WO2001014718A1

WO2001014718A1 - Injector

Info

Publication number: WO2001014718A1
Application number: PCT/DE2000/002679
Authority: WO
Inventors: Wolfgang Stoecklein
Original assignee: Robert Bosch Gmbh
Priority date: 1999-08-20
Filing date: 2000-08-10
Publication date: 2001-03-01
Also published as: CZ20011385A3; JP2003507643A; DE19939448A1; KR20010083912A; EP1125048A1

Abstract

The invention relates to an injector (10, 210), in particular for controlling injection of fuel into the combustion chamber of an internal combustion engine having a closing member (14, 214) which controls an injection port (16, 216) and an actuating device (44, 244). Said device consists of a piezoelectric actuator (52, 252) and a valve element (50, 250) for regulating hydraulic fluid communication between the channels conducting hydraulic fluid (28, 228, 36, 236, 46, 246, 48, 248). According to the invention, the valve element (50, 250) enables pressure or needle lift controlled injection cycles (10, 210) of the injector by controlling hydraulic fluid connections between at least one inlet (46, 246), one return (48, 248) and two control channels (28, 228 and 36, 236) respectively and can be brought into at least three switch positions.

Description

In ector

State of the art

The invention relates to an injector according to the preamble of claim 1. Such an injector is already known for example from DE 196 24 001 AI. The actuating device of this injector consists of a piezoelectric actuator and a valve with a displaceably guided valve element. This controls a pressure medium connection between a pressure medium

High pressure and a pressure medium under low pressure channel and thus determines the pressure in a pressure chamber acting on the closing element of the injector. When the pressure medium connection is closed, the closing element of the injector is subjected to high pressure and is thereby held in its closed position. With the opening of the pressure medium connection, the high pressure is reduced, so that the closing member carries out a lifting movement. Injection openings are opened in the injector, through which fuel injects into a combustion chamber of an internal combustion engine. Such injectors are also referred to as needle stroke controlled injectors. These are particularly characterized in that the actuation of the closing member - a needle - takes place independently of the pressure level in the interior of the injector. In addition to needle-stroke controlled injectors, so-called pressure-controlled injectors are also known. Their locking members perform a lifting movement as soon as a certain one in the interior space surrounding the locking members

Opening pressure is exceeded. When the pressure is below the opening pressure, the locking elements are in the closed position.

Due to the speed of their switching movements, injectors with piezoelectric actuators are particularly suitable for representing injection cycles from a plurality of injections separated in time, which are referred to, for example, as pre-injection, as main injection and as post-injection. It has proven to be extremely advantageous to carry out the pre-injection and the main injection in a pressure-controlled manner and to carry out the post-injection in a needle-stroke controlled manner. Disadvantageously, the known injectors only allow one type of control.

Advantages of the invention

In contrast, an injector with the characterizing features of claim 1 has the advantage that it allows a pressure-controlled pre-injection and main injection and a needle stroke-controlled post-injection, in which high pressure is present in the interior of the injector. Such injectors enable particularly low-noise and low-emission operation of an internal combustion engine.

This is achieved by using a

Actuating device for the closing member, which in addition to the actuator comprises a 4/3 way valve for controlling the pressure conditions in the interior of the injector. It is advantageous this 4/3 way valve is equipped with two valve elements that form seat valves. A valve slide, which creates an additional slide valve, is arranged between these two seat valves. With a single actuation of the actuator, an injection cycle can be generated with several injections that are time-controlled, pressure-controlled or needle-stroke-controlled. The drive frequency of the actuator and the heat loss generated by it is relatively low and thus the stability of the actuator is high. Furthermore, the injector according to the invention is distinguished by the fact that it does not have any noteworthy pressure medium leakage in the uncontrolled state.

Further advantages or advantageous developments of the invention result from the subclaims and the description.

drawing

Exemplary embodiments of the invention are shown in the drawing and explained in more detail in the description below.

Figure 1 shows the In ector according to the invention schematically in longitudinal section, in the

Figures 2 to 4 are diagrams for explaining the various control options of the injector; Figures 5 and 6 show two advantageous developments of the injector according to the invention;

Figure 7 shows a second embodiment of a

Injector also in longitudinal section. Description of the embodiments

FIG. 1 shows a schematic representation of an injector 10 according to the invention. This has a closing member 14 which is slidably arranged in a nozzle bore 18 of a housing 20 for controlling injection openings 16. The closing member 14 is designed in the form of a needle which is divided into different needle sections 22a to 22e with different outside diameters. The needle sections 22a and 22c act together with the wall of the nozzle bore 18 as guide sections; the needle sections 22b and 22d are recessed in the outer diameter with respect to the wall of the nozzle bore 18. This results in an annular space 24 filled with pressure medium in the area of the needle section 22d, which is expanded at the point of transition from the needle section 22c to the needle section 22d. There, a first pressure medium channel 28 opens into the annular space 24. The needle section 22e is designed as a tip, which closes the injection openings 16 in a pressure-tight manner in the position of the closing member 14 shown.

The closing member 14 is held in the closed position by two compression springs 30 and 32. For this purpose, the first compression spring 30 engages the shoulder between the needle sections 22b and 22c of the closing member 14 and is supported on a ring 34 fixed in the interior of the nozzle bore 18, while the second compression spring 32 between the end face of the closing member 14 and a closing the nozzle bore 18 Wall is clamped.

The installation space of the second compression spring 32 forms a pressure chamber 33, into which a second pressure medium-carrying channel 36 opens and from which a third pressure medium-carrying channel 38 emerges. In both channels 36 and 38 Dossein 40 and 42 are arranged to determine the course of the lifting movement of the closing member 14.

The first channel 28 and the second channel 36 act as control channels which act hydraulically on the closing element 14 in addition to the mechanical forces of the compression springs 30, 32. For this purpose, these channels 28 and 36 are coupled to an actuating device 44 which

Pressure medium connections between at least four channels - an inlet 46, a return 48 and the two channels 28 and 36 - controls.

The actuating device 44 has a slide bore 45 formed in the housing 20 with a valve element 50 which is displaceably guided therein, and an externally controllable piezoelectric actuator 52. This interacts with the valve element 50 with the interposition of a hydraulic translator 54. The translator 54 has two pistons 56 and 58 of differently sized pressure areas for translating the stroke movement of the actuator 52, which enclose a translator chamber 60 between them. The piston 56 with the larger pressure area faces the actuator 52 and the piston 58 with the smaller pressure area faces the valve element 50.

The valve element 50 consists of two valve members 62 and 64 in the form of balls and an essentially cylindrical valve slide 66 located therebetween. The end of this valve valve 64 is designed as a truncated cone 68. The valve slide 66 is provided with a centrally arranged channel 70, which branches at its one end facing the pin 68 into a plurality of radial channels 71. The latter emerge at the transition of the pin 68 into the cylindrical region of the valve slide 66 into the interior of the slide bore 45. The opposite end of the longitudinal bore 70 forms a first valve seat 72. This is controlled by the first valve member 62. The latter abuts the piston 58 of the translator 54 via a support element 74. For this purpose, the valve member 62 interacts with a valve spring 76 which is supported on the end face of the valve slide 66 which has the first valve seat 72 and which acts on the valve member 72 in the direction of its open position. The installation space of the valve spring 76 is hydraulically connected to the return 48. A second valve spring 78 surrounds the first valve spring 76 on the circumference and bears on the one hand on a plate 80 covering the slide bore 45 and penetrated by the piston 58 of the translator 54 and on the other hand on the end face of the valve slide 66.

To form a slide valve, a transverse channel 83 penetrating the channel 70 at right angles is provided approximately in the middle of the valve slide 66. Its ends emerge from the circumference of the valve slide 66 and form with the

Slider bore 45 a pressure medium-filled cavity 110. This is sealed with the aid of a control edge 112 on the valve slide 66 against the housing-side channel 36. With a corresponding deflection of the valve slide 66, a connection of this cavity 110 to the housing-side channel 36 is created, via which the pressure level in the pressure chamber 33 of the closing element 14 can be influenced.

According to FIG. 1, the pin 68 of the valve slide 66 lies against the second valve member 64, but without lifting it off its second valve seat 82, which is formed on the housing side at a constriction 69 of the slide bore 45. In the flow direction of the pressure medium before the valve seat 82, the inlet 46 and in the flow direction after the valve seat 82 the channel 28 opens into the slide bore 45 a. The second valve member 64 is acted upon in the closing direction by a closing spring 84 which is supported on a wall 86 closing the slide bore 45.

The injection cycles shown in FIGS. 2 to 4 and explained below can be represented with the injector 10. For this purpose, the valve element 50 can be brought into three different switching positions, the basic position being shown in FIG. 1. Depending on the switching position, the injection cycles are pressure or needle stroke controlled.

In the various diagrams 100 to 108 of FIGS. 2 to 4, the stroke course of the actuator 52, the valve member 62, the valve member 64, the pressure course in each case

Channel 28, as well as the stroke of the closing member 14 are graphically plotted over time. In all cases it is assumed that the injector 10 is initially in its basic position shown in FIG. 1. In this basic position, the valve seat 70 is open and the valve seat 82 is closed. Due to the position of the valve spool 66, the pressure medium connection between the channels 36 and 70 is interrupted.

If the actuator 52 is now actuated, it generates a lifting movement which is transmitted to the valve member 62 in a hydraulically translated manner (diagram 100). At the time T1, the valve member 62 bears against the first valve seat 72, closes it (diagram 102) and thus establishes a mechanical operative connection between the actuator 52 and the actuator 52

Valve slide 66 forth. With increasing stroke of the actuator 52, the valve member 64 of the second seat valve (diagram 106) opens after T1, so that pressure medium under high pressure can flow into the channel 28 from the inlet 46. The channel 36 is still closed. According to diagram 108 increases thereby the pressure level in the channel 28 or in the annular space 26 surrounding the closing member 14. Because of the pressure surface formed by the needle section 22c, the closing member 14 is thereby loaded with a hydraulic opening force which counteracts the mechanical closing force specified by the pressure fields 30 and 32. When the opening pressure is reached, the closing member 14 executes an opening movement (diagram 108) at time T2 and thereby releases the injection openings 16.

This injection cycle is ended by withdrawing the actuation of the actuator 52 in a single stage (time T3). First, the second valve member 64 closes and shuts off the inlet 46. At time T4, the valve slide 66 has reached its starting position and the valve member 62 (diagram 102) opens a pressure medium passage from the channel 70 to the return 48. The channel 28 is thus relieved of pressure via the radial channels 71 and the channel 70, as a result of which the closing member 14 due to the the pressure springs 30 and 32 applied force is moved back into the closed position and thereby closes the injection openings 16 again. The injection cycle described is therefore pressure-controlled.

In contrast, a needle stroke controlled

Injection process explained below with reference to Figure 3. Actuator 52 executes a first stroke movement H1 according to diagram 100 up to time T1, which continues with a certain time delay at time T2 in a second stroke movement H2 up to the maximum stroke. From time T3, the actuation of actuator 52 is reduced to zero in a single step S1. Due to the stroke movement Hl, the valve member 62 first closes the valve seat 72 (time T5) and keeps it closed until time T6. Until the beginning of the second Stroke movement H2 (time T2), the closing member 14, ie the pressure medium connection of the transverse channel 83 to the channel 36 is interrupted, then opened. This is expressed by the dotted curve in diagram 102. With the exception of a time delay at the beginning, the movement of the second valve member 64 (diagram 104) follows the course of the stroke movement of the actuator 52 (diagram 100). Due to the connection of the inlet 46 to the channel 28, which is caused by the opening of the second valve seat 82, the pressure in the annular space 24 increases around the closing member 14, the course of this

Rise over the throttle 40 in the channel 28 is affected. The maximum pressure does not change with the start of the second stroke movement H2 of the actuator 52. The lifting movement of the closing member 14 (diagram 108) is ended in this injection cycle from time T2, in which the transverse channel 83 is connected to the channel 36 during the second lifting section H2 of the actuator 52, although the actuator 52 is still electrically controlled (Diagram 100) and high pressure is still present in the annular space 24 (diagram 106). This is due to the pressure increase in the pressure chamber 33 at this point in time T3, the pressure force exerted on the closing member 14 in conjunction with the forces of the compression springs 30 and 32 is sufficient to complete the injection process in a needle-stroke controlled manner.

FIG. 4 shows a further injection cycle. In this case, the actuator 52 executes a first stroke movement H1 up to the time T1 and, comparable to FIG. 3, performs a second stroke movement H2 with a smaller time delay from the time T2 up to the maximum stroke. From the time T3, this maximum stroke is withdrawn in two stages S1 and S2. The second stage S2 takes place at time T4. Between the times T2 and T3, as the dotted characteristic curve in diagram 102 shows, there is a pressure medium connection between the channels 70 and 36 - l ü ¬

the transverse channel 83, whereby the pressure chamber 33 comes under high pressure. As explained in connection with FIG. 3, this high pressure is sufficient to end the injection process under needle stroke control (diagram 108). The closing movement S1 of the actuator 52 interrupts the pressure medium connection of the channels 70 and 36 up to the point in time T3, the first valve seat 72 is still closed according to diagram 102, solid line, and the second valve seat 82 is opened. In this position of the valve spool 50, the high pressure builds up in the

Pressure chamber 33 via the third pressure medium channel 38 and the throttle 42 built therein gradually from. After falling below a pressure threshold determined by the compression springs 30 and 32, the pressure force in the annular space 24 suppresses the closing forces of the compression springs 30 and 32, so that the closing member 14 opens again at time T4 under pressure control. The second injection process that occurs as a result of this allows, after the main injection, a post-injection of fuel, which is completed when the actuation of the actuator 52 is withdrawn in stage S2 (time T5). As diagram 102 shows, the first valve member 62 releases the first valve seat 72 again at time T5, so that the basic position shown in FIG. 1 is reached again.

FIG. 5 shows a first advantageous development of an injector 10 according to the invention, which differs from the embodiment according to FIG. 1 primarily in that the valve slide 66 does not require a transverse bore 83. This is done by training a second

Pressure medium under high pressure leading inlet 47 reached in the housing 20, which opens in the region of a constriction 88 of the valve slide 66. This constriction 88 is dimensioned in its axial extent so that a pressure medium connection in the case of the maximum stroke of the actuator 52 exists between the inlet 46 and the channel 36 leading to the pressure chamber 33. Of course, it would also be possible to design the inlet 47 as a branch to the already existing inlet 46. An injector 10 developed in this way is characterized in particular by its better dynamic behavior when closing the closing member 14 (FIGS. 3 and 4).

A second advantageous development of the injector 10 is shown in FIG. 6. In the installation space of the closing spring 84 according to FIG. 1 formed by the slide bore 45, an intermediate stroke stop 90 is installed, which facilitates the positioning of the valve element 50 in an intermediate position and the overshoots when the actuator moves rapidly 52 avoids. This is in the intermediate position

Valve element 50 in a position in which the valve seat 82 is already open, but the channel 36, which cannot be seen in FIG. 6, is still hydraulically blocked. Such an intermediate position can be seen graphically in the diagrams 100 in FIGS. 3 and 4 at the end of the stroke movement H1 of the actuator 52. The intermediate stroke stop 50 is designed in the form of a two-spring system and accordingly has a first spring 91, which ensures that the second valve member 64 bears against the pin 68 of the valve slide 66, and a second spring 92, which loads a stop disk 93. This stop disk 93 is provided with a central opening 94 through which the first spring 91 interacts with the valve slide 66. Furthermore, the stop disc 93 is guided in an axially movable manner in a groove-shaped extension 95 of the slide bore 45, the limits of the extension 45 forming stop shoulders. The stop shoulder facing the second valve member 64 defines the intermediate position of the valve element 50, while the stop facing away from it defines its maximum stroke. The inlet 46 opens in the direction of flow before Stop disk 93 in the slide bore 45. The rest of the structure of the injector 10 according to FIG. 6 corresponds to that according to FIG. 1.

Figure 7 shows a second construction variant of an inventive

Injector 210 m a simplified schematic representation. This differs mainly in the structural design of an actuating device 244 from the first construction variant described above, but has essentially the same functional properties. Differences exist due to the reversal of movement of the valve slide 250 explained below and the initially open starting position of the valve member 264.

Consistent with the first construction variant, the

Actuating device 244 consisting of an externally controllable piezoelectric actuator 252, a hydraulic translator 254 and a valve element 250 for controlling pressure medium connections between an inlet 246, a return 248 and two control channels 228 and 236 leading to a closing element 214. The valve element 250 comprises a multiply offset Slide bore 245 of a housing 220 displaceably guided valve slide 266 and a valve member 264 which can be actuated by the valve slide in the form of a ball. The latter is used with the aid of a closing spring 284 to rest on the valve slide

Brought 266. For this purpose, the valve slide 266 has a pin 268 at one of its ends, which penetrates the opening of a constriction 269 of the slide bore 245. The constriction 269 forms a valve seat 282 controlled by the valve member 264, which is open in the illustrated basic position of the injector 210 according to FIG. 2. An additional valve seat 272 is formed on the side of the constriction 269 opposite the valve seat 282. This is from the valve member 264 facing Face of the valve spool 266 controlled. This valve seat 272 is closed in the basic position, so that there is no pressure medium connection between the inlet 246 and the control channel 228. This control channel 228 is coupled to the return 248 via the opened valve seat 282 and is thus relieved of pressure. As a result, the closing member 214 of the injector 210 is held by its two compression springs 230, 232 m in the closed position - the injection openings 216 are closed.

The valve spool 266 is at least partially penetrated by channels 270 carrying pressure medium, which pass the pressure level of the inlet 246 to a cavity 310 that results between a constriction of the valve spool 266 and the slide bore 245. In the illustrated

In the basic position, a control edge 312 on the circumference of the valve slide 266 seals this cavity 310 from the second control channel 236 leading to the closing element 214. Of course, it would also be possible to provide an additional inlet instead of channels 270 in valve slide 266, which opens directly into cavity 310. This inlet could also be designed as a branch to the inlet 246 formed in the housing 220.

The end of the

Valve slide 266 interacts with an intermediate stroke limiter 290. This is arranged coaxially to the valve slide 266 and has two plungers 314, 316 which are arranged coaxially to one another and are guided so as to be movable relative to one another. One of the plungers 314, 316 acts directly on the valve slide 266. Both plungers 314, 316 are loaded by separate springs 291, 292, one of which is in the slide bore 245 Stπnse tig closing plug 318 supports, while the other is supported on a m of the slide bore 245 anchored support ring 320. The support ring 320 also forms the stroke limitation for the tappet 314. With such an intermediate stroke limitation 290, the valve slide 266 m can be moved into an intermediate position without this resulting in an undesired connection of the second control channel due to inaccuracies in the actuation of the actuator 252 or by overshoots 236 can come with the cavity 310.

In contrast to the first construction variant, the actuator 252 is arranged perpendicular to the longitudinal axis of the valve slide 266. It interacts directly with a first piston 256 of the translator 254. This has a second piston 258, which in the exemplary embodiment is made in one piece with the valve slide 266 and is arranged perpendicular to the first piston 256. To translate the stroke movement of the actuator 252 into a stroke movement of the valve slide 266, the pistons 256, 258 have piston diameters of different sizes and enclose a pressure medium-filled transmission chamber 260. In addition to the two pistons 256 and 258, the tappet 316 of the intermediate stroke stop 290 forms a further limitation of this translation chamber 260.

In order to exclude a hydraulic short circuit between the booster chamber 260 and the adjacent second control channel 236, a leakage channel 322 opens into the slide bore 245 between the two devices. This leakage channel 322 leads any pressure medium leakage to a pressure medium reservoir, which cannot be seen in FIG. 2. When the actuator 252 is actuated, it performs a lifting movement which is transmitted to the first piston 256 of the translator 254. Its pressure medium displacement m in the booster chamber 260 causes a corresponding deflection of the one pushing ice 316 of the intermediate stroke stop 290. The aim is to lift it off the end face of the valve slide 266. However, the force exerted by the compression spring 284 on the valve member 264 and transmitted as a result of the mechanical coupling to the valve slide 266 ensures that it is in contact, so that the valve slide 266 is also deflected. First, the valve member 264 closes the valve seat 282, at the same time the valve member 262, which is formed in one piece with the valve slide 266, releases the valve seat 272. The first control channel 228 thus comes under high pressure, on the basis of which the closing member 214 has one

Opening movement executes as soon as the opening pressure in the annular space 224 is exceeded.

As actuator 252 is actuated, valve slide 266 lifts off valve member 264 and control edge 312 opens a pressure medium connection from cavity 310 to second control channel 236. The pressure medium channels 270 in valve slide 266 thus prevail in the two control channels 228, 236 and m Pressure chamber 233 identical pressure level. As a result of the now largely pressure-balanced hydraulic load on the control member 214, the latter closes due to the force of its compression springs 230, 232, although high pressure is still present in the annular space 224. When the actuation of the actuator 252 is withdrawn, the control edge 312 of the valve slide 266 closes off the second control channel 236 again. Its pressure level then decreases via the connection to the return 238 provided with a throttle 242, so that the Closing member 214 opens again for post-injection. This is abruptly ended as soon as the valve seat 272 is closed by the valve member 262 and the valve seat 282 thus opens at the same time.

Further changes or additions to the described exemplary embodiments are of course possible without deviating from the basic idea of the invention.

Claims

Expectations

1. injector (10, 210), in particular for controlling the injection processes of fuel into the combustion chamber of an internal combustion engine, with a closing member (14, 214) which is movably guided in a housing (20, 220) and controls injection openings (16, 216) and one this closing element (14, 214) actuating device (44, 244) comprising an externally controllable piezoelectric actuator (52, 252) and a valve element (50, 250) which is slidably arranged in a slide bore (45, 245) and with the actuator (52, 252) cooperates, characterized in that the valve element (50, 250) pressure medium connections between at least one inlet (46, 246), one return (48, 248) and two control channels (28 , 228, 36, 236) controls and can be moved by the actuator (52, 252) in at least three switching positions.

2. Injector according to claim 1, characterized in that the valve element (50, 250) has a, a control edge (112, 312) having valve spool {66, 266) and at least two, each a valve seat (72, 272, 82, 282) associated valve members (62, 262, 64, 264).

3. Injector according to claim 1 or 2, characterized in that the first valve seat (72, 272) a pressure medium connection from the inlet (46, 246) to the return (48, 248), the second valve seat (82, 282) a pressure medium connection from the inlet (46, 246) to the first control channel (28, 228) and the control edge (112, 312) a pressure medium connection from the inlet (46, 246) to the second

Control channel (36, 236) regulates and that the first control channel (28, 228) opens into an annular space (24, 224), the pressure of which loads the closing member (14, 214) in the opening direction, while the second control channel (36, 236) a pressure chamber (33, 233) acting on the closing member (14, 214) in the closing direction.

4. Injector according to one of claims 1 to 3, characterized in that the valve seats (72, 82) on the valve slide (66) leading slide bore (45) and on the valve slide (66) are formed and that the two valve members (62, 64) are balls which are operatively connected to the valve slide (66).

5. Injector according to claim 4, characterized in that the two valve members (62, 64) are arranged on the opposite end faces of the valve slide (66) and that the valve member (82) associated valve member (62) with the actuation of the actuator ( 52) simultaneously transfers its stroke movement to the valve slide (66).

6. Injector according to one of claims 1 to 3, characterized in that the valve seats (272, 282) on the valve slide (266) leading slide bore (245) are formed in that the valve member (262) in one piece with the valve slide (266) is connected, while the second valve member (264) is a ball which is acted upon by elastic elements (284) in operative connection with the valve spool (266) and that both Valve members (262, 264) are arranged on a common end face of the valve slide (266)

7 injector according to one of claims 1 to 6, characterized in that the closing member (14, 214) of a first and a second elastic element (30, 230, 32, 232) is held in its closed position and that the second elastic element ( 32, 232) m of the pressure chamber (33, 233) is arranged.

8 injector according to one of claims 1 to 7, characterized in that the pressure chamber (33, 233) with the interposition of a throttle (42, 242) with the return (38, 48, 238) and in that m the pressure chamber ( 33, 233) containing control channel (36, 236) a second throttle (40, 240) is arranged.

9 injector according to one of claims 1 to 8, characterized in that the piezoelectric actuator (52, 252) acts with the aid of an intermediate hydraulic translator (54, 254) on the first valve member (62, 252) of the valve element (50, 250) and that the translator (54, 254) has two pistons (56, 256, 58, 258) of different diameters, which enclose a pressure medium-filled translation chamber (60, 260).

10 Injector according to one of claims 1 to 9, characterized in that in the valve slide (66, 266) pressure medium leading channels (70, 270) are provided which connect the inlet (46, 246) with one of the valve slide (66, 266 ) and the slide bore (45, 245) form a limited cavity (110, 310) and that the cavity (110, 310) with appropriate Control of the actuator (52, 252) with the control channel (36, 236) can be hydraulically coupled.

11. Injector according to one of claims 1 to 10, characterized in that the actuating device (44, 244) with an intermediate stroke stop (90, 290) from at least two coaxially arranged and relatively movable compression springs (91, 291, 92, 292) and a stop plate (93, 293), the stop plate (93, 293) forming a support for the compression spring (92, 292).

12. Injector according to claim 11, characterized in that the intermediate stroke stop (90, 290) forms one of the boundaries of the translation chamber (260).