JP7477759B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire with a carcass layer made of organic fiber cords.

Pneumatic tires generally have a carcass layer mounted between a pair of bead portions, and the carcass layer is composed of multiple reinforcing cords (carcass cords). Organic fiber cords are mainly used as carcass cords. In particular, for tires that require excellent driving stability, rayon fiber cords with high rigidity are sometimes used (see, for example, Patent Document 1).

On the other hand, in recent years, there has been an increasing demand for lighter tires and lower rolling resistance, and studies have been conducted to reduce the rubber gauge of the tread. However, in the case of tires with a carcass layer made of the above-mentioned rayon fiber cord, there is a concern that the shock burst resistance will decrease as the tread is made thinner. Note that shock burst resistance refers to the durability against damage (shock burst) caused by a large shock to the tire during driving, which causes the carcass to break, and is measured, for example, by a plunger energy test (a test in which a plunger of a specified size is pressed against the center of the tread to measure the breaking energy when the tire breaks). Therefore, in order to improve shock burst resistance while ensuring good steering stability equivalent to that when rayon fiber cord is used, the use of polyester fiber cords with specified physical properties has been considered. However, if polyester fiber cords are simply used instead of rayon fiber cords, there is a problem that load durability cannot be sufficiently ensured due to the difference in their physical properties (for example, heat generation).

JP 2015-205666 A

The object of the present invention is to provide a pneumatic tire that improves shock burst resistance and load durability while maintaining good steering stability, achieving a high degree of compatibility between these performance characteristics.

In order to achieve the above object, the pneumatic tire of the present invention comprises a tread portion extending in the circumferential direction of the tire 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 on the radially inner side of the sidewall portions, a bead core arranged in each of the bead portions, a bead filler arranged on the radially outer side of the bead core, and at least one carcass layer mounted between the pair of bead portions, the carcass layer being composed of a carcass cord made of polyester fiber cord, the breaking elongation of the carcass cord being 20% to 30%, and the carcass layer being wound from the inner side of the tire to the outer side around the bead core and the bead filler arranged in each bead portion. The tire is characterized in that it is made up of a main body portion located between the pair of bead portions and a rolled-up portion rolled up on the tire width direction outer side of the bead core and the bead filler, a second filler is provided on the tire width direction outer side of the main body portion and the rolled-up portion, the upper end of the second filler is located radially outward of the upper end of the bead filler, the lower end of the second filler is located radially inward of the upper end of the bead filler, the tire radial height h1 of the upper end of the bead filler is 50% or less of the tire cross-sectional height SH, the tire radial height h2 of the upper end of the second filler is 80% or less of the tire cross-sectional height SH, and the tire radial length L of the second filler is 20% to 70% of the tire cross-sectional height SH.

In the present invention, since the carcass cord constituting the carcass layer is a polyester fiber cord with a breaking elongation of 20% to 30%, shock burst resistance can be improved while ensuring the same level of good steering stability as when a rayon fiber cord is used. That is, since the carcass cord has the above-mentioned breaking elongation, the rigidity of the carcass cord can be appropriately ensured, and good steering stability can be exhibited. In addition, since the carcass cord has the above-mentioned breaking elongation, the carcass cord is more likely to follow local deformation, and it is possible to fully tolerate deformation during the plunger energy test (when pressed by the plunger), and the fracture energy can be improved. In other words, the fracture durability against the projection input of the tread portion during driving is improved, and shock burst resistance can be improved. On the other hand, since the second filler is provided as described above, the load durability, which is a concern for reduction when a polyester fiber cord is used instead of a rayon fiber cord, can be maintained and improved. In particular, since the positional relationship between the second filler and the bead filler (the positional relationship between the respective ends) is set as described above, stress concentration can be suppressed and further improvement of load durability can be achieved. This cooperation allows the tire to maintain excellent handling stability while improving shock burst resistance and load durability, achieving a high level of compatibility between these performance characteristics.

In the present invention, it is preferable that the tire radial height h3 of the lower end of the second filler is 10% or more of the tire cross-sectional height SH. By placing the second filler in such a position, effective reinforcement can be achieved, which is advantageous for improving load durability.

In the present invention, when the distance between the upper end of the bead filler and the lower end of the second filler along the tire radial direction is distance D1, and the distance between the upper end of the bead filler and the upper end of the second filler along the tire radial direction is distance D2, it is preferable that these distances D1 and D2 are each 5 mm or more. By setting the positional relationship between the bead filler and the second filler in this way, stress concentration can be suppressed, which is advantageous for improving load durability.

In the present invention, when the distance in the tire radial direction between the rolled-up end of the carcass layer and the upper end of the bead filler is distance d1, the distance in the tire radial direction between the rolled-up end of the carcass layer and the upper end of the second filler is distance d2, and the distance in the tire radial direction between the rolled-up end of the carcass layer and the lower end of the second filler is distance d3, it is preferable that each of these distances d1, d2, and d3 is 5 mm or more. By setting the positional relationship between the rolled-up end of the carcass layer, the bead filler, and the second filler in this way, stress concentration can be suppressed, which is advantageous for improving load durability.

In the present invention, it is preferable that the thickness G of the second filler measured on a line passing through the upper end of the bead filler and perpendicular to the inner surface of the tire is 1 mm or more. This allows the vicinity of the upper end of the bead filler to be adequately reinforced, which is advantageous for improving load durability.

In the present invention, it is preferable that the carcass layer in the center region of the tread portion is a single layer. This allows the tire weight to be reduced and rolling resistance to be reduced while still ensuring good shock burst resistance.

In the present invention, it is preferable that the intermediate elongation of the carcass cord at a load of 1.0 cN/dtex is 5.0% or less. This ensures sufficient rigidity of the carcass cord, which is advantageous for improving steering stability.

In the present invention, it is preferable that the carcass cord has a corrective fineness of 4000 dtex or more and 8000 dtex or less. This ensures sufficient rigidity of the carcass cord, which is advantageous for improving steering stability.

In the present invention, the twist coefficient K of the carcass cords represented by the following formula (1) is preferably equal to or greater than 2000. This makes it possible to ensure sufficient rigidity of the carcass cords, which is advantageous for improving steering stability.
K = T × D ^1/2 ... (1)
(In the formula, T is the number of twists of the carcass cord [turns/10 cm], and D is the total fineness of the carcass cord [dtex].)

In the present invention, the "center region of the tread" refers to an area that is 30% of the contact width centered on the tire equator. The "contact width" refers to the length measured along the tire width between both ends (contact ends) of the contact area formed when a tire is mounted on a standard rim, inflated to the standard internal pressure, placed vertically on a flat surface, and subjected to a standard load. The "standard rim" refers to 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. The term "normal internal pressure" refers to the air pressure determined for each tire by the respective standards, including the standards on which the tire is based. In the case of JATMA, this is the maximum air pressure, in the case of TRA, this is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, this is the "INFLATION PRESSURE", but in the case of a tire for a passenger car, this is 180 kPa. "Normal load" is the load determined for each tire by each standard, including the standard on which the tire is based. For JATMA, it is the maximum load capacity. For TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." For ETRTO, it is the "LOAD CAPACITY." However, if the tire is for passenger cars, it is a load equivalent to 88% of the above load.

1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment 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, and the symbol E indicates the ground contact edge. 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.

Between the pair of left and right bead portions 3, a carcass layer 4 including a plurality of reinforcing cords (carcass cords described later) extending in the tire radial direction is installed. The number of layers of the carcass layer 4 is not particularly limited, but from the viewpoint of reducing the tire weight and rolling resistance, it is preferable that the carcass layer 4 is one layer in the center region Ce of the tread portion 1 (a region that is 30% of the ground contact width W centered on the tire equator CL). A bead core 5 is embedded in each bead portion 3, 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 4a 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 rolled-up portion 4b (the portion folded back around the bead core 5 in each bead portion 3 and extending toward each sidewall portion 2). In the illustrated example, the rolled-up portion 4b extends from the outer end of the bead filler 6 in the tire radial direction along the main body portion 4a, and the end of the rolled-up portion 4b (hereinafter referred to as the "rolled-up end") reaches near the end of the belt layer 7 described below.

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, for example, steel cords are preferably used.

Furthermore, a belt reinforcing layer 8 is provided on the outer periphery of the belt layer 7 for the purpose of improving high-speed durability. The belt reinforcing layer 8 includes a reinforcing cord (cover cord) oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the cover cord with respect to the tire circumferential direction is set to, for example, 0° to 5°. The belt reinforcing layer 8 may be a full cover layer 8a that covers the entire width of the belt layer 7, or a pair of edge cover layers 8b that locally cover both ends of the belt layer 7 in the tire width direction, either alone or in combination (in the illustrated example, both the full cover layer 8a and the edge cover layer 8b are provided). The belt reinforcing layer 8 may be formed, for example, by winding a strip material in the tire circumferential direction, in which at least one cover cord is aligned and covered with a coating rubber. For example, an organic fiber cord is preferably used as the cover cord.

In the present invention, the carcass cord constituting the carcass layer 4 is composed of a polyester fiber cord made by twisting together filament bundles of polyester fibers. The breaking elongation of this carcass cord (polyester fiber cord) is 20% to 30%, preferably 22% to 28%. Since a carcass cord (polyester fiber cord) having such physical properties is used for the carcass layer 4, it is possible to improve shock burst resistance while ensuring good steering stability equivalent to that of a conventional rayon fiber cord. That is, since the carcass cord has the above-mentioned breaking elongation, it is possible to ensure a moderate rigidity of the carcass cord and to exhibit good steering stability. In addition, since the carcass cord has the above-mentioned breaking elongation, the carcass cord is more likely to follow local deformation, and it is possible to fully tolerate deformation during the plunger energy test (when pressed by the plunger), and the breaking energy can be improved. In other words, the breaking durability of the tread portion against the projection input during driving is improved, and shock burst resistance can be improved. In particular, even if the carcass layer 4 is a single layer in the center region Ce of the tread portion 1 as described above, the physical properties of the carcass cord ensure good shock burst resistance. If the breaking elongation of the carcass cord is less than 20%, the breaking elongation is too low and the effect of improving shock burst resistance cannot be obtained. If the breaking elongation of the carcass cord exceeds 30%, the intermediate elongation also tends to be large, which may reduce rigidity and steering stability. The "breaking elongation" is the elongation rate (%) of the sample cord measured when the cord is cut 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 "Test method for chemical fiber tire cords".

In addition to having the above physical properties, the carcass cord (polyester fiber cord) preferably has an intermediate elongation at a load of 1.0 cN/dtex of 5.0% or less, more preferably 4.0% or less. By using a cord with such physical properties, it is possible to ensure sufficient rigidity, which is advantageous for improving steering stability. If the intermediate elongation at a load of 1.0 cN/dtex of the carcass cord exceeds 5.0%, there is a risk that the rigidity cannot be sufficiently ensured and the effect of improving steering stability will be limited. The "intermediate elongation at a load of 1.0 cN/dtex" is the elongation rate (%) of the sample cord measured at a load of 1.0 cN/dtex in a tensile test performed under conditions of a grip interval of 250 mm and a tensile speed of 300±20 mm/min in accordance with JIS L1017 "Test method for chemical fiber tire cords".

In addition to having the above physical properties, the carcass cord (polyester fiber cord) preferably has a corrected fineness of 4000 dtex or more and 8000 dtex or less, more preferably 5000 dtex or more and 7000 dtex or less. By using a cord with such a corrected fineness, it is possible to ensure sufficient rigidity, which is advantageous for improving steering stability. If the corrected fineness of the carcass cord is less than 4000 dtex, it becomes difficult to ensure sufficient steering stability. If the corrected fineness of the carcass cord is more than 8000 dtex, it becomes difficult to ensure sufficient shock burst resistance.

In addition to having the above physical properties, the carcass cord (polyester fiber cord) preferably has a heat shrinkage rate of 0.5% to 2.5%, more preferably 1.0% to 2.0%. By using a cord with such a heat shrinkage rate, it is possible to suppress the occurrence of kinks (twisting, breaking, twisting, deformation, etc.) in the organic fiber cord during vulcanization, which can lead to a decrease in durability and a decrease in uniformity. If the heat shrinkage rate of the carcass cord is less than 0.5%, kinks are likely to occur during vulcanization, making it difficult to maintain good durability. If the heat shrinkage rate of the carcass cord exceeds 2.5%, there is a risk of the uniformity deteriorating. The "heat shrinkage rate" is the dry heat shrinkage rate (%) of the sample cord measured when heated under the conditions of a sample length of 500 mm and heating conditions of 150°C x 30 minutes in accordance with JIS L1017 "Test method for chemical fiber tire cords".

In addition to having the above-mentioned physical properties, the carcass cord (polyester fiber cord) preferably has a twist coefficient K represented by the following formula (1) of 2000 or more, more preferably 2100 to 2400. Note that this twist coefficient K is the value of the carcass cord after dip treatment. By using a cord having such a twist coefficient K, it is possible to ensure sufficient rigidity, which is advantageous for improving steering stability. In addition, it is possible to improve cord fatigue properties and ensure excellent durability. In this case, if the twist coefficient K of the carcass cord is less than 2000, there is a risk that sufficient rigidity cannot be ensured and the effect of improving steering stability will be limited.
K = T × D ^1/2 ... (1)
(In the formula, T is the number of twists of the carcass cord [turns/10 cm], and D is the total fineness of the carcass cord [dtex].)

The type of fiber constituting the carcass cord (polyester fiber cord) is not particularly limited, but examples include polyethylene terephthalate fiber (PET fiber), polyethylene naphthalate fiber (PEN fiber), polybutylene terephthalate fiber (PBT), and polybutylene naphthalate fiber (PBN), with PET fiber being preferred. Whichever fiber is used, the physical properties of each fiber are advantageous in achieving a good balance between steering stability and shock burst resistance. In particular, PET fiber is inexpensive, which allows for a reduction in the cost of pneumatic tires. It also allows for improved workability when manufacturing the cord.

The above-mentioned carcass cord (polyester fiber cord) can achieve a good balance between steering stability and shock burst resistance due to its physical properties, but there is a concern that the load durability cannot be sufficiently ensured compared to conventional rayon fiber cords. Therefore, in the present invention, a second filler 9 is provided on the tire width direction outer side of the main body portion 4a and the rolled up portion 4b of the carcass layer 4. The second filler 9 is a rubber layer made of a rubber different from the surrounding rubber (rubber constituting the sidewall portion 2), and can be provided adjacent to the main body portion 4a and the rolled up portion 4b of the carcass layer 4 as in the illustrated example. In addition, the upper end (end on the outer side in the tire radial direction) of the second filler 9 is located radially outward of the upper end (end on the outer side in the tire radial direction) of the bead filler 6, and the lower end (end on the inner side in the tire radial direction) of the second filler 9 is located radially inward of the upper end of the bead filler 6. Since the second filler 9 is provided in this way, the rigidity of the sidewall portion 2 can be appropriately improved, and the load durability, which is a concern to be reduced when the above-mentioned polyester fiber cord is used instead of the rayon fiber cord, can be maintained and improved.

When providing the second filler 9 in this manner, the positional relationship between the second filler 9 and the bead filler 6 (the positional relationship between their respective ends) is set as follows, from the perspective of suppressing stress concentration and further improving load durability.

The tire radial height h1 of the upper end of the bead filler 6 is 50% or less of the tire cross-sectional height SH, preferably 15% to 45%. The tire radial height h2 of the upper end of the second filler 9 is 80% or less of the tire cross-sectional height SH, preferably 15% to 75%. The tire radial length L of the second filler 9 is 20% to 70% of the tire cross-sectional height SH, preferably 25% to 45%. By setting it in this way, stress concentration at the ends of each tire component can be suppressed and load durability can be further improved. If the tire radial height h1 of the upper end of the bead filler 6 exceeds 50% of the tire cross-sectional height SH, stress concentration cannot be suppressed and it becomes difficult to ensure load durability. If the tire radial height h2 of the upper end of the second filler 9 exceeds 80% of the tire cross-sectional height SH, the shoulder portion becomes difficult to deform, and the tread portion 1 becomes easily deformed accordingly, making it difficult to ensure shock burst resistance. If the tire radial length L of the second filler 9 is less than 20% of the tire cross-sectional height SH, the second filler 9 is too small and the reinforcing effect of the second filler 9 is not sufficient. If the tire radial length L of the second filler 9 exceeds 70% of the tire cross-sectional height SH, the sidewall portion 2 becomes difficult to deform, and the tread portion 1 becomes easily deformed, making it difficult to ensure shock burst resistance.

The tire radial height h3 of the lower end of the second filler 9 is preferably 10% or more, and more preferably 15% to 20% of the tire cross-sectional height SH. By setting it in this way, effective reinforcement by the second filler 9 can be achieved, which is advantageous for improving load durability. If the tire radial height h3 of the lower end of the second filler 9 is less than 10% of the tire cross-sectional height SH, the second filler 9 will reach the vicinity of the bead core 5, but even if the second filler 9 is provided at this position, no further reinforcing effect can be expected.

As described above, when defining the tire radial heights h1 to h3 of each portion as a percentage of the tire cross-sectional height SH, the tire cross-sectional height SH is not particularly limited, but may be, for example, 70 mm to 120 mm. Also, the aspect ratio of the tire may be, for example, 25% to 50%. Since it is difficult to ensure load durability with tires of this size, the above-mentioned second filler 9 can significantly improve load durability.

As shown in FIG. 2, when the distance D1 is the distance between the upper end of the bead filler 6 and the lower end of the second filler 9 along the tire radial direction, and the distance D2 is the distance between the upper end of the bead filler 6 and the upper end of the second filler 9 along the tire radial direction, the distance D1 is preferably 5 mm or more, more preferably 5 mm to 25 mm, and the distance D2 is preferably 5 mm or more, more preferably 5 mm to 25 mm. By setting them in this way, it is possible to suppress stress concentration at the ends of each tire component, which is advantageous for improving load durability. If the distances D1 and D2 are each less than 5 mm, the upper end of the bead filler 6 and the upper and lower ends of the second filler 9 are close to each other, making it difficult to sufficiently suppress stress concentration. The sum of the distances D1 and D2 is the tire radial length L of the second filler 9, so that the tire radial length L of the second filler 9 is preferably 10 mm or more, more preferably 10 mm to 50 mm.

As shown in FIG. 2, the distance between the rolled-up end of the carcass layer 4 and the upper end of the bead filler 6 in the tire radial direction is distance d1, the distance between the rolled-up end of the carcass layer 4 and the upper end of the second filler 9 in the tire radial direction is distance d2, and the distance between the rolled-up end of the carcass layer 4 and the lower end of the second filler 9 in the tire radial direction is distance d3. Distance d1 is preferably 5 mm or more, more preferably 10 mm to 90 mm, distance d2 is preferably 5 mm or more, more preferably 10 mm to 90 mm, and distance d3 is preferably 5 mm or more, more preferably 10 mm to 90 mm. By setting them in this way, stress concentration at the ends of each tire component can be suppressed, which is advantageous for improving load durability. If the distances d1, d2, and d3 are each less than 5 mm, the rolled-up end of the carcass layer 4 approaches the upper end of the bead filler 6 and the upper and lower ends of the second filler 9, making it difficult to sufficiently suppress stress concentration.

The second filler 9 is preferably used to reinforce the vicinity of the upper end of the bead filler 6. Therefore, the thickness G of the second filler 9 measured on a line passing through the upper end of the bead filler 6 and perpendicular to the inner surface of the tire is preferably set to 1 mm or more, more preferably 1.5 mm to 4.5 mm. This allows the vicinity of the upper end of the bead filler to be appropriately reinforced, which is advantageous for improving load durability. If the thickness G of the second filler 9 is less than 1 mm, the second filler 9 is too thin and the reinforcing effect of the second filler 9 cannot be expected to be sufficient. As shown in the figure, the second filler 9 has a structure in which the thickness gradually decreases toward its upper and lower ends, but the maximum thickness of the second filler 9 measured on a line perpendicular to the inner surface of the tire can be set to, for example, 1.5 mm to 4.5 mm.

The present invention improves steering stability and shock burst resistance through the physical properties of the carcass cord (polyester fiber cord), while maintaining and improving load durability through the second filler 9. Therefore, the above-mentioned physical properties of the carcass cord (polyester fiber cord) and the above-mentioned features of the second filler 9 (such as the positional relationship between the second filler 9 and the bead filler 6) can be adopted in appropriate combination. In either case, the cooperation of the physical properties and features adopted in combination improves shock burst resistance and load durability while maintaining good steering stability, making it possible to achieve a high degree of compatibility between these performances.

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.

The tire size is 315/30ZR21 (105Y), and has the basic structure shown in Figures 1 and 2. The material (type of organic fiber) and physical properties (breaking elongation, intermediate elongation at a load of 1.0 cN/dtex, correct fineness, twist coefficient K) of the carcass cord that constitutes the carcass layer, the presence or absence of a second filler in relation to the tire structure, the ratio of the tire radial height h1 of the upper end of the bead filler to the tire cross-sectional height SH (h1/SH x 100%), the ratio of the tire radial height h2 of the upper end of the second filler to the tire cross-sectional height SH (h2/SH x 100%), the ratio of the tire radial height h3 of the lower end of the second filler to the tire cross-sectional height SH (h3/SH x 100%), and the tire radial length of the second filler to the tire cross-sectional height SH. The ratio of L (L/SH x 100%), the distance D1 between the top end of the bead filler and the bottom end of the second filler in the tire radial direction, the distance D2 between the top end of the bead filler and the top end of the second filler in the tire radial direction, the distance d1 between the rolled-up end of the carcass layer and the top end of the bead filler in the tire radial direction, the distance d2 between the rolled-up end of the carcass layer and the top end of the second filler in the tire radial direction, the distance d3 between the rolled-up end of the carcass layer and the bottom end of the second filler in the tire radial direction, and the thickness G of the second filler measured on a line passing through the top end of the bead filler and perpendicular to the inner surface of the tire were varied as shown in Tables 1 to 3 to produce pneumatic tires of Conventional Example 1, Comparative Examples 1 to 6, and Examples 1 to 16.

In the "Type of organic fiber" column of Tables 1 to 3, the case where a rayon fiber cord was used is indicated as "Rayon," the case where a polyethylene terephthalate fiber (PET fiber) cord was used is indicated as "PET," and the case where a polyethylene naphthalate fiber (PEN fiber) cord was used is indicated as "PEN."

These test tires were evaluated for shock burst resistance, load durability, rolling resistance performance, and handling stability using the following evaluation methods, and the results are shown in Tables 1 to 3.

Shock Burst Resistance Each test tire was mounted on a wheel with a rim size of 21×11.5J, and the air pressure was set to 220 kPa. In accordance with JIS K6302, a plunger with a plunger diameter of 19±1.6 mm was pressed against the center of the tread at a load speed (plunger pushing speed) of 50.0±1.5 m/min to perform a tire destruction test (plunger destruction test), and tire strength (tire destruction energy) was measured. The evaluation results were expressed as an index with the measured value of Conventional Example 1 taken as 100. The larger this value, the larger the destruction energy and the better the shock burst resistance.

Load durability Each test tire was mounted on a wheel with a rim size of 21 x 11.5J, and the air pressure was set to 220 kPa. In accordance with the durability performance test of JIS D4230, an indoor drum test machine (drum diameter: 1707 mm) was used to measure the running distance until the tire broke under the conditions of an ambient temperature of 38 ± 3 ° C and a running speed of 81 km / h, with the load being increased by 15% every 4 hours from 85% of the maximum load specified by JATMA. When the load reached 280% of the maximum load specified by JATMA, the load was set as the final load and the tire was run until it broke. The evaluation results were shown as an index with the measured value of Conventional Example 1 being 100. The higher the index value, the better the load durability.

Low rolling resistance Each test tire was mounted on a wheel with a rim size of 21 x 11.5J, and mounted on a rolling resistance tester equipped with a drum with a radius of 854 mm. The rolling resistance was measured after a preliminary run for 30 minutes under the conditions of an initial temperature of 5°C, an air pressure of 250 kPa, a load of 5.80 kN, and a speed of 80 km/h. The evaluation results were expressed as an index with the measured value of Conventional Example 1 being 100. The smaller the index value, the smaller the rolling resistance and the better the low rolling resistance.

Steering stability Each test tire was mounted on a wheel with a rim size of 21×11.5J, and the air pressure was set to 240 kPa and attached to a test vehicle (a 3L class European car (sedan)). The vehicle was driven at a speed of 60 km/h to 100 km/h on a test course consisting of a flat, circular, dry road surface, and a sensory evaluation was performed on the steering stability (steering ability when the test driver changes lanes and corners, and stability when traveling straight). The evaluation results were expressed as an index with Conventional Example 1 being 100. The higher the index, the better the steering stability.

As can be seen from Tables 1 to 3, the tires of Examples 1 to 16, compared to Conventional Example 1, maintained or improved the steering stability and low rolling resistance while improving the shock burst resistance and load durability. On the other hand, in Comparative Example 1, the breaking elongation of the carcass cord was small, so the shock burst resistance was reduced. In Comparative Example 2, the breaking elongation of the carcass cord was large, so the effect of improving steering stability was not obtained. In Comparative Example 3, the ratio of the tire radial height h1 of the upper end of the bead filler to the tire cross-sectional height SH (h1/SH x 100%) was large, so the load durability was reduced. In Comparative Example 4, the ratio of the tire radial height h2 of the upper end of the second filler to the tire cross-sectional height SH (h2/SH x 100%) was large, so the shock burst resistance was reduced. In Comparative Example 5, the ratio of the tire radial length L of the second filler to the tire cross-sectional height SH (L/SH x 100%) was small, so the load durability was reduced. In Comparative Example 6, the ratio of the tire radial length L of the second filler to the tire cross-sectional height SH (L/SH x 100%) was large, so shock burst resistance was reduced.

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 reinforcing layer 9 Second filler CL Tire equator E Ground contact edge

Claims (9)

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 tire radially inward side of the sidewall portions, a bead core disposed in each of the bead portions, a bead filler disposed on the tire radially outward side of the bead core, and at least one carcass layer mounted between the pair of bead portions,
The carcass layer is composed of a carcass cord made of a polyester fiber cord, and the breaking elongation of the carcass cord is 20% to 30%.
The carcass layer is wound up from the inside to the outside of the tire around the bead core and the bead filler arranged in each bead portion, and is composed of a main body portion located between the pair of bead portions and a wound-up portion wound up on the outside of the bead core and the bead filler in the tire width direction,
a second filler is provided on the outer side of the main body portion and the turned-up portion in the tire width direction, an upper end of the second filler is located outer in the tire radial direction than an upper end of the bead filler, and a lower end of the second filler is located inner in the tire radial direction than the upper end of the bead filler,
A pneumatic tire characterized in that a tire radial height h1 of an upper end of the bead filler is 50% or less of a tire cross-sectional height SH, a tire radial height h2 of an upper end of the second filler is 80% or less of the tire cross-sectional height SH, and a tire radial length L of the second filler is 20% to 70% of the tire cross-sectional height SH. The pneumatic tire according to claim 1, characterized in that the tire radial height h3 of the lower end of the second filler is 10% or more of the tire cross-sectional height SH. The pneumatic tire according to claim 1 or 2, characterized in that the distance D1 between the upper end of the bead filler and the lower end of the second filler along the tire radial direction and the distance D2 between the upper end of the bead filler and the upper end of the second filler along the tire radial direction are each 5 mm or more. The pneumatic tire according to any one of claims 1 to 3, characterized in that the distance between the rolled-up end of the carcass layer and the upper end of the bead filler in the tire radial direction is distance d1, the distance between the rolled-up end of the carcass layer and the upper end of the second filler in the tire radial direction is distance d2, and the distance between the rolled-up end of the carcass layer and the lower end of the second filler in the tire radial direction is distance d3, and each of these distances d1, d2, and d3 is 5 mm or more. A pneumatic tire according to any one of claims 1 to 4, characterized in that the thickness G of the second filler measured on a line passing through the upper end of the bead filler and perpendicular to the inner surface of the tire is 1 mm or more. A pneumatic tire according to any one of claims 1 to 5, characterized in that the carcass layer in the center region of the tread portion is a single layer. A pneumatic tire according to any one of claims 1 to 6, characterized in that the intermediate elongation of the carcass cord at a load of 1.0 cN/dtex is 5.0% or less. A pneumatic tire according to any one of claims 1 to 7, characterized in that the carcass cord has a normal fineness of 4000 dtex or more and 8000 dtex or less. The pneumatic tire according to any one of claims 1 to 8, characterized in that the twist coefficient K of the carcass cords, represented by the following formula (1), is 2000 or more.
K = T × D ^1/2 ... (1)
(In the formula, T is the number of twists of the carcass cord [turns/10 cm], and D is the total fineness [dtex] of the carcass cord.)

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