FORM 2
THE PATENT ACT, 1970, (39 OF 1970)
& THE PATENTS RULE, 2003
PROVISIONAL SPECIFICATION
"Noise barrier structure for passenger compartment of an automotive vehicle"


Mahindra & Mahindra Limited An Indian Company, R&D Center, Automotive Sector, 89, M.I.D.C, Satpur, Nashik-422 007, Maharashtra, India.

The following specification describes the nature of the invention


Field of the Invention:
The present invention relates to noise barrier structure for automotive vehicles. More, particularly the present invention relates to the noise barrier structure for passenger compartment of an automotive vehicle to improve the silence characteristics in passenger compartment.
Background & Prior Art Search:
The modern automotive vehicles are becoming quieter and quieter by introduction of effective interiors. Of these interior parts dash inner insulation, carpet and the headliner plays a vital role in improving the silence characteristics of the vehicle.
Noise, vibration and harshness characteristics of the passenger compartment have been able to be obtained with the conventional structure of the dash insulator and the floor carpet. However, in order to obtain the highei- silence characteristics of the passenger compartment it is essential to increase the amount of sound absorbable materials in the dash insulator and the floor carpet. For example, in case of dash insulators and floor carpet the amount of high density layers are required to increase. However, by thus merely increasing the amount of sound absorbable materials, the weight of the interior parts is increased, which is very disadvantageous or not desirable.
American patent No. US.5817408 relates to a sound insulating structure including low-density and high density layers. The low density layer has first and second fibrous layers made of thermoplastic synthetic fibers. . The high density layer is formed on the low-density layer and is made of an air-impermeable polymer material and has a surface density that is higher than that of the low-density layer. The low density layer is high in sound-absorption coefficient and at the same time low in spring constant.
United Kingdom patent No. GB.2322862 discloses fibrous sound-proofing material for reducing noise transmission. This fibrous acoustical material comprises first, second and third fibers. The first fiber has first fineness of 1.5-20 deniers and a first softening point. The second fiber has a second fineness of 1.5-15 deniers. The third fiber has a third fineness of 1.5-15 deniers. The first, second anq third fibers are respectively in amounts of 10-90 wt%, 5-85 wt% and 5-85 wt% based on a total weight of the first, second and third fibers. The fibrous acoustical material is light in weight and superior in acoustical capability, heat resistance and resistance to compressive force.
2

This invention talks about the process by which a fibrous material is manufactured by using the different fiber deniers, and does not talk about the layers. It educates on the chemical composition and how the material can be processed by using different deniers and not on the formation of the layers and its function. The application area of the same is on the floor insulator and the trunk carpet insulation.
American patent No. US.6102465 describes noise insulating structure for a passenger compartment of an automotive vehicle comprising first, second and third sound absorbing material which are disposed respectively to a head lining, a dash insulator and a floor carpet disposed in the passenger compartment. The first sound absorbing material is capable of absorbing sound within a first frequency range of from 0.8 to 10 KHz. The second sound absorbing material is capable of absorbing sound within a second frequency range of from 0.3 to 2 KHz. The third sound absorbing material is capable of absorbing sound within a third frequency range of from 0.1 to 1 KHz. Each sound absorbing material is formed of a unshaped polyester fiber mixture which is prepared by mixing polyester (main) fibers and binder fibers for bonding the polyester fibers to each other.
The drawback of this invention is that the there is only a single layer of heavy mass and the performance in the mass law region would not be effective for the reason in the above section. If we need to enhance the performance of the material used in this invention, the surface weight of the heavy mass needs to be enhanced which would increase the overall weight of the insulator which is not advantageous.
Thus, none of the prior art concept talks about multi-layered noise absorbing structure having one absorber and two or more sound barriers of different densities.
Objects of the Present Invention:
The main object of the invention is to provide an improved noise barrier structure for a passenger compartment of a vehicle.
Another object of the present invention is to provide an improved multi-layered noise barrier structure with dual density for the passenger compartment of the vehicle.
Another object of the present invention is to provide an improved multi-layered noise barrier structure for the passenger compartment of the ;-vehicle,. which suppresses the weight of the interior parts to a minimum level and can achieve improved silence characteristics of the passenger compartment.


Another object of the present invention is to provide noise insulating structure with a dual density barrier keeping the weight lesser than that of the conventional barrier like EVA and with increased thickness
Still another object of the present invention is to provide an improved noise barrier structure for the passenger compartment of the vehicle with enhanced sound transmission loss characteristics.
Still further object of the present invention is to overcome the drawbacks encountered in the conventional noise insulating structure available in prior art.
Description of the Figures:
The objectives, features and advantages of the present invention will become apparent from the following description and claims and from the accompanying drawings wherein,
Figure 1 shows fragmentary sectional view of the conventional noise barrier used in dash panel of an automotive vehicle.
Figure 2 shows fragmentary sectional view of the conventional noise barrier used in floor carpet of an automotive vehicle.
Figure 3 shows fragmentary sectional view of dual density noise barrier used in dash panel of an automotive vehicle in accordance with the present invention.
Figure 4 shows fragmentary sectional view of dual density noise barrier used as floor carpet of an automotive vehicle in accordance with the present invention.
Figure '5 shows performance comparison of dual density noise barrier with conventional means.
Detailed Description of the Present Invention:
Referring to Fig. 3, the noise barrier structure (1) of the present invention used on inner dash panel (P1) of an automotive vehicle comprises of three layers namely an absorber (2) and two heavy mass layers or noise barrier layers (3 & 4) of different densities. The combined layer of barrier (3) and barrier (4) is termed as 'dual density layer'. Thus, the present invention focuses on a novel noise barrier structure comprising at least three layers namely low density layer (2), medium density layer (3) and high density layer (4).
4

The absorber layer (2) is primarily made fronvmateria is like polyurethane foam, felt and like materials. The heavy mass (barrier) layers (3 & 4) in the present invention are made of different material of different density. The barrier layer (3) is higher in thickness and is made of hard felt and like material. The barrier iayer (4 is of low) thickness as compared to barrier layer (3) and is made of EVA (Ethyl Vinyl Acetate). Thus, a typical noise barrier structure in the present invention will constitute of an absorbing layer (2) and the mass backed layers or noise' barrier layers (3 & 4).
The primary function of the absorbing layer (2) is to absorb the sound energy by converting it to heat energy. The absorbing layer (2) is porous in nature and can be cellular or fibrous capable of absorbing ■ the sound energy. The performance or efficiency of the absorber layer (2) is measured by a term known as absorption coefficient, which is the ratio of the amount of sound energy absorbed to the total amount of sound energy impinged on the material. The absorber performance is the function of frequency. When a noise wave impinges on the absorber material/layer (2),
the molecules are entrapped in the porous structure and due to the friction the energy
dissipation takes place.
The performance of the absorber (2) mainly depends on the density and the thickness of the material used. The thickness is mainly driven by the packaging point of view and always there is a limit for thickness from the cost and weight point of view. Hence an absorber (2) should be always integrated with the heavy mass layers or noise barrier layers (3 & 4) to improve the efficiency of the noise barrier structure (1). Typical working range of the absorber (2) in the automotive passenger cabin is above 400 Hz and the acoustic energy impinging on it is mainly airborrne noise in the nature.
Heavy mass barrier or noise barrier layer is a combination of high density layer (4) made of Ethyl Vinyl Acetate (EVA) and medium density layer (3) made of the Hard Felt. For heavy mass layer which is the combination of layer (3) and layer (4), the performance measurement parameter is sound transmission Loss (dB). Sound transmission loss is defined as the ratio of the Sound energy transmitted through the surface to the sound energy incident on the surface. Apart from the surface weight the thickness of the barrier plays a vital role in providing tne resistance to the noise from entering into the passenger cabin. The thickness and the surface weight will define the mass law region, the region where barrier works effectively and mass law states that for every doubling the thickness the sound transmission loss would increase by 6 dB.
5

The unit weight of the low density layer (2) varies from 0.8 to 1.0 kg/m2 and thickness of 5 to 20 mm. The unit weight of medium density layer (3) varies from 1.2 to 2.0 kg/m2 and thickness of 2 to 5 mm. The unit weight of high density layer (4) varies from 1.5 to 3.0 kg/m2 and the thickness of 1 to 3 mm. In the present invention Surface - weight of the hard felt / medium density layer (3) is 1000 gsm with thickness of 6 mm and the surface weight of high density layer / EVA (4) is 1500 gsm with thickness of 1.2 mm: This gives the total thickness of about 7.2 mm for combined noise barrier / heavy mass layer and the total weight of 3 to 4 kgs for inner dash panel of an automotive vehicle. By enhancing the thickness by two times the performance in the mass law region also can be enhanced as shown in Figure 5.
In another embodiment of the invention, the noise barrier structure (1) as disclosed above is used as floor carpet as shown in Figure 4 wherein floor panel (P2) of an automotive vehicle comprises of three layers namely an absorber (12) and two heavy mass layers or. noise barrier layers (13 & 15) of different densities. The barrier layer (13) is higher in thickness and is made of hard felt and like material. The barrier layer (15) is of low thickness as compared to barrier layer (13) and is made of EVA (Ethyl Vinyl Acetate).
The noise barrier structure as disclosed above can be effectively used in bonnet insulation, floor carpet insulation, roof application and like area apart from dash insulation (inner and outer) to achieve silence characteristics inside the passenger compartment.
Advantages of the Present Invention:
• Overall weight reduction is achieved by 50%.
• Enhanced acoustic performance and improved silence characteristics in the passenger compartment are achieved.
• The structure has wide application area in the automotive field.
Dated this 20th Day of February 2009

A.A.Kirpekar (Agent for the applicant)