GB2281104A

GB2281104A - Fuel pump

Info

Publication number: GB2281104A
Application number: GB9414706A
Authority: GB
Inventors: James Martin Anderton Askew
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1993-08-11
Filing date: 1994-07-21
Publication date: 1995-02-22
Also published as: GB9414706D0

Abstract

A unit injector includes a pump body (10) which houses a pumping plunger (12) in a bore (11). The pump body also carries a fuel injection nozzle (20) and the pump body has a passage (23) which connects the pumping chamber (13) with the inlet of the injection nozzle. A spill control valve (28) is provided but is positioned at a remote point and is connected to the passage by a pipeline (30). <IMAGE>

Description

FUEL PUMP This invention relates to a so called unit injector for supplying fuel to a combustion chamber of an engine and comprising a pump body in which is defined a bore, a pumping plunger slidable in the bore, the plunger extending from the bore and being engagable at its free end by an engine driven actuator which drives the plunger inwardly in timed relationship with the associated engine, resilient means for biasing the plunger outwardly, a fuel injection nozzle mounted on the pump body, a passage connecting the inner end of the bore to an inlet of the nozzle and a spill control valve having a valve inlet which is connected to said passage, the arrangement being such that when the control valve is closed fuel displaced from the bore during inward movement of the plunger will flow to the nozzle inlet and then to a nozzle outlet and when the valve is open or opened during the inward movement of the plunger the fuel displaced by the plunger will flow to a drain.

Such unit injectors are well known in the art and it has been the practice to locate the spill valve in or on an integral lateral extension of the pump body. Whilst it is possible to machine the body from solid material such a method is prohibitively expensive and it has been the practice to produce the body by a forging process which in itself is expensive.

Moreover, the unit injectors of an engine are located within the space enclosed by the cam shaft cover and the lateral extension of the pump body can be difficult to accommodate since it lies in the vicinity of the engine inlet and exhaust valves.

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

According to the invention in a unit injector of the kind specified the spill valve is positioned at a point remote from the pump body and the inlet of the valve is connected to said passage by a pipeline.

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

Referring to the drawing the pump injector includes a pump body 10 which is of generally cylindrical form and in which is formed a bore 11.

The inner end of the bore is blind and defines with a plunger 12, a pumping chamber 13. The plunger 12 extends from the bore and is provided with a spring abutment 14 between which and the adjacent end of the body is located a coiled compression spring 15. The spring abutment is engagable by one end of a rocker 16 which is actuated by an engine driven cam 17. In practice the spring abutment will be formed as a separate item to the plunger 12 and furthermore, the bore 11 may be formed in a pump barrel which is located and secured within the pump body.

Opening into the wall of the bore 11 is an inlet port or ports 18 which is/are positioned to be covered by the plunger 12 shortly after the commencement of inward movement of the plunger 12 under the action of the cam 17.

The pump body 10 at its end remote from the spring 15 is of reduced diameter and is engaged by a cap nut 19 which serves to secure a fuel injection nozzle 20 to the pump body. In the example a distance piece 21 is interposed between the nozzle body and the pump body and a valve member of the nozzle extends into a spring chamber which is defined in the reduced portion of the pump body and the distance piece.

The spring chamber is occupied by a spring 22 which biases the valve member of the nozzle to the closed position. The nozzle body has a fuel inlet which is connected by way of a passage 23 to the pumping chamber 13.

The pump body is of generally cylindrical form and it is located within a bore formed in the cylinder head 25 of the engine in such a manner that the tip of the nozzle body projects into the respective cylinder of the engine. In the particular example the bore in the cylinder head has an enlargement 27 which serves as a fuel supply gallery. The ports 18 opens into the gallery and the gallery is connected to a source of fuel at low pressure by means of a passage formed in the cylinder head.

Positioned at a remote point is a spill control valve which is shown diagrammatically at 28 and it has an inlet port 29 which is connected to the passage 23 by a pipeline 30. Since the pressure of fuel within the passage 23 and therefore the pipeline will in the use of the unit injector, be high the pipeline is defined by a pipe having a substantial wall thickness. The joint connection to the passage 23 is effected in the particular example, by providing in the wall of the pump body a conical recess 31 which leads into a short passage communicating with the passage 23. The end of the pipe is shaped in a manner complementary to the recess and a fuel tight joint is provided by applying a clamping force to the pipe. Alternatively the recess 31 may be deeper so as to allow the provision of screw threads in the pump body to receive a screw threaded end portion of the pipe.

In operation, when the plunger 12 moves downwardly, fuel is initially displaced from the pumping chamber 13 through the port 18 and this flow of fuel continues until the plunger covers the port. As the plunger continues to move and if the spill control valve 28 is closed, the fuel will be pressurised and will flow along the passage 23 to the nozzle. When the pressure of fuel attains a sufficiently high value, the valve member in the nozzle will be lifted against the action of the spring 22 to permit fuel to flow through an outlet orifice or orifices 32 of the nozzle, into the engine cylinder. If during the inward movement of the plunger after the port 18 has been covered, the control valve 28 is open or opened, the fuel displaced by the plunger will flow by way of the control valve to a drain and therefore the amount of fuel which is supplied to the engine can be controlled. Preferably the spill control valve is actuated by an electromagnetic device under the control of an electronic control system.

By isolating the spill control valve the pump body can be readily machined since it is of generally cylindrical form. Furthermore, the pump body can have a shorter axial length since it is no longer provided with a lateral extension for the spill valve. In addition, since the spill valve is located at a position remote from the pump body it is less likely to interfere with the disposition of the engine valves and furthermore, the solenoid of the electromagnetic device is removed from the hot oily environment which prevails beneath the cam shaft cover of the engine.

Claims

1. A unit injector comprising a pump body in which is defined a bore, a pumping plunger slidable in the bore, the plunger extending from the bore and being engagable at its free end by an engine driven actuator which drives the plunger inwardly in timed relationship with the associated engine, resilient means for biasing the plunger outwardly, a fuel injection nozzle mounted on the pump body, a passage connecting the inner end of the bore to an inlet of the nozzle and a spill control valve having a valve inlet which is connected to said passage, the arrangement being such that when the control valve is closed fuel displaced from the bore during inward movement of the plunger will flow to the nozzle inlet and then to a nozzle outlet and when the valve is open or opened during the inward movement of the plunger the fuel displaced by the plunger will flow to a drain, said spill control valve being positioned at a point remote from the pump body and a pipeline connecting the inlet of the valve with said passage.

2. A unit injector according to Claim 1, in which said pipeline includes a pipe having a substantial wall thickness to withstand the high pressure developed during delivery of fuel, and a fuel tight joint at the junction of the pipe and the pump body.

3. A unit injector according to Claim 2, in which said joint is defined by a conical recess in the pump body the end of the pipe being shaped in a complementary manner and a clamping force is applied between the pipe and the pump body.

4. A unit injector according to Claim 2, in which said joint is defined by a screw threaded recess in the pump body and a screw threaded end portion of the pipe which is secured in the recess.

5. A unit injector according to Claim 1, in which the pump body is of cylindrical form.