JP7529974B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire that has 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 sound range. Examples include cavity resonance noise, which is generated by the vibration of the air filled in the tire cavity, and mid-frequency road noise, which is generated when the tire picks up unevenness in the road surface during high-speed driving and the vibration resonates inside the vehicle cabin through the axle. As a method for reducing cavity resonance, it has been proposed to attach a sound-absorbing material made of a porous material such as sponge to the inner surface of the tire (the inner surface of the tread portion) (see, for example, Patent Document 1).

However, when sound-absorbing material is attached to the inner peripheral surface of the tread, there is a risk that the temperature will rise due to heat accumulation in the sound-absorbing material during high-speed driving, resulting in a decrease in high-speed durability. Furthermore, while the above-mentioned sound-absorbing material can reduce cavity resonance, it is not necessarily effective enough against mid-frequency road noise, and measures to address this issue were also required.

Patent No. 5267288

The object of the present invention is to provide a pneumatic tire that has a porous sound-absorbing material on the inner surface of the tire to improve noise performance while suppressing the deterioration of high-speed durability and further improving noise performance.

In order to achieve the above object, a pneumatic tire of the present invention includes a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewall portions, the pneumatic tire having a carcass layer mounted between the pair of bead portions, a plurality of belt layers disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer disposed on the outer peripheral side of the belt layer, the belt cover layer comprising organic fiber cords covered with a coating rubber and arranged in the circumferential direction of the tire. the organic fiber cord is a polyethylene terephthalate fiber cord having an elastic modulus in the range of 3.5 cN/(tex·%) to 5.5 cN/(tex·%) at 100°C under a load of 2.0 cN/dtex, the cord tension in the area of the organic fiber cord overlapping with the belt layer is 0.9 cN/dtex or more, a sound absorbing material made of a porous material and having a glass transition temperature of -60°C to -45°C is installed on the inner surface of the tread portion, and a cross-sectional area of the sound absorbing material is 10% to 30% of the cross-sectional area of the tire cavity.

In the present invention, as described above, a sound-absorbing material of an appropriate size is installed on the inner surface of the tread portion, so that cavity resonance can be suppressed and 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 compensate for the high-speed durability that is feared to be reduced by the sound-absorbing material. Specifically, the inventor has studied pneumatic tires equipped with a belt cover layer made of PET fiber cords intensively, and has found that by optimizing the dip treatment of the PET fiber cords and setting the elastic modulus at 100°C under a load of 2.0 cN/dtex within a predetermined range, the fatigue resistance and hoop effect of the cord suitable for the belt cover layer can be obtained. Therefore, as described above, by using a PET fiber cord having an elastic modulus at 100°C under a load of 2.0 cN/dtex in the range of 3.5 cN/(tex·%) to 5.5 cN/(tex·%) as the organic fiber cord constituting the belt cover layer, it is possible to maintain and improve the high-speed durability that is feared to be reduced by the sound-absorbing material. Furthermore, the belt cover layer made of such low-elasticity PET fiber cords is expected to have the effect of reducing mid-frequency road noise due to its physical properties, further improving noise performance.

In the present invention, as described above, the cord tension in the region where the organic fiber cord overlaps with the belt layer is 0.9 cN/dtex or more, which is advantageous for suppressing heat generation and improving durability of the tire.

In the present invention, it is preferable that the density of the sound-absorbing material is 10 kg/ ^m3 to 30 kg/ ^m3 , and the number of cells of the sound-absorbing material is 30 cells/25 mm to 80 cells/25 mm. This makes the sound-absorbing material low-density, suppressing heat accumulation and improving high-speed durability. In addition, by ensuring an appropriate number of cells in the sound-absorbing material, the air bubbles can be made fine, allowing the sound-absorbing material to exhibit a good sound-absorbing effect.

In the present invention, it is preferable that the sound-absorbing material has a missing portion in at least one location in the tire circumferential direction. This promotes heat dissipation from the sound-absorbing material, which is advantageous for suppressing heat accumulation during driving and improving high-speed durability. It also makes it possible to withstand for a long period of time the expansion caused by tire inflation and the shear strain of the adhesive surface caused by rolling contact with the ground.

In this case, it is preferable that the total length of the sound-absorbing material along the tire circumferential direction is 75% to 95% of the maximum inner circumference of the tire. Ensuring a sufficient total length of the sound-absorbing material in this way is advantageous for improving the sound absorption effect.

In the present invention, it is preferable that the hardness x [N/314 cm ² ] and the breaking elongation y [%] of the sound-absorbing material satisfy the relationships 130≦y≦500, y≦−21x+2770, and x≧60. By optimizing the relationship between the hardness and breaking elongation of the sound-absorbing material in this manner, peeling or breakage of the sound-absorbing material can be effectively prevented even under high load or low temperature.

In the present invention, as described above, the glass transition temperature of the sound absorbing material is -60°C to -45°C. In addition, it is preferable that the sound absorbing material is made of polyurethane foam resin. By making the sound absorbing material out of such a material, it is possible to effectively improve the sound absorbing performance. The glass transition temperature of the sound absorbing material can be measured by a differential scanning calorimeter (DSC).

In the present invention, the hardness, breaking elongation, density and cell number of the sound absorbing material are measured in accordance with JIS-K6400. Regarding the hardness of the sound absorbing material, the D method is used for the hardness test of the sound absorbing material. In addition, the various dimensions and the inner volume of the tire are measured in a state where the tire is mounted on a regular rim and filled with regular internal pressure. In particular, the inner 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 that is determined for each tire by the standard system that includes the standard on which the tire is based, for example, the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. However, if the tire is a tire installed on a new car, the volume of the cavity is determined using the genuine wheel on which the tire is mounted. "Normal internal pressure" refers to the air pressure set for each tire by the standards on which the tire is based, including the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and the "INFLATION PRESSURE" for ETRTO. However, if the tire is a new vehicle tire, the air pressure indicated on the vehicle should be used.

1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. 1 is an equatorial cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. 4 is a graph showing the relationship between hardness x [N/314 cm ² ] and breaking elongation y [%] in the sound-absorbing material used in the pneumatic tire of the present invention.

The configuration of the present invention will be described in detail below with reference to the attached drawings.

As shown in FIG. 1, the pneumatic tire of the present invention comprises a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the tire radial inner side of the sidewall portions 2. In FIG. 1, the symbol CL indicates the tire equator. Although not depicted because FIG. 1 is a meridian cross section, the tread portion 1, the sidewall portions 2, and the bead portions 3 each extend in the tire circumferential direction to form an annular shape, which constitutes the basic toroidal structure of a pneumatic tire. The following explanation using FIG. 1 is basically based on the meridian cross section shown in the figure, but each tire component extends in the tire circumferential direction to form an annular shape.

In the illustrated example, multiple main grooves (four 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. In addition to the main grooves, various grooves and sipes including lug grooves extending in the tire width direction can also be formed.

Between the pair of left and right bead portions 3, a carcass layer 4 including a plurality of reinforcing cords (carcass cords) extending in the tire radial direction is installed. 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 back 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 wrapped by the main body portion of the carcass layer 4 (the portion extending from the tread portion 1 through each sidewall portion 2 to each bead portion 3) and the folded back portion (the portion folded back around the bead core 5 at each bead portion 3 and extending toward each sidewall portion 2). For example, a polyester cord is preferably used as the carcass cord constituting the carcass layer 4.

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

Furthermore, a belt cover layer 8 is provided on the outer periphery of the belt layer 7 in order to compensate for the high-speed durability that may be reduced due to heat accumulation in the sound-absorbing material 10 described later, and to reduce mid-frequency road noise. 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 cord (in the following description, this cover cord may be referred to as an "organic fiber cord"). In the belt cover layer 8, the cover cord is set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction. In the present invention, the belt cover layer 8 necessarily includes a full cover layer 8a that covers the entire belt layer 7, and can optionally include 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 configured by winding a strip material in the tire circumferential direction, in which at least one organic fiber cord is aligned and covered with a coating rubber, in a spiral shape, and it is particularly preferable to have a jointless structure.

In the present invention, a polyethylene terephthalate fiber cord (PET fiber cord) having an elastic modulus of 3.5 cN/(tex·%) to 5.5 cN/(tex·%) at 100°C under a load of 2.0 cN/dtex is used as the organic fiber cord constituting the belt cover layer 8. By using a specific PET fiber cord as the organic fiber cord constituting the belt cover layer 8 in this way, it is possible to effectively reduce mid-frequency road noise while compensating for and maintaining the high-speed durability that may be reduced due to heat storage in the sound absorbing material 10 described below. If the elastic modulus of this PET fiber cord at 100°C under a load of 2.0 cN/dtex is less than 3.5 cN/(tex·%), it is not possible to sufficiently reduce mid-frequency road noise. If the elastic modulus of the PET fiber cord at 100°C under a load of 2.0 cN/dtex exceeds 5.5 cN/(tex·%), the fatigue resistance of the cord decreases and the durability of the tire decreases. In the present invention, the elastic modulus [N/(tex·%)] at 100°C under a load of 2.0 cN/dtex is calculated in accordance with JIS-L1017 "Testing Method for Chemical Fiber Tire Cords" by conducting a tensile test under conditions of a gripping distance of 250 mm and a tensile speed of 300±20 mm/min, and converting the slope of the tangent at the point on the load-elongation curve corresponding to a load of 2.0 cN/dtex into a value per 1 tex.

Furthermore, when this organic fiber cord (PET fiber cord) is used as the belt cover layer 8, the cord tension in the area overlapping with the belt layer 7 is preferably 0.9 cN/dtex or more, more preferably 1.5 cN/dtex to 2.0 cN/dtex. By setting the cord tension in the tire in this manner, heat generation can be suppressed and the durability of the tire can be improved. If the cord tension in the area overlapping with the belt layer 7 of this organic fiber cord (PET fiber cord) is less than 0.9 cN/dtex, the peak of tan δ increases, and the effect of improving the durability of the tire cannot be sufficiently obtained. The cord tension in the area overlapping with the belt layer 7 of the organic fiber cord (PET fiber cord) constituting the belt cover layer 8 is measured at least two revolutions inside the end of the strip material constituting the belt cover layer 8 in the tire width direction.

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 manner, it is possible to effectively reduce road noise while more effectively maintaining the durability of the pneumatic tire. If the heat shrinkage stress of the PET fiber cord at 100°C is less than 0.6 cN/tex, the hoop 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 it is preferably set to 2.0 cN/tex, for example. In the present invention, the heat shrinkage stress at 100°C (cN/tex) is the heat shrinkage stress of the sample cord measured when heated under the conditions of a sample length of 500 mm and heating conditions of 100°C x 5 minutes in accordance with JIS-L1017 "Test Method for Chemical Fiber Tire Cords".

In order to obtain a PET fiber cord having the above-mentioned physical properties, for example, the dipping process may be optimized. That is, prior to the calendaring process, the PET fiber cord is dipped in an adhesive, and in the normalizing process after the two-bath process, it is preferable to set the atmospheric temperature in the range of 210°C to 250°C and the cord tension in the range of 2.2×10 ^-2 N/tex to 6.7×10 ^-2 N/tex. This makes it possible to impart the above-mentioned desired physical properties to the PET fiber cord. If the cord tension in the normalizing process is less than 2.2×10 ^-2 N/tex, the cord elastic modulus becomes low and the mid-frequency road noise cannot be sufficiently reduced, and conversely, if it is more than 6.7×10 ^-2 N/tex, the cord elastic modulus becomes high and the fatigue resistance of the cord decreases.

In the pneumatic tire of the present invention, as shown in FIG. 1, a sound-absorbing material 10 is attached along the tire circumferential direction in an area 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 an adhesive layer 11 made of, for example, an adhesive or a double-sided adhesive tape. The sound-absorbing material 10 is made of a porous material having continuous bubbles, and has a predetermined sound-absorbing characteristic based on its porous structure. For example, polyurethane foam resin (polyurethane foam) may be used as the porous material constituting the sound-absorbing material 10. 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 low temperatures, exerting a sound-absorbing effect, and reducing cavity resonance sounds. In addition, from the viewpoint of adhesion to the inner surface of the tire, it is desirable that the sound-absorbing material 10 does not contain a water repellent agent. In the embodiment of FIG. 1, the sound-absorbing material 10 is made 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%, of the volume of the cavity (cavity volume) formed between the tire and the rim. The width of the sound-absorbing material 10 is preferably 30% to 90%, more preferably 40% to 70%, of the tire ground contact width. This ensures sufficient sound absorbing effect of the sound-absorbing material 10, leading to improved quietness. If the volume of the sound-absorbing material 10 is less than 10% of the tire's cavity volume, the sound-absorbing effect cannot be adequately obtained. If the volume of the sound-absorbing material 10 exceeds 30% of the tire's cavity volume, heat accumulation during driving increases, and there is a risk of high-speed durability decreasing.

The density of the sound-absorbing material 10 is preferably 10 kg/m ³ to 30 kg/m ³ , more preferably 15 kg/m ³ to 25 kg/m ³ . The number of cells of the sound-absorbing material 10 is preferably 30/25 mm to 80/25 mm, more preferably 40/25 mm to 70/25 mm. By setting the density of the sound-absorbing material 10 in this manner, the sound-absorbing material 10 has a low density and heat storage is suppressed, which leads to maintaining and improving high-speed durability. In addition, the sound-absorbing material 10 can be made lighter when it has a low density, so that it is possible to reduce the rolling resistance. On the other hand, by ensuring the number of cells of the sound-absorbing material 10 appropriately as described above, the bubbles can be made fine, 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 , there is a risk that the durability of the sound-absorbing material 10 itself will decrease. If the density of the sound-absorbing material 10 exceeds 30 kg/ ^m3 , it is not possible to achieve a low density, and the effect of suppressing heat accumulation is not sufficiently obtained. If the number of cells in the sound-absorbing material 10 is less than 30 cells/25 mm, the bubbles cannot be made sufficiently fine, and further improvement in sound absorption performance cannot be expected. If the number of cells in the sound-absorbing material 10 exceeds 80 cells/25 mm, the individual bubbles may become too fine, and it may become difficult to ensure sound absorption performance.

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

When the missing portion 12 is provided in this way, the total length of the sound absorbing material 10 along the tire circumferential direction is preferably 75% to 95% of the maximum inner circumference of the tire, and more preferably 80% to 90%. Even when the missing portion 12 is present in this way, the sound absorbing effect can be reliably ensured by ensuring a sufficient total length of the sound absorbing material 10. Note that when there are multiple missing portions 12, the total sum of the lengths along the tire circumferential direction of the individual sound absorbing materials 10 divided by the missing portions 12 is the "total length". If the total length along the tire circumferential direction of the sound absorbing material 10 is less than 75% of the maximum inner circumference of the tire, the total amount of the sound absorbing material 10 is reduced, making it difficult to ensure sufficient sound absorbing performance. If the total length along the tire circumferential direction of the sound absorbing material 10 exceeds 95% of the maximum inner circumference of the tire, the missing portion 12 cannot be sufficiently ensured, and the effect of suppressing heat accumulation by heat dissipation from the missing portion 12 cannot be expected to be sufficient.

In the present invention, it is preferable that the hardness x [N/314 cm ² ] and the breaking elongation y [%] of the sound-absorbing material 10 satisfy the relationships of 130≦y≦500, y≦-21x+2770, and x≧60. It is more preferable that the relationships of 80<x≦120, 140≦y≦490, and/or y≦-21x+2700 are satisfied, and it is even more preferable that the relationships of 80<x≦100, 150≦y≦480, and/or y≦-21x+2600 are satisfied. The hardness x and breaking elongation y of the sound-absorbing material 10 are hardness and breaking elongation measured under standard conditions (temperature of 23° C., relative humidity of 50%).

Specifically, the shaded area S in Fig. 3 indicates a preferred range for the physical properties of the sound-absorbing material 10. In Fig. 3, if the hardness x of the sound-absorbing material 10 exceeds the upper limit specified by the above relational expression, it will not be able to follow the deformation of the tire during load endurance, and there will be a tendency for the sound-absorbing material 10 to peel off, and if it is 80 N/314 ^cm2 or less, the sound-absorbing material 10 will deform due to compression set during high-speed driving, and will not be able to obtain a sufficient sound-absorbing effect. In addition, if the breaking elongation y of the sound-absorbing material 10 is smaller than 130%, there will be a tendency for the sound-absorbing material 10 to break easily during high tire deformation, and this tendency will be particularly noticeable at low temperatures.

The present invention achieves a good balance between high-speed durability and noise performance through cooperation between the above-mentioned belt cover layer 8 and sound-absorbing material 10. In other words, the present invention uses the sound-absorbing material 10 to suppress noise caused by cavity resonance, while the belt cover layer 8 maintains and improves high-speed durability, which is feared to decrease due to heat accumulation in the sound-absorbing material 10, and further suppresses mid-frequency road noise through the physical properties of the belt cover layer 8 (further improving noise performance). Therefore, the preferred physical properties and structural features of the above-mentioned belt cover layer 8 and sound-absorbing material 10 can be adopted in appropriate combinations.

The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

Tires were produced as Conventional Example 1, Comparative Examples 1 to 6, and Examples 1 to 6, having a tire size of 225/60R18 and the basic structure illustrated in FIG. 1, in which the elastic modulus [cN/(tex·%)] at 100° C. under a load of 2.0 cN/dtex of the organic fiber cord (nylon fiber cord (shown as "N66" in the table) or polyethylene terephthalate fiber cord (shown as "PET" in the table)) constituting the belt cover layer, the cord tension [cN/dtex] in the area overlapping with the belt layer, the ratio [%] of the cross-sectional area of the sound-absorbing material to the cross-sectional area of the tire cavity, the density [kg/ ^m3 ] of the sound-absorbing material, the number of cells [pcs/25 mm] of the sound-absorbing material, and the number of intermittent portions were varied as shown in Tables 1 to 2.

In both examples, the belt cover layer has a jointless structure in which a strip of a single organic fiber cord (nylon fiber cord or polyethylene terephthalate fiber cord) covered with coating rubber is wound spirally in the tire circumferential direction. The cord density in the strip is 50 cords/50 mm. In both cases, the organic fiber cord has a structure of 1100 dtex/2.

In each example, the modulus of elasticity [cN/(tex·%)] at 100°C under a load of 2.0 cN/dtex was calculated by performing a tensile test under conditions of a grip interval of 250 mm and a tensile speed of 300±20 mm/min in accordance with JIS-L1017 "Testing Method for Chemical Fiber Tire Cords" and converting the slope of the tangent at the point corresponding to a load of 2.0 cN/dtex on the load-elongation curve into a value per 1 tex. The cord tension [cN/dtex] in the tire was also calculated by removing the tread rubber from the tread portion 1 to expose the belt cover layer, peeling off the organic fiber cord from a predetermined length range of the belt cover layer, measuring the length after the extraction, and determining the amount of shrinkage relative to the length before the extraction. In particular, the average amount of shrinkage was calculated for five fiber cords located in the center of the outermost belt layer. The load corresponding to the amount of shrinkage (%) was then calculated from the S-S curve and converted into a value per 1 dtex.

These test tires were evaluated for road noise and high-speed durability using the following evaluation methods, and the results are shown in Tables 1 and 2.

Road noise Each test tire was mounted on a wheel with a rim size of 18x7J and installed as the front and rear wheels of a passenger car (front-wheel drive vehicle) with an engine displacement of 2.5L, the air pressure was set to 230kPa, a sound-collecting microphone was installed inside the driver's seat window, and the sound pressure level was measured at a frequency of about 315Hz when the vehicle was driven on a test course consisting of an asphalt road surface at an average speed of 50km/h. The evaluation results were shown as the amount of change (dB) relative to Conventional Example 1, which was used as the standard. A negative value for the amount of change means that the road noise has been reduced.

High-Speed Durability Each test tire was mounted on a wheel with a rim size of 18×7J, inflated to an internal pressure of 230 kPa, and mounted on a drum testing machine equipped with a steel drum with a diameter of 1707 mm and a smooth surface. The ambient temperature was controlled to 38±3° C., and the speed was accelerated from 120 km/h at 50 km/h intervals for 24 hours, and the running distance until the tire broke down was measured. The evaluation results were expressed as an index using the measured running distance, with Conventional Example 1 being set at 100. The larger the index value, the longer the running distance until the tire broke down and the better the high-speed durability. Note that 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 reference conventional example 1. On the other hand, the tires of Comparative Examples 1 and 2 had a high elastic modulus at 2.0 cN/dtex load at 100 ° C of the polyethylene terephthalate fiber cord constituting the belt cover layer, and the cross-sectional area ratio of the sound absorbing material was large, so the high-speed durability was reduced. The tire of Comparative Example 3 had a low elastic modulus at 2.0 cN/dtex load at 100 ° C of the polyethylene terephthalate fiber cord constituting the belt cover layer, so the road noise reduction effect of the belt cover layer could not be expected and sufficient sound absorption performance was not obtained. In addition, the cross-sectional area ratio of the sound absorbing material was large, so the high-speed durability was reduced. The tire of Comparative Example 4 had a small cross-sectional area ratio of the sound absorbing material, so the sound absorbing performance was not sufficient. The tire of Comparative Example 5 had a large cross-sectional area ratio of the sound absorbing material, so the effect of improving high-speed durability was not sufficiently obtained. In the tire of Comparative Example 6, the belt cover layer was made of nylon fiber cords, so the belt cover layer did not provide the effect of improving high-speed durability.

Reference Signs List 1 tread portion 2 sidewall portion 3 bead portion 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 portion CL tire equator

Claims (6)

A pneumatic tire comprising a tread portion extending in a circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewall portions, the pneumatic tire having a carcass layer mounted between the pair of bead portions, a plurality of belt layers disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer disposed on the outer peripheral side of the belt layer,
the belt cover layer is formed by winding an organic fiber cord covered with a coating rubber in a spiral shape along the circumferential direction of the tire, the organic fiber cord being a polyethylene terephthalate fiber cord having an elastic modulus in the range of 3.5 cN/(tex·%) to 5.5 cN/(tex·%) at 100° C. under a load of 2.0 cN/dtex, and a cord tension in a region of the organic fiber cord overlapping with the belt layer is 0.9 cN/dtex or more,
A pneumatic tire characterized in that a sound-absorbing material made of a porous material and having a glass transition temperature of -60°C to -45°C is installed on the inner surface of the tread portion, and the cross-sectional area of the sound-absorbing material is 10% to 30% of the cross-sectional area of the tire cavity. 2. The pneumatic tire according to claim 1 , wherein the density of the sound absorbing material is 10 kg/m ³ to 30 kg/m ³ , and the number of cells of the sound absorbing material is 30 cells/25 mm to 80 cells/25 mm. 3. The pneumatic tire according to claim 1, wherein the sound absorbing material has a missing portion at least at one location in the circumferential direction of the tire. The pneumatic tire according to claim 3 , characterized in that a total length of the sound absorbing material along the tire circumferential direction is 75% to 95% of a maximum inner circumference of the tire. The pneumatic tire according to any one of claims 1 to 4, characterized in 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 130≦y≦ 500 , y≦-21x+2770, and x≧60. 6. The pneumatic tire according to claim 1, wherein the sound absorbing material is made of a polyurethane foam resin.

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