FR2979086A1 - Acoustical baffle for rear shelf of vehicle, has plastic part extending only to periphery of sound absorbing part, where plastic part includes overlap region arranged to partly cover rim area of sound absorbing part, so as to stiffen baffle - Google Patents

Abstract

The baffle (1) has a sound absorbing part (2) made of a sound absorbing material such as felt, where the part includes a sound absorption area of a thickness, and a rim area of another thickness that is smaller than the former thickness. A plastic part (3) extends only to the periphery of the sound absorbing part. The plastic part is integral with the sound absorbing part, and includes an overlap region arranged to partly cover the rim area, so as to stiffen the baffle, where the density of sound absorbing material in the rim area is greater than that in the sound absorption area. Independent claims are also included for the following: (1) an assembly for a vehicle (2) a method for manufacturing an acoustical baffle.

Description

The present invention relates to an acoustic screen, including its application in the automotive field, a rear shelf provided with such a screen, a mudguard comprising such a screen, a set for a vehicle consisting of an engine equipped with such screen and a method of manufacturing this screen. Conventional acoustic screens consist of a screen formed of a plastic layer provided with an underlay of sound-absorbing material (in the form of fibrous material or foam) or consisting of a screen completely formed of a fibrous material .

Generally, the screens comprising a plastic layer are relatively heavy by the use of injected, high density and high thickness plastics and by the use of the absorbent underlayer. Moreover, they can be quite bulky because of the cumulative thicknesses of the plastic layer and the underlayer. In addition, the method of manufacturing such screens requires to provide an assembly step between the plastic layer and the underlayer. The screens consist solely of fibers are generally less bulky and less heavy but they are more difficult to rigidify and it is quite difficult to affix a registration such as a logo or to obtain a metallic appearance via a painting operation. Furthermore, the cutting of the fibrous material to the punch typically generates an unclear finish of the periphery of the fibrous material that forms the edges of the screen. Fasteners are also visible on fibrous screens which leads to less massive aspects.

In this context, the invention aims to overcome one or more of these disadvantages. According to a first aspect, the invention thus relates to an acoustic screen, in particular for vehicles, comprising: a first part made at least partly of an acoustic absorbent material, for example of fibrous material, the first part comprising a zone of a first thickness and a periphery of a second thickness, the second thickness being smaller than the first thickness - a second portion consisting of a plastic material extending only at the periphery of the first thickness part, the second part being integral with the first part and having a covering area arranged so as to cover at least part of the periphery area, so as to stiffen the acoustic screen. By the term 'acoustic absorbing material' is meant a material whose absorption coefficient is greater than 50% at 2000 Hz for a thickness of between 5 and 10 mm and an absorption coefficient of greater than 50% at 1000 Hz. for a thickness of about 20 mm. By "perimeter area" is meant either an area forming the entire periphery of the first part or one or more distinct regions along the periphery and sufficiently wide to reach a solidarity between the second and the first part and obtain the effect. stiffener required depending on the intended applications. By the term "cover" is meant to 'cover at least part of a surface', especially a part of the surface of the perimeter area. The term "thickness" is defined in the direction extending between the two faces of the first or second portion. "First thickness" defines a constant thickness over the entire acoustic absorption zone or a variable thickness according to different regions of this zone. In the latter case, the value of the first thickness is defined by the value of the thickness of the portion of the absorption zone having the largest area. The term "portion" may mean the sum of distinct portions having the same thickness. Thus, the constitution of the two parts of this screen makes it possible to combine the advantages of conventional screens such as the rigidity of the screens comprising a plastic layer and the lightness properties of the screens entirely made of fibrous material, while maintaining absorption properties. similar acoustics. Indeed, the second part of the screen, composed of a plastic layer extending on the periphery of a first part provided with an acoustic absorbent material, makes it possible to stiffen the screen without making it heavier compared to the traditional screen formed of a plastic layer provided with an underlayer. Furthermore, the second plastic part forming the contour of the screen, it ensures a peripheral finish cleaner than that obtained by cutting a fibrous material of the conventional screen entirely made of fibers. The second plastic part 35 also makes it possible to integrate fasteners or decoupling pads. In addition, the second thickness of the perimeter zone is smaller than the first thickness of the sound absorption zone. Thus, the superimposition of the perimeter zone and the overlap zone forms a thickness less than that which would be obtained by superposition of the overlap zone and the sound absorption zone. The footprint generated by the superposition according to the invention is therefore less than that of the conventional screen formed of a plastic layer and an undamped acoustic absorption sub-layer. According to a particular embodiment, the first thickness is between 15 and 20 mm and the second thickness is between 2 and 3 mm. Thus, when the thickness of the second portion is between 2.5 and 3 mm thick, the cumulative thicknesses of the second portion and the periphery of the first portion remain less than 6 mm. The overlap region between the first and the second portion thus has a thickness less than the sound absorption area of the first portion.

According to an alternative embodiment, the periphery zone has a return forming an angle of between 30 and 90 ° with respect to the mean plane of the acoustic absorption zone. This arrangement makes it possible to form an acoustic lateral barrier so as to contain and absorb the sound waves in the first part of the screen.

Advantageously, the periphery zone has an acoustic absorbent material of a density greater than the density of the material of the sound absorption zone. This provides greater rigidity to the perimeter area so as to ensure good solidarity with the overlap area of the second part.

The second portion of plastic material is typically adapted to receive a decoration placed by a method of marking such as pad printing or hot stamping. It is thus possible to register any type of marking, such as a logo, on the second part of the screen which is particularly interesting because the screen can play the part of aspect and be visible from the user. Preferably, the acoustic screen comprises at least one means for fixing the screen on a vehicle, the fastening means being integral with the second part and projecting from a face of the second part so that the screen remains fixed on the vehicle despite the vibrations of it. By the expression 'being material' is meant that the fixing means is molded and forms an integral part of the second plastic part. Furthermore, when the screen is attached to an element of the vehicle, by means of a stud for example, the means preferably protrudes on the face which is against the element. Therefore, the fastening means of this face is invisible to the user and the screen once fixed has a beautiful aesthetic appearance. According to a particular embodiment of the invention, the acoustic absorbent material consists of a fibrous material such as a nonwoven textile material and in particular a felt. The fibrous material has the particularity of including binder thermoplastic fibers. The fibrous character gives the material acoustic absorption properties by its porosity and tortuosity. The thermoplastic nature allows the material to be heated to be shaped. According to another particular embodiment of the invention, the acoustic absorbent material is made of a material such as foam, porous rock and glass wool. According to a particular embodiment of the invention, the plastic material is chosen from polyamides 6 or 66 and noble or recycled polypropylenes comprising between 0 and 30% of mineral fillers and 0 to 30% of glass fibers. The presence of these mineral fillers and / or glass fibers reinforces the plastic so that it achieves the desired mechanical properties. The densities of the plastics concerned are between 1.37 and 1.47, which corresponds for a thickness of 3 mm to a basis weight of 5.11 to 5.41 kg / m 2. Advantageously, the acoustic screen has a surface mass of between 2.8 and 4 kg / m 2, which is less than the mass per unit area of a conventional screen with a layer of plastic and a layer of fibrous material, which is generally superior. at 5 kg / m2, while exhibiting similar properties of rigidities and acoustic absorptions. Thus, the low mass of the screen of the invention makes it possible to respond to the problem of the lightening of parts used in the automotive industry defined in particular by the European Directive CE / 443/2009 on the emissions of O2. a second aspect, the invention relates to a vehicle rear shelf having an acoustic screen as described above, the frame of the rear shelf being formed by the second part of a plastic material and the pencil of the rear shelf being formed by the first part of an acoustic absorbing material. According to a particular embodiment of the invention, the second face of the second portion of the screen comprises at least one fastening means so that the second face is fixed against one or other of the surfaces of the tablet. . The securing means of the second face of the screen is thus invisible to the user, which improves the aesthetic appearance of the tablet comprising the acoustic screen. According to a third aspect, the invention relates to a vehicle assembly comprising an acoustic screen as described above and a motor having a cylinder head, the screen being fixed to the engine cylinder head so as to attenuate the noise nuisances coming from the engine. engine. According to a particular embodiment of the invention, the second face 5 of the second part of the screen comprises at least one fixing means so that the second face 5 is fixed against the cylinder head of the engine. The fixing means of the plastic part of the screen is thus invisible to the user, which improves the aesthetic appearance of the engine with the acoustic screen. According to a fourth aspect, the invention relates to a vehicle fender comprising an acoustic screen as described above. According to a fifth aspect, the invention relates to a method of manufacturing an acoustic screen as described above comprising the following steps: - Cutting the first part according to a pattern of a predetermined shape, - Heating the first part, Positioning of the first part on a matrix of a mold; closing of the mold to effect differential compression of the first part so as to form the acoustic absorption zone and the peripheral zone; injection of a mold; plastic material in the mold creating a second part extending only at the periphery of the first part, being integral with the first part and comprising a covering area arranged so as to cover at least part of the periphery area by overmolding, so as to stiffen the acoustic screen.

Differential compression means that the applied compression is different between the sound absorption zone and the periphery zone of the first part. In particular, the periphery area is further compressed which gives it greater rigidity and facilitates the obtaining of solidarity with the overlap area of the second part during overmolding. Such a method is advantageous in that the formation of the second plastic part is simultaneous with the assembly of the two parts of the screen during overmolding. This allows the reduction of the number of steps and the cycle time compared to the conventional manufacturing method comprising a step of forming the plastic layer followed by another distinct step of assembly with the sub-layer of acoustic absorbing material. The invention will be better understood on reading the description which will follow, given solely by way of non-limiting example and with reference to the drawings in which: FIG. 1 is a schematic illustration of an acoustic screen according to a embodiment of the invention. FIG. 2 is a schematic sectional view illustrating an acoustic screen according to one embodiment of the invention. FIG. 3 is a schematic illustration of a periphery zone comprising a return according to one embodiment of the invention. FIG. 4 is a schematic illustration of a step of heating an acoustic absorbent material to form a first part of an acoustic screen according to one embodiment of the invention. FIG. 5 is a schematic illustration of a positioning of the acoustic absorbent material on a matrix of a mold according to one embodiment of the invention. FIG. 6 is a schematic illustration of a step of differential compression or shaping of the material in a mold according to one embodiment of the invention. FIG. 7 is a schematic illustration of an overmoulding step by injection of a second plastic part in a mold according to one embodiment of the invention. FIG. 8 illustrates a vehicle engine on which an acoustic screen is fixed according to one embodiment of the invention. - Figure 9 illustrates a vehicle rear shelf according to one embodiment of the invention. - Figure 10 illustrates a means of fixing the acoustic screen in which a stud has been arranged. - Figure 11 illustrates a pad adapted to the attachment of the acoustic screen. In these figures, the identical reference numerals designate similar elements. Figure 1 illustrates an acoustic vehicle screen 1 that includes a first portion 2 of acoustic absorbent material and a second portion 3 of plastic material. The second part 3 extends around the periphery of the first part 2 and is integral with it. The acoustic absorbent material may be made of a fibrous material such as a nonwoven fabric material and in particular a felt. This material absorbs at least partly the noise of the vehicle on which it is attached and gives a lightness to the entire screen 1. In fact, the acoustic screen 1 may have a mass per unit area of between 2.8 and 4 kg / m2 which is less than that of a conventional screen consisting of a layer of plastic and a fibrous underlayer. The acoustic absorbent material may also be made of a material such as foam, glass wool or porous rock whose porosity is of open type. The acoustic absorbing material generally consists of a solid skeleton comprising pores filled with air. When the sound wave encounters such material, a generally large first portion of its intensity is reflected, a second, generally very small portion is transmitted through the material and a third portion is absorbed. This absorption consists of a transformation of acoustic energy into mechanical and sometimes calorific energy. The acoustic absorbing material preferably has a low absorption coefficient at low frequencies, which increases in relation to the rise of the frequency. The absorption at low frequencies is all the more important that the material is thick and that its pores or cavities are large. The second part 3 made of plastic material confers rigidity on the whole of the acoustic screen 1 so as to obtain a good mechanical strength especially in the face of the vibrations of the vehicle. The plastic material may be selected from polypropylenes and polyamides 6 or 66, noble or recycled. They may advantageously have 30% of mineral fillers, 20% of mineral fillers and 20% of glass fibers, 10% of mineral fillers and 20% of glass fibers, 20% of mineral fillers and 10% of glass fibers, or still 30% of glass fibers, so as to improve its mechanical properties. Moreover, the rigidity of the second part 3 authorizes it to receive a marking process in order to inscribe a logo or other distinctive sign on a first face 4 of this part, the first face 4 being the visible face for the user when the screen 1 is attached to the vehicle. A second face 5 of the plastic part, opposite to the first face 4, is provided with a fixing means 6 which is then not visible to the user (FIG. 2). FIG. 2 represents a sectional section of the screen 1 which illustrates the thicknesses 7.8 of the first part 2. The first part 2 comprises indeed an acoustic absorption zone 9 having a first thickness 7 and a surrounding zone 11 having a second thickness 8 smaller than the first thickness 7. As shown in Figure 2, the first face 4 of the second portion 3 comprises a covering zone 12 superimposed on the periphery zone 11 of the first portion 2.

Because of the lower second thickness 8 of the periphery zone 11, the superposition with the overlap zone 12 has a smaller thickness than if the superposition was on the acoustic absorption zone 9. The bulk of the Screen 1 is thus limited. The first thickness 7 may for example have a value between 15 to 20 mm while the second thickness 8 may have a value of between 2 to 3 mm. As a result, the superposition of the peripheral zone 11 with the overlap zone 12 of the second plastic part 3, for example having a thickness of 2.5 to 3 mm, does not reach the first thickness 7 of the zone 9. Thus, the fineness of the second thickness 8 reduces the overall size of the screen 1 compared to the size of conventional screens provided with a plastic layer and a sub-layer of fibrous material. As illustrated in FIG. 2, a fixing means 6 of the screen 1 protrudes from the second face 5 of the second plastic part 3 so as to be invisible to the user. Indeed, the first face 4 extended by the overlap zone 12 is disposed on the side location or side visible to the user when the screen 1 is attached to a vehicle. The second face 5, opposite the first face 4, is then located on the non-visible side of the screen 1 so that the fastening means 6 is invisible to the user. FIG. 3 shows an alternative embodiment of the covering 5 of the first part 2 by the second part 3. The surrounding area 11 of a thickness 8 has a return 13 forming an angle of 90 ° on which the covering zone 12 is molded so as to partially cover the surface of the circumferential zone 11. Thus, when the acoustic screen 1 is placed on a vehicle element, the return 13 forms an acoustic barrier for confining the sound waves coming from the vehicle. element and to increase the absorption capacity of the screen 1 at the level of the acoustic absorption zone 9. FIG. 4 represents the first step of the method of manufacturing the acoustic screen 1. The first part 2 made of material Acoustic absorbent was initially cut, for example by punch, so as to obtain the shape according to the desired pattern. As shown in FIG. 4, the first portion 2 is heated to the melting temperature of the binder thermoplastic fibers in order to shape the fibrous material. In FIG. 5, the material is placed on a matrix 14 of an injection mold 15. As shown in FIG. 6, the material is shaped by a differential compression intended to apply a different compression depending on the zones. determined. Thus, the material delimiting the sound absorption zone 9 is little or not compressed and the material constituting the surrounding zone 11 is strongly compressed. As a result, the periphery zone 11 has a thickness 8 which is smaller than the thickness 7 of the acoustic absorption zone 9. The material of the peripheral zone 11 then has a higher density, which leads to forming a more rigid area and facilitates solidarity with the second part 3 plastic. In addition, the smaller thickness 8 of the peripheral zone 11 makes it possible to reduce the final thickness after covering by the second plastic part 3. In FIG. 7, the plastic material is injected into the mold 15 in order to manufacture the second portion 3 of the screen 1 equipped with a covering zone 12 intended to cover the peripheral zone 11 of the first part 2 by overmolding.

FIG. 8 illustrates a vehicle assembly 16 comprising an engine having a cylinder head 17 on which the acoustic screen 1 is fixed so as to absorb the acoustic waves during operation of the engine. FIG. 9 shows a rear shelf 18 comprising an acoustic screen 1, the frame of the tablet being formed by the second part 3 and the pencil case being formed by the first part 2. FIG. 10 represents a fastening means 6 which protrudes of the second part 3 on the invisible face 5 of the user when the acoustic screen 1 is fixed by the pad 19 to the vehicle.

FIG. 11 illustrates a stud 19 adapted to fit into the fastening means 6 of the acoustic screen 1. Thus, the present invention provides a decisive improvement to the state of the prior art by providing a screen 1 having a first part 2 of acoustic absorbing material and a second part 3 of plastic material extending around the periphery of the first part 2 so as to provide a high performance, lightened, rigid acoustic screen 1 capable of supporting a marking process and whose fastening means 6 is invisible to the user. This screen 1 is also manufactured by a manufacturing process with few steps and a small cycle time.

It goes without saying that the invention is not limited to the embodiments described above as examples but that it includes all the technical equivalents and variants of the means described as well as their combinations.

Claims (11)

REVENDICATIONS1. Acoustic screen (1), in particular intended for vehicles, comprising: - a first part (2) made at least partly of an acoustic absorbent material, for example of fibrous material, the first part (2) comprising an acoustic absorption zone (9) of a first thickness (7) and a periphery zone (11) of a second thickness (8), the second thickness (8) being smaller than the first thickness (7), - and a second part (3) consisting of a plastic material extending only at the periphery of the first part (2), the second part (3) being integral with the first part (2) and having a covering area (12) arranged so as to cover at least part of the surrounding area (11), so as to stiffen the acoustic screen (1). 2. Acoustic screen (1) according to claim 1 characterized in that the periphery zone (11) has a return (13) forming an angle of between 30 and 90 ° with respect to the mean plane of the acoustic absorption zone ( 9). 3. Acoustic screen (1) according to one of claims 1 to 2 characterized in that the periphery zone (11) has an acoustic absorbing material of a density greater than the density of the material of the acoustic absorption zone. (9). 4. Acoustic screen (1) according to one of claims 1 to 3 characterized in that the second portion (3) of plastic material is adapted to receive a marking method. 30 5. Acoustic screen (1) according to one of claims 1 to 4 characterized in that the acoustic screen (1) comprises at least one means (6) for fixing the screen (1) to a vehicle, the means fixing piece (6) being integral with the second part (3) and protruding from a face (5) of the second part (3). 25 6. Acoustic screen (1) according to one of claims 1 to 5 characterized in that the acoustic absorbent material is made of a fibrous material such as a nonwoven fabric material and in particular a felt. 7. Acoustic screen (1) according to one of claims 1 to 6 characterized in that the plastic material is selected from polypropylenes and polyamides 6 or 66, noble or recycled, comprising between 0 and 30% mineral fillers and 0 30% glass fibers. 8. Acoustic screen (1) according to one of claims 1 to 7 characterized in that the acoustic screen (1) has a mass per unit area of between 2.8 and 4 kg / m2. 9. Vehicle rear shelf 18 characterized in that it comprises an acoustic screen (1) according to one of claims 1 to 8, the frame of the rear shelf (18) being formed by the second portion (3) of a plastic material and the pencil case of the rear shelf (18) being formed by the first part (2) of acoustic absorbing material. 10. Assembly (16) for vehicle characterized in that it comprises an acoustic screen (1) according to one of claims 1 to 8 and a motor with a yoke (17), the screen (1) being fixed at the cylinder head (17) of the engine. 11. A method of manufacturing an acoustic screen (1) according to one of claims 1 to 8 characterized in that the method comprises the following steps: - Cutting the first part (2) according to a pattern of a shape predetermined, - heating the first part (2), - positioning the first part (2) on a die (14) of a mold (15), - closing the mold (15) to perform a differential compression of the first portion (2) so as to form the acoustic absorption zone (9) and the periphery zone (11), - injecting a plastic material into the mold (15) creating a second portion (3) extending only at the periphery of the first part (2), being integral with the first part (2) and comprising a covering zone (12) arranged so as to cover at least part of the peripheral zone (11), so as to rigidify the acoustic screen (1).