EP0579542A1 - Noise insulating hollow body - Google Patents

Abstract

The window includes two parallel glass panes separated by an air gap and assembled within a window frame. The frame is filled with a drying substance and glued with butyl. A waveguide is built at the window edge which communicates, through eight holes, with the air gap between the panes.

Description

The invention relates to the acoustic insulation of a flat box with multiple walls and more particularly of an insulating glazing.

Insulating glazing, consisting of two or more sheets of glass associated together by means of an intermediate frame which keeps them at a certain distance from each other by trapping between them a blade of gas, air dry in general, are used in the majority of cases to improve the thermal insulation of premises or even possibly of land transport vehicles.

The most common systems use glasses with a common thickness of 4 mm separated by a space between 6 and 12 mm. As they are, these glazings have limited acoustic performance, notably lower than that of a monolithic glass with the same overall surface mass.

Various means are available in industry to improve the acoustic performance of insulating glazing. The most common is to use glasses of large and different thicknesses. This means has limited effectiveness, it increases the weight of the glazing which may require the use of a reinforced window, moreover, the increase in cost is not negligible. Another common way is to replace monolithic glass with laminated glass. Here, the efficiency is limited and the increase in cost, greater than the previous case.

A means which is difficult to use for glazing intended to equip windows but which is common in interior partitions or in railway vehicles consists in increasing the thickness of the air space. But it is only for air thicknesses of several centimeters (5 or 6) that the effect is appreciable, which prohibits the production of such variants in sealed insulating glazing.

One effective way is to use special laminates. This is how European patent application EP 100 701 B1 describes an insulating glazing unit comprising one or two laminated elements, the resin of which is "such as a bar 9 cm in length and 3 cm in width, consisting of a laminated glass comprising two sheets of glass 4 mm thick joined by a layer of 2 mm of this resin, has a critical frequency which differs at most 35% from that of a glass rod having the same length, the same width and 4 mm thick ". The operating principle of this type of glazing based on a low stiffness of the resin, independently of its damping allows a very clear improvement compared to ordinary laminated glazing but the price is also significantly higher.

The problem that the invention sets out to solve is to provide insulating glazing made of common monolithic glasses but with improved performance, without the manufacturing cost and the weight increasing too much.

The invention also sets itself the task - more generally, of providing a simple and inexpensive solution to the problem of sound insulation of watertight boxes with double or multiple walls filled with gas and / or air.

None of the technical solutions mentioned previously in the case of glazing uses sealed insulating glazing made of conventional monolithic glasses since they propose to act on their thicknesses or on their nature (normal or special laminates). On the other hand, some studies have proposed using standard thickness plates and installing Helmholtz resonators tuned to the cavity of the box at the periphery of the box (see MASON and FAHY, Journal of Sound and Vibration, Vol 124 (2) page 367 to 379 Academic Press Ltd 1988). Patent application WO-A-85 02640 thus proposes a box with a improved sound insulation at certain frequencies. In one of its variants, it includes spherical resonators located outside the box and in communication with the internal volume, not ducts of small cross section. This system, since it is tuned on one frequency, acts mainly in a domain around it, but, on the other frequencies, either it acts only little, or even it acts negatively. Furthermore, the volume of the resonator must be a significant fraction of that of the cavity proper - of the order of 15% - which for example for a glazing of 1 m² with an air gap of 12 mm thick requires installing several "bottles" at the periphery of the glazing, with a total capacity of almost 2 liters: this solution is not suitable for the usual conditions for manufacturing insulating glazing or, in general, for insulation acoustics of boxes of comparable thickness.

A variant of a resonator is also known in which the resonator-interior connection of the box is not made by pipes as in the general case of Helmoltz resonators, but by a continuous connection. Patent application DE-A-34 01 996 thus proposes a glazing whose glasses have different thicknesses and are mechanically separated from one another. At the periphery of the glazing, a cavity of very large section has been produced which allows, taking into account its volume and the characteristics of the continuous slot which connects it inside the glazing, to tune the resonator to improve the insulation at a given frequency.

There is also known a variant of glazing comprising an absorbent peripheral material in which the latter is contained in a tube situated inside the glazing, at its periphery. Patent application DE-A-27 48 223 proposes that the connection between the inside and the outside of the tube containing the absorbent material is made by a narrow and very long channel which extends from one end to the other. other from the tube. The operating principle of this type of glazing is to cause sound absorption by an appropriate absorbent material. No variant without material absorbent is not envisaged in DE-A-27 48 223.

The invention does not use to improve the acoustic performance of a box or the principle of Helmoltz resonators located outside the box or that of sound absorption by a suitable material located between the plates, at the periphery internal space.

The invention provides a box comprising at least one flat cavity consisting of two substantially parallel plates assembled at their periphery using an intermediate frame, the cavity being filled with gas and / or air, which comprises a guide wave in communication with the cavity by one or more localized orifices, their shape, their section and their position as well as the section of the waveguide are determined so as to detune the acoustic and mechanical waves which arise, respectively in the cavity and on the plates when the box is subjected to an incident sound field.

The disagreement between acoustic and mechanical waves is evaluated by calculating the energy coupling coefficients between the acoustic and mechanical modes and it is these coefficients which are minimized.

Preferably, the waveguide is placed at the periphery of the cavity and it is closed on itself. Advantageously, the box is polygonal.

In the case where it is an insulating glazing with glass sheets as plates, the waveguide is integrated into the intermediate frame of the insulating glazing. The preferred embodiment of the invention comprises a waveguide and an intermediate frame which consist of a single profile comprising two compartments in communication by a narrow slot over their entire length, the external compartment containing the desiccant.

Preferably, the profile constituting the waveguide and the intermediate frame is obtained by folding a thin sheet of aluminum.

A preferred embodiment of the invention provides that the communication orifices between the waveguide and the cavity each constitute an assembly whose width is, at least locally, close to that of the waveguide and the length of which is between 2 and 25% of the length of the side concerned and preferably between 2 and 5%. When the glazing is rectangular, the orifices are preferably located in the middle of the sides and they consist of a series of equidistant circles.

The technique of the invention as it is in its most elaborate variant, rectangular insulating glazing with peripheral wave guide connected to the cavity by openings located along the guide, makes it possible to significantly improve the acoustic performance of traditional glazing with means that are easy to implement and inexpensive.

The description and the figures which follow will make it possible to understand the invention and to appreciate its advantages.

• la figure 1 montre un exemple de réalisation d'un caisson selon l'invention,
• la figure 2 présente un détail du même caisson,
• la figure 3 représente un vitrage selon l'invention,
• et la figure 4, la section du profilé constituant le cadre de ce même vitrage.
• la figure 5 montre les résultats acoustiques d'un vitrage selon l'invention en comparaison avec le même vitrage non équipé du dispositif de l'invention.

Among the figures,

• FIG. 1 shows an exemplary embodiment of a box according to the invention,
• FIG. 2 shows a detail of the same box,
• FIG. 3 represents a glazing according to the invention,
• and Figure 4 , the section of the profile constituting the frame of the same glazing.
• FIG. 5 shows the acoustic results of a glazing unit according to the invention in comparison with the same glazing unit not fitted with the device of the invention.

The principle of the invention is as follows: to increase the acoustic insulation of a box made of two parallel plates, separated by a small space and connected at their periphery by a frame, thus producing a cavity, it is proposed to produce on the periphery of the box a section waveguide (A) which communicates with the air or gas layer trapped between the two walls, via section openings (s) placed at appropriate locations. The main role of this waveguide being to detune the acoustic and mechanical waves which arise respectively in the air or gas space and on the walls when the double-walled box system is subjected to an incident acoustic field.

To determine the optimal geometric characteristics (A, s, and the position of the openings), we use a calculation method which consists in discretizing the air or gas layer and the walls by acoustic and mechanical finite elements. The acoustic finite elements make it possible to calculate very precisely the modification of the internal acoustic modes of the air gap by the addition of the waveguide, while the mechanical finite elements make it possible to calculate as precisely the eigen modes of the two walls.

To take into account the vibro-acoustic coupling between the walls and the gas or air layer, we use a mixed formulation developed by the team of Professor HAMDI at the University of Technology of Compiègne. See "Methods of discretization by finite elements and finite elements of border" by HAMDI in Acoustic radiation of structures, Eyrolles editor, Paris 1988. This formulation rests on the application of the principle of Hamilton to the coupled fluid-structure system, described in terms of acoustic and mechanical modal components which constitute the unknowns of the problem. The main advantage of this formulation is to show explicitly the energy coupling coefficients between the internal acoustic modes and the mechanical modes of the walls.

The principle of the method therefore consists in finding the characteristic dimensions of the waveguide so as to minimize the energy coupling coefficients.

To calculate the weakening index of the double wall system fitted with the waveguide, we then use a boundary finite element method, also developed by the research team of Professor HAMDI, which makes it possible to calculate the radiation impedance of the walls and the weakening index of the double-wall system subjected to an acoustic field of incident plane waves.

In summary, the method is as follows: from a given basic structure, for example an insulating glazing comprising two glass plates 4 mm thick separated by a 12 mm air gap, we imagine a guide compatible with the characteristics of the structure. In the case of a glazing for example, it will generally be preferable to place it at the periphery. The calculation dictates the elements A, s and the position of the openings which, a priori, will give the best results while remaining compatible with the final product. (Thus for insulating glazing, we will prevent the peripheral waveguide from encroaching too deeply into the field of vision of the glazing. Similarly, always in the case of glazing, we will place the openings in symmetrical locations, preferably in the middle of the sides).

• 1. Maillage par éléments finis de la lame de gaz ou d'air et des parois,
• 2. Calcul des modes vibratoires des parois,
• 3. Calcul des modes acoustiques de la lame de gaz ou d'air en absence et en présence du guide d'onde,
• 4. Calcul des coefficients de couplage énergétique entre les modes acoustiques et mécaniques. C'est à ce moment que l'on peut voir si le découplage se produit et pour quelles fréquences. Le but est en effet de provoquer une rupture d'impédance entre plaques et guide d'onde,
• 5. Calcul des matrices d'impédance de rayonnement acoustique des parois,
• 6. Calcul de l'indice d'affaiblissement du système double paroi.

The calculation software developed ultimately consists of performing the following 6 steps:

• 1. Mesh by finite elements of the gas or air layer and the walls,
• 2. Calculation of the vibratory modes of the walls,
• 3. Calculation of the acoustic modes of the gas or air plate in the absence and in the presence of the waveguide,
• 4. Calculation of the energy coupling coefficients between the acoustic and mechanical modes. It is at this point that we can see if decoupling occurs and for what frequencies. The goal is to cause an impedance break between plates and waveguide,
• 5. Calculation of the acoustic radiation impedance matrices of the walls,
• 6. Calculation of the weakening index of the double wall system.

The result of this modeling of the box materialized by the curve of the acoustic attenuation index as a function of the frequency makes it possible to judge the effect provided by the chosen waveguide. The calculation makes it possible to modify iteratively one, two or three of the parameters A, s and position of the openings which define the guide so as to improve the weakening index, the experiment then makes it possible to verify the validity of the acoustic result of the new housing - waveguide assembly.

Example 1

The previous method was applied to double glazing 4 (12) 4 made of two float glass plates 4 mm thick separated by a 12 mm air gap and assembled with an aluminum frame filled with a desiccant (molecular sieve) and bonded using butyl and polysulfide. The glazing dimensions were 1.23 x 1.48 m².

The different stages of the method described above applied to glazing ended up, following successive approximations, with a product represented in FIGS. 1 and 2.

• Sur la figure 1 on voit le vitrage 1 avec ses verres 2 et son profilé périphérique 3,
• Sur la figure 2, on a représenté la colle 4 et le desséchant 5. Tous ces éléments sont traditionnels. Le guide d'onde, lui est représenté en 6 sur les figures 1 et 2. Il est matérialisé par quatre parois : les surfaces internes 7 et 8 des verres, la paroi interne 9 du cadre intercalaire et pour la quatrième paroi, on a utilisé la face externe 10 d'un profilé 11 identique au profilé du cadre. Ce profilé est collé entre les deux verres comme le profilé du cadre. Il est découpé en tronçons de longueur telle qu'ils laissent entre eux les orifices de liaisons définis plus haut, c'est-à-dire avec une surface de 54 mm² pour l'orifice 12 des coins et de 480 mm² pour ceux 13 du milieu des côtés. Les profilés sont vides mais leurs extrémités sont bouchées.

It was a question of producing, on the periphery of the glazing, a waveguide of section 240 mm² communicating by eight holes of connection with the cavity including four, of section 54 mm² at the four corners of the glazing and four, of section 480 mm² in the middle of his sides.

• In FIG. 1 we see the glazing 1 with its glasses 2 and its peripheral profile 3,
• In Figure 2, there is shown the glue 4 and the desiccant 5. All these elements are traditional. The waveguide is shown at 6 in FIGS. 1 and 2. It is materialized by four walls: the internal surfaces 7 and 8 of the glasses, the internal wall 9 of the intermediate frame and for the fourth wall, we used the outer face 10 of a profile 11 identical to the profile of the frame. This profile is glued between the two glasses like the profile of the frame. It is cut into sections of length such that they leave between them the connection orifices defined above, that is to say with an area of 54 mm² for the orifice 12 of the corners and 480 mm² for those of the 13 middle of sides. The profiles are empty but their ends are blocked.

The experimental acoustic measurements carried out on the prototype that has just been described have shown a significant improvement in performance in comparison with identical glazing except for the section 11 which is absent. The results according to French standard NF-S 31 051 were better by 3 dB (A) for road noise and according to ISO standard 717 (R _w ), also by + 3 dB.

Example 2

The glazing of the second example was produced under the conditions of industrial mass production.

It was produced by folding aluminum strip, a profile intended to constitute the interlayer of a glazing insulating. This profile has a double role, on the one hand it must play the usual role of an insulating glazing frame and on the other hand, it also incorporates the waveguide of the invention. The section of the profile is shown in Figure 4. We see at 16 the compartment reserved for desiccant and fixing the corners at the four corners of the glazing. In 17, the waveguide was formed. We have chosen here a section of 150 mm². The glazing prototype was produced with 4 mm glass in the same dimensions as before: 1.23 x 1.48 m². By applying the method of the invention, the energy coupling coefficients between the acoustic and mechanical modes were calculated and then, by calculation, we examined how the choice of position, shape and section of the openings in the streamlined managed to minimize these coefficients. The position retained for the openings was in the middle of the four sides of the glazing, the corners being assembled at a bevel at 18, FIG. 3 without being waterproof. The shape of the orifices has been determined by a series of circles 19 almost tangent to each other. It is important that their diameter is close to the thickness of the profile. Another important criterion is the total length occupied by all of the circles 19 in the middle of the sides of the glazing. This must be at least 2% and at most 25% of the side length. Optimization provided as a number of juxtaposed circular openings, the number 4 for both the side of 1.23 m in length and that of 1.48 m.

The profile shown in Figure 4 has an interesting feature: it was designed with a communication orifice between the two chambers. The partition wall 20 does not come into contact with the perpendicular wall 21 put leaves a space 22 of, for example, 0.2 mm free. This passage allows the desiccant (not shown) filling the compartment 16 to act through the compartment 17 and the openings 19 on the internal space 23 of the insulating glazing which it always keeps dry.

Full-scale acoustic measurements were made on the glazing which has just been described and, by comparison, on glazing of the same dimensions but which was not equipped with the inventive waveguide.

The tests were carried out according to ISO 140 in two reverberant chambers with respective volumes 62 and 86 m³.

The results are shown in Figure 5 . We see on the abscissa the frequencies (in kHz) and on the ordinate, the acoustic attenuation indices. Curve 14 represents the results of traditional insulating glazing 4 (12) 4 filled with air while curve 15 shows those of glazing of the same dimensions, still in 4 (12) 4, but with the waveguide peripheral of Figures 3 and 4 . It is noted that between 200 Hz and 2500 Hz, the glazing of the invention is greater by a value between 2 and 5 dB than an ordinary glazing. The general shape of the curve shows that the effect does not manifest itself at a localized frequency as is the case with Helmholtz resonators but over a wide band of the audible spectrum.

From the previous curves, the overall values of the sound reduction index were calculated, on the one hand according to French standard NF-S 31 051 (loss index respectively for road noise, R _rte and for pink noise, R _pink ) and according to ISO 717 (R _w ).

The results were as follows: 4 (12) 4 4 (12) 4 + waveguide R _rte 26.3 29.6 R _pink 29.5 32.1 R _w 30 33

The waveguide produces its effect perfectly by disturbing the coupling that the air gap usually achieves between the first and the second plate. The function of the guide is to allow the sound wave to circulate, this is why it is important that the number of communication orifices between the cavity and the guide is not too large, which would hinder this free movement.

Examples 1 and 2 of making the boxes of the invention use transparent glass plates but, of course, the acoustic results are not dependent on the nature of this material. Sheets of sheet metal or any other material with a modulus of elasticity of the same order would have led to comparable results.

It emerges from the above that the invention proposes an unexpected and very distant solution not only from the systems which act on the plates themselves (thicknesses, laminated assemblies, special resins) but even from those which act on the cavity (resonators of Helmholtz or peripheral absorbents). Compared to these other treatments, it has the advantage of being inexpensive, easy to use in industry and aesthetically discreet.

Claims (12)

Box comprising at least one flat cavity consisting of two substantially parallel plates assembled at their periphery using an intermediate frame, the cavity being filled with gas and / or air, characterized in that it includes a guide wave in communication with the cavity by one or more localized orifices, their shape, their section and their position as well as the section of the waveguide are determined so as to detune the acoustic and mechanical waves which arise respectively in the cavity and on the plates when the box is subjected to an incident sound field. Box according to claim 1, characterized in that the discrepancy between acoustic and mechanical waves is evaluated by calculating the energy coupling coefficients between the acoustic and mechanical modes and in that it is these coefficients which are minimized. Box according to one of the preceding claims, characterized in that the waveguide is placed at the periphery of the cavity. Box according to claim 3, characterized in that the waveguide is closed on itself. Box according to claim 3 or 4, characterized in that the box is polygonal. Box according to claim 5, characterized in that the box is an insulating glazing whose plates are sheets of glass and in that the waveguide is integrated into the intermediate frame of the insulating glazing. Box according to claim 6, characterized in that the waveguide and the intermediate frame consist of a single profile comprising two compartments in communication with one another and in that the external compartment contains the desiccant. Box according to claim 7, characterized in that the communication takes place via a narrow slot, possibly along the entire length of the profile. Box according to claim 7 or claim 8, characterized in that the profile constituting the waveguide and the intermediate frame is obtained by folding of a thin sheet of aluminum. Box according to one of claims 5 to 9, ca characterized in that the communication orifices located between the waveguide and the cavity each constitute an assembly whose length is between 2 and 25% of the length of the side concerned and preferably between 2 and 5%. Box according to claim 10, characterized in that the width of the orifices is, at least locally, close to that of the waveguide. Box according to claim 10 or claim 11, characterized in that the glazing is rectangular, that the orifices are located in the middle of the sides and that they consist of a series of equidistant circles.

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