JP2021167158A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire that can be improved in high-speed durability, while reducing road noise.SOLUTION: A belt cover layer 8 constituted of an organic fiber cord wound around spirally along a tire circumferential direction is provided at an outer periphery side of a belt layer 7 in a tread part 1. As the organic fiber cord constituting the belt cover layer 8, a polyethylene terephthalate fiber cord whose elasticity modulus under a load of 2.0cN/dtex at 100°C is in a range of 3.5cN/(tex.%)-5.5cN/(tex.%) is used. Meanwhile, a sound absorbing material 10 constituted of a porous material is installed on an inner surface of the tread part 1, and a cross sectional area of the sound absorbing material 10 are set to be equal to 10%-30% of a cross sectional area of a tire inner cavity.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pneumatic tire provided with a sound absorbing material made of a porous material on the inner surface of the tire.

There are various types of noise caused by tires, depending on the source and range. For example, the cavity resonance sound generated by the vibration of the air filled in the tire cavity, and the medium frequency road noise generated by the vibration of the tire picking up the unevenness of the road surface during high-speed driving resonating the passenger compartment through the axle. Can be mentioned. Among such noises, as a method of reducing the cavity resonance sound, it has been proposed to attach a sound absorbing material made of a porous material such as a sponge to the inner surface of the tire (inner peripheral surface of the tread portion) (for example, a patent). Reference 1).

However, if the sound absorbing material is attached to the inner peripheral surface of the tread portion, the temperature may rise due to the heat storage of the sound absorbing material during high-speed running, and the high-speed durability may decrease. Further, although the above-mentioned sound absorbing material can reduce the cavity resonance sound, the effect on the medium frequency road noise is not always sufficient, and countermeasures against this have been required.

Japanese Patent No. 5267288

An object of the present invention is air that, when a sound absorbing material made of a porous material is provided on the inner surface of a tire to obtain noise performance, it is possible to suppress a decrease in high-speed durability and further improve the noise performance. It is to provide tires with tires.

The pneumatic tire of the present invention for achieving the above object has a tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and these sidewall portions. A pair of bead portions arranged inside in the tire radial direction, a carcass layer mounted between the pair of bead portions, and a plurality of layers of belts arranged on the outer peripheral side of the carcus layer in the tread portion. In a pneumatic tire having a layer and a belt cover layer arranged on the outer peripheral side of the belt layer, the belt cover layer spirally winds an organic fiber cord coated with a coated rubber along the tire circumferential direction. The organic fiber cord is a polyethylene terephthalate fiber having an elastic coefficient in the range of 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%) under a load of 2.0 cN / dtex at 100 ° C. It is a cord, and a sound absorbing material made of a porous material is installed on the inner surface of the tread portion, and the cross-sectional area of the sound absorbing material is 10% to 30% with respect to the cross-sectional area of the tire cavity.

In the present invention, as described above, since the sound absorbing material having an appropriate size is installed on the inner surface of the tread portion, the cavity resonance sound can be suppressed and the noise performance can be improved. On the other hand, since the belt cover layer made of the above-mentioned organic fiber cord is provided, it is possible to supplement the high-speed durability that may be reduced by the sound absorbing material. Specifically, the present inventor has diligently studied a pneumatic tire provided with a belt cover layer made of PET fiber cords, optimized the dipping process of PET fiber cords, and under a 2.0 cN / dtex load at 100 ° C. It was found that by setting the elastic modulus within a predetermined range, fatigue resistance and a tagging effect of a cord suitable as a belt cover layer can be obtained. Therefore, as described above, the elastic modulus of the organic fiber cord constituting the belt cover layer under a load of 2.0 cN / dtex at 100 ° C. is 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%). By using a PET fiber cord in the range of%), it becomes possible to maintain and improve high-speed durability, which is feared to be reduced by the sound absorbing material. Further, the belt cover layer made of such a low elasticity PET fiber cord can be expected to have an effect of reducing medium frequency road noise due to its physical properties, so that the noise performance can be further improved.

In the present invention, the cord tension in the region of the organic fiber cord overlapping with the belt layer is preferably 0.9 cN / dtex or more. This is advantageous for suppressing heat generation and improving the durability of the tire.

In the present invention, the density of the sound absorbing material is ^{10kg / m 3 ~30kg / m 3} , it is preferable cell number of the sound absorbing material is 30 / 25Mm～80 pieces / 25 mm. As a result, the density of the sound absorbing material becomes low, and heat storage can be suppressed, leading to improvement in high-speed durability. Further, by securing an appropriate number of cells of the sound absorbing material, bubbles can be made finer, and the sound absorbing effect of the sound absorbing material can be satisfactorily exhibited.

In the present invention, it is preferable that the sound absorbing material has a missing portion at at least one position in the tire circumferential direction. As a result, heat dissipation of the sound absorbing material is promoted, which is advantageous in suppressing heat storage during traveling and improving high-speed durability. In addition, it becomes possible to withstand the expansion due to the inflation of the tire and the shear strain of the adhesive surface caused by the ground rolling for a long period of time.

At this time, the total length of the sound absorbing material along the tire peripheral direction is preferably 75% to 95% of the maximum inner peripheral length of the tire. By ensuring a sufficient total length of the sound absorbing material in this way, it is advantageous to improve the sound absorbing effect.

In the present invention, the hardness x [N / 314 cm ² ] of the sound absorbing material and the breaking elongation y [%] of the sound absorbing material satisfy the relationships of 130 ≦ y ≦ 500, y ≦ -21x + 2770, and x ≧ 60. Is preferable. By making the relationship between the hardness of the sound absorbing material and the elongation at break appropriate in this way, it is possible to effectively prevent the sound absorbing material from peeling or breaking even under a high load or a low temperature.

In the present invention, the glass transition temperature of the sound absorbing material is preferably −60 ° C. to −45 ° C. Further, it is preferable that the sound absorbing material is made of polyurethane foam resin. By constructing the sound absorbing material with such a material, the sound absorbing performance can be effectively improved. The glass transition temperature of the sound absorbing material can be measured by a differential scanning calorimeter (DSC).

In the present invention, the hardness of the sound absorbing material, the breaking elongation of the sound absorbing material, the density of the sound absorbing material and the number of cells of the sound absorbing material are measured in accordance with JIS-K6400. Regarding the hardness of the sound absorbing material, the D method is adopted in the hardness test of the sound absorbing material. In addition, various dimensions and lumen volume of the tire are measured in a state where the tire is rim-assembled on a regular rim and the regular internal pressure is applied. In particular, the lumen volume of the tire is the volume of the cavity formed between the tire and the rim in this state. A "regular rim" is a rim defined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATTA, a "Design Rim" for TRA, or ETRTO. If so, it is set to "Measuring Rim". However, if the tire is a tire installed on a new car, the volume of the cavity will be calculated using the genuine wheel on which this tire is assembled. "Regular internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. If it is JATTA, it is the maximum air pressure, and if it is TRA, it is the table "TIRE LOAD LIMITED AT VARIOUS". The maximum value described in "COLD INFLATION PRESSURES", if it is ETRTO, it is "INFRATION PRESSURE", but if the tire is a new car tire, it is the air pressure displayed on the vehicle.

FIG. 5 is a cross-sectional view taken along the meridian showing a pneumatic tire according to an embodiment of the present invention. It is an equator line sectional view which shows the pneumatic tire which comprises the embodiment of this invention. ^{It is a graph which shows the relationship between the hardness x [N / 314cm 2} ] and the breaking elongation y [%] in the sound absorbing material used for the pneumatic tire of this invention.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the pneumatic tire of the present invention is arranged inside the tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and the sidewall portion 2 in the tire radial direction. It is provided with a pair of bead portions 3. In FIG. 1, the reference numeral CL indicates the tire equator. Although FIG. 1 is a cross-sectional view of the meridian, it is not depicted, but the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape, whereby the toroidal of the pneumatic tire is formed. The basic structure of the shape is constructed. Hereinafter, the description using FIG. 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component extends in the tire circumferential direction to form an annular shape.

In the illustrated example, a plurality of main grooves (4 in the illustrated example) extending in the tire circumferential direction are formed on the outer surface of the tread portion 1, but the number of main grooves is not particularly limited. Further, in addition to the main groove, various grooves and sipes including a lug groove extending in the tire width direction can be formed.

A carcass layer 4 including a plurality of reinforcing cords (carcass cords) extending in the tire radial direction is mounted between the pair of left and right bead portions 3. A bead core 5 is embedded in each bead portion, and a bead filler 6 having a substantially triangular cross section is arranged on the outer periphery of the bead core 5. The carcass layer 4 is folded around the bead core 5 from the inside to the outside in the tire width direction. As a result, the bead core 5 and the bead filler 6 are formed around the main body portion of the carcass layer 4 (the portion extending from the tread portion 1 to each bead portion 3 via each sidewall portion 2) and the folded portion (in each bead portion 3 around the bead core 5). It is wrapped by a portion) that is folded back and extends toward each sidewall portion 2 side. As the carcass cord constituting the carcass layer 4, for example, a polyester cord is preferably used.

On the other hand, a plurality of layers (two layers in the illustrated example) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords (belt cords) that are inclined with respect to the tire circumferential direction, and is arranged so that the belt cords intersect each other between the layers. In these belt layers 7, the inclination angle of the belt cord with respect to the tire circumferential direction is set in the range of, for example, 10 ° to 40 °. As the belt cord constituting the belt layer 7, for example, a steel cord is preferably used.

Further, on the outer peripheral side of the belt layer 7, a belt cover layer 8 is provided for the purpose of compensating for high-speed durability that may decrease due to heat storage of the sound absorbing material 10 described later and reducing medium-frequency road noise. It is provided. The belt cover layer 8 includes a reinforcing cord (cover cord) oriented in the tire circumferential direction. In the present invention, an organic fiber cord is used as the cover code (in the following description, this cover code may be referred to as an "organic fiber cord"). In the belt cover layer 8, the cover cord has an angle set to, for example, 0 ° to 5 ° with respect to the tire circumferential direction. In the present invention, the belt cover layer 8 always includes a full cover layer 8a that covers the entire area of the belt layer 7, and optionally includes a pair of edge cover layers 8b that locally cover both ends of the belt layer 7. (In the illustrated example, both the full cover layer 8a and the edge cover layer 8b are included). The belt cover layer 8 may be formed by spirally winding a strip material in which at least one organic fiber cord is aligned and coated with a coated rubber in the tire circumferential direction, and it is particularly desirable to have a jointless structure.

In the present invention, as the organic fiber cord constituting the belt cover layer 8, the elastic modulus under a load of 2.0 cN / dtex at 100 ° C. is 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%). A range of polyethylene terephthalate fiber cords (PET fiber cords) are used. By using a specific PET fiber cord as the organic fiber cord constituting the belt cover layer 8 in this way, the high-speed durability that may be lowered due to the heat storage of the sound absorbing material 10 described later is compensated for, and this is supplemented. Medium frequency road noise can be effectively reduced while maintaining good performance. If the elastic modulus of this PET fiber cord under a load of 2.0 cN / dtex at 100 ° C. is less than 3.5 cN / (tex ·%), the medium frequency road noise cannot be sufficiently reduced. If the elastic modulus of the PET fiber cord under a load of 2.0 cN / dtex at 100 ° C. exceeds 5.5 cN / (tex ·%), the fatigue resistance of the cord is lowered and the durability of the tire is lowered. In the present invention, the elastic modulus [N / (tex ·%)] under a load of 2.0 cN / dtex at 100 ° C. conforms to the “chemical fiber tire cord test method” of JIS-L1017, and has a grip interval of 250 mm. It is calculated by conducting a tensile test under the condition of a tensile speed of 300 ± 20 mm / min and converting the slope of the tangent line at the point corresponding to the load 2.0 cN / dtex of the load-elongation curve into a value per tex. ..

Further, when this organic fiber cord (PET fiber cord) is used as the belt cover layer 8, the cord tension in the region overlapping with the belt layer 7 is preferably 0.9 cN / dtex or more, more preferably 1.5 cN / dtex to. It is preferably 2.0 cN / dtex. By setting the cord tension in the tire in this way, heat generation can be suppressed and the durability of the tire can be improved. If the cord tension in the region overlapping the belt layer 7 of the organic fiber cord (PET fiber cord) is less than 0.9 cN / dtex, the peak of tan δ rises, and the effect of improving the durability of the tire is sufficient. I can't get it. The cord tension in the region of the organic fiber cord (PET fiber cord) constituting the belt cover layer 8 overlapping with the belt layer 7 is two or more turns inside the end of the strip material constituting the belt cover layer 8 in the tire width direction. It shall be measured in.

The PET fiber cord used as the organic fiber cord constituting the belt cover layer 8 preferably has a heat shrinkage stress of 0.6 cN / tex or more at 100 ° C. By setting the heat shrinkage stress at 100 ° C. in this way, it is possible to effectively reduce road noise while maintaining good durability of the pneumatic tire more effectively. If the heat shrinkage stress of the PET fiber cord at 100 ° C. is smaller than 0.6 cN / tex, the tagging effect during running cannot be sufficiently improved, and it becomes difficult to sufficiently maintain high-speed durability. The upper limit of the heat shrinkage stress of the PET fiber cord at 100 ° C. is not particularly limited, but may be set to 2.0 cN / tex, for example. In the present invention, the heat shrinkage stress (cN / tex) at 100 ° C. conforms to the "chemical fiber tire cord test method" of JIS-L1017, and has a sample length of 500 mm and a heating condition of 100 ° C. for 5 minutes. This is the heat shrinkage stress of the sample cord measured when heated in.

In order to obtain a PET fiber cord having the above-mentioned physical characteristics, for example, it is advisable to optimize the dip treatment. That is, prior to the calendar process, the PET fiber cord is subjected to an adhesive dip treatment, but in the normalization process after the two-bath treatment, the ambient temperature is set within the range of 210 ° C to 250 ° C, and the cord tension is applied. Is preferably set in the range of 2.2 × 10 ⁻² N / tex to 6.7 × 10 ^{−2 N / tex.} This makes it possible to impart the desired physical properties as described above to the PET fiber cord. If the cord tension in the normalization process ^{is smaller than 2.2 × 10 −2} N / tex, the cord elastic modulus becomes low, and the medium frequency road noise cannot be sufficiently reduced, and conversely, 6.7 × 10 ^{− If} it is larger than 2 N / tex, the elastic modulus of the cord becomes high and the fatigue resistance of the cord decreases.

In the pneumatic tire of the present invention, as shown in FIG. 1, the sound absorbing material 10 is mounted along the tire circumferential direction in the region corresponding to the tread portion 1 on the inner surface of the tire. The sound absorbing material 10 is fixed to the inner surface of the tire via, for example, an adhesive layer 11 made of an adhesive or double-sided adhesive tape. The sound absorbing material 10 is made of a porous material having open cells, and has predetermined sound absorbing characteristics based on the porous structure. As the porous material constituting the sound absorbing material 10, for example, a polyurethane foam resin (polyurethane foam) may be used. The glass transition temperature of the sound absorbing material 10 is preferably −60 ° C. to −45 ° C. from the viewpoint of maintaining the flexibility of the polyurethane foam resin even at a low temperature, exhibiting the sound absorbing effect and reducing the cavity resonance sound. Further, from the viewpoint of adhesiveness to the inner surface of the tire, it is desirable that the sound absorbing material 10 does not contain a water repellent. In the embodiment of FIG. 1, the sound absorbing material 10 is composed of a single strip having a rectangular cross-sectional shape.

The volume of the sound absorbing material 10 is 10% to 30%, preferably 10% to 20%, based on the volume of the cavity formed between the tire and the rim (lumen volume). The width of the sound absorbing material 10 is preferably 30% to 90%, more preferably 40% to 70% with respect to the tire contact width. As a result, the sound absorbing effect of the sound absorbing material 10 can be sufficiently ensured, leading to an improvement in quietness. At this time, if the volume of the sound absorbing material 10 is less than 10% of the lumen volume of the tire, the sound absorbing effect cannot be appropriately obtained. If the volume of the sound absorbing material 10 exceeds 30% of the lumen volume of the tire, heat storage during traveling increases, and high-speed durability may decrease.

Density of the sound absorbing material 10 is preferably ^{10kg / m 3 ~30kg / m 3} , more preferably ^{15kg / m 3 ~25kg / m 3} . The number of cells of the sound absorbing material 10 is preferably 30 pieces / 25 mm to 80 pieces / 25 mm, and more preferably 40 pieces / 25 mm to 70 pieces / 25 mm. By setting the density of the sound absorbing material 10 in this way, the density of the sound absorbing material 10 becomes low and heat storage is suppressed, which leads to maintenance and improvement of high-speed durability. Further, when the sound absorbing material 10 has a low density, the weight can be reduced, so that the rolling resistance can be reduced. On the other hand, by appropriately securing the number of cells of the sound absorbing material 10 as described above, the bubbles can be made finer, so that the sound absorbing performance of the sound absorbing material can be effectively exhibited. If the density of the sound absorbing material 10 ^{is less than 10 kg / m 3} , the durability of the sound absorbing material 10 itself may decrease. If the density of the sound absorbing material 10 ^{exceeds 30 kg / m 3} , the density cannot be reduced and the effect of suppressing heat storage cannot be sufficiently obtained. If the number of cells of the sound absorbing material 10 is less than 30 cells / 25 mm, the bubbles cannot be made sufficiently fine, and further improvement in sound absorbing performance cannot be expected. If the number of cells of the sound absorbing material 10 exceeds 80 cells / 25 mm, individual bubbles may become too fine and it may be difficult to secure the sound absorbing performance.

In providing the sound absorbing material 10, as shown in FIG. 2, it is preferable to provide the missing portion 12 at at least one position in the tire circumferential direction. The missing portion 12 is a portion on the tire circumference where the sound absorbing material 10 does not exist. By providing the missing portion 12 in this way, heat dissipation from the missing portion 12 can be expected, which is advantageous in suppressing heat storage of the sound absorbing material 10 and improving high-speed durability. Further, it is possible to withstand the shear strain of the adhesive surface caused by the expansion due to the inflation of the tire and the ground rolling for a long time, and it is possible to effectively alleviate the shear strain generated on the adhesive surface of the sound absorbing material 10. Such missing portions 12 may be provided at one location or at three to five locations on the tire circumference. If the missing portions 12 are provided at two locations on the tire circumference, the deterioration of tire uniformity becomes remarkable due to mass imbalance, and if the missing portions 12 are provided at six or more locations on the tire circumference, the manufacturing cost increases significantly. Become.

When the missing portion 12 is provided in this way, the total length of the sound absorbing material 10 along the tire peripheral direction is preferably 75% to 95%, more preferably 80% to 90% of the maximum inner peripheral length of the tire. Even when the missing portion 12 is present as described above, the sound absorbing effect can be reliably ensured by ensuring a sufficient total length of the sound absorbing material 10. When a plurality of missing portions 12 are present, the total length of the individual sound absorbing materials 10 divided by the missing portions 12 along the tire circumferential direction is the "total length". If the total length of the sound absorbing material 10 along the tire peripheral direction is less than 75% of the maximum inner peripheral length of the tire, the total amount of the sound absorbing material 10 decreases, and it becomes difficult to sufficiently secure the sound absorbing performance. If the total length of the sound absorbing material 10 along the tire peripheral direction exceeds 95% of the maximum inner peripheral length of the tire, the missing portion 12 cannot be sufficiently secured, and the effect of suppressing heat storage by heat dissipation from the missing portion 12 is sufficient. You can't expect it.

In the present invention, the hardness x [N / 314 cm ² ] of the sound absorbing material 10 and the breaking elongation y [%] of the sound absorbing material 10 satisfy the relationships of 130 ≦ y ≦ 500, y ≦ -21x + 2770, and x ≧ 60. Is preferable. More preferably, the relationship of 80 <x ≦ 120, 140 ≦ y ≦ 490, and / or y ≦ -21x + 2700 may be satisfied, and more preferably 80 <x ≦ 100, 150 ≦ y ≦ 480, and / or y. It is preferable to satisfy the relationship of ≦ -21x + 2600. The hardness x and the elongation at break y of the sound absorbing material 10 are the hardness and the elongation at break measured in a standard state (temperature 23 ° C., relative humidity 50%).

Specifically, the shaded area S shown in FIG. 3 indicates a preferable range as the physical characteristics of the sound absorbing material 10 described above. In FIG. 3, when the hardness x of the sound absorbing material 10 exceeds the upper limit value specified by the above relational expression, the deformation of the tire cannot be followed during the load endurance, and the sound absorbing material 10 tends to peel off. If it is 80 N / 314 cm ² or less, the sound absorbing material 10 is deformed due to compression set during high-speed running, and a sufficient sound absorbing effect cannot be obtained. Further, when the breaking elongation y of the sound absorbing material 10 is smaller than 130%, the sound absorbing material 10 tends to break easily when the tire is highly deformed, and this tendency becomes particularly remarkable at a low temperature.

According to the present invention, the belt cover layer 8 and the sound absorbing material 10 cooperate with each other to achieve both high-speed durability and noise performance in a well-balanced manner. That is, in the present invention, the sound absorbing material 10 suppresses the noise caused by the cavity resonance, while the belt cover layer 8 maintains and improves the high-speed durability, which is feared to be reduced by the heat storage of the sound absorbing material 10. Further, the physical characteristics of the belt cover layer 8 suppress the medium frequency road noise (to further improve the noise performance). Therefore, features such as suitable physical properties and structures of the belt cover layer 8 and the sound absorbing material 10 described above can be appropriately combined and adopted.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited to these Examples.

The tire size is 225 / 60R18, has the basic structure illustrated in FIG. 1, and constitutes an organic fiber cord (nylon fiber cord (indicated as "N66" in the table) or polyethylene terephthalate fiber cord (table). (Indicated as "PET")) Elastic modulus [cN / (tex ·%)] under 2.0 cN / dtex load at 100 ° C., cord tension [cN / dtex] in the region overlapping the belt layer, tire Tables 1 and 2 show the ratio of the cross-sectional area of the sound absorbing material to the cross-sectional area of the lumen [%], the density of the sound absorbing material [kg / m ³ ], the number of cells of the sound absorbing material [pieces / 25 mm], and the number of intermittent parts. The tires of Conventional Example 1, Comparative Examples 1 to 6, and Examples 1 to 6 were produced.

In each example, the belt cover layer has a jointless structure in which a strip formed by coating one organic fiber cord (nylon fiber cord or polyethylene terephthalate fiber cord) with coated rubber is spirally wound in the tire circumferential direction. Have. The cord driving density in the strip is 50 lines / 50 mm. Further, the organic fiber cord has a structure of 1100 dtex / 2 in each case.

In each example, the elastic modulus [cN / (tex ·%)] under a load of 2.0 cN / dtex at 100 ° C. conforms to the “chemical fiber tire cord test method” of JIS-L1017, and has a grip interval of 250 mm and a tensile speed. A tensile test was carried out under the condition of 300 ± 20 mm / min, and the calculation was made by converting the slope of the tangent line at the point corresponding to the load 2.0 cN / dtex of the load-elongation curve into a value per tex. Further, for the cord tension [cN / dtex] in the tire, the tread rubber is removed from the tread portion 1 to expose the belt cover layer, the organic fiber cord is peeled off from the predetermined length range of the belt cover layer, and after the collection thereof. The length of the tire was measured, and the amount of shrinkage with respect to the length before collection was determined. In particular, the average value of the shrinkage amount was calculated for the five fiber cords located at the center of the outermost belt layer. Then, the load corresponding to the shrinkage amount (%) was obtained from the SS curve and measured by converting it into a value per 1 dtex.

Road noise and high-speed durability were evaluated for these test tires by the following evaluation methods, and the results are also shown in Tables 1 and 2.

Road noise Each test tire is assembled to a wheel with a rim size of 18 x 7J, mounted as the front and rear wheels of a passenger car (front wheel drive vehicle) with a displacement of 2.5L, the air pressure is set to 230kPa, and the sound collecting microphone is inside the driver's seat window. The sound pressure level near the frequency of 315 Hz was measured when the test course composed of the asphalt road surface was run under the condition of an average speed of 50 km / h. As the evaluation result, the amount of change (dB) with respect to the standard was shown with reference to the conventional example 1. If the value of the amount of change is negative, it means that the road noise is reduced.

High-speed durability Each test tire is assembled to a wheel with a rim size of 18 x 7J, filled with an internal pressure of 230 kPa, mounted on a drum tester equipped with a steel drum with a smooth surface and a diameter of 1707 mm, and the ambient temperature is 38 ± 3 ° C. The speed was increased from 120 km / h to 50 km / h in 24 hours, and the mileage until the tire failed was measured. The evaluation result is shown by an index with Conventional Example 1 as 100 using the measured value of the mileage. The larger the index value, the longer the mileage until a failure occurs, and the better the high-speed durability. If the index value is less than "105", the effect of improving high-speed durability is insufficient.

As can be seen from Tables 1 and 2, the tires of Examples 1 to 6 reduced road noise and improved high-speed durability in comparison with the standard Conventional Example 1. On the other hand, in the tires of Comparative Examples 1 and 2, the elastic modulus of the polyethylene terephthalate fiber cord constituting the belt cover layer under a load of 2.0 cN / dtex at 100 ° C. is high, and the ratio of the cross-sectional area of the sound absorbing material is large. Therefore, the high-speed durability was lowered. In the tire of Comparative Example 3, since the elastic modulus of the polyethylene terephthalate fiber cord constituting the belt cover layer under a 2.0 cN / dtex load at 100 ° C. is small, the road noise reduction effect of the belt cover layer cannot be expected, and the sound absorption performance is not expected. Was not obtained sufficiently. In addition, since the ratio of the cross-sectional area of the sound absorbing material is large, the high-speed durability is lowered. In the tire of Comparative Example 4, the ratio of the cross-sectional area of the sound absorbing material was small, so that the sound absorbing performance could not be sufficiently obtained. Since the tire of Comparative Example 5 has a large proportion of the cross-sectional area of the sound absorbing material, the effect of improving high-speed durability could not be sufficiently obtained. In the tire of Comparative Example 6, since the belt cover layer was composed of a nylon fiber cord, the effect of improving the high-speed durability by the belt cover layer could not be obtained.

1 Tread part 2 sidewall part 3 bead part 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt cover layer 8a full cover layer 8b edge cover layer 10 sound absorbing material 11 adhesive layer 12 intermittent part CL tire equatorial

Claims (8)

A tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged inside the tire radial direction of these sidewall portions. A carcass layer mounted between the pair of bead portions, a plurality of belt layers arranged on the outer peripheral side of the carcass layer in the tread portion, and a belt cover arranged on the outer peripheral side of the belt layer. In pneumatic tires with layers
The belt cover layer is formed by spirally winding an organic fiber cord coated with coated rubber along the tire circumferential direction, and the organic fiber cord has an elastic modulus at 100 ° C. under a 2.0 cN / dtex load. A polyethylene terephthalate fiber cord in the range of 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%).
A pneumatic tire in which a sound absorbing material made of a porous material is installed on the inner surface of the tread portion, and the cross-sectional area of the sound absorbing material is 10% to 30% with respect to the cross-sectional area of the tire lumen. The pneumatic tire according to claim 1, wherein the cord tension in the region of the organic fiber cord overlapping with the belt layer is 0.9 cN / dtex or more. The density of the sound absorbing member is ^{10kg / m 3 ~30kg / m 3} , the air according to claim 1 or 2, wherein the cell number of said sound absorbing material is a 30 / 25Mm～80 pieces / 25mm Entered tire. The pneumatic tire according to any one of claims 1 to 3, wherein the sound absorbing material has a missing portion at at least one position in the tire circumferential direction. The pneumatic tire according to claim 4, wherein the total length of the sound absorbing material along the tire peripheral direction is 75% to 95% of the maximum inner peripheral length of the tire. The feature is that the hardness x [N / 314 cm ² ] of the sound absorbing material and the breaking elongation y [%] of the sound absorbing material satisfy the relationships of 130 ≦ y ≦ 500, y ≦ -21x + 2770, and x ≧ 60. The pneumatic tire according to any one of claims 1 to 5. The pneumatic tire according to any one of claims 1 to 6, wherein the glass transition temperature of the sound absorbing material is −60 ° C. to −45 ° C. The pneumatic tire according to any one of claims 1 to 7, wherein the sound absorbing material is made of a polyurethane foam resin.

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