GB2324343A

GB2324343A - A control valve for a high pressure fuel pump in a fuel supply system providing pre-injection and main injection for an i.c. engine

Info

Publication number: GB2324343A
Application number: GB9806938A
Authority: GB
Inventors: Jaroslaw Hlousek
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-04-18
Filing date: 1998-03-31
Publication date: 1998-10-21
Anticipated expiration: 2018-03-31
Also published as: FR2762362B1; GB9806938D0; DE19716221B4; FR2762362A1; GB2324343B; JPH10299601A; DE19716221A1

Abstract

A fuel supply system for an internal combustion engine having a pre-injection and a main injection procedure, in particular for fuels that do not readily ignite, having a first high pressure pump 17, which is connected by way of a first delivery line 22 to a pre-injection nozzle 13, and a low pressure pump 33 which supplies a main injection nozzle 14 by way of a second delivery line 38, 42, wherein a second high pressure pump 41 is interposed in the delivery line 38, 42; the second high pressure pump 41 can be controlled by a servo-system comprising an electrically controlled 3 port, 2 position directional valve 91 and a hydraulically controlled 3 port, 2 position directional, spool type, valve 61, where the electrically controlled valve 91 is connected to the hydraulically controlled valve 61.

Description

2324343 1 DESCRIMON FUEL-INJECTION DEVICE PROVIDING A PRE-INJECTION AND

MAIN INJECTION PROCEDURE IN AN WMRNAL COMBUSTION ENGINE. IN PARTICULAR FOR FUELS WHICH DO NOT READILY IGNTFE The present invention relates to fuel-injection devices in internal combustion engines and is concerned in particular with fuel-in ection devices of the type having a j pre-injection and main injection procedure in internal combustion engines, in particular for fuels, which do not readily ignite, having a high pressure injection pump, which is connected by way of a first delivery line to a pre-injection nozzle, having a low pressure injection pump, which supplies a main injection nozzle by way of a second delivery line, wherein a high pressure pump is interpositioned in the second delivery line.

DE 33 30 774 Al discloses a fuel-injection device having a pre-injection and ain injection procedure in internal combustion engines, which is provided in particular for diesel internal combustion engines. This fuel-injection device comprises a main injection nozzle which is supplied with a main injection quantity by a high pressure injection pump. By way of a hydraulic pre-injection auxiliary pump, which is driven by the delivery pressure of the high pressure injection pump, a pre-injection piston is controlled from which a pre-injection quantity is delivered to a pre- injection nozzle. In the region of the main injection a storage piston is separately provided and is initially influenced exclusively by the delivery pressure of the high pressure injection pump without any mechanical connection to the pre-injection piston without 2 pressure division and is not opened until during the course of the pre- injection piston stroke at least indirectly of a line for the delivered fuel, which line leads further to the storage piston.

This fuel device has the disadvantage that the pre-injection procedure is controlled in dependence upon the main injection procedure. Owing to this dependency the formation of the injection progression, for example for the preinjection procedure, cannot be controlled independently by means of a diesel fuel for the purpose of increasing the ignition quality of an alternative fuel delivered by way of the main injection nozzle, whereby it is not possible to influence the formation of the injection progression and the combustion in the combustion chamber.

In accordance with the present invention, the high pressure pump can be controlled by means of a servo-system which comprises an electrically controlled valve and a hydraulically controlled valve, wherein the electrically controlled valve is connected to the hydraulically controlled valve.

In contrast to the known arrangement, a fuel-injection device in accordance with the present invention has the advantage that the preinjection and the main injection procedure can be controlled independently of each other in an electronic manner, so that corresponding to the respective case of application and the alternative fuel to be used it is possible to meter specific quantities of fuel. By virtue of this separate control of the pre-injection and main injection procedure it is possible to control in a precise manner a plurality of parameters, such as for example the preinjection quantity, the commencement of the injection of the ignition quantity and of the ignition quantity pressure and the main injection quantity and the commencement of the injection of the main injection quantity and also the injection pressure of the 3 alternative fuel. As a result, it is possible to achieve an optimal level of combustion for an alternative fuel, which does not readily ignite, in the case of which, e.g heavy oils having an extremely low cetane number are controlled in the diesel engine independently of the fuel quality, the engine rotational speed and the engine load, so that it is possible to achieve reliable ignition and complete combustion.

By virtue of the advantageous embodiment of the servo-system, which comprises a connection between a hydraulically controlled 3 port, 2 position directional valve by means of a first bore to the electrically controlled 3 port, 2 position directional valve and leading off from this 3 port, 2 position direction valve a second bore in turn to the hydraulically controlled 3 port, 2 position directional valve, it is possible to achieve a precise control of the hydraulically controlled 3 port, 2 position directional valve, which serves to supply the alterative fuel. This is achieved in an advantageous manner by virtue of the fact that high pressure is present at the inlet of the hydraulically controlled 3 port, 2 position directional valve which high pressure acts by way of the first and second bore in dependence upon the position of the electric solenoid valve upon a control surface of the control valve in the hydraulically controlled 3 port, 2 position directional valve. It is thus possible to achieve a corresponding control position of the control valve member of the hydraulic 3 port, 2 position directional valve independently of the high pressure, which is present at the hydraulically controlled 3 position, 2 port directional valve, owing to the control of the control valve member by way of the electrically controlled 3 port, 2 position directional valve.

In accordance with a further advantageous embodiment of the invention it is provided that the control valve member of the hydraulic 3 port, 2 position directional 4 valve comprises a first control piston, a second control piston, which separates by way of a control edge the inlet having a delivery line with respect to the high pressure pump in a first control position and opens in a second control position, and comprises a third control piston which in a first control position opens the connection between the delivery line and the run-off and in a second control position closes the connection by way of a control edge. Consequently it is possible to form and produce in a straightforward manner the control valve member of the hydraulic 3 port, 2 position directional valve by means of which it is possible to control the different switching states for the purpose of controlling main injection nozzle for the alternative fuel. Furthermore, this embodiment of the control valve member renders it possible to provide a control by way of the solenoid valve and the first and second control position of the hydraulic valve can be adjusted.

In accordance with a further advantageous embodiment of the invention it is provided that the first control piston of the control valve member is larger than the second control piston. Consequently, it is possible to move in a convenient manner the control valve member from a first switching position to a second switching position since the high pressure fuel acts upon an annular surface lying opposite to the control surface of the first control piston. In this switching position the fuel can be urged out of the pressure chamber of the hydraulic valve so that the volume of fuel displaced can be returned to a fuel storage device by way of the solenoid valve. Owing to the different surface ratios, it is thus possible to control the control valve member without additionally interpositioning any further switching elements.

In accordance with a further advantageous embodiment of the invention it is provided that the control valve member is provided on an end lying opposite to the pressure chamber a preferably adjustable stop which defmes the working stroke. Consequently the maximum stroke movement from a first switching position to a second switching position can be limited, wherein the stop is preferably provided as an adjusting screw and protrudes into a receiving chamber of the control valve member in such a manner that in a first switching position the second control piston closes the control edge lying opposite thereto, so that the connection between the inlet and the high pressure pump can be separated. This stroke limitation renders it possible to switch the hydraulically controlled 3 port, 2 position directional valve in an optimum manner with respect to time and travel.

In accordance with a further advantageous embodiment of the invention it is provided that the electric 3 port, 2 position directional valve in a first switching position opens a through-flow chamber between the first and the second bore, whereby the pressure chamber is filled with high pressure fuel, so that the control valve member of the hydraulic valve can be positioned in a second switching position. As a result the high pressure pump, which controls the main injection nozzle, can be switched to unpressurized. In this switching position [sic] can be opened by way of a further control valve which is provided in the pressure line leading to the pre-injection nozzle, so that the pre-injection procedure can be performed. By virtue of this embodiment it is possible simultaneously to control the servo-system by way of the high pressure fuel.

With respect to the main injection of the alternative fuel it is provided in an advantageous manner that the electric 3 port, 2 position directional valve is supplied with current, whereby the through-flow chamber between the first and the second bore is separated and simultaneously the fuel located in the pressure chamber of the 6 hydraulic valve is discharged in an unpressurized manner by way of the electric 3 port, 2 position directional valve. As a result, the control valve member can be moved to a second switching position so that the high pressure pump can be influenced by means of fuel by way of the inlet.

In an advantageous manner a restrictor is provided in the electrically controlled 3 port, 2 position directional valve, whereby the rate of the working stroke of the control valve member can be controlled from a first switching position to a second switching position.

In accordance with a further advantageous embodiment of the invention it is provided that the high pressure pump which is connected downstream of the servosystem, in particular of the hydraulically controlled 3 port, 2 position directional valve, comprises a first control piston which is connected to the inlet and is operatively connected to a second piston which compresses the alternative fuel. Therefore, it is possible to deliver the alternative fuel by means of the high pressure fuel.

It is provided in an advantageous manner that the first piston of the high pressure pump comprises a piston surface which is larger in diameter than the second piston so that an increased injection pressure can be produced for the alternative fuel in a structurally convenient manner.

By virtue of the electric and hydraulic 3 port, 2 position directional valves of the servo-systern, which directional valves can be controlled in an advantageous manner independently of each other, the pre-injection quantity, the main injection quantity and the commencement of the injection of the main injection can be 7 controlled electronically in an exact manner. An exact control renders possible an exact injection formation, which in turn can be reproduced for the engine management.

The invention is described farther hereinafter, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic switching arrangement of an injection system for fuels, which do not readily ignite, having a servo-system formed in accordance With the invention, Figure 2 shows a schematic cross-sectional illustration of a servo-system in a first control position of a valve member of a hydraulically controlled 3 port, 2 position directional valve, Figure 3 shows a schematic cross-sectional illustration of the servosystem having a control valve member of the hydraulically controlled 3 port, 2 position directional valve, which is moved from a first switching position to a second switching position, Figure 4 shows a schematic cross-sectional illustration of the servo- system having a control valve member, which is arranged in a second switching position, of the hydraulically controlled 3 port, 2 position directional valve, and Figure 5 shows a schematic cross-sectional illustration of the control valve 8 member of the hydraulically controlled 3 port, 2 position directional valve which is moved from a second switching position to a first switching position.

Figure 1 schematically illustrates an electronically controlled injection system 11 for fuels which do not readily ignite. This injection system 11 comprises an injection unit 12 having a pre-injection nozzle 13 and a main injection nozzle 14. Diesel fuel, for example, is injected by way of the pre-injection nozzle 13 and/or the ignition jet nozzle 13 in order to render it possible to ignite in a reliable manner an alternative fuel, for example bio-fuels, which are delivered into a combustion chamber by way of the main injection nozzle 14. The injection procedure by way of the ignition jet nozzle 13 is dimensioned to be extremely short and merely serves to initialise the ignition of the alternative fuel, which for example does not readily ignite and comprises a lower cetane number, Le a low ignition quality.

The injection system I I comprises a fuel container 15, which comprises diesel fuel for the pre-injection quantity and/or ignition quantity and also the fuel for the purpose of controlling a second circuit which delivers the alternative fuel. A fuel delivery line 16 supplies the fuel to a high pressure accumulator 18 by way of a high pressure pump 17. On the high pressure accumulator 18 there is provided a pressure sensor 19 which detects the pressure in the central storage device 18 and controls the electronically controlled high pressure pump 17 by way of a preferably central control unit 21 in order to build up the required pressure therein. A delivery line 22 leads off from the high pressure accumulator 18 by way of a prestorage device 23, which serves to form the injection progression, to a preferably electrically controlled 3 port, 9 2 position directional valve 24. A bore 26, which leads to the pre- injection nozzle 13 and is connected to the 3 port, 2 position directional valve 24, supplies, in dependence upon the switching position of the valve 24, fuel to the pre-injection nozzle 13. In the state, in which the 3 port, 2 position directional valve 24 is supplied with current by way of the control unit 21, the fuel is delivered from the prestorage device 23 by way of the delivery line 26 to the ignition jet nozzle 13. In a currentless state of the 3 port, 2 position directional valve 24 the delivery of the diesel fuel is terminated and by way of a connection line 27, which is connected to the bore 26 and leads into the fuel container 15, an unpressurized connection is created so that the remaining diesel fuel can be returned.

A second delivery circuit is provided for the purpose of delivering the alternative fuel. Fuel is delivered into a distributor 34 from a second fuel container 31 for alternative fuel by way of a delivery line 32 by means of a low pressure pump 33. Between the low pressure pump 33 and the distributor 34 a delivery line 36 branches off in which a pressurecontrolled control valve 37 is provided, which opens in the event of overpressure produced by virtue of the low pressure pump 33, so that the excessively delivered fuel, which does not readily ignite, and/or the alternative fuel can be returned once again to the fuel container 31. The distributor 34 comprises a plurality of lines which lead off therefrom and correspond to the number of injection units 12 provided per cylinder. Between the delivery line 38 and the injection unit 12 there is provided a high pressure pump 41 which during operation draws alternative fuel from the distributor 34 and supplies said fuel to the injection unit 12 and/or the main injection nozzle 14 by way of a delivery line 42.

The high pressure pump 41 is controlled by virtue of high pressure fuel. A delivery line 43 branches off from the delivery line 22 leading off from the high pressure accumulator 18 and leads into a prestorage device 44 and leads by way of an inlet 46 to the servo-system 47 which controls the delivery of the alternative fuel by way of the high pressure pump 41. The servo-system 47, which is explained hereinunder in even more detail with reference to Figures 2 to 5, comprises a connection 48 to a pressure chamber 49 of the high pressure pump 41. By way of the pressure chamber 49 a piston 51 is influenced against the resilient force of a return spring 52, whereby a second piston 53 is actuated which has a smaller diameter than the first piston 51. This second piston 53 is guided in a high pressure chamber 54 which in a delivery movement pumps alternative fuel against the resilient force of a return spring 52 into the delivery line 42 which leads to the main injection nozzle 14. The connection 38 provided between the high pressure pump 41 and the distributor 34 is closed by way of a non-return valve 55 as the alternative fuel is delivered and compressed. In order to deliver an alternative fuel into a high pressure chamber 54, it is necessary that the servo system 47 is switched to currentless by way of the control unit 21, so that a connection is created between the connection line 48 of the high pressure pump 41 and a run-off leading into the fuel container 15. The return spring 52 urges the fuel located in the pressure chamber 59 back into the fuel container 15, whereby a negative pressure is produced in the high pressure chamber 54, so that alternative fuel is drawn from the distributor 34 into the high pressure chamber 54. By way of the surface ratio of the pistons 51, 53 the alternative fuel can be compressed in the high pressure chamber 54, so that the said fuel can be injected at increased pressure.

Figure 2 illustrates a schematic cross-section of the servo-system 47 in 11 accordance with the invention in a first starting position prior to the commencement of an injection of diesel fuel and alternative fuel. The servo-system 47 comprises a hydraulically controlled 3 port, 2 position directional valve 61 and an electrically controlled 3 port, 2 position directional valve 91 which is associated therewith. A housing 62 of the hydraulically controlled 3 port, 2 position directional valve 61 comprises a first duct 63 which is connected to the inlet 46, a duct 64 which is connected to the run-off 56 and a third duct 66 which leads to the connection 48 of the high pressure pump 41. A control valve member 67 which is disposed in the housing 62 renders possible in a second switching position 86 a connection between the first duct 63 and the third duct 66, whereby the piston 51 is influenced with fuel and in a first switching position 84, as illustrated, said control valve member renders possible a connection between the third duct 66 and the second duct 64 for the purpose of returning the fuel to the fuel container 15. To this end, the control valve member 47 and the housing 62 are formed in the following manner:

The control valve member 67 comprises a first control piston 68 which is guided in a bore 69. On an end which is directed towards the electrically controlled 3 port, 2 position directional valve 91 there is provided a pressure chamber 71, by way of which the control valve member 67 can be influenced and controlled with the system pressure of the diesel fuel. For this purpose, a first bore 72 is provided in the first duct 63, leads into a pressure chamber 92 of the electric 3 port, 2 position directional valve 91 and is diverted into a second bore 93 in order to pass into the pressure chamber 71.

The control piston 68 of the control valve member 67 comprises in a first working chamber 73 a shaft 74 which is tapered in cross-section with respect to the 12 control piston 68 and which in turn becomes a control piston 76 which has a larger diameter than the shaft 74 and which however has a smaller diameter than the control piston 68. The control piston 76 cooperates with a first control edge 77 of the housing 62 in the position of the control valve member 67 illustrated in Figure 2 and separates the inlet 46 with respect to the connection 48. A second shaft 87, which crosses the third duct 66 and becomes a third control piston 79, is connected to the piston 76. This control piston 79 cooperates with a second control edge 81 in a second switching position 86, as illustrated for example in Figure 4. By virtue of the arrangement of the control valve member 67 illustrated in Figure 2 the third duct 66 is connected to the second duct 64, so that the fuel can flow off.

The control valve member 67 lies with its end lying opposite to the pressure chamber 71 against a stroke stop 82, whereby the working stroke of the control valve member 67 is defined. The stroke stop 82 is provided in an advantageous manner as an adjusting screw having a locking nut so that a reliable adjustment can be provided.

The hydraulically controlled 3 port, 2 position directional valve 61 and the electrically controlled 3 port, 2 position directional valve 91 are mutually connected by way of the first bore 72 and the second bore 93. The first bore 72 leads to a control valve member 94 of the electrically controlled 3 port, 2 position directional valve 91, which comprises between the first bore 72 and second bore 93 a valve 96 having a conical valve seat 97. Furthermore, a second valve 98 is provided on the control valve member 94 and closes or opens a pressure chamber 92 connected to the second bore 93 and returns a control volume, which flows off from the pressure chamber 71, by way of the run-off 56 to the fuel container 15. The second valve 98 comprises a flat seat 101 and is connected to a restrictor 102 [not illustrated in detail].

13 The servo-system 47 in accordance with the invention will be explained in detail in the description hereinunder with reference to Figures 2 to 5:

Figure 2 illustrates a starting position of the servo-system 47 prior to the commencement of an injection phase. The electrically controlled valve 91 and/or the solenoid 103 thereof is not supplied with current. As a result, the control valve member 94 is arranged in a first control position 104, in which the second valve 98 seals the pressure chamber 99 by means of its flat seat 101 and the first valve 96 is opened so that a passage is provided between the first bore 72 and the second bore 93. The high pressure fuel, present in the prestorage device 44, ensures that by way of the inlet 46 the first bore 72 and the second bore 93 the pressure chamber 71 is influenced with a control volume, so that the control valve member 67 lies in a second switching position 86 against the stroke stop 82 and/or is urged into this position. In this position the pressure chamber 49 of the high pressure pump 41 is not influenced with pressure, so that by way of the return spring 52 the piston 51 is moved in such a manner that the fuel located in the pressure chamber 49 is urged outwards, in order to flow by way of the connection 48 into the third duct 66 to the second duct 64 and subsequently into the run-off 56. The pressure chamber 49 is thus switched to unpressurized. The first duct 63 is sealed with respect to the third duct 66 by virtue of the second control piston 76 by way of the first control edge 77. In contrast, the second control edge 81 is not sealed by virtue of the third control piston 79, but rather opened so that the fuel can flow off.

The commencement of the delivery for the ignition of fuels, which do not readily ignite, is controlled by way of the control unit 21, wherein the 3 port, 2 position directional valve 24 is initially supplied with current, so that diesel fuel is 14 supplied to the ignition jet nozzle 13 by way of the prestorage device 23, so that a pre-injection quantity and/or ignition quantity passes into the combustion chamber. The control device 21 serves to adjust the commencement of the injection of the ignition quantity and the termination of the injection of the ignition quantity. At the same time the electro-hydraulic solenoid valve 91 is supplied with current by way of the control unit 21, so that the control valve member 94 is moved into a second control position 105, as illustrated in Figure 3. In this control position 105 the conical seat 97 of the valve 96 is closed, so that a connection between the first bore 72 and the second bore 93 is interrupted. By virtue of this second control position 105 of the control valve member 94, the second valve 98 rises from the flat seat 101, so that a passage is created between the bore 93 and the run-off 56.

By way of the inlet 46 the high pressure fuel is guided out of the prestorage device 44 by way of the duct 63 into the first working chamber 73, whereby owing to the fact the fact that the first control piston 68 has a larger diameter than the second control position 76, the control valve member 67 is moved in the direction towards the second bore 93 and the control volume is displaced from the pressure chamber 71, in order to be discharged in a restricted manner by way of the restrictor 102 of the electric 3 port, 2 position directional valve 91. By virtue of this movement of the control valve member 67 from a second switching position 86 to a first switching position 84, as illustrated in Figure 3, the connection between third duct 66 and the second duct 64 is sealed on the second control edge 82 by virtue of the third control piston 79 and the second control piston 76 opens a connection on the first control edge 77, so that the diesel fuel can be transferred to the pressure chamber 69 by way of the inlet 46. As a result, the piston 51 of the high pressure pump 41 is moved against the force of a return spring 52, whereby the piston 53 compresses the alternative fuel in the pressure chamber 54 and delivers said fuel by way of the delivery line 42 to the main injection nozzle 14. The stroke movement of the control valve member 67 is then terminated if a stop 87, which is disposed on the control surface of the first control piston 68, lies against a limiting device of the pressure chamber 71 formed by the electric 3 port, 2 position directional valve 91.

As soon as the main injection procedure is performed, it is possible to terminate the pre-injection procedure by way of the control unit 21, whereby the 3 port, 2 position directional valve 24 is switched to a currentless state. The main injection procedure or the main injection quantity can in turn be controlled in an electric manner by way of the control unit 21. The main injection procedure is terminated by virtue of the fact that the electric 3 port, 2 position directional valve 91 is set to a currentless state, whereby at least one spring 106 moves the control valve member 94 to a second control position 105, in which the second valve 98 is sealed by way of the flat seat 101 thereof.

The termination of the injection procedure is illustrated in Figure 5. By virtue of the currentless electric 3 port, 2 position directional valve 91 the high pressure fuel is supplied to the inlet 46 by way of the prestorage device 44, wherein this fuel flows by way of the first bore 72 and the second bore 93 into the pressure chamber 71 and the control valve member 67 performs a stroke movement in the direction towards the stroke stop 82. Consequently, the second control piston 76 seals the first working chamber 73 on the first control edge 77. At the same time the third control piston 79 opens a connection on the second control edge 82 between the duct 66 and 64, whereby the pressure chamber 69 of the high pressure pump is switched to 16 unpressurized. By way of the return spring 42 the piston 51 is influenced and the control volume in the pressure chamber 69 is returned by way of the run-off 56 to the fuel container 15. The piston 51 is suddenly relieved of pressure by opening the connection of the duct 66 with respect to the duct 64 on the control edge 82, whereby the delivery of the high pressure pump is immediately terminated. This means that by virtue of the electric control of the electric 3 port, 2 position directional valve 91 it is possible to predetermine an exact commencement and termination of the injection quantity.

The working stroke of the control valve member 67 is then terminated ifthe said control valve member moves into position against the stroke stop 82, as illustrated in Figure 2.

This embodiment of the servo-system 47 in accordance with the invention thus renders possible freely controllable injection parameters for the purpose of controlling in an optimum manner the ignition and combustion of alternative fuels, which do not readily ignite, in all load and rotational speed ranges.

Claims

17 CLAIMS

1. A fuel-injection device providing a pre-injection and main injection procedure in an internal combustion engine, in particular for fuels which do not readily ignite, having a high pressure injection pump, which is connected by way of a first delivery line to a pre-injection nozzle, and a low pressure injection pump which supplies a main injection nozzle by way of a second delivery line, wherein a high pressure pump is interpositioned in the second delivery line and wherein the high pressure pump can be controlled by means of a servo-system which comprises an electrically controlled valve and a hydraulically controlled valve, the electrically controlled valve being connected to the hydraulically controlled valve.

2. A fuel-injection device according to claim 1, wherein for the purpose of controlling a control valve member of the hydraulic valve, which is preferably a 3 port, 2 position directional valve, an inlet, which is connected to the high pressure injection pump, comprises a first bore which branches off therefrom and can be connected to a second bore by way of a first valve of the electrically controlled, preferably 3 port, 2 position directional valve and leads into a pressure chamber of the hydraulic 3 port, 2 position directional valve, in which a control surface, disposed on a first control piston, of the control valve member can be influenced.

3. A fuel-injection device according to claim 2, wherein the control valve member of the hydraulic 3 port, 2 position directional valve comprises a first control piston, a second control piston, which by way of a first control edge separates the inlet having a delivery line with respect to the high pressure pump in a first switching position and opens in a second switching position, and comprises a third control piston, which in a first switching position opens the connection between the delivery 18 line and a run-off and in a second switching position closes this connection by way of a second control edge.

4. A fuel-injection device according to claim 3, wherein the first control piston of the control valve member is larger in diameter than the second control piston.

5. A fuel-injection device according to any of the claims 2 to 4, wherein the control valve member comprises on an end lying opposite to the pressure chamber a preferably adjustable stop which defines the working stroke.

6. A fuel-injection device according to any of the preceding claims, wherein in a first control position the electric 3 port, 2 position directional valve opens a through-flow chamber between the first bore and the second bore and the high pressure present at the inlet moves the control valve member to a second switching position, in which the high pressure pump, which controls the main injection nozzle, can be switched to unpressurized.

7. A fuel-injection device according to any of the preceding claims, wherein for the purpose of delivering the alternative fuel after the preinjection of readily ignitable fuel, the electric 3 port, 2 position directional valve is supplied with current and the control valve member disposed therein separates the through-flow chamber between the first bore and the second bore and a second valve, which leads to the unpressurized run-off, of the electric 3 port, 2 position directional valve opens, whereby the control volume in the pressure chamber flows off by way of the second valve and the control valve member can be moved, as far as to the stop, to a first switching position.

8. A fuel-injection device according to claim 7, wherein the discharge of the 19 control volume out of the pressure chamber can be controlled by means of a restrictor disposed on the second valve.

9. A fuel-injection device according to any of the preceding claims, wherein the high pressure pump comprises in a pressure chamber, which is connected to the delivery line, a first piston which is operatively connected to a second piston, which is disposed in a pressure chamber, and the alternative fuel is compressed by means of the second piston.

10. A fuel-injection device according to claim 9, wherein the control surface of the first piston is larger in diameter than the control surface of the second piston.

11. A fuel-injection device according to any of the preceding claims, wherein the commencement of the injection procedure and the termination of the injection procedure can be controlled independently of each other by way of a control unit by virtue of an electric valve, which controls the pre-injection nozzle, and by virtue of a servo-systern which controls the main injection nozzle.

12. A fuel-injection device substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.