully open position.

The clearance which exists between the other end of the lever and the stop surface 28 determines the extent of the limited movement of the valve member away from its seating and the latter will be less than the aforesaid clearance.

It will be appreciated that the force exerted by the spring determines the initial fuel pressure required to lift the valve member from its seating and also the fuel pressure required to move the valve through its second phase of movement. If it is required to vary the difference between the two pressures for a given initial spring force, the various lever ratios must be altered. For example, if the line of action of the spring is moved towards the pivot, the difference will be reduced.

The nozzle which is shown in Figure 2, is substantially identical to that which is shown in Figure 1 with the exception that a spacer member 29 is interposed between the nozzle body 10 and the beam housing 12. In this example the surface of the spacer member defines the first stop surface. It will also be noted that the spacer member has a central drilling through which extends the extension 18 of the valve member. In this case the extension is of longer length.

Moreover, the aperture in the spacer member is smaller in diameter than the valve member 17 so that the spacer member forms the stop to limit the maximum movement of the valve member away from its seating.

In the nozzle shown in Figures 1 and 2 the passage 20 is formed in a relatively weak portion of the beam housing. The fuel is supplied at high pressure and therefore may cause distortion of the wall of the housing. This can be minimised as shown in Figure 4, by altering the shape of the beam and the opening in the housing to enable the wall thickness about the passage 20 to be increased. Alternatively, as shown in Figure 5, the passage 20 can be repositioned, such repositioning also requiring repositioning of the passages 19 and 21. In this case the apertures 22 for the dowels are also repositioned.

By the arrangement described a single spring only is required to provide for two stage opening of the valve member of the injection nozzle. Moreover, the need to provide pistons or sleeves which are also subjected to the fuel pressure at the inlet of the nozzle, is avoided.

As shown, the spring 25 will tend to bow so that some of the coils of the spring will rub on the surface of the recess 26. The recess can be enlarged or shaped to avoid such contact. As an alternative the location 24 can be in the form of a separate flanged spring abutment which has a knife edge connection with the beam or the latter may be provided with a peg having a part spherical end surface, the abutment having a complementary surface.

Claims

1. A fuel injection nozzle of the inwardly opening type, for supplying fuel to a compression ignition engine, the nozzle comprising a fuel pressure operable valve member movable in a bore in which is defined a seating with which one end of the valve member engages to prevent flow of fuel from an inlet to an outlet, a pivot defined at the other end of the valve member, said pivot being aligned with the axis of movement of the valve member, a beam pivotally mounted intermediate its ends on the pivot, resilient means acting on the beam at a position offset from the pivot point, the resilient means biasing the valve member into engagement with the seating, a first stop surface engaged by one end of the beam when the valve member is in engagement with the seating, a second stop surface for engagement by the other end of the beam, the arrangement being such that when fuel under pressure acts on the valve member to cause movement thereof away from the seating the valve member will cause the beam to pivot about its point of engagement with the first stop surface until said other end of the beam engages said second stop surface, the valve member moving through a predetermined distance to allow restricted flow of fuel through the outlet, and with an increase in the fuel pressure the valve member moving further to pivot the beam about its point of engagement with the second stop surface, the further movement of the valve member allowing substantially unrestricted flow of fuel through the outlet.

2. A nozzle according to Claim 1 in which the beam is located within an opening extending through a housing located between a nozzle body which defines the bore, an d a nozzle holder.

3. A nozzle according to Claim 2 in which the resilient means is in the form of a coiled compression spring which is located in a chamber formed in the holder.

4. A nozzle according to Claim 2 or Claim 3 including a spacer member positioned between the nozzle body and the housing, said spacer member acting as a stop to limit the movement of the valve member away from the seating.

5. A fuel injection nozzle for supplying fuel to an internal combustion engine substantially as described with reference to Figure 1 of the accompanying drawings.

6. A fuel injection nozzle for supplying fuel to an internal combustion engine substantially as described with reference to Figure 2 of the accompanying drawings.