WO1993021439A1

WO1993021439A1 - Fuel pump

Info

Publication number: WO1993021439A1
Application number: PCT/GB1993/000659
Authority: WO
Inventors: Anthony John Williams
Original assignee: Lucas Industries Public Limited Company
Priority date: 1992-04-10
Filing date: 1993-03-30
Publication date: 1993-10-28
Also published as: GB2280228B; GB9417794D0; GB9207986D0; GB2280228A; DE4391586T1

Abstract

A pump/injector includes a pumping plunger (13A) movable inwardly in a bore to displace fuel from a pumping chamber (16) through an outlet. A fuel flow path into the pumping chamber includes an inlet port (20) connected to an annulus (20A) in the surrounding body (11A) and a passage (29, 30) in the plunger communicating with the pumping chamber. The port and passage are brought into communication towards the end of the outward movement of the plunger to allow fuel flow into the pumping chamber and the fuel flow path includes a non-return valve (28) which closes to prevent escape of fuel from the pumping chamber along the flow path when inward movement of the plunger takes place and before the port and passage move out of communication.

Description

FUEL PUMP

This invention relates to a pump/injector for supplying fuel to a combustion chamber of a compression ignition engine and of the kind comprising a housing which mounts a fuel injection nozzle incorporating a fuel pressure actuated valve which controls the flow of fuel through an outlet orifice of the nozzle, a reciprocable pumping plunger mounted in the housing and which in use is driven inwardly by an engine driven cam to displace fuel from a pumping chamber which communicates with a fuel inlet of the nozzle, an inlet formed in the wall of the bore in which the plunger is located, the inlet forming part of a fuel flow path through which fuel can flow into the pumping chamber, said inlet being covered by the plunger during the initial portion of the inward movement of the plunger and valve means operable during inward movement of the pumping plunger to spill fuel displaced from the pumping chamber to a drain so that the quantity of fuel delivered through the injection nozzle to the engine can be controlled.

Such pump/injectors are well known in the art and the inlet port is closed at a predetermined position during the inward movement of the plunger. Apart from the fact that some of the inward movement of the plunger cannot contribute to fuel delivery, at the point of inlet port closure a pressure spike is generated which may influence the operation of the valve means and may even cause premature opening of the pressure actuated valve in the nozzle.

The object of the invention is to provide a pump/injector of the kind specified in a simple and convenient form. According to the invention in a pump/injector of the kind specified said fuel flow path includes a non¬ return valve which opens to allow fuel flow into the pumping chamber but closes to prevent escape of fuel from the pumping chamber through said inlet.

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

Figure 1 is a part sectional side elevation of a known form of pump/injector, and

Figure 2 shows to an enlarged scale a part of the pump/injector seen in Figure 1 modified in accordance with the invention_^

Referring to Figure 1 of the drawings the pump/injector comprises a housing 10 in which is mounted a pump barrel 11 which defines a bore 12. Slidable in the bore is a pumping plunger 13 which extends from the bore and is coupled at its end to a spring abutment 14. A coiled compression spring 15 is interposed between the abutment and the housing, the spring serving to move the pumping plunger outwardly after its inward movement under the action of an engine driven cam.

The opposite end of the pumping plunger to the spring abutment in conjunction with the bore, forms a pumping chamber 16 which is connected by means of a passage 17, to a -fuel injection nozzle 18 which is secured to the housing. The injection nozzle -^~ incorporates the usual spring loaded valve which controls the flow of fuel through orifices which are formed in a nozzle tip 19.

Formed in the wall of the pump barrel is an inlet port 20 which communicates with a fuel supply gallery 21 defined in the housing, the gallery communicating with a fuel supply passage 22 which in use is connected to a source of fuel under pressure. At its outermost position the inner end of the plunger uncovers the port 20 to allow fuel flow into the pumping chamber 16. During inward movement of the plunger under the action of the engine driven cam, fuel initially is displaced from the pumping chamber through the port 20 until the port is covered by the end of the plunger. Thereafter, the fuel in the pumping chamber is pressurised to a level sufficiently high to lift the valve member of the nozzle from its seating and fuel flow takes place to the associated engine.

The quantity of fuel which is delivered to the engine is controlled by a spill valve 23 which includes a valve member 24 having a head 25. The valve member is coupled to the armature of an electromagnetic actuator 26 and when the actuator is energised, the head 25 is drawn into engagement with a seating to prevent flow of fuel through a spill passage 27 which communicates with the passage 17. The valve can be closed at any time during the inward movement of the pumping plunger to achieve delivery of fuel to the associated engine and the period of valve closure determines the quantity of fuel which is supplied to the engine.

The maximum amount of fuel which can be delivered is obtained if the spill valve is closed immediately prior to closure of the port 20 by the plunger.

The fact that some movement of the plunger has to occur before the port 20 is closed means that a portion of the pumping stroke of the plunger is not effective to deliver fuel to the associated engine. Moreover, closure of the port 20 creates a pressure spike in the pumping chamber which is transmitted through the passages to the valve 23 and also to the pressure actuated valve in the nozzle.

In order to avoid the pressure spike and also to extend the effective pumping stroke of the plunger, it is proposed to introduce a one way valve into the fuel flow passage to the pump chamber 16. Conveniently and as shown in Figure 2, the one way valve is mounted in the plunger. The valve comprises a spring loaded ball 28 which is urged by the spring into engagement with a seating formed in a short axial passage 29 which communicates with a diametrically disposed passage 30 formed in the plunger. The passage 30 at the outermost position of the plunger, communicates with an annulus 20A which corresponds to the ports 20 and because of the axial space taken up by the provision of the valve, the barrel 11A has to be modified by the fact that the annulus 20A is further from the end of the barrel. It will be appreciated -that the annulus 20A is closed during the course of inward movement of the plunger but by operation of the ball 28, the escape of fuel from the pumping chamber during the initial movement when the passage 30 is open to the annulus, is prevented. In this manner a pressure spike is not generated on closure of the ports 20 and the full stroke of the plunger is therefore available to deliver fuel to the associated engine.- Moreover, the annulus could be formed on the plunger.

The engine driven cam has a profile such that the initial inward movement of the plunger is at a comparatively low acceleration so that a pressure spike is not developed.

Claims

1. A pump/injector for supplying fuel to a combustion chamber of a compression ignition engine comprising a housing (10) which mounts a fuel injection nozzle (18) incorporating a fuel pressure actuated valve which controls the flow of fuel through an outlet orifice (19) of the nozzle, a reciprocable pumping plunger (13) mounted in the housing and which in use is driven inwardly by an engine driven cam to displace fuel from a pumping chamber (16) which communicates with a fuel inlet of the nozzle, an inlet (20) formed in the wall of the bore (12) in which the plunger is located, the inlet (20) forming part of a fuel flow path through which fuel can flow into the pumping chamber (16), said inlet being covered by the plunger during the initial portion of the inward movement of the plunger and valve means (23) operable during inward movement of the pumping plunger to spill fuel displaced from the pumping chamber (16) to a drain so that the quantity of fuel delivered through the injection nozzle (18) to the engine can be controlled, characterised in that said fuel flow path includes a non¬ return valve (28) which opens to allow fuel flow into the pumping chamber (16) but closes to prevent escape of fuel from the pumping chamber through said inlet.

2. A pump/injector according to Claim 1, characterised in that said non-return valve (28) is located in a part of the flow path formed in the plunger (13).

3. A pump/injector according to Claim 2, characterised in that said flow passage means includes an axial portion (29) in which the non-return valve is located, and a diametrical portion (30) extending to the periphery of the plunger, and an annulus (20A) through which said inlet (20) and said diametral portion (30) of the passage means are placed in communication with each other towards the end of the outward movement of the plunger and for a corresponding portion of the inward movement of the plunger.