EP3803152A1

EP3803152A1 - System and method for passive damping of mechanical vibrations

Info

Publication number: EP3803152A1
Application number: EP19742849.3A
Authority: EP
Inventors: Gilles Grosso; Frédéric MOSCA
Original assignee: Pytheas Technology SAS
Current assignee: Pytheas Technology SAS
Priority date: 2018-06-06
Filing date: 2019-06-06
Publication date: 2021-04-14
Also published as: FR3082258A1; FR3082258B1; US20210226116A1; WO2019234366A1; JP2021527782A

Abstract

The invention relates to a system for the passive damping of mechanical vibrations generated by a vibrating structure carried by a support, the system comprising a transducer inserted between the vibrating structure and the support for converting the mechanical energy of the vibrations into electrical energy, characterised in that the transducer comprises a flextensional structure having a first axis and a second axis which are perpendicular to each other, and a stack of piezoelectric elements which is designed to produce electrical energy when it is stressed, said stack being compressively stressed by the flextensional structure along the first axis such that a deformation of said structure modifies the compressive stress applied to said stack, two peripheral attachments are secured to the flextensional structure, each of the attachments being arranged along the second axis, a first attachment being used to secure the flextensional structure to the vibrating structure and a second attachment being used to secure the flextensional structure to the support, at least one of the attachments comprises an elastic suspension, and a shunt is connected to the piezoelectric stack in such a way as to dissipate all or some of the electrical energy produced by the stress applied to said piezoelectric stack.

Description

SYSTEM AND METHOD FOR PASSIVE AMORTIZATION OF

MECHANICAL VIBRATIONS

Description

Technical Field of the Invention

The invention relates to a system and a method for passive damping of mechanical vibrations.

It concerns the technical field of passive vibratory isolators, that is to say which do not function as actuators transforming electrical vibrations into mechanical vibrations acting in phase opposition with the vibrations to be attenuated.

State of the art

Vibratory isolators are usually mounted between a vibration-producing structure on one side and a potentially vibration-sensitive part on the other. They absorb the vibrations of the vibrating structure and prevent them from being transmitted to the receiving part. For example, a vibratory isolator may be interposed between the support piece of a rotating machine and the rotating machine itself so that the vibrations generated by the rotating machine are not transmitted to the support piece.

There are different types of vibratory isolators based on different techniques. Fluid chamber and orifice isolators or elastomeric or metallic suspensions are particularly known. These purely mechanical isolators transform the mechanical energy of vibrations into thermal energy (heat). These technologies are mature and proven but can present a number of limitations in terms of performance and adaptability to the operating conditions (temperature, operating speed of the vibrating structure, transmission of a static force, etc.).

Electromagnetic, magnetostrictive or piezoelectric suspensions are also known which use electroactive materials to convert the mechanical energy of the vibrations into electrical energy. These technologies are efficient and allow a better adaptability to the context of use. However, they are not very widespread and are sometimes perceived as less robust than purely mechanical insulators mentioned above. Moreover, these solutions, when they are used in passive assemblies (the suspension does not have an actuator role), do not allow effective damping at low frequency of the relative rigidity of the electro-magnetic materials. assets used.

FIG. 1 is a diagram illustrating the attenuation that can be obtained with a piezoelectric stack. The abscissas correspond to the frequency in Hertz of the vibrations and the ordinates correspond to the transmissibility in Decibels (ratio of the force transmitted on the force of excitation). Up to about 100 Hz, it is found that the transmissibility is zero, that is to say that the piezoelectric stack passes all the vibrations, without producing any attenuation. A positive transmissibility peak of about 20 dB appears around 500 Hz, this rejection meaning that the piezoelectric stack amplifies the vibration phenomenon instead of attenuating it. It is only from this peak of frequencies that the transmissibility becomes negative. The piezoelectric stack attenuates the vibrations of about 40 dB / decade over a frequency range from about 500 Hz to about 20 KHz, this frequency range (Z) corresponding to noise nuisances that it is particularly advantageous to mitigate. Document WO2017 / 048906 (UNIV MICHIGAN) and JP 3790255 (TAIHEIYO CEMENT CORP) disclose mechanical vibration damping systems comprising a transducer. This transducer is in the form of a bi-blades operating only in bending. In practice, the performance of this type of system is limited in terms of damping and vibration mitigation, including static resistance.

Also known from US 2005/134149 (DENG KEN K) a mechanical vibration damping system comprising a cymbal-type transducer. A piezoelectric element is compressed radially by the cymbals. Here again, the performance of this system is not optimal in terms of damping and damping of vibrations.

In view of this state of affairs, an object of the invention is to propose a vibratory isolator having increased performances compared with those of vibratory isolators of the aforementioned prior art.

Another object of the invention is to provide a vibratory isolator to optimize the adaptability to the operating conditions.

Yet another object of the invention is to provide a robust vibration isolator whose design is simple, robust and inexpensive.

A further object of the invention is to provide a vibratory isolator for effective damping of vibrations, over a wide frequency band, particularly at low frequencies and with increased attenuation in the frequency band from about 500 Hz to about 20 KHz.

Disclosure of the invention. The solution proposed by the invention is a system for passive damping of mechanical vibrations generated by a vibrating structure supported by a support, the system comprising:

a transducer interposed between the vibrating structure and the support for transforming the mechanical energy of the vibrations into electrical energy and comprising:

a flextensional structure having a first axis and a second axis perpendicular to each other,

piezoelectric elements stacked along the first axis so as to form a piezoelectric stack, which piezoelectric stack is adapted to produce electric energy when it is constrained, which stack is constrained in compression by the flextensional structure along the first axis of whereby a deformation of said structure modifies the compressive stress applied to said stack,

two peripheral fasteners are integral with the flexural structure, each of the fasteners being arranged along the second axis,

a first fastening for securing the flextensional structure to the vibrating structure,

a second fastening for securing the flextensional structure to the support,

at least one of the fasteners preferably incorporates an elastic suspension,

means for modifying the electrical stiffness of the piezoelectric stack, which means is a shunt connected to said piezoelectric stack so as to dissipate all or part of the electrical energy produced by the stress applied to said piezoelectric stack.

This damping system, or vibratory isolator comprises a piezoelectric transducer of flextensional type advantageously combined with an elastic suspension placed in series of said transducer. The plaintiff found that this particularly robust vibratory isolator had increased performance compared to those vibration isolators of the aforementioned prior art. It notably allows effective damping of vibrations over a frequency range from about 50 Hz to 20 KHz, with an attenuation of 40 dB / Decade at 60 dB / Decade over the frequency band from about 500 Hz to about 20 Hz. KHz. The shunt can furthermore be easily controlled to modify the stiffness of the piezoelectric stack according to the operating conditions, and in fact further improve the attenuation of the vibrations as well as, in general, improve the electromechanical coupling of the system.

Other advantageous features of the invention are listed below. Each of these features may be considered alone or in combination with the outstanding characteristics defined above, and may be subject, where applicable, to one or more divisional patent applications:

Advantageously, the elastic suspension is integrated in the fastener which is furthest away from the vibrating structure.

- The elastic suspension may be an elastomeric suspension, or a metal suspension or pneumatic or hydraulic.

- The shunt may consist of an electrical resistance connected across the piezoelectric stack so as to thermally dissipate all or part of the electrical energy produced by the stress applied to said piezoelectric stack.

According to an alternative embodiment, the shunt consists of an electrical resistance and an inductance connected to the terminals of the piezoelectric stack so as to form an RLC resonant electronic circuit tuned to a band of frequencies to attenuate.

Advantageously, an electronic management unit is connected to an accelerometer placed so as to capture the vibrations of the support and / or to an accelerometer placed so as to capture the vibrations of the vibrating structure, which electronic management unit controls the shunt to modify stiffness said piezoelectric stack according to the signals emitted by the accelerometer.

Advantageously, a part of the electrical energy produced by the stress applied to the piezoelectric stack, and which is not dissipated by the shunt, supplies one or more electronic components.

- Advantageously, the flextensional structure has: - two opposite end pieces, arranged perpendicular to the first axis and symmetrically on either side of the second axis; - two opposite transverse flanges arranged perpendicular to the second axis and symmetrically on either side of the first axis; identical longitudinal arms which extend along the first axis and which connect the lateral end pieces to the transverse soles.

- The connections between the longitudinal arms on the one hand and on the other hand the lateral tips and the transverse flanges, advantageously consist of joints, which joints are formed by hinge-less zones formed at the ends of each arm .

- Advantageously, an elastomeric pad is interposed between the transverse flanges so as to limit the deflection of the flextensional structure along the second axis.

- Advantageously, the piezoelectric stack is prestressed, the prestressing force applied to said stack being produced: - by the cooperation of a rod installed along the first axis and on which is mounted the piezoelectric stack, with hardware elements installed in the flextensional structure; - or directly by the flextensional structure.

Another aspect of the invention relates to a method for damping mechanical vibrations of a wiper motor of a motor vehicle, which motor is supported by a support, said method of using the damping system according to the invention. one of the preceding features, by interposing the transducer between said wiper motor and said support. Yet another aspect of the invention relates to a method for damping mechanical vibrations generated by a vibrating structure supported by a support (3), said method comprising the steps of:

- Use the damping system according to one of the preceding characteristics, by interposing the transducer between said vibrating structure and said support,

modifying the electrical stiffness of the piezoelectric stack by means of the shunt, as a function of the band of frequencies to be attenuated.

Yet another aspect of the invention relates to a method for damping mechanical vibrations in a frequency band of 50 Hz ± 10 HZ at 20 KHz ± 100 HZ, which vibrations are generated by a vibrating structure supported by a support, said method comprising using the damping system according to one of the preceding characteristics, by interposing the transducer between said vibrating structure and said support.

Yet another aspect of the invention relates to a method for damping mechanical vibrations, with attenuation of 40 dB / decade ± 10 dB / decade at 60 dB / decade ± 10 dB / decade, in a frequency band of 500 Hz ± 100 HZ at 20 KHz ± 100 HZ, which vibrations are generated by a vibrating structure supported by a support, said method of using the damping system according to one of the preceding features, by interposing the transducer between said vibrating structure and said support.

Description of the figures.

Other advantages and characteristics of the invention will appear better on reading the description of a preferred embodiment which will follow, with reference to the accompanying drawings, carried out as indicative and non-limiting examples and in which: FIG. 1 is a diagram illustrating the attenuation that can be obtained with a piezoelectric stack,

FIG. 2 is a perspective view of a transducer according to the invention showing a flextensional structure,

FIG. 3 is a side view of the transducer of FIG. 2,

FIG. 4a is a sectional view along A-A of the transducer of FIG. 3,

FIG. 4b is a sectional view along A-A of the transducer of FIG. 3, according to an alternative embodiment,

FIG. 5 illustrates the transducer of FIGS. 2 to 4a-4b interposed between a vibrating structure and a support, the piezoelectric stack being connected to a shunt,

FIG. 6 is a diagram illustrating the attenuation that can be obtained with a damping system according to the invention.

Preferred embodiments of the invention

The terms right / left, upper / lower, up / down, horizontal / vertical which may be used in the present description are essentially references to the position of the elements illustrated in the accompanying drawings. They are only used as indicative and non-limiting examples.

In FIG. 5, the damping system that is the subject of the invention comprises a transducer 1 interposed between a vibrating structure 2 and a support 3 supporting said vibrating structure. This vibrating structure 2 is for example a rotating machine or a wiper motor of a motor vehicle. In the latter case, the support 3 may correspond to the linkage which supports the windscreen wiper or to a chassis element of the vehicle. The function of the transducer 1 is to transform the mechanical energy of the vibrations generated by the vibrating structure 2 into electrical energy, so that these vibrations are not or only slightly transmitted to the support 3.

Referring to Figures 2 to 5, the transducer 1 has a flextensional structure 10. "Flextensional structure" means a combined flexural and tension structure. This mechanical structure is deformable and forms a mechanical amplifier, transmitting and amplifying the vibratory forces of the vibrating structure 2 towards a piezoelectric stack 4.

The structure 10 has a first axis A-A and a second axis B-B perpendicular to each other. In the appended figures, the axis A-A is a horizontal longitudinal axis and the axis B-B is a vertical transverse axis. The structure 10 has a generally octagonal shape, elongated along the first axis A-A. It can be written in an envelope whose length is between 5 cm and 30 cm, the width between 2 cm and 10 cm and the height between 2 cm and 10 cm.

The structure 10 preferably has:

- Two small side or side ends 12a, 12b identical (or not) opposite, arranged perpendicular to the first axis A-A and symmetrically on either side of the second axis B-B; these tips have a parallelepipedal or cylindrical general shape,

- two small transverse flanges 13a, 13b identical (or not) opposite, arranged perpendicularly to the second axis B-B and symmetrically on either side of the first axis A-A; these soles have a parallelepipedal or cylindrical general shape;

identical longitudinal arms 14a, 14b, 15a, 15b which extend along the first axis AA and which connect the end pieces 12a, 12b to the transverse flanges 13a, 13b; these arms can be square, rectangular, round, oval, etc. More particularly, the structure 10 has:

a pair of upper arms 14a which connect the upper sole 13a to an upper edge of the left lateral end piece 12b,

a pair of lower arms 14b which connect the upper sole 13a to a lower edge of the left lateral end piece 12b,

a pair of upper arms 15a which connect the upper sole 13a to an upper edge of the right lateral end piece 12a,

a pair of lower arms 15b which connect the upper sole 13a to a lower edge of the right lateral end piece 12a.

In an alternative embodiment not shown, each pair of arms 14a, 14b, 15a, 15b is replaced by a single arm. The use of pairs of arms, however, allows to better distribute the mechanical stresses in said arms. In another alternative embodiment not shown, each pair of arms 14a, 14b, 15a, 15b is replaced by a combination of three or more arms.

The end pieces 12a, 12b, the flanges 13a, 13b and the arms 14a, 14b, 15a, 15b preferentially form a rigid one-piece piece made of steel, stainless steel, aluminum, or composite and obtained by machining or injection. These elements may however be in the form of separate parts assembled together for example by welding, screwing or bolting.

The links between on the one hand the arms 14a, 14b, 15a, 15b and on the other hand the end pieces 12a, 12b and the flanges 13a, 13b advantageously consist of articulations. To simplify the design of the structure 10, these joints consist of thinner areas 140, 150 forming a hinge which are arranged at the ends of each arm 14a, 14b, 15a, 15b. This limits the number of mechanical parts, which provides significantly improved maintenance of the transducer. The mechanical structure 10 is thus elastically deformable. When it undergoes compression (bending) stress along the axis BB, the flanges 13a, 13b tend to get closer. This approximation of the flanges 13a, 13b increases the distance separating the end pieces 12a, 12b. Conversely, when the compressive stress along the axis BB is reversed (extension), the flanges 13a, 13b move away, and the distance separating the end pieces 12a, 12b decreases. It is understood that these compression stresses are generated by the vibrations of the vibrating structure 2.

To limit the displacement of the structure 10 along the axis B-B, there may be an elastomeric pad 8 interposed between the two flanges 13a, 13b. This buffer 8 prevents excessive displacement of the structure 10 may damage.

A stack 4 of piezoelectric elements is installed in the structure 10. It is adapted to produce electrical energy when it is forced. The piezoelectric elements of the stack 4 are advantageously in the form of washers or piezocomposite discs adapted to be electrically polarized under the action of a mechanical stress. The number of washers can vary from 3 to 20 depending on the length of the structure 10. For example, we use 8 hard ceramic washers PZT (Titano-Lead Zirconate), the stack 4 having a stiffness of 16 MN / m and a Young's modulus of about 50 GPa. This stack 4 is capable of delivering a voltage of 73 volts under a force of 100 newtons.

In Figures 2 to 5, the stack 4 is installed along the first axis AA, between the end pieces 12a, 12b, so that a deformation of the structure 10 modifies the compressive stress applied to said stack. More particularly, and as explained in the preceding paragraph, when the vibrating structure 2 vibrates, the structure 10 deforms along the axis BB, By a pinch effect, a compressive stress is applied to the stack 4. The structure 10 thus plays the role of mechanical amplifier, transmitting and amplifying the vibratory forces of the vibrating structure 2 to the stack 4.

The stack 4 is advantageously prestressed to improve the tensile strength of the transducer 1. In Figure 4a, the stack 4 is mounted on a rod 40 installed along the first axis A-A. Fastening elements 40a, 40b, installed in the end pieces 12a, 12b, are engaged with the threaded ends of the rod 40. The cooperation of the fastener elements 40a, 40b with the rod 40 makes it possible to apply prestressing on the stacking 4.

In FIG. 4b, it is the structure 10 that directly produces the prestressing force applied on the stack 4. The structure 10 is elastically deformed to allow the stack 4 to be put in place. In practice, a constraint of compression along the axis BB is applied on the flanges 13a, 13b so that the end pieces 12a, 12b move away so as to allow the insertion of the stack 4. By releasing the flanges 13a, 13b, the end pieces 12a, 12b approach and compress the stack 4 which is thus prestressed. To facilitate the insertion of the stack 4, it is mounted on a guide rod 400 held in position along the axis A-A by fastener elements 400a, 400b installed in the end pieces 12a, 12b.

The transducer 1 is mounted very simply and very rapidly in the following manner: the rod 40 is inserted into the stack 4; the stack 4 is installed in the structure 10, between the end pieces 12a, 12b; the fastener elements 40a, 40b are positioned in the end pieces 12a, 12b so that said elements engage with the threaded ends of the rod 40; the hardware elements 40a, 40b are screwed with a dedicated tool (eg torque wrench) so as to pre-force the stack 4 according to a desired prestressing force. To facilitate the installation of the stack 4 inside the structure 10, the upper sole 13a and / or the lower sole 13b can be made in two parts so as to provide a day of passage. Two peripheral fasteners 5a, 5b are secured to the structure 10. The upper attachment 5a is secured to the upper sole 13a and the lower attachment 5b to the lower sole 13b. The fasteners 5a, 5b are thus arranged along the second axis B, B. The fastening of the fasteners 5a, 5b on the flanges 13a, 13b can for example be obtained by welding, screwing or bolting. The shape of the fasteners 5a, 5b is complementary to that of the flanges 13a, 13b. In Figures 2 to 5, the fasteners 5a, 5b are in the form of parallelepipedal and rigid flat flanges, steel, stainless steel, aluminum, or composite, obtained for example by machining. Their dimensions in length and width correspond to those of the flanges 13a, 13b. Their thickness can vary from 1 cm to 10 cm.

In Figure 5, the upper attachment 5a is used to secure the structure 10 to the vibrating structure 2, by screwing or bolting. And the lower attachment 5b is used to secure the structure 10, also by screwing or bolting.

According to an advantageous characteristic of the invention, at least one of the fasteners 5a and / or 5b incorporates an elastic suspension. By "integrate" is meant that the attachment 5b and the suspension 6 may be two separate parts assembled together or on the contrary formed a single piece.

In FIGS. 2 to 5, it is the lower fastener 5b which incorporates this suspension 6. This serves as an interface between the lower fastener 5b and the support 3. The lower fastener 5b can be constituted by this single suspension 6 The suspension 6 can, however, be integrated only in the upper attachment 5a, between the vibrating structure 2 and said attachment. The two fasteners 5a and 5b could also each incorporate an elastic suspension. The best results in terms of damping are however obtained when the elastic suspension is integrated in the attachment 5b which is furthest away from the vibrating structure 2. To simplify the design, improve the robustness and overcome complex and expensive solutions, this suspension 6 is preferably in the form of an elastomer sole, for example natural or synthetic rubber, whose shape is complementary to that of fixing 5b. In Figures 2 to 5, it is in the form of a parallelepipedal sole whose dimensions in length and width correspond to those of the lower attachment 5b. Its thickness can vary from 1 cm to 10 cm. For example, using a natural rubber sole having a stiffness of 250 kN / m and a Young's modulus of about 1.5 MPa. In practice, the stiffness of the suspension 6 is chosen as a function of the frequency band of the vibrations to be attenuated. The assembly of the elastomer sole 6 on the sole 5b is done by gluing, screwing or bolting. The suspension 6 may also be in the form of one or more elastomeric pads assembled between the lower fastener 5b and the support 3. The suspension 6 may also be in the form of a metal suspension, for example a helical spring or blades, or pneumatic or hydraulic suspension.

Referring to Figure 5, a shunt 7 is connected to the piezoelectric stack 4. This shunt 7 is used to modify the electrical stiffness of the stack 4 and more generally, to improve the electromechanical coupling of the system. Electromechanical coupling reflects the efficiency of the system to the conversion of mechanical energy into electrical energy and vice versa. It is characterized by a coefficient of electromechanical coupling (CCEM) which can be defined by the ratio below:

Electric energy

CCEM = -

Electric energy + Mechanical energy where the electrical energy is that produced by the stack 4 and the mechanical energy is that applied to the flextensional structure 10.

The shunt 7 serves in particular to dissipate all or part of the electrical energy produced by the stress applied to the stack 4 during the deformation of the structure 10. The stack 4 produces an electrical signal transmitted to the shunt 7. At the reception of the signal, the shunt 7 provides resistance to the electrical signal. Following this resistance, the stack 4 resists the deformation of the structure 10, so that its electrical stiffness is changed. The stack 4 then serves as a damper.

The electrical stiffness of the stack 4 (and more generally the electromechanical coupling coefficient of the system) can thus be modified as a function of the frequency band to be attenuated. The inventors have found that the electromechanical coupling of the system was improved with the shunt 7 (the CCEM coefficient of the shunt system is greater than the CCEM coefficient of an equivalent system without shunt).

The shunt 7 may consist of an electrical resistance connected in parallel or in series to the terminals of the stack 4, dissipating thermally (that is to say in the form of heat) all or part of the electrical energy. Knowing that the piezoelectric stack 4 is equivalent to an electric capacitor, an electronic circuit RC is obtained making it possible to produce a low-pass or high-pass filter tuned to the frequency band to be attenuated.

The shunt 7 may also consist of an electrical resistance and an inductance (coil) connected to the terminals of the stack 4 so as to form a resonant electronic circuit RLC, parallel or series, tuned to the frequency band to be attenuated. This type of shunt 7 (resistive or resistive-inductive) is passive, stable, simple and compact. In an alternative embodiment, a shunt 7 with a negative capacitance is used which further improves the electromechanical coupling of the system. This shunt 7 comprises a resistor and a synthetic negative capacitor having a real and imaginary impedance tuned to the frequency band to be attenuated. The electrical impedance of the negative capacitance modifies the stiffness of the piezoelectric stack 4 to increase the damping and to optimize the electromechanical coupling of the system.

In FIG. 5, an electronic management unit 70 is connected to an accelerometer 71 placed so as to capture the vibrations of the support 3 and / or to an accelerometer placed so as to capture the vibrations of the vibrating structure 2. management 70 is then adapted to drive the shunt 7 so as to modify the electrical stiffness of the stack 4 as a function of the signals emitted by the accelerometer 71. For example, the shunt 7 can integrate a variable resistor or a variable impedance whose value is modified by the management unit 70 according to the signals emitted by the accelerometer 71.

Part of the electrical energy produced by the stress applied to the piezoelectric stack 4, and which is not dissipated by the shunt 7, can be used to power one or more electronic components. This electrical energy can for example be used to supply the management unit 70 and / or the accelerometer 71.

FIG. 6 is a diagram illustrating the attenuation that can be obtained with a damping system according to the invention. The abscissae correspond to the frequency in Hertz of the vibrations and the ordinates correspond to the transmissibility in Decibels. Curve 1 in dashed lines shows the attenuation curve of FIG. 1 (piezoelectric stack alone). Curve 2 in solid line is the attenuation curve obtained with the piezoelectric stack 4 combined with the elastic suspension. Up to about 50 Hz (± 10 HZ), the transmissibility remains virtually nil. Compared to curve 1, the system According to the invention, the inflection point of the attenuation curve of about 50 dB ± 10 HZ can be retracted. From this frequency zone, the transmissibility becomes negative, with attenuation of 40 dB / decade (± 10 dB / decade) up to a frequency of 500 Hz (± 100 HZ). Around this frequency, a peak of transmissibility of about 20 dB appears, the attenuation of the vibrations being less important. The setting of the shunt 7 (for example the value of the resistor, the inductance or the negative capacitance) however makes it possible to treat and attenuate this rejection. From this peak, the attenuation is 40 dB / decade ± 10 dB / decade at 60 dB / decade ± 10 dB / decade over the frequency range z ranging from 500 Hz ± 100 HZ to 20 KHz ± 100 HZ. In summary, the system according to the invention allows vibration damping over a wider frequency range (50 Hz - 20 KHz) than that obtained by a piezoelectric stack alone (100 Hz - 20 KHz). In addition, the attenuation of noise is better (more than 40 dB / decade).

The arrangement of the various elements and / or means and / or steps of the invention, in the embodiments described above, should not be understood as requiring such an arrangement in all implementations. In any case, it will be understood that various modifications may be made to these elements and / or means and / or steps, without departing from the spirit and scope of the invention.

Claims

claims

A system for passive damping of mechanical vibrations generated by a vibrating structure (2) supported by a support (3), the system comprising a transducer (1) interposed between the vibrating structure and the support for transforming the mechanical energy of the vibrations. in electrical energy, characterized by the fact that:

the transducer (1) comprises:

a flextensional structure (10) having a first axis (A-A) and a second axis (B-B) perpendicular to each other,

piezoelectric elements stacked along the first axis (AA) so as to form a piezoelectric stack (4), which piezoelectric stack is adapted to produce electrical energy when it is constrained, which stack is constrained in compression by the structure flexural tension along the first axis (AA) so that a deformation of said structure modifies the compressive stress applied to said stack,

two peripheral fasteners (5a, 5b) are integral with the flextensional structure (10), each of the fasteners being arranged along the second axis (B, B),

^■ a first attachment (5a) for the fastening of the flextensionnelle structure (10) to the vibrating structure (2),

^■ a second attachment (5b) for securing the flextensionnelle structure (10) to the support (3),

^■ at least one of the fasteners (5b) includes an elastic suspension (6),

a means for modifying the electrical stiffness of the piezoelectric stack (4), which means is a shunt (7) connected to said stack piezoelectric so as to dissipate all or part of the electrical energy produced by the stress applied to said piezoelectric stack.

2. System according to claim 1, wherein the elastic suspension is integrated in the fastener (5b) which is furthest from the vibrating structure (2).

3. System according to one of claims 1 or 2, wherein the elastic suspension (6) is an elastomeric suspension.

4. System according to one of claims 1 or 2, wherein the elastic suspension (6) is a metal suspension or pneumatic or hydraulic.

5. System according to one of claims 1 to 4, wherein the shunt (7) consists of an electrical resistance connected to the terminals of the piezoelectric stack (4) so as to thermally dissipate all or part of the electrical energy produced. by the stress applied to said piezoelectric stack.

6. System according to one of claims 1 to 4, wherein the shunt (7) consists of an electrical resistor and an inductor connected to the terminals of the piezoelectric stack (4) so as to form a resonant electronic circuit RLC granted on a band of frequencies to attenuate.

7. System according to one of claims 1 to 6, wherein an electronic management unit (70) is connected to an accelerometer (71) placed so as to capture the vibrations of the support and / or an accelerometer placed so as to sensing the vibrations of the vibrating structure, which electronic control unit controls the shunt (7) to modify the electrical stiffness of said piezoelectric stack according to the signals emitted by the accelerometer (71).

8. System according to one of claims 1 to 7, wherein a portion of the electrical energy produced by the stress applied to the piezoelectric stack (4), and which is not dissipated by the shunt (7), supplies one or more electronic components (70, 71).

9. System according to one of claims 1 to 8, wherein the flextensional structure (10) has:

two opposite lateral tips (12a, 12b) arranged perpendicularly to the first axis (A-A) and symmetrically on either side of the second axis (B-B),

- two transverse flanges (13a, 13b) opposite, arranged perpendicular to the second axis (B-B) and symmetrically on either side of the first axis (A-A);

- Identical longitudinal arms (14a, 14b, 15a, 15b) which extend along the first axis (A-A) and which connect the end caps (12a, 12b) to the transverse flanges (13a, 13b).

10. System according to claim 9, wherein the connections between firstly the longitudinal arms (14a, 14b, 15a, 15b) and secondly the lateral end pieces (12a, 12b) and the transverse flanges (13a, 13b). ), consist of joints, which joints are formed by hinge-less areas (140, 150) formed at the ends of each arm.

11. System according to one of claims 9 or 10, wherein an elastomeric pad (8) is interposed between the transverse flanges (13a, 13b) so as to limit the deflection of the flextensional structure (10) along the second axis (BB).

12. System according to one of claims 9 to 11, wherein the piezoelectric stack (4) is prestressed, the prestressing force applied to said stack being produced:

- by the cooperation of a rod (40) installed along the first axis (AA) and on which is mounted the piezoelectric stack (4), with hardware elements (40a, 40b) installed in the flextensional structure (10) , or

- directly by the flextensionnelle structure (10).

13. A method for damping mechanical vibrations of a wiper motor (2) of a motor vehicle, which motor is supported by a support (3), said method of using the damping system according to the claim 1 by interposing the transducer (1) between said wiper motor and said support.

A method for damping mechanical vibrations generated by a vibrating structure (2) supported by a support (3), said method comprising the steps of:

- Use the damping system according to claim 1 by interposing the transducer (1) between said vibrating structure and said support,

- Modifying the electrical stiffness of the piezoelectric stack (4) by means of the shunt (7), depending on the frequency band to be attenuated.

A method for damping mechanical vibrations in a frequency band of 50 Hz ± 10 HZ at 20 KHz ± 100 HZ, which vibrations are generated by a vibrating structure (2) supported by a carrier (3), said method of using the damping system according to claim 1 by interposing the transducer (1) between said vibrating structure and said support.

16. Process for damping mechanical vibrations, with attenuation of 40 dB / decade ± 10 dB / decade at 60 dB / decade ± 10 dB / decade, in a frequency band from 500 Hz ± 100 HZ to 20 KHz ± 100 HZ, which vibrations are generated by a vibrating structure (2) supported by a support (3), said method of using the damping system according to claim 1 by interposing the transducer (1) between said vibrating structure and said support.