JP2016055727A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that effectively improves steering stability while maintaining wear resistance.SOLUTION: A pneumatic tire comprises a tread part 1, a pair of sidewall parts 2, and a pair of bead parts 3. The tread part includes at least three main grooves 11-14 extending in the tire circumferential direction, and at least four rows of land parts 21-25 partitioned by the main grooves. The tread part has a profile line TL in the tire width direction specified based on edge positions of the land parts and ground end positions of the tread part, and the fitting direction of the tread part is specified. The center land parts 22-24 are projected from the profile line TL, the projection amounts T-Tof the center land parts from the profile line TL are sequentially increased toward the center land part located on the vehicle outer side, and the maximum projection position Pmax of each of the center land parts 22, 24 excluding the center land part 23 located on a tire center line CL is set closer to the vehicle outer side than a center position Pc in the width direction of each of the center land parts 22, 24.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire having at least three main grooves extending in the tire circumferential direction in a tread portion and at least four rows of land portions defined by the main grooves, and more particularly, maintaining good wear resistance. However, the present invention relates to a pneumatic tire that can effectively improve steering stability and further improve uneven wear resistance.

  In some pneumatic tires, a plurality of main grooves extending in the tire circumferential direction are provided in a tread portion, and a plurality of rows of land portions having rib foundations are defined by these main grooves. In such a pneumatic tire, the contact pressure at the edge portion of each land portion is relatively high, and the contact pressure tends to be uneven within the land portion. And if it drive | works in the state where the contact pressure in the edge part of each land part is relatively high, the contact length in the center part of each land part will reduce, and this will become a factor which reduces steering stability. Further, when the vehicle is traveling in a state where the contact pressure at the edge portion of each land portion is relatively high, the frictional energy at the edge portion increases, so that there is a disadvantage that the wear resistance is deteriorated.

  On the other hand, it is proposed to optimize the ground contact state of each land portion by causing the tread surface of the land portion partitioned by the main groove to bulge outward in the tire radial direction (for example, Patent Documents 1 to 3). However, the current situation is that the steering stability and the wear resistance cannot always be sufficiently improved by simply expanding the tread surface of the land portion toward the outer side in the tire radial direction.

JP 2004-122904 A JP 2002-29216 A JP 2005-263180 A

  An object of the present invention is to provide a pneumatic tire capable of effectively improving steering stability while further improving uneven wear resistance while maintaining good wear resistance.

In order to achieve the above object, a pneumatic tire according to the present invention includes a tread portion that extends in the tire circumferential direction to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and the sidewall portions. A pair of bead portions disposed on the inner side in the tire radial direction, the tread portion has at least three main grooves extending in the tire circumferential direction and at least four rows of land portions defined by the main grooves, In the pneumatic tire in which the tread portion has a profile line in the tire width direction specified based on the edge position of the land portion and the contact end position of the tread portion, and the mounting direction with respect to the vehicle is designated,
The land portion includes a pair of shoulder land portions located on the outermost side in the tire width direction and a plurality of center land portions located between the pair of shoulder land portions, and the center land portion is a profile line of the tread portion. Each center land except for the center land portion located on the tire center line, and gradually increasing the projecting amount of the center land portion from the profile line toward the center land portion located outside the vehicle. The maximum projecting position of the portion is arranged on the outer side in the tire width direction than the center position in the width direction of the center land portion.

  In the present invention, in the pneumatic tire in which the mounting direction with respect to the vehicle is specified, the center land portion is protruded from the profile line of the tread portion, thereby making the ground pressure of the center land portion uniform, and the ground contact of the center land portion It is possible to improve the steering stability by securing the length and to improve the wear resistance by reducing the friction energy of the edge portion of the center land portion. At that time, the effect of extending the ground contact length of the center land portion becomes stronger toward the outside of the vehicle by sequentially increasing the protruding amount of the center land portion toward the center land portion located outside the vehicle. Steering stability can be improved effectively. Further, by disposing the maximum projecting position of each center land portion excluding the center land portion located on the tire center line outside the center position in the width direction of the center land portion, the tires of these center land portions are arranged. Since the contact length of the portion on the outer side in the width direction increases, it is possible to improve the uneven wear resistance by reducing the contact pressure of the shoulder land portion. As a result, according to the present invention, it is possible to effectively improve steering stability while maintaining good wear resistance, and further improve uneven wear resistance.

  In the present invention, similarly to the center land portion, the shoulder land portion is protruded from the profile line of the tread portion, and the maximum protruding position of each shoulder land portion is larger than the center position in the width direction in the ground contact region of the shoulder land portion It is preferable to arrange on the outer side in the tire width direction. Thereby, the improvement effect of steering stability and wear resistance can be further enhanced. In this case, the protrusion amount of the shoulder land portion should be smaller than the protrusion amount of the center land portion adjacent to the shoulder land portion.

  The protrusion amount of the center land portion is preferably 0.05 mm to 2.0 mm. Similarly, the protrusion amount of the shoulder land portion is preferably 0.05 mm to 2.0 mm. Thereby, steering stability and abrasion resistance can be improved more effectively.

  Moreover, it is preferable that the difference of the protrusion amount of the center land part adjacent to a tire width direction shall be 0.1 mm-0.8 mm. Thereby, steering stability and abrasion resistance can be improved more effectively.

  In each center land portion excluding the center land portion located on the tire center line, the distance in the tire width direction from the end position of the center land portion in the tire width direction to the maximum projecting position is the width of the center land portion. It is preferable to set it as 55%-95%. Similarly, in each shoulder land portion, the distance in the tire width direction from the end position on the inner side in the tire width direction within the ground contact region of the shoulder land portion to the maximum projecting position is the width within the ground contact region of the shoulder land portion. It is preferable to set it as 55 to 95% of this. Thereby, uneven wear resistance can be improved more effectively.

  In the present invention, the contact area of the tread portion is the contact width in the tire axial direction measured when a normal load is applied by placing the tire on a regular rim and filling the regular internal pressure vertically on a plane. Specified based on. The ground contact edge is the outermost position in the tire axial direction of the ground contact region. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO. Then, “Measuring Rim” is set. “Regular internal pressure” is the air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. If JATMA, the maximum air pressure is indicated. The maximum value described in "INFLATION PRESOURS", "INFLATION PRESOURE" for ETRTO, but 180 kPa when the tire is a passenger car. “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 JATMA, and the table “TIRE ROAD LIMITS AT VARIOUSIOLD” In the case of ETRTO, the maximum value described in “INFLATION PRESOURES” is “LOAD CAPACITY”. However, when the tire is a passenger car, the load corresponds to 88% of the load.

  Further, the profile line of the tread part is specified based on the edge position of the land part and the ground end position of the tread part. For example, the profile line in the center land portion passes through the tire meridian cross section through the edge positions on both sides of the center land portion and the edge positions on the near side of other center land portions adjacent to the center land portion in the tire radial direction inner side. It is depicted by an arc with a center at. In addition, the profile line in the shoulder land portion includes a ground end position of the shoulder land portion, an edge position facing the main groove of the shoulder land portion, and a center land portion adjacent to the shoulder land portion in the tire meridian section. It is depicted by an arc that passes through the edge position on the near side and has a center on the inner side in the tire radial direction.

It is meridian sectional drawing which shows the pneumatic tire which consists of embodiment of this invention. FIG. 2 is a development view showing a tread pattern of the pneumatic tire of FIG. 1. It is meridian sectional drawing which shows the outline shape of the tread part in the pneumatic tire of this invention. It is other meridian sectional drawing which shows the outline shape of the tread part in the pneumatic tire of this invention. It is meridian sectional drawing which shows the outline shape of the land part which has a chamfer. It is a top view which shows an example of the footprint of the conventional pneumatic tire. It is a top view which shows an example of the footprint of the pneumatic tire of this invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 to 2 show a pneumatic tire according to an embodiment of the present invention. This pneumatic tire is a tire in which the mounting direction of the tire front and back when the vehicle is mounted is designated. 1 to 2, IN is the inside of the vehicle when the vehicle is mounted, and OUT is the outside of the vehicle when the vehicle is mounted. The mounting direction with respect to the vehicle is displayed at an arbitrary position on the tire surface. CL is a tire center line.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, and a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1. And a pair of bead portions 3 and 3 disposed inside the sidewall portion 2 in the tire radial direction.

  A carcass layer 4 is mounted between the pair of bead portions 3 and 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the inside of the tire to the outside around the bead core 5 disposed in each bead portion 3. A bead filler 6 made of a rubber composition having a triangular cross-section is disposed on the outer periphery of the bead core 5.

  On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. A steel cord is preferably used as the reinforcing cord of the belt layer 7. For the purpose of improving high-speed durability, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of, for example, 5 ° or less with respect to the tire circumferential direction is disposed on the outer peripheral side of the belt layer 7. Yes. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

  In addition, although the tire internal structure mentioned above shows the typical example in a pneumatic tire, it is not limited to this.

  As shown in FIG. 2, four main grooves 11, 12, 13 and 14 extending in the tire circumferential direction are sequentially formed in the tread portion 1 from the vehicle inner side toward the vehicle outer side. These main grooves 11 to 14 define five rows of land portions 21, 22, 23, 24, and 25. More specifically, the tread portion 1 includes a pair of shoulder land portions 21 and 25 positioned on the outermost side in the tire width direction, and a center land portion 22 positioned between the pair of shoulder land portions 21 and 25. , 23, 24 are provided. In FIG. 2, Ein and Eout respectively indicate the grounding ends on the vehicle inner side and the vehicle outer side, and the tread portion 1 forms a grounding region having a grounding width TCW.

  A plurality of lug grooves 31 extending in the tire width direction are arranged on the shoulder land portion 21 inside the vehicle at intervals in the tire circumferential direction. Each lug groove 31 is formed so that one end extends to the outer side in the tire width direction from the ground contact end Ein and the other end is not in communication with the main groove 11.

  A plurality of closing grooves 32 extending in the tire width direction are arranged at intervals in the tire circumferential direction in the center land portion 22 located on the vehicle outer side than the shoulder land portion 21. One end of each closing groove 32 communicates with the main groove 11 located inside the center land portion 22 and the other end is closed in the center land portion 22. Further, a chamfered portion 42 is formed at a portion adjacent to the main groove 11 of the center land portion 22. The chamfered portion 42 has a chamfer width gradually decreasing toward one side in the tire circumferential direction between a pair of closing grooves 32 and 32 adjacent in the tire circumferential direction.

  A plurality of closing grooves 33 extending in the tire width direction are arranged at intervals in the tire circumferential direction in the center land portion 23 located on the vehicle outer side than the center land portion 22. One end of each closing groove 33 communicates with the main groove 12 located inside the center land portion 23 and the other end is closed in the center land portion 23. Further, a chamfered portion 43 is formed at a portion adjacent to the main groove 12 of the center land portion 23. The chamfered portion 43 gradually decreases in chamfer width toward one side in the tire circumferential direction between a pair of closing grooves 33 and 33 adjacent in the tire circumferential direction.

  A plurality of closing grooves 34 extending in the tire width direction are arranged at intervals in the tire circumferential direction in the center land portion 24 located on the vehicle outer side than the center land portion 23. One end of each closing groove 34 communicates with the main groove 13 located inside the center land portion 24 and the other end is closed in the center land portion 24. Further, a chamfered portion 44 is formed at a portion adjacent to the main groove 13 of the center land portion 24. The chamfered portion 44 has a chamfer width gradually decreasing toward one side in the tire circumferential direction between a pair of closing grooves 34, 34 adjacent in the tire circumferential direction.

  A plurality of lug grooves 35 extending in the tire width direction are arranged on the shoulder land portion 25 outside the vehicle at intervals in the tire circumferential direction. Each lug groove 35 is formed such that one end extends to the outer side in the tire width direction from the ground contact end Eout and the other end communicates with the main groove 14. Further, a chamfered portion 45 is formed at a portion adjacent to the main groove 14 of the shoulder land portion 25. The chamfered portion 45 has a chamfer width gradually decreasing toward one side in the tire circumferential direction between a pair of lug grooves 35 adjacent to each other in the tire circumferential direction.

  3 and 4 show the contour shape of the tread portion 1 in the pneumatic tire of the present invention. 3 and 4 depict the outline shape exaggerated for easy understanding of the characteristics of the tread portion 1, and do not necessarily match the actual outline shape. 3 and 4, the profile line TL of the tread portion 1 is composed of a center-side arc formed by the curvature radius Rc and both shoulder-side arcs formed by the curvature radius Rsh. Such a profile line TL of the tread portion 1 is specified based on the edge positions of the land portions 21 to 25 and the ground end position of the tread portion 1.

More specifically, the profile line TL in the shoulder land portion 21 includes a ground contact end position P ₁ of the shoulder land portion 21, an edge position P ₂ facing the main groove 11 of the shoulder land portion 21, and the shoulder land portion 21. The arc is centered on the inner side in the tire radial direction through the edge position P ₃ on the near side of the center land portion 22 adjacent to the portion 21. The profile line TL in the center land portion 22 includes edge positions P ₃ and P ₄ on both sides of the center land portion 22 and an edge position P ₅ on the near side of the other center land portion 23 adjacent to the center land portion 22. It is depicted as an arc with a center on the inner side of the tire radial direction. The profile line TL in the center land portion 23 includes edge positions P ₅ and P ₆ on both sides of the center land portion 23 and an edge position P on the near side of another center land portion 21 or 24 adjacent to the center land portion 23. It is depicted as an arc passing through ₄ or P ₇ and centered on the inside in the tire radial direction. The profile line TL in the center land portion 24 includes edge positions P ₇ and P ₈ on both sides of the center land portion 24 and an edge position P ₆ on the near side of the other center land portion 23 adjacent to the center land portion 24. It is depicted as an arc with a center on the inner side of the tire radial direction. The profile line TL in the shoulder land portion 25 is adjacent to the ground contact end position P ₁₀ of the shoulder land portion 25, the edge position P ₉ facing the main groove 14 of the shoulder land portion 25, and the shoulder land portion 25. It is depicted by an arc having a center on the inner side in the tire radial direction through the edge position P ₈ on the near side of the matching center land portion 24.

FIG. 5 shows a contour shape of a land portion having a chamfered portion. As shown in FIG. 5, for example, if the chamfered portion 43 is formed in the land portion 23, the end point which is located in the tire radial direction outermost chamfer 43 and edge position P _5, the profile of this edge position P ₅ The reference position of the line TL is used. Such a reference position is also applied to other land portions.

  In the pneumatic tire, the center land portions 22 to 24 protrude from the profile line TL of the tread portion 1. More specifically, each of the center land portions 22 to 24 has a maximum protrusion position Pmax where the protrusion amount from the profile line TL is a maximum value, and protrudes from the maximum protrusion position Pmax toward both sides in the tire width direction. The cross-sectional shape is such that the amount gradually decreases.

Here, as shown in FIG. 3, the protruding amounts T _{22 to} T ₂₄ of the center land portions 22 to 24 from the profile line TL are set to increase sequentially toward the vehicle outer side, and T ₂₂ <T ₂₃ <T Satisfied ₂₄ relationships. Further, in the center land portions 22 and 24 excluding the center land portion 23 located on the tire center line CL, the maximum projecting position Pmax is disposed outside the center position Pc in the tire width direction of the center land portions 22 and 24. Has been. Note that the center land portion 23 positioned on the tire center line CL has a width direction center position Pc that coincides with the tire center line CL, and therefore it is not necessary to displace the maximum protrusion position Pmax outward in the tire width direction. When the width direction center position Pc does not coincide with the tire center line CL, the maximum projecting position Pmax may be displaced outward in the tire width direction.

In the pneumatic tire in which the mounting direction with respect to the vehicle is specified as described above, the ground contact pressure of the center land portions 22 to 24 is made uniform by causing the center land portions 22 to 24 to protrude from the profile line TL of the tread portion 1. Thus, the ground contact length of the center land portions 22 to 24 can be secured to improve the handling stability, and the frictional energy of the edge portions of the center land portions 22 to 24 can be reduced to improve the wear resistance. At that time, by increasing the projecting amounts T _{22 to} T ₂₄ of the center land portions 22 to 24 toward the outside of the vehicle, the effect of extending the contact length of the center land portions 22 to 24 becomes stronger toward the outside of the vehicle. In particular, the steering stability during turning can be effectively improved. That is, since the ground contact state on the outside of the vehicle greatly contributes to the steering stability when turning, it is important to secure the contact length on the outside of the vehicle. Further, the maximum projecting position Pmax of each of the center land portions 22 and 24 excluding the center land portion 23 located on the tire center line CL is disposed outside the center position Pc in the width direction of the center land portions 22 and 24 in the tire width direction. By doing so, the contact length of the center land portions 22 and 24 on the outer side in the tire width direction is increased, so that the contact pressure of the shoulder land portions 21 and 25 can be reduced to improve uneven wear resistance. That is, the shoulder land portions 21 and 25 are likely to wear preferentially in the tread portion 1, but the wear balance with the center land portions 22 to 24 can be improved by lowering the ground pressure of the shoulder land portions 21 and 25. it can.

  In the pneumatic tire, similarly to the center land portions 22 to 24, the shoulder land portions 21 and 25 protrude from the profile line TL of the tread portion 1. More specifically, each of the shoulder land portions 21 and 25 has a maximum protrusion position Pmax where the protrusion amount from the profile line TL is a maximum value, and protrudes from the maximum protrusion position Pmax toward both sides in the tire width direction. The cross-sectional shape is such that the amount gradually decreases. Further, in the shoulder land portions 21 and 25, the maximum protruding position Pmax is disposed on the outer side in the tire width direction with respect to the width direction center position Pc in the ground contact region of each shoulder land portion 21 and 25.

In this way, the shoulder land portions 21 and 25 are projected from the profile line TL of the tread portion 1, and the maximum projecting position Pmax of each shoulder land portion 21 and 25 is the width direction in the ground contact region of the shoulder land portions 21 and 25. By disposing the outer side in the tire width direction than the center position Pc, it is possible to further improve the steering stability and wear resistance improving effects. In this case, the protrusion amount T ₂₁ of the inboard shoulder land portion 21 is smaller than the projection amount T ₂₂ of the center land portion 22 adjacent to it, the projection amount T ₂₅ on the vehicle outer side of the shoulder land portion 25 adjacent to it Center It had better be smaller than the protrusion amount T ₂₄ of the land portion 24. Thereby, the grounding state as a whole of the tread part 1 can be maintained satisfactorily.

The protrusion amounts T _{22 to} T _{24 of the} center land portions 22 to ₂₄ and the protrusion amounts T ₂₁ and T ₂₅ of the shoulder land portions 21 and ₂₅ are preferably 0.05 mm to 2.0 mm. Thereby, steering stability and abrasion resistance can be improved more effectively. When the protruding amounts T _{21 to} T ₂₅ are out of the above range, the improvement effect of the steering stability and the wear resistance is lowered. In particular, the protrusion amounts T _{22 to} T ₂₄ of the center land portions 22 to ₂₄ are 0.2 mm to 0.6 mm, and the protrusion amounts T ₂₁ and T ₂₅ of the shoulder land portions 21 and ₂₅ are 0.1 mm to 0.5 mm. It is preferable.

The difference between the protrusion amount T ₂₂ through T ₂₄ of the center land portion 22 to 24 adjacent in the tire width direction (for example, T ₂₄ -T ₂₃ or T ₂₃ -T ₂₂₎ is to the 0.1mm~0.8mm Is good. Thereby, steering stability and abrasion resistance can be improved more effectively. When the difference between the protruding amounts T _{22 to} T ₂₄ is out of the above range, the improvement effect of the steering stability and the wear resistance is lowered.

As shown in FIG. 4, in each center land part 22 and 24 except the center land part 23 located on the tire center line CL, the maximum projecting position from the end position on the inner side in the tire width direction of the center land part 22 and 24 The distances D ₂₂ and D _{24 in} the tire width direction up to Pmax are preferably 55% to 95% of the widths W ₂₂ and W ₂₄ of the center land portions 22 and ₂₄ . That is, it is preferable to satisfy the relationship of 0.55 ≦ D ₂₂ / W ₂₂ ≦ 0.95 and 0.55 ≦ D ₂₄ / W ₂₄ ≦ 0.95. Similarly, in each of the shoulder land portions 21 and 25, distances D ₂₁ and D _{25 in} the tire width direction from an end position on the inner side in the tire width direction within the ground contact region of the shoulder land portions 21 and 25 to the maximum projecting position Pmax. Is preferably 55% to 95% of the widths W ₂₁ and W ₂₅ in the ground contact area of the shoulder land. That is, it is preferable to satisfy the relationship of 0.55 ≦ D ₂₁ / W ₂₁ ≦ 0.95 and 0.55 ≦ D ₂₅ / W ₂₅ ≦ 0.95. Thereby, uneven wear resistance can be improved more effectively. If the ratio is less than 55%, the effect of improving uneven wear resistance is lowered. Conversely, if it exceeds 95%, the ground contact shape is deteriorated, and the improvement effect of steering stability and wear resistance may be impaired. In particular, the ratio is preferably in the range of 60% to 80%. The distance D ₂₃ of the tire width direction from the end position in the tire width direction inner side to the maximum protruding position Pmax of the center land portion 23 positioned on the tire centerline CL is the width W ₂₃ of the center land portion 23 It is not specified in particular.

  FIG. 6 shows an example of a footprint of a conventional pneumatic tire, and FIG. 7 shows an example of a footprint of the pneumatic tire of the present invention. In the conventional pneumatic tire, each land portion of the tread portion is not protruded from the profile line of the tread portion. As shown in FIG. 6, in the footprint X1 of the conventional pneumatic tire, the ground contact length of the center land portion is short (refer to the portion A), and the ground contact area of the shoulder land portion is insufficient (B Section). On the other hand, as shown in FIG. 7, it can be seen that in the footprint X2 of the pneumatic tire of the present invention, the ground contact state of the portions corresponding to the A portion and the B portion is improved.

  In the above-described embodiment, the case where four main grooves are provided in the tread portion and five rows of land portions are partitioned by these four main grooves has been described. However, the present invention provides at least three main grooves in the tread portion. The present invention can be applied to a tread pattern in which grooves are provided and at least four rows of land portions are defined by these at least three main grooves. By applying the above structure to such a tread pattern, it is possible to obtain an improvement effect of steering stability, wear resistance, and uneven wear resistance.

  The tire size is 185 / 65R15, and includes a tread portion, a pair of sidewall portions, and a pair of bead portions, and the tread portion includes four main grooves extending in the tire circumferential direction and five rows of land portions defined by the main grooves. Comparative example in which the amount of protrusion of each land part from the profile line of the tread part and the maximum protrusion position in each land part are set as shown in Table 1 Tires 1 to 3 and Examples 1 to 6 were manufactured.

  In Table 1, the five rows of land portions are expressed as L1, L2, L3, L4, and L5 sequentially from the inside of the vehicle to the outside of the vehicle. Moreover, the maximum protrusion position in each land part was represented by ratio of the distance of the tire width direction from the edge part position inside the tire width direction of each land part to the maximum protrusion position with respect to the width of each land part.

  These test tires were evaluated for wear resistance, uneven wear resistance, and steering stability by the following test methods, and the results are also shown in Table 1.

Abrasion resistance:
Each test tire was assembled to a wheel with a rim size of 15 × 5.5J and mounted on a sedan type front-wheel drive vehicle. Monitor running was performed under the condition of an air pressure of 200 kPa, and the running distance until the tread portion was completely worn was measured. . The evaluation results are shown as an index with Comparative Example 1 as 100. A larger index value means better wear resistance.

Uneven wear resistance:
Simultaneously with the evaluation of the wear resistance, the difference in wear amount between the center land portion and the shoulder land portion was measured. The evaluation results are shown as an index using Comparative Example 1 as 100, using the reciprocal of the measured value. The larger the index value, the better the uneven wear resistance.

Steering stability:
Each test tire is mounted on a wheel with a rim size of 15 x 5.5J and mounted on a sedan type front-wheel drive vehicle. Sensory evaluation is performed at a speed range of 100 km / h or less on a test course consisting of an asphalt road surface under conditions of an air pressure of 200 kPa. Went. Steering stability was evaluated separately when traveling straight and turning. Steering stability during straight travel is an evaluation of the handle responsiveness when the vehicle is traveling straight and the vehicle responsiveness during steering. Steering stability during a turn is an evaluation of the steerability and stability of the vehicle when making a circular turn with a radius of 30 m. The evaluation results are shown as an index with Comparative Example 1 as 100. The larger the index value, the better the steering stability.

  As can be seen from Table 1, in the tires of Examples 1 to 6, the steering stability was effectively improved in comparison with Comparative Example 1, and in particular, the steering stability during turning was good. . Further, the tires of Examples 1 to 6 had improved uneven wear resistance, and the wear resistance was improved accordingly. On the other hand, in the tire of Comparative Example 2, since the maximum protruding position in each land portion coincided with the center position in the width direction of each land portion, the effect of improving uneven wear resistance was insufficient. Further, the tire of Comparative Example 3 had an insufficient effect of improving steering stability because the amount of protrusion at the center land portion was constant.

1 Tread part 2 Side wall part 3 Bead part 11, 12, 13, 14 Main groove 21, 25 Shoulder land part 22, 23, 24 Center land part TL Profile line

Claims (8)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the inner side in the tire radial direction of the sidewall portions. The tread portion has at least three main grooves extending in the tire circumferential direction and at least four rows of land portions defined by the main grooves, and the tread portion includes an edge position of the land portion and the tread portion. In a pneumatic tire having a profile line in the tire width direction that is specified based on the position of the contact end, and in which the mounting direction with respect to the vehicle is specified,
The land portion includes a pair of shoulder land portions located on the outermost side in the tire width direction and a plurality of center land portions located between the pair of shoulder land portions, and the center land portion is a profile line of the tread portion. Each center land except for the center land portion located on the tire center line, and gradually increasing the projecting amount of the center land portion from the profile line toward the center land portion located outside the vehicle. A pneumatic tire characterized in that the maximum projecting position of the portion is arranged on the outer side in the tire width direction than the center position in the width direction of the center land portion.   The pneumatic tire according to claim 1, wherein an amount of protrusion of the center land portion is set to 0.05 mm to 2.0 mm.   3. The pneumatic tire according to claim 1, wherein a difference in a protruding amount between center land portions adjacent to each other in a tire width direction is set to 0.1 mm to 0.8 mm.   In each center land portion excluding the center land portion located on the tire center line, the distance in the tire width direction from the end position inside the tire width direction of the center land portion to the maximum protruding position is the width of the center land portion. The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire is 55% to 95%.   The shoulder land portion is protruded from the profile line of the tread portion, and the maximum projecting position of each shoulder land portion is arranged outside the center position in the width direction in the ground contact region of the shoulder land portion. The pneumatic tire according to any one of claims 1 to 4, characterized in that:   6. The pneumatic tire according to claim 5, wherein a protruding amount of the shoulder land portion is smaller than a protruding amount of a center land portion adjacent to the shoulder land portion.   The pneumatic tire according to claim 5 or 6, wherein a protruding amount of the shoulder land portion is 0.05 mm to 2.0 mm.   In each shoulder land portion, the distance in the tire width direction from the inner end position in the tire width direction within the ground contact area of the shoulder land portion to the maximum projecting position is 55% of the width in the ground contact area of the shoulder land portion. The pneumatic tire according to any one of claims 5 to 7, wherein the pneumatic tire is -95%.

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