EP2884088B1 - Fuel injector - 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.

State of the art

A fuel injector of the type mentioned above is an example of the published patent application DE 10 2008 040 680 A1 out. The known fuel injector comprises for injecting fuel into a combustion chamber of an internal combustion engine an adjustable between an open position and a closed position, multi-part injection valve element, wherein a first part and a second part are coupled via a hydraulic coupler. The hydraulic coupler is limited in the axial direction by a first guide for the first part and by a second guide for the second part. The guides are acted upon radially from the outside by high pressure, while in the hydraulic coupler, a lower pressure is realized. The radially outside applied higher pressure counteracts widening of the guides, so that the fuel injector can be operated comparatively low leakage. The lower pressure in the hydraulic coupler also has the consequence that the parts of the injection valve element coupled thereto are permanently connected to each other during operation of the fuel injector and with considerable forces, so that from a functional point of view they can be regarded as one part. Further, it is proposed in this document that within the hydraulic coupler, a pressure stage is realized which causes a force acting in the closing direction of the injection valve element hydraulic force to accelerate the switching time of the injection valve element. In order to realize the pressure stage, the hydraulically coupled parts of the injection valve element have different diameters, the part lying closer to a nozzle hole arrangement having a smaller diameter than the part remote from the nozzle hole.

The from the DE 10 2008 040 680 A1 known fuel injector is switched indirectly. For this purpose, the fuel injector has a solenoid valve designed as a servo valve, which causes a pressure drop in a control chamber in the open position, which is limited in the axial direction of an end face of the injection valve element. The pressure drop in the control chamber thus causes a relief of the injection valve element until it opens. By means of the coordination of inlet and outlet throttles, which are in communication with the control chamber, it is ensured that the required pressure drop for opening the injection valve element is achieved in a defined period of time after opening the servo valve. When sizing the actuator for actuating the servo valve, therefore, only the force required to open the servo valve must be taken into account.

In addition, fuel injectors are for example off DE102008002415A known, which are connected directly via a magnetic or piezoelectric actuator. In this case, the required opening force for opening the injection valve element or the nozzle needle must be taken into account when dimensioning the actuator. The force applied by the actuator is transmitted via a switching chain on the end face of the nozzle needle. In order to effect a translation of the actuator force and / or the Aktorhubes, the switching chain between the actuator and the nozzle needle may have a device for force and / or stroke ratio. Accordingly reduces or increases the required actuator force and increases or decreases in return the required Aktorhub.

Based on the above-mentioned prior art, the present invention seeks to provide a fuel injector for a fuel injection system, in particular a common rail injection system, which allows the use of comparatively small-volume actuators by reducing the required opening force. In particular, the use of a small-volume piezoelectric actuator should be possible, via which the fuel injector is directly switchable.

The object is achieved by a fuel injector with the features of claim 1. Advantageous developments of the invention are described in the dependent claims.

Disclosure of the invention

The proposed fuel injector comprises a nozzle body and an injector body, each enclosing a high-pressure chamber in which a single- or multi-part nozzle needle for releasing and closing at least one injection opening is received in a liftable manner. The nozzle needle is guided by a low-pressure chamber which is sealed off via at least one guide gap between the nozzle needle and a body limiting the low-pressure space and / or a guide element supported thereon relative to the high-pressure chambers. To form a pressure chamber arranged in the low pressure chamber, the nozzle needle has different sized guide diameter d _o , d _u . According to the invention, it is provided that the guide diameter d _o, which is farther away with respect to the injection opening, is smaller than the guide diameter d _u , so that the nozzle needle is partially relieved of force in the opening direction. The partial release of force of the nozzle needle causes a reduction in the required opening force, so that - with directly connected injectors - by a small-volume actuator, such as a piezoelectric actuator can be applied. In indirectly connected injectors, the partial force relief of the nozzle needle causes the switching times can be reduced because the required pressure drop in the control room can be realized faster.

The effect of the partial force relief of the nozzle needle can also be represented by the following formulas.

wobei p dem Hochdruck und d_s dem Sitzdurchmesser eines Düsennadelsitzes entspricht. Die üblicherweise zusätzlich vorhandene Vorspannkraft einer in Schließrichtung wirkenden Feder ist dabei so gering, dass sie vernachlässigt werden kann.In the closed position of the nozzle needle corresponds to the required opening force of the hydraulic pressure force F _seat , which presses the nozzle needle into its seat. For F _seat : $$F_{\mathit{Seat}}=p\cdot \frac{\mathrm{<figure-callout\; id="4"\; label="\pi "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{4}\cdot {{\mathrm{<figure-callout\; id="2"\; label="d\; s"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d\; </figure-callout>}}_s}^2.$$

where p corresponds to the high pressure and d _s corresponds to the seat diameter of a nozzle needle seat. The usually additionally existing biasing force of a spring acting in the closing direction is so small that it can be neglected.

The formula shows that the seat diameter d _{s has a} great influence on F _seat and thus on the required opening force. Due to the different sized guide diameter of the nozzle needle for the realization of a pressure stage, the hydraulic pressure force F _seat can be reduced because it now applies: $$F_{\mathit{Seat}}=p\cdot \frac{\mathrm{<figure-callout\; id="4"\; label="\pi "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{4}\cdot \left({{\mathrm{<figure-callout\; id="2"\; label="d\; s"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d\; </figure-callout>}}_s}^2+{d_O}^2-{{\mathrm{<figure-callout\; id="2"\; label="d\; u"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d\; </figure-callout>}}_u}^2\right)$$

According to a preferred embodiment of the invention, the body limiting the low-pressure chamber is a plate-shaped body component which is arranged between the nozzle body and the injector body and which is preferably braced axially with the nozzle body and the injector body via a nozzle retaining nut. In this case, the body forms a fixed body component or housing part of the fuel injector. Alternatively or additionally, it is proposed that preferably the body limiting the low-pressure space has at least one flow channel for the hydraulic connection of the high pressure spaces formed in the nozzle body and in the injector body. The at least one flow channel ensures the supply of fuel to the at least one injection opening. It is thus part of the flow path of the fuel to be injected.

According to an alternative preferred embodiment of the invention, the body limiting the low-pressure space is received in a lift-movable manner in at least one of the high pressure spaces formed in the nozzle body and / or in the injector body. Accordingly, the body limiting the low-pressure space does not necessarily have to be designed as a fixed body component or housing part. For example, the body can also be a coupler body of a hydraulic coupler, which preferably serves to reinforce the force of an actuator and forms a functional unit with it. This is particularly advantageous if the fuel injector is designed as a directly switchable injector.

Preferably, the low-pressure space is connected via at least one connecting channel to a low-pressure region of the fuel injector. This ensures that an additional amount of fuel entering the low-pressure space by means of the leakage does not lead to an undesired pressure increase in the low-pressure space. Preferably, the connecting channel is at least partially formed as a radially extending bore. Further preferably, the radially extending Hole in the region of an outer peripheral surface of the low pressure space limiting body, which is preferably formed in this case as a plate-shaped body member, in the low pressure region. For this purpose, the low-pressure region may comprise at least one axially extending connecting channel arranged radially outside with respect to the plate-shaped body component. The low-pressure region is furthermore preferably connectable to a return line of the fuel injection system.

The pressure prevailing in the low-pressure chamber preferably corresponds to the return pressure of the fuel injection system. In addition, the pressure prevailing in the low-pressure chamber can also be above the return pressure, so that a pressure is possible which lies between the return pressure and the high pressure of a high-pressure accumulator to which the fuel injector is preferably connected. The intermediate pressure level in the low-pressure space can be generated in a manner known per se. For example, equal-pressure valves or pressure divider devices can be used. However, the pressure in the low-pressure space is preferably at most 20 bar, preferably at most 10 bar, in order to achieve the desired effect of a partially force-loaded nozzle needle.

To form different sizes of guide diameter, the nozzle needle is preferably in several parts, preferably in two parts, formed. The multi-part design simplifies the realization of different sizes of guide diameter, since a diameter jump can be realized in each case in the region of the connection of two parts, which differ in terms of their diameter. Preferably, the nozzle needle comprises a first part and a second part having cooperating contact surfaces arranged in the low pressure space. The low pressure in the low pressure chamber and the high pressure applied externally cause a mechanical coupling of the two parts of the nozzle needle. Because while the injection opening facing the second part is always acted upon by a hydraulic opening force, the first part, which is located further away from the injection opening, always acted upon by a hydraulic closing force, so that both parts are axially pressed against each other and form a functional unit ,

As a further development measure, it is proposed that the first part and the second part of the nozzle needle have, in the region of their contact surfaces, a geometry forming a joint. The joint in the contact area can compensate for any axial misalignment between the parts. To form a joint suitable in particular spherically shaped contact surfaces, wherein one contact surface should be concave or flat and the other convex.

According to the invention, at least one guide of the nozzle needle is realized by a separate guide element, which is designed as a sleeve and is preferably supported by a biting edge on the body limiting the low-pressure space. The trained as a sleeve separate guide element allows the compensation of any axial offset between the parts of the nozzle needle, since the sleeve relative to the body is radially displaceable. The biting edge of the sleeve increases the sealing force in order to seal the low-pressure space with respect to one of the high-pressure chambers. Alternatively or additionally, it is proposed that the sleeve is acted upon by the spring force of a spring in the direction of the body. Also by this measure, the sealing force is increased in the contact area of the sleeve with the body. Since the sleeve is surrounded on the outside by high pressure, the high pressure environment causes an additional hydraulic contact pressure. Further preferably, the lifting movement of the nozzle needle via an actuator is directly controlled. The actuator may be, for example, a piezoelectric actuator or a magnetic actuator. A directly controllable or switchable fuel injector has over an indirectly controllable or switchable fuel injector the advantage that no Absteuermenge accumulates, which must be returned and again promoted to high pressure. This can increase the efficiency of the system. Alternatively or additionally, it is proposed that a hydraulic coupler is provided for the transmission of the force and / or the stroke of an actuator.
According to a first preferred embodiment, the hydraulic coupler has a coupler body with a hollow cylindrical projection for receiving an end portion of the nozzle needle and for forming a control chamber, wherein the control chamber is formed completely in the coupler body.
Alternatively, it is proposed that the hydraulic coupler has a coupler body on which a sealing sleeve for receiving an end portion of the nozzle needle and for forming a control chamber is supported. A hollow cylindrical projection on the coupler body is thus unnecessary, which simplifies the production of the hydraulic coupler. The sealing sleeve can also be displaced in the radial direction on Supported coupler body, so that it allows the compensation of any misalignment between the hydraulic coupler and the nozzle needle.
Since the sealing sleeve is surrounded on all sides by high pressure, in the case of a short-term overpressure in the control chamber there is the risk that the sealing sleeve will detach from the coupler body and the control chamber will open. This can be counteracted by the fact that the one-piece solution described above (without separate sealing sleeve) or a sealing sleeve is selected, which has a radially inner biting edge, via which it is supported on the coupler body. In this way, acting on the sealing sleeve opening forces are avoided at a pressure in the control room.

• Figur 1 einen schematischen Längsschnitt durch einen Kraftstoffinjektor welcher nicht gemäß der Erfindung ausgeführt ist,
• Figur 2 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer ersten bevorzugten Ausführungsform der Erfindung,
• Figur 3 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer zweiten bevorzugten Ausführungsform der Erfindung,
• Figur 4 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer dritten bevorzugten Ausführungsform der Erfindung,
• Figur 5 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer vierten bevorzugten Ausführungsform der Erfindung,
• Figur 6 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer fünften bevorzugten Ausführungsform der Erfindung,
• Figur 7 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer sechsten bevorzugten Ausführungsform der Erfindung,
• Figur 8 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer siebten bevorzugten Ausführungsform der Erfindung und
• Figur 9 einen schematischen Längsschnitt durch einen Kraftstoffinjektor gemäß einer achten bevorzugten Ausführungsform der Erfindung, jeweils im Bereich eines von Niederdruck umgebenen Durchmessersprungs der Düsennadel.

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

• FIG. 1 a schematic longitudinal section through a fuel injector which is not executed according to the invention,
• FIG. 2 a schematic longitudinal section through a fuel injector according to a first preferred embodiment of the invention,
• FIG. 3 a schematic longitudinal section through a fuel injector according to a second preferred embodiment of the invention,
• FIG. 4 a schematic longitudinal section through a fuel injector according to a third preferred embodiment of the invention,
• FIG. 5 a schematic longitudinal section through a fuel injector according to a fourth preferred embodiment of the invention,
• FIG. 6 a schematic longitudinal section through a fuel injector according to a fifth preferred embodiment of the invention,
• FIG. 7 a schematic longitudinal section through a fuel injector according to a sixth preferred embodiment of the invention,
• FIG. 8 a schematic longitudinal section through a fuel injector according to a seventh preferred embodiment of the invention and
• FIG. 9 a schematic longitudinal section through a fuel injector according to an eighth preferred embodiment of the invention, in each case in the region of a diameter jump of the nozzle needle surrounded by low pressure.

Detailed description of the drawings

The Indian FIG. 1 The nozzle body 1 and the injector body 2 are clamped together axially by means of a nozzle lock nut 26, wherein between the nozzle body 1 and the injector 2 in addition a plate-shaped body member as a Low-pressure chamber 7 limiting body 6 is inserted. The low-pressure chamber 7 is connected via a connecting channel 13 designed as a radial bore to a low-pressure region 14, which is arranged radially outside with respect to the body 6. Further, an obliquely extending flow channel 15 is formed in the body 6, which connects the high-pressure chamber 3 of the nozzle body 1 with the high-pressure chamber 4 of the injector body 2.
The Indian FIG. 1 shown fuel injector further comprises a liftable nozzle needle 5 for releasing and closing at least one injection port (not shown). The nozzle needle 5 extends from the high-pressure chamber 3 of the nozzle body 1 into the high-pressure chamber 4 of the injector body 2, being guided in the region of the low-pressure chamber 7 by the plate-shaped body component or body 6. An upper end portion of the nozzle needle 5 is received in a sealing sleeve 23 which is supported on a coupler body 20 of a not shown hydraulic coupler 19 via a radially inner biting edge 24 and acted upon in the direction of the coupler body 20 by the spring force of a spring 17. The coupler body 20, the sealing sleeve 23 and an end face 25 of the end portion of the nozzle needle 5 accommodated in the sealing sleeve 23 thus jointly delimit a control chamber 22 in which a control chamber pressure prevails which causes a pressure force acting on the nozzle needle 5 in the closing direction. If the nozzle needle 5 is raised to release the injection port, the pressure in the control chamber 22nd be lowered. This is done in the present case by actuation of an actuator (not shown), which may be formed for example as a piezoelectric actuator. On the one hand, a reversal of the direction of movement and on the other an amplification of the actuator force or the Aktorhubes be effected via the switched between the piezoelectric actuator and the nozzle needle hydraulic coupler 19, so that the piezoelectric actuator for direct control of the lifting movement of the nozzle needle 5 can be used.

In a fuel injector according to the invention, the nozzle needle 5 is partially relieved of force. The partial release of force is caused by a diameter jump of the nozzle needle 5 in the region of the low-pressure space 7. The diameter jump leads to the formation of a low pressure surrounded pressure stage 12, wherein the diameter d _{o of} the nozzle needle 5 above the pressure stage 12 is smaller than the diameter d _u below the pressure stage 12 is selected. At the same time, the diameters d _o and d _u together with the plate-shaped body component or the body 6 form guide gaps 8, 9, via which the low-pressure space 7 is sealed off from the high-pressure spaces 3, 4 by way of the gap seal.

Due to the partial power relief of the nozzle needle 5, the opening can be effected with a comparatively small actuator, in particular when the fuel injector is directly switchable via the actuator.

In the FIG. 2 is a modification of the fuel injector of FIG. 1 shown. In the present case, the guidance of the nozzle needle 5 is not effected via the plate-shaped body component or the body 6, but via sleeve-shaped guide elements 10, 11 supported thereon. The support is in each case via a biting edge in order to optimize the sealing of the low-pressure chamber 7 with respect to the high-pressure chambers 3, 4. In addition, the sleeve-shaped guide elements 10, 11 are acted upon in the direction of the body 6 in each case by the spring force of a spring 17, 18. In the present case, the sleeve-shaped guide element 10 is acted upon by the spring force of the spring 17, which at the same time holds the sealing sleeve 23 in contact with the coupler body 20. For this purpose, the spring 17 is supported, on the one hand, on the sleeve-shaped guide element 10 and, on the other hand, on the sealing sleeve 23. The sleeve-shaped guide member 11 is pressed by the spring force of the spring 18 to the body 6, which also serves as a closing spring and is supported on the nozzle needle 5. The sleeve-shaped guide elements 10, 11 are radially displaceable relative to the presently formed as a plate-shaped body member body 6 and allow in this way the compensation of any Axis offset. The guide gaps 8, 9 sealing the low-pressure space 7 are formed between the sleeve-shaped guide elements 10, 11 and the guide diameters d ₀ , d _{u of} the nozzle needle 5. The low pressure chamber 7 is formed as a simple axial bore within the body 6, which is thus easy to manufacture.

Another preferred embodiment is in FIG. 3 shown. This is different from the one of FIGS. 1 and 2 in that the nozzle needle 5 is designed in several parts, namely in two parts. The two parts 5.1, 5.2 of the nozzle needle 5 each have a different diameter, wherein the diameter d _{o of} the part 5.1 is smaller than the diameter d _{u of} the part 5.2 is selected. The parts 5.1, 5.2 form with the sleeve-shaped guide elements 10, 11 supported on the body 6 guiding gaps 8, 9, via which the low-pressure space 7 formed in the plate-shaped body component 6 is sealed against the high-pressure spaces 3, 4. The contact area of the two parts 5. 1, 5.2 is located in the low-pressure chamber 7 and forms the pressure required to relieve the pressure of the nozzle needle 12 from. A possible axial offset between the two parts 5.1, 5.2 can be effected by a radial displacement of the sleeve-shaped guide elements 10, 11 relative to the body 6.

A modification of the embodiment of the FIG. 3 is in the FIG. 4 shown. In order to allow the compensation of any axial offset between the two parts 5.1, 5.2, they each have a geometry in the region of their contact surfaces, which cooperate forming a joint 16. In the present case, the contact surface of the part 5.1 is convex-shaped, while the contact surface of the part 5.2 has a concave-shaped depression, so that the contact region is reduced to a circular line. The geometries also cause a self-centering of the two parts 5.1, 5.2 to each other.

Another modification of the embodiment of the FIG. 3 is in the FIG. 5 shown. Here was dispensed with the arrangement of a sealing sleeve 23 for forming the control chamber 22. Instead, the coupler body 20 of a hydraulic coupler 19, not shown, a hollow cylindrical projection 21 for receiving the upper end portion of the nozzle needle 5 and the formation of the control chamber 22. Since the control chamber 22 is completely formed in the coupler body 20, there is no danger - in contrast to the embodiment with sealing sleeve 23 - that this opens.

Other modifications are in the FIGS. 6 to 9 shown. They are different from those of FIGS. 1 to 5 in particular, that the body 6 is not necessarily designed as a fixed plate-shaped body member which is axially braced between the nozzle body 1 and the injector body 2 by means of a nozzle lock nut 26. Accordingly, the body 6 may have any desired shape and / or be liftably received in the high-pressure space 3.

In the embodiment of the FIG. 6 is the nozzle needle 5 in one piece and - to form the pressure stage 12 - stepped formed. Below the pressure stage 12, the nozzle needle 5 has a guide diameter d _u and above a guide diameter d _o , where also d _o <d _u . The guide diameter d _u acts together with a sleeve-shaped guide element 11, which is supported on the body 6, forming a guide gap 9. The guide gap 9 seals a trained in the body 6 low-pressure chamber 7, which is formed as an axial bore. The axial bore is stepped, so that adjoining the low-pressure chamber 7 is a guide section which cooperates with the guide diameter d _{o of} the nozzle needle 5 forming a guide gap 8. The guide gap 8 seals the low-pressure chamber 7 against a further pressure chamber formed in the body 6, which may be designed as a control chamber 22 or as a coupler chamber of a hydraulic coupler. In the latter case, the body 6 also serves as a coupler body 20 of the hydraulic coupler (see reference numerals in parentheses). As a coupler body 20, the body 6 is received in a liftable manner in the high-pressure chamber 3. The trained in the body 6 control chamber 22 and coupler space is bounded by an end face of the nozzle needle 5, so that prevails at the nozzle needle 5 of the prevailing in the control chamber 22 or coupler hydraulic pressure, via which the lifting movement of the nozzle needle 5 is preferably directly controlled.

The embodiment according to the FIG. 7 is different from that of FIG. 6 in that the nozzle needle 5 is formed in two parts and has a first part 5.1 with the guide diameter d _o and a second part 5.2 with the guide diameter d _u , again d _o <d _u . Since in the control chamber 22 or coupler space and in the high pressure chamber 3 prevail significantly higher pressures than in the low pressure chamber 7, the two parts 5.1, 5.2 of the nozzle needle 5 are pressed together with high forces and form a functional unit. The advantage of this embodiment is in particular that the multi-part design of the nozzle needle 5 allows the compensation of an axial and / or angular offset. Furthermore, the two parts 5.1, 5.2 the nozzle needle 5 are ground continuously when the guide diameter is equal to the outer diameter over the entire height of the part. While the first part 5.1 in this case has a convex end for abutment on and for mechanical coupling with the second part of the nozzle needle 5 5. 2, the second part 5. 2 ends in a flat end face. Other face geometries are also conceivable.
A modification of the embodiment of the FIG. 7 is in the FIG. 8 shown. The first part 5.1 of the nozzle needle 5 is here performed stepped to make the first part 5.1 receiving bore in the body 6 as a simple axial bore.
A development of the embodiment of FIG. 8 is the FIG. 9 refer to. In contrast to the embodiment of FIG. 8 shows the the FIG. 9 an annular groove 27 connected to the flow channel 15 via a branch 15 'in the region of the guide of the first part 5.1 of the nozzle needle 5. The guide gap 8 is connected in this way to the high-pressure chamber 3. In the region of the annular groove 27 is located over the entire circumference of the first part 5.1 of the nozzle needle 5 high pressure. In this way, the annular groove 27 counteracts leakage from the control chamber 22 or coupler space in the direction of the low-pressure space 7. In Injektorkonzepten that provide a constant coupler volume, for example in direct-switching injectors, causes a leakage from the coupler space in the low-pressure chamber, a permanent reduction of the coupler space pressure. This has the consequence that the injector behavior changes. This must be prevented. The proposed high-pressure connection of the guide gap 8 represents a measure to effectively prevent leakage from the coupler space and thus a reduction of the coupler space pressure.
The in connection with the FIGS. 1 to 9 described features can each be used individually or in various combinations. In this way one obtains further modifications and / or alternative embodiments, all of which are part of the invention as defined in the appended claims.

Claims (11)

1. Fuel injector for a fuel injection system, in particular a common-rail injection system, comprising a nozzle body (1) and injector body (2) which in each case surround a high-pressure chamber (3, 4) in which a single-part or multi-part nozzle needle (5) for opening up and closing off at least one injection opening is received such that it can perform stroke movements, wherein the nozzle needle (5) is guided through a low-pressure chamber (7) which is sealed off with respect to the high-pressure chambers (3, 4) by way of at least one guide gap (8, 9) between the nozzle needle (5) and a guide element (10, 11), which guide element is in the form of a sleeve and is supported on a body (6) which delimits the low-pressure chamber (7), and wherein the nozzle needle (5), in order to form a pressure stage (12), arranged in the low-pressure chamber (7), has guide diameters (d_o, d_u) of different size, wherein that guide diameter (d_o) which is situated further remote from the injection opening is smaller than the guide diameter (d_u), such that the nozzle needle (5) is partially relieved of force in the opening direction.
2. Fuel injector according to Claim 1,
   characterized in that the body (6) which delimits the low-pressure chamber (7) is a plate-shaped body component arranged between the nozzle body (1) and the injector body (2), which plate-shaped body component is preferably axially clamped to the nozzle body (1) and to the injector body (2) by way of a nozzle clamping nut (26) and/or has at least one flow duct (15) for the hydraulic connection of the high-pressure chambers (3, 4).
3. Fuel injector according to Claim 1,
   characterized in that the body (6) which delimits the low-pressure chamber (7) is received, such that it can perform stroke movements, in the high-pressure chamber (3) and/or in the high-pressure chamber (4), wherein the body (6) is preferably a coupler body (20) of a hydraulic coupler (19).
4. Fuel injector according to one of the preceding claims,
   characterized in that the low-pressure chamber (7) is connected via at least one connecting duct (13) to a low-pressure region (14) of the fuel injector, wherein the connecting duct (13) is preferably formed at least in sections as a radially running bore.
5. Fuel injector according to one of the preceding claims,
   characterized in that the nozzle needle (5), in order to form the guide diameters (d_o, d_u) of different size, is of multi-part form, preferably of two-part form, wherein a first part (5.1) and a second part (5.2) preferably have interacting contact surfaces which are arranged in the low-pressure chamber (7).
6. Fuel injector according to Claim 5,
   characterized in that the first part (5.1) and the second part (5.2) of the nozzle needle (5) have, in the region of their contact surfaces, a geometry which forms a joint (16).
7. Fuel injector according to one of the preceding claims,
   characterized in that the guide element (10, 11) which is in the form of a sleeve is supported on the body (6) by way of a biting edge, and/or is forced in the direction of the body (6) by the spring force of a spring (17, 18).
8. Fuel injector according to one of the preceding claims,
   characterized in that the stroke movement of the nozzle needle (5) is controllable directly by way of an actuator, and/or a hydraulic coupler (19) is provided for boosting the force and/or the stroke of an actuator.
9. Fuel injector according to Claim 8,
   characterized in that the hydraulic coupler (19) has a coupler body (20) with a hollow cylindrical projection (21) for receiving an end section of the nozzle needle (5) and for forming a control chamber (22).
10. Fuel injector according to Claim 8,
    characterized in that the hydraulic coupler (19) has a coupler body (20) on which there is supported a sealing sleeve (23) for receiving an end section of the nozzle needle (5) and for forming a control chamber (22).
11. Fuel injector according to Claim 10,
    characterized in that the sealing sleeve (23) has a biting edge (24) situated radially at the inside, by way of which biting edge said sealing sleeve is supported on the coupler body (20).

Images