EP2324230B1 - Fluid injection device - Google Patents

Description

The invention relates to a device for injecting a pressurized fluid, for example a fuel, in particular for an internal combustion engine.

• un boîtier 2 comprenant au moins une cavité 20 axiale remplie du fluide pressurisé 1 et s'ouvrant sur l'intérieur 20 du boîtier 2,
• un actionneur 3 présentant un empilement incluant au moins une partie électroactive 30 comportant un matériau électroactif 300 et doté
  o d'une première face frontale 31, prolongée axialement d'un organe pénétrant 33, et
  o d'une deuxième face frontale 32 opposée axialement à la première 31,
  l'actionneur 3 étant monté mobile axialement dans le boîtier 2 et ledit organe 33 comprenant un piston 330 engagé de manière sensiblement étanche dans la cavité 20 et formant un lien fluidique entre l'actionneur 3 et le boîtier 2,
• des moyens d'excitation adaptés à mettre la partie électroactive 30 de l'actionneur 3 en vibration avec une période de consigne τ.

More specifically, the invention relates, according to a first aspect, to a device 7 for injection of pressurized fluid 1, said injector, such as that of the state of the art partially illustrated on the figure 1 and described, for example, in the French patent application FR 2,888,889 . This known injector 7 has a main injection axis AB and comprises at least:

• a housing 2 comprising at least one axial cavity filled with the pressurized fluid 1 and opening on the inside 20 of the housing 2,
• an actuator 3 having a stack including at least one electroactive part 30 comprising an electroactive material 300 and provided with
  o a first end face 31, extended axially by a penetrating member 33, and
  o a second end face 32 axially opposed to the first 31,
  the actuator 3 being mounted axially movable in the housing 2 and said member 33 comprising a piston 330 substantially sealingly engaged in the cavity 20 and forming a fluid connection between the actuator 3 and the housing 2,
• excitation means adapted to put the electroactive portion 30 of the actuator 3 in vibration with a set period τ.

In the prior art, the fluidic link is rendered imperfect by the It is necessary to ensure a seepage (imperceptible flow) of the liquid at the piston 330 to reduce the frictional forces between the oscillating piston 330 and the immobile cavity 20.

où n est un coefficient multiplicateur, entier positif.In this context, the invention aims to overcome this difficulty and provide a more efficient fluid connection. To this end, the injection device, which is also in accordance with the generic definition given in the preamble above, is essentially characterized in that the said penetrating member has an axial length such that the propagation time T of the acoustic waves , called "acoustic flight time", produced by the vibrations of the electroactive part of the actuator and traversing this length corresponds to the following equation: $$\mathrm{T}\mathrm{=}\left[\mathrm{2}\mathrm{not}\mathrm{+}\mathrm{1}\right]\mathrm{*}\left[\mathrm{\tau }\mathrm{/}\mathrm{4}\right]\mathrm{,}$$

where n is a multiplying coefficient, positive integer.

Such an arrangement of the injector should allow to reach a perfect seal between the piston and the cavity. Thanks to a particular acoustic structure and, in particular, to the selective axial acoustic length of the penetrating member, the piston and, in particular, its free end oriented towards the cavity and axially opposed to the first end face of the actuator, tends to to present a vibration node, that is to say, to remain quasi-immobile relative to the cavity without preventing a vibratory movement of the actuator in the housing. Therefore, it is no longer necessary to lubricate the piston which can then be machined to the fairest of the cavity, so as to prohibit said oozing and to provide the most effective fluid connection.

According to a second of its aspects, the invention relates to an internal combustion engine using the fluid injection device according to the invention, that is to say, such a motor where is disposed this injection device.

• la figure 1 est un schéma d'un injecteur selon l'état de l'art agencé dans un moteur et équipé d'une aiguille à tête dite sortante liée à un actionneur monté axialement dans un boîtier,
• la figure 2 est un schéma d'un injecteur selon l'invention agencé dans un moteur et équipé d'une aiguille à tête dite sortante liée à un actionneur monté axialement dans un boîtier,
• les figures 3 et 4 représentent un organe pénétrant d'un injecteur selon l'invention comprenant un piston et un corps intermédiaire ajouré à section transversale unidirectionnelle, en vues schématiques simplifiées : vue de côté (figure 3) ; vue de dessus (figure 4),
• la figure 5 représente de manière schématique une coupe longitudinale simplifiée d'un organe pénétrant d'un injecteur selon l'invention comprenant un piston et un corps intermédiaire comportant au moins un repli,
• les figures 6 et 7 représentent un organe pénétrant d'un injecteur selon l'invention comprenant un piston et un corps intermédiaire à section transversale bidirectionnelle pleine, en vues schématiques simplifiées : vue de côté (figure 6) ; vue de dessus (figure 7),
• les figures 8 et 9 représentent un organe pénétrant d'un injecteur selon l'invention comprenant un piston et un corps intermédiaire à section transversale bidirectionnelle creuse, en vues schématiques simplifiées : vue de côté (figure 8) ; vue de dessus (figure 9).
• les figures 10 et 11 représentent des schémas illustrant un fonctionnement d'un clapet formé par une buse et une aiguille à tête sortante : clapet fermé (figure 10) ; clapet ouvert (figure 11).

Other features and advantages of the invention will become apparent from the description which is given below, as a indicative and in no way limiting, with reference to the accompanying drawings, in which:

• the figure 1 is a diagram of an injector according to the state of the art arranged in a motor and equipped with a so-called outgoing head needle linked to an actuator mounted axially in a housing,
• the figure 2 is a diagram of an injector according to the invention arranged in a motor and equipped with a so-called outgoing head needle connected to an actuator mounted axially in a housing,
• the Figures 3 and 4 represent a penetrating member of an injector according to the invention comprising a piston and a perforated intermediate body with unidirectional cross section, in simplified schematic views: side view ( figure 3 ); top view ( figure 4 )
• the figure 5 schematically represents a simplified longitudinal section of a penetrating member of an injector according to the invention comprising a piston and an intermediate body comprising at least one fold,
• the Figures 6 and 7 represent a penetrating member of an injector according to the invention comprising a piston and an intermediate body with a full bidirectional cross section, in simplified schematic views: side view ( figure 6 ); top view ( figure 7 )
• the Figures 8 and 9 represent a penetrating member of an injector according to the invention comprising a piston and an intermediate body with hollow bidirectional cross-section, in simplified schematic views: side view ( figure 8 ); top view ( figure 9 ).
• the Figures 10 and 11 are diagrams illustrating an operation of a valve formed by a nozzle and a needle with a head outgoing: closed flap ( figure 10 ); open flapper ( figure 11 ).

The figure 1 presenting the state of the art, has already been discussed above.

• dans une chambre de combustion 80 d'un moteur 8 à combustion interne (figure 2), ou
• dans un conduit d'admission d'air (non représenté), ou
• dans un conduit d'échappement et, notamment, dans un moyen de dépollution logé dans ledit conduit d'échappement, pour y faciliter une réaction d'oxydation des suies (non représenté).

As previously announced and illustrated on Figures 2-11 , the invention relates to an injection device 7, or injector, for injecting a pressurized fluid 1 outside the injector 7. It may be, for example, a pressurized fuel 1 injected:

• in a combustion chamber 80 of an internal combustion engine 8 ( figure 2 ), or
• in an air intake duct (not shown), or
• in an exhaust duct and, in particular, in a depollution means housed in said exhaust duct, to facilitate a soot oxidation reaction (not shown).

The injector 7 has a main injection axis AB which preferably coincides with its axis of symmetry.

The injector 7 comprises at least one housing 2, preferably of cylindrical shape (for example, of revolution), comprising at least one axial cavity (bore) filled with the pressurized fluid 1 and opening on the inside 21 of the housing 2. As shown in figure 2 the housing 1 can be connected to at least one pressurized circuit 9 of the engine 8 via at least a first pressurized opening 22. The pressurized circuit 9 comprises at least one treatment device 90 for the pressurized fluid 1 comprising, by example, a pump, a tank, a filter, a valve. As in the state of the art cited above, channels for supplying pressurized fluid 1 can be arranged in the housing 2 to connect the pressurized circuit 9 with the pressurized opening 22.

The injector 7 comprises at least one actuator 3 having a stack, of cylindrical shape (for example, of revolution), including at least one electroactive part 30 comprising an electroactive material 300. The latter is intended to produce vibrations (illustrated with the aid of an arrow Y ₁ Y ₂ on the Figures 3, 5 , 6, 8 ) with a predetermined frequency v, for example, ultrasound which can spread between about 20 kHz and about 60 kHz, that is to say, with the vibration setpoint τ between respectively about 50 μs and about 16 μs . By way of example, for a steel, a wavelength λ of vibration is about 10 ^-1 m at v = 50 kHz (τ = 20 μs). The actuator 3 comprises at least excitation means 14 adapted to put the electroactive part 30 in vibration (in particular axial) with said reference period τ.

The stack can be confused with the actuator 3 ( figure 2 ) and is provided with a first end face 31, extended axially by a penetrating member 33, and a second end face 32 axially opposed to the first one. The linear dimensions of the penetrating member 33, for example, its measured width perpendicular to the axis AB and / or its length measured along the axis AB, are smaller than those of the stack. Said penetrating member 33 may comprise a piston 330 engaged (for example axially) substantially sealingly in the cavity 20 and forming a fluid link between the actuator 3 and the housing 2. Said fluidic link operates, as in a jack, to the using a pressure difference acting on the piston 330 between the pressurized fluid 1 (from the pressurized zones of the injector 7 inside 21 of the housing 2 on the figure 2 ) and this same depressurized fluid 10 from the depressurized zones of the injector 7 represented on the figure 2 by a depressurized circuit 12 connected to the cavity 20 via a depressurized opening 23 and at least one closure means 120 such as a valve.

The actuator 3 is movably mounted in the housing 2. Thus, the actuator 3 is adapted to axially oscillate therein. It can also be adapted to turn on itself around the AB axis. Through this link fluidic, it is possible to put the actuator 3 in a predetermined axial position relative to the housing 1 and keep it unchanged during an established operating regime of the injector 7, that is to say, when its operation at a predetermined temperature outside the starting and stopping phases of the engine 8.

où n est un coefficient multiplicateur, entier positif (figures 2-3, 5-6, 8).According to the invention, said penetrating member 33 has an axial length L that is said to be acoustic, such that the propagation time T of the acoustic waves produced by the vibrations of the electroactive part 30 of the actuator 3 and traversing this length L responds to the following equation: $$\mathrm{T}\mathrm{=}\left[\mathrm{2}\mathrm{not}\mathrm{+}\mathrm{1}\right]\mathrm{*}\left[\mathrm{\tau }\mathrm{/}\mathrm{4}\right]\mathrm{,}$$

where n is a multiplier, positive integer ( figures 2-3 , 5-6, 8 ).

It should be understood that the acoustic axial length L and the linear (non-acoustic) axial dimensions of the penetrating member 33 are generally presented as two distinct physical values. It should be noted that figures 2-3 , 5-6, 8 illustrate particular cases where these two values are confounded.

Preferably, said penetrating member 33 comprises at least one intermediate body 331 disposed axially between the piston 330 and the first end face 31. In addition, the piston 330 radially exceeds the intermediate body 331.

With this arrangement, it is possible, on the one hand, to make the penetrating member 33 lighter, and, on the other hand, to create, on the piston 330, a first bearing surface 3301 ( figures 3 , 5-6, 8 ) oriented towards the first end face 31 and adapted to transmit to the intermediate body 331 (and, ultimately, to the actuator 3) a pressure force from the pressurized fluid 1. Thus, it is possible to push the piston 330 axially ( and, therefore, the actuator 3), by the pressurized fluid 1 acting on the first bearing surface 3301 ( figures 3 , 5-6, 8 ), in a direction outward of the housing 2, opposite the arrow AB on the figure 2 .

Preferably, the axial axial length h _p of the piston 330 is negligible compared with that h _c of the intermediate body 331: h _{p hc} ( figure 8 ). Similarly, the linear axial thickness (non-acoustic) of the piston 330 may be negligible compared to the linear axial dimensions (non-acoustic) of the intermediate body 331. These arrangements contribute to making the penetrating member 33 lighter.

Said intermediate body 331 may be one of the following bodies: (a) first body 3310 (such as a plate 3310 illustrated on the Figures 3-4 ) having, transverse to said axis AB, at least one unidirectional section; (b) second body 3311 (such as a solid axial bar 3311 of cylindrical shape of revolution illustrated on the Figures 5-7 ) having, transverse to said axis AB, at least one bidirectional full section; (c) third body 3312 (such as a sleeve 3312 illustrated on the Figures 8-9 ) having, transversely to said axis AB, at least one bidirectional hollow section.

With these arrangements, it is possible to further lighten the penetrating member 33.

Preferably, said intermediate body 331 is perforated ( figures 3,5 ).

These arrangements also contribute to a reduction in the weight of the penetrating member 33.

Said intermediate body 331 may comprise at least one fold 3313. The figure 5 illustrates an alternative embodiment of the intermediate body 331 comprising two folds 3313 disposed symmetrically with respect to the axis AB. In addition, said intermediate body 331 may comprise at least one zone of axial discontinuity 3314, as illustrated in FIG. figure 3 using an axial aperture 3315 and on the figure 5 using the full axial bar 3311 discontinuous.

With these arrangements, it is possible to reduce only the axial size of said intermediate body 331 without changing its axial axial length L.

The injector 7 comprises at least one nozzle 6 having a length along the axis AB and having along said axis AB, an injection port 60 and a seat 61. In contrast, the nozzle 6 is connected to the housing 2 ( figure 2 ). The linear dimensions of the housing 2, for example, its width measured perpendicular to the axis AB and / or its length measured along the axis AB, may be greater than those of the nozzle 6. The density of the housing 2 may be greater than the nozzle 6.

The injector 7 comprises at least one needle 5. It has, along said axis AB, a free end 50 defining a valve in an area of contact with the seat 61. In contrast, the needle 5 is connected at the stacking of the actuator 3 and, in particular, at its second end face 32, by a first junction zone Z ₁ J ₁ ( figure 2 ). The linear dimensions of the actuator 3, for example, its width measured perpendicular to the axis AB and / or its length measured along the axis AB, may be greater than those of the needle 5. The density of the the actuator 3 may be greater than that of the needle 5. The actuator 3 is adapted to put the needle 5 in vibration with said reference period τ, ensuring between its end 50 and the seat 61 of the nozzle 6 a relative movement to open and close the valve alternately, as shown in the Figures 10-11 . The actuator 3 thus plays a role of an active "master" controlling the needle 5 which then presents itself as a passive "slave" piloted.

Thanks to these arrangements, a web formed by the pressurized fluid 1 escaping from the nozzle 6 at the opening of the valve, is fractionated and forms fine droplets (not shown). In an application of the injector 7 in which it sprays fuel into the combustion chamber 80, the fine droplets favor a mixture air / fuel more homogeneous which makes the engine 8 less polluting and more economical.

The end 50 of the needle 5 defining the valve is preferably extended longitudinally along the axis AB, opposite the actuator 3, by a head 51 closing the seat 61, so as to ensure better sealing of the injector 7 with the closed flap ( figure 10 ).

The figures 2 , 10-11 illustrate the case of the needle 5 with the head 51, said outgoing, having a flared shape (preferably frustoconical) divergent oriented, along the arrow AB on the figure 2 , the housing 2 outwardly of the nozzle 6 in the combustion chamber 80. Preferably, at least one side wall 510 (frustoconical in the example on the figure 11 ) of the head 51 forms with the axis AB a predetermined obtuse angle α (α> 90 °). The valve is defined at the place of the outgoing head 51, in a contact zone of the outgoing head 51 with the seat 61. The outgoing head 51 closes the seat 61 on the outside of the nozzle 6 (oriented opposite of the housing 1 according to the arrow AB on the figure 2 ). The seat 61 of the nozzle 6 may be of respective flared (preferably frustoconical) shape diverging towards the outside of the nozzle 6. These arrangements contribute to improving the tightness of the injector 7 with the closed valve ( figure 10 ).

As illustrated on the figure 2 , the stack comprises at least one portion 34, called amplifier 34, axially connected with the needle 5 at the location of the second end face 32, the electroactive part 30 and the needle 5 being arranged axially on both sides. other of the amplifier 34. The latter is adapted to transmit the vibrations of the electroactive material 300 to the needle 5 by amplifying them so that the movements of the needle 5 at the valve are greater than the integral of the deformations of the electroactive material 300. The amplifier 34 may have a substantially cylindrical shape, for example rotation ( figure 2 ). Alternatively, the amplifier 34 may have another shape (not shown), for example example, frustoconical, which narrows in the direction of the oriented axis AB of the electroactive portion 30 to the needle 5.

The stack further comprises at least one other part 35, called rear mass 35, the amplifier 34 and the rear mass 35 being disposed axially on either side of the electroactive portion 30. The rear mass 35 has a opposite wall axially to the electroactive portion 30, said wall being merged with the first end face 31 of the stack.

The rear mass 35 contributes to a more homogeneous distribution (transverse to the axis AB) of the axial stresses on the electroactive material 300 following mechanical stresses. Thus, it is possible to reduce the number of cracks and / or breaks in the electroactive material 300 during, for example, assembly and / or operation of the injector 7.

Preferably, the electroactive material 300 is piezoelectric which may be, for example, one or more ceramic piezoelectric washers stacked axially on each other to form the electroactive portion 30 of the stack. The selective deformations of the electroactive material 300, for example, the periodic deformations with the reference period τ, generating the acoustic waves in the injector finally lead to the relative longitudinal movements of the head 51 of the needle 5 relative to the seat 61 of the nozzle 6 or vice versa, able to open and close alternately the valve, as mentioned above in connection with the figures 2 and 10-11 . These selective deformations are controlled by corresponding excitation means 14 adapted to put the electroactive part 30 of the stack in vibration with the reference period τ, for example, using an electric field created by a difference of applied potential, through the son (not shown), to electrodes 301 integral with the electroactive material 300 piezoelectric. Alternatively, the electroactive material 300 may be magnetostrictive. Selective deformations of the latter are controlled by corresponding unrepresented excitation means, for example, by means of a magnetic induction resulting from a selective magnetic field obtained using, for example, a not shown exciter, and in particular, by a coil integral, for example, the stack or other coil surrounding the stack.

• d'une part, serrés ensemble par un moyen de précontrainte 36 adapté à précontraindre au moins partiellement ledit empilement, et,
• d'autre part, adaptés à être traversés par des ondes acoustiques initiées par les vibrations de la partie électroactive 30.

The amplifier 34, the electroactive part 30 and the rear mass 35 are:

• on the one hand, clamped together by a prestressing means 36 adapted to preload at least partially said stack, and,
• on the other hand, adapted to be traversed by acoustic waves initiated by the vibrations of the electroactive part 30.

Thanks to these arrangements, the actuator 3 (with, on the one hand, the penetrating member 33, and, on the other hand, the needle 5) forms an acoustic wave propagation medium having at least one acoustic impedance linear I which depends on a surface Σ of a section of the middle perpendicular to the axis AB, of a density ρ of the medium and of a speed c of sound in the medium: I = f _l (Σ, ρ , vs). It is thus possible to obtain an opening of the valve of the injector 7 which is not very sensitive to the pressure in the combustion chamber 80 by moving the end 50 of the needle 5 in displacement. Likewise, given the said acoustic length L selective of the penetrating member 33 written using the equation E1 above, it is possible to maintain dynamically immobile or axially fixed, in the manner of a displacement node, a second bearing surface 3302 ( and, more generally, the piston 330) of the penetrating member 33 oriented towards the cavity 20 and adapted to transmit, once in contact with the fluid 1, an axial force specific to said fluidic connection for regulating said predetermined axial position of the actuator 3 in the injector 7. Maintaining the second surface dynamically immobile support 3302 is obtained by maintaining its longitudinal speed along the axis AB equal to zero, taking advantage of the periodicity of the phenomenon of the propagation of acoustic waves leaving the rear mass 35 in the penetrating member 33.

The intermediate body 331 is a body whose radial dimensions perpendicular to the axis AB are small compared to its linear axial dimensions (non-acoustic). As mentioned above, the linear (non-acoustic) axial dimensions of the piston 330 (as well as its axial thickness) may be negligible compared to those of the intermediate body 331. As a result, a simplified acoustic model of the penetrating member 33 can be represented by a bar (solid ( figure 6 ) or hollow ( figure 8 ), for example, longitudinally pierced) embedded in the rear mass 35 in a second junction zone Z ₂ J ₂ . The propagation of acoustic waves combines the propagation of a voltage jump (force) ΔF ₀ and a speed jump Δv using an equation: ΔF ₀ = Σ * Δσ = Σ * z * Δv, where Σ is a surface of a section of the bar perpendicular to its preferred axis AB, for example, its axis of symmetry, Δσ = z * Δv is a stress jump, z is an acoustic impedance defined by an equation: z = ρ * c where ρ is a density of the bar and c is a speed of sound in the bar. It is understood that the voltage F ₀ is positive for a compression and the speed v is positive in the propagation direction of the acoustic waves. The product I = Σ * z = Σ * ρ * c representative of the acoustic properties of the bar - solid or hollow - is called "linear acoustic impedance" or "linear impedance".

At least a first linear impedance break I occurs in the second junction zone Z ₂ J ₂ . The term "break" shall be understood as "a linear impedance variation I exceeding a predetermined threshold representative of a difference between the upstream and downstream linear impedance, with respect to the direction of acoustic wave propagation, of a rupture zone linear impedance located in a propagation medium acoustic waves a small distance to the wavelength, preferably less than one-eighth of the wavelength λ / 8 ". A second linear impedance break I occurs at the end of the penetrating member 33 (or, when the axial axial length h _p of the piston 330 is negligible, at the end of the intermediate body 331), axially opposite the mass. As for the acoustic axial length L = f (T) expressed in acoustic flight time T, it is measured between the first and the second linear impedance I breaks.

It should be understood that the equation referenced E1 above must be considered as verified with a certain tolerance to take account of manufacturing constraints, for example, to a tolerance of the order of ± 10% of the reference period τ , that is to say, of the order of ± 40% of said quarter of the setpoint period τ / 4. Taking into account this tolerance, the equation referenced E1 above can be rewritten as follows: $$\mathrm{T}\mathrm{=}\left[\mathrm{2}\mathrm{not}\mathrm{+}\mathrm{1}\right]\mathrm{*}\left[\mathrm{\tau }\mathrm{/}\mathrm{4}\right]\pm 0.4*\left[\mathrm{\tau }\mathrm{/}\mathrm{4}\right]\mathrm{,}$$

In practice, the acoustic axial length L = f (T) expressed in acoustic flight time T, measured on corresponding parts manufactured on an industrial scale, may have slight variations from the reference values calculated with the aid of equation E1 above. These slight variations may be due to an effect of reported masses. The latter may correspond, for example, to a guiding boss (not shown) in a plane perpendicular to the axis AB of the intermediate body 331. Said tolerance makes it possible to take into account said effect of masses reported so as to correct the expression in acoustic flight time of the acoustic axial length L = f (T) using equation E2 above.

• radialement, entre le piston 330 et la cavité 20 pour former une zone d'étanchéité entre eux, et
• axialement, entre la première 3301 et la deuxième 3302 surfaces d'appui du piston 330, pour éviter des suintements axiaux du fluide 1 pouvant perturber une balance des forces axiales exercée sur le piston 330 et, in fine, ledit lien fluidique.

Preferably, the injector 7 may comprise an interposed sealing means 4:

• radially, between the piston 330 and the cavity 20 to form a sealing zone between them, and
• axially, between the first 3301 and the second 3302 bearing surfaces of the piston 330, to prevent axial seepage of the fluid 1 may interfere with a balance of axial forces exerted on the piston 330 and, ultimately, said fluid link.

The second bearing surface 3302 of the piston 330 being dynamically immobile because of the acoustic axial length L = f (T) of the penetrating member 33 described by at least one of the equations E1 or E2 above, the presence of the seal does not brake the vibrations Y ₁ Y ₂ of the rear mass (and, more generally, of the actuator 3) and ultimately does not disturb the opening and / or closing of the valve of the injector 7.

Means of return 11 of the actuator 3 can be provided to hold the head 51 of the needle 5 in abutment against the seat 61 of the nozzle 6, so as to ensure the closure of the valve in the absence of the fluid 1 and, therefore, , of the fluidic link, for example, after the assembly of the injector 7 and before its connection to the pressurized circuit 9 of the fluid 1 during its installation on a cylinder head 13 of the engine 8. This advantageously makes it possible to protect the interior 21 of the injector 7 against dust which may cause, for example, a short circuit between the electrodes 301 of the electroactive part 30.

The return means 11 may be represented by a prestressed spiral spring disposed along the axis AB downstream of the housing 2 relative to the direction of flow of the pressurized fluid 1 towards the nozzle 6.

Claims (10)

1. Injection device (7) for injecting pressurized fluid (1), having a main axis of injection (AB) and comprising at least:

   - a housing (2) comprising at least one axial cavity (20) filled with pressurized fluid (1) and opening to the inside (21) of the housing (2),

   - an actuator (3) exhibiting a stack including at least one electroactive part (30) comprising an electroactive material (300) and endowed
   o with a first transverse face (31) extended axially by a penetrating member (33), and
   o with a second transverse face (32) axially opposite the first (31),
   the actuator (3) being mounted so that it can move axially in the housing (2) and said member (33) comprising a piston (330) engaged in a substantially fluidtight manner in the cavity (20) and forming a fluidic connection between the actuator (3) and the housing (2),

   - energizing means designed to set the electroactive part (30) of the actuator (3) in vibration with a set period τ,
   characterized in that said penetrating member (33) has an acoustic axial length (L) such that the propagation time T of the acoustic waves produced by the vibrations of the electroactive part (30) of the actuator (3) and traveling along this acoustic axial length (L) satisfies the following equation: T = [2n+1]*[τ/4], where n is a positive integer coefficient.
2. Injection device (7) according to Claim 1, characterized in that said penetrating member (33) comprises at least one intermediate body (331) positioned axially between the piston (330) and the first transverse face (31), and in that the piston (330) protrudes radially beyond the intermediate body (331).
3. Injection device (7) according to Claim 2, characterized in that said intermediate body (331) is one of the following bodies: (a) a first body (3310) having, transversely to said axis (AB), at least one one-way section; (b) a second body (3311) having, transversely to said axis (AB), at least one solid two-way section; (c) a third body (3312) having, transversely to said axis (AB), at least one hollow two-way section.
4. Injection device (7) according to Claim 2 or 3, characterized in that said intermediate body (331) is perforated.
5. Injection device (7) according to any one of Claims 1 to 4, characterized in that it comprises a sealing means (4) inserted radially between the piston (330) and the cavity (20).
6. Injection device (7) according to any one of the preceding claims, characterized in that it comprises at least one needle (5), and in that the stack comprises at least one part (34), known as an amplifier (34), axially connected to the needle (5) at the site of the second transverse face (32), the electroactive part (30) and the needle (5) being positioned axially one on each side of the amplifier (34).
7. Injection device (7) according to Claim 6, characterized in that the stack comprises at least one other part (35), known as the rear mass (35), the amplifier (34) and the rear mass (35) being arranged axially one on each side of the electroactive part (30), and in that the rear mass (35) has a wall axially at the opposite end to the electroactive part (30), said wall coinciding with the first transverse face (31) of the stack.
8. Injection device (7) according to Claim 7, characterized in that the stack coincides with the actuator (3), and in that the amplifier (34), the electroactive part (30) and the rear mass (35) are clamped together by a preload means (36) and designed to have passing through them acoustic waves initiated by the vibrations of the electroactive part (30).
9. Injection device (7) according to any one of Claims 6 to 8, characterized in that it comprises a nozzle (6) comprising, along said axis (AB), an injection orifice (60) and a seat (61) and being, at the opposite end, connected to the housing (2), and in that the needle (5) has, along said axis (AB), a free end (50) defining a valve, in a region of contact with the seat (61) and being, at the opposite end, connected to the stack of the actuator (3) which sets this needle (5) in vibration, bringing about, between its end (50) and the seat (61) of the nozzle (6), a relative movement capable of opening and closing the valve alternately.
10. Internal combustion engine (8) using the pressurized fluid (1) injection device (7) according to any one of the preceding claims.

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