WO1993016281A1

WO1993016281A1 - Fuel pump

Info

Publication number: WO1993016281A1
Application number: PCT/GB1993/000194
Authority: WO
Inventors: Robin Christopher Wall
Original assignee: Lucas Industries Public Limited Company
Priority date: 1992-02-08
Filing date: 1993-01-29
Publication date: 1993-08-19
Also published as: GB9202675D0

Abstract

A pump/injector for supplying fuel to a compression ignition engine includes a fluid pressure controlled spill valve (23) in the housing (10) which carries the injection nozzle (11) and the engine cam operated pumping plunger (16). The spill valve includes a piston (27) slidable in a cylinder and movable to one end of the cylinder to prevent spillage of fuel by fluid pressure in the other end of the cylinder. The fluid pressure in the other end of the cylinder is controlled by an externally mounted control valve (33).

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 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.

One example of such an apparatus is seen in GB-A- 2125115. In this case the valve means takes the form of an electromagnetically operable valve which is mounted in a lateral extension of the housing. The provision of the lateral extension, the valve and the electromagnetic actuator for the valve adds substantially to the overall dimensions of the pump injector making it difficult if not impossible to employ pump/injectors of this type with certain forms of engine.

It would be possible to mount the valve and its actuator at some remote point however, one of the advantages of a pump/injector over a separate pump and injection nozzle is that the volume of fuel which has to be raised to a high pressure during delivery of fuel to the engine, is low and therefore connecting the pumping chamber to a separately mounted electromagnetically operable valve by way of a pipeline, would eliminate this advantage and probably introduce further disadvantages .

The object of the present 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 valve means comprises a cylinder defined in said housing, a piston slidable in said cylinder, a spring biasing the piston towards an end wall at one end of the cylinder, a port formed in said end wall, the port communicating with said pumping chamber, inner and outer spaced annular valving lands defined on said end wall or the adjacent wall of the piston, said inner land surrounding said port, passage means communicating the zone defined between said lands with the other end of said cylinder, a drain passage connected with said one end of the cylinder at a position outside the outer valving land and control valve means connected to said other end of the cylinder and mounted exterior of the housing, said control valve means being operable during the inward movement of the pumping plunger to prevent escape of fuel from said other end of the cylinder whereby the piston is urged by the spring and the fuel pressure in said other end of the cylinder towards said one end wall thereby to substantially prevent flow of fuel through said port.

According to another aspect of the invention a fuel system for an internal combustion engine comprises a plurality of pump/injectors as defined above, said control valve means comprising a single solenoid operable on/off valve.

According to a further feature of the invention there is disposed in series with said on/off valve, a pressurising valve.

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 part of a pump/injector in accordance with the invention,

Figure 2 is a diagrammatic view showing a further part of the pump/injector, and

Figure 3 is a diagrammatic drawing showing the lay out of a fuel injection system for a compression ignition engine employing a number of pump injectors.

Referring to Figures 1 and 2 of the drawings, the pump injector comprises a housing 10 at one end of which is secured a fuel injection nozzle generally indicated at 11. The fuel injection nozzle is of conventional form employing a fuel pressure actuated valve member which controls the flow of fuel through outlet orifices 12 formed in a tip of the nozzle. Fuel under pressure is supplied to the nozzle inlet by way of a passage 13.

Mounted in the housing is a pump barrel 14 in which is defined a bore 15 in which is located a reciprocable pumping plunger 16. The plunger extends from the end of the bore and is in use, moved inwardly by the action of an engine driven cam through the intermediary of a push member 17.

Formed in the wall of a bore is an inlet port 18 which communicates with a fuel supply gallery 19 surrounding the barrel and which in turn communicates with a fuel inlet passage 20 which is connected to a source of fuel under pressure. The plunger and bore define a pumping chamber 21 which is connected to the passage 13 by way of a further passage 22. The passage 22 also communicates with the inlet of a valve 23 to be described, the valve 23 having an outlet which communicates with the fuel inlet passage 20.

The pumping plunger 16 is shown in its outermost position to which it is biased by means of a spring 24. In this position the port 18 is uncovered by the end of the plunger so that the pumping chamber 21 is completely full of fuel. Assuming for the moment that the valve 23 is closed, as the_ plunger moves inwardly fuel will initially flow from the pumping chamber through the port 18 but when the port is covered by the plunger, the fuel in the pumping chamber 21 will be pressurised and is delivered at a sufficiently high pressure to lift the valve member in the fuel injection nozzle 11 so that flow of fuel takes place to the associated engine.

The valve 23 is utilised to control spillage of fuel from the pumping chamber and hence it is able to control the quantity of fuel which is delivered to the associated engine. Referring particularly now to Figure 2, the valve 23 includes a cylinder 25 formed in the housing 10, the cylinder having an end wall 26. Slidable in the cylinder is a cup shaped piston 27 which is biased towards the end wall 26 by means of a spring 28. The end surface of the piston presented to the end wall 26 defines inner and outer annular lands 29, 30. The land 29 surrounds a port 31 formed in the end wall and which is in communication with the pumping chamber 21. The outer land 30 is spaced inwardly from the periphery of the piston and the space surrounding the land 30 is connected by way of a passage 32, with the fuel inlet passage 20.

The opposite end of the cylinder to the end wall 26 communicates with a low pressure by way of an on/off valve 33. This valve is electromagnetically actuated and is mounted exterior of the housing at some convenient position and it is connected to the cylinder by way of a conduit. The flow of current to the solenoid of the valve 33 is under the control of an engine control system.

In operation, if the valve 33 is open and the pumping plunger is moved inwardly, the pressure at which fuel is delivered by the pumping plunger and which is applied to the piston by way of the port 31, will be sufficient to move the piston away from the end wall 26 so that flow of fuel occurs through the passage 32. The gaps between the lands 29 and 30 and the end wall 26 of the cylinder constitute restrictors which are effectively connected in series . A passage 34 which is formed in the piston, connects a zone intermediate the lands with the interior of the cylinder and fuel flows into the interior by way of the passage 34 but by virtue of the fact that the valve 33 is open, it then flows to a drain. The pressure which is developed in the pumping, chamber is not sufficient to lift the valve member of the nozzle from its seating. However, if during the inward movement of the plunger the valve 33 is closed, the pressure in the cylinder rises to the pressure in the aforesaid zone and since this pressure acts upon the whole end area of the piston a force is developed which supplements the force exerted by the spring 28, to urge the piston towards the end wall 26. This has the effect of urging the lands 29, 30 closer to the end wall 26 so that the degree of restriction offered by the aforesaid restrictors increases and as a result less fuel flows through the passage 32 and the pressure of fuel in the pumping chamber further increases. Further increase in the pressure applied to the piston takes place and eventually the pressure of fuel in the pumping chamber attains a value sufficient to open the valve of the fuel injection nozzle to allow injection of fuel to the associated engine. The piston 27 acts as a pressure amplifier since the diameter of the piston is considerably greater than the diameter of the land 29. The area ratio is about 5:1 so that with an injection pressure of 2000 Bar, the pressure in the cylinder is about 400 Bar.

Since the fuel under pressure which biases the piston is derived from the zone intermediate the 'lands 29, 30, the lands do not form a fuel tight seal with the end wall of the cylinder and slight leakage of fuel takes place whilst fuel is being delivered to the associated engine. This leakage of fuel however is very small. If the valve 33 is opened the pressure in the cylinder falls very quickly and the pressure of fuel at the port 31 is more than sufficient to move the piston away from the end wall of the cylinder to allow spillage of fuel from the pumping chamber and therefore termination of fuel delivery to the associated engine. The lands may be provided on the end wall 26 in which case the passage 34 is formed in the piston at a position to communicate with the zone defined between the lands.

In the pump/injector as described the high pressures which are generated during delivery of fuel are confined within the pump housing and the volume of fuel which is subject to the high pressure is no more and may even be less than in the more usual pump/injector. Moreover, the bulky electromagnetically operable spill valve is no longer mounted on the housing.

It is preferred to provide a pressurising valve downstream of the on/off valve 33 so that the pressure in the cylinder 25 when the on/off valve is open, is at a controlled value.

Figure 3 illustrates a system for supplying fuel to a four cylinder compression ignition engine and four pump/injectors 40 are provided which are constructed as described. However the cylinders of the respective valves 23 are connected together and the pressure therein, controlled by a single on/off valve 41. The aforesaid pressurising valve is illustrated at 42. The system operates as described for a single pump/injector and the valve 41 is closed at the appropriate time and for the appropriate length of time each time fuel is to be delivered to the associated engine. The pump/injector whose plunger is moving inwardly functions as described above and the lands of the pistons 27 of the valves of the other pump injectors will be urged by the pressure into firm engagement with the respective end walls 26. The system as described is intended for use with a four cylinder four stroke compression ignition engine but the number of engine cylinders and therefore pump injectors, can be increased providing there is no partial overlap in the fuel delivery periods of the individual pump/injectors. The system can also be applied to two stroke compression ignition engines. In the case where partial overlap of the fuel delivery periods can occur for example with an eight cylinder engine the pump/i jectors can be divided into two groups with a valve 33 for controlling each group.

The connecting conduits from the individual pump/i jectors to the valve 41 can have a small internal volume owing to their short length and the low volume of fuel which is displaced when the valve 33 is opened.

Claims

1. A pump/injector for supplying fuel to a compression ignition engine comprising a housing (10) upon which is mounted a fuel injection nozzle (11) which incorporates a fuel pressure actuated valve which controls the flow_, of fuel through an outlet orifice (12), an engine cam actuated pumping plunger (16) reciprocably mounted in the housing, the plunger in use being driven inwardly by the engine driven cam to displace fuel from a pumping chamber (21) which communicates with an inlet of the nozzle (11) and valve means (23) operable during inward movement of the pumping plunger to spill fuel displaced from the pumping chamber (21) to a drain so that the quantity of fuel delivered through the nozzle to the associated engine can be controlled, characterised in that the valve means comprises a cylinder (25) defined in the housing (10) a piston (27) slidable in the cylinder, a spring (28) biasing the piston towards an end wall (26) at one end of the cylinder, a port (31) formed in said end wall, the port communicating with said pumping chamber (21), inner and outer valving lands (29, 30) defined on said end wall (26) or the adjacent wall of the piston, the inner land (29) surrounding said port, passage means (34) communicating the zone defined between said lands with the other end of the cylinder, a drain passage (32) connected with said one end of the cylinder at a position outside the outer valving land (30) and control valve means (33) connected to said other end of the cylinder (25), said control valve means being operable during the inward movement of the plunger (16) to prevent escape of fuel from said other end of the cylinder so that the piston is urged by the spring and the pressure in said other end of the cylinder towards said one end wall thereby to substantially prevent flow of fuel through said port (31).

2. A pump/injector according to Claim 1, characterised in that said control valve means (33) is electromagnetically operated.

3. A pump/injector according to Claim 1 or Claim 2, including a pressurising valve (42) positioned downstream of said control valve means .

4. A fuel system for a compression ignition engine comprising a plurality of engine cam operated pump injectors operable in turn to supply fuel to the combustion space of the associated engine respectively, each pump/injector having a fluid pressure actuated spill valve (23), each spill valve including a piston (27) slidable in a cylinder (25) and movable towards one end of the cylinder to prevent spillage of fuel from a pumping chamber (21), and a single solenoid operable valve (33) for controlling the fluid pressure in the other ends of the cylinders, said valve (33) being operated during the inward movement of each plunger to increase the fluid pressure in said other ends of the cylinders to effect movement of all the pistons towards said one ends of the respective cylinders .

5. A fuel system for a compression ignition engine comprising a plurality of pump/injectors as claimed in Claim 1, for supplying fuel to the combustion spaces of the associated engine in turn respectively, characterised in that the other ends of the cylinders (25) are each connected to said control valve means (33) whereby a single control valve means controls the amount of fuel delivered by each pump/injector.

6. A fuel system according to Claim 5, characterised in that said control valve means (33) is an ON/OFF valve.