JP6059429B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that can effectively prevent a crack that tends to occur at the bottom of a shoulder longitudinal groove and improve durability.

  Conventionally, a pneumatic tire has a band ply in which a band cord made of an organic fiber cord or the like is arranged at an angle of 5 degrees or less with respect to the tire circumferential direction on the outer side in the tire radial direction of the belt layer for fastening the carcass. A band layer is provided (see, for example, Patent Document 1 below).

Such a band layer restrains the movement of the belt layer (for example, lifting etc.) during running by restraining the belt layer and improves high-speed durability, steering stability, noise resistance performance, etc. Useful. In order to effectively exhibit such an action, it is generally performed that the binding force of the band cord is relatively increased toward the outer side in the tire axial direction.

JP 2005-263137 A

  However, in the pneumatic tire as described above, the tread end side of the tread portion is firmly restrained when the inner pressure is filled due to the large restraining force of the band cord, and the inflation deformation is suppressed, while the tire equator side is greatly inflated. Due to the deformation, the tread radius tends to be small. As a result, as shown in FIG. 7, there is a problem that a radial tensile strain is generated in the groove bottom 16 b of the shoulder vertical groove 16 extending in the tire circumferential direction on the tread end side, and a crack c is likely to occur. .

  The present invention has been devised in view of the actual situation as described above. The band layer is divided into a shoulder band portion and a center band portion, and the band constraint coefficient R of the shoulder band portion is smaller than that of the center band portion. Moreover, cracks that tend to occur at the bottom of the shoulder vertical groove are effectively prevented by limiting the positional relationship between the inner end of the shoulder band in the tire axial direction and the groove center line of the shoulder vertical groove to a certain range. Thus, the main purpose is to provide a pneumatic tire capable of improving durability.

According to one aspect of the present invention includes a carcass extending to a bead core of a bead portion through a sidewall portion from a tread portion, Rutotomoni disposed within the radially outer tread portion of the carcass, the belt cord A belt layer composed of at least two belt plies arranged at an angle of 10 to 40 degrees with respect to the tire equator, and a belt cord disposed on the outer side in the tire radial direction of the belt layer with respect to the tire circumferential direction. A pneumatic tire comprising a band layer composed of a band ply arranged at an angle of less than or equal to a degree, wherein the tread portion comprises a shoulder longitudinal groove extending in the tire circumferential direction on the most tread end side, and the band layer is A center band portion that extends across the tire equator, and a shoulder band portion that is disposed on the outer side in the tire axial direction of the center band portion. The shoulder band portion has a band constraint coefficient R expressed by the following formula (1) smaller than that of the center band portion, and the inner end of the shoulder band portion in the tire axial direction is a groove of the shoulder vertical groove. It is inside the tire axial direction from the center line,
The distance X in the tire axial direction between the inner end of the shoulder band portion and the groove center line of the shoulder longitudinal groove is a tire axial distance from the tire equator to the outer end in the tire axial direction of the band layer. It is characterized by being 5% or less of the half width.
R = E / S (1)
(Where E is the number of band cords included per 5 cm width of the band ply, and S is the intermediate elongation (%) when the band cord is loaded with 50N)

  In the invention according to claim 2, the intermediate elongation Ss (%) of the band cord of the shoulder band portion is larger than the intermediate elongation Sc (%) of the band cord of the center band portion, The pneumatic tire according to claim 1, wherein the difference in elongation (Ss-Sc) is 1 to 5.5%.

  In the invention according to claim 3, the band cord of the shoulder band portion is a fine yarn nylon cord having a total fineness of 900 to 1350 dtex, and the band cord of the center band portion has a total fineness of 1350 to 1700 dtex. The pneumatic tire according to claim 1, wherein the pneumatic tire is a thick thread nylon cord.

  The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 3, wherein the end Es of the shoulder band portion is 50 to 80% of the end Ec of the center band portion. is there.

The invention according to claim 5 is the pneumatic tire according to any one of claims 1 to 4 , wherein the sidewall portion is provided with a side reinforcing rubber layer having a crescent cross section inside the carcass.

  In the present specification, unless otherwise specified, the dimensions of each part of the tire are values specified in a normal state in which a rim is assembled on a normal rim and a normal internal pressure is filled.

  The “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, JATMA is a standard rim, TRA is “Design Rim”, and ETRTO is a standard rim. If present, it means "Measuring Rim".

  The “regular internal pressure” is the air pressure defined by the standard for each tire. If JATMA, the maximum air pressure, if TRA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” Then, “INFLATION PRESSURE” is set, but when the tire is for a passenger car, the pressure is uniformly set to 180 kPa.

  The pneumatic tire of the present invention includes a carcass extending from a tread portion through a sidewall portion to a bead core of the bead portion, a belt layer disposed radially outside the carcass and inside the tread portion, and a tire of the belt layer And a band layer made of a band ply arranged radially outside and having a band cord arranged at an angle of 5 degrees or less with respect to the tire circumferential direction.

The tread portion includes a shoulder longitudinal groove extending in the tire circumferential direction on the most tread end side. Furthermore, the said band layer consists of a center band part distribute | arranged straddling a tire equator, and a shoulder band part distribute | arranged to the tire axial direction outer side of this center band part. The shoulder band portion has a band constraint coefficient R shown by the following expression (1) smaller than that of the center band portion.
R = E / S (1)
(Where E is the number of band cords included per 5 cm width of the band ply, and S is the intermediate elongation (%) when the band cord is loaded with 50N)

  Further, a tire axial distance X between the inner end of the shoulder band in the tire axial direction and the groove center line of the shoulder longitudinal groove is a tire axial distance from the tire equator to the outer end of the band layer in the tire axial direction. It is 20% or less of the band half width.

  In such a pneumatic tire band layer, the band restraint coefficient R of the shoulder band portion is set smaller than that of the center band portion, so that the restraining force on the tread end side is reduced, and when the inner pressure is filled, the tread end side The tread radius can be increased by relatively expanding and deforming. Thereby, in the pneumatic tire of this invention, it can suppress that the tensile strain of radial direction arises in the groove bottom of a shoulder vertical groove, can prevent generation | occurrence | production of a crack effectively, and can improve durability.

It is sectional drawing of the pneumatic tire of this embodiment. It is a tread enlarged view of FIG. It is sectional drawing which expands and shows the shoulder longitudinal groove at the time of internal pressure filling. It is a tread enlarged view of other embodiments. It is a tread enlarged view of other embodiment. It is sectional drawing of the pneumatic tire of other embodiment. It is sectional drawing which expands and shows the shoulder vertical groove at the time of internal pressure filling of the conventional pneumatic tire.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a pneumatic tire (hereinafter sometimes simply referred to as “tire”) 1 according to the present embodiment includes a carcass 6 that extends from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3. A radial tire for a passenger car comprising: a belt layer 7 disposed on the outer side in the tire radial direction of the carcass 6 and inside the tread portion 2; and a band layer 9 disposed on the outer side in the tire radial direction of the belt layer 7. It is configured as.

  In the tread portion 2 of the present embodiment, a pair of crown longitudinal grooves 15 extending linearly in the tire circumferential direction on both sides of the tire equator C, and the tread end 2e side being linearly continuous in the tire circumferential direction. A pair of extending shoulder longitudinal grooves 16 are formed. Such vertical grooves 15 and 16 can smoothly guide and discharge the water film interposed between the tread surface 2T of the tread portion 2 and the road surface in the tire circumferential direction, and can improve drainage performance. 2, the groove width W1 of the longitudinal grooves 15 and 16 is preferably set to about 5.0 to 9.0 mm and the groove depth D1 is set to about 6.0 to 9.0 mm. Is desirable.

  Here, the tread end 2e is defined by an edge when the edge can be clearly identified by an edge or the like. When such an edge is not clear, a tire is rim-assembled on the regular rim, and The tread end 2e is the contact position on the outermost side in the tire axial direction when the normal internal pressure is charged and the normal load is applied and the camber angle is 0 degrees to contact the plane.

  The “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is set for JATMA, and the table “TIRE LOAD LIMITS” is set for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”. If ETRTO, “LOAD CAPACITY”. In addition, when neither standard exists, a tire manufacturer's recommendation value is applied.

  Further, as shown in FIG. 1, the crown longitudinal groove 15 and the shoulder longitudinal groove 16 are formed from arcuate groove bottoms 15b and 16b and groove bottoms 15b and 16b in a groove cross section perpendicular to the groove length direction. The tread portion includes a pair of groove walls 15w and 16w extending linearly to the tread surface 2T. The radius of curvature r (shown in FIG. 2) of the groove bottoms 15b and 16b is preferably set to about 30 to 200% of the groove width W1.

  The carcass 6 is composed of at least one carcass ply 6A, in this embodiment, one carcass ply 6A. The carcass ply 6A is folded back from the inner side to the outer side in the tire axial direction around the bead core 5 extending from the main body 6a and extending from the main body 6a to the bead core 5 of the bead part 4 through the sidewall part 3 and the bead part 4. And the folded portion 6b.

  Further, a bead apex 8 made of hard rubber extending from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b, and the bead portion 4 is appropriately reinforced.

  Further, the carcass ply 6A has carcass cords arranged at an angle of, for example, 80 to 90 degrees with respect to the tire equator C. As the carcass cord, for example, an organic fiber cord such as polyester, nylon, rayon, or aramid is suitably employed.

  The belt layer 7 includes at least two belt plies 7A, in which the belt cord is inclined with respect to the tire equator C at a small angle of, for example, 10 to 40 degrees, and in the present embodiment, the inner and outer two belt plies 7A, 7B is configured by superimposing the belt cords so that the belt cords cross each other. Steel cords are used for the belt cords of the present embodiment, but highly elastic organic fiber cords such as aramid and rayon can also be used as necessary.

  The band layer 9 is constituted by a band ply 9A in which band cords 12 (shown in FIG. 2) are arranged at an angle of 5 degrees or less with respect to the tire circumferential direction. The band ply 9A is formed as a full band ply that covers the entire width of the belt layer 7, for example.

  Further, the band ply 9A of the present embodiment is formed by spirally winding a small band ply in which one or a plurality of band cords 12 are covered with a topping rubber around the belt layer 7.

  Further, as shown in FIG. 2, the band layer 9 of the present embodiment includes a center band portion 13 disposed in the center portion of the tread portion 2 across the tire equator C, and a tire axial direction of the center band portion 13. It is comprised from a pair of shoulder band part 14 distribute | arranged on both outer sides. The band cord 12 is divided into a center band cord 12c arranged at the center band portion 13 and a shoulder band cord 12s arranged at the shoulder band portion 14.

  The shoulder band portion 14 of the present embodiment is set to a band constraint coefficient R that is smaller than that of the center band portion 13.

Here, the “band constraint coefficient R” is E (number / 5 cm), which is the number of the band cords 12 included per 5 cm width of the band ply 9A, and the intermediate elongation of the band cord 12 at 50 N load is S. (%), It is shown by the following formula (1).
R = E / S (1)

  For this reason, the band constraint coefficient R becomes larger as the ending E (lines / 5 cm) is larger and / or the intermediate elongation S (%) is smaller. On the other hand, the band constraint coefficient R becomes smaller as the end E (lines / 5 cm) is smaller and / or the intermediate elongation S (%) is larger.

  The “intermediate elongation S (%)” is the elongation at 50 N load in the “load-elongation” curve of the cord. This “load-elongation” curve is obtained in accordance with the provisions of “Test method for chemical fiber tire cord” of “JISL1017” in an environment of room temperature (25 ° C.). In the case of the center band cord 12c, the vulcanized finished tire is disassembled, and the intermediate elongation (%) of each of the eight center band cords 12c extracted at random is measured, and the average is obtained. Shall. In the case of the shoulder band cord 12s, the intermediate elongation (%) of 16 shoulder band cords 12s randomly extracted from the pair of shoulder band portions 14 and 14 is measured, and the average is obtained. It is done. It should be noted that the rubber adhered around the band cord 12 is carefully removed.

  In the present embodiment, the end band Ec (line / 5 cm) of the center band portion 13 and the end band Es (line / 5 cm) of the shoulder band portion 14 are set to be the same, while the shoulder band cord 12 s has an intermediate elongation. A cord having Ss (%) larger than the intermediate elongation Sc (%) of the center band cord 12c is employed. Thereby, the band constraint coefficient Rs of the shoulder band part 14 is set smaller than the band constraint coefficient Rc of the center band part 13.

  In order to satisfy the relationship between the intermediate elongations Sc and Sr (%), the shoulder band cord 12s and the center band cord 12c include cords in which at least one of cord total fineness, cord material, twist, and the like is different. Can be adopted. Typical cords and their intermediate elongation are as follows.

  Further, the tire 1 of the present embodiment includes an inner end 14i in the tire axial direction of the shoulder band portion 14 and a groove center line 16c of the shoulder vertical groove 16 (in this embodiment, an intersection of the groove center line 16c and the virtual tread 2v. The distance X in the tire axial direction with respect to 17) is set to 20% or less of the band half width BW that is the distance in the tire axial direction from the tire equator C to the outer end 9o in the tire axial direction of the band layer 9. The inner end 14i of the shoulder band portion 14 is specified by the innermost end in the tire axial direction of the shoulder band cord 12s arranged on the innermost side in the tire axial direction.

  Thus, in the tire 1 of the present embodiment, the band restraint coefficient Rs of the shoulder band portion 14 is set to be smaller than the band restraint coefficient Rc of the center band portion 13, so the band layer 9 on the tread end 2 e side. The binding force can be reduced. As a result, as shown in FIG. 3, the tire 1 is relatively expanded and deformed on the tread end 2 e side in the direction of closing the vertical groove 16 starting from the groove bottom 16 b of the shoulder vertical groove 16 when filling with internal pressure. To increase the tread radius. Therefore, in the present invention, the groove bottom 16b of the shoulder longitudinal groove 16 can be compressed and deformed in the radial direction. Such compressive strain is less likely to cause cracks in the groove bottom 16b than tensile strain. Therefore, in the pneumatic tire of the present invention, groove bottom cracks can be suppressed over a long period of time, and durability performance can be improved.

  As shown in FIG. 2, when the distance X exceeds 20% of the band half width BW, the inner end 14i of the shoulder band portion 14 is located outside the groove center line 16c of the shoulder vertical groove 16 in the tire axial direction. In this case, the tread portion 2 near the shoulder longitudinal groove 16 may not be sufficiently expanded and deformed. On the other hand, when the inner end 14i is on the inner side in the tire axial direction from the groove center line 16c, the movement of the belt layer 7 during traveling cannot be sufficiently suppressed, and noise resistance performance, high-speed durability performance, and steering stability performance May decrease. From such a viewpoint, the distance X is preferably 10% or less of the band half width BW, more preferably 5% or less.

  Further, the difference (Ss−Sc) in the intermediate elongation between the intermediate elongation Ss (%) of the shoulder band cord 12s and the intermediate elongation Sc (%) of the center band cord 12c is preferably 1% or more. Preferably it is 2% or more. If the difference in intermediate elongation (Ss−Sc) is excessively small, the restraining force on the tread end 2e side may not be sufficiently reduced. Conversely, when the difference in intermediate elongation (Ss−Sc) becomes excessively large, a large difference occurs in the restraining force between the center band portion 13 and the shoulder band portion 14, and the uneven wear resistance performance and the steering stability performance are degraded. There is a fear. From such a viewpoint, the difference in the intermediate elongation (Ss−Sc) is preferably 5.5% or less, more preferably 4% or less.

  From the same viewpoint, the difference (Rc−Rs) between the band constraint coefficient Rc of the center band portion 13 and the band constraint coefficient Rs of the shoulder band portion 14 is preferably 0.5 or more, more preferably 0.8 or more. Also, it is preferably 2.0 or less, more preferably 1.5 or less.

  In the present embodiment, the shoulder band cord 12s is made of a fine yarn nylon cord, and the center band cord 12c is made of the thick yarn nylon cord. In this case, the thermal shrinkage rate after vulcanization of the shoulder band cord 12s and the center band cord 12c is substantially equal. This is useful for improving tire uniformity.

  When the shoulder band cord 12s is made of a thin nylon cord, if the total fineness is excessively small, the restraining force of the shoulder band portion 14 is reduced and the shoulder band cord 12s is broken. There is a possibility that the uneven wear performance and the high-speed durability performance may be deteriorated. On the contrary, if the total fineness becomes excessively large, there is a possibility that the restraining force of the band layer 9 on the tread end 2e side cannot be reduced. From such a viewpoint, the total fineness is preferably 900 dtex or more, more preferably 940 dtex or more, preferably 1350 dtex or less, more preferably 1000 dtex or less.

  Furthermore, when the center band cord 12c is made of thick nylon cord, if the total fineness is excessively small, the movement of the belt layer 7 on the tire equator C side cannot be sufficiently suppressed, and noise resistance performance and high speed durability performance are achieved. May decrease. On the contrary, when the total fineness is excessively large, the rigidity of the center band portion 13 is excessively increased, and the uneven wear resistance may be deteriorated. From such a viewpoint, the total fineness is preferably 1350 dtex or more, more preferably 1400 dtex or more, preferably 1700 dtex or less, more preferably 1670 dtex or less.

FIG. 4 shows a tire 1 according to another embodiment of the present invention.
In the tire 1 according to this embodiment, the center band cord 12c and the shoulder band cord 12s are cords having the same intermediate elongation S, while the es Es (mains / 5cm) of the shoulder band portion 14 are used as the center band portion. It is set to be smaller than 13 endings Ec (lines / 5 cm). Thereby, the band constraint coefficient Rs of the shoulder band part 14 is set smaller than the band constraint coefficient Rc of the center band part 13.

  The tire 1 of this embodiment also reduces the restraining force of the band layer 9 on the tread end 2e side, increases the tread radius during internal pressure filling, and suppresses the occurrence of tensile strain on the groove bottom 16b of the shoulder vertical groove 16 Yes.

  The end Es of the shoulder band portion 14 is preferably 80% or less, more preferably 70% or less of the end Ec of the center band portion 13. If the end Es is increased, the tread radius may not be sufficiently increased during filling with the internal pressure. On the other hand, if the end Es becomes small, the restraining force on the tread end 2e side is excessively reduced, and there is a possibility that the noise resistance performance, the steering stability performance, and the like are reduced. From such a viewpoint, the end Es is preferably 50% or more, more preferably 60% or more of the end Ec of the center band portion 13.

  In the present embodiment, the same band cord is employed for the center band cord 12c and the shoulder band cord 12s. In this embodiment, a fine yarn nylon cord having a total fineness of 900 to 1350 dtex is employed. Thereby, in the tire 1 of this embodiment, since heat shrinkage after vulcanization becomes uniform, uniformity can be improved, and it is not necessary to stock a plurality of band cords, so that productivity can be improved.

FIG. 5 shows still another embodiment of the present invention.
In this embodiment, the ending Es (lines / 5 cm) of the shoulder band portion 14 is set to be smaller than the ending Ec (lines / 5 cm) of the center band portion 13, and the intermediate elongation Ss (%) of the shoulder band cord 12s is set. ) Is set to be larger than the intermediate elongation Sc (%) of the center band cord 12c. As a result, the band constraint coefficient Rs of the shoulder band portion 14 is set to be smaller than the band constraint coefficient Rc of the center band portion 13.

  The tire 1 of this embodiment also reduces the restraining force of the band layer 9 on the tread end 2e side, increases the tread radius during internal pressure filling, and suppresses the occurrence of tensile strain on the groove bottom 16b of the shoulder vertical groove 16 Yes. In addition, in this embodiment, the band restraint coefficients Rc and Rs are set by changing both the ends Ec and Es (lines / 5 cm) and the intermediate elongations Ss and Sc (%). Therefore, the tread radius can be set more finely and the uniformity can be improved.

FIG. 6 shows still another embodiment of the present invention.
The tire 1 of this embodiment has a band layer 9 including the center band portion 13 and the shoulder band portion 14, and a side reinforcing rubber layer 18 having a crescent cross section inside the carcass 6 of the sidewall portion 3. A case where the tire is a run-flat tire provided with is shown.

  The side reinforcing rubber layer 18 is continuously arranged in the tire circumferential direction on the inner side in the tire axial direction of the carcass 6 and on the outer side in the tire axial direction of the inner liner rubber 19 forming the tire cavity surface. Further, the side reinforcing rubber layer 18 has a thickness W2 measured in a direction normal to the main body portion 6a of the carcass ply 6A, gradually decreasing from the central portion toward the inner end 18i and the outer end 18o in the tire radial direction. The cross section is formed in a substantially crescent shape.

  Further, the inner end 18 i of the side reinforcing rubber layer 18 is provided, for example, on the inner side in the tire radial direction than the outer end 8 t of the bead apex 8 and on the outer side in the tire radial direction than the bead core 5. Further, the outer end 18 o of the side reinforcing rubber layer 18 is provided, for example, at a position on the inner side in the tire axial direction from the outer end 7 t of the belt layer 7.

  Such a side reinforcing rubber layer 18 can efficiently increase the bending rigidity of the sidewall portion 3, so that it supports a tire load in place of air pressure at the time of puncture, and has a constant distance at a speed of 60 to 80km / h. You can continue to drive. In order to effectively exhibit such action, the rubber hardness of the side reinforcing rubber layer 18 is desirably set to, for example, about 60 to 95 degrees, and the maximum thickness W2m of the side reinforcing rubber layer 18 is set. Is preferably set to about 40 to 60% of the thickness W3 of the sidewall portion 3.

  In the present specification, the “rubber hardness” is a hardness according to durometer type A in an environment of 23 ° C. in accordance with JIS-K6253.

  By the way, in this type of run-flat tire, since the rigidity on the tread end 2e side is enhanced by the side reinforcing rubber layer 18 having a large rubber hardness, the expansion deformation on the tread end 2e side is excessively suppressed, and the tread radius is different. It tends to be smaller than the tire of the embodiment.

  However, in the tire 1 of this embodiment, the band restraint coefficient Rs of the shoulder band portion 14 is set to be smaller than the band restraint coefficient Rc of the center band portion 13 as in the tire 1 of the other embodiments. The tread end 2e side can be effectively expanded, and the tread radius can be increased. Therefore, the tire 1 can compress and deform the groove bottom 16b of the shoulder longitudinal groove 16 in the radial direction, and can effectively prevent the occurrence of cracks.

  In order to effectively exhibit the above action, the difference (Rc−Rs) between the band constraint coefficient Rc of the center band portion 13 and the band constraint coefficient Rs of the shoulder band portion 14 is the difference (Rc−Rs) of the other embodiments. ) Is desirable. Thereby, the tread end 2e side can be effectively expanded, and the tread radius can be increased. Specifically, the difference (Rc−Rs) is preferably 1.0 or more, more preferably 1.5 or more, and preferably 3.5 or less, more preferably 3.0 or less.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

Tires having the basic structure shown in FIG. 1 and having the band layer shown in Table 2 were manufactured, and their performance was evaluated. The details of the band code are as shown in Table 1. The common specifications are as follows.
Tire size: 175/60 R16
Rim size: 16 × 5J
Band half width BW: 72mm
Crown flutes, shoulder flutes:
Groove width W1: 7.0 mm
Groove depth D1: 7.6 mm
Curvature radius r: 5.0mm
Ratio (r / W1): 71%
The test method is as follows.

<Groove opening amount>
Each test tire is assembled to the rim, and the innermost pressure is filled with a cut groove having a length of 8 mm and a depth of 2 mm along the longitudinal direction of the shoulder longitudinal groove in a state where the internal pressure is not filled, and an internal pressure of 180 kPa is filled. The maximum width of the cut opening was measured. The smaller the numerical value, the smaller the groove opening amount, and the better.

<Noise resistance>
Each test tire is assembled to the above rim under the above conditions and mounted on all the wheels of a 1500cc domestic FF vehicle, and the dry asphalt road test course is run at a speed of 80 km / h and is heard in the passenger compartment. The noise level dB (A) of the overall was measured at the position of the driver's left ear. Evaluation was made with an index with Comparative Example 1 as 100. The smaller the value, the smaller the noise and the better.

<Uneven wear resistance>
Each test tire is assembled on the rim under the above conditions, mounted on all the wheels of the vehicle, and after running on a dry asphalt road surface for 8000 km, three treads on the inner side in the tire axial direction from the shoulder longitudinal groove at three locations on the tire circumference The difference in wear amount with the tread portion on the outer side in the tire axial direction than the shoulder longitudinal groove was measured. The results are averaged over the difference in the amount of wear, and the reciprocal thereof is displayed as an index with Comparative Example 1 as 100. The smaller the value, the better.

<Durability>
Each sample tire was aged in an oven at 70 ° C. for 10 days, assembled to the rim under the above conditions, and left in an ozone chamber with an ozone concentration of 50 pphm to observe the state of cracks in the shoulder flutes. . The evaluation is as follows.
○: No cracks occurred △: Wrinkles or fine cracks occurred ×: Clearly cracks occurred

<High-speed durability performance>
Each sample tire was assembled on the rim under the above-described conditions, and the test was performed by a step speed method in accordance with a load / speed performance test defined by ECE30 using a drum testing machine. In the test, the running speed was sequentially increased and the running distance until the tire broke was measured. Evaluation is indicated by an index with Comparative Example 1 being 100, and the larger the value, the better.

<Steering stability>
Each test tire is assembled to the rim under the above conditions, mounted on all the wheels of the vehicle, and handle responsiveness, rigidity, grip, stability at high speed driving, etc. when traveling on the test course Was evaluated by driver's sensory evaluation. A result is a score which sets the comparative example 1 to 100, and it is so favorable that a numerical value is large.

<Uniformity>
Based on the uniformity measurement method of JASO C607, the low speed RFV and the high speed TFV of 50 tires were measured using a uniformity machine, and the average value and the standard deviation were obtained. The result was an index with the average value and standard deviation of Comparative Example 1 as 100. The smaller the numerical value, the higher the uniformity and the better.
Table 2 shows the test results.

  As a result of the test, it was confirmed that the tires of the examples can effectively prevent cracks that tend to occur at the bottoms of the shoulder longitudinal grooves and can improve the durability.

Run-flat tires having the basic structure shown in FIG. 6 and having the band layer shown in Table 1 were manufactured, and their performance was evaluated. The details of the band code are as shown in Table 1, and the common specifications are the same as those of the first embodiment except for the items shown below.
Tire size: 245/40 RF18
Rim size: 18 × 8.0J
Side reinforcement rubber layer maximum thickness W2m: 6.0mm
Side wall thickness W3: 15.0mm
W2m / W3: 40%
The test method is the same as that of Example 1 except for the items shown below.

<Runflat durability>
Each test tire was assembled on the rim from which the valve core had been removed, and the test was carried out by the step speed method in accordance with the load / speed performance test defined by ECE30 using a drum tester in a state where the internal pressure was zero. The test increased the running speed sequentially and measured the speed and time when the tire broke down. Evaluation was made with an index with Comparative Example 1 as 100. The larger the value, the better.
Table 3 shows the test results.

  As a result of the test, it was confirmed that the tires of the examples can effectively prevent cracks that tend to occur at the bottoms of the shoulder longitudinal grooves and can improve the durability.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 6 Carcass 7 Belt layer 9 Band layer 13 Center band part 14 Shoulder band part 16 Shoulder vertical groove

Claims (5)

A carcass from the tread part through the sidewall part to the bead core of the bead part,
Rutotomoni disposed within the radially outer tread portion of the carcass, and a belt layer composed of belt cords of at least two belt plies are arranged inclined at an angle of 10 to 40 degrees with respect to the tire equator,
A pneumatic tire comprising a band layer made of a band ply arranged outside the belt layer in the tire radial direction and having a band cord arranged at an angle of 5 degrees or less with respect to the tire circumferential direction,
The tread portion includes a shoulder longitudinal groove extending in the tire circumferential direction on the most tread end side,
The band layer is composed of a center band portion disposed across the tire equator and a shoulder band portion disposed on the outer side in the tire axial direction of the center band portion,
The shoulder band portion has a band constraint coefficient R shown by the following formula (1) smaller than the center band portion,
The inner end in the tire axial direction of the shoulder band portion is on the inner side in the tire axial direction from the groove center line of the shoulder longitudinal groove,
The distance X in the tire axial direction between the inner end of the shoulder band portion and the groove center line of the shoulder longitudinal groove is a tire axial distance from the tire equator to the outer end in the tire axial direction of the band layer. A pneumatic tire characterized by being 5% or less of a half width.
R = E / S (1)
(Where E is the number of band cords included per 5 cm width of the band ply, and S is the intermediate elongation (%) when the band cord is loaded with 50N)
The intermediate elongation Ss (%) of the band cord of the shoulder band portion is larger than the intermediate elongation Sc (%) of the band cord of the center band portion,
The pneumatic tire according to claim 1, wherein the difference in intermediate elongation (Ss−Sc) is 1 to 5.5%. The band cord of the shoulder band portion is a fine yarn nylon cord having a total fineness of 900 to 1350 dtex,
The pneumatic tire according to claim 1 or 2, wherein the band cord of the center band portion is a thick yarn nylon cord having a total fineness of 1350 to 1700 dtex.   The pneumatic tire according to any one of claims 1 to 3, wherein the end Es of the shoulder band portion is 50 to 80% of the end Ec of the center band portion. The pneumatic tire according to any one of claims 1 to 4 , wherein a side reinforcing rubber layer having a crescent-shaped cross section is provided inside the carcass in the sidewall portion .

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