Electromechanically controlled fuel injection valve for internal combustion engines

Abstract

A fuel injection valve for use with internal combustion engines, especially Diesel engines, includes a valve needle cooperating with a valve seat to control the flow of fuel out of the valve injection orifice. The valve needle can be loaded in the closing direction of the valve by a main pressure spring exerting its force via a plunger which may be lifted by pressurized fuel. It is also loaded in the closing direction by a valve spring. A coaxial force equalizer piston opposes the hydraulic force tending to lift the valve needle from its seat. An electromagnet, when energized, exerts a valve-opening force on the force equalizer piston. The force of the main pressure spring is so great that, when pressurization of fuel ceases, it can overcome the force of the electromagnet and close the valve. An electric switch, actuated by the plunger, can control the energization of the electromagnet, alone or in combination with an electronic controller.

Description

BACKGROUND OF THE INVENTION

The invention relates to an electro-mechanically controlled fuel injection valve for internal combustion engines, especially for Diesel engines, of the type including an electro-mechanical converter, especially an electromagnet, controlling the onset of injection and further including a valve needle influenced by a valve spring and sealingly guided in a bore of a housing for the fuel injection valve. The closure element of the valve needle obturates a valve seat which controls the fluid flow through at least one nozzle orifice. The fuel injection valve further includes a fuel accumulation system whose accumulation space is connected through a pressure line to a pressure chamber located adjacent to the valve seat and it is also connected, through a check valve, to a fuel supply line through which a metering pump delivers the correct amount of fuel required for each operating cycle into the accumulation space.

The electromechanical converter used and described in the present invention for the control of the onset of injection is an electromagnet (solenoid), although other electromechanical converters may be used, e.g. piezoelectric or magnetostrictive converters.

Fuel injection valves of the type of construction described above are especially suitable for fuel injection processes employing very high injection pressures because they permit the control of the onset of injection within a wide rpm domain without necessitating expensive and mechanically highly stressed parts. In these known fuel injection valves, the electromagnet which controls the onset of injection operates a valve slide disposed in the pressure line between the fuel accumulation system and the pressure chamber of the injection nozzle. The fuel pressure acts on the shoulder of the valve needle against the force of the valve spring to open the nozzle orifice but the opening is delayed with respect to the opening control pulse because of the response delay of the electromagnet, the time taken by the valve slide to traverse its control path and because of the throttling effect at the control apertures. In addition, this delay is very dependent on manufacturing tolerances, so that the simultaneous adjustment of all the injection valves in a multicylinder, fuel-injected engine to the same setting is very difficult.

The disadvantages of indirect, i.e. hydraulic actuation of the valve needle could be obviated by direct actuation of the valve needle by the electromagnet. Such injection valves have already found use in very large numbers in gasoline injection systems. But they are not suitable for fuel injection at very high injection pressures (up to 1000 bars), because, in these known valves, actuation of the valve needle requires the electromagnet to overcome a closing force which depends both on the area of the valve seat and on the fuel pressure and may necessitate very powerful electromagnets. Such magnets would require a large space and lead to difficulties of assembly and their current consumption would be excessively high when used, for example, in motor vehicles. Furthermore, the known apparatus creates difficulties due to the time behavior of the injection process. Research conducted with a view to improving the exhaust gas characteristics in Diesel engines has shown that the characteristic time behavior of the injection process, i.e. the time of occurrence of the onset and the termination of fuel injection, greatly influences the combustion process and hence also the formation of toxic components in the exhaust gases.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide an electromechanically controlled fuel injection valve which does not suffer from the above described disadvantages and which opens the nozzle orifices with the least possible delay and permits a rapid termination of the closing stroke. It is a further object of the invention to provide for external influence on the time behavior of the injection process.

This object is achieved, according to the invention, by equipping the fuel injection valve with a force equalizer piston, disposed coaxially with the valve needle within the valve housing and in sealing connection with a coaxial bore thereof. The electromechanical converter is provided with an actuating member which is in operative connection with the valve needle via the force equalizer piston.

One end of the force equalizer piston is pressure-relieved and the other end is acted upon by the fuel pressure prevailing in the accumulation space of the fuel accumulation system. The effective cross-sectional area of the force equalizer piston is so dimensioned that, when the valve seat is closed, the hydraulic forces acting on the valve needle in the opening and closing directions, respectively, are equal or at least approximately equal.

Finally, the forces acting on the valve needle in the closing direction can be increased by a supplemental force which is at least mediately exerted by a control plunger when it arrives in its starting position at the termination of the injection cycle.

Due to the above described combination of characteristics, the electromechanical converter requires only a very simple control circuit for the opening actuation of the valve needle. When the injection valve is closed, the hydraulic pressure acting on the valve needle is fully, or at least partially, compensated by the force equalizing piston and the termination of injection is triggered, independently of the opening control pulse, by the arrival of the control plunger in its starting position. This results in a very reliable and rapid operation even at very high injection pressures such as are required for the direct injection of fuel into Diesel engines. A particularly advantageous characteristic of the invention provides that the control plunger is coaxial with the valve needle, the force equalizing piston and the actuating member of the electro-mechanical converter, and that it is operatively coupled to the valve needle, at the very latest when it reaches its starting position, and presses the valve needle onto its valve seat. This disposition insures rapid closure of the valve because the elements of the fuel accumulation system are in mechanical contact with the valve needle at the termination of injection and since, due to the high injection pressures, they are loaded by a very great spring force.

A particularly advantageous further development of the invention provides a throttle, located in the pressure line, between the accumulation space and the pressure chamber. The restrictive effect of this throttle can change the pressure in the pressure chamber when the valve seat is open and this effect is exploited to make the force then acting on the valve needle in the opening direction at least approximately equal to the force acting on the valve from within the same pressure chamber when the valve seat is closed. Fuel flowing through this throttle during the injection process results in a pressure drop which opposes a supplementary hydraulic force that is present when the valve is open and that acts in the opening direction of the valve. This supplementary force is due to a larger effective cross-section of the valve needle when the valve seat is open. Thus, the effective forces are compensated both dynamically as well as statically.

A still further advantageous development of the object of the invention provides that, when the control plunger reaches its starting position at the termination of the injection cycle, it actuates an electrical switch which, directly or indirectly, interrupts the current to an electromagnet serving as an electromechanical converter. Thus, no electromagnetic force opposes the closure motion of the valve needle, i.e., the closure motion is enhanced and the current requirement of the electromagnet is reduced without necessitating a complicated electrical circuit for controlling the timed switching of the electromagnet as a function of the injected fuel quantity. The invention will be better understood, as well as further objects and advantages will become more apparent, from the ensuing detailed specification of two exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing consists of four figures of which FIG. 1 is an axial cross-section of a first exemplary embodiment of the electromechanically controlled fuel injection valve according to the invention.

FIG. 2 is a section through the upper portion of a second exemplary embodiment of the fuel injection valve according to the invention, showing the region of the fuel accumulation system.

FIG. 3 is a schematic block diagram of a fuel injection system equipped with the fuel injection valve according to the invention.

FIG. 4 is a circuit diagram of an electronic control system for the electromagnet of the second exemplary embodiment of the fuel injection valve according to the invention and shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIG. 1 relating to the first preferred embodiment of the object of the invention, the fuel injection valve 10 illustrated therein has a housing 11 which contains a fuel accumulation system 15 consisting substantially of an accumulation space 12, a control plunger 13 (henceforth called plunger 13), and a compressed pressure spring 14. The accumulation space 12 communicates, through a pressure line 16, consisting substantially of regions 16a and 16b, with a pressure chamber 18, located adjacent to a valve seat 17. The accumulation space 12 also communicates, through a fuel supply line 21 and a check valve 19, with a fuel metering pump (see also below in reference to FIG. 3) which delivers the quantity of fuel required for each injection cycle to the accumulation space 12.

The term accumulation space 12 is used to refer specifically to the space formed by a graduated bore 22 in the center of a multipartite housing 23 of an electromagnet 24, because this space changes its volume, depending on the fuel quantity admitted and to the degree that the plunger 13 moves upwardly against the force of spring 14. Precisely state, the accumulation space is formed by the entire interior volume of the fuel injection valve 10 lying between the check valve 19 and the valve seat 17. In both exemplary embodiments, the electromagnet 24 serves as an electromechanical converter and, without going beyond the essential characteristics of the invention, the electromechanical converter could be replaced by a piezoelectric or magnetostrictive actuating mechanism.

The check valve 19 is inserted in a threaded boss 25 which is screwed into the housing 11. The part of the fuel supply line contained within the threaded boss 25 is designated 21a and the part of the fuel supply line located within the housing 11 is designated 21b.

The housing 23 of the electromagnet 24 is inserted into a bore 26 within the housing 11 and is made pressure-tight therewith by means of a threaded bushing 27. The threaded bushing 27 also serves to fasten an intermediate plate 28, a guide block 29, an intermediate ring 31 and a nozzle body 32 to the housing 11 in a pressure-tight manner. The winding 33 of the electromagnet 24 is electrically connected through plug connections 34 with two connector vanes 35 cast in the housing 11 to which a connector cable, suggested by the line 36, may be electrically coupled. The nozzle body 32, which includes the valve seat 17 and the pressure chamber 18 has a nozzle orifice 37, located beneath the valve seat 17 and facing the combustion chamber (not further shown) of the internal combustion engine. The nozzle body has a guide bore 38 above the pressure chamber 18 in which a lapped-in valve needle 39 slides in fluid-tight manner. The valve needle 39 is hollow to reduce its mass and has a conical tip 41 serving as the closure member when cooperating with the valve seat 17. The effective diameter of the valve needle in the region of the guide bore 38 is designated by Dv. The end 39a of valve needle 39 remote from valve seat 17 extends beyond the guide bore 38 and forms an abutment shoulder for a spring support ring 42, supporting a valve spring 43 whose other end rests on the guide block 29. Thus, the closure member 41 of the valve needle 39 is pressed against the valve seat 17 and closes it. A main spring chamber 44 which surrounds the valve spring 43 and the spring support ring 42 is pressure-relieved and communicates with a space 51 containing the pressure spring 14. This communication is established by a bore 45 within the guide block 29, a connecting bore 46 in the intermediate plate 28, a bore 47 within the housing 23 of the electromagnet 24, an annular groove 48 and an axial bore 49 (shown in broken lines within the housing 11. The space 51 containing the pressure spring 14 is closed by a threaded plug 52 which also serves as a counter bearing for the pressure spring 14. The wall of the housing 11 is penetrated by a fuel return bore 53 to which a fuel return line 54 may be connected. The mechanical connection between the plunger 13 and the pressure spring 14 is established by a spring support plate 55.

The plunger 13 has an edge 56 which so cooperates with an overflow bore 50 that fuel in excess of a maximum permissible quantity can escape through the bore 50 into the space 51 and thence through the fuel return line 54 back to the fuel tank (see also FIG. 3). For example, an excess fuel quantity, exceeding the maximum permissible amount, might be delivered into the accumulation space 12 when the predelivered fuel quantity is not actually injected because of malfunctions in the electrical circuits or at the valve needle. The end of the plunger 13 remote from the pressure spring 14 is a cylindrical stud 57. Adjacent thereto, a force equalizer piston 59, henceforth called equalizer piston 59, is disposed within the bore 58 of the guide block 29 which is part of the valve housing 11. FIG. 1 shows the plunger 13, the equalizer piston 59 and the valve needle 39 in a position in which the force of the pressure spring 14 holds them in positive operational contact. When fuel is predelivered to the accumulation space 12, the plunger 13 is lifted off from the end face of the equalizer piston 59, against the force of the pressure spring 14 to an extent which corresponds to the volume of the predelivered fuel quantity. However, during this motion, the equalizer piston 59 and the valve needle 39 are still held in mutually positive operational contact due to the fuel pressure acting upon them. A downward force acts on the equalizer piston 59, i.e., a force directed toward the valve seat 17 and an opposite force acts on the valve needle 39, i.e., a force directed away from the valve seat 17. These forces keep both elements in positive operational contact because the spring chamber 44 is pressure-relieved, as has already been described. The effective cross-sectional area of the equalizer piston 59, corresponding to its diameter DK, is made equal to the effective annular area of the valve needle which is acted upon by fuel pressure in the direction of opening. This annular area is equal to the difference between the cross-sectional area of valve needle 39, corresponding to the diameter DV and the cross-sectional area of the valve seat 17.

Thus, the hydraulic forces acting upon the valve needle 39 in the opening and in the closing direction are equal and, after the predelivery of fuel, when the plunger 13 no longer makes contact with the equalizer 59, the only force urging the valve needle 39 with its valve cone 41 onto the valve seat 17 is the force exerted by the valve spring 43. Thus, an armature 61, acting as the operating member of the electromagnet 24, is able to attract the equalizer piston 59 and hence also the valve needle 39 when the electromagnet 24 is energized, opening the valve seat 17 and creating a communication between the pressure chamber 18 and the nozzle orifice 37. The end 59a of the equalizer piston 59 adjacent to the valve needle 39 is pressure-relieved since it extends into the spring chamber 44 which, as has already been described, communicates with the fuel return line 54. The other end 59b of the equalizer piston 59 is acted upon by the fuel pressure prevailing in the accumulation space 12 of the fuel accumulation system 15. This end 59b carries the armature 61 of the electromagnet 24.

A throttle 62 is disposed between the two sections 16a and 16b of the fuel pressure channel 16. The throttle reduces the pressure in pressure chamber 18 when the valve seat 17 is open so that the force then acting within pressure chamber 18 on the valve needle 39 in the direction of opening is made at least approximately equal to the force acting in the same direction and in the same location when the valve seat 17 is closed. The throttle 62 is a restricted bore within the intermediate ring 31 and forms the only communication between the accumulation space 12 and the pressure chamber 18.

As previously described, the throttle 62 is so dimensioned that the pressure drop at the throttle 62 compensates for the additional force acting on the valve needle 39 in the opening direction of the valve when the valve seat 17 is open, so that the same hydraulic forces act on the valve needle 39 whether the valve is open or closed. In order to achieve a more rapid opening or closing of the valve needle 39, it may be desirable to provide a small excess force either in the direction of opening or closing. Thus, the disposition of throttle location 62 has made possible a so-called dynamic force equalization in addition to the static force equalization performed by the equalizer piston 59.

This dynamic force equalization is not always necessary in the present construction because the plunger 13, loaded by the very great closing force of pressure spring 14, mechanically presses the valve needle 39 onto its valve seat 17 via the equalizer piston 59 when the predelivered fuel quantity has been injected, so that the throttle 62 could be dispensed with. However, the throttle is necessary in a different embodiment of the invention (not shown) in which the plunger 13 does not have a mechanical connection with the valve needle 39. Such a design would have the advantage, among others, that the fuel accumulation system 15 would not have to be disposed coaxially with the valve needle 39 and the equalizer piston 59, but, instead, could be installed in any suitable manner. The great supplementary force exerted by the plunger 13 after it has returned to its starting position at the termination of the injection cycle as shown in FIG. 1, is capable of pressing the valve nnedle 39 and its closure member 41 onto the valve seat 17 even when the electromagnet 24 is energized. The special advantage of this design is that the electromagnet 24 may be controlled by a controller which produces control pulses of fixed duration. Such a controller is substantially simpler and cheaper to manufacture than one which produces pulses of a particular, precisely determined duration which are required for Diesel fuel injection due to the very short injection times of the order of 1 millisecond.

FIG. 2 is an illustration of a second exemplary embodiment of the fuel injection valve according to the invention in a partial section showing those parts which are different from those shown in FIG. 1. Identical parts retain the same reference numerals and the sectional plane of the right half of the Figure is rotated by 120.degree. with respect to that shown in FIG. 1. The plunger 13 is shown here also in its starting position which it occupies at the termination of the injection cycle. A spring support plate 55' touches a contact pin 71 belonging to an electrical switch 72 located in the valve housing 11' of the fuel injection valve 10'. The contact pin 71 is guided in an insulating sleeve 73 and is in electrical connection with a contact vane 74 to which a line 75 is connected. The contact pin 71 is spring-loaded and its length determines when the spring support plate 55' touches it. The spring support plate 55' is connected to ground through the pressure spring 14 and, when the spring support 55' makes contact with pin 71, the current supply to the electromagnet 24 is indirectly interrupted. The mechanism for current interruption will be described below with reference to FIG. 4. The winding 33 of the electromagnet 24, shown in FIG. 1 but not further shown in FIG. 2, is connected via contact vances 35' with connecting lines 36', of which only one is shown here. Thw switch 72 shown in FIG. 2 represents only one of many possible types.

The block diagram of FIG. 3 shows the fuel injection valve 10' and a fuel injection pump 81 serving as a fuel metering pump. The fuel injection pump 81 is a known four-cylinder serial injection pump having a mechanical centrifugal rpm governor 82 whose operating lever 83 predetermines the fuel quantity to be delivered by the injection pump 81 if it is a feed governor or whose operating lever 83 presets an rpm to be maintained. The fuel supply line 21 leading to the fuel injection valve 10' is at the same time the so-called pressure line of the injection pump 81. The excess leakage fuel is returned from the fuel injection valve 10' through the fuel return line 54 to a fuel reservoir 84. The fuel required by the fuel injection pump 81 is delivered in a known manner by a predelivery pump 85 and a delivery line 86 to the suction chamber of the fuel injection pump 81 and excess fuel is returned through a line 87 and the fuel return line 54 to the fuel reservoir 84. An electronic controller 88 is coupled to the fuel injection valve 10' by the connector line 36' and is further described with reference to FIG. 4. The electronic controller 88 is also connected to the fuel injection valve 10' through the control line 75. The controller 88 generates control pulses 89 which, in the case of controlling the fuel injection valve 10 according to FIG. 1, have a constant duration ti.

In the embodiment represented in FIG. 3, the pulse duration is adapted to the injected fuel quantity by the switching pulse triggered by switch 72 (see FIG. 2) which is fed through line 75 to the controller 88. The onset of fuel injection is initiated by an angle-of-rotation sensor 91 which is preferably mounted on the shaft of the fuel injection pump 81 and which connects through line 92 with the electronic controller 88. In order to permit an rpm-dependent shift of the onset of injection, it is advantageous if the angle-of-rotation sensor 91 is combined with an rpm-sensor and if both respective signals are fed to the electronic controller 88.

FIG. 4 is a schematic diagram of the electronic controller 88 which obtains its operating voltage from a starter battery 101 through a positive conductor 102 and a negative conductor 103. The controller 88 is triggered by a signal generator embodied as an angle-of-rotation sensor 91 and coupled to the cam shaft of the injection pump 81 (see FIG. 3). The sensor 91 is represented in FIG. 4 by a switch contact 104 and a switching element 105. The switching element 105 is connected through a resistor 106 to the negative conductor 103 and is also connected with one of the electrodes of a differentiating capacitor 107.

The control pulses 89 are generated in the controller 88, here embodied as a transistorized switching system, by a monostable control multivibrator 108, which includes a normally conducting input transistor 109 whose collector 109 is connected through a resistor 110 to the base of a normally non-conducting output transistor 111, and further includes a timing circuit which determines the appropriate pulse duration ti. In the multivibrator 108, which is to be regarded merely as an exemplary embodiment, this timing circuit consists of a resistor 112 and a capacitor 113 which are connected in series between the base of transistor 109 and the collector of transistor 111. In addition to being coupled to the capacitor 113, the collector of the output transistor 111 is connected through a resistor 114 with the negative conductor 103 and also, through a control line 115, to the base of a power transistor 116 which is the essential element of a power stage 117. The power stage 117 is preceded in a known manner, not further described, by an intermediate amplifier inserted in the control circuit 115. One side of the winding 33 of the electromagnet 24 is connected through a resistor 118 and a diode 119 to the common positive conductor 102 and the other side of the winding is connected to the collector of the power transistor 116. The emitter of the power transistor 116 is connected to the negative conductor 103 although other conducting elements connected to ground could replace the negative conductor.

The timing capacitor 113, the resistor 112, which is preferably adjustable for setting the pulse duration ti and the base of the input transistor 109 of the multivibrator 108 are all connected to the junction P of two resistors 121 and 122 which are disposed as voltage dividers between the negative conductor 103, connected to ground, and the common positive conductor 102. Both transistors 109 and 11 are of the pnp type and their emitters are connected to the positive conductor 102. Whenever the angle-of-rotation sensor 91 generates a switching pulse, which, in the present example, corresponds to closing the switch 104, 105, the multivibrator 88 is switched into its unstable state whose duration corresponds to the pulse width ti which, in turn, depends on the timing elements 112, 113. In order to permit blocking the input transistor 109 at triggering time, the capacitor 107 is connected through a diode 123 to the base of the input transistor 109 and also, through a load resistor 124, to the positive conductor 102. As long as the switch 104, 105 is open, the differentiating capacitor 107 can charge up, and when switch 104, 105 closes, it can deliver its charge for the purpose of blocking the input transistor 109. As soon as the input transistor 109 blocks, the output transistor 111 goes over into its conducting state. The exponentially increasing collector current within transistor 111 produces a feedback voltage in the timing elements 112, 113, which keeps the input transistor 109 blocked beyond the closing time of switch 104, 105 until the feedback voltage falls below a value determined by the potential at point P of the voltage divider 121, 122. When this voltage is reached, the input transistor 109 returns to its initial, conducting state. The pulse ti for opening the injection valves is indicated by the numeral 89 and is generated during the conducting state of the output transistor 111.

The electromagnetically controlled fuel injection valve shown in FIG. 1 requires only a fixed pulse duration ti to determine the energization time of the electromagnet 24 and this time is always larger than or at least as large as the longest possible injection time. The second exemplary embodiment of the invention, shown in FIG. 2, contains the switch 72 which, when closed, as indicated by broken lines in FIG. 4, connects point P of the voltage divider circuit and, hence, the base of the input transistor 109 through control line 75 to the negative conductor 103. This shortens the pulse duration ti and adapts it to the duration of injection which not only reduces the current consumption, but it also reduces the force required to close the injection valve 10'.

Another possible circuit for the switch 72 is indicated in broken lines by the numeral 72', where it is shown connected, through a control line 75', to the control circuit 115 and to the base of the power transistor 116 and thus, when closed, it connects the base of this transistor to the negative conductor 103.

The method of operation of the fuel injection pump according to the invention will now be described with the aid of the drawing. The block diagram of FIG. 3, which is intended to be used with the secondary exemplary embodiment can also be used with the first exemplary embodiment according to FIG. 1 if the injection valve 10' is replaced by the injection valve 10 according to FIG. 1, and the connecting line 36' is replaced by the connecting line 36. The first exemplary embodiment according to FIG. 1 contains no control line 75.

The fuel injection valve according to FIG. 1 is supplied with fuel by the fuel injection pump 81 which delivers a quantity of fuel that is precisely adapted to the operational state of the engine and is set by the centrifugal rpm-governor 82 (see FIG. 3). The fuel is predelivered to the accumulation space 12 below the plunger 13. During this predelivery, the plunger 13 is displaced upwardly and compresses the pressure spring 14 serving as a storage spring. The fuel pressure prevailing in the accumulation space 12, and hence also in the pressure chamber 18, is determined by the degree of compression of the pressure spring 14 and this pressure acts on the valve needle 39, in both the opening and the closing directions. Now, the diameter DK of the force equalizer piston 59 is so dimensioned that the effective cross section of that piston 59 is equal to the annular cross section of the valve needle 39 which is subjected to the fuel pressure in the pressure chamber 18. This annular cross section is defined, on the one hand, by the diameter Dv of the valve needle 39 and, on the other hand, by the diameter of the valve seat 17. Thus, a complete equalization of forces is achieved, i.e., the forces, due to the fuel pressure, which act on the valve needle 39 in the opening and closing directions, respectively, are equal. Intentional, small deviations from these fixed diameters can serve to produce a supplementary force for acceleration the opening or closing motion of the valve member. The electromagnet 24 needs to overcome only the force of the valve spring 43 and, since the hydraulic forces are equalized, the force of this spring 43 is relatively small. Thus, the electromagnet 24 may also be relatively small and still able to effect a rapid opening of the valve. When the controller 88 (see FIG. 4) produces a control pulse 89, the electromagnet 24 acts via its armature 61 and the force equalizer piston 59 to attract the valve needle 39 which is held in operative connection with the force equalizer piston 59 by fuel pressure. This motion opens the valve seat 17 and the fuel which was predelivered to the accumulation space 12 and the pressure chamber 18 can be injected through the nozzle orifice 37 into the compression chamber of the engine which is not further shown. At the termination of the injection cycle, the plunger 13 returns to its starting position as drawn in FIG. 1, and its end 57, under the influence of the pressure spring, again presses down on the force equalizer piston 59 and hence also on the valve needle 39, forcing it back onto the valve seat 17, which is thereby closed. This closure process prevents a slow closing of valve needle 39 which might result in dribbling of fuel into the combustion chamber of the engine. Since the pressure spring 14 determines the injection pressure, it is very highly precompressed and its closing force is so great that the closing motion is very rapid and is not impeded by the still-energized electromagnet 24. This results advantageously in a very rapid closure process and makes a precise, timed control of the energization time of the electromagnet unnecessary. This latter advantage is especially significant because it is extremely difficult to produce the required switching times which, for Diesel engine injection, lie in the region from 1 to 3 milliseconds, by means of electronic control. Furthermore, the predelivery of fuel by the injection pump guarantees that, even during malfunctions of the control electronics, the injected fuel quantity will never be greater than that which has been predelivered. The force of the pressure spring 14 is so great that it is able to return the valve onto its seat 17 in spite of the additional hydraulic force acting in the opening direction which occurs due to the additional effective surface of the valve needle 39 which is subjected to fuel pressure when the valve is open.

This above-mentioned additional force acting in the opening direction is not effective, however, in the exemplary embodiment of the fuel injection valve according to FIG. 1, because a throttle 62 is inserted between the sections 16a and 16b of the pressure line 16, i.e. between the accumulation space 12 and the pressure chamber 18. When the injection valve is open, this throttle reduces the fuel pressure in the pressure chamber 18 with respect to the pressure prevailing in storage space 12 so that the hydraulic force which now acts upon the entire cross-sectional area of the valve needle 39, corresponding to the diameter Dv, is equal to the force which had acted on the previously described annular cross section which is effective when the valve is closed. This results in a dynamic equalization of forces so that the closure of the valve needle 39 does not require additional force. In the second exemplary embodiment of FIG. 2, the injection process is changed only in that, at the termination of the injection cycle, the plunger 13, when returning to its starting position shown in FIG. 2, actuates the switch 72 via the spring support plate 55'. The switch 72 then delivers a control pulse through line 75 to the electronic controller 88, shortening the pulse duration ti of the control pulse 89, i.e., more exactly, it terminates the energization time of the electromagent 24. The interaction of the control pulse with the electronic controller can occur in many different ways and two examples thereof have already been described with reference to FIG. 4.

Claims

What is claim is:

1. In an electromechanically controlled fuel injection valve for internal combustion engines, especially Diesel engines, including a valve housing, an electromechanical converter, especially an electromagnet, mounted within said housing for controlling the onset of fuel injection, means forming part of the housing and defining a valve seat communicating with at least one nozzle orifice and a fuel pressure chamber located near the valve seat, a valve spring, a valve needle sealingly guided within the valve housing and loaded by the valve spring for closing off the valve seat, and a fuel accumulation system, the fuel accumulation system including means defining an accumulation space, a displaceably mounted accumulation plunger, elastically yielding means for controlling the displacement of the accumulation plunger, and a fuel supply line connected to a fuel metering pump and to the fuel pressure chamber wherein the accumulation space communicates with the fuel supply line and with the fuel pressure chamber, the improvement comprising:

a force equalizer piston;

means defining a bore within the valve housing within which said equalizer piston is sealingly and displaceably disposed coaxially with said valve needle, and in positive operational connection therewith; and

an actuating member responsive to the energization of the electromagnet and in positive operational connection with said force equalizer piston;

whereby the accumulation plunger and the elastically yielding means are disposed with the valve housing;

whereby said valve needle and said force equalizer piston are so dimensioned that, when said valve seat is obturated, the hydraulic force acting on said valve needle tending to open said valve seat is at least approximately equal to the force acting on said valve needle tending to obturate said valve seat and

whereby the force acting on said valve needle tending to obturate said valve may be augmented by a force exerted mediately by said accumulation plunger on said valve needle.

2. An improved fuel injection valve as defined in claim 1, wherein said accumulation plunger is disposed so that its axis is an extension of and parallel with the axes of said valve needle, said force equalizer piston, said actuating member, and is so disposed that it can establish a positive operational connection with said valve needle to urge said valve needle onto said valve seat.

3. An improved fuel injection valve as defined in claim 2, further comprising a throttle, located between said accumulation space and said fuel pressure chamber, whereby the force acting on the valve needle tending to open said valve seat when said valve seat is obturated is rendered approximately equal to the force acting on the valve needle tending to open said valve seat when said valve seat is open.

4. An improved fuel injection valve as defined in claim 1, further comprising a throttle, located between said accumulation space and said fuel pressure chamber, whereby the force acting on the valve needle tending to open said valve seat when said valve seat is obturated is rendered approximately equal to the force acting on the valve needle tending to open said valve seat when said valve seat is open.

5. An improved fuel injection valve as defined in claim 1, further comprising an electric switch, disposed within the valve housing, whereby said accumulation plunger actuates said electrical switch and interrupts the current to said electromechanical converter.

6. An improved fuel injection valve as defined in claim 5, further comprising, in combination, a controller containing at least one switching transistor for controlling the timing of the energization of said electromagnet, wherein said electric switch is connected to the base of said at least one switching transistor in said controller.

7. An improved fuel injection valve as defined in claim 5, further comprising, in combination, a controller containing at least one power transistor connected in series with said energizing winding of said electromagnet, wherein said electric switch is connected to the base of said at least one power transistor.