GB2073315A - Fuel injection nozzle unit - Google Patents

Abstract

In a fuel injection nozzle unit of the type having an outwardly opening spring bias closed valve member including a stem 21 and a head 20 for co-operation with a seating 19, the valve is prevented from 11 opening too rapidly by the stem mounting a piston 28 which cooperates with the interior surface of the surrounding body of the unit. The piston is acted upon by fuel under pressure supplied through an inlet 14 and displaces fuel through an outlet defined by the head and the seating. Valve means defined in part by the piston operates to allow fuel flow from the inlet to the outlet when the stem reaches the limit of its travel. <IMAGE>

Description

SPECIFICATION Fuel injection nozzle units This invention relates to a fuel injection nozzle unit of the kind intended to supply fuel to the combustion chamber of an internal combustion engine, and comprising a hollow body part defining an outlet passage in an end wall thereof, a seating defined in the outlet passage, a valve member having a stem and a head, said head being shaped for co-operation with said seating and being located within said outlet passage, the stem extending into the hollow body part, a resilient means acting on said stem to urge the head into contact with the seating, a fuel inlet to the interior of said body part and through which in use, liquid fuel is supplied to the interior of the body part, the pressure of fuel acting on said valve member to urge the valve member against the action of said resilient means thereby to lift the head from the seating, the head moving in a direction towards the exterior of the nozzle unit, the head and outlet passage defining an annular flow path through which liquid fuel can flow from the interior of the body part, and the cross sectional area of said flow path varying as the head moves away from the seating.

Such nozzle units are well known in the art and one reason for constructing the valve head and the outlet in a manner such that the area of the flow path varies, is to control the rate of delivery of fuel through the nozzle unit.

Usually it is arranged that the initial area of the flow path is small and remains small until the head has moved a predetermined distance away from the seating whereafter the area increases either in steps or at a constant rate as the distance increases.

In use the nozzle unit is supplied with fuel by an engine driven pump which may include a cam and a pumping plunger. The rate of delivery of fuel by the pump for a given engine speed depends upon the design of the cam and the rate of delivery of fuel through the nozzle therefore besides depending upon the design of the cam also depends upon the area of the flow path. The area of the flow path depends upon the position of the valve member.

The rate of delivery of fuel to certain types of compression ignition engine particularly the initial rate of delivery of fuel, is very important and even though the valve member and the outlet may be shaped to define a small area and hence a restricted flow of fuel at the start of fuel delivery, it sometimes happens that the valve member moves to the fully open position too quickly with the result that the initial rate of delivery of fuel is too high. The reason why the valve member moves to the fully open position is thought to be due to the fact that the rapid rise in the pressure of fuel delivered by the pump propels the valve member against the action of its spring in the manner of a piston, before there has been time for delivery of fuel at the restricted rate.

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

According to the invention a fuel injection nozzle unit of the kind specified comprises a piston mounted on the valve member, said piston co-operating with the interior surface of the hollow body part and acting to divide the interior of the body part into a pair of chambers, said outlet passage communicating with one of said chambers and the fuel inlet communicating with the other of said chambers, stop means for limiting the movement of the valve member against the action of said resilient means, and valve means operable to allow fuel to flow from said other chamber to said one chamber when during the delivery of fuel to said other chamber, the movement of the valve member is halted by said stop means.

An example of a fuel injection nozzle unit of the kind specified will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of the nozzle unit; and Figure 2 is a view to an enlarged scale of a portion of the nozzle unit of Fig. 1.

Referring to the drawings the nozzle unit comprises a body part 10 which has an integral skirt portion 11. The body part has peripheral screw threads with which is engaged a cap nut 1 2 which retains a nozzle assembly generally indicated at 13, in engagement with the end of the skirt.

The skirt portion has a cylindrical internal surface and communicating with the chamber defined by the skirt portion is a fuel inlet passage 14 which in use, is connected to the outlet of a fuel injection pump which is indicated at 1 5. An edge filter member 1 6 is provided in the fuel inlet.

The nozzle assembly includes a portion 1 7 having a flange 1 7A which is trapped between the end of the skirt portion 11 and the cap nut 1 2. Extending through the portion 1 7 is a cylindrical bore 1 8 which constitutes an outlet passage. Formed in the outlet passage is a seating 1 9 and for engagement with the seating there is provided the head 20 of a valve member which has a stem 21 extending through the bore 1 8. The stem is provided with a fluted portion 30 which guides the movement of the stem in the bore and in addition the stem has a cylindrical guide portion 22 which is part located in the bore 18.

The guide portion 22 mounts a spring abutment 23, the abutment being retained upon the stem by means of a retainer 24 which is located about a reduced portion of the stem and which engages a projection 25 formed at the end of the stem remote from the head 20.

The abutment 23 has an outwardly extending flange with which is engaged one end of a coiled compression spring 26 the other end of which engages the flange on the portion 1 7.

The portion 1 7 is provided with a pair of ports 27 through which fuel can flow from the interior of the skirt portion along the annular clearance defined between the stem 21 and the portion 1 8 of the bore, past the fluted portion of the stem and when the valve member is in the open position, through the annular clearance defined between the head of the valve member and the portion of the outlet downstream of the seating. The extent of movement of the valve member away from the seating is limited by the abutment of the spring abutment 23 with the portion 1 7.

The head 20 of the valve member as shown more clearly in the enlarged portion of the figure, has a tapered portion 20A and a plain cylindrical portion 20B. The outlet downstream of the seating 19, is of right cylindrical form. As the valve head moves away from the seating the area of the flow path through which fuel can flow, is defined between the right cylindrical portion 20B and the outlet however, when the right cylindrical portion 20B projects beyond the portion 17, the area of the flow path starts to increase.

The nozzle thus far described is well known in the art and as fuel is supplied under pressure from the injection pump, a force acts upon the valve member to move the valve member against the action of the spring 26.

Fuel flows through the ports 27 and through the annular space defined between the valve head and the outlet downstream of the seating. The initial flow of fuel, in theory at least, is at a restricted rate because the area of the flow path is small. As the valve member continues to move away from the seating, the area of the flow path increases and so also does the rate of delivery of fuel.

As explained earlier in some cases the valve member acts as a piston and moves very quickly to the fully open position as determined by the engagement of the spring abutment 23 with the portion 1 7 so that the delivery of fuel at the restricted rate is very small.

In order to overcome this problem the valve member is provided with a piston and this takes the form of a ring 28 which is positioned against the under side of the retainer 24. The ring and retainer have co-operating surfaces which establish a fuel seal and the periphery of the ring forms a seal with the interior surface of the skirt as also do the cooperating surfaces of the retainer 24 and spring abutment 23. The ring is biassed into engagement with the retainer by means of a spring in the form of a coiled compression spring 29. The piston constituted by the ring 28 and the retainer divide the space defined by the skirt into a pair of chambers, the one being in communication with the outlet and the other with the inlet.When fuel is supplied through the inlet passage 14 the fuel under pressure acts on the one side of the piston to impart movement thereto, but because of this movement the fuel in the one chamber is also pressurised and as the piston and valve member move, fuel is displaced through the ports 27 and through the outlet. At least the initial flow of fuel takes place at a restricted rate because it must flow through the restricted flow path defined by the valve head and the outlet. The movement of the valve member continues and as the portion 20B of the valve head moves out of the outlet, the rate of flow of fuel can increase.The movement of the valve member, as before, is halted by the engagement of the abutment 23 with the portion 1 7 and when this occurs the fuel pressure acting on the ring 28 urges the ring away from the retainer 24 against the action of the spring 29 allowing fuel to flow between the chambers. The ring 28 and the retainer 24 therefore act as valve means. When the flow of fuel ceases the parts return to the position shown in the drawings, the ring 28 being held away from the retainer 24 by the flow of fuel until the valve head engages the seating. There is substantially no restriction on the rate of closure of the valve member.

The quantity of fuel which is delivered at the restricted rate depends upon the movement of the piston and valve member before the portion 20B of the valve head leaves the outlet and the volume of fuel displaced by the piston during this movement. Thus by altering the axial length of the portion 20B the amount of fuel delivered at the restricted rate can be varied. Variation can also be achieved by varying the area of the piston in relation to the area of the valve member.

Claims (6)

1. A fuel injection nozzle unit of the kind intended to supply fuel to the combustion chamber of an internal combustion engine comprising a hollow body part defining an outlet passage in an end wall thereof, a seating defined in the outlet passage, a valve member having a stem and a head, said head being shaped for co-operation with said seating and being located within said outlet passage, the stem extending into the hollow body part, a resilient means acting on said stem to urge the head into contact with the seating, a fuel inlet to the interior of said body part and through which in use, liquid fuel is supplied to the interior of the body part, the pressure of fuel acting on said valve member to urge the valve member against the action of said resilient means thereby to lift the head from the seating, the head moving in a direction towards the exterior of the nozzle unit, the head and outlet passage defining an annular flow path through which liquid fuel can flow from the interior of the body part, and the cross sectional area of said flow path varying as the head moves away from the seating, characterized by a piston mounted on the valve member, said piston co-operating with the interior surface of the hollow body part and acting to divide the interior of the body part into a pair of chambers, said outlet passage communicating with one of said chambers and the fuel inlet communicating with the other of said chambers, stop means for limiting the movement of the valve member against the action of said resilient means, and valve means operable to allow fuel to flow from said other chamber to said one chamber when during the delivery of fuel to said other chamber, the movement of the valve member is halted by said stop means.

2. A nozzle unit according to claim 1 characterized in that said piston is located about said stem and co-operates with a part carried by said stem to form said valve means and spring means acting on said piston to urge the piston into contact with said part.

3. A nozzle unit according to claim 2 characterized in that said part constitutes a retaining member for a spring abutment located about said stem.

4. A nozzle unit according to claim 3 characterized in that said spring means comprises a coiled spring disposed intermediate said piston and a flange defined on said spring abutment.

5. A nozzle unlit according to claim 4 characterized in that the piston is in the form of a ring.

6. A fuel Injection nozzle unit of the kind intended to supply fuel to the combustion chamber of an internal combustion engine and comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.