GB2266933A

GB2266933A - Fuel pump

Info

Publication number: GB2266933A
Application number: GB9210152A
Authority: GB
Inventors: Lukhbir Singh Panesar
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1992-05-12
Filing date: 1992-05-12
Publication date: 1993-11-17
Also published as: GB9210152D0

Abstract

A unit injector includes a cylindrical body 12 part of which locates in a recess 11 in the cylinder head 10 of an engine so that a fuel injection nozzle 13 mounted en the body projects into a combustion space. The injector also includes a reciprocable plunger 24 operable to pressurise fuel in a pumping chamber 22 and a spill valve 36 is provided which is mounted on a lateral extension 35 of the body. The action of the spill valve is to spill fuel from the pumping chamber and this fuel is returned to a passage (42) in the cylinder head by way of a spill channel (39) in the extension and which is 28 connected to the passage in the cylinder head by way of a sleeve 41 or a gasket. <IMAGE>

Description

FUEL PUMP This invention relates to a unit injector for supplying fuel to a combustion chamber of an internal combustion engine and of the kind comprising an elongated body at one end of which is mounted an injection nozzle, a pumping plunger reciprocably mounted in a blind bore defined in the body, the plunger and the blind end of the bore defining a pumping chamber from which fuel can flow to the injection nozzle during inward movement of the plunger, the plunger extending from the bore and the extended end thereof being engaged by an actuating member, a lateral extension on the body, an electrically operated spill control valve carried by the extension, the spill valve having an inlet channel which is connected by a passage to the pumping chamber and an outlet channel for connection to a drain, and the valve in use acting to control the amount of fuel which is supplied to the injection nozzle, a fuel inlet port formed in the wall of the bore, the inlet port being positioned to be covered by the plunger during the inward movement thereof and a fuel supply channel which is in communication with said port and which extends to the exterior of the body for connection in use to a source of fuel under pressure.

Unit injectors of the aforesaid type are well known in the art and in use the portion of the body which lies intermediate the extension and the nozzle together with the nozzle, is housed in a recess formed in the cylinder head of the engine. The remaining portion of the body including the extension and the spill control valve are located beneath a cover secured to the cylinder head and which houses the pumping plunger actuating mechanism for example a rocker, which is associated with an engine driven cam. The rocker is engaged with the actuating member. In order to limit the length of the unit injector which projects from the recess, the blind end of the bore is arranged to lie between the lateral extension and the nozzle body.It has been the practice to form the outlet channel from the spill control valve with an axially extending portion which lies alongside the bore and opens onto the exterior of the body at a position to communicate with a drain in the recess of the cylinder head. The standard diameter for the portion of the body lying between the extension and the nozzle body is 35 mm and with this diameter there is an adequate wall thickness about the bore in which the axially extending portion of the outlet channel can be formed.

In order to facilitate the design of the engine cylinder head it is required to reduce the diameter of the aforesaid portion of the body whilst at the same time maintaining the high values of fuel pressure during the inward movement of the plunger.

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

According to the invention in a unit injector of the kind specified said outlet channel opens onto the underface of the lateral extension.

An example of a unit injector in accordance with the invention will now be described with reference to the accompanying drawing which shows in diagrammatic form the injector mounted in the cylinder head of an engine.

Referring to the drawing there is shown at 10, the cylinder head of the engine in which is formed a recess 11 to accommodate a portion of the unit injector. The unit injector comprises a body 12 to which is secured a fuel injection nozzle 13, the injection nozzle defining an end portion 14 which extends through a bore 15 at the inner end of the recess 11. The end portion 14 of the nozzle just projects into a combustion chamber of the engine. In the particular example there is interposed between the body 12 and the injection nozzle 13, a distance piece 16 and a cylindrical sleeve 17. The sleeve defines a chamber 18 which accommodates the spring which biases the valve member of the nozzle to the closed position. The distance piece and the sleeve are formed with passages 19, 20 respectively.The passage 20 communicates with the fuel inlet of the nozzle and the passage 19 communicates with a short passage 21 which is in communication with the pumping chamber 22 of the pump/injector and which is defined by the inner end of a blind bore 23.

Slidable within the bore is a pumping plunger 24 which projects from the bore and is engaged with a hollow spring abutment 25 which is slidable about a portion 26 of the body 12. Interposed between the body 12 and a flange on the spring abutment is a coiled compression spring 27 which biases the plunger outwardly. The extent of outward movement of the plunger is limited by an abutment member in the form of a ball 28 which is accommodated within a drilling formed in the portion 26 of the body and which engages with a step defined on the plunger.

The spring abutment carries an actuating member 29 which in the particular example, is engaged by an adjustable component 30 which is mounted on a rocker 31.

The rocker is pivotally mounted and has a part not shown engagable by an engine driven cam.

Formed in the wall of the bore 23 is a fuel inlet port 32 which by way of a laterally extending fuel supply channel 33 formed in the body 12 communicates with an annular space 34 defined between the wall of the recess 11 and the wall of the body 12. This space is in communication with a source of fuel under pressure by way of drilling which is seen in dotted outline, formed in the cylinder head.

The body 12 is provided with a lateral extension 35. The extension supports an electrically operated spill valve generally indicated at 36 and the spill valve has an inlet channel 37 and an outlet channel 38. The outlet channel communicates with a drilling 39 formed in the extension and which communicates with the inner end of a cylindrical recess 40 in which in use, is mounted a sleeve member 41 which locates in a complimentary recess in the cylinder head. The recess communicates with a drilling 42 formed in the cylinder head.

The inlet channel 37 communicates by way of a passage 43 formed in the extension, with a port 44 formed in the wall of the bore. The port 44 is in constant communication with a circumferential groove 45 which is formed in the pumping plunger and which communicates by way of a transverse drilling 46 and an axial drilling 47, with the pumping chamber 22.

In the position shown the plunger is at the outermost limit of its travel as determined by the base circle of the cam which actuates the rocker 31. It will be noted that the inlet port 32 is uncovered to the pumping chamber 22 and therefore the pumping chamber and the associated passages will be completely full of fuel.

As the plunger is moved inwardly the port 32 is covered by the plunger and prior to this a small quantity of fuel will be displaced from the pumping chamber along the channel 33. As soon as the port 32 is covered then providing the spill valve is closed, the fuel in the pumping chamber 22 will be pressurised and delivered to the fuel injection nozzle. At a predetermined pressure the valve member of the fuel injection nozzle will lift and fuel will be delivered to the combustion space of the engine. The delivery of fuel will continue as the plunger moves inwardly providing the spill valve 36 is maintained closed. If during the inward movement the spill valve is opened then the pressure in the pumping chamber falls so that the valve member of the nozzle will close.The remaining quantity of fuel which is displaced during the inward movement of the plunger will flow by way of the passages 47, 46, 45 and 43, through the spill valve and by way of the passage 39, to the passage 42 in the cylinder head. The quantity of fuel which is supplied to the associated engine can therefore be controlled by opening the spill valve at the correct instant. It is also possible to determine the commencement of fuel delivery by maintaining the spill valve open during the initial inward movement of the pumping plunger.

By the arrangement described the diameter of the nozzle body which lies within the recess 11 can be considerably reduced since the axial portion of the drilling 39 which connects the spill valve with the drilling 42 is formed in the lateral exterior and not in the thickness of the portion of the body which surrounds the bore 23. As a result it is possible to reduce the diameter of the body. In the particular example the diameter has been reduced from the standard 32 mm to 24 mm. This reduction in diameter facilitates the design of the cylinder head of the engine. It is necessary to maintain the chamber 18 at a low pressure and a drilling 48 is formed in the cap nut which is utilised to retain the nozzle 13 the sleeve and the distance piece in assembly with the body 12. The drilling connects with the annular space 34.

In the example the nozzle 13 is clamped against a step defined between the recess 11 and the bore 15. A sealing washer 49 is provided to form a gas tight seal.

In a modification the sleeve 41 is replaced by a gasket located between the exterior and the cylinder head 10.

In this case since it is necessary to provide a clamping force to activate the gasket, the sealing washer 49 is replaced by a flexible gas seal.

Claims

1. A unit injector for supplying fuel to a combustion chamber of an internal combustion engine comprising an elongated body at one end of which is mounted an injection nozzle, a pumping plunger reciprocably mounted in a blind bore defined in the body, the plunger and the blind end of the bore defining a pumping chamber from which fuel can flow to the injection nozzle during inward movement of the plunger, the plunger extending from the bore and the extended end thereof being engaged by an actuating member, a lateral extension on the body, an electrically operated spill control valve carried by the extension, the spill valve having an inlet channel which is connected by a passage to the pumping chamber and an outlet channel for connection to a drain, and the valve in use acting to control the amount of fuel which is supplied to the injection nozzle, a fuel inlet port formed in the wall of the bore, the inlet port being positioned to be covered by the plunger during the inward movement thereof and a fuel supply channel which is in communication with said port and which extends to the exterior of the body for connection in use to a source of fuel under pressure, said outlet channel opening onto the underface of the lateral extension.

2. A unit injector according to Claim 1, in which said outlet channel is formed to accommodate a sleeve member which in use extends between the extension and the cylinder head of the engine.