tire

Abstract

To provide a tire that maintains the same dry handling stability performance as conventional tires while improving wet handling stability and wet braking performance. [Solution] At least two circumferential main grooves (12a to 12d) form a lug groove (16a) that is inclined with respect to the tire width direction in the center land portion (14a) of at least one land portion (14a to 14e) that includes the tire equatorial plane (CP) or is closest to the tire equatorial plane. At both ends (241x, 242x) of two adjacent lug grooves in the tire circumferential direction, on the side opposite to the circumferential main groove, a circumferential narrow groove (262) is formed in the region opposite to the tire width direction. Both ends (262x, 262y) of the circumferential narrow groove terminate within the land portion, and the circumferential narrow groove is curved so as to be convex in the tire width direction on the side opposite to the lug groove.

Description

Technical Field

[0001] The present disclosure relates to a tire.

Background Art

[0002] There is disclosed a tire in which lug grooves and sipes are formed at a predetermined period in the tire circumferential direction on a center land portion including the tire equatorial plane (see FIGS. 2 and 4 of Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the tire disclosed in Patent Document 1, since the negative ratio is low in the center land portion, sufficient drainage performance cannot be obtained, and there is room for improvement in wet handling stability performance and wet braking performance.

[0005] However, when the normal negative ratio is increased, although the drainage performance improves, the land rigidity decreases, so the dry handling stability performance tends to decrease. Therefore, even when the groove formation area is increased in the center land portion compared to the conventional case, it has been desired to develop a tire capable of obtaining the same land rigidity as the conventional one, and thus the same dry handling stability performance.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a tire that improves wet handling stability performance and wet braking performance while maintaining the same dry handling stability performance as a conventional tire.

Means for Solving the Problems

[0007] The tire of the present invention is characterized in that, in a plan view of the tire, at least one land area is demarcated by at least two circumferential main grooves, a lug groove inclined with respect to the tire width direction is formed in the center land area of ​​the land area that includes the tire equatorial plane or is closest to the tire equatorial plane, a circumferential fine groove is formed at both ends of two adjacent lug grooves in the circumferential direction of the tire, on the side of the land area that is furthest from the circumferential main groove, both ends of the circumferential fine groove terminate within the land area, and the circumferential fine groove is curved so as to be convex in the tire width direction toward the side opposite to the lug groove. [Effects of the Invention]

[0008] According to the present invention, in a plan view of the tire, curved circumferential grooves with ends are periodically formed at predetermined positions on both ends of adjacent lug grooves in the circumferential direction of the tire. This makes it possible to provide a tire that maintains the same dry handling stability performance as conventional tires while improving wet handling stability performance and wet braking performance. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a plan view of the tire according to this embodiment. [Figure 2] Figure 2 is an enlarged view of the circled area in Figure 1. [Figure 3] Figure 3 is a plan view of a tire showing a modified example of the example shown in Figure 1. [Figure 4] Figure 4 is a plan view of the tire showing the groove width W1 of the circumferential narrow grooves in the circled area of ​​Figure 1. [Figure 5] Figure 5 is a plan view of the tire showing the sipe groove width W2 and lug groove width W3 for the circled area in Figure 1. [Figure 6] Figure 6 is a plan view showing the spacing S1 and S2 between the sipe and the circumferential groove in the circled area of ​​Figure 2. [Figure 7]Figure 7 is a plan view showing the dimension D1 from the straight line connecting both ends of the circumferential groove (both ends in the circumferential direction of the tire) to the curved peak, and the dimension D2 from the circumferential main groove on the side closer to the curved peak, for the circled area in Figure 1. [Figure 8] Figure 8 is a plan view showing the shape of the region enclosed by the circumferential main groove, inclined recess and circumferential fine groove based on the value of [D2 / (D1+D2)]. Figure 8(A) shows the case where the value of [D2 / (D1+D2)] is less than 1.0, and Figure 8(B) shows the case where the value of [D2 / (D1+D2)] is 1.0. [Figure 9] Figure 9 is a plan view showing the circumferential tire dimension D3 from the curved top of the circumferential groove to the foot-side end, and the circumferential tire dimension D4 from the curved top of the circumferential groove to the kick-off end, for the circled area in Figure 1. [Modes for carrying out the invention]

[0010] <Mode of the present invention> The present invention encompasses the following embodiments. [Form 1] A tire in which, in a plan view of the tire, at least one land area is demarcated by at least two circumferential main grooves, and a lug groove inclined with respect to the tire width direction is formed in the center land area of ​​the land area that includes the tire equatorial plane or is closest to the tire equatorial plane, A circumferential narrow groove is formed in the region opposite to the circumferential main groove in the tire width direction from the circumferential main groove at both ends of the two adjacent lug grooves in the circumferential direction of the tire, on the side furthest from the circumferential main groove. Both ends of the aforementioned circumferential grooves terminate within the land area. A tire characterized in that the circumferential grooves are curved such that they are convex in the tire width direction on the opposite side from the lug grooves. [Form 2] The tire according to Embodiment 1, wherein the groove width W1 of the circumferential narrow groove is 0.30 mm or more. [Form 3] Further comprising a sipe communicating with the end of the lug groove, The groove width W2 of the sipe and the groove width W3 of the lug groove are 0.40 ≦ W3 / (W2 + W3) The tire according to Form 1 or 2 that satisfies the above condition. [Form 4] The tire according to Form 3, wherein the distance between the sipe and the circumferential groove is 0.30 mm or more and 2.50 mm or less. [Form 5] The maximum dimension D1 from the straight line connecting both circumferential ends of the circumferential groove to the circumferential groove and the minimum dimension D2 from the circumferential main groove on the opposite side of the lug groove in the tire width direction to the circumferential groove of the circumferential groove satisfy 0.02 ≦ D2 / (D1 + D2) < 1.00 The tire according to Form 1 or 2 that satisfies the above condition. [Form 6] The dimension D3 from the curved top of the circumferential groove to the end on the indentation side and the dimension D4 from the curved top of the circumferential groove to the end on the kick-out side satisfy 0.10 ≦ D4 / D3 ≦ 0.80 The tire according to Form 1 or 2 that satisfies the above condition.

[0011] <Definition> The tire radial direction refers to the direction perpendicular to the tire rotation axis. The tire radial inner side refers to the side facing the tire rotation axis in the tire radial direction, and the tire radial outer side refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the circumferential direction around the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The tire width inner side refers to the side facing the tire equatorial plane in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane refers to the plane that is perpendicular to the tire rotation axis and passes through the center of the tire width. The main groove is a groove having a wear indicator indicating the end stage of wear on the groove wall, for example, a circumferential groove. In this embodiment, it has a groove width of 3.0 [mm] or more and a groove depth of 5.0 [mm] or more. The sub-groove and the fine groove are grooves other than the main groove, for example, a circumferential fine groove, and have a groove width and a groove depth smaller than those of the main groove. In this embodiment, they have a groove width of less than 3.0 [mm] and a groove depth of less than 5.0 [mm]. A sipe is a recess with an extremely small groove width and groove depth, and in this embodiment, it has a groove width of 1.0 mm or less and a depth of 1.0 mm or less. The groove width is the maximum distance between opposing groove walls at the groove opening on the tread surface when the tire is mounted on a standard rim and filled to the standard internal pressure in an unloaded state (the distance measured in a direction perpendicular to the direction in which the groove extends). If there is a notch or chamfer at the groove opening, the groove width is the value measured with the endpoint being the intersection of the extension line of the tread surface and the extension line of the groove wall in a cross-sectional view parallel to the groove width direction and groove depth direction. The groove depth is the maximum distance from the tread surface to the bottom of the groove (measured in the radial direction of the tire) when the tire is mounted on a standard rim, filled to the standard internal pressure, and under no load. If the groove in question has partial unevenness or sipes at the bottom of the groove, the groove depth shall be the value measured excluding the unevenness or sipes. In this specification, unless otherwise specified, the shape, position, and length (distance) of each component refer to the shape, position, and length in the meridional cross-section of the tire (in an unloaded state with the tire mounted on a standard rim and filled to standard internal pressure). A "regular rim" refers to an "applicable rim" as defined by JATMA, a "Design Rim" as defined by TRA, or a "Measuring Rim" as defined by ETRTO. Standard internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "INFLATION PRESSURES" specified by ETRTO. Standard load refers to the "maximum load capacity" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO.

[0012] <Basic tire configuration 1 (when there is an even number of circumferential main grooves)> One embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a plan view of the tire of this embodiment. The figure shows the tire portion in an unloaded state, mounted on a standard rim and subjected to standard internal pressure. Furthermore, the tire 10 shown in Figure 1 has a specified vehicle mounting direction, with the left side of the figure being the inner side of the vehicle mounting.

[0013] In this embodiment, the tire 10 has five rows of land sections 14 (14a to 14e) formed by four circumferential main grooves 12 (12a to 12d) in a plan view of the tire. Each land section 14 is divided into a center land section 14a, second land sections 14b and 14c, and shoulder land sections 14d and 14e, and recesses (lug grooves and sipes) are formed in each of these land sections 14 as follows. The center land section 14a will be described later.

[0014] The second land section 14b is located on the vehicle-mounted side of the center land section 14a. The second land section 14b has lug grooves 16b1 and 16b2 formed alternately in the circumferential direction of the tire, and sipes 18b1 and 18b2 formed alternately. The lug grooves 16b1 and sipes 18b1 communicate between the circumferential main grooves 12a and 12b, and the lug grooves 16b2 and sipes 18b2 also communicate between the circumferential main grooves 12a and 12b. These lug grooves and sipes form a bypass path between the circumferential main grooves 12a and 12b.

[0015] The second land section 14c is located on the vehicle-mounted outer side of the center land section 14a. The second land section 14c has lug grooves 16c and sipes 18c communicating with the lug grooves 16c, which are periodically formed in the circumferential direction of the tire.

[0016] The shoulder portion 14d is located on the vehicle-mounted side of the second portion 14b. Lug grooves 16d are formed periodically in the circumferential direction of the tire on the shoulder portion 14d, and sipes 18d1 and 18d2 are formed alternately.

[0017] The shoulder portion 14e is located on the vehicle-mounted outer side of the second portion 14c. The shoulder portion 14e has a circumferential sub-groove 19, and lug grooves 16e, sipes 18e1 and 18e2 are formed periodically in the circumferential direction of the tire. Furthermore, a decorative groove 20e consisting of three parts and a decorative sipe 22e are formed.

[0018] [Characteristics of Basic Tire Form 1] (Circumferential narrow grooves 26 formed in the central land area 14a) Figure 2 is an enlarged view showing the circled area in Figure 1. As shown in Figure 2, the center land portion 14a has inclined recesses 24 (241, 242) that are inclined with respect to the tire width direction, consisting of lug grooves 16a extending from the circumferential main groove 12b and sipes 18a communicating with the lug grooves 16a, and are formed at a predetermined period in the circumferential direction of the tire. In the example shown in Figure 2, the inclined recesses 24 extend from the inside to the outside of the vehicle mounting, and from the kicking side to the treading side in the circumferential direction of the tire.

[0019] Furthermore, circumferential narrow grooves 26 (261, 262, 263) are formed at a predetermined period in the circumferential direction of the tire on both ends 16aE, 16aE of two adjacent lug grooves 16a, 16a that are furthest from the circumferential main groove 12b, in the region opposite to the circumferential main groove 12b in the tire width direction.

[0020] Focusing on the circumferential groove 262, both ends 262x and 262y terminate within the land area 14a and do not communicate with any other recesses provided within the land area 14a (i.e., the lug grooves 16a and sipes 18a that constitute the inclined recess 24) or with any of the circumferential main grooves 12b and 12c that partition the land area 14a. The same applies to the other circumferential grooves 261, 263, etc.

[0021] Under these conditions, the circumferential grooves 26 are curved such that they are convex in the tire width direction on the opposite side from the lug grooves 16a. The curvature can be any form, as long as there is a point other than the ends 262x and 262y of the circumferential grooves 26 that is located on the outside of the vehicle mounting position than the ends 262x and 262y, and there are no particular restrictions on the curvature.

[0022] [Technical knowledge, function, and effects related to the basic form of the tire 1] In the center of the tire in the width direction, the tire contact pressure is relatively high, so the extent to which water enters the depressions formed in the tire tread is higher than in the outer part of the tire in the width direction. From this perspective, excellent drainage performance is required in the center of the tire located in the width direction.

[0023] In conventional tires (for example, the tires shown in Figures 2 and 4 of Patent Document 1, in which only lug grooves are periodically formed in the circumferential direction of the tire as grooves that contribute to drainage in the center land area), only these lug grooves have a circumferential component in the center land area. For this reason, there is room for improvement in terms of drainage performance for conventional tires, and there has been a demand to improve wet handling stability and wet braking performance.

[0024] Therefore, the inventors have found that forming grooves having a circumferential component over almost the entire circumference of the tire, in addition to the lug grooves described in Patent Document 1, in the center land area, efficiently improves drainage performance and, consequently, wet handling stability and wet braking performance.

[0025] However, increasing the number of grooves formed on the land portion reduces the rigidity of the land portion, thus reducing dry handling stability performance. For this reason, the inventors further investigated how to make dry handling stability performance equivalent to that of conventional tires by further forming circumferential narrow grooves (in this embodiment, grooves with a depth of 0.2 mm to 5.0 mm) that have a circumferential component of the tire and have relatively small groove width and groove depth (in this embodiment, grooves with a depth of 0.2 mm to 5.0 mm) in addition to the configuration of Patent Document 1, while avoiding an excessive reduction in the rigidity of the land portion.

[0026] As a result, the inventors have discovered that by not extending the circumferential grooves continuously around the entire circumference of the tire, but terminating their ends within the ground portion, and by making the direction (shape) of the circumferential grooves curved rather than straight, even when stress is applied to the tire tread from various directions during steering, the entire circumferential groove will not collapse (close). This ensures excellent drainage performance in the parts where the circumferential grooves are not collapsed, while ensuring excellent ground rigidity in the parts where the circumferential grooves are collapsed. Consequently, the dry handling stability performance can be made equivalent to that of conventional tires. Based on these findings, the inventors have completed the present invention.

[0027] In other words, in the tire 10 of this embodiment shown in Figures 1 and 2, multiple circumferential narrow grooves 26 are formed in the center land portion 14a, where excellent drainage performance is required. These grooves have a relatively small volume (specifically, at least one of the groove width and groove depth) and a circumferential component (which contributes to drainage performance), and are curved with ends. Therefore, drainage performance can be improved compared to when there are no circumferential narrow grooves, and consequently, wet handling stability and wet braking performance can be improved (Effect 1).

[0028] Furthermore, in the tire 10 of this embodiment shown in Figures 1 and 2, by providing ends to the circumferential grooves 26 and curving the circumferential grooves 26, when stress is applied to the tire tread during steering, the circumferential grooves 26 are partially compressed, thereby ensuring excellent ground rigidity, and consequently, dry handling stability performance can be made equivalent to that of conventional tires (Effect 2).

[0029] As described above, as shown in Figure 2, in the tire 10 of this embodiment, two adjacent lug grooves 16a, 16a, have curved circumferential narrow grooves 26 formed on both ends of the lugs 16a that are farther from the circumferential main groove 12b, in the region opposite to the circumferential main groove 12b in the tire width direction. The above effects 1 and 2 work together to improve wet handling stability and wet braking performance while maintaining dry handling stability performance equivalent to that of conventional tires.

[0030] In Figure 2, the circumferential grooves 26 are curved so as to be convex on the opposite side of the lug grooves 16a in the tire width direction. This is to prevent differences in rigidity between the land portions on each side of the circumferential grooves 26 in the tire width direction in the land portion 14a shown in Figure 2, thereby suppressing localized uneven wear within the land portion 14a. Specifically, in the land portion 14a shown in Figure 2, lug grooves 16a and sipes 18a are formed on the vehicle-mounted side of the circumferential grooves 26, while no grooves or sipes exist on the vehicle-mounted side of the circumferential grooves 26. Therefore, in Figure 2, by curving the circumferential grooves 26 so as to be convex on the opposite side of the lug grooves 16a in the tire width direction, differences in rigidity between the land portions on each side of the circumferential grooves 26 in the tire width direction can be prevented, thereby suppressing localized uneven wear within the land portion 14a.

[0031] <Basic tire configuration 2 (when there is an odd number of circumferential main grooves)> The above is an example where there is an even number of circumferential main grooves 12 (four in Figure 1), but below we will describe in detail an example where there is an odd number of circumferential main grooves 12 (for example, three).

[0032] Figure 3 is a plan view of a tire showing a modified example of the example shown in Figure 1. Note that the same reference numerals in Figure 3 as those in Figure 1 indicate the same components as those shown in Figure 1. In the tire shown in Figure 3, three circumferential main grooves 12e, 12f, and 12g divide four rows of land areas 14f, 14g, 14h, and 14i. In the example shown in Figure 3, the groove width centerline of the circumferential main groove 12f coincides with the tire equatorial plane CP. On each side of the tire width relative to this circumferential main groove 12f, the same pattern of center land areas 14f and 14g is formed. Shoulder land areas 14h and 14i are formed on the outer sides of these center land areas 14f and 14g in the tire width direction, respectively.

[0033] As shown in Figure 3, when there is an odd number of circumferential main grooves 12, the same pattern is formed on the center land sections 14f and 14g on each side in the tire width direction, with reference to the tire equatorial plane CP. In this case, it is sufficient that the pattern formed on the center land section 14a shown in Figure 1 (i.e., the pattern in which inclined recesses 24 composed of lug grooves 16a and sipes 18a, and circumferential narrow grooves 26 are formed) is formed on at least one of the center land sections 14f and 14g shown in Figure 3. As a result, in the example shown in Figure 3, as in the example shown in Figure 1, it is possible to improve wet handling stability and wet braking performance while maintaining dry handling stability performance equivalent to that of a conventional tire. Note that in the example shown in Figure 3, the pattern formed on the center land section 14a shown in Figure 1 is also formed on both the center land sections 14f and 14g shown in Figure 3.

[0034] Furthermore, in the case of a tire with an odd number of circumferential main grooves (for example, three as shown in Figure 3), if the pattern formed on the center land portion 14a shown in Figure 1 is to be formed on only one of the center land portions 14f and 14g shown in Figure 3, it is preferable to form the pattern on the center land portion 14f rather than the center land portion 14g, because this provides sufficient drainage, especially on the outer side of the vehicle, even when mounted on a vehicle with a large camber angle.

[0035] Furthermore, as shown in Figure 3, if the pattern formed on the center land portion 14a shown in Figure 1 is also formed on both the center land portions 14f and 14g, it is preferable because it can achieve an even higher level of improvement in wet handling stability and wet braking performance while maintaining the same level of dry handling stability as conventional tires.

[0036] <Preferred tire configuration> Figure 4 is a plan view of the tire showing the groove width W1 of the circumferential groove in the circled area of ​​Figure 1. In Figure 4, the groove width W1 of the circumferential groove 26 refers to the dimension in the direction perpendicular to the extension direction of the circumferential groove 26 (or the maximum dimension if the groove width changes relative to the extension direction).

[0037] Under these premises, in the tire 10 of this embodiment, it is preferable that the groove width W1 of the circumferential grooves 26 is 0.30 mm or more. By making the groove width W1 of the circumferential grooves 26 0.30 mm or more, the drainage effect of the circumferential grooves 26 can be further enhanced, and in particular, wet handling stability and wet braking performance can be further improved.

[0038] Furthermore, the groove width W1 of the circumferential narrow groove 26 is more preferably 0.33 mm or more, and more preferably 0.35 mm or more.

[0039] Figure 5 is a plan view of a tire showing the sipe groove width W2 and lug groove width W3 for the circled area in Figure 1. In Figure 5, both the sipe groove width W2 and the lug groove width W3 refer to the dimensions measured in a direction perpendicular to the line segment passing through the midpoint of the line segment connecting the two ends of the tire in the circumferential direction.

[0040] Under these premises, in the tire 10 of this embodiment, it is preferable that the groove width W2 of the sipe 18a and the groove width W3 of the lug groove 16a satisfy 0.40 ≤ W3 / (W2 + W3). By satisfying 0.40 ≤ W3 / (W2 + W3), the groove width of the lug groove 16a can be further increased, thereby further enhancing the drainage effect of the lug groove 16a and, in particular, further improving wet handling stability and wet braking performance.

[0041] Furthermore, it is even more preferable that the groove width W2 of the sipe 18a and the groove width W3 of the lug groove 16a satisfy 0.45 ≤ W3 / (W2 + W3), and it is extremely preferable that they satisfy 0.50 ≤ W3 / (W2 + W3).

[0042] Figure 6 is a plan view showing the spacing S1 and S2 between the sipe and the circumferential groove in the circled area of ​​Figure 2. In Figure 6, the spacing S1 (S2) between the sipe 18a and the circumferential groove 261 (262) refers to the shortest distance between the sipe 18a and the circumferential groove 261 (262).

[0043] Under these premises, in the tire 10 of this embodiment, it is preferable that the distance S1 (S2) between the sipe 18a and the circumferential narrow groove 261 (262) is 0.30 mm or more and 2.50 mm or less.

[0044] The spacing S1 between the sipe 18a shown in Figure 6 and the circumferential groove 261 located on the treadward side relative to the sipe 18a is 0.3 mm or more. This ensures excellent rigidity of the land area L1 surrounded by the sipe 18a and the circumferential groove 261 when stress is applied during steering, thereby further enhancing both dry and wet handling stability. This effect is achieved because the edge E1 of the circumferential groove 261 shown in Figure 6 extends with a certain degree of inclination angle both in the tire width direction and the tire circumferential direction. It is particularly preferable when the edge E1 extends at a 45-degree angle with respect to the tire width direction, as this allows for the most effective response to inputs from various angles during steering. If the edge E1 is curved, a straight line connecting both ends of the edge E1 in the tire circumferential direction is considered a virtual edge, and the extension angle of this linear virtual edge is evaluated.

[0045] Furthermore, if the distance S2 between the sipe 18a shown in Figure 6 and the circumferential groove 262 located on the kick-off side relative to the sipe 18a is 0.30 mm or more, then excellent rigidity of the land area L2 surrounded by the sipe 18a and the circumferential groove 262 can be ensured when stress is applied during braking, thereby further improving wet braking performance. This effect is achieved because the edge E2 of the circumferential groove 262 shown in Figure 6 extends to have a sufficient component in the tire width direction, and it is particularly preferable when the edge E2 extends in the tire width direction, as this can most effectively respond to input during braking. If the edge E2 is curved, a straight line connecting both ends of the edge E2 in the tire width direction is considered a virtual edge, and the tire width direction component of this straight virtual edge is evaluated.

[0046] In contrast, by having a distance S1 of 2.50 mm or less between the sipe 18a shown in Figure 6 and the circumferential groove 261 located on the treading side relative to the inclined recess 24, water movement from the circumferential groove 261 to the sipe 18a is achieved at an even higher level during tire rotation, further improving wet handling stability and wet braking performance.

[0047] Similarly, by having a distance S2 of 2.50 mm or less between the sipe 18a shown in Figure 6 and the circumferential groove 262 located on the kicking side relative to the inclined recess 24, water movement from the circumferential groove 261 and sipe 18a to the circumferential groove 262 is achieved at an even higher level during tire rotation, further improving wet handling stability and wet braking performance.

[0048] Furthermore, the spacing S1 (S2) between the sipe 18a and the circumferential narrow groove 261 (262) is more preferably 0.40 mm or more and 2.40 mm or less, and most preferably 0.50 mm or more and 2.30 mm or less.

[0049] Figure 7 is a plan view showing the dimension D1 from the straight line connecting both ends of the circumferential groove (both ends in the circumferential direction of the tire) to the curved apex (the part of the circumferential groove located furthest outward on the vehicle mounting surface) and the dimension D2 from the circumferential main groove on the side closer to the curved apex to the curved apex, for the circled area in Figure 1. In Figure 7, dimension D1 from the straight line connecting both ends of the circumferential groove to the curved apex refers to the maximum dimension from the straight line SL to the circumferential groove 262, and dimension D2 from the circumferential main groove 12c on the side closer to the curved apex refers to the minimum dimension from the circumferential main groove 12c to the circumferential groove 262.

[0050] Under these premises, in the tire 10 of this embodiment, the maximum dimension D1 from the straight line SL connecting the circumferential ends 262x and 262y of the circumferential groove 262 to the circumferential groove 262, and the minimum dimension D2 from the circumferential main groove 12c on the opposite side of the tire width direction from the lug groove 16a to the circumferential groove 262, are such that 0.02 ≤ D2 / (D1 + D2) < 1.00 It is preferable that the following conditions be met.

[0051] By setting the value of D2 / (D1+D2) to 0.02 or greater, a certain distance can be secured from the circumferential main groove 12c to the curved top of the circumferential narrow groove 262, as shown in Figure 7. This ensures sufficient rigidity of the land portion L3 between the circumferential main groove 12c and the curved top, further improving both dry and wet handling stability.

[0052] In contrast, by setting the value of D2 / (D1+D2) to 1.00 or less, a certain distance can be secured between the circumferential main groove 12b and the curved apex, as shown in Figure 7. This ensures sufficient rigidity of the land portion L4 between the circumferential main groove 12b and the curved apex, further improving both dry and wet handling stability.

[0053] Furthermore, the value of D2 / (D1+D2) is more preferably 0.05 or more and 0.95 or less, and most preferably 0.10 mm or more and 0.90 mm or less.

[0054] Figure 8 is a plan view showing the shape of the region enclosed by the circumferential main groove, inclined recess and circumferential fine groove based on the value of [D2 / (D1+D2)]. Figure 8(A) shows the case where the value of [D2 / (D1+D2)] is less than 1.00, and Figure 8(B) shows the case where the value of [D2 / (D1+D2)] is 1.00.

[0055] As shown in Figure 8(A), when the value of [D2 / (D1+D2)] is less than 1.00, D1≠0, so the land area L41 between the circumferential main groove 12b and the circumferential narrow groove becomes approximately pentagonal. On the other hand, as shown in Figure 8(B), when the value of [D2 / (D1+D2)] is 1.00, D1=0, so the land area L42 between the circumferential main groove 12b and the circumferential narrow groove 262 becomes approximately parallelogram.

[0056] In the examples shown in Figure 8(A) and Figure 8(B), when a stress is applied in the tire width direction during steering, the land sections L41 and L42 attempt to deform in the direction indicated by symbol A in both figures. However, land section L41 deforms less easily than land section L42. This is because a larger dimension of the land section in the tire width direction is advantageous against stress in the tire width direction. For this reason, as mentioned above, it is preferable that the value of [D2 / (D1+D2)] is less than 1.00.

[0057] Furthermore, it is even more preferable that the value of [D2 / (D1+D2)] is between 0.08 and 0.90, and extremely preferable that it is between 0.15 and 0.80.

[0058] Figure 9 is a plan view showing the circumferential tire dimension D3 from the curved top of the circumferential groove to the foot-in end, and the circumferential tire dimension D4 from the curved top of the circumferential groove to the kick-out end, for the circled area in Figure 1. Here, the circumferential tire dimension D3 from the curved top of the circumferential groove to the foot-in end refers to the circumferential tire dimension between the shortest distance position P1 from the circumferential main groove 12c of the circumferential groove 262 and the tire circumferential foot-in end position P2 of the circumferential groove 262, and the circumferential tire dimension D4 from the curved top of the circumferential groove to the kick-out end refers to the circumferential tire dimension between the shortest distance position P1 from the circumferential main groove 12c of the circumferential groove 262 and the tire circumferential kick-out end position P3 of the circumferential groove 262.

[0059] Under these premises, in the tire 10 of this embodiment, the dimension D3 from the curved top (position P1) of the circumferential groove 262 to the treading side end (position P2) and the dimension D4 from the curved top (position P1) of the circumferential groove 262 to the kicking side end (position P3) of the circumferential groove are, 0.10 ≤ D4 / D3 ≤ 0.80 It is preferable that the following conditions be met.

[0060] A value of [D4 / D3] of 0.10 or greater ensures sufficient rigidity of the land portion L5 in the circumferential range from position P1 to position P3 among the ribs sandwiched between the circumferential main groove 12c and the circumferential narrow groove 262, thereby further improving both dry and wet handling stability.

[0061] In contrast, if the value of [D4 / D3] is 0.80 or less, the rigidity of the land portion L6 in the circumferential range from position P1 to position P2 among the ribs sandwiched by the circumferential main groove 12c and the circumferential narrow groove 262 can be sufficiently ensured, and the dry and wet handling stability performance can be further improved.

[0062] Furthermore, the value of [D4 / D3] is more preferably 0.20 or more and 0.70 or less, and more preferably 0.30 or more and 0.60 or less.

[0063] The tire of this embodiment, as shown above, has a meridional cross-sectional shape similar to that of a conventional tire, although it is not shown in the illustration. Here, the meridional cross-sectional shape of a tire refers to the cross-sectional shape of the tire as it appears on a plane perpendicular to the tire's equatorial plane. In a meridional cross-sectional view of the tire, the tire of this embodiment has a bead portion, a sidewall portion, a shoulder portion, and a tread portion, extending from the inside to the outside in the radial direction of the tire. The tire, for example, in a meridional cross-sectional view of the tire, comprises a carcass extending from the tread portion to the bead portions on both sides and wound around a pair of bead cores, a belt layer and a belt reinforcing layer sequentially formed on the radially outer side of the carcass, and further comprising a predetermined tread rubber on the radially outer side of the tire.

[0064] <Tire manufacturing method> The tire of this embodiment is obtained through the usual manufacturing processes, namely the mixing process of the tire material, the processing process of the tire material, the molding process of the green tire, the vulcanization process, and the inspection process after vulcanization. When manufacturing the tire of this embodiment, protrusions and recesses corresponding to the grooves and protrusions formed in the tread portion shown in Figure 1 or Figure 3 are formed on the inner wall of the vulcanization mold, and vulcanization is performed using this mold. [Examples]

[0065] The following test tires were manufactured, and their wet braking performance, wet handling stability, and dry handling stability were evaluated.

[0066] (Preparation of test tires) Test tires were manufactured for the conventional example, each comparative example, and each inventive example, with a tire size of 245 / 45R20 103W and having the tire pattern in a plan view as shown in Figures 1 and 2 (however, the specifications of the recesses (lug grooves 16a, sipes 18a, and circumferential narrow grooves 26) formed in the land portion 14a shown in detail in Figure 2 are as shown in Table 1).

[0067] Next, each test tire prepared in this manner was mounted on a 20x8.0J rim and a front-engine, front-wheel-drive (FF) vehicle (2000cc engine displacement). With the air pressure set to 230kPa in all four tires, the performance evaluations were performed according to the following procedure.

[0068] Note that the terms in Table 1 are all equivalent to the terms explained in this specification, and their descriptions have been partially simplified. For example, in Table 1, "no end" for the circumferential groove 26 means that the circumferential groove is formed in a continuous, annular shape in the circumferential direction of the tire, and "curved" shape of the circumferential groove 26 means that, as shown in Figures 1 and 2, the circumferential groove is curved so that the outer side of the circumferential groove when mounted on the vehicle is convex.

[0069] (Evaluation of wet braking performance) The test vehicle was driven on a water-sprayed asphalt road (water depth 1 mm), and the braking distance from an initial speed of 100 km / h was measured. Based on the measurement results, an index evaluation was performed using conventional examples as the baseline (100). This evaluation indicates that a higher number indicates better wet braking performance.

[0070] (Evaluation of wet handling stability performance) The test vehicle was driven on a water-sprayed asphalt road (water depth 1 mm), and a test driver performed subjective evaluations of lane changes and cornering maneuvers. Based on the results of these subjective evaluations, an index evaluation was performed using the conventional example as the baseline (100). A higher index value indicates better wet handling stability.

[0071] (Evaluation of dry handling stability performance) The test vehicle was driven on a dry asphalt road, and a subjective evaluation was conducted by a test driver during lane changes and cornering maneuvers. Based on the results of this subjective evaluation, an index evaluation was performed using the conventional example as the baseline (100). A higher index value indicates better wet handling stability. The results of the three performance evaluations described above are shown together in Table 1.

[0072] [Table 1-1] [Table 1-2]

[0073] As shown in Table 1, each of the tires of the invention examples, which fall within the technical scope of the present invention (where circumferential fine grooves are formed in the region opposite to the circumferential main groove in the tire width direction from a predetermined circumferential main groove at both ends of two adjacent lug grooves in the circumferential direction of the tire, both ends of the circumferential fine grooves terminate within the land portion, and the circumferential fine grooves are curved so as to be convex in the tire width direction opposite to the lug grooves), can be seen to improve wet handling stability and wet braking performance while maintaining dry handling stability performance, compared to conventional and comparative example tires that do not fall within the technical scope of the present invention. [Explanation of symbols]

[0074] 10 tires 12, 12a, 12b, 12c, 12d, 12e, 12f, 12g Circumferential main groove 14 Land Department 14a, 14f, 14g Center Track and Field Club 14b, 14c Second Track and Field Club 14d, 14e, 14h, 14i Shoulder Track and Field Club 16a, 16b1, 16b2, 16c, 16d, 16e lug grooves 16aE End of lug groove 18a, 18b1, 18b2, 18c, 18d1, 18d2, 18e1, 18e2 sipes 19 Circumferential minor groove 20e Decorative groove 22e Decorative sipes 24, 241, 242 Inclined recess 26, 261, 262 Circumferential narrow groove 262x, 262y End of circumferential narrow groove A Arrow CP Tire Equatorial Plane D1, D2, D3, D4 dimensions E1, E2 edges L1, L2, L3, L4, L41, L42, L5, L6 land area P1, P2, P3 position SL straight line W1, W2, W3 groove width

Claims

1. A tire in which, in a plan view of the tire, at least one land area is demarcated by at least two circumferential main grooves, and a lug groove inclined with respect to the tire width direction is formed in the center land area of ​​the land area that includes the tire equatorial plane or is closest to the tire equatorial plane, A circumferential narrow groove is formed in the region opposite to the circumferential main groove in the tire width direction at both ends of the two adjacent lug grooves in the circumferential direction of the tire, on the side furthest from the circumferential main groove. Both ends of the aforementioned circumferential grooves terminate within the land area. A tire characterized in that the circumferential grooves are curved such that they are convex in the tire width direction on the opposite side from the lug grooves.

2. The tire according to claim 1, wherein the groove width W1 of the circumferential narrow groove is 0.30 mm or more.

3. The lug groove further comprises a sipe communicating with the end of the lug groove, The groove width W2 of the sipe and the groove width W3 of the lug groove are 0.40≦W3 / (W2+W3) A tire according to claim 1 or 2, satisfying the requirements.

4. The tire according to claim 3, wherein the distance between the sipe and the circumferential groove is 0.30 mm or more and 2.50 mm or less.

5. The maximum dimension D1 from the straight line connecting the two ends of the circumferential groove in the tire to the circumferential groove, and the minimum dimension D2 from the circumferential main groove on the side of the circumferential groove opposite to the lug groove in the tire width direction to the circumferential groove, 0.02≦D2 / (D1+D2)<1.00 A tire according to claim 1 or 2, satisfying the requirements.

6. The dimension D3 from the curved top of the circumferential groove to the foot-side end and the dimension D4 from the curved top of the circumferential groove to the kick-out end are, 0.10 ≤ D4 / D3 ≤ 0.80 A tire according to claim 1 or 2, satisfying the requirements.

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