EP3368763B1 - Fuel injector - Google Patents

Description

Technical area

The present invention generally relates to the field of fuel injectors and more specifically an injector equipped with a device for detecting the position of the needle.

State of the art

A fuel injector conventionally comprises a needle controlled in opening and closing as a function of the pressure prevailing in a control chamber, which pressure is a function of the position of a control solenoid valve. These small displacements are carried out at high speed and, the regularly increased performances now require for an optimal piloting a feedback on the actual position of the needle. Devices are known in which a sensor is arranged on the injector, or even an injector in which the surfaces of the components of the body are electrically insulated so that a measurement of electrical resistance can be carried out between two elements of the body of the injector . These complex and expensive devices have not yet proven their industrial realism and it is advisable to propose a simple and effective device.

We will quote for example the FR 3 013 080 in which the injector comprises resistive surface coatings arranged on several contact surfaces between parts, and in which the overall electrical resistivity of the injector between the body of the solenoid actuator and the body of the injector varies from at least three distinct ohmic values intermittently depending on the kinetics of the injector injection needle.

A difficulty in the systems proposed is linked to the tolerances on the needle which generate positioning / misalignment games with the seat. Indeed, it happens that the tip of the needle laterally touches the nozzle body, just on the periphery of the seat, generating anticipated contact openings / closings relative to the actual opening or closing.

Subject of the invention

The object of the present invention is to provide a fuel injector with another opening detection device having good reliability.

General description of the invention

With this objective in mind, the present invention provides a fuel injector for an internal combustion engine, comprising an injection nozzle with a body in which is arranged a needle movable between a closed position (PF), in which a first end of the needle rests on a seat and closes injection ports of the nozzle, and a fully open position (PO), in which the first end of the needle is lifted from its seat and allows injection. A control chamber is filled, in operation, with fuel so as to exert pressure on the second end of the needle. A control valve is associated with the control chamber making it possible to selectively vary the fuel pressure in the control chamber and thus controlling an opening or closing movement of the needle, the control valve being driven by an actuator .

The injector comprises a device for detecting the position of the needle defining a detection circuit, the detection device comprising a contacting element, actuated by the upper part of the needle, the device being designed so that the element contactor is in contact, in the closed position, with a terminal element of the position detection device, thus closing the detection circuit, and so that the raising of the needle interrupts the contact between the contactor element and the terminal element, thereby opening the detection circuit.

The detection device therefore comprises the contactor element and the terminal, which cooperate in the manner of a switch. The contactor element is actuated by the movement of the needle. The actuation of the contactor element by the upper part of the needle can be direct or indirect. This detection principle allows avoid the implementation of insulating and resistive layers at the needle.

The detection circuit is closed when the contactor element is in contact with the terminal; and the circuit opens when the needle rises and modifies the contactor element. The moment of interruption of the electrical contact between the contactor element and the terminal, that is to say the transition from closed to open circuit, is therefore here an indication of the timing of the opening of the needle. Conversely, when the needle returns to position in its seat at the end of the actuation sequence, the contactor will again come into contact with the terminal, closing the circuit.

The detection of the position of the needle in the upper part of the latter avoids problems of alignment of the needle at its seat, which in known solutions can generate false contacts. It will be noted here that the needle guide clearance partly at the top (at the top guide) where the contactor element and the terminal are positioned is reduced when the pressure increases, thereby improving the quality of the contact.

The detection device is designed so that the detection circuit is closed only in the closed position of the injector, and possibly in the open position, but not in the ballistic area.

The contactor element comprises a flexible part which is configured in the closed position of the needle so as to be in electrical contact with the terminal; the configuration of the flexible part changing when the needle leaves the closed position so as to interrupt the electrical contact with the terminal (opening of the circuit).

The contactor element is placed in the control chamber and the needle includes a rod end in the control chamber which forms a contact terminal and biases the deformation of the contactor element so that the contactor element is deformed elastically when the needle is in the closed position and is in contact with the rod to establish electrical contact, the shape of the contactor element being modified during the opening stroke of the needle so that the contact is interrupted (the circuit opens).

The contactor element is a generally cylindrical part arranged around the needle rod, coming to bear against an electrically insulated stop and placed on the rod, and against a conductive stop placed in the control chamber and electrically insulated from its support. The conductive stop can be constituted by the inner radial edge of a conductive shoulder socket mounted in the control chamber.

The contacting element is a helical spring, a tubular element or another elastically deformable element, in particular transversely, under the action of the needle in the closed position so that the contact element touches the needle rod, and able to spontaneously resume a shape in which it is not in contact with the rod when the needle leaves the closed position.

In order to detect the fully open position of the needle, the detection device may include a second terminal positioned in the control chamber, the needle abutting against this terminal at the end of its opening stroke, closing the circuit for detection. This second terminal can be formed by the ceiling of the control chamber.

Alternatively, the detection device can be designed so that the contactor element moves in translation with the needle, the terminal being positioned so that contact between the contactor element and the terminal is established in the closed position (circuit closed).

Alternatively, the needle is guided in the upper part by a high guide, and the device comprises a contact sleeve surrounding the high guide. The contact sleeve is electrically isolated from the top guide and can slide axially on it. The contactor element takes the form of a washer fixedly mounted on the upper part of the needle. The switch function of the detection device is therefore performed here outside the control chamber.

In particular, the washer forming contactor element is positioned against a shoulder of the needle; the needle is biased in the closing direction by a needle spring surrounding the needle and resting on the one hand on the washer, respectively the needle shoulder, and on the other hand against a lower edge of the guide high. The contact sleeve extends, in an axial direction, over a part of the high guide, around the spring and up to the height of the shoulder receiving the washer.

In this embodiment, the terminal is advantageously formed by an inner radial edge of the contact sleeve, placed under the washer, so as to be in contact with the latter in the closed position.

The electrical supply of the contact socket can be made via a conductive pin passing through, electrically insulated, a radial flange of the high guide. An elastic contact element is preferably provided to establish the electrical contact between the pin and the conductive sleeve.

To absorb manufacturing tolerances, the contact sleeve is not fixedly mounted but is guided around the top guide. An electrically insulated spring is preferably arranged around the contact sleeve so as to exert an axial force in the opening direction, in particular to compensate for wear or manufacturing play. The contact sleeve is then configured so as to define with the top guide an annular cavity filled, in use, with fuel and forming an axial damping chamber limiting the axial movement of the contact sleeve in the opening direction of the needle, when opening the injector. Although the contact socket is not mounted fixed, the presence of the damping cavity means that in practice the contact socket is substantially static. But above all, this configuration makes it possible to ensure that the washer will be in good contact with the edge of the contact sleeve in the closed position of the needle, so that the detection circuit is closed and allows the detection of this position by current flow.

It remains to be noted that although the present invention has been developed within the framework of a diesel injector, it is fully transposable to a petrol or other fuel injector.

Detailed description using the figures

• Figure 1 : une vue en coupe axiale d'un premier mode de réalisation du présent injecteur, l'injecteur étant en position (a) fermée, (b), intermédiaire et (c) ouverte ;
• Figure 2 : une vue en coupe axiale d'un deuxième mode de réalisation du présent injecteur ;
• Figure 3 : un vue du détail A de la Fig.2 ;
• Figures 4 et 5 : deux graphes illustrant la réponse (courant) du dispositif de détection de position en fonction de la course de l'aiguille, pour les variantes des figures 1 et 3, respectivement. Dans ces figures, la course de l'aiguille est tracée en trait continu et correspond à l'axe C; et le signal détecté S est représenté en trait mixte.

Other features and characteristics of the invention will emerge from the detailed description of at least one advantageous embodiment presented below, by way of illustration, with reference to the accompanying drawings. These show:

• Figure 1 : a view in axial section of a first embodiment of the present injector, the injector being in position (a) closed, (b), intermediate and (c) open;
• Figure 2 : a view in axial section of a second embodiment of the present injector;
• Figure 3 : a view of detail A of the Fig.2 ;
• Figures 4 and 5 : two graphs illustrating the response (current) of the position detection device as a function of the needle stroke, for the variants of the figures 1 and 3 , respectively. In these figures, the stroke of the needle is drawn in a solid line and corresponds to the axis C; and the detected signal S is shown in phantom.

The figure 1 illustrates a first embodiment of the invention relating to a fuel injector 10, here a diesel injector although the invention is fully transposable to a gasoline or other fuel injector, the injector 10 generally being part of an injection system comprising several injectors. The description will detail the elements of the invention and will remain more succinct and general as to the surrounding elements. The injector 10 extends along a main axis A and comprises, from bottom to top, in the conventional and non-limiting sense of the figures, a nozzle 12 comprising a needle 14 arranged in a nozzle body 16 then a control valve arranged in a valve body 22 and then an actuator arranged in an actuator body 26. The control valve and the actuator can be of the conventional type and are therefore not shown or described in detail. The nozzle bodies 16, valve bodies 22 and actuator bodies 26 are held integral with each other by any suitable means. Conventionally, a nut can be used which rests on a shoulder of the nozzle body and is screwed onto the actuator body, the valve body 22 being sandwiched between the other two bodies, the three bodies and the nut forming the injector body.

The nozzle body 16 comprises a stepped inner axial bore 30, extending from an upper end, where it has a wide diameter, to a lower end which ends in a point so as to form a conical nozzle body seat 32 for controlling the access of fuel to injection orifices 34 extending through the conical wall of the nozzle body 16. At the bottom, the bore 30 forms a low cylindrical guide 36 at which the needle 14 includes a projecting annular section 38 sliding in the low guide 36. The passage of the fuel at the level of this low guide is done for example by one or more grooves (straight or helical) in the wall of the low cylindrical guide or in the annular projection . The guide of the needle in the upper part is obtained by an independent part 40, called the upper guide, arranged between the nozzle body 16 and the valve body 22 and kept fixed by the assembly of the parts of the injector, in particular by the compression exerted by the injector nut. The upper guide 40 guides the upper portion of the needle 14, called the needle head 42, through a guide bore 44. The needle head 42 in combination with the valve body 22 and the bore of guide 44 define a control chamber 46.

The terms "top" and "bottom" are used here not only with reference to the orientation of the figure, but also with reference to the usual name assigned to these elements by professionals.

The needle 14 is generally cylindrical and extends axially A between the needle head 44, at the top of the figure, and a pointed end 48, at the bottom of the figure, forming a needle seat 50 cooperating with the seat valve body 32 of body 16.

When the needle rests on the seat 32 of the body, it is in the closed position PF, the injection of fuel via the orifices 34 is prevented. The needle 14 is raised by adjusting the pressure in the control chamber 46, which makes it possible to bring the needle into a fully open position denoted PO (typically at the upper stop), in which the fuel can pass to the injection ports 34.

As can be seen, the bottom guide 36 is close to the needle seats 50 and the nozzle body 32. Furthermore, the needle 14 is provided with an annular protuberance 52, the upper face 54 of which faces towards the head d needle 42 provides a bearing surface for a spring 56 urging the needle 14 towards its closed position PF in which the needle point 48 rests on its seat 32 and closes the injection orifices 34. The spring 56 is arranged under the top guide 40 and it is compressed against the bottom surface 58 of the top guide.

The injector 10 is moreover conventionally provided with a fuel circulation circuit which, on the one hand, allows the supply of high pressure fuel via a high pressure circuit, brought from an inlet mouth to the orifices of injection 34 and, on the other hand, the recirculation of fuel to a low pressure tank via an internal low pressure circuit. The high pressure circuit notably comprises a bypass channel leading to the control chamber 46, chamber 46 from which the low pressure circuit starts again via a discharge channel controlled in opening and closing by the control valve. When the actuator, typically an electromagnet, is electrically powered, it attracts the magnetic armature linked to the shutter member of the control valve, which opens the evacuation channel and allows the fuel trapped in the chamber to command to evacuate to the low pressure circuit. The pressure in the control chamber 46 then drops, and the needle 14 moves in the bore of the nozzle body to a fully open position PO in which the needle seat 50 is distant from the valve body seat 32, so as to allow the injection of fuel via the injection holes 34, the top of the needle head 42 being in contact with the ceiling surface 59 (constituted by the underside of the valve body 22) of the control chamber 46.

When the actuator is not supplied, the magnetic armature and valve shutter assembly is pushed back by a valve spring to a position in which the discharge channel is closed, which retains in the control chamber 46 the high pressure fuel that gets there. The pressure in the control chamber then rises and, the needle, pushed back by the spring and by the pressure in the control chamber 46, moves to the closed position PF in which the needle seat 50 is in sealed contact against the valve body seat 32, so as to prevent fuel injection and in which the top of the needle head 42 is remote from the ceiling surface 59 of the control chamber 46.

In order to accurately determine when the needle is opened, the injector is equipped with a device for detecting the position of the needle, generally indicated 60.

It will be appreciated that the device 60 for detecting the position of the needle comprises a detection circuit with a switch function actuated by the upper part 42 of the needle.

In the variant of the Figure 1 , the detection device 60 comprises an elastic contactor element 62 placed in the control chamber 46 and which is deformed under the action of the needle 14 when it is in the closed position PF.

For example, the contactor element 62 can take the form of a spring associated with the needle head 42. As can be seen, the needle head comprises a rod-shaped end portion 64 of reduced cross section, compared with the section of the needle head 42 guided by the hole 44 of the high guide 40. The rod is positioned centrally in the control chamber 46 along the axis A, and the contacting spring element 62 surrounds the needle rod 64.

The reference sign 66 designates a stepped socket made of an electrically conductive material (generally metallic), placed in the control chamber 46. The reference sign 68 designates a intermediate insulating layer, so that the sleeve 66 is electrically isolated from the top guide 40, and the latter is isolated from the valve body 22. The valve body which will constitute the starting point of the detection circuit is in fact electrically insulated not only from the high guide 40 but also from the other parts which surround it, except at the level of the ceiling 59 of the control chamber 46.

The rod 64 of the needle 14 crosses the shoulder 66 ₁ of the sleeve 66 and carries an insulated stop 70, for example a washer. The spring 56 bears against the stop 70 and the shoulder 66 ₁ of the sleeve, and is, in PF of the injector, compressed so as to be deformed, here radially / transversely, and in contact with the rod 64 d needle 14.

The spring contactor element 62 and the needle rod 64 therefore have functions respectively of movable contact and switch terminal in the detection device 60. In this configuration of the fig.1 which corresponds to the PF, the detection device 60 is closed, the current being able to circulate between the spring 62 and the rod 64. As will be understood, the detection circuit comprises at least the elements forming the switch function. However, it can be considered that the elements involved in the current flow loop between two electrical poles are also part of the detection circuit.

By referring for example to the figure 1 , the conductive element 62 constituted by the spring allows the circulation of current between the upper part of the injector and the needle. For example, if the valve body 59 is connected by the ceiling to a positive potential, the current then passes through the shouldered sleeve 66 with which it is in electrical contact, via the spring 62 to the needle rod 64, and therefore from needle 14 to ground. The path followed by the current is symbolized by the arrow in broken lines. The electric detection circuit is therefore closed, which is detected by the flow of current.

The figure 1B represents an intermediate position of the travel of the needle 14, between the PF and PO. The needle 14 is lifted from its seat and the spring 62 has stiffened / straightened, which has opened the electrical contact with the end rod 64 and therefore interrupted (open circuit) the passage of current to the needle 14 and the mass.

Advantageously, the device is designed so that the compression of the spring 62 in PF is chosen for a frank break in electrical contact, from the start of the opening stroke of the needle 14.

In figure 1C , the needle 14 has reached its maximum open position PO. The needle is in abutment against the ceiling 59 of the control chamber 46, that is to say that the rod 64 touches the ceiling. In this position, the current flows directly from the valve body 22 into the rod 64 and therefore the needle 14, to ground. This again closes the detection circuit and allows detection of the maximum opening position of the injector.

The figure 4 represents on a same graph the stroke of the needle and the electrical signal (current) delivered by the detection device 60. In PF ( Fig.1A ), the current flows from the spring 62 to the rod 64 and the electrical signal is at level 1. As soon as the needle rises the circuit opens and the current drops to 0. When the needle reaches the stop ( Fig.1C ), the electrical circuit is closed and the current returns to 1. Although the electrical signal takes the same value in the positions PF and PO of the injector, these two positions can be distinguished according to the actuation sequence.

The figure 2 illustrates a second variant, which differs mainly in the embodiment of the needle position detection device designated 100. The detection device 100 here also cooperates with the upper part of the needle, but is placed outside the control chamber. The needle head therefore has a more conventional shape, without the rod 64, which reduces the volume of the control chamber 46. The elements identical or similar to those of the embodiment of the figure 1 are designated by the same reference signs.

The detection device 100 comprises a conductive socket 102, also known as a contact socket, which is mounted around the high guide 40 and is electrically insulated from that, via an insulating layer 104. contact socket 102 is in electrical contact with an electrical pin 106 passing through the top guide 40 through a channel 108 in which the pin 106 is electrically insulated. Preferably, the contact between the pin 106 and the socket 102 is made via an elastic element 110. The elastic element 110 has a low force and aims mainly to maintain the electrical contact. It can have any suitable form. The contact parts do not necessarily have a smooth annular shape, but may include indentations etc.

The reference sign 112 designates a contact washer (therefore electrically conductive) fixedly mounted on the needle head 42 and forming the contact element displaced by the needle 14. The washer 112 rests on a shoulder 54 'of a protuberance annular 52 'of the needle.

The device 100 is designed so that in PF, the washer 112 is in contact with the socket 102. In the variant, the washer 112 touches an inner radial edge 114 of the contact socket 102, which forms a terminal.

In this configuration, current can flow from pin 106 through spring 110 to contact socket 102. In the FP illustrated in Fig.3 , the washer 112 rests on the flange 114, thus closing the circuit, which allows current to pass from the washer 112 to the needle spring 56 and therefore in the high guide 40, and to return it through the carcass of the injector to ground. The detection circuit is therefore closed, which is detected by the passage of a current through the parts mentioned.

When the injector is actuated, the needle 14 rises from its seat, moving upwards. The washer 112 moves with the needle 14, which interrupts the electrical contact with the contact socket 102, and therefore opens the circuit. The contact remains open (current interrupted) as long as the needle is moved away from the needle body seat 32. Thus, when the needle moves, the washer 112 moves inside the contact sleeve 102; the outside diameter of the washer 112 is less than the inside diameter of the socket 102, so that the washer 112 never touches the socket 102, except in PF.

The figure 5 represents on a same graph the stroke C of the needle 14 and the electrical signal S (current) delivered by the detection device 100. The circuit is only closed in PF, when the washer 112 touches the rim 114, which is indicated by an electrical signal at "1". As soon as the needle leaves its seat, the washer 112 / rim 114 contact is interrupted and the current goes to "0". This embodiment of the detection device 100 does not make it possible to determine the PO of the injector.

Preferably, the contact socket 102 is configured so that there is an annular cavity 116 between it and the top guide 40. This annular cavity is, in use, filled with fuel and will therefore act as a damping chamber . Indeed, the sleeve 102 is guided around the top guide 40 and is therefore movable relative to the latter. It is not mounted fixed in order to be able to absorb manufacturing tolerances, which will always ensure contact between the socket 102 and the contact washer 112 in PF. For this purpose also, a compensation spring 120, isolated from the main body, is advantageously provided to guarantee contact 114 in PF and compensate for wear of the interfaces in the system, in particular at the level of the spring seat 56, washer seat and contact area 114.

In practice, however, the sleeve 102 can be considered to be quasi-fixed, since its movement is limited by the annular cavity 116 which forms a hydraulic blocking preventing rapid movements of the sleeve 102.

One or more holes 118 (vents) are provided in the main part of the sleeve 102 to facilitate pressure balancing and to avoid localized pressure effects.

It will also be noted that in this second variant, the contact washer 102 forming the contactor element is an insert, fixed in operation against the shoulder 54 'of an annular portion 52'. Since the needle spring 56 is carried by the washer 102, it is not necessary to provide an annular protuberance 52 as in the variant of the Fig.1 , although this cannot be excluded. So the surface support 54 ′ can be obtained by a simple shoulder cut in the mass of needle 14.

In the variant of figures 2 and 3 , a washer 112 is used to facilitate assembly of the assembly.

In other variants, the washer 102 could be in one piece with the needle. For example, with a suitable dimensioning of the assembly, the annular protuberance 52 of the needle of the figure 1 can act as a contact washer.

It should be noted that in the variant of figures 2 and 3 , the PO can be detected by means of an additional contact element, shown in broken lines and indicated 122, mounted on the needle head 42. The additional contact element 122 is positioned on the needle lower than the washer 112. The additional contact element 122 may also take the form of a radial protuberance of the needle 14 or of a washer locked axially against a shoulder. The position of the additional contactor element 122 on the needle and its thickness are chosen so that it is in contact, in PO, with the terminal formed by the inner radial edge 114 of the contact sleeve 102. As shown in FIG. 'will have understood, in this case the additional contactor element 122 comes to touch the underside of the radial edge 114.

When such an additional contactor element 122 is present, the detection current goes to the value "1" in PO, and the current diagram corresponds to that of the figure 4 rather than the figure 5 .

Claims (7)

1. Fuel injector for an internal combustion engine, comprising:

   an injection nozzle (12) with a body (16) in which there is placed a needle (14) able to move between a closed position (PF), in which a first end (48) of the needle rests on a seat (32) and closes off injection orifices (34) of the nozzle, and a fully-open position (PO), in which the first end of the needle is lifted off its seat (32) and allows injection;

   a control chamber (46) filled, in operation, with fuel so as to exert pressure on the second end (42) of the needle;

   a control valve associated with the control chamber (46) making it possible selectively to vary the fuel pressure in the control chamber (46) and thus command an opening or closing movement of the needle (14), the control valve being driven by an actuator;

   a needle-position detection device (60; 100) defining a detection circuit;

   characterized in that the detection device for detecting the position of the needle (14) comprises a contactor element (62; 112) actuated by the top part of the needle (14), the device being designed so that the contactor element (62; 112) is in contact, in the closed position, with a terminal-forming element (64; 114) of the position-detection device, thus closing the detection circuit, and so that the lifting of the needle (14) breaks the contact between the contactor element (62; 112) and the terminal-forming element (64; 114), thus opening the detection circuit, and in that

   the contactor element (62; 112) comprises a flexible component (62) which is configured when the needle (14) is in the closed position, in such a way as to be in electrical contact with the terminal (64; 114); the configuration of the flexible component (62) altering when the needle (14) leaves the closed position so as to break the electrical contact, and in which

   the contactor element (62; 112) is placed in the control chamber (46); the needle (14) comprises a shank end in the control chamber (46) which forms a contact terminal and urges the deformation of the contactor element (62; 112) such that the contactor element (62; 112) is elastically deformed when the needle (14) is in the closed position and is in contact with the shank (64) so as to establish the electrical contact, the shape of the contactor element (62; 112) altering during the opening travel of the needle (14) so that contact is broken, and in which the contactor element (62; 112) is a generally cylindrical component arranged around the needle shank (64), coming to bear against an electrically insulated end stop (70) placed on the shank (64), and against a conducting end stop (66) placed in the control chamber and electrically insulated from its support; and,

   for preference, the conducting end stop consists of the interior radial edge of a conductive stepped bushing mounted in the control chamber (46), and in which

   the contactor element (62; 112) is a helical spring, a tubular element or some other element that is elastically deformable, particularly transversely, under the action of (14) in the closed position so that the contact element touches the needle shank (64), and able spontaneously to return to a shape in which it is not in contact with the shank (64) when the needle (14) leaves the closed position.
2. Fuel injector the preceding claim, characterized by a second terminal (59) positioned in the control chamber (46), the needle (14) resting against this second terminal in the open position (PO) so as to close the detection circuit, the said second terminal (59) preferably being formed by the roof of the control chamber (46).
3. Fuel injector according to Claim 1, characterized in that the contactor element (112) moves translationally with the needle (14) and in that the terminal (64) is positioned in such a way that contact between the contactor element and the terminal is established in the closed position.
4. Fuel injector according to Claim 3, in which the needle is guided in the upper part by a top guide (40), characterized in that the device comprises a contact bushing (102) surrounding the top guide, the contact bushing being electrically insulated from the top guide and able to slide axially thereon; and in that the contactor element takes the form of a washer (112) mounted fixedly on the top part of the needle.
5. Fuel injector according to Claim 4, characterized in that the washer (112) forming the contactor element is positioned against a shoulder (54') of the needle; in that the needle is urged in the direction of closing by a needle spring (56) surrounding the needle and bearing, on the one hand, on the washer or, respectively, the needle shoulder and, on the other hand, against a lower edge of the top guide; and in that the contact bushing (102) extends, in the axial direction, over part of the top guide, around the spring, and up to the level of the shoulder that accepts the washer;
   the terminal preferably being formed by an inner radial edge (114) of the contact bushing, placed beneath the washer (112), so as to be in contact therewith in the closed position.
6. Fuel injector according to Claim 5, characterized by an additional contactor element (122) arranged on the needle lower down than the said contactor element (112), so as to come into contact with the inner radial edge (114) of the contact bushing (102) in the fully-open position.
7. Fuel injector according to either one of Claims 5 and 6, characterized in that an electrically insulated spring (120) is arranged around the contact bushing so as to exert an axial force in the direction of opening, particularly to compensate lash caused by wear;
   the contact bushing (102) is configured in such a way as to define, with the top guide, an annular cavity (116) which, in use, is full of fuel and forms a hydraulic axial damping chamber limiting the axial movement of the contact bushing in the direction of opening of the needle.

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