CA2556199A1 - Light weight noise absorption system - Google Patents

Abstract

A noise absorption assembly (20) has a first layer (24) and second layer (26) adhered to the first layer. The first is formed from a polymeric fibrous material that includes mixture of first and second fiber (25, 27) for absorbing the transmission of sound. The second layer (26) is formed form a non-woven polymeric material for providing a barrier to prevent the transmission of sound.

Description

LIGHT WEIGHT NOISE ABSORPTION SYSTEM
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional application serial number 60/544,938 filed February 13, 2004.
BACKGROUND OF THE INVENTION
1. Field of the Invention [0002] The invention relates generally to the field of noise absorption assemblies for use in motor vehicles.
2. Description of the Prior Art (0003] In the increasingly competitive vehicle market, vehicle manufacturers have strived to reduce the amount of noise transmitted into the passenger compartment from both the road and the engine powering the vehicle.
The most common method of stopping this noise transmission is through the addition of .
high mass sound deadeners affixed to both the floor pan, and the fire wall separating the passenger compartment from the engine compartment. The historical problem with this strategy is that these noise dampeners add a significant amount of mass to the vehicle which reduces the average miles per gallon rating of the vehicle.

[0004] The primary method of blocking noise transmission from the engine compartment into the passenger compartment is through the installation of an interior dash mat that is generally positioned between the instntment panel and the firewall of the vehicle. These dash mats have primarily been manufactured from a layer of, urethane foam that is laminated to a heavy plastic or rubber barrier. The urethane foam abuts the firewall to absorb vibrational noise from the ~rewall while the barrier prevents most of the noise transmitted from the engine compartment from reaching the passenger compartment by blocking the transmission of sound.

[0005] This type of interior dash mat has provided adequate noise reduction in the passenger compartment but has presented many drawbacks.
First, this dash mat adds a significant amount of mass to the vehicle. Second, a dash mat typically covers the entire firewall and toe pan area of the floor plan. Due to the size and mass of the dash mat, it is very,, difEcult to install in an accurate location within the vehicle and usually requires multiple people for installation. The installation _-- 1 process has required various types of fastening devices including, weld studs, insertion fasteners, and clips. Occasionally, the dash mat is attached first to the instrument panel prior to installing the instrument panel into the vehicle, which has resulted in problems with installing the instrument panel into the vehicle. In an effort to reduce the mass of these interior dash mats, light weight materials have been undergoing development to create a low mass dash mat, but have not yet obtained wide scale acceptance in the automotive industry.

[0006] One such low mass dash mat that has been tested is formed from dual density cotton. A first layer of cotton having a Erst areal mass and a second layer of cotton having a second areal mass is laminated to the first layer of cotton using adhesives. Typically, the areal mass of the second layer is approximately 1828 g/m2. An additional layer, consisting of an airflow film, is also adhered to the cotton layers to provide a barrier for preventing the flow of air through the dual density cotton of the dash mat. Preventing the flow of air through the dual density cotton is required just to approach near the amount of noise reduction achieved by conventional dash mats. An alternative to cotton has been attempted using dual density polyester.
In this type of dash mat, a first layer of polyester having a first density and a second layer of polyester having a second density is laminated to the first layer and an airflow film is attached to the polyester layers prevent the flow of air through the dash mat.

[0007] These new types of dash mats have proven to be lighter than conventional dash mats, and it is believed that further mass savings can still be achieved. Additionally, it is believed that the noise reduction achieved by these new types of dash mats can still be improved upon while reducing cost and complexity.
SUMMARY OF THE INVENTION AND ADVANTAGES

[0008] The present invention relates to a noise absorption assembly comprising a first layer and a second layer. The first layer includes a mixture of first fibers having a first melting temperature and second fibers having a second melting temperature greater than the first melting temperature with the first fibers interwoven with the second fibers. The first fibers are fused to the second layer for holding the first layer to the second layer while maintaining the second fibers free of the second layer.

[0009] The subject invention also provides a method of malting a noise absorption assembly having a first layer and a second layer. The first layer includes a mixture of first fibers with a first melting temperature and second fibers with a second melting temperature greater than the first melting temperature. The method includes the steps of overlaying the first layer onto the second layer to form a sub-assembly and melting the first fibers of the first layer by raising the temperature of the sub-assembly to a bonding temperature between the first and the second temperatures to fuse the first fibers to the second layer without melting the second fibers.

[0010] Accordingly, it would be . advantageous to have a noise absorption assembly which is light weight to provide a mass savings while providing significant noise reduction. Additionally, it would be advantageous to have a noise absorption assembly that is easier to manufacture while being light weight to improve the installation of the assembly into the vehicle. To solve these problems, the noise absorption assembly is constructed using light weight polymeric materials to form the layers of the assembly while having good noise absorption and airflow resistivity properties to reduce the transmission of noise.
BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0012] Figure 1 is a perspective view of a noise absorption assembly for a vehicle;

[0013] Figure 2 is a partial cross-sectional side view of the noise absorption assembly; and [0014] Figure 3 shows a scatter-graph of a sound absorption coefficient relative to the frequency of noise as produced by the absorption assembly.
DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring to the Figures, wherein lilce numerals indicate corresponding parts throughout the several views, a noise absorption assembly is shown generally at 20. The noise absorption assembly 20 is used in any application that requires the absorption of noise. One such application is an interior dash mat 22 for reducing the .level of noise transmitted into a passenger compartment of a vehicle from either the road or the engine through a floor pan (not shown) or firewall (not shown).

[0016] The noise absorption assembly 20 includes a first layer 24 and a second layer 26. The first layer 24 provides stiffness and noise absorption properties for the assembly 20. Stiffness of the assembly 20 is desired for maintaining the assembly 20 in a desired three-dimensional shape. The first layer 24 includes a mixture of first fibers 25 having a first melting temperature and second fibers 27 having a second melting temperature greater than the first melting temperature. The first fibers 25 are interwoven with the second fibers 27.
Preferably, the fibers 25, 27 are polyester with the second fibers 27 being more flexible than the first fibers 25. These fibers 25, 27 also act to absorb noise through the assembly 20.
The second layer 26 provides a barrier providing air resistivity for preventing the transmission of noise through the assembly 20.

[0017] The first layer 24 has an areal mass in the range of 430 g/mz to 1290 g/m2 and an initial thickness in the range of 20 mm to 35 mm. A first layer 24 having an areal mass of 484 glm2 is represented in Figure 3. The second layer 26, which is formed from a non-woven mixture of polyester and rayon, has an areal mass in the preferred range of generally 90 g/m2 to 110 g/m2 and a thiclcness in the range of 0.5 mm to 2.0 mm. Additionally, the second layer 26 is generally imperforate and has an airflow resistivity in the range of 700 Rn/m3 to 800 Rnm3, which is lcnown to reduce sound transmission. A second layer 26 having an areal mass of 100 g/m2 is represented in Figure 3. The low areal mass of the second layer 26, combined with the high airflow resistivity, functions to limit airflow through the assembly 20.
Limiting airflow through the assembly 20 reduces the amount of noise that is transmitted.

[0018] The noise absorption assembly 20 is constructed by overlaying the first layer 24 onto the second layer 26 to form a sub-assembly. If an assembly 20 requires additional bonding strength between the layers, an adhesive is applied in addition to fusing the first fibers 25 to the second layer 26 between the first and the second layers 24, 26. However, this is not required. The sub-assembly is then inserted into a press. The temperature of the press is heated to a bonding temperature between the first and the second melting temperatures of the fibers. The bonding temperature is sufficient to melt only the first fibers 25 while not melting the second fibers 27 or any other layer 24, 26 of the sub-assembly.

[0019] After the sub-assembly is inserted into the press, the press is closed. When the press is closed, the press compresses and applies heat; at the bonding temperature, to the layers 24, 26 of the sub-assembly. The press is essentially a three-dimensional mold for shaping the sub-assembly to the contours of the desired location of the vehicle. As the press applies the bonding temperature and compression to the layers 24, 26 of the sub-assembly, the first fibers 25 of the first layer 24 melt and fuse to the second layer 26. Additionally, because the first fibers 25 are melted and mixed throughout the first layer 24, the first layer 24 compresses to conform to the three-dimensional shape of the press. For example, the first layer 24 is compressed to form strengthening ribs 28, for providing additional stiffness to the assembly 20, or indents 30, for providing clearance to various vehicle components.
By virtue of the fusion between the first and the second layer 24, 26, the entire assembly 20 takes on the three-dimensional shape of the press. Therefore, the sub-assembly is compressed and permanently deformed into any desired three-dimensional form.

[0020] The first fibers remain fused to the second layer 26 or in the compressed state once they are cured. The first fibers 25 cure when their temperature drops below the first melting,temperature and solidify to a state more rigid than the second fibers 27. After the sub-assembly is compressed and heated to form the desired three-dimensional assembly 20, the melted first fibers of the first layer 24 are cured. Chilling the sub-assembly to cure the first fibers 25 of the first layer 24 improves the cycle-time of producing the noise absorption assembly 20 by accelerating the time it takes to cool the first fibers 25. Once the melted first ftbers 25 are cured, the first fibers 25 are fused to the second layer 26 of material and permanently maintain the three-dimensional shape of the assembly 20 by virtue of the fusion between the layers 24, 26 and the reformation of the first fibers 25.
Additionally, because the second fibers 27 do not melt order application of the bonding temperature to the sub-assembly, and the second fibers 27 are interwoven with the first fibers 25, the second fibers 27 are maintained free of the second layer __, 5 26. Thus, in addition to providing strength to the assembly 20, the second layer 26 is capable of absorbing noise.

[0021] Additionally, holes 32 and openings 34 are formed through the assembly 20 to provide clearance for vehicle components. One way that the holes 32 and openings 34 are formed is by using a water jet. However, other methods of forming openings 34 can also be used, such as, for example, piercing in a die press.

[0022] To provide an assembly 20, with even greater noise absorption properties, a layer of closed-cell polymer foam (not shown) is fused to the first layer 24, in addition to the first layer 24 being fused to the second layer 26. The closed-cell foam layer can be adhered to the first layer 24 when the first fibers 25 are fused to the closed-cell foam layer for holding the first layer 24 to the closed-cell foam layer while maintaining the second fibers 27 free of the closed-cell foam layer. A layer of closed-cell foam provides additional benefits by providing an added barrier of air flow resistance.

[0023] To provide additional stiffness to the assembly ~ 20, a scrim layer (not shown) is optionally adhered to the first andlor the second layer 24, 26.
Preferably, the scrim layer is placed on the appropriate layer 24, 26 of the sub-assembly prior to the sub-assembly being placed in the press. When the scrim layer is adhered to the first layer 24, the first fibers 25 are fused to the scrim layer for holding the first layer 24 to the scrim layer while maintaining the second fibers 27 free of the scrim layer. However, adhesive may also be used to fuse the scrim layer to the assembly 20. In addition to providing additional thickness, the scrim layer is used as a protective sheet for the first or the second layer 24, 26.
[0024] Due to the assembly 20 being light weight, fasteners are not required for attachment of the assembly 20 into the vehicle. Preferably, the assembly 20 is attached to the vehicle using an adhesive, such as a double-sided tape 38 or glue.
Additionally, the assembly 20 is installed into the vehicle by a single person.

[0025] While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the . __ _-_ 6 invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
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Claims (32)

1. ~A noise absorption assembly comprising;
a first layer including a mixture of first fibers having a first melting temperature and second fibers having a second melting temperature greater than said first melting temperature with said first fibers interwoven with said second fibers, a second layer, and said first fibers fused to said second layer for holding said first layer to said second layer while maintaining said second fibers free of said second layer.

2. ~An assembly as set forth in claim 1 wherein said second fibers are more flexible than said first fibers

3. ~An assembly as set forth in claim 1 wherein said first layer has a larger areal mass than said second layer.

4. ~An assembly as set forth in claim 3 wherein said second layer has an areal mass in the range of 90 g/m2 to 110 g/m2.

5. ~An assembly as set forth in claim 3 wherein said first layer has an areal mass in the range of 430 g/m2 to 1290 g/m2.

6. ~An assembly as set forth in claim 5 wherein said first layer has an areal mass in the range of 430 g/m2 to 645 g/m2.

7. ~An assembly as set forth in claim 1 wherein said first and said second fibers are polyester.

8. ~An assembly as set forth in claim 1 wherein said first layer has a thickness in the range of 20 mm 35 mm.

9. ~An assembly as set fouth in claim 1 wherein said second layer has an airflow resistivity in the range of 700 Rn/m3 to 800 Rn/m3.

10. ~An assembly as set forth in claim 1 wherein said second layer is formed from a non-woven mixture of polyester and rayon.

11. ~An assembly as set forth in claim 1 wherein said second layer has a thickness in the range of 0.5 mm to 2.0 mm.

12. ~An assembly as set forth in claim 1 further including a scrim layer adhered to said first layer.

13. ~An assembly as set forth in claim 12 wherein said first fibers are fused to said scrim layer for holding said first layer to said scrim layer while maintaining said second fibers free of said second layer.

14. ~An assembly as set forth in claim 1 further including a third layer adhered to one of said first or said second layers.

15. ~An assembly as set forth in claim 14 wherein said third layer is comprised of closed-cell foam.

16. ~A method of making a noise absorption assembly, having a first layer including a mixture of first fibers with a first melting temperature and second fibers with a second melting temperature greater than the first melting temperature and a second layer including the steps of;
overlaying the first layer onto the second layer to form a sub-assembly and melting the first fibers of the first layer by raising the temperature of the sub-assembly to a bonding temperature between the first and the second temperatures to fuse the first fibers to the second layer without melting the second fibers.

17. ~A method as set forth in claim 16 wherein the step of melting further includes the step of curing the first fibers to a state more rigid than said second fibers.

18. ~A method as set forth in claim 17 wherein the step of curing is further defined as chilling the sub-assembly to solidify the first fibers.

19. ~A method as set forth in claim 18 further including the step of applying a scrim layer over the first layer.

20. ~A method as set forth in claim 16 further including the step of inserting the sub-assembly into a press.

21. ~A method as set forth in claim 20 further including the step of compressing the sub-assembly in the press to form a three-dimensional assembly.

22. ~A method as set forth in claim 21 further including the step of piercing the sub-assembly to form holes in the assembly.

23. ~A noise absorption assembly comprising:
a first layer formed from a polymeric fibrous material including a mixture of first fibers having a first melting temperature and second fibers having a second melting temperature greater than said first melting temperature with said first fibers interwoven with said second fibers for absorbing the transmission of sound; and a second layer formed from a non-woven polymeric material and adhered on said first layer with said second layer being generally imperforate for providing a barrier to prevent the transmission of sound.

24. ~An assembly as set forth in claim 23 wherein said first layer has a thickness in the range of 20 mm to 30 mm.

25. ~An assembly as set forth in claim 23 wherein said second layer has an airflow resistivity in the range of 700 Rn/m3 to 800 Rn/m3.

26. ~An assembly as set forth in claim 23 wherein said second layer has a thickness in the range of 0.5 mm to 2.0 mm.

27. ~An assembly as set forth in claim 23 wherein said polymeric fibrous material of said first layer is polyester.

28. ~An assembly as set forth in claim 23 wherein said non-woven polymeric material of said second layer is rayon and polyester.

29. ~An assembly as set forth in claim 23 wherein said first layer has a larger areal mass than said second layer.

30. ~An assembly as set forth in claim 29 wherein said second layer has an areal mass in the range of 90 g/m2 to 110 g/m2.

31. ~An assembly as set forth in claim 29 wherein said first layer has an areal mass in the range of 430 g/m2 to 1290 g/m2.

32. ~An assembly as set forth in claim 31 wherein said first layer has an areal mass in the range of 430 g/m2 to 645 g/m2.