EP2158398A2

EP2158398A2 - Fluid injection device

Info

Publication number: EP2158398A2
Application number: EP08806079A
Authority: EP
Inventors: André AGNERAY; Nadim Malek; Laurent Levin; Marc Pariente
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2007-06-27
Filing date: 2008-06-25
Publication date: 2010-03-03
Also published as: WO2009007596A3; JP2010531410A; CN101784784B; FR2918123A1; RU2010102516A; WO2009007596A2; CN101784784A; US20100187329A1; RU2457353C2; KR20100040735A

Abstract

The invention relates to a fluid injection device (131) having a main injection axis (AB) and including at least: a housing (1); an actuator (2) axially mounted in the housing (1) and comprising a stack with two axially opposed front faces (C, D) and including at least one electro-active portion (22) with an electro-active material; and a pre-stressing means adapted for at least partially pre-stressing said stack. According to the invention, the pre-stressing means includes at least a tightening clamp (25) outside the stack and provided between the stack and the housing (1).

Description

Fluid injection device

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

More specifically, the invention relates, according to a first aspect, to a fluid injection device, said injector, having a main axis of injection and comprising at least:

- a housing,

an actuator axially mounted in the housing and having a stack with two axially opposite end faces and including at least one electroactive part comprising an electroactive material, and

prestressing means adapted to preload at least partially said stack,

A prestressing means adapted to prestress said stack and, in particular, an electroactive material, for example, piezoelectric ceramic washers or magnetostrictive elements distributed in the stack, is well known to those skilled in the art as shown, for example, European patent application EP 1 172 552. The establishment of this prestressing means requires drilling of the electroactive material which weakens it. The ceramic washers crack and break easily during drilling, and / or assembly, and / or operation of the injector thereby reducing its service life.

To avoid problems of electrical short circuit that can affect an operation of the injector, a delicate compromise must generally be made between the compactness of the actuator housed in the housing and the complexity of a spatial distribution of the electrodes with their son connecting each ceramic washer with means for exciting the electroactive material outside the housing. This makes assembly of the injector difficult, any unexpected contact of the stack against the housing, for example, during insertion of the actuator into the housing, which can damage the spatial distribution of the electrodes with their son.

The present invention, which is based on this original observation, is primarily intended to provide a fluid injection device for at least reducing at least one of the limitations mentioned above. For this purpose, the injection device, which is also in accordance with the generic definition given in the preamble above, is essentially characterized in that the prestressing means comprises at least one clamping flange external to the stack and disposed between the stack and the housing.

With this arrangement, the drilling of the electroactive material is no longer essential, which makes it less fragile, in particular, to mechanical stresses, for example, during assembly and / or operation of the injector. In addition, the presence of the clamping flange between the stack and the housing protects the stack against unintentional contact and / or crumbling with the housing, for example, during assembly of the injector, which may be damaged by for example, the spatial distribution of the electrodes with their wires, or even the ceramic material itself.

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.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limiting, with reference to the accompanying drawings, in which: which: FIG. 1 is a diagram of an injection device 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,

FIG. 2 is a diagram of an injection device according to the invention arranged in the engine and equipped with an incoming said head needle connected to the actuator, FIGS. 3 and 4 represent diagrams illustrating a functioning of the valve. formed by a nozzle and an outgoing needle: closed valve (Figure 3); open flap (figure 4),

Figures 5 and 6 show diagrams illustrating an operation of the valve formed by a nozzle and an incoming needle needle: closed valve (Figure 5); open flap (figure 6),

FIG. 7 schematically shows, in simplified side view, the stack prestressed by a clamping clamp external to the stack and arranged between the stack and the casing,

FIG. 8 schematically represents a simplified section of the injector in a plane perpendicular to an axis of symmetry of the injector,

FIGS. 9-11 diagrammatically show in simplified side views respectively three different diagrams of the stack prestressed by clamping clamps of different structure, an axial clamping force adjusting means of the stack being arranged axially between each flange and the stack,

FIGS. 12-14 schematically show in simplified side views respectively three different diagrams of the stack prestressed by structural clamps; different, the adjustment means completed by an elastic means being disposed axially between each flange and the stack,

FIG. 15 schematically shows a side view in partial longitudinal section of a one-piece needle in the form of a cylindrical bar,

Figure 16 schematically shows a simplified side view in partial longitudinal section a cylindrical one-piece nozzle.

As previously announced, the invention relates to an injection device, or injector, for injecting a fluid, for example a fuel 131 into a combustion chamber 15 of an internal combustion engine 151 (FIG. 1 (or 2) ), or in an air intake duct (not shown), or in an exhaust gas duct (not shown).

The injector comprises two bodies, for example, cylindrical. A first body representing a housing 1, is extended, along a preferred axis AB of the injection device, for example, its axis of symmetry, by at least one nozzle 3 having a length along the axis AB and having an orifice of injection and a seat 5 (or 5 '). The linear dimensions of the housing 1, for example, its width measured perpendicularly to the axis AB and / or its length measured along the axis AB, may be greater than those of the nozzle 3. The density of the housing 1 may greater than that of the nozzle 3. The housing 1 can be connected to at least one fuel circuit 131 131 via at least one opening 9. The fuel circuit 131 comprises a fuel treatment device 13 131 comprising, for example, a tank, a pump, a filter.

A second body representing an actuator 2 is axially mounted, preferably movable, in the housing 1. A needle 4 has, along the axis AB, a length and a first end 6 defining a valve in a zone of contact with the seat 5 (or 5 ') of the nozzle 3. The linear dimensions of the actuator 2, for example, its width measured perpendicular to the axis AB and / or its measured length along the axis AB, may be greater than those of the needle 4. The density of the actuator 2 may be greater than that of the needle 4. The needle 4 and the actuator 2 are connected between them by a junction zone ZJ (Figure 2). The first end 6 is preferably extended longitudinally, along the axis AB, opposite the actuator 2, by a head 7 (or T) closing the seat 5 (or 5 '), so as to ensure a better seal of the valve of the injector.

The actuator 2 is extended, along the axis AB, by the needle 4, and is arranged for a direct vibration of the needle 4 with a reference period τ, thus ensuring between the first end 6 of the needle 4 and the seat 5 (or 5 ') of the nozzle 3 a relative axial movement to open and close alternately the valve, as shown in Figures 3-4 and 5-6. The actuator 2 thus plays a role of an active "master" driving the needle 4 which then presents itself as a passive "slave" piloted.

The actuator 2 has a stack with two opposite end faces C, D axially and including at least one electroactive part 22 comprising an electroactive material 221 (FIGS. 7-14). The latter is intended to produce vibrations with a predetermined frequency v, for example, ultrasound that can spread from about v = 20 kHz to about v = 60 kHz, that is to say, with the reference period τ of vibrations respectively between 50 microseconds and 16 microseconds. For example, for a steel, a wavelength λ of vibration is about 10 ^{~ 1} m at v = 50 kHz (τ = 20 microseconds). As illustrated in FIGS. 1 and 2, the stack can be confused with the actuator 2.

The stack comprises at least one part, called amplifier

21, axially connected with the needle 4 at the location of a D of said end faces C, D, the electroactive portion 22 and the needle 4 being arranged axially on either side of the amplifier 21. The latter is intended to transmit the vibrations of the electroactive material 221 to the needle 4 by amplifying them so that the movements of the needle 4 at the valve are greater than the integral of the deformations of the electroactive material 221. The amplifier 21 may have a substantially cylindrical shape (FIGS. 7, 9-10, 12-13). Alternatively, the amplifier 21 may have another shape, for example, frustoconical, which narrows in the direction of the oriented axis AB of the electroactive portion 22 to the needle 4 (Figure 11, 14).

The stack further comprises at least one other part 23, called the rear mass 23, which plays a homogeneous distribution role of the stresses on the electroactive material 221. The amplifier 21 and the rear mass 23 are arranged axially on either side of the the electroactive portion 22. The rear mass 23 has a wall axially opposed to the electroactive portion 22, said wall being merged with the front face C of the stack axially opposed to the needle 4.

The amplifier 21, the electroactive part 22 and the rear mass 23 are, on the one hand, clamped together by a prestressing means 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 22.

The prestressing means comprises at least one clamping flange 25 external to the stack and arranged between the stack and the casing 1.

Preferably, the electroactive material 221 is piezoelectric which may be, for example, one or more ceramic piezoelectric washers stacked axially on each other to form the electroactive portion 22 of the stack. The selective deformations of the electroactive material 221, for example, the periodic deformations with the reference period τ, generating the acoustic waves in the injector ultimately lead to relative longitudinal movements of the head 7 (or T) of the needle 4 relative to the seat 5 (or 5 ') or vice versa , capable of alternately opening and closing the valve, as mentioned above with reference to FIGS. 3-4 and 5-6. These selective deformations are controlled by corresponding excitation means 14 adapted to turn the electroactive part 22 of FIG. the vibration stack with the reference period τ, for example, using an electric field created by an applied potential difference, via the wires (not shown), to electrodes 220 integral with the material electroactive 221 piezoelectric. Alternatively, the electroactive material 221 may be magnetostrictive. The 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, an exciter not shown, and in particular by a coil integral, for example, the stack or other coil surrounding the stack.

The prestressing means comprises at least one axial force adjusting means 250 for clamping the stack. This allows the prestressing means to clamp the electroactive portion 22, for example, between the rear mass 23 and the amplifier 21, as illustrated in FIGS. 1 and 2, with a "case-by-case" adjustable force as a function of for example, the piezoelectric or magnetostrictive nature of the electroactive material 221 and / or the section in a plane perpendicular to the AB axis of the piezoelectric ceramic washers or magnetostrictive elements in the stack, and / or the spatial distribution said washers in the stack, and / or their shapes, and / or their linear dimensions (and / or in fine their shapes). The adjusting means 250 may be connected with the clamping flange 25 (FIGS. 1, 2, 7, 9-14). In particular, it is possible to provide that the adjusting means

250 is disposed axially between the clamping flange 25 and the stack (Figures 7, 9-10, 12-14). Apart from the fact that this facilitates the assembly of the injector, the axial positioning of the adjusting means 250 contributes to preserving a structural and / or acoustic symmetry of a "needle 4 + actuator 2" assembly so that, respectively, neither movements reciprocating axial axes of the needle 4, nor the propagation of acoustic waves as a whole

"Needle 4 + actuator 2" are not disturbed by an asymmetric mass spurious effect.

Preferably, the clamping flange 25 has a thermal expansion (in particular, a coefficient of thermal expansion) substantially identical to that of the stack and, in particular that of the electroactive material 221. For example, the difference between the coefficients of Expansion of the electroactive material 221 and the materials of the stack can be chosen so that the differential expansions of these parts do not induce, within the operating temperature range of the injector, a variation of the prestressing of the electroactive material 221. greater than 10% of the nominal stress value (induced by the prestressing means 250). For the ceramic electroactive material 221, the clamping flange 25 may be made of an alloy of iron and nickel with carbon and chromium, for example, of alloy "invar" type. With this arrangement, the prestressing of the electroactive material 221 tends to remain constant regardless of the temperature variations of the injector. The same expansion of the stack (and, in particular, the electroactive material 221 and that of the clamping flange 25) provides a thermal compensation for the expansions due to temperature variations of the injector. The assembly of the stack and, therefore, the actuator 2, becomes faster because no other means is required to compensate for said thermal expansions. In this embodiment, the rear mass 23 may be merged with the adjusting means 250 (not shown in the figures). Alternatively, the clamping flange 25 may have a thermal expansion (in particular, a coefficient of thermal expansion) different from that of the stack and, in particular, that of the electroactive material 221. In this case, the prestressing means comprises at least one elastic means 251 (for example, at least one rubber seal, a spring washer, a spring) disposed between the clamping flange 25 and the stack. The elastic means 251 makes it possible to ensure quasi-constant prestressing of the electroactive part 22 and, in particular, of the electroactive material 221, independently of the elongations of the clamping flange 25 due to the thermal expansions. Thanks to this arrangement, it is possible to continue assembling the stack and, therefore, the actuator 2, on an industrial scale, for example, when a stock out of the clamps 25 in invar . Thus, this embodiment contributes to making the manufacture of the injector more reliable.

Preferably, the elastic means 251 is disposed between the stack and the adjusting means 250 (Figures 7, 12-14), so as to make the assembly of the stack faster.

Preferably, the adjusting means 250 is in the form of a screw, preferably a threaded screw, the clamping flange 25 having a corresponding, preferably central, bore, that is to say, aligned on the AB axis and tapped (Figures 7, 9-14).

In particular, the clamping flange 25 is supported on the two opposite end faces C, D of the stack (FIG. 7), so as to ensure a homogeneous distribution of the stresses during clamping of the stack.

The amplifier 21 may have at least one narrowing segment along the axis AB oriented towards the needle 4, for example, a connecting segment 211 with the electroactive portion 22. In this case, the clamping flange 25 can marry at least partially the shape of said narrowing segment of the amplifier 21, as illustrated in Figures 10-11, 13-14. This makes it possible to reduce an axial length of the clamping flange 25 as can be seen by comparing respectively the clamps 25 in FIGS. 9 and 12 with those in FIGS. 10-11 and 13-14. This possibility of shortening the clamping flange 25 makes it possible either to make the lighter flanges (all other parameters of the flange remaining unchanged) or to be more resistant (for example, by proportionally increasing a thickness of the shortened flange) to mechanical wear. and / or high clamping forces.

It should be understood that the prestressing means may comprise a plurality of clamping flanges 25 arranged symmetrically around the stack and spaced apart radially from each other at a predetermined angle measured in a plane perpendicular to the axis AB. The presence of several flanges ensures the homogeneous distribution of stresses during tightening of the stack.

FIG. 1 illustrates the case of the needle 4 with the so-called outgoing head 7, having a diverging (preferably frustoconical) flared shape in a direction of the oriented axis AB of the casing 1 towards the outside of the nozzle 3 in the combustion chamber 15. The outgoing head 7 closes the seat 5 of the outer side of the nozzle 3 facing away from the housing 1, in the direction of the axis AB.

FIG. 2 illustrates the case of the needle 4 with the so-called tapered, preferably frustoconical, head T going narrowing in the direction of the oriented axis AB of the casing 1 towards the outside of the nozzle 3 and closing off the seat 5 'on the inside of the nozzle 3 facing the housing 1.

Returning means 11 (or 11 ') of the actuator 2 may be provided to hold the head 7 (or T) of the needle 4 in abutment with the seat 5 (or 5') of the nozzle 3, so as to to ensure the closure of the valve regardless of the pressure in the combustion chamber 15. The clamping flange 25 and the housing 1 may have minus a longitudinal contact zone, represented with the aid of the dotted lines referenced UW in FIG. 8. The possible presence of the longitudinal contact zone UW can make assembly of the injector easier, in particular by protecting the electrodes 220 against any unexpected contact with the housing 1, for example, during insertion of the stack into the housing 1 during assembly of the injector provided with the needle 4 to 7 outgoing head taking care to control friction and alignments.

The nozzle 3 with the housing 1 and the needle 4 with the actuator 2 respectively form a first and a second acoustic wave propagation medium. Each of these two media has at least one linear acoustic impedance I which depends on a surface Σ of a section of the middle perpendicular to the axis AB, a density p of the medium and a c velocity of the sound in the middle: I = fι (Σ, p, c). To illustrate this report, let us examine various simplified examples relating to the needle 4 or the nozzle 3 and illustrated respectively in FIGS. 15-16. For the sake of simplification, it is understood that for all these examples, the second body, the actuator 2 and the stack are merged. In order to obtain an opening of the valve of the injector that is not very sensitive to the pressure in the combustion chamber 15, the pilot injector moves the first end 6 of the needle 4 while the seat (represented in a simplified manner in the figures 15-16 and referenced 50) of the nozzle 3 is kept dynamically stationary or fixed thus behaving as a displacement node.

The needle 4 and the nozzle 3 are each a body whose radial dimensions perpendicular to the axis AB are small relative to its length along the axis AB. In a solid bar 400 cited here as a simplified model of the needle 4 (Figure 15) or in a pierced bar 300 longitudinally cited here as a simplified model of the nozzle 3 (Figure 16), the propagation of acoustic waves combines the propagation a voltage jump (force) ΔF ₀ and of 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 p is a density of the bar and c is a velocity of sound in the closed off. It is understood that the voltage Fo is positive for a compression and the velocity 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".

Any variation in linear acoustic impedance I induces an echo, i.e., a weakening of the acoustic wave propagating in one direction of the bar (e.g., from right to left in Figs. 15-16) by another acoustic wave propagating in the opposite direction of the bar (for example, from left to right in FIGS. 15-16) from a linear impedance variation point I, for example, at a junction between the needle 4 and the actuator 2 (Figure 15) or at another junction between the nozzle 3 and the housing 1 (Figure 16). This same reasoning is applicable to any linear impedance break I, the term "break" to be understood as "a linear impedance variation I exceeding a predetermined threshold representative of a difference between the linear impedance upstream and that downstream from the acoustic wave propagation direction, a linear impedance breaking zone located in an acoustic wave propagation medium at a small distance in front of the wavelength, preferably less than one-eighth of the wavelength λ / 8 ".

The injector may comprise at least one linear acoustic impedance breaking zone, existing at a distance from the contact zone of the seat 50 with the first end 6 of the needle 4 along the nozzle 3 (FIG. housing 1, and at least one other zone of linear acoustic impedance breaking existing away from the contact area of the first end 6 with the seat 50 along the needle 4 (Figure 15) or the actuator 2. Said zone and other rupture zone of linear acoustic impedance being each first in order from said contact zone between the first end 6 of the needle 4 and the seat 50, in a propagation direction of acoustic waves directed respectively to the housing 1 and the actuator 2.

As illustrated schematically in FIG. 1 (or 2), the distance, called the first distance I_ _B , between, on the one hand, the contact zone between the seat 5 (or 5 ') and the first end 6, and, d on the other hand, the first linear acoustic impedance breaking zone along the nozzle 3 or the casing 1, is such that the propagation time, called "acoustic flight time" T _B , acoustic waves initiated by the party electroactive 22 of the stack and traversing this first distance I_ _B = f _B (T _B ) meets the following equation:

T _B = n _B * [τ / 2], (E1)

where n _B is a multiplier, non-zero positive integer, said first multiplier, and distance, said second distance I_ _A, between, on the one hand, the contact area between the first end 6 and the seat 5 (or 5 '), and, on the other hand, the first linear acoustic impedance breaking zone along the needle 4 or the actuator 2, is such that the propagation time, called "acoustic flight time" T _A, acoustic waves initiated by the electro-active portion 22 of the stack and the second browsing I_ distance _A = fAOΑ) satisfies the following equation:

T _A = n _A ^* [τ / 2], (E2) where Π _A is another multiplier coefficient, nonzero positive integer, said second multiplier coefficient, for example, n _A ≠ n _B.

It should be understood that the equations referenced E1 and E2 below above must be considered as verified to 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 order of ± 20% of the half-period τ / 2. Taking into account this tolerance, the equations referenced E1 and E2 above can respectively be rewritten as follows:

T _B = n _B ^* [τ / 2] ± 0.2 ^* [τ / 2] (AND)

T _A = n _A * [τ / 2] ± 0.2 * [τ / 2] (EZ)

It should be noted that in practice, the first I_ _B = distance f _B (T _B) expressed in acoustic time flight T _B and the second distance I_ _A = f _A (T _A) expressed in acoustic time flight T _A , measured on corresponding parts manufactured on an industrial scale, may show slight variations from the reference values calculated using equations E1 and E2 above. These slight variations may be due to an effect of reported masses. The latter may correspond, for example, to the head 7 (or T) of the needle 4 and / or to a guiding boss (not shown) in a plane perpendicular to the axis AB of the end 6 of the needle 3 in the nozzle 3. Said tolerance makes it possible to take into account said effect of reported masses so as to correct the expressions in acoustic flight time of the first I_ _B = f _B (T _B ) and the second I_ _A = f _A (T _A ) distances using equations EV and E2 'above.

Preferably, n _A = n _B for the second and the first multiplying coefficients with, in particular, n _A = n _B = 1 in order to minimize the linear dimensions of the injector along the axis AB to allow maximum space for intake and / or exhaust ducts. Thus, starting from the contact zone between the seat 5 (or

5 ') and the first end 6 of the needle 4, the nozzle 3 has constant acoustic properties on successions of length representative of the first distance I_ _B = f _B (T _B ) substantially equal to each other in acoustic flight time and whose expression in acoustic flight time T _B is preferably a single half-period τ / 2. Similarly, starting from the contact zone between the seat 5 (or 5 ') and the first end 6 of the needle 4, the latter has constant acoustic properties on successions of length representative of the second distance L _A = f _A (T _A ) substantially equal to each other in acoustic flight time and whose expression in acoustic flight time T _A is preferably reduced to a single half-period of reference τ / 2.

During an established regime of its operation, that is to say, during operation at a predetermined temperature outside the start and stop phases of the injector, it advantageously allows alternately to open and close the valve in a way that is not very sensitive to the pressure in the combustion chamber 15. In the example illustrated in FIG. 1, it is a question of both driving the first extended end 6 of the head 7 of the needle in displacement. 4 and to keep the seat 5 of the nozzle 3 dynamically still. As mentioned above, the driving in displacement of the head 7 of the needle 4 is carried out thanks to the selective deformations, for example, periodic with the set period τ, electroactive material 221 of the stack transmitted to the needle 4 through the actuator 2, using the amplifier 21 (Figure 1) of the stack. Maintaining the dynamically immobile seat 5 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. Each closure of the valve during periodic landings with the set period τ of the head 7 of the needle 4 on the seat 5, produces a shock. The latter generates an acoustic wave, called incident wave, associating a jump of speed Δv and a stress jump Δσ. This wave propagates in the nozzle 3 towards the casing 1 by traversing the first distance L _B , then is reflected in the first linear acoustic impedance breaking zone which is merged in FIG. 1 with an embedding point SX of the buzzard 3 in the housing 1 section, in a plane perpendicular to the axis AB, much larger than that of the nozzle 3. Once the incident wave reflected, its echo, said reflected wave, returns to the nozzle 3 to browse the first distance I_ _B in the opposite direction, that is to say, from the housing 1 to the seat 5. The reflected wave has the same sign of the stress jump Δσ as the incident wave and the inverse sign of the jump of speed Δv that the incident wave (the direction of propagation being reversed, the jump of speed Δv changed sign if we consider now all the positive velocities in the direction arriving on the seat 5 and not in the direction of propagation waves). Given that the first distance is preferably conditioned by the equation: I_ _B = fB (Te) = fβ (nB ^* [τ / 2]), the reflected wave enters the seat 5 at exactly the same moment that new incident wave is produced by the shock due to the closing of the valve, the displacement of the head 4 of the needle 4 being conditioned, too, by the second distance L _A preferably dependent on a multiple of the half-period setpoint τ / 2: L _A = fAOΑ) = fA (nA ^* [x / 2]). As a result, in the seat 5, the stresses are maintained and the speeds are canceled. The seat 5 thus has a displacement node. Under these conditions, a variation of the pressure in the combustion chamber 15 will induce an amplification of the shocks but without modifying their synchronism. The operation of the injector will therefore not be affected by this pressure variation in the combustion chamber 15.

In the light of the precisions above, it should be understood that, in the general case for the first and second multiplying coefficients such that n _B ≠ n _A , it is the incident waves and the reflected waves shifted by a few periods τ offset each other in the seat 5 to make it dynamically fixed. This compensation may not be complete when, for example, the difference between n _B and n _A is greater than a predetermined value and / or a dissipation of the acoustic waves in the nozzle 3 (and, ultimately, its linear acoustic impedance) , exceeds a certain threshold. It is why, the configuration of the injector with n _B = n _A and, in particular n _B = n _A = 1, appears as a priori more acoustically reliable and remains to be preferred over that where n _B ≠ n _A.

It should be understood that the first I_ _B = f _B (T _B) and the second I_ _A = f _A (T _A) distances respectively associated with the first "nozzle 3 + casing 1" and the second "needle 4 + actuator 2 »acoustic wave propagation media are defined, preferably using the respective acoustic flight times T _B = n _B * [τ / 2] and T _A = n _A * [τ / 2], in a context acoustic. The latter is due to the presence of vibration, for example, ultrasonic, of the setpoint period τ, initiated by the electroactive portion 22 of the stack coincident with the actuator 2 in the present example, as mentioned above. In other words, the first I_ _B = f _B (T _B ) and the second I_ _A = f _A (T _A ) distances are between two acoustic limits. In general, a first acoustic limit for defining both the first I_ _B and the second I_ _A distances, is represented by an end of a set in question ("nozzle 3 + housing 1" or "needle 4 + actuator 2 "). In a simplified manner, it can be considered that this first acoustic limit merges with the zone of contact between the first end 6 of the needle 4 (possibly extended axially by the head 7 (or 7 ')) and the seat 5 (or 5 ') of the nozzle 3, as shown in Figure 1 (or 2).

In the example illustrated in Figure 1 with the needle 4 to outgoing head 7, it should be understood that the first acoustic limit used to determine the second distance I_ _A related to the second medium "needle 4 + actuator 2" of propagation of the acoustic waves, is taken at the mid-height of the outgoing diverging frustoconical head 7. Similarly, the first acoustic limit used to determine the first distance I_ _B = f _B (T _B ) in relation to the first medium "nozzle 3 + housing 1" of propagation of acoustic waves is taken at the mid-height of the seat 5 divergent frustoconical corresponding.

In the example shown in Figure 2 with the needle 4 headed incoming 7 ', it should be understood that the first acoustic limit used to determine the second distance L _A in relation to the second medium "needle 4 + actuator 2" acoustic wave propagation, is taken at the mid-height of the head entering convergent t-cone. Similarly, the first acoustic limit used to determine the first distance I_ _B = fB (Te) in relation to the first medium "nozzle 3 + housing 1" for propagation of acoustic waves is taken at the mid-height of the frustoconical seat 5 ' corresponding convergent.

The second acoustic limit specific to each of the two sets is represented by the respective first linear acoustic impedance breaking zone I, as detailed above. For example, the second acoustic limit may correspond to where the diameter of the assembly in question varies in a plane perpendicular to the axis AB, for example, at the junction zone ZJ of the needle 4 with the amplifier 21 of the stack or recess SX of the nozzle 3 in the housing 1 (FIG. 1, 2), it being understood that:

in the junction zone ZJ, the needle 4 and the amplifier 21 are made, for example, by machining in a monobloc piece made of material preferably having the same density and the same speed of sound, and

- In the recess SX, the nozzle 3 and the housing 1 are made, for example, by machining in a monobloc piece of material preferably having the same density and the same velocity of sound.

Indeed, the machining in a single piece provides a simplest solution to implement during a manufacturing of said parts on an industrial scale.

It should be understood, however, that the acoustic limits of bodies may not match their physical limits. Indeed, besides the geometry of the bodies, the acoustic properties translated, for example, using the linear acoustic impedance discussed above, also depend on the other parameters such as the density of the bodies and the speed of sound in the bodies.

To make the injector even more efficient in acoustic terms, the length L measured between the two opposite end faces C, D of the stack formed by the amplifier 21, the electroactive part 22 and the rear mass 23 (FIG. , 7, 9-14), is such that the propagation time T of the acoustic waves initiated by the vibrations of the electroactive part 22 and traversing this length L = f (T) corresponds to the following equation:

T = n * [τ / 2], (E3)

where n is a multiplier coefficient, nonzero positive integer, said third multiplier coefficient, for example, n ≠ n _B ≠ n _A. By analogy with the nozzle 3 and the needle 4, the actuator 2 (confused in the present example with the stack as already specified above) can therefore have a symmetrical acoustic structure such as an echo of an acoustic wave emitted in one place of the symmetrical stack tends to return, after one or more reflections at the stacking boundaries represented by the opposite end faces C, D in Figures 1-2, 7, 9-14, in this same place for transmitting the acoustic wave a non-zero positive integer number of periods after its emission. For example, any acoustic wave up the needle 4 of the valve towards the actuator 2 and penetrating (for example, when the acoustic embedding of the needle 4 in the actuator 2 is not perfect) in the latter via the face D, said first face of the stack, between the needle 4 and the amplifier 21, is propagated axially in the actuator 2 to then reflect on the face C, said second face of the stack, opposite said first face D. Thanks to the symmetrical resonant structure of the actuator 2, a first reflected wave, that is to say, a first echo of the wave emitted to the first face D, returns to this same first face D a period later after its emission. It is the same for the acoustic waves, initiated by the electroactive material 221 of the electroactive part 22 of the stack and propagating axially towards the needle 4, which can, in turn, be reflected on the first face D, return to the actuator 2 to reflect on the second face C, then return to the first face D a period later after their departure from the first face D. The symmetrical resonant structure of the actuator 2 therefore generates no delay, nor change of sign of the waves - in particular for that of the sinusoidal type where a part of the sinusoid in positive follows a symmetrical part of the sinusoid in negative - emitted with the first face D whatever the source of these waves (of the needle 4 or actuator 2). The symmetrical resonant structure of the actuator 2 thus contributes to an orderly operation of the injector.

By analogy with the equations referenced E1 and E2 above, it must be understood that the equation referenced E3 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 plus or minus ± 20% of the half-period τ / 2. Taking into account this tolerance, the equation referenced E3 above can be rewritten as follows:

T = n ^* [τ / 2] ± 0.2 ^* [τ / 2] (E3 ')

It should be noted that in practice, the length L = f (T) expressed in acoustic flight time T and measured on corresponding parts manufactured on an industrial scale, may have slight variations from the reference values calculated at using E3 above. These slight variations may be due to an effect of reported masses. The latter may correspond, for example, appendages or machining operations or assembly.

Said tolerance makes it possible to take into account said effect of reported masses so as to correct the expression in time of flight acoustic length L = f (T) using the equation E3 'above.

For the same reasons as those mentioned above in relation to n _B and n _A , it is preferable that n = n _B = n _A and, in particular, n = n _B = n _A = 1. It must be understood that from its geometry (and in particular its thickness, measured in a plane perpendicular to the axis AB, negligible with respect to the diameter D ₄ of the needle 4), its density, its speed of sound, the clamping flange 25, has a negligible acoustic contribution. The presence of the clamping flange 25 therefore does not significantly influence the length L = f (T) of the stack expressed in acoustic flight time T.

When the clamping flange 25 has the same coefficient of thermal expansion as that of the stack and, in particular, that of the electroactive material 221, it must be understood that, acoustically, the second end face C of the stack corresponds to that of the adjusting means 250 opposite the needle 4 (and not that of the rear mass 23 opposite the needle 4), the definition already discussed above of the first front face D of the stack remaining unchanged, so that the length L = f (T) of the stack always remains between the two opposite end faces C, D, as shown in Figures 9-11.

When the clamping flange 25 has the coefficient of thermal expansion different from that of the stack and, in particular, that of the electroactive material 221, it should be understood that, acoustically, the definitions already discussed above of the first D and the second C front faces of the stack remain unchanged (in particular, the second front face C of the stack corresponds to that of the rear mass 23 opposite the needle 4), so that the length L = f (T) of the stack remains always between the two opposite end faces C, D, as illustrated in Figures 7, 12-14. Indeed, the resilient means 251 has an impedance linear low and the acoustic waves are reflected at the face C forming an interface between the rear mass 23 and the elastic means 251 so that no acoustic wave coming axially from the rear mass 23 enters the adjustment means 250 through the elastic means 251. The rupture of the linear acoustic impedance between the rear mass 23 and the elastic means 251 is total, so there is no longer any continuity of the acoustic medium between the rear mass 23 and the adjustment means 250 as shown in Figures 7, 12-14.

Claims

A fluid injection device (131) having a main injection axis (AB) and comprising at least:

a housing (1),

an actuator (2) axially mounted in the housing (1) and having a stack with two opposite end faces (C), (D) axially and including at least one electroactive portion (22) comprising an electroactive material (221), and

prestressing means adapted to preload at least partially said stack,

characterized in that the prestressing means comprises at least one clamping flange (25) external to the stack and arranged between the stack and the housing (1).

2. Injection device according to claim 1, characterized in that the prestressing means comprises at least one means (250) for adjusting the axial clamping force of the stack, said adjustment means (250) being linked with the clamping flange (25).

3. Injection device according to claim 2, characterized in that the adjusting means (250) is arranged axially between the clamping flange (25) and the stack.

4. Injection device according to any one of claims 1 to 3, characterized in that the clamping flange (25) has a thermal expansion different from that of the stack, and in that the prestressing means comprises at less resilient means (251) disposed between the clamp (25) and the stack.

Injection device according to any one of Claim 2 and 3 combined with Claim 4, characterized in that the resilient means (251) is disposed between the stack and the adjusting means (250).

Injection device according to one of the preceding claims, characterized in that the clamping flange

(25) is supported on the two opposite end faces (C), (D) of the stack.

7. Injection device according to any one of the preceding claims, characterized in that it comprises at least one needle (4), in that the stack comprises at least one portion (21), said amplifier (21). , axially connected with the needle (4) at one of said end faces (C), (D), the electroactive part (22) and the needle (4) being disposed axially on both sides other of the amplifier (21).

8. Injection device according to claim 7, characterized in that the amplifier (21) has at least one narrowing segment along the axis (AB) facing the needle (4), and in that the flange of clamping (25) at least partially matches the shape of said narrowing segment of the amplifier (21).

9. Injection device according to any one of the preceding claims, characterized in that the stack comprises at least one other part (23), said rear mass (23), the amplifier (21) and the rear mass ( 23) being arranged axially on either side of the electroactive part (22), and in that the rear mass (23) has a wall axially opposed to the electroactive part (22), said wall being merged with the end face (C) of the stack opposite axially to the needle (4).

Injection device according to one of the preceding claims, characterized in that the clamping flange (25) and the housing (1) have at least one contact zone. longitudinal (UW).

11. Injection device according to any one of the preceding claims combined with claims 7 and 9, characterized in that it comprises excitation means (14) for putting the electroactive part (22) of the stack in vibrations. with a set period τ, in that the stack coincides with the actuator (2), and in that the amplifier (21), the electroactive part (22) and the rear mass (23) are clamped together by the prestressing means and adapted to be traversed by acoustic waves initiated by the vibrations of the electroactive part (22).

12. Injection device according to claim 11, characterized in that the length (L) of the stack, measured between the two opposite end faces (C), (D), is such that the propagation time (T) acoustic waves initiated by the vibrations of the electroactive part (22) and traversing this length (L) respond to the following equation: T = n ^* [τ / 2], with a tolerance and where n is a multiplying coefficient, nonzero positive integer.

13. Injection device according to claim 11 or 12, characterized in that it comprises a nozzle (3) comprising, along said axis (AB), an injection port and a seat (5) and being, at opposite, linked to the case (1),

in that the needle (4) has, along said axis (AB), a first end (6) defining a valve, in a zone of contact with the seat (5) and being, on the opposite side, connected to the stacking of the actuator (2) which puts this needle (4) in vibration, ensuring between its first end (6) and the seat (5) of the nozzle (3) a relative movement able to open and close alternately the flapper, and

in that

the nozzle (3) with the housing (1) and the needle (4) with the actuator (2) respectively form a first and a second propagation of acoustic waves, each medium having a linear acoustic impedance (I) defined by the following equation: I = Σ ^* ρ ^* c, where Σ is a surface of a section of the middle perpendicular to the axis (AB) , p is a density of the medium, it is a speed of sound in the medium,

at least one linear acoustic impedance breaking zone, existing at a distance from the contact zone of the seat (5) with the first end (6) along the nozzle (3) or the housing (1), and at minus another linear acoustic impedance breaking zone existing at a distance from the contact area of the first end

(6) with the seat (5) along the needle (4) or the actuator (2), and

said zone and other linear acoustic impedance breaking zone being each first in order from said contact zone between the first end (6) of the needle (4) and the seat (5), in a sense propagation of acoustic waves directed respectively to the housing (1) and the actuator (2).

14. Injection device according to claim 13, characterized in that the distance, called the first distance (I_ _B ), between, on the one hand, the contact zone between the seat (5) and the first end (6). , and, on the other hand, the first linear acoustic impedance breaking zone along the nozzle (3) or the housing (1), is such that the propagation time (T _B ) of the acoustic waves initiated by the electroactive part (22) of the stack and traversing this first distance (I_ _B ) corresponds to the following equation: T _B = n _B ^* [τ / 2], with a tolerance and where n _B is a multiplying coefficient, nonzero positive integer, and

in that the distance, called the second distance (I_ _A ), between, on the one hand, the contact zone between the first end (6) and the seat (5), and, on the other hand, the first zone of linear acoustic impedance breaking along the needle (4) or the actuator (2), is such that the propagation time (T _A ) of the acoustic waves initiated by the part electroactive (22) of the stack and traversing this second distance (I_ _A ) meets the following equation: T _A = n _A ^* [x / 2], with a tolerance and where n _A is a multiplying coefficient, integer positive non-zero.

An internal combustion engine (151) utilizing the fluid injection device (131) according to any one of the preceding claims.