EP1593839B1 - Fuel injector for combustion engines with a multi-stage control valve - Google Patents

Description

Technical area

To supply combustion chambers of self-igniting internal combustion engines with fuel, both pressure-controlled and stroke-controlled injection systems can be used. As fuel injection systems come next pump-nozzle units, pump-line-nozzle units and accumulator injection systems (common rail) are used. Storage injection systems advantageously make it possible to adapt the injection pressure to the load and speed of the internal combustion engine. In order to achieve high specific performance and to reduce the emissions of the internal combustion engine, the highest possible injection pressure is generally required.

State of the art

DE 101 23 915.6 relates to a fuel injection device. This is used on an internal combustion engine. The combustion chambers of the internal combustion engine are each supplied with fuel via fuel injectors. The fuel injectors are acted upon by a high pressure source, further comprising the fuel injection device according to the DE 101 23 915.6 known solution a pressure booster having a movable pressure booster piston which separates a connectable to the high pressure source chamber from a connected to the fuel injector high-pressure chamber. The fuel pressure in the high pressure space can be varied by filling a back space of the pressure booster with fuel or by emptying this back space of fuel.

The fuel injector comprises a movable closing piston for opening or closing the injection openings of the fuel injector facing the combustion chamber. The closing piston protrudes into a closing pressure chamber, so that it can be acted upon by fuel pressure. As a result, a force acting on the closing piston in the closing direction is achieved. The closing pressure chamber and another room are shared by a common Workspace formed, with all parts of the working space are permanently connected to each other for the exchange of fuel.

With this solution can be achieved by controlling the booster over the rear space that the drive losses in the high-pressure fuel system compared to a control via a temporarily connected to the high-pressure fuel source working space can be kept small. Furthermore, the high-pressure space is relieved only up to the pressure level of the high pressure accumulator and not up to leakage pressure level. On the one hand this improves the hydraulic efficiency, on the other hand, a faster pressure reduction can take place up to the system pressure level, so that the lateral distances lying between the injection phases can be shortened. In pressure-controlled injection systems with pressure booster the problem arises that the stability of the injected into the combustion chamber injection quantities, especially the representation of very small injection quantities such. required in the pre-injection, can not be guaranteed. This is mainly due to the fact that an injection valve member opens very quickly in pressure-controlled injection systems. Therefore, very small variations in the driving time of the control valve can greatly affect the injection quantity. Attempts have been made to remedy this problem by employing a separate needle stroke damper piston, which defines a damping space and must be guided in a high pressure tight clearance fit. Although this solution allows a reduction in the needle opening speed, on the other hand, the design effort and thus the cost of the injection system are greatly increased by this solution.

From DE 102 29 418 a device for damping the Nadelhubs the fuel injector is known. According to this solution, the fuel injection device comprises a high pressure accumulator, a pressure booster and a metering valve. The pressure booster comprises a working space and a control space, which are separated from each other by axially movable pistons. A pressure change in the control chamber of the pressure booster results in a pressure change in a compression space, which acts on a fuel inlet via a nozzle chamber. The nozzle chamber surrounds an injection valve member, which may be formed, for example, as a nozzle needle. A nozzle spring chamber which acts upon the injection valve member can be filled from the compression space of the pressure booster via a line which contains an inlet throttle point. On the outlet side, the nozzle spring chamber is connected to a space of the pressure booster via a line containing an outlet throttle point.

From DE 102 29 415 a device for Nadelhubdämpfung to pressure-controlled fuel injectors is also known. According to this solution, a device for injecting fuel comprises a fuel injector, which via a high-pressure source with under high pressure fuel can be acted upon and actuated via a metering valve. The injection valve member is associated with a independently movable from this damping element, which limits a damping chamber. The damping element has at least one overflow channel for connecting the damping chamber to a further hydraulic space.

In the solutions known from DE 102 29 418 and DE 102 29 415, the control valve is designed as a 3/2-way valve and controls a relatively large Rücklaufinenge the pressure booster. Servo valves are used in particular for this purpose. A disadvantage of the illustrated drive variants of fuel injectors with only one valve is the lack of flexibility with regard to the shaping of the injection pressure curve (guessing) in comparison to fuel injectors with two independent actuators.

Presentation of the invention

In order to increase the flexibility with regard to the shaping of the injection pressure curve (rate shaping) of fuel injectors, a servo-control valve is proposed which permits a shaping of the injection pressure curve at the fuel injector by different opening speeds of the valve member of the servo-control valve. Different opening speeds of the valve member, e.g. of a servo piston of a servo control valve may be connected via a multi-stage control valve within the servo loop, e.g. be realized via a 3/3-solenoid valve. Thus, the amount of fuel to be injected in each case into the combustion chamber of the internal combustion engine, i. the injection rate can be adjusted via the engine control unit of the internal combustion engine. The flexibility, i. the shaping of the injection pressure curve (rate shaping) can thereby be increased and thus the injection can be optimally adapted to the respective requirements of an internal combustion engine.

For this purpose, the invention proposes to use a three-stage 3/3-control valve to control the servo loop of a fuel injector actuated servo control valve. Depending on the switching position of the three-stage 3/3-control valve different flow restrictor cross sections can be released, via which different Absteuervolumina can be removed, which allow different opening speeds of the valve member in the form of a servo valve piston.

By means of a suitable design of control edges of the 3/2 valve member, a shaping of the injection pressure can be represented with these different opening speeds. Following the solution proposed according to the invention, furthermore, only one actuator is used in each case, for example a piezoelectric actuator or a solenoid valve per fuel injector, so that the manufacturing effort is limited. Also remains to be carried out at the control unit of the internal combustion engine modification effort low, since only one output stage per fuel injector, the corresponding number of cylinders to be supplied with fuel cylinders of the internal combustion engine, low.

As multi-stage control valves can be used solenoid valves or piezo valves, as well as valves that allow a continuous cross-sectional control.

drawing

The invention will be described in more detail below with reference to the drawing.

Figur 1

eine schematische Darstellung einer Ausführung eines Kraftstoffinjektors mit einem Servoventil, dessen Servokreis über ein 3/3-Magnetventil gesteuert wird,

Figur 2

Ansteuervarianten des 3/3-Magnetventils mit unterschiedlichen Ansteuerströmen,

Figur 3

sich gemäß des Ansteuerstromniveaus aus Figur 2 einstellende Hübe des Ventilglieds,

Figur 4

sich entsprechend der Hubverläufe einstellende Düsendrücke,

Figur 5

sich einstellende Hubbewegungen des Einspritzventilglieds und

Figur 6

eine weitere Ausführungsvariante des in Figur 1 dargestellten Kraftstoffinjektors, wobei das Magnetventil anstelle eines Schiebers mit einem Sitz-Sitz-Ventil versehen ist.

It shows:

FIG. 1

a schematic representation of an embodiment of a fuel injector with a servo valve whose servo circuit is controlled by a 3/3-way solenoid valve,

FIG. 2

Control variants of the 3/3-solenoid valve with different drive currents,

FIG. 3

according to the Ansteuerstromniveaus from Figure 2 adjusting strokes of the valve member,

FIG. 4

according to the Hubverläufe adjusting nozzle pressures,

FIG. 5

adjusting strokes of the injection valve member and

FIG. 6

a further embodiment of the fuel injector shown in Figure 1, wherein the solenoid valve is provided instead of a slide with a seat-seat valve.

variants

Figure 1 shows a first embodiment of a fuel injector containing a fuel injector with a multi-stage configured valve for controlling.

It can be seen from the illustration according to FIG. 1 that a fuel injector 3 containing a pressure booster 5 is connected via a high-pressure line 2 to a pressure accumulator 1 (common rail). The fuel injector 3 comprises a preferably multi-part injector housing 4, in which a pressure booster 5 is received. The pressure booster 5 comprises a first piston part 6, which is acted upon by a restoring spring 7. The return spring 7 is based on an example annular configured stop 10, which is received in a working chamber 8 of the booster 5. The working space 8 of the pressure booster 5 is permanently connected to the pressure accumulator 1 (common rail) and is acted upon by the pressure prevailing in the accumulator 1 system pressure level. About the first piston part 6 of the working space 8 and a differential pressure chamber 9 (rear space) of the pressure booster 5 are separated from each other. The differential pressure chamber 9 is depressurized via a control line 11.

Pressure amplifier 5 also includes a compression chamber 12, which is acted upon via an end face 14 of a second piston part 13 of the pressure booster 5. According to the pressure transmission ratio, which occurs depending on the design of the booster 5, the volume of fuel received in the compression chamber 12 is compressed to a higher pressure. From the compression chamber 12 of the booster 5 branches off a nozzle chamber inlet 23, which acts on a nozzle chamber 24 of the fuel injector 3 with a correspondingly the transmission ratio of the booster 5 achievable higher pressure level.

From the differential pressure chamber 9 (back space) of the pressure booster 5 extends an overflow 15, in which a first throttle point 16 is formed to a pressure chamber 17. In the pressure chamber 17 is a damping piston 19, whose one end face an opposite end face of an example formed in one piece, as Nozzle needle provided injection valve member 18 acted upon. The damping piston 19 comprises a bore 20 in which a second throttle point 21 is formed. In addition, the damping piston 19 is acted upon by a spring 22, which is supported on a surface of the pressure chamber 17.

The nozzle chamber inlet 23 extending from the compression chamber 12 of the pressure intensifier 5 to the nozzle chamber 24 acts on the nozzle chamber 24 with a fuel volume under increased pressure. Within the nozzle chamber 24, which surrounds the injection valve member 18, which can be embodied in one piece, for example, a pressure stage 25 is formed on it. By flowing into the nozzle chamber 24, fuel at elevated pressure level, acts on the pressure stage 25 of the integrally formed injection valve member 18, for example, an acting in the opening direction hydraulic force. From the nozzle chamber 24, the fuel received there flows through an annular gap injection openings 26 to release the injecting an amount of fuel into a not shown here combustion chamber of an internal combustion engine when set in the open position injection valve member 18. The control line 11 for pressure relief of the differential pressure chamber 9 (back space) of the pressure booster 5 opens into a control valve 32 of a multi-stage valve 30, which is arranged in the upper region of the fuel injector 3. The control line 11 opens into a first hydraulic chamber 33 of the control valve 32. To close the first hydraulic chamber 33 of the control valve 32, a flat seat 38 is formed on the servo valve piston 35. The flat seat 38 in the lower region of the servo valve piston 35 closes a first control edge 36. In addition, a second control edge 37 is formed in the housing 42 of the control valve 32. Above the first hydraulic chamber 33 is located in the housing 42 of the control valve 32, a second hydraulic chamber 34 which is connected to a branch 40 of the high-pressure line 2. As a result, in the second hydraulic chamber 34, the pressure in the accumulator 1 (common rail) prevailing system pressure level always. In the upper region of the housing 42 is a pressure chamber 39. This is a third throttle 41 upstream, which leads away from the branch 40 of the high-pressure line 2. In addition, a low-pressure space is arranged in the housing 42 of the control valve 32 below the first control edge 36, which is released or closed by the servo valve piston 35 according to its position. From this space, a first return 43 extends into the low pressure region of a fuel injection system, not shown here.

From the pressure chamber 39 of the control valve 32 extends a conduit in which a fifth throttle body 56 is formed. This line runs parallel to the branch 40 from the high-pressure line 2, which opens at a fourth control edge 54 in the housing 50 of the actuating valve 31. In the housing 50 of the actuating valve 31 is a movable in the vertical direction valve member 51. At the lower end of a further flat seat 52 is formed, which releases a third control edge 53 and closes. Below the flat seat 52 is a low-pressure side hydraulic chamber from which a return 62 extends to a low-pressure region of a fuel injection system not shown here. In the branch 40 of the high pressure line 2, which extends within the housing 50 of the control valve 31, a fourth throttle body 55 is formed. The housing 50 of the control valve 31 further comprises a hydraulic space 57 which is separated from the second return 62 via the further flat seat 52 in cooperation with the first control edge 53.

Above the housing 50 of the control valve 31, an armature 58 is provided, which cooperates with a magnetic coil 60. Instead of the magnet armature / magnet coil arrangement 58, 60, the actuation valve 31 can also be actuated via a piezoactuator, not shown in FIG.

In the illustration according to FIG. 1, the armature 58 of the actuation valve 31 is acted upon by a closing spring 59. Parallel to the closing spring 59, a further spring element 61, which biases a stop for the armature 58 of the actuating valve 31 and serves as a stroke limiter or damping device during energization of the solenoid 60 for insulating the bruise of the armature 58 extends.

Figure 2 are different from each other Bestromungsniveaus of the actuating valve 31 can be seen.

Figure 2 shows the stroke 70 of the valve member 51 of the actuating valve 31, plotted against the time axis at different energization. At a first Bestromungsniveau 71, a first stroke of the valve member 51 is set, starting at a drive time 73, in which the solenoid 60 or a piezoelectric actuator of the actuating valve 31 is energized. The stroke, which covers the valve member 51 of the actuating valve 31 when energized with a second Bestromungsniveau 72 is also shown. In the latter case, the valve member 51 of the actuating valve 31 returns a maximum stroke.

When the solenoid 60 is energized with a first, relatively low current level 71, the valve member 51 of the actuating valve 31 is placed in a first, middle switching position. In this state, the armature 58 is located on a magnetic coil 60 surrounding, biased by the other spring 61, for example, annular stop. In this switching position, the fifth throttle point 56 is released, wherein the fourth throttle point 55 remains closed. The further flat seat 52 is open, so that the volume of fuel contained in the hydraulic space 57 can flow into the second return to the low-pressure region of the fuel injection system. This results in a pressure relief of the pressure chamber 39 by means of control valve 32. The servo valve piston 35 opens and in turn releases the flat seat 38. As a result, the fuel supply contained in the differential pressure chamber 9 (rear space) of the pressure booster 5 flows via the second hydraulic chamber 33 into the first return line 43 onto the low-pressure side of the fuel injection system.

The servo valve piston 35 opens slowly, so that a delayed, slow pressure builds up in the compression chamber 12, which sets a slow opening of the injection valve member 18, which can be embodied in one piece, for example, via the nozzle chamber inlet 23 and the nozzle chamber 24. Accordingly, the injection openings 26 are opened only slowly in the combustion chamber of a self-igniting internal combustion engine, so that one in FIG. 4 during the injection at the nozzle, indicated by reference numeral 91.

In FIG. 3, the stroke of the servo valve piston 35 of the valve 32 which adjusts itself at the first energization level 71 and the stroke of the servo valve 35 which adjusts itself at the second current level 72 are reproduced.

If, as shown in FIG. 2, the solenoid coil 60 of the actuation valve 31 is acted on by a second, higher current level 72, then a stroke profile 95 of the valve member 51 of the actuation valve 31 is established (see FIG. In this case, the valve member 51 is placed in a further, second switching position, in which the armature 58, which is connected to the valve member 51, against the action of the closing spring 59 continues in a vertical upward direction, so that both the fourth orifice 55th as well as the fifth throttle point 56 are released. The release of the fifth throttle body 56 is carried out by opening the further flat seat 52 at the third control edge 53, whereas the release of the fourth throttle body 55 is achieved by a successful in the vertical direction ascending the valve member 51 with annular groove of the actuating valve 31. As a result, a control volume flows via the two open throttling points 55, 56 acting as outlet throttle into the second return line 62 to the low-pressure side of the fuel injection system. Due to this, a faster pressure reduction occurs in the pressure chamber 39, which contributes to a faster opening of the servo valve piston 35 with a high opening speed into the pressure chamber 39. Because of this results in a faster pressure relief of the differential pressure chamber 9 (back space) of the booster 5 and consequently a faster pressure build-up in the compression chamber 12 and thus - via the nozzle chamber inlet 23 - in the nozzle chamber 24, which surrounds the injection valve member 18. The injection valve member 18 accelerates faster so that a higher pressure is established at the injection openings 26, which leads to the pressure increase at the injection nozzle identified by reference numeral 92 in FIG.

While in FIG. 2, the drive current levels of the valve member 51 of the operation valve 31 are opposed to each other, both at the drive timing 73, in FIG. 3, stroke paths 80 of the servo valve piston 35 of the control valve 32 are opposed to each other. In the case of the energization of the solenoid coil 60 and the magnetic actuator with a first lower current level 71, there is a ramp-shaped stroke of the servo valve piston 35, indicated by reference numeral 82, which is characterized by a first slope 84.

When the solenoid 60 or a piezoelectric actuator of the actuating valve 31 is energized with a second current level 72, however, a second ramp-shaped stroke arises 83, as Figure 3 can be removed, which has a second slope 85. Both strokes 82, 83 are limited by the maximum stroke H _max , which is indicated in the illustration of Figure 3 by a plateau 81, which extends only slightly below the maximum stroke H _{max of} the servo valve piston 35.

FIG. 4 shows the pressure curve at the injection nozzle.

When the magnet coil 60 or the piezoelectric actuator of the actuation valve 31 is energized with a first lower current level 71, a first pressure increase 91 occurs at the injection nozzle according to FIG. 4, while when the magnet coil 60 or a piezoactuator of the actuation valve 31 is energized with a higher current level (FIG. see Figure 2, there reference numeral 72) adjusts a second pressure increase 92 at the injection nozzle at the combustion chamber end.

The resulting Hubverläufe 93 of the injection valve member 18 are shown in the representation of Figure 5. The stroke of the injection valve member 18 when energizing the solenoid 60 and the piezoelectric actuator with a first, lower current level 71 is indicated by reference numeral 94 and has a compared to the energization of the solenoid 60 and the piezoelectric actuator of the actuating valve 31 with a second higher current level 72, flatter rise on. When the magnet coil 60 or a piezoactuator of the actuation valve 31 is energized with the second energization level 72, the stroke profile of the injection valve member 18 is indicated by reference numeral 95 in the illustration according to FIG.

In the deactivated state of rest, the multi-stage valve 30 is closed. Thus, the flat seat 38 of the control valve 32 is also closed, so that the differential pressure chamber 9 (back space) of the pressure booster 5 and the control line 11 are separated from the first return 43 in the low pressure region of the fuel injector. Pressure amplifier 5 is pressure balanced in this state, so that no pressure gain takes place by this.

To activate the booster 5, the differential pressure chamber 9 (back space) is depressurized by the multi-stage valve 30. This is done by energizing the solenoid 60, whereupon the valve member 51 rises and the further flat seat 52 releases. Via the opened, further flat seat 52, the control volume, which is present via the branch 40 and the fourth throttle point 56, flows into the second low-pressure-side return 62. Due to the resulting pressure relief of the pressure chamber 31, the servo valve piston 35 opens and releases the flat seat 38, so that fuel flows from the differential pressure chamber 9 via the control line 11 in the first return 43 to the low pressure side of the fuel injection system. The pressure in the compression chamber 12 increases sharply and is guided in accordance with the transmission ratio of the booster 5 through the nozzle chamber inlet 23 into the nozzle chamber 24. At the pressure stage 25 of the injection valve member 18, a force acting in the opening direction hydraulic force builds up, so that the injection openings 26 are released in the combustion chamber end of the fuel injector 3 and fuel can be injected into it.

To complete the injection operation, the actuation valve 31 is deactivated, i. the energization of the solenoid 60 and a piezoelectric actuator canceled. The closing spring 59 places the valve member 51 in its closed position, so that the further flat seat 52 is closed. For a pressure build-up in the pressure chamber 39 of the control valve 32 is ensured, so that the servo valve piston 35 is placed with its flat seat 38 in its closed position. In this state, the first control edge 36 is above the low-pressure side hydraulic space, from which the first return 43 is fed to the low pressure region of the fuel injection system, closed and the piston parts 6, 13 of the pressure booster 5 move back to its rest position. Because of this, the pressure in the pressure chamber 24 drops, the hydraulic force acting there in the opening direction breaks down, so that the injection valve member 18 moves through the pressure relief of the pressure chamber 17 in its closed position, supported by the spring 22nd

The refilling of the compression chamber 12 of the booster 5 via a check valve, which is interposed between the pressure chamber 17 above the injection valve member 18 and the compression chamber 12 of the booster 5.

The achievable injection forms which can be set via the different energization levels 71, 72 of the solenoid coil 60 or of a piezoactuator of the actuation valve 31 can be varied within a map via a control device assigned to the internal combustion engine. Thus, the opening speeds of the multi-stage valve 30 can be adapted to the particular operating conditions of the self-igniting internal combustion engine. If a slow movement of the servo valve piston 35 of the control valve 32 or a slow movement of the valve member 51 of the actuating valve 31 is ensured, in particular, small injection quantities can be reproducibly represented, which are required for pilot injections of fuel into the combustion chamber of an internal combustion engine.

The illustration according to FIG. 6 shows a further embodiment of the fuel injector shown in FIG.

The mode of operation of the fuel injector 3 shown in FIG. 6 substantially corresponds to the mode of operation of the fuel injector 3 shown in FIG. 1, which reference is made to avoid repetition.

In contrast to the representation according to FIG. 1, the multi-stage valve 30 illustrated in FIG. 1 and in particular the actuating valve 31 has a modification. While in the embodiment according to FIG. 1 the valve member 51 has a sliding seal closing the fourth control edge 54, the valve member 51 is provided with a valve seat 100 in the illustration according to FIG. The valve seat 100, which may be formed on the housing side on the housing 50 of the actuating valve 31, cooperates with a conical surface 102 of the valve member 51. The conical surface 102 of the valve member 51 cooperates with a seat edge 101. The embodiment of the actuation valve 31 with a valve seat 100 advantageously allows the achievement of a high sealing effect, which is not always achievable with small strokes on a slide seal, as shown in FIG. Denoted by reference numeral 103 is a low pressure space from which the return 62 extends into the low pressure region of the fuel supply system.

In the embodiment variant shown in FIG. 6, the switching functions are therefore reversed. In the middle switching position of the valve member 51 serving as a drain throttle throttling points 55 and 56 are opened so that the servo valve piston 35 opens quickly, which sets a rapid pressure build-up at the beginning of the injection. In contrast, in the upper switching position, ie when energizing the solenoid 60 or a piezoelectric actuator of the actuating valve 31 with a higher current level, the fifth throttle point 56 is opened, whereas the fourth throttle point 55 is closed. In this case, the servo valve piston 35 of the control valve 33 opens slower, so that sets a delayed pressure build-up at the beginning of the injection. With the embodiment variant shown in FIG. 6, it is just the opposite with regard to the achievable opening speeds compared to the statements made in connection with FIG. 1 for influencing the opening speed of the multi-stage valve 30.

LIST OF REFERENCE NUMBERS

1

accumulator

2

High-pressure line

3

fuel injector

4

injector

5

booster

6

1st piston part

7

Return spring

8th

working space

9

Differential pressure chamber (backspace)

10

attack

11

control line

12

compression chamber

13

2nd piston part

14

face

15

overflow

16

1. restriction

17

pressure chamber

18

Injection valve member

19

damping piston

20

drilling

21

2. Throttling point

22

feather

23

Nozzle chamber inlet

24

nozzle chamber

25

pressure stage

26

Injection ports

30

multi-stage valve

31

actuation valve

32

control valve

33

1. hydraulic space

34

2. hydraulic space

35

Servo valve piston

36

1st control edge

37

2nd control edge

38

flat seat

39

pressure chamber

40

Branch high-pressure line

41

3. Throttling point

42

casing

43

1st return (low pressure)

50

casing

51

valve member

52

flat seat

53

3rd control edge

54

4th control edge

55

4. Throttling point

56

5. Throttling point

57

hydraulic room

58

anchor

59

closing spring

60

solenoid

61

another spring

62

second return (low pressure)

70

Stroke valve member 51st

71

1. current level

72

2. Power level

73

control time

80

Stroke from servo valve piston 35

81

plateau

82

Rise ramp at 1st current level 71

83

Rise ramp at 2nd current level 72

84

1st slope

85

2nd slope

90

Nozzle pressure curve

91

1. pressure rise

92

2. Pressure increase

93

Hub injection valve member

94

Stroke progression at 1st current level 71

95

Stroke course at 2nd level 72

100

valve seat

101

seat edge

102

conical surface

103

Low-pressure chamber

Claims (12)

1. Fuel injector (3) for the injection of fuel into one of the combustion spaces of an internal combustion engine, with a pressure intensifier (5) which has a working space (8) which is connected permanently to a pressure accumulator (1), such as, for example, a common rail, and which is separated from a differential pressure space (9) by a piston part (6, 13), the differential pressure space (9) of the pressure intensifier (5) being capable either of being relieved of pressure or of being acted upon by pressure via a valve (30), and with an injection-valve member (18), characterized in that the valve (30) relieving of pressure or acting with pressure upon the differential pressure space (9) of the pressure intensifier (5) and controlling the injection-valve member (18) has a control valve (32) containing a servovalve piston (35) and also an actuator-actuated multi-stage actuation valve (31).
2. Fuel injection device according to Claim 1, characterized in that the control valve (32) has a pressure space (39) which acts upon the servovalve piston (35) and which is flow-connected to a hydraulic space (57) of the actuation valve (31).
3. Fuel injection device according to Claim 1, characterized in that the control valve (32) and the actuation valve (31) are flow-connected to one another via a branch (40) running from a high-pressure line (2).
4. Fuel injection device according to Claim 1, characterized in that, in an intermediate position of a valve member (51) of the actuation valve (31), with current at a first current level (71) being applied to an actuator (60), a throttle point (56) acting as an outflow throttle is released in order to relieve the pressure space (39) of the control valve (32) of pressure.
5. Fuel injection device according to Claim 1, characterized in that, with current at a second current level (72) higher than the first current level (71) being applied to the actuator (60) of the actuation valve (31), for relieving the pressure space (39) of pressure, the throttle point (56) and a further throttle point (55) are released in order to relieve the pressure space (39) of the control valve (32) of pressure.
6. Fuel injection device according to Claim 5, characterized in that the further throttle point (55) of the actuation valve (31) is capable of being released or of being closed by means of a slide seal formed by the valve member (51).
7. Fuel injection device according to Claim 1, characterized in that the valve member (51) of the actuation valve (31) has formed on it a valve seat (100) which closes the further throttle point (55) when current at the second higher current level (72) is applied to the actuator (60) of the actuation valve (31), so that a relief of the pressure space (39) of pressure takes place only via the throttle point (56) and a slow opening of the servovalve piston (35) is established.
8. Fuel injection device according to Claim 1, characterized in that, when current is applied to the actuator (60) of the actuation valve (31), the valve member (51) of which has a valve seat (100), in an intermediate position of the valve member (51) both the throttle point (56) and the throttle point (55) are released, so that a rapid relief of the pressure space (39) of the control valve (32) of pressure takes place.
9. Fuel injection device according to Claim 1, characterized in that a 3/3-way valve is used for controlling the control valve (32) designed as a servovalve.
10. Fuel injection device according to Claim 9, characterized in that a valve having a magnet-coil arrangement (58, 60) or an actuation valve (31) having a piezoelectric actuator is used as an actuation valve (31) of the control valve (32).
11. Fuel injection device according to Claim 1, characterized in that, by means of different switching positions of the multi-stage actuation valve (31), various opening speeds of the servovalve piston (35) are achieved and the injection-pressure profile (90) is varied.
12. Fuel injection device according to Claim 11, characterized in that, injection takes place with the first slower pressure rise (91) in the case of a slower opening speed of the servovalve piston (35) and injection with a second faster pressure build-up (92) takes place in the case of a second faster opening speed of the servovalve piston (35).

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