EP2914838B1 - Fuel injector comprising a piezoactuator - Google Patents

Description

The invention relates to a fuel injector for a fuel injection system, in particular a common rail injection system, having the features of the preamble of claim 1.

Such a fuel injector comprises a nozzle needle guided in a high-pressure bore of a nozzle body for releasing and closing at least one injection port, a recorded in a low pressure piezoelectric actuator for direct control of the lifting movement of the nozzle needle and a coupling device, via which the piezoelectric actuator with the nozzle needle is hydraulically coupled.

State of the art

From the publication DE 10 2009 001 131 A1 is a fuel injector with a arranged in a low pressure region of the injector piezoelectric actuator for direct control of the lifting movement of a nozzle needle, in which the nozzle needle is arranged largely pressure-balanced. For this purpose, a plunger-like extension is arranged at the nozzle-side end of the nozzle needle, which is guided axially displaceably and tightly in a communicating with the combustion chamber guide bore. The piezoelectric actuator can be hydraulically coupled to the nozzle needle via a coupler space. The coupling takes place in such a way that when the piezoelectric actuator is energized, the nozzle needle assumes its closed position and the energization of the piezoelectric actuator must be interrupted to open it. That is, the actuator is charged during the comparatively long injection pauses and discharged only during the comparatively short injections (so-called inverse control). As a result, the piezoceramic of the actuator is exposed to a strong electric field for a long time during the operating period, as this is the case with non-inverse control. The result can be a significantly shortened life of the actuator.

In addition, the describe DE 10 2010 016100 A1 and the DE 10 2009 027552 A1 a similar fuel injector with a nozzle needle, which is hydraulically coupled by means of a coupling device with the piezoelectric actuator.

The present invention is therefore an object of the invention to provide a fuel injector with a piezoelectric actuator for direct control of the lifting movement of a nozzle needle, which is durable. In particular, a fuel injector with a piezoelectric actuator is to be specified, which does not control the nozzle needle inversely.

The object is achieved by a fuel injector with the features of claim 1. Advantageous developments of the inventions can be found in the dependent claims.

Disclosure of the invention

The proposed fuel injector comprises a nozzle needle for lifting and closing at least one injection opening, a piezoelectric actuator accommodated in a low-pressure region for direct control of the lifting movement of the nozzle needle and a coupling device, via which the piezoactuator can be coupled hydraulically to the nozzle needle in a high-pressure bore of a nozzle body. According to the invention, the coupling device comprises a coupler volume, which is formed within a sleeve-shaped coupler piston. The coupler piston is guided in a liftable manner via an inner pin defining the coupler volume in an axial direction. Furthermore, an end section of the nozzle needle protrudes into the coupler volume or into a volume of fuel hydraulically connected to the coupler volume, so that the pressure in the coupler volume acts on the end face of this end section of the nozzle needle with an axial force acting in the closing direction. The hydraulic separation between the part of the nozzle needle connected to the coupler volume and the lower part of the nozzle needle, which is surrounded by high-pressure fuel, takes place via a guide with little play. This guide can either directly in a bottom part of the coupler piston or in an arranged below the coupler piston sleeve be arranged. The coupling device allows direct control of the nozzle needle, in which an elongation of the actuator causes the opening of the nozzle needle. In order to lift the nozzle needle from its sealing seat, the sleeve-shaped coupler piston with respect to the inner pin in the direction shifted the sealing seat of the nozzle needle, so that increases the coupler volume. The concomitant decrease in pressure in the coupler volume causes the nozzle needle to be drawn into the coupler volume or into the fuel volume connected to the coupler volume and located above the end portion of the nozzle needle. The nozzle needle lifts off from its sealing seat. Accordingly, a direction reversal is effected via the coupling device. This means that the piezo actuator only has to be charged if an injection is to take place. During the injection pauses the piezo actuator is discharged. As a result, the load of the piezoelectric actuator is reduced so that the life of the actuator increases. This also contributes to the fact that the piezoelectric actuator is arranged in a low-pressure region of the fuel injector, that is, that it is not exposed to high pressure. This additionally makes it possible to encapsulate the actuator in an actuator module surrounded by a metal sleeve and thus to reliably and completely avoid contact between fuel and actuator. If this option is used, it must be correct to speak of an actuator module instead of an actuator. Since this distinction is not relevant in the context of the present invention, the term "actuator" is also used in the following as a synonym for "actuator module". The specified coupling device is also simple and requires only a small space.

For power transmission, a power transmission element is further arranged between the piezoelectric actuator and the coupling device. This comprises a pressure plate penetrating, pin-shaped portion and a plate-shaped portion for axially supporting the sleeve-shaped coupler piston. The pressure plate, which is penetrated by the pin-shaped portion of the force transmission member, serves to separate the low-pressure region from a high-pressure region of the fuel injector. The diameter of the pin-shaped portion of the power transmission member is therefore as small as possible and / or the guide clearance chosen as narrow as possible in the pressure plate for receiving the pin-shaped portion of the hole provided. Alternatively or additionally, the pin-shaped portion of the force transmission member may be surrounded in the high pressure region by a sealing sleeve, which is supported via a biting edge on the pressure plate. If at the same time the guide play in the pressure plate is designed to be large, this embodiment enables a displacement of the force transmission member including the sealing sleeve in the radial direction and thus a compensation of any axial offset. Furthermore, on the sealing sleeve is a very good Sealing of the low pressure area relative to the high pressure area causes.

Preferably, the coupler piston is acted upon by the spring force of a compression spring, which is supported on the one hand on the coupler piston and on the other side of the housing. The spring force of the compression spring pushes the coupler piston in the direction of the piezoelectric actuator and thus causes a return of the coupler piston when the energization of the piezoelectric actuator is terminated and this contracts. In addition, the spring force of the compression spring at rest ensures a bias of the actuator with a mechanical compressive stress. This avoids that at least parts of the actuator ceramic are exposed during operation of a tensile stress, which would lead to destruction of the actuator. In particular, this danger exists especially immediately after the end of the charging process of the actuator and immediately at the beginning of the unloading process.

According to a first preferred embodiment of the invention, the inner pin is made in one piece with the coupler plate.

According to an alternative preferred embodiment of the invention it is provided that the inner pin is pivotally mounted in a bore of a coupler plate and / or displaceable in the radial direction. The coupler plate serves as a further housing part and can be attached axially, for example, to the above-mentioned pressure plate. In order to effect a displacement in the radial direction, the bore of the coupler plate, in which the inner pin is received, must be provided with a sufficient clearance. Furthermore, a flat or spherically shaped support surface is preferably formed on the inner journal, via which the inner journal is supported on the coupler plate. For example, can be formed on the inner pin an end-side collar portion with a flat or spherical shaped support surface over which the inner pin is slidably and / or pivotally mounted.

In order to allow a radial displacement of the inner pin, the support surface formed on the inner pin is preferably designed plane and supported on a support surface of the coupler plate formed opposite. to pivotable mounting of the inner pin, this preferably has a spherically shaped support surface, via which the inner pin is supported on a plane flat, conical or spherical shaped support surface of the coupler plate. Alternatively or additionally, however, an intermediate ring between the inner pin and the coupler plate are inserted, which preferably allows both a pivoting and a radial displacement of the inner pin relative to the coupler plate.

Preferably, the coupler plate has at least one further serving as an inlet bore and / or as a passage opening recess. A recess serving as an inlet bore is preferably arranged laterally and continues a feed bore formed in a holding body and arranged laterally. The inlet bore may be slightly inclined running inwardly to connect the inlet bore of the holding body with the high-pressure bore in the nozzle body. Furthermore, at least one further recess is provided as a passage opening for the sleeve-shaped coupler piston or power transmission elements integrally connected to the coupler piston. Such power transmission elements may for example be formed pin-shaped and arranged at the same angular distance from each other in the axial extension of the coupler piston. Instead of pin-shaped elements and part-circular wall pieces of the coupler piston can serve as a power transmission elements. The recesses of the coupler plate are preferably adapted to the cross section of the power transmission elements. However, it must be ensured that the coupler piston remains axially displaceable.

Furthermore, it is proposed that the inner pin is acted upon by the spring force of a compression spring which is supported on the one hand on the coupler plate and on the other hand on a radially extending shoulder of the inner pin. This applies in particular if the inner pin is arranged to be pivotable and / or radially displaceable. If the radially extending shoulder on the inner pin for supporting the spring is oriented radially inward, the spring can be made conical and engage with its tapering end in the recess formed on the inner pin. In addition, the spring can also be cylindrical and be supported on a radially extending shoulder which extends radially outward. For this purpose, for example, be pressed onto the inner pin a sleeve. The spring force of the spring holds the inner pin in contact with the coupler plate, even if occurring during the closing process in the coupler volume dynamic overpressure peaks push the inner pin in the direction of the piezoelectric actuator.

Further preferably, the nozzle needle is acted upon by the spring force of a compression spring, said spring being supported on the one hand directly on the coupler piston or indirectly via a sealing sleeve on the coupler piston and on the other hand on the nozzle needle.

Furthermore, the end portion of the nozzle needle can be guided in a liftable manner directly in a bore in the region of a bottom part of the coupler piston.

In a further preferred embodiment of the invention, the end portion of the nozzle needle is guided in a lifting sleeve, which is acted upon by the spring force of a compression spring in the direction of the coupler piston and is preferably arranged below the coupler piston. Further preferably, the sealing sleeve between the coupler piston and the compression spring is arranged, so that the sealing sleeve is held by the spring force of the compression spring in contact with the lower end face of the coupler piston. The sealing sleeve, the end portion of the nozzle needle and the coupler piston preferably define a volume of fuel which is connected to the coupler volume. The connection may be accomplished by projecting the end portion of the nozzle needle above its guide in the sealing sleeve through a bore in the bottom portion of the coupler piston into the coupler volume and having a large diameter clearance between the bore in the bottom portion of the coupler piston and the end portion of the nozzle needle. Another way to connect the volume enclosed by the sealing fuel volume with the coupler volume, is to execute the nozzle needle only so long that the upper end face of its end portion in the region of the sealing sleeve below the lower end face of the coupler piston and that of the sealing sleeve, the End portion of the nozzle needle and the lower end face of the coupler piston limited volume is connected via a passage in the bottom part of the coupler piston with the coupler piston and the inner pin enclosed, original coupler volume. The passage is preferably designed as a bore, wherein the diameter of which may now be smaller than the diameter of the end portion of the nozzle needle. In a further development of this embodiment the passage is designed as a throttle point. Such an embodiment of the passage as a throttle point counteracts the excitation of hydraulic and / or mechanical vibrations in the region of the nozzle needle.

The embodiments in which the nozzle needle is guided in a sealing sleeve, allow the compensation of axial offset tolerances between the coupler piston and the nozzle needle, at the same time over the guide gap between the sealing sleeve and nozzle needle, the coupler volume is sealed against the high-pressure region.

In this context, it is noted that the coupling device is intrinsically safe. Because in the event of a fault, for example accidentally permanently charged actuator, the coupler volume fills gradually, thus causing the closing of the nozzle needle. The high pressure volume surrounding the coupling device can at the same time serve as an additional pressure reservoir (so-called "minirail").

Furthermore, a defined throttle point is preferably provided in the flow region between the nozzle needle and the high-pressure bore, so that a closing force always acts on the nozzle needle in the open state. Because with an open nozzle, the pressure at the nozzle seat is always slightly smaller due to the throttle point than in the area of the coupling device. Such a throttle point also counteracts or dampens hydraulic and mechanical vibrations in the region of the nozzle needle. Furthermore, this counteracts a pressure increase in the coupler volume beyond the system pressure.

Advantageously, the force transmission member is acted upon by the spring force of a compression spring which is supported on the one hand directly or indirectly via a sealing sleeve on the pressure plate and on the other hand on the plate-shaped portion of the force transmission member. When arranging a sealing sleeve around the pin-shaped portion of the power transmission member, the compression spring holds the sealing sleeve in contact with the pressure plate. In this way, an optimized seal is effected. Furthermore, the arrangement of a sealing sleeve with simultaneous formation of a sufficiently large sized guide clearance between the power transmission member and the pressure plate allows a radial displacement the power transmission member relative to the pressure plate. Thus, this arrangement also compensates for any axial misalignment.

As a further development measure, it is proposed that an adjusting piece be arranged between the force transmission member and the piezoelectric actuator. The height of the adjusting piece can be used to influence the height of the coupler volume. Furthermore, the actuator force is transmitted uniformly to the power transmission member via the adjusting piece. Alternatively, such a setting piece can also be arranged between the force transmission member and the coupler piston.

In addition, it is proposed that a sleeve-shaped housing part is arranged between the coupler plate and the nozzle body, which accommodates the coupling device at least partially. The sleeve-shaped housing part is therefore subjected to high pressure, which surrounds the coupling device. Depending on the size of the pressure chamber formed inside the sleeve-shaped housing part, it can serve as a so-called "minirail".

An inventive fuel injector has the advantage of a long service life. On the one hand, the piezoelectric actuator is arranged in the low-pressure region, on the other hand can be coupled via a direction-reversing coupler with the nozzle needle, so that it is only charged when an injection is to take place. During the injection pauses the piezo actuator is discharged. The intended to realize a reversal of direction coupling device is simple and requires little space. Due to the arrangement of the coupling device in the high-pressure region, wherein the high-pressure fuel surrounds the coupling device, a guide play widening in a guide region of the coupling device is counteracted. This also reduces the pressure and temperature-dependent functional influence of the coupler leakage. By means of simple measures, the compensation of any axial offsets can also be realized.

Depending on requirements or manufacturing requirements can be selected between one-piece and modular design of the individual components, such as nozzle needle, coupler piston, power transmission member. This means that these components in any places in several components can be separated, for example, if this offers advantages for the production or assembly. For example, the power transmission elements penetrating the coupler plate may be integral with the coupler piston or integral with the force transmitting member. Furthermore, they can be present as separate components.

The recorded in the low pressure region of a holding body piezoelectric actuator can - as shown in the following drawings - be encapsulated, or sealed alternatively by means of a membrane against the actuator space filling, under low pressure fuel, the membrane is preferably inserted sealingly between the actuator head and the inner wall of the holder body , Further preferably, the intermediate space between the actuator and the holding body may be filled with a thermally conductive potting compound to optimize the heat dissipation.

Figur 1

einen teilweisen Längsschnitt durch einen erfindungsgemäßen Kraftstoffinjektor,

Figur 2

einen vergrößerten Ausschnitt der Figur 1 im Bereich der Kopplungseinrichtung,

Figur 3

einen Querschnitt durch den Kraftstoffinjektor der Figur 1 im Bereich der Kopplerplatte,

Figur 4

den Kraftstoffinjektor der Figur 1 in Offenstellung, das heißt bei geladenem Piezoaktor,

Figur 5

einen Längsschnitt durch ein Kraftübertragungsglied eines weiteren erfindungsgemäßen Kraftstoffinjektors,

Figur 6a

einen teilweisen Längsschnitt durch eine Kopplungseinrichtung eines weiteren erfindungsgemäßen Kraftstoffinjektors,

Figur 6b

einen teilweisen Längsschnitt durch eine Kopplungseinrichtung, die eine alternative Ausführungsform zu der Kopplungseinrichtung gemäß Figur 6a darstellt,

Figur 7a-c

jeweils einen Längsschnitt durch eine Kopplungseinrichtung eines erfindungsgemäßen Kraftstoffinjektors im Bereich des Innenzapfens und

Figur 8a-c

jeweils einen Längsschnitt durch eine Kopplungseinrichtung eines erfindungsgemäßen Kraftstoffinjektors im Bereich eines Innenzapfens.

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. These show:

FIG. 1

a partial longitudinal section through a fuel injector according to the invention,

FIG. 2

an enlarged section of the FIG. 1 in the area of the coupling device,

FIG. 3

a cross section through the fuel injector of FIG. 1 in the area of the coupler plate,

FIG. 4

the fuel injector the FIG. 1 in the open position, that is to say when the piezoactuator is loaded,

FIG. 5

a longitudinal section through a power transmission member of another fuel injector according to the invention,

FIG. 6a

a partial longitudinal section through a coupling device of another fuel injector according to the invention,

FIG. 6b

a partial longitudinal section through a coupling device, which is an alternative embodiment of the coupling device according to FIG. 6a represents,

Figure 7a-c

in each case a longitudinal section through a coupling device of a fuel injector according to the invention in the region of the inner journal and

Figure 8a-c

in each case a longitudinal section through a coupling device of a fuel injector according to the invention in the region of an inner journal.

Detailed description of the drawings

The longitudinal section of the FIG. 1 shows the fuel injector according to the invention in the closed position. Shown is a recorded in a holding body 4 of the fuel injector piezoelectric actuator 6, which is supported via an adjusting piece 30 on a power transmission member 14. The power transmission member 14 has a pin-shaped portion 16, with which it passes through a pressure plate 15 to come into abutment with the setting piece 30. At its other end, the force transmission member 14 on a plate-shaped portion 17, which cooperates with a coupling device 7. The diameter of the pin-shaped portion 16 is chosen to be significantly smaller than that of the plate-shaped portion, at the same time, the pin-shaped portion 16 receiving bore of the pressure plate 15 has a narrow guide gap. As a result, the seal between a low-pressure region 5, in which the piezoelectric actuator 6 is accommodated, and a high-pressure region 18, in which the coupling device 7 is accommodated, is effected and the piezoelectric actuator 6 is protected from high pressure. The coupling device 7 comprises a sleeve-shaped coupler piston 9, within which a coupler volume 8 is formed. The coupler piston 9 is guided axially displaceably via an inner journal 10, so that the coupler volume 8 can be changed via an axial displacement of the coupler piston 9. In a the inner pin 10 opposite bottom part 11 of the coupler piston 9, a bore is formed, in which an end portion 12 of a nozzle needle 3 is received axially displaceable. If the piezoelectric actuator 6 is energized and expands while it pushes the setting piece 30 and the power transmission member applied thereto 14 in the direction of a sealing seat (not shown) of the nozzle needle 3. The force transmission member 14 moves while the sleeve-shaped coupler piston 9 against the spring force of a compression spring 13 in the direction of the sealing seat. This increases the coupler volume 8, which has the consequence that the pressure in the coupler volume 8 decreases and the nozzle needle 3 against the spring force of a compression spring 25 opens. If the energization of the piezoelectric actuator 6 is terminated, this contracts again, wherein the compression spring 13, the coupler piston 9 and the power transmission member 14 resets in the respective starting position. The coupler volume 8 decreases and the pressure increase in the coupler volume 8 and the spring force of the compression spring 25 cause the nozzle needle 3 is reset in its sealing seat. The nozzle needle 3 is arranged for lifting this in a high-pressure bore 1 of the nozzle body 2. The fuel injector in the open position is in the FIG. 4 shown.

The enlarged detail of the FIG. 2 shows the fuel injector the FIG. 1 in the region of the coupling device 7. Shown are the sleeve-shaped coupler piston 9, the inner pin 10 and the end portion 12 of the nozzle needle 3, which is guided in the bottom part 11 of the coupler piston 9. About the coupler volume 8, the nozzle needle 3 is hydraulically coupled to the piezoelectric actuator 6. For this purpose, the coupler volume 8 and the pressure prevailing in the coupler volume 8 pressure via an axial displacement of the coupler piston 9 can be changed, wherein the axial displacement of the coupler piston 9 is effected via the piezoelectric actuator 6. The force of the piezo actuator 6 (see black arrows in FIG. 2 ) pushes the coupler piston 9 in the direction of the sealing seat of the nozzle needle 3, whereby the pressure in the coupler volume 8 decreases and the nozzle needle 3 opens against the direction of force of the piezoelectric actuator 6. About in the FIG. 2 Coupling device 7 shown is thus causes a reversal of direction, which leads to the nozzle needle 3, the nozzle needle 3 moves toward the piezoelectric actuator 6 at an elongation of the piezoelectric actuator 6.

FIG. 3 shows a cross section through the injector of FIG. 1 wherein the section is laid through a coupler plate 20. The diameter range of the inner pin 10, which is embodied here in one piece with the coupler plate 20, is in the Fig. 3 separately marked. This diameter range of the inner pin 10 is surrounded by recesses, wherein two kidney-shaped recesses 22 as passage openings for force transmission elements 33 of the coupler piston 9th and a laterally arranged recess serve as an inlet bore 21. In alternative embodiments of the invention, the inner pin 10 may also be designed as a separate component and received in a bore 19 of the coupler plate. The storage of the inner pin 10 in the bore 19 of the coupler plate 20 may be configured differently. Specific embodiments of this are the FIGS. 7a-c such as 8a-c refer to.

The FIGS. 7a-c show embodiments by means of which a possible axial offset can be compensated. The inner pin 10 is for this purpose in the bore 19 of the coupler plate 20 radially displaceable (see Figure 7a ) or swiveling (see FIG. 7b ) stored. The radial displaceability is effected via flat support surfaces on the inner journal 10 and the coupler plate 20, while spherical shaped support surfaces (see FIG. 7b ) Ensure the pivotability of the inner pin 10. A combination of both degrees of freedom is provided by the embodiment FIG. 7c achievable, in which between the inner pin 10 and the coupler plate 20, an intermediate ring 32 is arranged. The intermediate ring 32 allows both a radial displacement of the inner pin 10 against the intermediate ring 32 and thus relative to the coupler plate 20 and a pivoting of the intermediate ring 32 and thus of the inner pin 10 relative to the coupler plate 20th

According to the Figures 8a-c can the inner pin 10 also be acted upon by the spring force of a compression spring 23 which is supported on the one hand on a radial shoulder 24 of the inner pin 10 and on the other hand on the coupler plate 20. Since the radial shoulder 24 extends radially inward, the compression spring 23 is conically shaped. However, this is not absolutely necessary, since the radially extending shoulder 24 can also extend radially outward, so that a cylindrical spring 23 can also be used.

An alternative embodiment of a fuel injector according to the invention shows FIG. 5 , in which the force transmission member 14 is surrounded by a sealing sleeve 29 in the region of its pin-shaped portion 16. The sealing sleeve 29 is supported on the pressure plate 15 and is held by the spring force of a compression spring 28 into contact with the pressure plate 15. For this purpose, the compression spring 28 is supported on the one hand on the sealing sleeve 29 and on the other hand on the plate-shaped portion 17 of the power transmission member 14. The pin-shaped portion 16th the power transmission member 14 receiving bore of the pressure plate 15 also has a larger guide play, so that a radial displacement of the power transmission member 14 in order to compensate for any axial offset is possible. At the same time, a sealing of the low-pressure region 5 with respect to the high-pressure region 18 is effected via the sealing sleeve 29. In addition to the possible compensation of an axial offset, this embodiment has the further advantage that the pressure prevailing in the high-pressure region 18 causes a reduction of the guide clearance between the sealing sleeve 29 and the force-transmitting member 14. In this way, the normally unavoidable rise of the leakage at the guide of the force transmission member 14 in the pressure plate 15 is counteracted with increasing high pressure.

A comparable arrangement can - as in Fig. 6a shown - also be provided for sealing the coupler volume 8 relative to the high-pressure region 18, wherein a sealing sleeve 26 surrounds the end portion 12 of the nozzle needle 3. Again, the bore, in which the end portion 12 of the nozzle needle 3 is received, provided with sufficient guide play, so that over a radial displacement of the nozzle needle 3 and the sealing sleeve 26, a compensation of any axial offset is possible. The sealing sleeve 26 is in turn axially biased by a compression spring 25 relative to the coupler piston 9, wherein the compression spring 25 is supported on the one hand on a radially extending shoulder 27 of the nozzle needle 3 and on the other hand on the sealing sleeve 26.

A further education of in Fig. 6a illustrated embodiment shows Fig. 6b , Here, the guided in the sealing sleeve 26 end portion 12 of the nozzle needle 3 is designed such that its upper end face is already arranged in the sealing sleeve 26, ie below the lower end face of the coupler piston 9. Thus, the diameter of the bore in the bottom part 11 of the coupler piston 9 can be significantly reduced. Namely, this hole no longer needs to receive the nozzle needle 3, but only a hydraulic connection between the actual coupler volume 8 and a Kopplerteilvolumen A, which is formed between the coupler piston 9 and inner pin 10, and a Kopplerteilvolumen B produce within the sealing sleeve 26th is trained. It is particularly advantageous to carry out the bore in the bottom part 11 of the coupler piston 9 as a throttle point. In this case arises with each movement of the coupler piston 9 and / or the nozzle needle 3, a pressure drop This bore, which is adapted to dampen hydraulic and / or mechanical vibrations in the nozzle needle 3.

The bore in the bottom part 11 of the coupler piston 9 can furthermore, regardless of whether it receives the end section 12 of the nozzle needle 3 or not, also be embodied as a passage channel with a non-circular cross section.

The high pressure surrounding the coupling device 7 can serve as an additional pressure accumulator or as a so-called "minirail". In order to form this pressure accumulator, in the present case the coupling device 7 is surrounded by a sleeve-shaped housing part 31, which is arranged between the coupler plate 20 and the nozzle body 2. All housing parts, in particular the holding body 4, the pressure plate 15, the coupler plate 20, the housing part 31 and the nozzle body 2, via a clamping nut (not shown) are clamped axially against each other. As a result, a sealing of the housing parts is achieved against each other.

Claims (11)

1. Fuel injector for a fuel injection system, in particular a common-rail injection system, comprising a nozzle needle (3), which is guided, such that it can perform stroke movements, in a high-pressure bore (1) of a nozzle body (2) and which serves for opening up and closing at least one injection opening, a piezo actuator (6), which is accommodated in a low-pressure region (5) and which serves for directly controlling the stroke movement of the nozzle needle (3), and a coupling device (7), by means of which the piezo actuator (6) is hydraulically couplable to the nozzle needle (3), wherein the coupling device (7) comprises a coupler volume (8) which is formed within a sleeve-shaped coupler piston (9), wherein the coupler piston (9) is guided, such that it can perform stroke movements, by means of an inner pin (10) which delimits the coupler volume (8) in an axial direction, and wherein an end portion (12) of the nozzle needle (3) projects into the coupler volume (8) or into a fuel volume connected to the coupler volume (8), characterized in that a force transmission element (14) is arranged between the piezo actuator (6) and the coupling device (7), which force transmission element comprises a pin-like portion (16), which extends through a pressure plate (15), and a plate-like portion (17) for axially supporting the sleeve-like coupler piston (9), wherein the pressure plate (15) separates the low-pressure region (5) from a high-pressure region (18) of the fuel injector.
2. Fuel injector according to Claim 1,
   characterized in that the coupler piston (9) is acted on by the spring force of a pressure spring (13) which is supported at one side on the coupler piston (9) and at the other side on a housing.
3. Fuel injector according to any of the preceding claims,
   characterized in that the inner pin (10) is formed in one piece with the coupler plate (20).
4. Fuel injector according to either of Claims 1 and 2,
   characterized in that the inner pin (10) is mounted pivotably, and/or displaceably in a radial direction, in a bore (19) of a coupler plate (20).
5. Fuel injector according to Claim 4,
   characterized in that the coupler plate (20) has at least one further recess, which serves as inflow bore (21) and/or as leadthrough opening (22).
6. Fuel injector according to Claim 4 or 5,
   characterized in that the inner pin (10) is acted on by the spring force of a pressure spring (23) which is supported at one side on the coupler plate (20) and at the other side on a radially running shoulder (24) of the inner pin (10).
7. Fuel injector according to any of the preceding claims,
   characterized in that the end portion (12) of the nozzle needle (3) is guided, such that it can perform stroke movements, in a bore in the region of a base part (11) of the coupler piston (9).
8. Fuel injector according to any of Claims 1 to 6,
   characterized in that the end portion (12) of the nozzle needle (3) is guided, such that it can perform stroke movements, in a sealing sleeve (26) which is acted on by the spring force of a pressure spring (25) in the direction of the coupler piston (9), wherein preferably, the sealing sleeve (26), the end portion (12) of the nozzle needle (3) and the coupler piston (9) delimit a fuel volume which is connected to the coupler volume (8).
9. Fuel injector according to any of Claims 1 to 8,
   characterized in that the force transmission element (14) is acted on by the spring force of a pressure spring (28) which is supported at one side directly or indirectly via a sealing sleeve (29) on the pressure plate (15) and at the other side on the plate-like portion (17) of the force transmission element (14).
10. Fuel injector according to any of Claims 1 to 9,
    characterized in that an adjustment piece (30) is arranged between the force transmission element (14) and the piezo actuator (6) or between the force transmission element (14) and the coupler piston (9).
11. Fuel injector according to any of Claims 3 to 10,
    characterized in that, between the coupler plate (20) and the nozzle body (2), there is arranged a sleeve-like housing part (31) which at least partially receives the coupling device (7).

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