Control arrangement for a fuel injection valve

Abstract: A fuel injection valve for an internal combustion engine, especially for a large diesel engine, includes a first control surface (11), which is arranged on a needle member (4) of the valve and which is continuously in communication with the pressure of the fuel to be injected for moving the needle member (4) against the force of a spring (7) in order to open the valve, a second control surface (12) located at the end of the needle member (4), a third control surface (20) arranged in association with the needle member (4), and a control valve (15), which depending on the phase of operation of the injection valve is arranged on the one hand to communicate and on the other hand to cut off the pressure of the fuel on the said third control surface (20). Before injection of fuel the control valve (15) is urged by a spring (16) to its end position, in which it is arranged to communicate the pressure of the fuel to be injected to the third control surface (20), and after opening of the fuel injection valve the control valve (15) is arranged to cut off the connection between the pressure of the fuel to the be injected and the third control surface (20).

Description: The present invention relates to a fuel injection valve for an internal combustion engine, as disclosed in FR-A-2 214 823, especially for a large diesel engine, in accordance with the preamble of claim 1. The expression "large diesel engines" includes, for example, the main propulsion engines or the auxiliary engines of ships or engines for power plants for producing electricity and/or heat energy. Fuel is injected directly into each cylinder of such an engine by means of injection valves. The injection of fuel has a critical effect on the NOx content of the exhaust gases. In an attempt to decrease the amount of nitrogen oxides created the formation of fuel droplets has been improved. The size of the droplets in a fuel spray can be decreased by increasing the pressure of the injection of fuel, which can be achieved for example by means of the design of the injection nozzle and by using a higher opening pressure for the valve. The operating conditions of the engine and the construction of the nozzle, however, set limits for increasing the opening pressure. In a conventional valve in which the pressure of the fuel acts only on one control surface when the valve is opened, the pressure needed for closing the needle of the valve is always substantially smaller than the opening pressure of the valve. This is due to the fact that once the valve is open the pressure of the fuel acts also on the area of a control surface located at the end of the needle against the same spring force, whereby because of the increased area the fuel pressure at which the valve closes is correspondingly smaller than the fuel pressure needed for opening. As a consequence, undesirable fuel injection under low pressure occurs at the end of the injection period. An aim of the invention is to provide a new improved control arrangement for a fuel injection valve by means of which the closing pressure of the injection valve and thus the injection pressure at the end of the injection period can advantageously be increased and hence the formation of droplets in the cylinder of an engine can be improved. A further aim is that the arrangement should not require any increase of the opening pressure of the valve. The aims of the invention are achieved by an injection valve as set forth in claim 1. In accordance with the invention, before starting the injection of fuel, the control valve is urged by a spring to its end position, in which it communicates the pressure of the fuel to be injected to the third control surface, and after opening of the fuel injection valve the control valve is arranged to cut off the connection between the pressure of the fuel to be injected and the third control surface. By making use of the control valve to selectively apply the pressure of the fuel to be injected to the third control surface in the way described it is possible to advantageously affect the pressures needed on the one hand for opening and on the other hand for closing the injection nozzle. In an advantageous embodiment of the invention there is a chamber in association with the control valve, which chamber is separately connected on the one hand with a fuel feeding duct and on the other hand with said third control surface when the control valve is in its end position preceding the injection of fuel. The control valve advantageously comprises a control surface which on increasing feeding pressure of the fuel, is arranged to move the control valve against the force of a spring so that the connection between the chamber and the fuel feeding duct is cut off at the same time as the chamber connects the third control surface to a substantially unpressurized space. From the viewpoint of manufacturing it is of advantage that the control valve and the third control surface are located in a separate part which is arranged between the first control surface of the needle member and the return spring for the injection valve. This is of further advantage due to the fact that in this case the nozzle part of the valve, being most susceptible to wear, can easily be changed. In this embodiment the needle member of the injection valve can be in a force transmitting connection with a guiding stem of the injection valve by means of a separate lifting member, which is supported to said part so as to be movable in the axial direction, and on which said third control surface is located. By selecting the areas of said second and third control surfaces to be at least substantially equal the closing pressure and the opening pressure of the injection valve are mutually equal. The formation of droplets of the fuel is thus as efficient as possible during the whole injection period. The invention will now be described by way of example with reference to the attached drawings, in which:- Figure 1 shows an embodiment of an injection valve according to the invention in section and in the closed position, Figure 2 shows the injection valve of Figure 1 in the open position, Figures 3 and 3a show a control arrangement for the injection valve of Figure 1 as an enlargement, and Figure 4 shows an enlargement of a control arrangement for the injection valve of Figure 2 in a position in which the injection valve itself is already closed in contrast to the situation in Figure 2. In the drawings, 1 indicates a body part of an injection valve and 3 an injection nozzle part of the valve, between which there is an intermediate part 2. A needle member 4 of the valve is movably supported to the intermediate part 2, by means of a lifting member 5 which ensures a force transmitting connection of the needle member with a guiding stem 6 of the valve, which is urged by a spring 7, located in an unpressurized space 8 in the body part 1, downwards in the figures towards a closed position of the valve. An injection pump (not shown) feeds fuel through a duct 9 into a chamber 10 in the nozzle part 3. The pressure of the the fuel acts on a control surface 11 of the needle member 4. In Figure 1, the needle member is in a closed position, a valve surface 12 preventing injection of the fuel through nozzle passages 13. When the pressure of the fuel in the chamber 10 becomes so high that the force on the control surface 11 exceeds the spring force of the spring 7 the valve opens and the fuel flows through a valve passage 14 (Figure 2) into the nozzle passages 13, injection of the fuel thus taking place. Since the common area of the control surface 11 and the valve surface 12, which also serves as a control surface, is of course substantially larger than the area of the control surface 11 alone, the pressure of the fuel providing closing of the valve would be substantially lower than the respective pressure of the fuel needed for opening of the valve. As a consequence injection under low pressure would occur at the end of the injection period, which would be undesirable. In order to avoid the above mentioned phenomenon, in accordance with the invention, the valve is provided with a control arrangement shown in the figures, which includes a control surface 20 arranged on the lifting member 5 located in the intermediate part 2 and a control valve 15 movable against the force of a spring 16 located in a space 21 in the body part 1, the control valve being associated with a chamber 19 which is connectable with a passage 17 connected to the fuel duct 9 and a passage 18 communicating with the control surface 20. Figure 3 shows the situation before opening of the injection valve. Fuel is fed through the duct 9 into the chamber 10, in which it acts on the control surface 11 as described above. At the same time fuel flows through the passage 17 into the chamber 19 and hence through the passage 18 to act on the control surface 20. Thus, the force provided by the pressure of the fuel and lifting the needle member 4 against the force of the spring 7 acts on both of the control surfaces 11 and 20. When the force exerted by the fuel exceeds the force of the spring 7 the injection of fuel starts. In practice this pressure can be for example 600 bar. As is more apparent from Figure 3a the fuel pressure also acts through a passage 24 on a control surface 23 located on the control valve 15 thereby tending to lift the control valve 15 upwards in the figures. As the feeding pressure of the fuel increases further, for instance up to 1000 bar, the control valve 15 moves against the force of the spring 16 from the position of Figure 3 into the position shown in Figures 2 and 4. In this position a surface 22 of the control valve 15 cuts off the connection between the passages 17 and 18. Thus, the pressure of the fuel to be fed can no longer act on the control surface 20, but the control surface 20 is connected to an unpressurized space 8 via the passage 18, the chamber 19 and passages 26, 27 and 28. The control valve 15 remains in this position during the whole remainder of the injection period. Thus the fuel pressure acts only on the control surfaces 11 and 12, and the injection period is finished when the compression force of the spring 7 overcomes the fuel pressure acting on the surfaces 11 and 12. If the areas of the control surfaces 20 and 12 are selected to be equal, the opening pressure of the valve corresponds to the closing pressure of the valve. In this way it is possible by means of the invention to avoid fuel injection at lower pressure towards the end of the injection period. After closing of the valve, in practice, the control valve 15 momentarily remains urged against the force of the spring 16 as is shown in Figure 4, since although the pressure of the fuel has already substantially decreased it continues to act on the surfaces 23 and 25 on the control valve 15 via the passage 17. The control valve 15 moves back into the position of Figure 3 for a new injection period only when the force of the spring 16 overcomes once more the pressure of the fuel acting on the valve 15, which in practice can be for instance 200 bar. The invention is not limited to the embodiment disclosed, but several variations thereof are feasible within the scope of any of the attached claims.

Claims: A fuel injection valve for an internal combustion engine, including a first control surface (11), which is arranged on a needle member (4) of the valve and which is continuously in communication with the pressure of the fuel to be injected, for moving the needle member(4) against the force of a spring (7) in order to open the valve, a second control surface (12) located at the end of the needle member (4) and serving as a valve surface and on which the pressure of the fuel to be injected acts during injection when the valve is open, a third control surface (20) arranged in association with the needle member(4), affecting the movement of the needle member (4) and the direction of action of which corresponds to that of said first and second control surfaces (11,12), and a control valve (15), which, depending on the phase of operation of the injection valve, is arranged on the one hand to communicate and on the other hand to cut off the pressure of the fuel on the said third control surface (20), characterized in that before injection of fuel the control valve (15) is urged by a spring (16) to its end position, in which it is arranged to communicate the pressure of the fuel to be injected to the third control surface (20), and in that after opening of the fuel injection valve the control valve (15) is arranged to cut off the connection between the pressure of the fuel to be injected and the third control surface (20). A fuel injection valve according to claim 1, characterized in that there is a chamber (19) in association with the control valve (15), which chamber is separately connected on the one hand with a fuel feeding duct (9) and on the other hand with said third control surface (20) via connections (17,18) when the control valve (15) is in its end position preceding the injection of fuel. A fuel injection valve according to claim 2, characterized in that the control valve (15) comprises a control surface (23), which on increasing feeding pressure of the fuel, is arranged to move the control valve against the force of the spring (16) so that the connection (17) between the chamber (19) and the fuel feeding duct (9) is cut off at the same time as the chamber (19) connects the third control surface (20) to a substantially unpressurized space (8). A fuel injection valve according to any one of the preceding claims, characterized in that the areas of said second (12) and third (20) control surfaces are selected to be at least substantially equal. A fuel injection valve according to any preceding claim, for use in a large diesel engine. A large diesel engine incorporating a fuel injection valve according to any of claims 1 to 4.

Inventors: FONTELL ERKKO, FONTELL, ERKKO
Applicants: WAERTSILAE NSD OY AB
Application year: 1996
Main classification: F02M47
IPC codes: F02M47, F02M61, F02M63