This invention relates to a pump/in ector 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.

An example of such an apparatus is seen in GB-A- 2125115 and 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 the high pressure required 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.

In the specification of our co-pending International Application GB93/00194 there is described a pump/injector of the kind specified in which the valve means is in the form of a piston slidable in a cylinder, the piston being biased by a spring towards one end wall of the cylinder and the end wall having a port therein which is connected to the pumping chamber. The piston has inner and outer valving lands which can engage said end wall of the cylinder to prevent any appreciable flow of fuel through the port. When the piston is allowed to move away from the end wall flow of fuel from the pumping chamber can take place into the cylinder through said port, the fuel then flowing through a passage to drain. The end of the cylinder remote from the end wall is supplied with fuel through a passage which communicates with the space defined between the lands and the escape of fuel from this end of the cylinder is controlled by a control valve means. When the control valve means is closed the piston moves to effectively close the port and fuel flow takes place through the injection nozzle during inward movement of the plunger. If the control valve means is open or is opened during the inward movement of the plunger the piston moves to allow fuel flow through the port and no fuel flow takes place through the nozzle.

The specification of the aforesaid application further describes how a number of such pump/injectors can be operated under the control of a single control valve means.

With the aforesaid system a small flow of fuel takes place through the passage from the space between the lands into the cylinder so that a pressure is applied to the piston to assist the action of the spring. For this flow of fuel to take place there has to be a very

small gap between the inner land and the end wall of the cylinder and this means that there is also a small gap between the outer land and the end wall of the cylinder which results in fuel leakage to drain.

The object of the present invention is to provide a pump/injector of the kind specified in an improved 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, resilient means biasing the piston towards one end wall of the cylinder, a port formed in said end wall and a valve member actuated by said piston in its movement towards said end wall to close said port, said port communicating with the pumping chamber and the port when open, connecting the pumping chamber to a drain, means for supplying fluid to the end of the cylinder remote from said end wall and a control valve means operable to control the fluid pressure in said end of the cylinder, said control valve means in one position allowing the fluid pressure in said end of the cylinder to increase to move the piston and valve member to close said port and in another position reducing the fluid pressure so that fuel can flow from the pumping chamber through the port.

An example of a pump/injector in accordance with the invention 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 of Figure 1, and

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

Referring to Figures 1 and 2 of the drawing, 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 by way of a passage 13.

Mounted in the housing is a pump barrel 14 in which is defined a bore 15 which locates 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 the bore is an inlet port 18 which communicates with a fuel supply gallery 19 surrounding the barrel and connected with a fuel inlet passage 20 which in turn is connected to a source 20A of fuel under pressure. The plunger and the 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 in detail, 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 of the plunger the port 18 is uncovered by the end of the plunger so that the pumping chamber 21 is completely filled with 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 will be pressurised and delivered at a sufficiently high pressure to lift the valve member in the fuel injection nozzle 11 so that fuel flow 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 now to Figure 2, the valve 23 comprises cylinder 25 which is formed in the housing 10 and the cylinder has an end wall 26 in which is formed a port 27 which is surrounded by a seating. The port 27 communicates with the passage 22. Moreover, extending from this end of the cylinder is a passage 28 which communicates with the inlet passage 20 and the source 20A of fuel under pressure.

Slidable within the cylinder is a cup shaped piston 29 which is biased towards the end wall 26 by means of a spring 30. The piston 29 carries a valve member 31 which is shaped to cooperate with the seating which surrounds the port. The end of the cylinder remote from the end wall communicates with the common port of a control valve means in the form of a changeover valve 33. One of the other ports of the valve 33 is connected to a source 34 of fluid under pressure and the other port communicates with a drain.

In operation if the valve 33 is set so that the common port is in communication with the drain, then during inward movement of the pumping plunger following closure of the port 18, the fuel pressure developed in the pumping chamber will be sufficient to move the piston against the action of the spring 30 so that the fuel pressure in the pumping chamber does not rise to a

sufficiently high value to open the valve in the nozzle 11. The fuel therefore is returned to the inlet passage 20 by way of the passage 28. If during the inward movement of the plunger following closure of the port 18, the changeover valve is moved to its alternative position, fluid under pressure from the source 34 acts on the piston 29 to assist the action of the spring 30 and the valve member 31 is firmly held in engagement with the seating to prevent flow of fuel through the port 27. In this situation fuel is delivered through the injection nozzle to the associated engine. The flow of fuel through the nozzle can be halted during inward movement of the plunger by moving the changeover valve 33 so that the cylinder 25 is connected to drain and in this situation the pressure of fuel which is developed in the pumping chamber will lift the valve member 31 away from the seating 27 to permit fuel flow from the pumping chamber to the inlet passage 20. If desired the port of the changeover valve 33 which is connected to drain may be connected to the inlet of a pressurising valve 33A so that a residual pressure is maintained in the cylinder.

Figure 3 of the drawings illustrates a system for supplying fuel to a four cylinder compression ignition engine and four pump/injectors 40 are shown, these being constructed as described incorporating respective valves 23. In order to control the operation of the valves 23 a single control valve means 43 is provided and this is in the form of an on/off valve controlled by an electromagnetic actuator 44. The ends of the cylinders containing the springs 30 of the valves 23 are connected together to the ON/OFF valve and the outlet of this valve is connected through a pressurising valve 45 to drain.

The supply of fluid conveniently fuel, under pressure is effected by means of a plunger pump 46 which conveniently is actuated by a cam 47 mounted on the cam

shaft 48 which carries the cams which actuate the individual pump/injectors. The cam 47 has four lobes so that the plunger 49 of the pump 46 is driven inwardly whenever a plunger of the pump/injectors is driven inwardly. The plunger 49 is located in a cylinder 50 which has an outlet which is connected to the cylinders 25 of the valves 23. Formed in the wall of the cylinder 50 is a port 51 which is uncovered to a groove 52 formed in the plunger 49 when the latter is at the outermost position in its stroke. The groove communicates with the cylinder 50 and the port 51 is connected to a source of fuel under pressure.

In operation, as the cam shaft 48 is rotated the plunger 49 is driven inwardly along with one of the pumping plungers of the pump/injectors. The fuel in the cylinder 50 if the valve 43 is open, flows to drain by way of the pressurising valve 45 and the control valve 23 associated with the pump/injector whose pumping plunger is being moved inwardly, will allow the fuel which is displaced by the pumping plunger, to flow to the respective inlet passage 20. If however the valve 43 is closed the fuel delivered by the plunger 49 will pressurise all the cylinders of the valves 23 and in particular the piston 29 of the pump/injector will urge its associated valve member 27 to prevent escape of fuel and therefore fuel will be delivered to the associated engine. The flow of fuel can be terminated by opening the valve 43. Since the plunger 49 is cam actuated, a spill accumulator valve 53 is provided to control the maximum pressure which is applied to the pistons 29 of the pump injectors .

It is convenient to arrange that at the end of the inward movement of the plunger 49, the pressure previously generated by the inward movement of the plunger is relieved and this is effected by arranging

that the groove 52 on the plunger 49 registers with a further port 54 which is connected by way of the pressurising valve 45 to drain. The system as described is intended for use with a four cylinder four stroke compression ignition engine and a single control valve 43 is possible because with such an engine only one pump/injector is delivering fuel at any one time. Providing there is no partial overlap in the fuel delivery periods of the individual pump/injectors, the number of engine cylinders and therefore pump/injectors can be increased. The system can also be applied to two stroke compression ignition engines.

It is possible to arrange for some or all of the fuel which is supplied to the pumping chamber or chambers 21 to flow through the valves 23. For this purpose the force developed on the piston 29 of each valve due to the fuel pressure in the passages 28 must be greater than the combined force exerted by the spring 30 and the force developed on the piston by the residual pressure ^' as determined by the pressurising valve 33A, 45. In this manner the valve member 31 of each valve following spillage of fuel will be held away from the respective seating to allow fuel flow into the pumping chamber.