FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13)
1. Title of the invention: NOISE REDUCTION IN VEHICLE TIRE
2. Applicant(s)
NAME NATIONALITY ADDRESS
CEAT LIMITED Indian RPG HOUSE, 463, Dr. Annie Besant Road, Worli, Mumbai, Maharashtra 400 030, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

TECHNICAL FIELD
[001] The present subject matter relates, in general, to vehicle tires and,
particularly but not exclusively, to noise reduction in vehicle tires.
BACKGROUND
[002] Tires support load of a vehicle and impact handling, drivability, and
safety of the vehicle. A tire has a crown or center region, a shoulder region and beads on either side of the center region. In an example, the center region may be understood as outer region of the tire formed along complete circumference of the tire that spreads along width of the tire. The center region contacts with surface during rotation. The beads may be understood as edges of the tire. The beads contact with rim when the tire is mounted in the vehicle. The shoulder region is portion of the tire joining the center region and the beads of the tire. When a tire is mounted on a rim, an air cavity is defined between the tire and the rim. During interaction of the tire with road surface and relative motion therebetween, air trapped inside the air cavity causes air cavity resonance which generates low frequency sound waves.
[003] The low frequency noises are hazardous as they are cause of hearing
impairment, neurasthenia and cardiovascular system hazards. Inadvertently, all-
human beings are exposed to low-frequency noises from the automobile or vehicle
tires. Apart from posing ill-effects on the nearby commuters, low-frequency noises
from the automobile tires are also harmful for the occupants of the vehicle.
[004] The other secondary disadvantage is the unpleasant atmosphere created
for the occupants of the vehicle. This is especially true for electric vehicles where the prime mover is substantially silent and the noises produced by the vehicle tires are the predominant source of disturbance to occupants and commuters. Henceforth, these low frequency noises need to be attenuated in tire itself to provide a better experience while driving in addition to safety.
BRIEF DESCRIPTION OF DRAWINGS
[005] The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit(s) of a reference number

identifies the figure in which the reference number first appears. The same numbers
are used throughout the drawings to reference like features and components.
[006] Figure 1 illustrates cross sectional view of a tire with a layered structure
of acoustic materials, according to an example implementation of the present
subject matter.
[007] Figure 2 illustrates the tire with an exploded view of layered structure
of acoustic materials, according to an example implementation of the present
subject matter.
[008] Figure 3A illustrates graphical representation of sound absorption
coefficient for varying frequencies by using the existing acoustic material
presented as a layer in the air cavity between a tire and a rim.
[009] Figure 3B and 3C illustrate graphical representation of sound
absorption coefficient for varying frequencies by using the existing acoustic
materials or cellulose rich PU (CRPU) foam with varying weight percentage of
cellulose filler presented as a layer of 6 mm and 10 mm thickness respectively in
the air cavity between a tire and a rim.
[0010] Figure 4 illustrates a graphical representation of the sound absorption
coefficient for varying frequencies by using the existing acoustic materials
presented as a layer of varying thickness in the air cavity in the air cavity.
[0011] Figure 5 illustrates a graphical representation of compressive strength
σ and elastic modulus E of existing acoustic materials and cellulose-rich PU foam
with a varying weight percentage of cellulose filler.
[0012] Figure 6 illustrates a graphical representation of the sound absorption
coefficient for varying frequencies, when CRPU foam with weight percentage of
cellulose filler as 1 wt.% presented as a layer of varying thicknesses in the air
cavity.
[0013] Figure 7 illustrates graphical representation of the sound absorption
coefficient for varying frequencies by using layered structure of CRPU foam with
weight percentage of cellulose filler as 10 wt.% presented as a first layer of acoustic
material of any of 6, 10 and 15 mm thicknesses and SILENTECHTM foam

presented as a second layer of acoustic material of anyone of 2, 6 and 10 mm thicknesses in the air cavity.
DETAILED DESCRIPTION
[0014] In vehicles, there are various sources of noise generated during motion
of a tire incorporated in a vehicle along a surface or road. One is a propulsion system of the vehicle, such as a combustion engine along with a power transmission shaft attached to it. Second, during motion of the vehicle, tread region of the tire contacts with surface of the motion. Upon contact with the surface ambient air gets trapped between grooves of the tire and the surface. The trapping of the air and improper air channeling generates noise in the tire during motion. Third, air trapped in an air cavity formed between a tire and a rim, generates low frequency noise during motion of the tire on a road surface. Thus, for a quiet ride for driver and passengers, it is desirable to have a tire with lower noise as compared to the conventional tire. More specifically, low frequency noise generated because of the air cavity between the tire and the rim, needs to be attenuated, since low frequency noise may be harmful to the health of occupants of the vehicle and nearby commuters.
[0015] A solution of attenuating noise generated through the air cavity
resonance is the inclusion of a layer of an acoustic material, such as polymeric foam layer in the inner wall of the tire to reduce volume of air cavity and enhance sound absorption. However, sound attenuation at low frequencies (e.g., in the range 150 - 400 Hz) poses a serious challenge, as most of the available acoustic materials exhibit high sound absorption coefficients at relatively medium to high frequencies (e.g., in the range 500 - 3000 Hz) and exhibit low sound absorption coefficients at low frequencies. Thus, conventionally, presence of a polymeric foam layer does not effectively suppress the low frequency noise. Also, low frequency sound waves cannot be effectively absorbed by a single-phase medium, in which no additional filler is added to a Polyurethane (PU) matrix. Experiments with a variety of available acoustic materials show that they are ineffective in attenuating low frequency sound waves.

[0016] To this end, the present subject matter provides a tire for a vehicle
which produces less noise during movement over a road surface, the tire may be modified to overcome the above-described problem associated with an air cavity that is formed between the tire and a rim on which, the tire is mounted and consequent low frequency noise generation during motion of the vehicle on the road surface.
[0017] In accordance with an embodiment of the present subject matter, a tire
having at least one layer of a first acoustic material at an inner wall of the tire is
disclosed. The tire may comprise at least one layer of second acoustic material on
the at least one layer of first acoustic material. In an example, density of the first
acoustic material is higher than density of the second acoustic material.
[0018] In an example, the first acoustic material is a cellulose rich polyurethane
(CRPU) foam which is a polymerized product of a polyol, diisocyanate and a cellulose filler.
[0019] In an example, the second acoustic material is a low-density off-the-
shelf acoustic foam, e.g., melamine foam, blue foam, ester-based foam, PU foam and thereof with variable relative densities, e.g., ranging up to 5% or an equivalent thereof. In an example, the second acoustic material is an off-the-shelf
SILENTECHTM foam.
[0020] The low-density acoustic material when placed next to high density
acoustic material adhered to the inner wall of the tire enables attenuating low-frequency noises in tires effectively and enhance the value of sound absorption coefficient presenting a significant noise reduction.
[0021] The above and other features, aspects, and advantages of the subject
matter will be better explained with regard to the following description and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and, should not be construed as a limitation to the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and

examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numbers are used throughout the drawings to reference like features and components.
[0022] Figure 1 illustrates schematics of a tire 100 with a layered structure of
acoustic materials, in accordance with an implementation of the present subject matter. While, Figure 2 illustrates the tire with an exploded view of the layered structure of acoustic materials, according to an example implementation of the present subject matter. For sake of ease of explanation, Figures 1 and 2 are explained together.
[0023] It would be appreciated that although Figures 1 and 2 depict an example
implementation of the tire 100 with the layered structure comprising two layers, other implementations of the layered structure are also possible. For instance, although it is not shown in the figures, a layered structure of acoustic materials with three layers may also be inserted in the tire 100.
[0024] In an implementation of the present subject matter, the tire 100 is
mounted on a rim 102. The tire 100 has a tread portion 104 and sidewalls 106 on either side of the tread portion 104. The tread portion 104 may comprise a center region and a shoulder region on each side of the center region connected to upper portions of corresponding sidewalls 106 of the tire. Center region which is formed along complete circumference of the tire 100, spreads along width of the tire 100 and contacts with a surface during rotation. Tire 100 also has beads 108 connected to lower portions of the sidewalls 106 of the tire 100. The beads 108 are edges of the tire 100 and contacts with rim 102 during mounting of the tire 100. The tire 100 forms an air cavity 110 with the rim 102. The air cavity 110 causes air cavity resonance during the movement of the tire 100 on a road surface which in turn lead to low frequency noise generation. The low frequency is harmful to the safety of occupant of a vehicle incorporating the tire and nearby commuters. To effectively reduce such low frequency noise generation, the tire 100 further comprises at least one layer of a first acoustic material 112 at an inner wall of the tire 100. In an example, the at least one layer of first acoustic material 112 is adhered to the inner wall of the tire 100 through an adhesive. The tire 100 also comprises at least one

layer of second acoustic material 114 adhered to the at least one layer of first acoustic material. In an example, the at least one layer of second acoustic material 114 is adhered to the at least one layer of first acoustic material 112 through an adhesive. In an example, the adhesive used for the adherence is a pressure sensitive adhesive without carrier. In an example, the first acoustic material has higher relative density than the second acoustic material.
[0025] In an example, as mentioned above, the first acoustic material is a
cellulose rich polyurethane (CRPU) foam developed by using a cellulose filler in
a PU foaming process. The CRPU foam is a polymerized product of a polyol,
diisocyanate and a cellulose filler. In an example, the cellulose filler is saw dust or
an equivalent thereof. In another example, the cellulose filler has a particle size in
a range of 20 to 60 µm and may be taken in a weight range of 1 to 10% with respect
to total weight of polyol and diisocyanate. In an example, polyol and diisocyanate
is in a weight ratio range of 10:6. In another example, the polyol may be selected
from polyester, polyether, polybutadiene, polycarbonate, and polyacrylate polyol
or combinations thereof; and the diisocyanate may be selected from methylene
diisocyanate (MDI), toluene diisocyanate, isophoronediisocyanate,
hexamethylenediisocyanate, aromatic isocyanates, or combinations thereof. In an example, the polyol used in the present invention is formulated type containing a proprietary blowing agent. The blowing Agent may be understood as a substance which produces a cellular structure via a foaming process.
[0026] The process of preparing the CRPU foam comprises sequential addition
of polyol, cellulose filler (e.g., saw-dust) and diisocyanate (e.g., MDI) under high-speed stirring (e.g., in a speed range of 1800 to 2400 rpm) to obtain a mixture and allowing the mixture to get settled for about 2 days to get the foam. The key components which require due consideration in the process of preparing the CRPU foam are grade of polyol and diisocyanate, the composition in which they are mix, the stirring speed while mixing polyol and diisocyanate. Furthermore, when saw-dust is added to PU and foamed in a larger volume, the uniform dispersion of cellulose filler within the PU system is an essential component which proves vital in determining the acoustical properties of CRPU foam. The other components

which require attention is the dimension of the mold in which PU foam is foamed as this brings variation in density of the CRPU foam. In an example, the CRPU foam has density in a range of 70 to 100 kg/m3; particle size in a range of 20 to 40 µm; and pore size in a range of 200 to 400 µm. In an example, the CRPU foam has elastic modulus in a range of 0.03 to 0.3 MPa.
[0027] The CRPU foams are thermally stable to about 260ºC with no
measurable weight loss when heated at a constant heating rate. The foaming procedure allows for fabricating CRPU foams to any intricate shape and size. These flexible CRPU foams and/or its derivative foams offer the flexibility of complying to any shape for installation purposes. Further, CRPU foams are thermally stable to about 260ºC with no measurable weight loss when heated at a constant heating rate.
[0028] The second acoustic material is a low-density foam. In an example, the
second acoustic material may be selected from melamine foam or PU foams having varying relative densities such as 2.83% or 5%. In an example embodiment, SILENTECHTM foam may be used as the second acoustic material. The low-density foam fabricated in the present work is an open cell flexible foam having a density in the range of 70 to 100 kg/m3. The pores are in the range of 200 – 300 µm with cell walls in a range of 50 – 100 µm. Open cell foams are the one where the cells within the material have been broken, allowing air to occupy the spaces within. Usually, open cell foams are lightweight and less dense compared with closed cell foams, and have a soft, cushioning and sponge-like appearance. During an open cell foams expansion and curing, the gas bubbles used in its production are released into the atmosphere as against being locked in place as with closed cell foams. These holes within open cell foams enable them to interlock and interconnect.
[0029] In an example, the at least one layer of first acoustic material or the at
least one layer of second acoustic material or both may be hollow or perforated. In an example, the thickness of hollow or perforated foam may have a thickness of 6mm.

[0030] In an example, thickness of the first acoustic material is in the range of
6 to 15 mm. In an example, the at least one layer of first acoustic material 112 has a uniform thickness such that the first acoustic material 112 has the same thickness consistently throughout the circumference of the tire. In another example, the at least one layer of first acoustic material 112 has a non-uniform thickness. In such example embodiments, the thickness of first acoustic material 112 may vary along the circumference of the tire.
[0031] In an example, thickness of the second acoustic material is in the range
of 2 to 10 mm. In an example, the at least one layer of second acoustic material 114 has a uniform thickness. In another example, the at least one layer of second acoustic material 114 has a non-uniform thickness.
[0032] In an example, density of the first acoustic material is in the range of
70 to 100 kg/m3.
[0033] In an example, density of the second acoustic material is in the range of
9 to 34 kg/m3. In an example, the second acoustic material is a SILENTECHTM having a density of 18 kg/m3. In another example, the low-density foam such as melamine foam having a density of 9 kg/m3 or a PU foam with a density of 34 kg/m3may be used as the second acoustic material.
[0034] In an example implementation, experiments have been carried out to
illustrate sound absorption coefficient α and corresponding noise reduction by using the existing acoustic material, e.g., melamine foam having relative density of 0.57%, blue foam having relative density of 1.91%, SILENTECHTM foam having relative density of 1.33%, PU foam having relative density of 2.83%, PU foam having relative density of 5% with varying thicknesses presented as a layer in the air cavity between the tire and the rim. Experiments have also been carried out to illustrate sound absorption coefficient α and corresponding noise reduction by using the CRPU foam with varying weight percentage of cellulose filler, e.g., 1 wt.%, 5 wt.% or 10 wt.% and with varying thicknesses presented as a layer in the air cavity between the tire and the rim. Further, experiments illustrate sound absorption coefficient α and corresponding noise reduction as exhibited by using

the layered structure of the CRPU foam as the first acoustic material and the other existing acoustic materials as the second acoustic material.
[0035] Figure 3A illustrates graphical representation of sound absorption
coefficient α for varying frequencies by using the existing acoustic material, e.g., melamine foam having relative density of 0.57%, blue foam having relative density of 1.91%, SILENTECHTM foam having relative density of 1.33%, PU foam having relative density of 2.83%, PU foam having relative density of 5% presented as a layer of 2 mm thickness in the air cavity between the tire and the rim. As can be shown from the Figure 3A, for 200 Hz frequency, SILENTECHTM foam performs better than other foams and exhibits a sound absorption coefficient α of 0.11 value and noise reduction of 1 dB.
[0036] Figure 3B and 3C illustrates graphical representation of sound
absorption coefficient α for varying frequencies by using the existing acoustic material, e.g., melamine foam having relative density of 0.57%, blue foam having relative density of 1.91%, SILENTECHTM foam having relative density of 1.33%, PU foam having relative density of 2.83%, PU foam having relative density of 5% and the CRPU foam with varying weight percentage of cellulose filler, e.g., 1 wt.%, 5 wt.% or 10 wt.% presented as a layer of 6 mm and 10 mm thickness respectively in the air cavity between the tire and the rim. As can be shown from the Figure 3B and 3C, for 150 Hz frequency and 10 mm thickness of the layer, and the CRPU foam with weight percentage of cellulose filler as 5 wt.% performs better than other foams and exhibits a sound absorption coefficient α of 0.08 value and noise reduction of 0.77 dB.
[0037] Figure 4 illustrates graphical representation of sound absorption
coefficient α for varying frequencies by using the existing acoustic materials, i.e., melamine foam having relative density of 0.57% presented as a layer of 8 mm thickness in the air cavity, and SILENTECHTM foam having relative density of 1.33% presented as a layer of 6 mm thickness in the air cavity. As can be shown from the Figure 4, for 150 Hz frequency, SILENTECHTM foam performs better than melamine foam, but maximum sound absorption coefficient α is 0.11 at 200 Hz which drops to 0.09 at 400 Hz.

[0038] Figure 5 illustrates compressive strength σ and elastic modulus E of existing acoustic material, e.g., melamine foam having relative density of 0.57%, blue foam having relative density of 1.91%, SILENTECHTM foam having relative density of 1.33%, PU foam having relative density of 2.83%, PU foam having relative density of 5% and the CRPU foam with varying weight percentage of cellulose filler, e.g., 1 wt.%, 5 wt.% or 10 wt.%. The elastic modulus provides a measure of a stiffness of a foam. The foam with a higher value of elastic modulus is one which is having stiffer cell walls. The addition of cellulose filler such as saw-dust to PU matrix results in an increment of elastic modulus values. The highest elastic modulus is observed for 10 wt. % foam which is about 0.3 MPa, while it is 0.09 MPa for melamine foam.
[0039] Figure 6 illustrates graphical representation of the sound absorption coefficient α for varying frequencies, when CRPU foam with weight percentage of cellulose filler as 1 wt.% presented as a layer of 6, 10 and 15 mm thickness in the air cavity. It can be seen that irrespective of the thickness, sound absorption coefficient α is high for 1 wt.% and only improves further with thickness of the material.
[0040] Figure 7 illustrates graphical representation of the sound absorption coefficient α for varying frequencies by using layered structure of CRPU foam with weight percentage of cellulose filler as 10 wt.% presented as a first layer of acoustic material of any of 6, 10 and 15 mm thicknesses and SILENTECHTM foam presented as a second layer of acoustic material of anyone of 2, 6 and 10 mm thicknesses in the air cavity. It is shown that α obtained for a combination of 15 mm CRPU foam and 10 mm SILENTECHTM foam corresponds to 0.4 and 0.7 at 400 Hz and 600 Hz respectively. Further, α of 0.4 and 0.7 corresponds to a noise reduction of 4.6 and 11.7 dB respectively. The results are based on impedance tube experiments. These α values are rounded off values to the nearest first decimal digit while the decibel values correspond to the actual values calculated from the plot using the relation d = -20 log(1 -\ α). Note that a one to one correspondence for \ α of 0.4 and 0.7 are 4.4369 and 10.4576 dB, respectively.

[0041] Thus, the use of stratified or multi-layer structure of high density and low density acoustic materials exhibit enhanced sound attenuating capabilities in the low frequency regime. Further, multilayer structure that includes CRPU foam along with any existing acoustic foam material exhibit an enhanced sound absorption coefficient α of 0.4.
[0042] Although Figures 1 and 2 depict an example implementation of the tire 100 with the layered structure comprising two layers and experiments described have been carried out with the implementation of the tire 100 having two layers, other implementations of the layered structure are also possible. For instance, although it is not shown in the figures, a layered structure of acoustic materials with three or four layers may also be inserted in the tire 100. [0043] Although implementations of a tire are described, it is to be understood that the present subject matter is not necessarily limited to the specific features of the systems described herein. Rather, the specific features are disclosed as implementations for the tire.

I/We Claim:
1. A tire 100 comprising:
at least one layer of first acoustic material 112 at an inner wall of the tire 100; and
at least one layer of second acoustic material 114 on the at least one layer of first acoustic material 112;
wherein density of the first acoustic material is higher than density of the second acoustic material.
2. The tire as claimed in claim 1, wherein the density of the first acoustic material is in the range of 70 to 100 kg/m3.
3. The tire as claimed in claim 1, wherein the density of the second acoustic material is in the range of 9 to 34 kg/m3.
4. The tire as claimed in claim 1, wherein the thickness of the at least one layer of first acoustic material 112 is in the range of 6 to 15 mm.
5. The tire as claimed in claim 1, wherein the thickness of the at least one layer of second acoustic material 114 is in the range of 2 to 10 mm.
6. The tire as claimed in claim 1, wherein the thickness of the at least one layer of the first acoustic material 112 is non-uniform.
7. The tire as claimed in claim 1, wherein the thickness of the at least one layer of the second acoustic material 114 is non-uniform.

8. The tire as claimed in claim 1, wherein the at least one layer of first acoustic material 112 or the at least one layer of second acoustic material 114 is perforated.
9. The tire as claimed in claim 8, wherein a thickness of the perforated layer is 6mm.