FR2901209A1 - Sound proofing screen for motor vehicle, has housing in its reverse side to form spacing zone between side and wall, where side has geometry corresponding to geometry of wall to take on wall`s shape - Google Patents

Abstract

The screen (1) has a housing (4) in its reverse side (3) to form a spacing zone between the side and a wall (2). The side has a geometry corresponding to geometry of the wall to take on wall`s shape, where the screen is formed with base of porous material. A body (6) is made with base of glass fiber mat or cotton felt. The glass fiber mat or cotton felt has a surface volume between 400 and 1800 grams per meter cube and an air passage resistance between 200 and 3000 Newton second per meter cube.

Description

The invention relates to a vehicle engine soundproofing screen

automobile.

  It is known to make such screens according to several arrangements.

  Firstly, the screens comprising a thin rigid structure, in particular made of injected plastic material or aluminum, said screen being generally associated with the motor by means of decoupling pads, for example based on elastomer, intended to prevent transmission of engine vibrations to the screen. This structure is generally associated with an acoustic absorbent, in particular based on felt or foam, on the reverse face of the structure, that is to say opposite the engine.

  This solution is quite effective but poses problems of space and peripheral acoustic leakage, this because of the existence of a game between the screen and the engine, and acoustic radiation at low and medium frequencies, related to the compromise to achieve between decoupling and mechanical strength or the impossibility of decoupling due to thermal stresses.

  In addition, the attachment of the screen by means of pads complicates the mounting operation and leads to additional costs.

  Finally, the standards in force, relating to the protection of pedestrians in the event of impact against the bonnet, require leaving a large space, of the order of 50 to 70 mm for example, between the bonnet and any rigid element disposed below. , and in particular a screen as described above. The presence of the game as described before goes against such requirements, if not at the cost of raising the hood.

  Mention will also be made of screens based on a principle of mass / spring type insulation, such screens being placed directly on the motor and matching the geometry of the motor. A screen thus produced may for example comprise a spring layer based on compressed glass felt and a heavy aluminum-based layer of mass.

  This solution is also relatively effective, but it generally poses low and medium frequency radiation problems related to the rigidity of the screen and mass / spring behavior.

  The invention aims to overcome the aforementioned drawbacks by providing a screen to minimize acoustic leakage, to eliminate the use of decoupling pads, to enlarge the space between the cover and the screen to meet the standards of safety in the event of a pedestrian impact and limit radiation at low and medium frequencies while offering the best cost / weight / efficiency compromise.

  For this purpose, the invention proposes a soundproofing screen intended to be arranged against a motor vehicle engine wall, the geometry of the backside of said screen corresponding substantially to that of said wall so as to be able to match the form, said screen being formed based on porous material.

  Acoustic noise leakage from the engine is minimized, since the screen is placed on the engine. In addition, the use of decoupling pads is removed, since the screen is based on the engine. In addition, the space between the hood and the screen is enlarged, which makes it possible to meet safety standards in the event of a pedestrian impact. Finally, the absence of a waterproof layer makes it possible to reduce radiation at low and medium frequencies.

  In this description, the terms of positioning in the space (location, upside down, ...) are taken with reference to the screen disposed in the vehicle. Other features and advantages of the invention will appear in the description which follows, made with reference to the attached figure showing a schematic section 3 of a screen according to one embodiment of the invention, said screen being placed on the surface superior of a motor vehicle engine.

  With reference to the figure, we now describe a soundproofing screen 1 intended to be disposed against a motor vehicle wall 2, the geometry of the rear face 3 of said screen substantially corresponding to that of said wall of so as to be able to marry the shape, said screen being formed based on porous material.

  According to the embodiment shown, the screen 1 comprises at least one housing 4 in its backside 3, so as to form a spacing zone between said backside face and the wall 2. Such an embodiment allows to locally create a space between the screen 1 and the engine 5, which may be essential for the proper functioning of said engine, for example in line with the injectors.

  According to one embodiment, the screen comprises a body 6 based on glass or cotton felt, bound for example by a phenolic resin, said felt being shaped for example by thermoforming or molding, with a mass per unit area in particular between 400 and 1800 g / m2 and resistance to the passage of air including between 200 and 3000 Nsm-3.

  Alternatively, the screen 1 may comprise a body 6 based on foam, in particular based on polyurethane foam, shaped for example by thermoforming or molding, resistance to the passage of air including between 200 and 3000 Nsm -3.

  According to one embodiment, the screen 1 has at least one zone of increased density 7 so as to form stiffening zone. Such a zone 7 can be obtained, in the case of a thermoformed felt-based body, by localized compression of said felt during its shaping. Such a zone 7 may be arranged for example facing the housing 4 previously mentioned, so as to locally guarantee the free standing of the screen 1 and its non-contact with the engine 5. 4

  According to the embodiment shown, the body 6 is covered, on its location face, with a protective layer of porous area 8, resistance to the passage of air, for example less than 500 Nsm "3. shown, the body 6 is covered on its back side 3 with a porous backing layer 9.

  In one embodiment, the protective layer 8, 9 is based on a nonwoven material, for example with a basis weight of the order of 100 g / m 2, such a material having a very low resistance to the passage of air.

  According to a particular embodiment, having a good cost / weight / acoustic efficiency compromise, a screen 1 disposed on the upper wall 2 of an engine 5 may comprise a nonwoven backing layer 9 of 30 g / m2, a body made of glass felt of 1200 g / m2 and thickness of 5 to 15 mm for resistance to the passage of air from 900 to 1400 Nsm-3, and a protective layer of place 8 in non-woven 100 g / m2 and resistance to the passage of air 100 Nsm "3. Such an embodiment avoids the introduction of decoupling pads, so reduce congestion and leakage Compared to mass / spring type screens, it greatly reduces the radiation problems at low and medium frequencies.Although the screen is, by nature, an absorbing screen, it still offers a potential for isolation This insulation is defined mainly by the thickness and resistivity to the passage of air of the absorbent material.

  The theoretical insulation at the base material of the screen 1 is lower than that of the prior art concepts. However, the actual performance of the screens of the prior art are often much lower than one would expect, this notably because of the peripheral acoustic leakage and the radiation of the screens.

  In fact, the insulation provided by a screen 1 according to the invention, measured on 5 motor, is: • at medium high frequencies, close to that of the screens known in the prior art, • at medium / low frequencies, greater than that of the screens known in the prior art, this due to the suppression of radiation.

  Another significant advantage of this type of screen 1 is the increase of the final absorption in the semi-closed volume formed by the engine compartment, this due to the absence of waterproof layer in place, which has an acoustic impact favorable, both in terms of acoustic protection vis-à-vis the cabin and vis-à-vis the outside of the vehicle.

  A screen 1 according to the invention can be used, in addition to facing the upper wall 2 of the engine 5, in parts such as the oil tank, the pulley cover, etc.

Claims (9)

  1. soundproofing screen (1) intended to be arranged against a motor vehicle wall (2) (5), the geometry of the backside (3) of said screen corresponding substantially to that of said wall so to be able to marry the shape, said screen being formed based on porous material.   2. Screen according to claim 1, said screen comprising at least one housing (4) in its backside (3), so as to form a spacing zone between said backside face and the wall (2).   3. Screen according to one of claims 1 or 2, said screen comprising a body (6) based on glass or cotton felt.   4. Screen according to claim 3, the felt having a density of between 400 and 1800 g / m2 and a resistance to the passage of air of between 200 and 3000 N.s.m-3. 20   5. Screen according to claim 1 or 2, said screen comprising a body (6) made of foam resistance to the passage of air between 200 and 3000 N.s.m-3.   6. Screen according to any one of claims 1 to 5, said screen 25 having at least one zone (7) of increased density so as to form stiffening zone.   7. Screen according to any one of claims 1 to 6, the body (6) being covered, on its side of the place, a protective layer of place (8) porous. 15 7   8. Screen according to any one of claims 1 to 7, the body (6) being covered on its back side (3), a porous backing layer (9).   9. Screen according to claim 7 or 8, the protective layer (8,9) being based on nonwoven.