Pneumatic tire

Abstract

This pneumatic tire comprises a shoulder land part demarcated by circumferential-direction grooves with a groove width of 3 mm or greater in a tread part, wherein the shoulder land part includes a plurality of width-direction grooves. The width-direction grooves include, at a reference position P in the center in the tire width direction of the shoulder land part, a plurality of lug grooves having a groove width of at least 1.5 mm and a groove depth that is at least 50% of the maximum groove depth of the width-direction grooves on the tire circumference. The circumferential-direction length at the reference position P of a plurality of block-shaped land parts demarcated by the lug grooves changes, and the maximum / minimum ratio of the circumferential-direction length is 1.2 to 1.8. In this pneumatic tire, when the number of block-shaped land parts is defined as N, the circumferential-direction length thereof is defined as P1, P2, ..., PN in order along the tire circumferential direction, the circumferential-direction length of any block-shaped land part is defined as Pi (i=1 to N), the number of block-shaped land parts satisfying Pi / min (Pi-1, Pi+1)≤0.95 is defined as M1, the number of block-shaped land parts satisfying 2Pi / (Pi-1+Pi+1)≤09.5 is defined as M2, and when R=(M1∙M2)1 / 2 / N, the index R is in the range of 0≤R≤0.2.

Description

Technical Field

[0001] The present invention relates to a pneumatic tire adopting pitch variation in a tread pattern, and more particularly to a pneumatic tire capable of suppressing adjacent block integral wear while maintaining the reduction effect of "loudness" of pattern noise based on pitch variation, and further improving the "rough feeling" of pattern noise.

Background Art

[0002] In a pneumatic tire for a passenger car, in order to reduce the "loudness" of pattern noise, pitch variation is adopted in the tread pattern (see, for example, Patent Documents 1 to 5). However, when pitch variation is adopted, although the effect of reducing the "loudness" can be obtained due to the dispersion of the frequencies of the pattern noise, temporal variation occurs in the noise due to the difference in block size on the tire circumference, and as a result, there is a problem that a "rough feeling" appears in the pattern noise. The "rough feeling" is a state in which a rough and unpleasant sound quality is felt, which is opposite to a smooth and pleasant sound.

[0003] On the other hand, in an area where a driving pattern with almost no acceleration or deceleration is frequently repeated, in the shoulder portion on the vehicle-mounted inner side of a pneumatic tire, a special wear mode (hereinafter referred to as "adjacent block integral wear") may occur in which blocks adjacent in the tire circumferential direction wear integrally. Such adjacent block integral wear is mainly caused by the rigidity difference between blocks adjacent in the tire circumferential direction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] An object of the present invention is to provide a pneumatic tire that can suppress adjacent block integral wear while maintaining the effect of reducing the "loudness" of pattern noise based on pitch variation, and further improve the "rough feeling" of pattern noise. [Means for Solving the Problems]

[0006] The pneumatic tire of the present invention for achieving the above object includes a shoulder land portion partitioned by a circumferential groove having a groove width of 3 mm or more in the tread portion, and the shoulder land portion includes a plurality of widthwise grooves extending in the tire width direction. The widthwise grooves include a plurality of lug grooves having a groove width of 1.5 mm or more and a groove depth of 50% or more of the maximum groove depth on the tire circumference of the widthwise grooves at a reference position in the center of the shoulder land portion in the tire width direction. The circumferential lengths of the plurality of block-shaped land portions partitioned by the lug grooves are changed at the reference position, and in the pneumatic tire in which the maximum-minimum ratio of the circumferential lengths of the block-shaped land portions is in the range of 1.2 or more and 1.8 or less, Let the number of the block-shaped land portions on the tire circumference be N, and let the circumferential lengths of the block-shaped land portions be P1, P2, ··· P N in order along the tire circumferential direction, and let the circumferential length of an arbitrary block-shaped land portion be P i (i = 1 to N), and let P i / min(P i-1 , P i+1 ) ≤ 0.95, and let the number of block-shaped land portions satisfying this condition be M1, and 2P i / (P i-1 + P i+1Let the number of block-shaped land portions satisfying ≦0.95 be M2, and the index R be R = (M1·M2) 1 / 2 / N, when At any position in the specified region of 30% to 70% from the inner end in the tire width direction of the shoulder land part toward the grounding end the index R is in the range of 0 ≦ R ≦ 0.2.

Effect of the Invention

[0007] In the present invention, in a pneumatic tire adopting pitch variation in the shoulder land portion, P i / min(P i-1 , P i+1 ) ≦ 0.95 is satisfied, and the number of block-shaped land portions is M1, 2P i / (P i-1 +P i+1 ) ≦ 0.95 is satisfied, and the number of block-shaped land portions is M2, and the index R is R = (M1·M2) 1 / 2 / N. When the index R is in the range of 0 ≦ R ≦ 0.2 moreover, while maintaining the reduction effect of the "loudness" of the pattern noise based on the pitch variation, adjacent block integrated wear can be suppressed, and furthermore, the "rough feeling" of the pattern noise can be improved.

[0008] In the present invention, it is preferable that the index R is in the range of 0 ≦ R ≦ 0.2 at any position in the specified region of 30% to 70% from the inner end in the tire width direction of the shoulder land portion toward the grounding end. Thereby, adjacent block integrated wear can be effectively suppressed, and the effect of improving the "rough feeling" of the pattern noise can be enhanced.

[0009] The ratio M1 / N of the number M1 of the block-shaped land portions to the number N is preferably in the range of 0 ≦ M1 / N ≦ 0.15. Thereby, adjacent block integrated wear can be effectively suppressed, and the effect of improving the "rough feeling" of the pattern noise can be enhanced.

[0010] The number of levels of the circumferential length of the block-shaped land portion is 3 or more. The maximum value of the circumferential length of the block-shaped land portion is P max and the minimum value of the circumferential length of the block-shaped land portion is P min and Pi <P min ·(P max / P min ) 1 / 3 Let the sum of the circumferential lengths of the block-shaped land portions satisfying this be PL, and P i >P mi n ·(P max / P min ) 2 / 3 Let the sum of the circumferential lengths of the block-shaped land portions satisfying this be PH. It is preferable to satisfy the following mathematical formulas (1) and (2) and the relationship of 0.4 ≦ PH / PL ≦ 3.0.

[0011]

Equation

[0012] Thereby, the circumferential lengths of the block-shaped land portions are dispersed so as not to be biased toward a specific circumferential length, so that the effect of "loudness" can be effectively reduced based on the pitch variation, and the effect of improving the "rough feeling" of the pattern noise can be enhanced.

[0013] In the shoulder land portion, it is preferable that narrow grooves having a groove width of 1 mm or more and 2 mm or less and a groove depth of 10% or more and less than 50% of the maximum depth of the lug groove are arranged at an angle of 35° or less with respect to the tire circumferential direction. By providing such narrow grooves oriented in the tire circumferential direction, the rigidity of the shoulder land portion can be reduced without causing an adverse effect on the pattern noise, and the pattern noise can be further reduced.

[0014] In each block-shaped land portion of the shoulder land portion, at least one sipe extending in the tire width direction and having a groove width of less than 1.5 mm and a groove depth of 50% or more and less than 100% of the maximum groove depth of the lug groove is preferably arranged. By providing such a sipe having little influence on the pattern noise, the rigidity of each block-shaped land portion of the shoulder land portion can be reduced, and the pattern noise can be further reduced.

[0015] The maximum value P of the circumferential length of the block-shaped land portionmax and the minimum value P min and the ratio P max / P min is 1.4 or more, and P i > P min ·(P max / P min ) 2 / 3 is arranged on the block-shaped land part that satisfies The number M of sipes i is the number M of sipes arranged on the block-shaped land part having the minimum value P min mi n It is preferably more than that. By increasing the sipes of such a block-shaped land part with a large land part length, the rigidity difference between the block-shaped land parts can be alleviated, and the adjacent block integrated wear can be effectively suppressed.

[0016] For any block-shaped land part, m i pieces (m i ≧2) of sipes are arranged so as to cross the reference position, and the block-shaped land part is divided into three or more small land parts by m i pieces of sipes. When the circumferential lengths of the small land parts at the reference position are sequentially S1, S2, ··· S along the tire circumferential direction, min(S1, S mi+1 )≧0.95·max(S2, S3, ··· S mi+1 ), and max(S1, S m )≦1.5·min(S2, S3, ··· S mi+1 ) preferably satisfies the relationship mi . By defining the relationship of the circumferential lengths of three or more small land parts partitioned within the block-shaped land part in this way, the rigidity difference between the small land parts can be alleviated, the adjacent block integrated wear can be effectively suppressed, and furthermore, the pattern noise reduction effect can be enhanced.

[0017] ​In the present invention, the reference position at the center in the tire width direction of the shoulder land portion is the position in the tire width direction that is the midpoint between the inner end in the tire width direction and the grounding end of the shoulder land portion. However, when there is a circumferential groove with a groove width of less than 3 mm at this position, the position is 5 mm away from the circumferential groove with a groove width of less than 3 mm toward the outer side in the tire width direction. The grounding end of the tread portion is the outermost position in the tire axial direction in the grounding shape measured under the condition of loading the normal load with the tire vertically placed on a flat surface after mounting the tire on a normal rim and filling it with the normal internal pressure. The "normal rim" is the rim defined for each tire in the standard system including the standard on which the tire is based. For example, it is the standard rim in JATMA, "Design Rim" in TRA, or "Measuring Rim" in ETRTO. The "normal internal pressure" is 230 kPa. The "normal load" is the load corresponding to 75% of the maximum load capacity defined for each tire in the standard system including the standard on which the tire is based.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited by the following embodiments. Also, the components of this embodiment include those that can be replaced and are self-evidently replaceable while maintaining the identity of the invention. Further, a plurality of modification examples described in this embodiment can be arbitrarily combined within the scope self-evident to those skilled in the art. FIGS. 1 to 4 show a pneumatic tire according to an embodiment of the present invention. In FIG. 1, CL is the tire center position. In FIG. 2, E is the grounding end.

[0020] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 that extends in the tire circumferential direction and forms an annular shape, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed on the inner side in the tire radial direction of these sidewall portions 2.

[0021] A carcass layer 4 is mounted between the pair of bead portions 3, 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and is folded back from the inner side to the outer side of the tire 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.

[0022] On one 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 such 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 the range of, for example, 10° to 40°. As the reinforcing cord of the belt layer 7, a steel cord is preferably used. On the outer peripheral side of the belt layer 7, at least one belt cover layer 8 is arranged for the purpose of improving high-speed durability, in which the reinforcing cords are arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

[0023] Note that the above-described tire internal structure shows a typical example in a pneumatic tire, but is not limited thereto.

[0024] As shown in FIG. 2, a plurality of main grooves 10 extending in the tire circumferential direction are formed in the tread portion 1. The main grooves 10 are circumferential grooves in which the groove width is 3 mm or more, preferably in the range of 4 mm or more and 18 mm or less, and the groove depth is in the range of 5 mm or more and 11 mm or less. The main grooves 10 include a center main groove 11 located near the tire center position CL and a pair of shoulder main grooves 12, 12 located on the outermost side in the tire width direction. Thereby, in the tread portion 1, a pair of center land portions 20, 20 located between the shoulder main grooves 12, 12 and a pair of shoulder land portions 30, 30 located outside the shoulder main grooves 12, 12 are defined.

[0025] In each of the center land portions 20, a plurality of closed grooves 21 are formed at intervals in the tire circumferential direction, one end of which communicates with the shoulder main groove 12 and the other end of which terminates within the center land portion 20. On the other hand, in each of the shoulder land portions 30, as shown in FIGS. 3 and 4, a plurality of lug grooves 31 (grooves in the width direction) extending in the tire width direction without communicating with the shoulder main groove 12 are formed at intervals in the tire circumferential direction.

[0026] Here, the reference position P in the tire width direction at the center of the shoulder land portion 30 is defined as the position in the tire width direction that is the midpoint between the inner end Eg in the tire width direction and the ground contact end E of the shoulder land portion 30. When the position of the shoulder main groove 12 in the tire width direction varies along the tire circumferential direction, the inner end Eg in the tire width direction of the shoulder land portion 30 is taken as the position that protrudes most inward in the tire width direction. The lug groove 31 has a groove width measured in the tire circumferential direction at the reference position P at the center of the shoulder land portion 12 in the tire width direction in the range of 1.5 mm or more, preferably in the range of 3 mm or more and 6 mm or less. The groove depth of the lug groove 31 at the reference position P may vary along the tire circumferential direction, but in any case, it is 50% or more of the maximum depth of the width direction groove extending in the tire width direction in the shoulder land portion 30 (in the embodiments shown in FIGS. 1 to 4, the maximum depth of the lug groove 31). For example, the groove depth of the lug groove 31 is preferably in the range of 2 mm or more and 6 mm or less or in the range of 30% or more and 80% or less of the main groove depth at the reference position P. With the lug groove 31 satisfying such dimensional requirements, a plurality of block-shaped land portions 32 are defined in the shoulder land portion 30. The block-shaped land portions 32 may be completely separated by the lug groove 31. Note that there may be width direction grooves in the shoulder land portion 30 that do not satisfy the above dimensional requirements, but they are not considered as the lug grooves that define the block-shaped land portions 32.

[0027] The circumferential length P of the block-shaped land portion 32 at the reference position P at the center of the shoulder land portion 30 in the tire width direction i varies along the tire circumferential direction, and the circumferential length P of the block-shaped land portion 32 i The maximum-minimum ratio (the ratio of the minimum value P min to the maximum value P max is set in the range of 1.2 or more and 1.8 or less. That is, pitch variation is applied to the block-shaped land portions 32 of the shoulder land portion 30.

[0028] In the above pneumatic tire, let the number of the block-shaped land portions 32 on the tire circumference be N, and the circumferential lengths of the block-shaped land portions 32 be P1, P2, ··· P in order along the tire circumferential direction N and so on , and the circumferential length of any block-shaped land portion be Pi Let (i = 1 to N), and P i / min(P i-1 , P i+1 ) ≤ 0.95, and let the number of block-shaped land portions 32 satisfying this be M1. Let 2P i / (P i-1 + P i+ 1) ≤ 0.95, and let the number of block-shaped land portions 32 satisfying this be M2. Let the index R be R = (M1·M2) 1 / 2 / N. When the index R is set in the range of 0 ≤ R ≤ 0.2. Here, when i = 1 , let i - 1 = N, and when i = N, let i + 1 = 1.

[0029] The index R defined in this way can be controlled, for example, by adjusting the ratio of the circumferential lengths P of adjacent block-shaped land portions 32 i , or by adjusting the number of levels of the circumferential length P of the block-shaped land portions 32 i , or by changing the arrangement of the block-shaped land portions 32.

[0030] In the pneumatic tire adopting pitch variation in the shoulder land portion 30 as described above, P i / min(P i-1 , P i+1 ) ≤ 0.95, and let the number of block-shaped land portions satisfying this be M1. Let 2P i / (P i-1 + P i+1 ) ≤ 0.95, and let the number of block-shaped land portions satisfying this be M2. Let the index R be R = (M1·M2) 1 / 2 / N. When the index R is in the range of 0 ≤ R ≤ 0.2 , based on this, while maintaining the reduction effect of the "loudness" of the pattern noise based on pitch variation, adjacent block integrated wear can be suppressed, and furthermore, the "coarse feeling" of the pattern noise can be improved.

[0031] Figure 5 shows the occurrence in the block-shaped land portion 32 where P i / min(P i-1 , P i+1 ) ≤ 0.95 shows adjacent block integrated wear, and Fig. 6 shows 2P i / (P i-1 +P i+1 ) ≤ 0.95 is satisfied It shows the adjacent block integrated wear that occurs on the block-shaped land portion 32. In Figs. 5 and 6, the broken line graph represents the change in the circumferential length of the block-shaped land portion in the tire circumferential direction.

[0032] According to the findings of the present inventor, as shown in Fig. 5, P i / min(P i-1 , P i+1 ) ≤ 0.9 5 is satisfied, and when the circumferential length of any block-shaped land portion becomes significantly smaller than the minimum value of the circumferential lengths of the two adjacent block-shaped land portions, a special wear pattern (adjacent block integrated wear) in which the block-shaped land portions adjacent in the tire circumferential direction wear together easily occurs. Also, as shown in Fig. 6, 2P i / (P i-1 +P i+1 ) ≤ 0.95 is satisfied, and when the circumferential length of any block-shaped land portion becomes significantly smaller than the average value of the circumferential lengths of the two adjacent block-shaped land portions, a special wear pattern (adjacent block integrated wear) in which the block-shaped land portions adjacent in the tire circumferential direction wear together easily occurs.

[0033] Fig. 7 shows the relationship between the index R and the ratio of the abnormal wear occurrence locations. In Fig. 7, an example with a low ratio of abnormal wear occurrence locations is indicated by "○", an example with a high ratio of abnormal wear occurrence locations is indicated by "×", and an example with a ratio of abnormal wear occurrence locations at the allowable level is indicated by "△". As shown in Fig. 7, it can be seen that by setting the index R in the range of 0 ≤ R ≤ 0.2, the ratio of the abnormal wear occurrence locations due to the adjacent block integrated wear decreases. In particular, it is desirable that 0 ≤ R ≤ 0.16.

[0034] In particular, it is preferable that the index R is in the range of 0 ≦ R ≦ 0.2 at any position in a specified region of 30% to 70% (i.e., a strip-shaped region having a width corresponding to 40% of the distance L from the inner end Eg in the tire width direction of the shoulder land portion 30 to the ground contact end E and centered on the reference position P) from the inner end Eg in the tire width direction of the shoulder land portion 30 toward the ground contact end E. By satisfying 0 ≦ R ≦ 0.2 in a wide specified region including the reference position P in this way, the integrated wear of adjacent blocks can be effectively suppressed, and the effect of improving the "coarse feeling" of the pattern noise can be enhanced.

[0035] FIG. 8 shows the relationship between M1 / N and the occurrence situation of abnormal wear with M2 / N. In FIG. 8, an example with a low ratio of the location where abnormal wear occurs is indicated by "○", an example with a high ratio of the location where abnormal wear occurs is indicated by "×", and an example with a ratio of the location where abnormal wear occurs at the allowable level is indicated by "△". As shown in FIG. 8, P i / min(P i-1 , P i+1 ) ≦ 0.95 is satisfied, and the ratio M1 / N of the number M1 of the block-shaped land portions 32 to the total number N of the block-shaped land portions 32 is preferably in the range of 0 ≦ M1 / N ≦ 0 .15. The circumferential length P of the block-shaped land portion 32 has a large or small i change. The number M1 of the locations where the change becomes large has a great influence on the "coarse feeling" of the pattern noise . However, by reducing the ratio of the number M1, the integrated wear of adjacent blocks can be effectively suppressed , and at the same time , the effect of improving the "coarse feeling" of the pattern noise can be enhanced.

[0036] In the pneumatic tire, the number of levels of the circumferential length of the block-shaped land portion 32 is 3 or more. The maximum value of the circumferential length of the block-shaped land portion 32 is P max , and the minimum value of the circumferential length of the block-shaped land portion 32 is P , and P min , P i < P min ·(P max / P min ) 1 / 3 ​Let the sum of the circumferential lengths of the block-shaped land portions 32 that satisfy be PL, and P i >P min ·(P max / P min ) 2 / 3 When the sum of the circumferential lengths of the block-shaped land portions 32 that satisfy is PH, it is preferable to satisfy the following mathematical formulas (1) and (2) and the relationship of 0.4 ≦ PH / PL ≦ 3.0.

[0037]

Equation

[0038] As a result, the circumferential lengths of the block-shaped land portions 32 are dispersed so as not to be biased toward a specific circumferential length. Therefore, it is possible to effectively reduce the effect of "loudness" based on pitch variation and enhance the effect of improving the "coarse feeling" of pattern noise.

[0039] Here, P i <P min ·(P max / P min ) 1 / 3 When the sum of the circumferential lengths of the block-shaped land portions 32 that satisfy is PL or P i >P min ·(P max / P min ) 2 / 3 If the sum of the circumferential lengths of the block-shaped land portions 32 that satisfy is too large or too small with respect to the whole, a bias occurs in the circumferential lengths of the block-shaped land portions 32, and the effect of improving the "coarse feeling" of pattern noise decreases. Similarly, if the value of PH / PL is out of the above range, a bias occurs in the circumferential lengths of the block-shaped land portions 32, and the effect of improving the "coarse feeling" of pattern noise decreases. In particular, it is desirable to satisfy the relationship of 0.7 ≦ PH / PL ≦ 2.2.

[0040] ​In addition, if the number of levels of the circumferential length of the block-shaped land portion 32 is less than 3, the change in the circumferential length between the levels becomes large, and the effect of improving the "coarse feeling" of adjacent block integrated wear and pattern noise is reduced. In particular, the number of levels of the circumferential length of the block-shaped land portion 32 is preferably 5 or more, and its upper limit is preferably 40% or less of the number N of the block-shaped land portions 32 on the tire circumference. Even if the number of levels exceeds 40% of the number N, there is no difference in the effect.

[0041] In FIGS. 2 to 4, in the shoulder land portion 30, fine grooves 33 having a groove width of 1 mm or more and 2 mm or less and a groove depth of 10% or more and less than 50% of the maximum depth of the lug groove 31 are arranged at an angle of 35° or less with respect to the tire circumferential direction. By providing the fine grooves 33 oriented in the tire circumferential direction in the shoulder land portion 30 in this way, the rigidity of the shoulder land portion 30 can be reduced without adversely affecting the pattern noise, and the pattern noise can be further reduced. Here, if the groove depth of the fine groove 33 is too large, the effect of improving the adjacent block integrated wear is reduced due to excessive rigidity reduction. Further, if the angle of the fine groove 33 with respect to the tire circumferential direction is too large, the fine groove 33 becomes a factor in generating pattern noise. Note that the angle of the fine groove 33 is the angle formed by a straight line connecting both ends of the fine groove 33 with respect to the tire circumferential direction.

[0042] In FIGS. 2 to 4, at least one sipe 34 extending in the tire width direction and having a groove width of less than 1.5 mm and a groove depth of 50% or more and less than 100% of the maximum groove depth of the lug groove 31 is arranged in each block-shaped land portion 32 of the shoulder land portion 30. By providing the sipe 34, which has little influence on the pattern noise, in each block-shaped land portion 32 of the shoulder land portion 30 in this way, the rigidity of each block-shaped land portion 32 can be reduced, and the pattern noise can be further reduced.

[0043] The sipe 34 is preferably arranged such that the straight line connecting both ends thereof forms an angle of 30° or less with respect to the tire width direction. In this case, the rigidity of each block-shaped land portion 32 in the longitudinal direction can be efficiently reduced. The sipe 34 is preferably arranged such that at least a part thereof is located in a specified region of 30% to 70% from the inner end Eg in the tire width direction of the shoulder land portion 30 toward the ground contact end E. More preferably, it is arranged so as to cross the 50% position (reference position P) from the inner end Eg in the tire width direction of the shoulder land portion 30 toward the ground contact end E. By arranging the sipe 34 in this way, since the rigidity near the center of each block-shaped land portion 32 is reduced, the rigidity of each block-shaped land portion 32 in the longitudinal direction can be efficiently reduced.

[0044] Further, when the sipe 34 is arranged so as to cross the 50% position (reference position P) from the inner end Eg in the tire width direction of the shoulder land portion 30 toward the ground contact end E, and the sipe 34 divides each block-shaped land portion 32 into a plurality of small land portions 35, the ratio of the larger value to the smaller value of the circumferential length of the small land portions 35 located at both ends in the tire circumferential direction of each block-shaped land portion 32 is preferably 1.2 or less. Thereby, when each block-shaped land portion 32 comes into contact with the ground during tire rolling, the rigidity of the leading contact side and the trailing contact side can be balanced, and adjacent block integrated wear can be effectively suppressed.

[0045] In the above pneumatic tire, the maximum value P of the circumferential length of the block-shaped land portion 32 max and the minimum value P min and the ratio P max / P min is 1.4 or more, and P i >P min ·(P max / P min ) 2 / 3 The number M of sipes 34 arranged in the block-shaped land portion 32 that satisfies i is preferably larger than the number M min of sipes 34 arranged in the block-shaped land portion 32 having the minimum value P min . This By increasing the number of sipes 34 in the block-shaped land portion 32 having a relatively large land portion length, the rigidity difference between the block-shaped land portions 32 can be alleviated, and the adjacent block integrated wear can be effectively suppressed. However, if the difference in the number of sipes 34 between the block-shaped land portions 32 is too large, a rigidity difference will conversely occur. Therefore, the upper limit value of the number M i of sipes is desirably set to M min ·(P max / P min ) + 1.

[0046] In the pneumatic tire described above, m i sipes (m i ≧2) are arranged so as to cross a reference position P in an arbitrary block-shaped land portion 32, and the block-shaped land portion 32 is divided into three or more small land portions 35 by the m i sipes. When the circumferential lengths of the small land portions 35 at the reference position P are sequentially S1, S2, ··· S along the tire circumferential direction, when min(S1, S mi+1 ) ≧ 0. mi+1 95·max(S2, S3, ··· S ), and max(S1, S m ) ≦ 1.5·min(S2, S3, ··· S mi+1 ), it is preferable to satisfy the relationship. mi By defining the relationship of the circumferential lengths of three or more small land portions 35 partitioned within the block-shaped land portion 32 in this way, the rigidity difference between the small land portions 35 can be alleviated, the adjacent block integrated wear can be effectively suppressed, and furthermore, the pattern noise reduction effect can be enhanced. Here, the circumferential lengths S1,

[0047] of the small land portions 35 located at both ends in the tire circumferential direction of the block-shaped land portion 32 S mi+1 If the minimum value of is less than 0.95 m times the maximum value of the circumferential lengths S2, S3, ··· S of the other small land portions 35, the rigidity difference between the small land portions 35 becomes excessive, and the desired effect cannot be obtained. Also, the circumferential lengths (S1, S mi+1If the maximum value of m is more than 1.5 times the minimum value of the circumferential lengths (S2, S3, ··· S

[0048] The pitch variation that satisfies the above specific requirements can be applied to at least one shoulder land portion of the pneumatic tire, and may be applied to both shoulder land portions. Further, in a pneumatic tire in which the mounting direction with respect to the vehicle is specified, it is preferable to apply the pitch variation that satisfies the above specific requirements to the shoulder land portion on the inner side of the vehicle mounting.

Example

[0049] In a pneumatic tire having a tire size of 225 / 55R17, a shoulder land portion partitioned by a circumferential groove having a groove width of 3 mm or more in the tread portion, the shoulder land portion having a plurality of widthwise grooves extending in the tire width direction, and these widthwise grooves having a groove width of 1.5 mm or more and a groove depth of 50% or more of the maximum groove depth on the tire circumference of the widthwise grooves at the reference position at the center in the tire width direction of the shoulder land portion, and adopting a pitch variation in which the circumferential length at the reference position of a plurality of block-shaped land portions partitioned by these lug grooves changes, the number N of the block-shaped land portions on the tire circumference is 54, the number of levels of the circumferential length of the block-shaped land portions is 7, and the maximum value P of the circumferential length of the block-shaped land portions max and the minimum value are P min and the ratio P max / P min is set to 1.5, and tires of a conventional example and Examples 1 to 11 with details set as shown in Table 1 were manufactured. In addition, in this specification, Example 1 is a reference example.

[0050] As the arrangement of the block-shaped land portions, any of the arrangements A to D shown in FIG. 9 was adopted. Further, as the type of the level of the circumferential length of the block-shaped land portions, the following type X (arithmetic progression) or type Y (geometric progression) was adopted. Type X: 1.00, 1.08, 1.17, 1.25, 1.33, 1.42, 1.5 Type Y: 1.00, 1.07, 1.14, 1.22, 1.31, 1.40, 1.5

[0051] Furthermore, in the conventional example and Examples 1 to 11, the index R at the reference position, the maximum value of the index R in the specified region, M1 / N, PH / PL, the presence or absence of fine grooves, the number of small block-shaped land portions, the number of large block-shaped land portions, and the ratio of the circumferential length of the small land portions located at both ends in the tire circumferential direction of the block-shaped land portion to the circumferential length of the small land portion located at the intermediate portion in the tire circumferential direction of the block-shaped land portion were varied in various ways. In the conventional example and Example 1, the angle of the lug groove was changed according to the circumferential length of the block-shaped land portion, and in Examples 2 to 11, the angle of the lug groove was made constant regardless of the change in the circumferential length of the block-shaped land portion.

[0052] For these test tires, the wear resistance and pattern noise performance were evaluated by the following test methods, and the results are shown together in Table 1.

[0053] Wear resistance: Each test tire was assembled on a wheel with a rim size of 17×7.5J and mounted on a front-wheel drive vehicle with a displacement of 2 liters. After driving 20,000 km on a dry road surface with an air pressure of 220 kPa, the circumferential profile at the reference position was measured for each of the shoulder land portions on the inner side of the vehicle mounting of the four wheels, the number of locations where adjacent block-integrated wear occurred was counted, and the total number of the four wheels was obtained. The evaluation result was shown by an index with the conventional example set as 100 using the reciprocal of the total number of wear occurrence locations. The larger this index value, the fewer the locations where adjacent block-integrated wear occurs, meaning that the wear resistance is excellent.

[0054] Pattern noise performance: Each test tire was assembled onto a wheel with a rim size of 17×7.5J and mounted on a front-wheel drive vehicle with a displacement of 2 liters. With the tire pressure set at 220 kPa, the in-vehicle noise (pattern noise) was measured while driving on a dry and smooth asphalt road surface at a speed of 60 km / h. Regarding the "loudness" and "roughness" of the pattern noise, a feeling evaluation was conducted at the driver's seat. The evaluation results were scored using an index value with the conventional example set as 100. A larger index value indicates better pattern noise performance.

[0055]

Table 1

[0056] As can be seen from Table 1, the tires of Examples 1 to 11 were able to maintain the reduction effect of the "loudness" of the pattern noise based on pitch variation, suppress the adjacent block integral wear, and further improve the "roughness" of the pattern noise.

Explanation of Reference Signs

[0057] 1 Tread portion 2 Sidewall portion 3 Bead portion 10 Main groove (circumferential groove) 11 Center main groove 12 Shoulder main groove 20 Center land portion 21 Closing groove 30 Shoulder land portion 31 Lug groove 32 Block-shaped land portion 33 Fine groove 34 Sipe 35 Small land portion Eg Inner end of the shoulder land portion in the tire width direction E Contact end P Reference position

Claims

1. An inflated tire having a shoulder land portion partitioned by circumferential grooves with a groove width of 3 mm or more in the tread portion, the shoulder land portion having a plurality of widthwise grooves extending in the tire width direction, the widthwise grooves including a plurality of lug grooves having a groove width of 1.5 mm or more and a groove depth of 50% or more of the maximum groove depth on the tire circumference of the widthwise grooves at a reference position at the center in the tire width direction of the shoulder land portion, the plurality of block-shaped land portions partitioned by the lug grooves having a changing circumferential length at the reference position, and the maximum-minimum ratio of the circumferential length of the block-shaped land portions being in the range of 1.2 or more and 1.8 or less, Let the number of the block-shaped land portions on the tire circumference be N, and let the circumferential lengths of the block-shaped land portions be P 1 , P 2 , ··· P N in order along the tire circumferential direction. Let the circumferential length of any block-shaped land portion be P i (i = 1 to N), and P i / min (P i-1 , P i+1 ) ≤ 0.

95. Let the number of block-shaped land portions satisfying this be M 1 . Let 2P i / (P i-1 + P i+1 ) ≤ 0.

95. Let the number of block-shaped land portions satisfying this be M 2 . Let the index R be R = (M 1 ·M 2 ) 1 / 2 / N. An inflated tire, characterized in that the index R is in the range of 0 ≤ R ≤ 0.2 at any position in a specified region of 30% to 70% from the inner end in the tire width direction of the shoulder land portion toward the grounding end.

2. The number M of the block-shaped land portions 1 and the ratio M 1 / N of the number M 1 / N to the number N is in the range of 0 ≤ M / N ≤ 0.15, and the pneumatic tire according to claim 1 is characterized in that

3. The number of levels of the circumferential length of the block-shaped land portion is 3 or more, and the maximum value of the circumferential length of the block-shaped land portion is P max is defined as, and the minimum value of the circumferential length of the block-shaped land portion is P min is defined as, P i < P min · (P max / P min ) 1 / 3 The sum of the circumferential lengths of the block-shaped land portions that satisfy is defined as PL, and P i > P min · (P max / P min ) 2 / 3 When the sum of the circumferential lengths of the block-shaped land portions that satisfy is defined as PH, the pneumatic tire according to any one of claims 1 to 2 is characterized by satisfying the following mathematical formulas (1) and (2) and satisfying the relationship of 0.4 ≤ PH / PL ≤ 3.

0. 【Number 1】

4. The inflated tire according to any one of Claims 1 to 3, wherein fine grooves having a groove width of 1 mm or more and 2 mm or less and a groove depth of 10% or more and less than 50% of the maximum groove depth of the lug grooves are arranged at an angle of 35° or less with respect to the tire circumferential direction in the shoulder land portion.

5. The inflated tire according to any one of Claims 1 to 4, wherein at least one sipe extending in the tire width direction and having a groove width of less than 1.5 mm and a groove depth of 50% or more and less than 100% of the maximum depth of the lug grooves is arranged in each block-shaped land portion of the shoulder land portion.

6. The maximum value P of the circumferential length of the block-shaped land portion max and the minimum value P min and the ratio P max / P min is 1.4 or more, and P i > P min ·(P max / P min ) 2 / 3 The number M of sipes arranged on the block-shaped land portion satisfying the above is i more than the number M of sipes arranged on the block-shaped land portion having the minimum value P min The pneumatic tire according to claim 5, characterized in that min it is larger than the number M of sipes arranged on the block-shaped land portion having the minimum value P

7. m is provided on any block-shaped land portion i The book (m i ≧2) of the sipes is arranged so as to cross the reference position, and the block-shaped land portion is divided into three or more small land portions by the m i books of the sipes. When the circumferential lengths of the small land portions at the reference position are sequentially S 1 , S 2 , ··· S mi+1 When set as, min(S 1 , S mi+1 ) ≧ 0.95 · max(S 2 , S 3 , ··· S m ), and max(S 1 , S mi+1 ) ≦ 1.5 · min(S 2 , S 3 , ··· S mi ), the pneumatic tire according to claim 5 or 6, characterized in that the relationship is satisfied.

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