WO2005098816A1

WO2005098816A1 - Soundproofed housing for the absorption of acoustic waves

Info

Publication number: WO2005098816A1
Application number: PCT/FR2005/000742
Authority: WO
Inventors: Richard Bourdon
Original assignee: Rhodia Chimie
Priority date: 2004-03-30
Filing date: 2005-03-29
Publication date: 2005-10-20
Also published as: FR2868502B1; FR2868502A1; EP1733380A1

Abstract

The invention relates to a soundproofed housing used to accommodate a mechanism comprising at least one frame and a microperforated plate disposed between the frame and the mechanism. The inventive housing enables acoustic waves from various mechanisms such as engines, particularly vehicle engines, to be absorbed.

Description

Soundproof housing for absorption of acoustic waves

The present invention relates to a soundproof casing for enveloping a mechanism comprising at least one frame and a microperforated plate disposed between the frame and the mechanism. The casing according to the invention allows in particular the absorption of acoustic waves from various mechanisms such as engines, in particular vehicle engines.

There is a need to reduce the noise caused by various types of mechanism, such as vehicle engines.

Motor encapsulation systems comprising porous materials, such as foam glued or clipped to rigid walls, can be used for this purpose. However, these systems are expensive to make and recycle. Furthermore, these systems do not allow their performance to be adapted to the specific requirements of the sources to be treated, particularly in terms of absorbed frequency ranges. Indeed, to effectively reduce the absorption of engine noise, this system must be able to absorb waves having a frequency around 1000 Hz. In addition, these systems do not make it possible to reduce the noise caused by vibrations. motors, but on the contrary can participate in the repercussions of these vibratory waves.

It is therefore necessary to develop casings having both good absorption capacities for acoustic waves and vibratory waves which are simple to manufacture and to assemble. Indeed, the assembly must be taken into account for the design of an article because it can generate additional costs and have an impact on the characteristics of said article, such as the deterioration of the mechanical properties, the creation of zone of brittleness, or poor sealing.

The Applicant has surprisingly discovered that the application of a rigid microperforated plate to the frame of a casing makes it possible to significantly reduce the noises caused by the motors by the absorption of the acoustic waves and the attenuation of the vibratory waves coming various mechanisms, such as motors, while avoiding the drawbacks mentioned above. This casing also has the advantage of being able to modulate its sound absorption coefficient as a function of the sources of noise generated by the mechanisms by notably modifying the distance between the rigid microperforated plate and the framework of the casing. This casing also makes it possible not to amplify the vibrations caused by the motorization and thus not to generate noise itself. This article also has many other advantages: it is light, rigid, simple to produce and has good thermal resistance of the system, in particular for applications under the bonnet, good recyclability and a reduction in implementation costs. For the purposes of the invention, the term “casing” protects a protective casing of a mechanism and / or the members of a mechanism, such as an engine, preferably a vehicle engine. The term “casing” is understood to mean any engine casing system, in particular of a vehicle engine, such as for example engine covers, timing belt casings and under-engine skiing. This housing can be used for any type of application. The present invention relates to a soundproof casing 6 for enveloping a mechanism, in particular a motorization, preferably a motorization of a vehicle, comprising at least one frame 2 and a soundproofing element 1 in the form of a microperforated plate comprising through holes is arranged. between the framework 2 and said mechanism, the element 1 and the framework 2 define a space 5 having a thickness of 1 to 400 mm, said element 1 having the following characteristics: a surface density of perforation from 0.2 to 30 %; and a hole diameter of 0.05 to 3 mm. The element 1 having the shape of a microperforated plate can have a thickness of 0.2 to 10 mm, preferably from 0.5 to 5 mm, such as for example 0.8, 1, 1, 5, 2, 2 , 5, 3, 3.5, 4 and 4.5. Element 1 has a surface density of perforation, that is to say the empty surface / full surface ratio, of 0.2 to 30%, preferably of 0.5 to 15%, such as for example 0.7, 1 , 1, 5, 2, 3, 4, 5 and 10%. The diameter of the holes in the microperforated plate is between 0.05 to 3 mm, preferably 0.1 to 1 mm, in particular 0.1 to 0.5 mm, such as for example 0.2, 0.3 and 0 , 4 mm. The microperforated plate can perfectly include holes of different diameters. The holes are preferably distributed uniformly on the microperforated plate. According to the invention, the element 1 having the shape of a microperforated plate can be of different forms conjugated or not conjugated with the framework 2 of the casing. The microperforated plate may in particular have a cross section having a plane and / or curved profile, such as for example in the shape of a U, a V, a semicircle, a rectangle with right and / or rounded angles, concave and / or convex. This microperforated plate may in particular have flat zones and / or zones comprising curvatures.

The perforation of the plate can be carried out in different ways. The plate can be perforated by laser or by punching, in particular hot, for example using needles. A high precision punching machine can be used for this purpose. It is also possible, for example, for a plastic plate to carry out the perforation in the enclosure of the mold for molding the plate. In particular, it is possible to use a mold fitted with movable pins for making a part comprising perforations. Said plate may optionally include stiffeners so that it is as rigid as possible in order to contribute to better resistance of the system to the vibratory stresses of the engine.

According to the invention, the framework 2 can be of different shapes. It may in particular have a planar and / or curved profile, such as for example in the shape of a U, a V, a semicircle, a rectangle with right and / or rounded angles, concave and / or convex. The frame 2 may in particular have flat zones and / or zones comprising curvatures. The framework 2 may have a more or less complex structure, with for example spaces for accommodating other parts, reinforcement ribs, preferably in the form of a zigzag or X, means of assembly with other parts or systems, for example clips, in particular in order to stiffen the part and limit the noise which it can generate by vibrations. The frame 2 may also comprise several sections that are substantially elongated and separated, for example, by elbows and / or changes in curvature.

This frame 2 may also have a closed cross section. By closed cross-section is meant any geometric shape to which it is possible to define a perimeter, such as for example a circle, a rectangle with right or rounded angles, an ellipse, an oval, ... The framework can for example be tubular.

The framework 2 may in particular comprise two walls 4 and a part 3. The part

3 is generally the one with the largest dimensions.

The framework 2 may have a thickness of 0.5 to 10 mm, preferably of

I to 5 mm, such as for example 2, 2.5, 3, 3.5, 4 and 4.5 mm. The framework 2 may optionally include flats inducing in particular a variation in the thickness less than or equal to 100%, relative to the average thickness of the part.

Element 1 and / or framework 2 can, independently of one another, be made up of one or more materials preferably chosen from the group comprising: metal, glass, wood, thermoplastic materials, thermosetting materials, and / or mixtures thereof.

It should be noted that the choice of a material for producing a casing according to the invention is generally guided by criteria of costs and properties, depending on the applications. Thus, depending on the use to be made of an object and the environment in which it will be used, different properties will be required, such as resilience, rigidity, flexibility, dimensional stability, the deformation temperature under load, the heat resistance, impermeability to certain chemical substances, resistance to contact with certain substances, etc.

The elements of the casing according to the invention can for example be formed from one or more metal parts. These parts can in particular be obtained by stamping a plate or a metal sheet. Steel sheets, in particular untreated or galvanized and / or provided with a primer and possibly with a bonding agent, as well as untreated or anodized aluminum sheets and / or provided with a primer and possibly of an adhesive agent, are particularly well suited.

It is also possible to use sheets of plastic material (s) formed by hot pressing, which are composed of thermoplastic materials into which may be inserted sheets of glass fibers or sheets of synthetic fibers, such as laminates. Thermoplastic materials can also be used, such as for example polyamide, polyethylene, polyester, polyurethane, polyolefin, such as polypropylene, polymethyl methacrylate, propylene polyoxide, polyvinyl chloride, polyacetal, polysulfone, polycarbonate, acrylonitrile butadiene styrene, poly (butylene terephthalate) and / or mixtures thereof; or thermosetting materials such as polyurethane. The polyamide is preferably chosen from semi-crystalline polyamides for example, the polymers obtained by polycondensation action of saturated aliphatic dicarboxylic acids having from 6 to 12 carbon atoms such as, for example adipic acid, azelaic acid, sebacic acid , dodecanoic acid or a mixture of these with linear or branched saturated, preferably aliphatic, biprimary diamines having from 4 to 12 carbon atoms such as, for example, hexamethylene diamine, trimethylhexamethylene diamine, tetramethylene diamine, m- xylene diamine or a mixture thereof; the polyamides obtained either by direct homopolycondensation of ω-aminoalkanoic acid comprising a hydrocarbon chain having from 4 to 12 carbon atoms, or by hydrolytic opening and polymerization of lactams derived from these acids; the copolyamides obtained from the starting monomers of the aforementioned polyamides, the acid component of these copolyamides possibly also partly consisting of terephthalic acid and or isophthalic acid; and mixtures of these polyamides or their copolymers.

By way of illustration of the polyamides obtained by polycondensation of diacids and diamines, there may be mentioned for example: polyamide 4.6, polyamide 6.6, polyamide 6.9, polyamide 6.10 and polyamide 6.12 . By way of illustration of the polyamides obtained by homopolycondensation which may be suitable, mention will be made of: polyamide 4, polyamide 5, polyamide 6, polyamide 7, polyamide 8, polyamide 9, polyamide 10, polyamide 11, and polyamide 12. By way of illustration of the copolyamides, there may be mentioned for example: polyamide 6.6 / 6.10 (copolymer of hexamethylenediamine, adipic acid and sebacic acid), polyamide 6.6 / 6 (copolymer of hexamethylenediamine, adipic acid and caprolactam), polyamide 6/12, polyamide 6/11, polyamide 6 / 6.36. It is in particular possible to use the mixtures of the (co) polyamides mentioned previously. The preferred polyamides of the invention are polyamides 6.6, polyamides 6, copolyamides 66/6 and 6 / 6.36.

Preferably, polyamides are used having a melt flow index greater than or equal to 20 g / 10 min, more preferably greater than or equal to 30 g / 10 min, measured according to ISO 1133 at 275 ° C. under a load of 325 g. .

For this purpose, it is possible, for example, to use a high-fluidity star polyamide obtained by mixing or adding in polymerization, in the presence of the monomers, of a multifunctional monomer having at least three initiating polymerization functions, such as acid and / or amino functions. . Particularly preferred is a polyamide obtained by polymerization of ω-aminoalkanoic acid monomers comprising a hydrocarbon chain having 4 to 12 carbon atoms, such as ε-caprolactam, in the presence of at least one multifunctional monomer having at least three functions polymerization initiators, such as acid or amino functions. One can in particular use a star polyamide as described in patents FR 2743077 and FR 2779730; or the multifunctional monomers mentioned in these references. The star polyamide used makes it possible to manufacture an element according to the invention having a good compromise in rigidity / dimensional stability, a good surface appearance and a good propensity for molding, and obtaining elements of fine thickness using standard injection machines. The element 1 and the framework 2 can be made of the same material, so as to facilitate the recycling procedure, such as for example polyamide. The thermoplastic materials from which the elements are shaped may advantageously comprise fillers, for example reinforcing and / or filling fillers, such as glass fibers, fibers made of thermosetting synthetic materials or having a higher melting point. at 325 ° C, carbon fibers, and / or mineral substances or powders such as talc, mica, kaolin, calcium carbonate. These fillers are commonly used in the plastics industries. Reinforcement fillers can represent from 0 to 80%, preferably from 5 to 55%, even more preferably from 10 to 40% by weight relative to the total weight of the thermoplastic composition. The thermoplastic materials from which the elements are shaped may also include additives such as thermal stabilizers, molding agents such as calcium stearate, UV stabilizers, antioxidants, lubricants, abrasion reducers, pigments, dyes, plasticizers, laser labeling promoters, impact modifiers or impact reinforcing agents, such as elastomers. By way of example, the antioxidants and heat stabilizers are, for example, alkali halides, copper halides, sterically hindered phenolic compounds, organic phosphites and aromatic amines. UV stabilizers are generally benzotriazoles, benzophenones or HALS, optionally in combination with antioxidants and / or other conventional additives. Any known method can be used for the production of shaped elements made of thermoplastic material comprising several compounds. We cite for example the shaping from granules of a composition containing all the elements; shaping from mixtures of granules of different compositions and optionally additives introduced in the form of powder or masterbatch, for example polyethylene, polyamide and ionomer granules; shaping from granules at least part of which is coated with an additive or other compound.

The elements of the casing according to the present invention can be obtained by different shaping methods, such as stamping and bending (for metal), extrusion, compression molding, rotational molding, thermoforming, conventional injection molding or gas injection or water injection. The microperforated plate is preferably obtained by shaping a thermoplastic composition by an injection molding process. The element 1 and the framework 2 define a space 5 having a thickness of 1 to 400 mm, preferably from 1 to 200 mm, more preferably from 5 to 30 mm, such as for example 6, 7, 8, 9, 10 , 11, 12, 13, 14 and 15 mm. According to the respective shapes of the element 1 and the framework 2, the thickness of the space 5 can be variable. It is preferable to consider that the thickness is included in the values indicated above for the major part of the space between the element 1 and the framework 2. The microperforated plate 1 can be positioned between the part 3 of the framework 2 and the mechanism, preferably in a parallel or slightly parallel manner, that is to say so as to form an angle preferably less than or equal to 20.

The microperforated plate 1 and the framework 2 can be associated together, directly or indirectly; that is, through one or more other elements. In the latter case, the microperforated plate 1 and the framework 2 are not associated with each other, but fixed independently of one another to one or more other elements, such as for example the hood, the engine, the cover. cylinder head, air filter and / or an air intake manifold, in the case of a motor vehicle.

The microperforated plate 1 is advantageously associated with the framework 2 with the part 3 and / or on the walls 4 of the framework 2. Said plate can for example bear on the framework 2 on singular points or in strips of continuous contact.

According to the invention, the microperforated plate 1 and the framework 2 can be assembled by any means known from the state of the art, such as for example clipping, stamping, screwing, bonding, riveting, embedding and / or welding. As known and suitable welding techniques for the invention, there may be mentioned by way of example: ultrasonic welding (the surfaces are brought to the desired temperature by ultrasound), vibration welding (the surfaces are brought into contact and in vibration with respect to each other, the friction between the surfaces causing heating and softening of the material), the welding by heating mirror (a heated mirror is placed between the welding surfaces, then removed when they these have reached the desired temperature; the surfaces are then brought into contact under a determined pressure), infrared welding (technique similar to that of the heating mirror, the heat source being an emitter of infrared rays), and laser welding. Figure 1 shows a schematic transverse view of a housing according to the invention in which the frame 2 has a planar profile. Figure 2 shows a schematic transverse view of a casing according to the invention in which the framework 2 has a concave curved profile. The framework 2 comprises two walls 4 and a part 3. A specific language is used in the description so as to facilitate understanding of the principle of the invention. It should nevertheless be understood that no limitation of the scope of the invention is envisaged by the use of this specific language. Modifications, improvements and improvements can in particular be envisaged by a person familiar with the technical field concerned on the basis of his own general knowledge.

The term and / or includes the meanings and, or, as well as all other possible combinations of the elements connected to this term.

Other details or advantages of the invention will appear more clearly in the light of the examples given below only for information.

Example 1: Motor cover type housing

An engine cover is produced for a 2-liter direct injection diesel engine comprising a microperforated plate 1 and a frame 2, in accordance with a casing according to FIG. 2.

Polyamide granules sold by the company Rhodia under the name TechnylStar S218MZ20V10 BK 2N are used for the manufacture of microperforated plate 1 and framework 2 by injection molding with a Billion H6860-750 injection press (closing force 750 tonnes ). A mold allows the manufacture of a plate in the form of a rectangular plate having a length of 340 mm, a width of 145 mm and a thickness of 1 mm and comprising five clipping zones (one zone for each angle and one zone in the middle) located on part 3. The perforation of the plate is obtained by laser micro-perforation performed using a CO ₂ laser machine with a power of 1000W, scanning the surface to be perforated. An installation of the VOTAN ™ D type from JENOPTIK is used to obtain such perforations. A plate is obtained having a surface density of perforation of 1% and a diameter of the holes of 0.3 mm. Another mold allows the fabrication of the framework 2 in the form of a rectangular plate having a length of 350 mm, a width of 160 mm and a thickness of 3 mm, and having a cross section having a curved profile and comprising five zones. clip (one area for each angle and one area in the middle). The two elements are assembled by positioning the microperforated plate 1 in the curved space of the frame 2 and clipping. The positioning of the two elements is such that the distance between the microperforated plate 1 and the framework 2 is 10 mm.

Example 2: Acoustic absorption measurement test a) Manufacture of the microperforated plate 1

Polyamide granules sold by the company Rhodia under the name TechnylStar S218MZ20V10 are used for the forming of a rectangular plate by sheet injection. A Billion H6860-750 injection molding machine is used to obtain this plate, which is then re-cut into a disc having a thickness of 0.8 mm, and having either a diameter of 100 mm or a diameter of 29 mm. The microperforated plate 1 is then obtained by laser micro-perforation, as mentioned above. A plate is obtained having a surface density of perforation of 1% and a diameter of the holes of 0.3 mm. b) Polyurethane foam

A disc with a diameter of 29 mm and a disc with a diameter of 100 mm of polyurethane foam with a thickness of 10 mm are used, cut by stamping in a foam of the timing belt casing of a 2.5L TDI 6-cylinder V diesel engine. from Volkswagen / AUDI. The foam has a density of 0.025 g. cm ³ and an average diameter of porosities 0.24 +/- 0.08 mm. c) Measurement of absorption of acoustic waves

Acoustic absorption measurements were carried out on a Kundt tube according to ISO standard 10534-2 of November 1998. The Kundt tube used is of the Bruel and Kjaer brand type 4206, comprising two microphones and a preamplifier. We use a large 100 mm tube to calculate the absorption factor for low and medium frequency waves (50 Hz-1600 kHz) and a small 29 mm tube to calculate the absorption factor for high frequency waves ( 500 Hz-6400 Hz).

The method is as follows: At one end of the tube, a loudspeaker generates a white noise type signal. The incident sound wave is reflected by the material at the other end, which forms a standing wave. The technique used is that of the two microphones: the reflection coefficient is calculated from the transfer function between the two microphones, the absorption coefficient is deduced therefrom.

In this case, the disc obtained in Example 2. a) is placed at a distance d of 10 mm or 30 mm from the end of the tube. The disc thus constitutes the microperforated plate 1 and the end of the tube constitutes the framework 2. As regards the test with the polyurethane foam of Example 2.b), the test procedure for measuring acoustic wave absorption is the same as that described above, with the distance d = 0 mm (the sample is pressed against the end of the tube). The results are listed in Table 1:

Table 1

Values are expressed as a percentage

It can thus be observed that a sound absorption system of the polyurethane foam type is not suitable for the noise source to be treated (diesel engine), in particular by the fact that the optimum of its sound absorption (between 2000 and 2500 Hz ) is not at the same frequencies as the maximum noise level emitted by the engine (between 800 and 2500 Hz for a conventional diesel engine with 1.8L displacement, 4 cylinders in lines). On the other hand, it is possible to modulate the sound absorption coefficient of the casing of the present invention according to the distance d used as a function of the frequency of the acoustic wave emitted. It is also observed that the casing according to the invention has good absorption capacity for acoustic waves, in particular between 800 and 2500 Hz. Example 3: Testing the acoustic radiation of vibratory origin

We study by simulation the acoustic radiation of an engine cover attached to an engine and stressed by a vibratory excitation. A vibration of frequency 0 to 1000 Hz is applied to the fixing points between the engine and the engine cover. For frequencies from 0 to 210 Hz, a displacement of 7.10 ^"2 mm is imposed on the fixing points. For frequencies from 210 to 1000 Hz, an acceleration of 3 G is imposed on the fixing points.

The simulations are carried out on an engine cover according to Example 1 comprising a microperforated plate and the same engine cover without a microperforated plate. The results are expressed in Table 2:

Table 2

*: on the frequency 6 to 75 Hz

**: on the frequency 2 to 45 Hz

The first mode corresponds to the first frequency for which the response of the structure to an excitation causes displacements of very large amplitudes.

Acceleration and displacement are correlated by the following relation: y = v ^ .x; with y corresponding to the acceleration, w corresponding to the pulsation and x corresponding to the displacement.

It is observed that the maximum acoustic pressure radiated by the structure (on a listening plate located approximately 70 cm from it, for a given frequency) is approximately 40 dB lower with the engine cover according to the invention compared to the engine cover without microperforated plate. It is thus observed that the microperforated plate makes it possible to increase the rigidity of the engine cover, thus significantly damping the vibrations coming from the engine, which results in a very significant reduction in the noise generated by them.

Claims

1. Housing (6) soundproofed to wrap a mechanism comprising at least one frame (2), characterized in that a soundproofing element (1) in the form of a microperforated plate having through holes is disposed between the framework (2) and said mechanism, element (1) and framework (2) define a space (5) having a thickness of 1 to 400 mm, said element (1) having the following characteristics: a surface density of 0.2 to 30% perforation; and a hole diameter of 0.05 to 3 mm.

2. Housing according to claim 1, characterized in that the element (1) and the framework (2) define a space (5) having a thickness of 5 to 30 mm.

3. Housing according to claim 1 to 2, characterized in that the element (1) having the shape of a microperforated plate has a thickness of 0.2 to 10 mm.

4. Housing according to any one of claims 1 to 3, characterized in that the surface density of perforation of the element (1) is between 0.5 to 15%.

5. Housing according to any one of claims 1 to 4, characterized in that the diameter of the holes of the element (1) is between 0.1 to 0.5 mm.

6. Housing according to any one of claims 1 to 5, characterized in that the element (1) having the shape of a microperforated plate has a cross section having a planar and / or curved profile.

7. Housing according to any one of claims 1 to 6, characterized in that the frame (2) comprises two walls (4) and a part (3), the element (1) is associated with the frame ( 2) on the walls (4) and / or on the part (3).

8. Housing according to any one of claims 1 to 7, characterized in that the element (1) and / or the frame (2) consist, independently of one another, of one or more materials chosen from the group comprising: metal, glass, wood, thermoplastic materials, thermosetting materials, and / or mixtures thereof.

9. Housing according to any one of claims 1 to 8, characterized in that the element (1) and / or the frame (2) consist, independently of one another, of one or more materials chosen from the group comprising: polyamide, polyethylene, polyester, polyurethane, polyolefin, such as polypropylene, polymethyl methacrylate, propylene polyoxide, polyvinyl chloride, polyacetal, polysulfone, polycarbonate , acrylonitrile butadiene styrene, poly (butylene terephthalate) and / or mixtures thereof.

10. Housing according to any one of claims 1 to 9, characterized in that the element (1) is obtained by shaping a polyamide having a melt flow index greater than or equal to 20 g / 10 min , measured according to ISO 1133 at 275 ° C under a load of 325 g.

11. Housing according to any one of claims 1 to 10, characterized in that the element (1) is obtained by shaping a thermoplastic composition by an injection molding process.