WO1994004818A1

WO1994004818A1 - Fuel injection nozzle

Info

Publication number: WO1994004818A1
Application number: PCT/GB1993/001587
Authority: WO
Inventors: Colin Thomas Timms
Original assignee: Lucas Industries Public Limited Company
Priority date: 1992-08-12
Filing date: 1993-07-27
Publication date: 1994-03-03
Also published as: GB9217085D0

Abstract

A fuel injection nozzle for use in a fuel system of a compression ignition engine includes a nozzle body (30) in which is formed a nozzle bore (31). A seating is defined about the bore at or adjacent one end and extending within the bore is an elastic member (37) which is coupled to a valve member (34) including a guide portion (36) and a valve head (35). The elastic member is secured to a reaction member (39) which is in different screw thread engagement with the wall of the bore and the elastic member. The nozzle body is secured to a pump housing which houses a pumping plunger and fuel is fed direct to the nozzle bore from the bore which contains the pumping plunger. The fuel under pressure acts on the valve head (35) to lift it away from the seating to allow fuel flow to the engine.

Description

FUEL INJECTION NOZZLE

This invention relates to a fuel injection nozzle for use in a fuel system for supplying fuel to a combustion chamber of a compression ignition engine, the fuel system comprising a pump housing, a plunger bore defined in the pump housing and a plunger slidable in the plunger bore, the fuel injection nozzle having a fuel pressure actuated valve member responsive to the fuel pressure in a fuel inlet chamber which is connected to said plunger bore, said valve member acting when the fuel pressure attains a predetermined value during inward movement of the plunger in the plunger bore, to allow fuel flow from the chamber through an outlet of the nozzle and means for controlling the quantity of fuel which can flow through the outlet.

One example of such a fuel system is the so called pump/injector in which the means for controlling the fuel flow through the outlet comprises an electromagnetically operable spill valve which when open, allows fuel to flow from the bore to a drain and in which the injection nozzle is mounted on the pump housing. Pump/injectors are being used increasingly to supply fuel to direct injection engines in which the fuel is delivered into the engine cylinder. The pump/injector is able to develop the high fuel pressures which are required in such engines so that exhaust emission regulations are met. It has been the practice to provide so called inwardly opening injection nozzles incorporating a differential area valve member and a sac volume located beneath the seating of the nozzle. The outlet orifice or orifices extend from the sac volume and are drilled in the bulbous tip of the nozzle body. As exhaust emission requirements become more stringent it is thought that the pressure at which fuel is supplied to the nozzle will have to be increased in order to achieve more complete atomization of the fuel. This raises a number of conflicting design problems. On the one hand with higher fuel pressures the diameter of the orifice or orifices must be decreased in order to achieve a comparable injection period and the length of the outlet orifice or orifices should be related to the size of the orifice to achieve satisfactory control of the fuel spray but on the other hand increasing the fuel pressure means that the wall thickness of the bulbous portion of the nozzle might need to be increased in order to withstand the increased stress brought about by raising the fuel pressure.

It is also thought that more outlet orifices should be provided and in order to minimise the stress in the bulbous portion of the nozzle the sac volume has to be increased and this means that the amount of fuel remaining in the sac volume at the end of fuel delivery will be increased leading to an increase in the hydrocarbon level in the engine exhaust. Moreover, the reduced diameter of the outlet orifice or orifices means that more efficient filtering of the fuel is required in order to avoid blockage of an outlet orifice by dirt. Various other problems arise concerned with the fuel delivery characteristics.

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

According to the invention a fuel injection nozzle for use in a fuel system of the kind specified comprises a stepped nozzle body, the wider end of which is adapted to seal against a mounting surface defined on the pump housing, a nozzle bore formed in the nozzle body, a seating defined about the nozzle bore at or adjacent the narrower end of the nozzle body, a valve member moveable in the nozzle bore, the valve member having a valve head for engagement with the seating and an elastic member integrally formed with the valve member, the elastic member extending between the valve member and an adjustable reaction member carried by the nozzle body, passage means connecting the chamber defined by the nozzle bore with the plunger bore and the pressure of fuel in said chamber acting on said valve member to lift the valve head from the seating.

An example of a fuel system in accordance with the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 is a sectional side elevation of a known form of fuel system incorporating a known form of nozzle,

Figure 2 shows to an enlarged scale a fuel injection nozzle in accordance with the invention,

Figure 3 shows to an enlarged scale part of the nozzle seen in Figure 2,

Figure 4 is a view similar to Figure 3 showing a modification, and

Figure 5 is a view similar to a part of Figure 2 showing a modification.

Referring to Figure 1 of the drawings there is illustrated a pump/injector which comprises a housing 10 within which is mounted a pump barrel 1 1 , the barrel being retained within the housing by means of a screw- threaded sleeve 11 a. Formed in the pump barrel is a plunger bore 12 in which is mounted a pumping plunger 13. The plunger 13 extends from the bore and is coupled to a spring abutment 14 between which and the housing is located a coiled compression spring 15. The spring acts to urge the plunger out of the bore 12 and the plunger is moved into the bore by means of an engine driven cam 16. Formed in the wall of the bore is a filling port 17 which communicates with a fuel inlet 18 and the port 17 is covered by the plunger during the initial inward movement thereof under the action of the cam 16. When the port 17 is covered, the fuel in the pumping chamber 19 which is defined by the end of the bore and the plunger, will be pressurized and communicating with this end of the bore is a passage 20 which leads to the inlet chamber of a conventional inwardly opening sac type fuel injection nozzle 21. The nozzle is retained upon an extended portion of the housing 10 by means of a cap nut 22 and formed in the extended portion of the housing is a spring chamber 23 in which is mounted a coiled compression spring 24 which acts between the end of the spring chamber 23 and a spring abutment 25 mounted on the end of the valve member of the nozzle.

Branching from the passage 20 is a further passage 26 which leads to the valve chamber of an electromagnetically operable spill valve shown generally at 27. The spill valve includes a solenoid which when energised, closes the spill valve to prevent escape of fuel through the passage 26. When the solenoid is de-energised the spill valve opens and fuel can flow from the passage 26 to a spill outlet 28 formed in the housing.

In operation, during inward movement of the plunger 13 after closure of the port 1 7 fuel will be displaced by way of the passage 20 from the pumping chamber, to the inlet chamber of the nozzle providing the spill valve 27 is closed. The fuel pressure in the inlet chamber acts upon the valve member of the nozzle and when the pressure is sufficient the valve member of the nozzle will be lifted against the action of the spring 24 to allow fuel flow through outlet orifices which are formed in the bulbous tip 29 of the nozzle. The fuel flow through the outlet orifices will continue so long as the plunger is being moved inwardly and the spill valve remains closed. If during the inward movement of the plunger the spill valve 27 is opened, flow of fuel through the outlet orifices ceases and the remaining quantity of fuel which is displaced by the pumping plunger will flow to the outlet 28. During outward movement of the plunger fuel will be drawn into the bore through the open spill valve and further fuel may flow into the bore through the port 17 when the port is uncovered by the end of the plunger.

In accordance with the invention is it proposed to replace the inwardly opening sac type nozzle 21 shown in Figure 1 with the form of nozzle which is seen in Figure 2 and referring to Figure 2 the nozzle comprises a stepped cylindrical nozzle body 30 the wider portion of which is secured by a cap nut to the extension of the housing 10. Extending within the nozzle body is a nozzle bore 31 having an enlarged portion 32 forming the fuel inlet chamber, within the larger portion of the body. The end of the bore at the narrower end of the body defines a seating 33 as more clearly seen in Figure 3, and slidable within the bore 31 is a valve member 34 which includes a valve head 35 and a fluted guide portion 36.

Extending within the nozzle bore 31 is an elastic member 37 which conveniently is integral with the valve member 34 but having a reduced section. At its end remote from the valve member the elastic member connects with an enlarged screw-threaded portion 38 which is connected to the body by a reaction member. In the particular example, the reaction member is of sleeve like form and is in screw-thread engagement with the threaded portion 38 and is also in screw-thread engagement with the internal surface of the enlarged portion 32 of the bore. Other forms of reaction member can be used for example, shims interposed between a step on the elastic member and a step on the nozzle body. Axial passages are formed in the reaction member to allow flow of fuel. The pitch of the two sets of screw-threads is slightly different so that rotating the reaction member 39 will vary the loading of the valve head 35 upon the seating 33. In order to prevent rotation of the screw-threaded portion 38 and therefore the elastic member 37 and the valve member 34, a reduced extension 40 of the threaded portion 38 is of non-circular form and is engaged by a clip 41 having a tongue which is located in a slot formed in the wall of the chamber. The chamber 32 is connected by way of the passage 20, to the pumping chamber 19 and in use, when the spill valve is closed and the pumping plunger is moved inwardly having covered the port 17, fuel under pressure will act against the valve head 35 to move the valve head axial ly to permit fuel flow from between the valve head and the seat 33. During such movement, the elastic member 37 is stretched slightly and will restore the valve head into engagement with the seating 33 when the spill valve is opened and the pressure of fuel in the bore 31 is reduced.

As will be seen from Figure 3, the underside of the valve head is flared to conical form and when the valve head is lifted from the seating an even conical spray is produced. The fluted portion 36 acts to maintain the concentricity of the valve head as it is lifted from the seating thus ensuring the evenness of the spray. The lift of the valve head from the seating increases linearly with pressure and the effect is therefore obtained of a variable flow area nozzle as opposed to the fixed flow area of the conventional inwardly opening sac type nozzle. Moreover, as compared with the inwardly opening nozzle there is practically no fuel which can be said to be retained downstream of the seating when the valve member is in the closed position. In addition the spray pattern is comparable to that of an inwardly opening sac type nozzle having a large number of orifices but the design problems of the inwardly opening nozzle outlined earlier are avoided.

Figure 4 shows a modification in which the end of the bore 31 is flared so that the seating edge 42 is spaced inwardly from the end ofthe body. The profile of the valve head is similar to that shown in Figure 3 but also defines an impingement surface 43 outwardly of the flared portion. The effect of this modification is to produce a greater lift for an equivalent flow area and it is thought that this will for a given rate of seat wear or relaxation of the resilience of the elastic member, effect a reduction in the change in the performance of the nozzle. Changes in the nozzle opening pressure which is initially adjusted using the reaction member 39, throughout the life of the nozzle are more critical to the performance of the nozzle than is the case with an inwardly opening injector. However, the nozzle can be used satisfactorily with a pump/injector type of fuel system since the control circuits which control the energisation of the spill valve, take into account the variation.

Figure 5 shows a modification to the nozzle shown in Figure 2 in which the clip 41 is replaced by a screw threaded locking bush 44 which is in screw thread engagement with the wall of the chamber. A clearance exists between the inner surface of the bush and the threaded portion of the valve member but the bush is provided with a flange which engages with a step 45 defined at the outer end of the threaded portion 38. Once the nozzle opening pressure has been set the locking bush is tightened to prevent rotation of the valve member.

The form of nozzle described with reference to Figures 2, 3 and 4 has a number of advantages over the inwardly opening nozzle as seen in Figure 1. The major advantage is that it can cope with the higher fuel pressures for example, of the order of 1500 Bar without encountering the problems outlined earlier in the specification in relation to stress and size of orifice. Any dirt in the fuel will initially block the gap between the seating and the valve member but with increasing fuel pressure will tend to open the gap further to allow the fuel to wash the dirt away. Furthermore, it is simpler and cheaper to manufacture. In addition, it is found that the variation of the injection period with speed for a given fuel delivery is lower than with the inwardly opening type of nozzle as also is the variation in the injection pressure. Similarly for a given speed the variation of injection period and the variation of injection pressure as the quantity of fuel delivered is varied is lower than with the inwardly opening type of nozzle. A major advantage is that at low engine speeds and low fuel delivery, the delivery pressure can be higher than with the inwardly opening type of nozzle, whilst still maintaining acceptable pressures at higher speeds. Although in the example the pumping plunger is actuated by a cam it can be actuated by a piston of larger diameter to which fluid under pressure can be applied to cause the pumping action of the pumping plunger.

Claims

1. A fuel injection nozzle for use in a fuel system for supplying fuel to a combustion chamber of a compression ignition engine the system comprising a pump housing defining a plunger bore in which is mounted a slidable plunger, means for moving the plunger inwardly, and further means for controlling the quantity of fuel which is supplied to the combustion chamber during inward movement of the plunger, the fuel injection nozzle comprising a stepped nozzle body having a wider end which is held in sealing engagement with a mounting surface defined on the pump housing, a nozzle bore formed in the nozzle DOG , a seating defined about the nozzle bore at or adjacent the narrower end of the nozzle body, a valve member movable in the nozzle bore, the valve member having a valve head for engagement with the seating and an elastic member integrally formed with the valve member, the elastic member extending between the valve member and an adjustable reaction member carried by the nozzle body, passage means connecting a chamber defined by the nozzle bore with the plunger bore, and the pressure of fuel in said chamber acting on the valve member to lift the valve head from the seating to allow fuel flow to the combustion chamber.

2. A nozzle according to Claim 1 , in which the valve member is provided with a fluted guide portion adjacent the valve head.

3. A nozzle according to Claim 1 or Claim 2, in which the seating is defined at the end of the nozzle bore and the underside of the valve head is flared outwardly to conical form.

4. A nozzle according to Claim 1 or Claim 2, in which the end of the nozzle bore is flared outwardly to define a recessed seating edge, the underside of the valve head being flared outwardly to conical form and also including an impingement surface outwardly of the flared portion.

5. A nozzle according to Claim 1 , in which said reaction member is of sleeve like form, and is located within an enlarged screw threaded portion of the nozzle bore the outer surface of the reaction member having a complementary screw thread and the inner surface of the reaction member being formed with a further screw thread of slightly different pitch and engaged with a screw threaded portion of the valve member.

6. A pump/injector for supplying fuel to a combustion chamber of a compression ignition engine comprising a pump housing defining a plunger bore in which is mounted a slidable pumping plunger, means engagable with a projecting outer end of the plunger for urging the plunger inwardly to displace fuel from the bore, resilient means for biasing the plunger outwardly, a spill valve mounted on the housing and operable to allow fuel displaced by the plunger to flow to a drain, and a fuel injection nozzle secured to the pump housing, the fuel injection nozzle comprising a stepped nozzle body having a wider end which is held in sealing engagement with a mounting surface defined on the pump housing, a nozzle bore formed in the nozzle body, a seating defined about the nozzle bore at or adjacent the narrower end of the nozzle body, a valve member movable in the nozzle bore, the valve member having a valve head for engagement with the seating and an elastic member integrally formed with the valve member, the elastic member extending between the valve member and an adjustable reaction member carried by the nozzle body, passage means connecting a chamber defined by the nozzle bore with the plunger bore, and the pressure of fuel in said chamber acting on the valve member to lift the valve head from the seating to allow fuel flow to the combustion chamber.