GB2104957A

GB2104957A - I.C. engine fuel injection nozzles

Info

Publication number: GB2104957A
Application number: GB08222499A
Authority: GB
Inventors: Dorian Farrar Mowbray
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1981-08-21
Filing date: 1982-08-04
Publication date: 1983-03-16

Abstract

The spring biasing force of the fuel pressure operated valve 12 is increased to assist valve closure by the engine driven cam 23 which moves the spring abutment 21. In a pump and nozzle unit, Fig. 3 (not shown), the spring abutment 21 is moved by a rod (34) which is engaged by the cam operated pumping plunger (27). The abutment 21 may be associated with one of a pair of biasing springs, Fig. 2 (not shown). <IMAGE>

Description

SPECIFICATION Fuel injection nozzles This invention relates to a fuel injection nozzle through which liquid fuel can be supplied to the combustion space of a compression ignition engine, the nozzle including a fuel pressure operable valve member which is lifted from a seating against the action of resilient means to allow fuel to flow through an outlet.

Such nozzles are well known in the art and the outlet is in the form of a small drilling or a number of such drillings. In use, when the supply of fuel to the nozzle ceases the valve member should move into contact with the seating as quickly as possible to prevent combustion gases flowing through the drilling or drillings. If flow of such gases does take place the drilling or drillings and also the space downstream of the seating from which the drilling or drillings extend, will become coated with carbon deposits which will impair the operation of the nozzle. It is advantageous so far as the performance of the engine is concerned to reduce the period of fuel delivery and this is achieved by using high injection pressures with rapid rates of rise and fall of the pressure.As the pressure falls quickly so the valve member must move quickly into contact with the seating to prevent the flow of combustion gases through the drilling or drillings.

It is an object of the present invention to provide a fuel injection nozzle of the kind set out about, in which the desideratum is achieved.

According to the invention a fuel injection nozzle of the kind specified comprises a cam follower operable by a cam driven in use by the associated engine, said cam follower acting to increase the resilient loading applied to the valve member at least when the valve member is required to move into contact with the seating.

Examples of fuel injection nozzles in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sectional side elevation of one example of the nozzle, Figure 2 shows a modification to the nozzle shown in Fig. 1 and Figure 3 shows a nozzle combined with a fuel pump.

Referring to Figure 1 of the drawings the fuel injection nozzle comprises a body part 10 in which is formed a bore 11 which accommodates a slidable valve member 12. A portion of the bore 11 intermediate its ends, is enlarged to form an inlet chamber 1 3 which is connected to a fuel inlet passage 14 this in use, being connected to an outlet of a fuel injection pump. The bore defines a seating which the shaped end 1 5 of the valve member can co-operate to prevent flow of fuel through outlets 1 6 constituted by small diameter drillings. The drillings communicate with what is known in the art as the "sac" this being disposed downstream of the seating.

At its other end the bore has an opening into a spring chamber 1 7 in which is located a coiled compression spring 18 which at one end, bears against an abutment 1 9 which is located on a reduced end portion of the valve member 12. The chamber 17 is in communication with a drain by way of a passage 20 and in use, when fuel is supplied under pressure through the passage 1 4, the fuel pressure acting upon the reduced portion of the valve member 12 creates a force which opposes the closing force exerted by the spring 18. When the force due to the fuel pressure is sufficient, the valve member moves away from ihe seating to permit flow of fuel through the outlets 1 6.This flow of fuel will continue until the output pressure of the fuel pump falls at the end of the delivery of fuel. The valve member 12 then moves under the action of the spring 1 8 into contact with its seating.

In order to move the valve member 12 quickly into contact with its seating to prevent combustion gases flowing through the outlets 1 6 into the sac the spring 1 8 at its end remote from 'the abutment 1 9 engages a further abutment 21 which is actuated by a cam follower 22. There is also provided an engine driven cam 23. This is positioned to engage with the cam follower 22 and is shaped to urge the cam follower 22 in the direction to compress the spring 18 at least during the time when the valve member is to be moved to the closed position. In this manner an increased force is applied to the valve member to urge it to the closed position thereby ensuring that the valve member will move more quickly into contact with its seating.

In the arrangement shown in Figure 2 the spring 1 8 engages a fixed abutment at its end remote from the abutment 1 9. In this case however an additional spring 24 is provided which engages the abutment 21 and it is the force exerted by this spring which normally supplements the force exerted by the spring 18, and which is increased by movement of the cam follower 22.

Turning now to Figure 3 there is shown what is known in the art as a pump/injector. The nozzle portion generally indicated at 25, has the same construction as the nozzle shown in Figure 1. The pump/injector includes a further bore 26 in which is located a pumping plunger 27 and the pumping chamber 28 defined by the bore and the plunger communicates with the passage 1 4 of the nozzle.

Also provided and coupled to the plunger 27, is a cam follower which includes a cup-shaped member 29 which mounts a roller 30 for engagement with an engine driven cam 31. A spring 32 is provided to maintain contact between the roller 30 and the cam and to urge the plunger outwardly after delivery of fuel has ceased.

The bore 26 is provided with a fuel inlet port 33 which port is covered by the plunger 27 during its inward movement. As soon as the port is covered then the fuel in the pumping chamber 28 will be pressurised and will flow along the passage 1 4 to actuate the valve member of the nozzle in the manner described. In order to assist closure of the valve member of the nozzle the abutment 21 of the spring Is engaged by a push rod 34 which is contacted by the plunger 27 towards the end of its stroke. In this manner the force exerted by the spring 1 8 on the valve member of the nozzle is increased at the time when the delivery of fuel cases. The diameter of the push rod 34 is such that the force developed on the push rod by the pressure of fuel in the pumping chamber is less than the force exerted by the spring 1 8 in the closed position of the valve member of the nozzle.

If desired, the nozzle portion 25 of the pump/injector may have the additional spring 24 shown in Figure 2.

Claims

1. A fuel injection nozzle through which liquid fuel can be supplied to a combustion space of a compression ignition engine, the nozzle comprising a fuel pressure operable valve member, resilient means biasing the valve member into contact with a seating, fuel under pressure acting on the valve member to lift the valve member from the seating to allow fuel to flow through an outlet, a cam follower operable in use by a carn driven by the associated engine, said cam follower acting to increase the resilient loading applied to the valve member when the valve member is required to move into contact with the seating.

2. A nozzle according to claim 1 in which said resilient means comprises a coiled compression spring, an abutment for said spring, said cam follower acting to move said abutment in order to increase the force exerted by said resilient means.

3. A nozzle according to claim 2 including a further coiled compression spring acting to bias the valve member into contact with the seating.

4. A nozzle according to claim 2 in which said cam follower is directly connected to said abutment.

5. A nozzle according to claim 2 including a fuel pumping plunger operable by said cam follower, a bore in which the plunger is mounted, passage means connecting the bore with an inlet of said nozzle, a push rod extending into said bore, said push rod engaging with said abutment, said push rod being engaged by said plunger towards the end of the inward movement of the plunger to effect movement of the push rod and abutment in a direction to increase the resilient loading applied to the valve member.

6. A nozzle according to claim 5 in which the diameter of said push rod is such that the force exerted on the push rod by the fuel pressure in said bore is less than the force exerted by said coiled compression spring in the closed position of the valve member.

7. A fuel injection nozzle through which liquid fuel can be supplied to the combustion space of a compression ignition engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.