tire

Abstract

To provide a tire capable of improving turning performance on a wet road surface and suppressing generation of squeal noise while maintaining good straight running performance on the wet road surface.SOLUTION: At least one row of the plurality of rows of land portions 30 formed in the tread portion 1 is formed as a convex rib 32 that extends continuously along the tire circumferential direction and has a shape in which a contour line of a tread surface in a tire meridian cross-sectional view in an unloaded state in which the tire is mounted on a regular rim and a regular internal pressure is applied bulges outward in the tire radial direction, when a point on the contour line of the convex rib 32 at which a distance from a straight line P connecting both end points p of the convex rib 32 in the tire widthwise direction is maximized is defined as a point PC, and an intersection point of a perpendicular line of the straight line P passing through the point PC and the straight line P is defined as a point x0, the contour line from the point p to the point PC is configured by a plurality of arcs, and a length W of the straight line P and a distance b from the point x0 to the point PC satisfy a relationship of 0.001≤b / W≤0.25.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire having rib-shaped land portions that extend continuously in the tire circumferential direction, and more specifically to a tire that exhibits good straight-line running performance and cornering performance on wet road surfaces and is capable of suppressing the occurrence of squealing noise. [Background technology]

[0002] To improve wet tire performance, a technology is known in which the contact surface of a land portion formed in the tread portion is partially bulged outward in the tire radial direction from the reference contour line of the tread profile (see, for example, Patent Document 1). In such tires, the bulged land portion increases the contact pressure at the bulged land portion, improving wet performance (especially straight-line performance when traveling on wet roads). However, there is a concern that the bulged land portion reduces the contact pressure at the tire widthwise ends (non-bulged portions) of the land portion, resulting in insufficient cornering performance on wet roads. Furthermore, there is a concern that the reduced contact pressure at the tire widthwise ends (non-bulged portions) leads to an uneven contact pressure distribution on the convex rib contact surface, making squealing more likely to occur at low speeds. Therefore, there is a need for a solution that suppresses squealing while achieving a balanced improvement in straight-line performance and cornering performance on wet roads. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-100170 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can maintain good straight-line performance on wet road surfaces, while also improving cornering performance on wet road surfaces and suppressing the occurrence of squealing. [Means for solving the problem]

[0005] In order to achieve the above object, the tire of the present invention provides a tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, the tread portion having at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions partitioned by the circumferential main grooves, at least one row of the plurality of land portions extending continuously along the tire circumferential direction, a convex rib having a shape in which a contour line of a tread surface in a meridian cross section of the tire when mounted on a normal rim and under normal internal pressure and in an unloaded state is bulged outward in the tire radial direction, both ends of the convex rib in the tire width direction are defined as points p, a line segment connecting a pair of points p is defined as a straight line P, a point on the contour line of the convex rib that is the greatest distance from the straight line P is defined as point PC, and an intersection point between the perpendicular line P passing through point PC and the straight line P is defined as point x0, the contour line from point p on one side of point PC to point PC is made up of a plurality of circular arcs, and the N-th circular arc from the side of point PC among the plurality of circular arcs is defined as R N (N is an integer greater than or equal to 1), and the arc R N and arc R N+1 The point where and connect is point T N Then, the arc R N and arc R N+1 is point T N and the length W of the straight line P and the distance b from the point x0 to the point PC satisfy the relationship 0.001≦b / W≦0.25. [Effects of the Invention]

[0006] In order to improve the wet performance, the tire of the present invention has a convex rib in which the contour line of the tread in the tire meridian cross-section bulges outward in the tire radial direction. Since this convex rib has the above-mentioned characteristics, the bulging shape of the convex rib becomes good, and while improving the straight running performance and the turning performance on a wet road surface in a balanced manner, the generation of skid noise can be suppressed. That is, while increasing the ground pressure at the bulged portion of the convex rib (near the point PC) to improve the straight running performance during traveling on a wet road surface, the ground pressure is prevented from decreasing by the fact that the end portion in the tire width direction of the convex rib (near the point p) does not bulge with respect to the vicinity of the point PC, and the turning performance on a wet road surface can be ensured well. Further, since the ground pressure distribution of the convex rib tread can be made uniform, the skid noise at low speed can be suppressed.

[0007] In the present invention, when an intersection point of a perpendicular line of the straight line P passing through the point T1 and the straight line P is defined as a point x1, it is preferable that the point x1 is arranged in a range of 40% or more and 90% or less of a distance ap between the point x0 and the point p from the point x0 toward the point p. Thereby, the balance between the first arc and the second and subsequent arcs from the point PC side becomes good, and it is advantageous for suppressing the generation of skid noise while improving the straight running performance and the turning performance on a wet road surface in a balanced manner.

[0008] In the present invention, when a perpendicular distance between the straight line P and the contour line of the convex rib at a position of 80% of the distance ap between the point x0 and the point p from the point x0 toward the point p is defined as a distance b1, it is preferable that a ratio b1 / b of the distance b and the distance b1 satisfies a relationship of 0.40 < b1 / b ≤ 0.90. Thereby, it is possible to prevent the outer side in the tire width direction of the convex rib from significantly dropping below the point PC, and it is advantageous for suppressing the generation of skid noise while improving the straight running performance and the turning performance on a wet road surface in a balanced manner.

[0009] Furthermore, when the perpendicular distance between the straight line P and the contour line of the convex rib at a position 60% of the distance ap between the point x0 and the point p, measured from the point x0 toward the point p, is defined as distance b2, it is preferable that the ratio b2 / b of the distance b to the distance b2 satisfies the relationship 0.40≦b2 / b≦0.90 and that the relationship b>b2>b1 with the distance b1 is satisfied. This improves the curved shape of the contour line of the convex rib as it moves from point PC toward the outer side of the convex rib in the tire width direction, which is advantageous for suppressing the occurrence of squealing while improving straight-line running performance and cornering performance on wet roads in a balanced manner.

[0010] In the present invention, the arc R N The radius of curvature of r N When defined as follows, the radius of curvature r N and the radius of curvature r N+1 Toga r N >r N+1 This satisfies the following relationship: The curved shape of the contour line of the convex rib is favorable, which is advantageous for suppressing the occurrence of squealing while improving straight-line running performance and cornering performance on wet road surfaces in a balanced manner.

[0011] In the present invention, the arc R N The radius of curvature of r N When the curvature radius r1 and the curvature radius r2 are defined as follows, it is preferable that they satisfy the relationship 2≦r1 / r2≦200. This results in a good balance between the curved shapes of the first and second circular arcs from the point PC side, which is advantageous for suppressing squealing while improving straight-line performance and cornering performance on wet roads in a balanced manner.

[0012] In the present invention, it is preferable that the distance b satisfy the relationship 0.05 mm≦b≦2.0 mm, which improves the bulging shape of the convex rib and is advantageous for improving straight-line running performance and cornering performance on wet roads in a balanced manner.

[0013] In the present invention, it is preferable that the point PC is located within a range of 30% of the length W of the straight line P on both sides in the tire width direction from the midpoint of the straight line P. This causes the central portion of the convex rib to bulge the most (the point PC at which the convex rib bulges the most is located near the center of the convex rib in the tire width direction), which promotes drainage over the rib and is advantageous for improving wet performance.

[0014] In the present invention, the hardness Hs of the tread rubber constituting the tread portion is preferably 55 or more and 78 or less. By having such an appropriate hardness, the bulging shape of the convex ribs is well maintained during running, and the effects of the convex ribs described above can be efficiently exhibited.

[0015] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof can be filled with air, an inert gas such as nitrogen, or other gases. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a meridian cross-sectional view of a tire according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram schematically showing a convex rib of a tire according to an embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory diagram showing an enlarged view of a main part of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0017] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] When the tire of the present invention is a pneumatic tire as shown in FIG. 1, it comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In FIG. 1, the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using FIG. 1 will be based basically on the meridian cross-section shape shown, but each tire component also extends in the tire circumferential direction and forms an annular shape.

[0019] A carcass layer 4 is installed between a pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and folded back from the inner side to the outer side in the tire width direction around a bead core 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of the bead core 5, and this bead filler 6 is wrapped by the main portion and folded back portion of the carcass layer 4. Meanwhile, a plurality of belt layers 7 (two layers in FIG. 1 ) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Furthermore, at least one belt reinforcing layer 8 (two layers in FIG. 1 ) is provided on the outer periphery of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction.

[0020] A tread rubber layer 11 is disposed on the outer peripheral side of the carcass layer 4 in the tread portion 1, a side rubber layer 12 is disposed on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the bead portion 3. The tread rubber layer 11 has a structure in which two types of rubber layers with different physical properties (a cap tread layer 11C that forms the tread surface of the tread portion 1 and an under tread layer 11U disposed on its inner peripheral side) are laminated in the tire radial direction.

[0021] As described below, the present invention relates to the tread portion 1 of the tire (particularly the cross-sectional shape of the convex ribs, etc., described below), and therefore the basic structure of the tire is not limited to the general structure described above. Also, the following description will be based on the pneumatic tire shown in Fig. 1, etc., but the present invention can be applied to various tires, including non-pneumatic tires, as long as they have a surface that comes into contact with the road surface (a portion corresponding to the surface of the tread portion 1 in a pneumatic tire) and have land portions (convex ribs) formed thereon.

[0022] As shown in FIG. 1, at least two circumferential main grooves 20 (four in the example of FIG. 1) extending linearly along the tire circumferential direction are provided on the surface of the tread portion 1 of the tire. The circumferential main grooves 20 are grooves that perform the main drainage function and have a maximum groove width of, for example, 3 mm to 30 mm and a maximum groove depth of, for example, 4 mm to 10 mm. These at least two circumferential main grooves 20 define multiple rows (five in the example of FIG. 1) of land portions 30 extending along the tire circumferential direction. In the following description, a pair of land portions 30 located on the tire widthwise outer side of a pair of circumferential main grooves 20 located on the outermost sides in the tire widthwise direction may be referred to as shoulder land portions 31. In the present invention, at least one row of these land portions 30 (one row in FIG. 1) is configured as a convex rib 32, which will be described later. When the land portion 30 excluding the shoulder land portion 31 is a convex rib 32, this land portion 30 (convex rib 32) is defined by a pair of circumferential main grooves 20, and therefore a profile shape described below is applied to the top surface (tread surface) of the land portion 30 (convex rib 32) sandwiched between the pair of circumferential main grooves 20. When the shoulder land portion 31 is a convex rib 32, the shoulder land portion 31 (convex rib 32) is defined on the outer side of the circumferential main groove 20 in the tire width direction, and therefore a profile shape described below is applied to the top surface (tread surface) of the shoulder land portion 31 (convex rib 32) sandwiched between the circumferential main groove 20 and the ground contact edge.

[0023] The convex rib 32 is a land portion having a shape in which the outline of the tread bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim, normal internal pressure is applied, and no load is applied, as shown in Fig. 2. Although not depicted in Fig. 2 because both are tire meridian cross sections, the convex rib 32 has a shape that extends continuously in the tire circumferential direction without being interrupted by lateral grooves extending in the tire width direction.

[0024] "Regular rim" refers to the rim specified for each tire by the standard system, including the standard on which the tire is based, such as the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. "Regular internal pressure" refers to the air pressure specified for each tire by the standard system, including the standard on which the tire is based, such as the maximum air pressure for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and the "INFLATION PRESSURE" for ETRTO.

[0025] As shown in Fig. 2, for this convex rib 32, both ends of the convex rib 32 in the tire width direction are defined as points p, the line segment connecting these pair of points p is defined as a line P, the point on the contour of the convex rib 32 that is the longest distance from the line P is defined as point PC, and the intersection of the line P and the perpendicular to the line P passing through point PC is defined as point x0. When defined in this way, the convex rib 32 of the present invention has a contour line from point p to point PC on one side of the contour line of the tread surface (i.e., the contour line on at least one side of point PC in the tire width direction) that is always made up of multiple circular arcs. Furthermore, of these multiple circular arcs, the Nth circular arc from the point PC side is defined as R N (N is an integer greater than or equal to 1), and the arc R N and arc R N+1 The point where and connect is point T N Then, the arc R N and arc R N+1 is point T N 2, the contour of the convex rib 32 is made up of two arcs R1 (the first arc from the point PC) and R2 (the second arc from the point PC), and these arcs R1 and R2 have a common tangent L (see the dashed line in the figure) at point T1. Furthermore, in the convex rib 32 of the present invention, the length W of the straight line P and the distance b from point x1 to point PC satisfy the relationship 0.001≦b / W≦0.25, preferably 0.001≦b / W≦0.20, and more preferably 0.001≦b / W≦0.18.

[0026] Such a bulging shape increases the ground contact pressure in the bulging portion of the convex rib 32 (near point PC) and improves straight-line running performance when traveling on wet roads, while preventing the tire width direction end (near point p) of the convex rib 32 from bulging out relative to the vicinity of point PC, thereby preventing a decrease in ground contact pressure and ensuring good cornering performance on wet roads. In addition, the above-mentioned bulging shape makes it possible to even out the ground contact pressure distribution on the tread surface of the convex rib 32, thereby suppressing squealing at low speeds.

[0027] In the above-described bulging shape, if the ratio b / W is less than 0.001, the amount of bulging becomes small relative to the width of the convex rib 32, and becomes essentially the same as when there is no bulging, limiting the effect of improving wet performance. If the ratio b / W exceeds 0.25, the amount of bulging becomes too large relative to the width of the convex rib 32, making it difficult to ensure a sufficient contact area, and limiting the effect of improving wet performance.

[0028] Point p is the both ends of the tread of the convex rib 32, and these are defined as the points (edges of the convex rib 32) where the side surface of the convex rib 32 (wall surfaces of the adjacent circumferential main grooves) and the tread of the convex rib 32 connect. If the edges of the convex rib 32 are chamfered, the end point of the chamfer on the tread side becomes point p. Also, the "arc R" in the above explanation N and arc R N+1 is point T N "Having a common tangent at" means that the arc R N Point T N Tangent to arc R N+1 Point T N This means that the difference in angle between the tangents at the arc R is within 5°. If the difference in angle between these tangents exceeds 5°, N and arc R N+1 and point T N Therefore, it becomes difficult to obtain a good shape for the convex rib 32.

[0029] In the present invention, it is sufficient that at least one of the plurality of land portions is a convex rib 32 that satisfies the above-mentioned conditions, and therefore the other land portions 30 may be land portions (conventional general land portions) having a shape in which the outline of the tread does not bulge outward in the tire radial direction in a meridian cross section of the tire when mounted on a regular rim, with regular internal pressure applied, and in an unloaded state. Also, the land portions may be land portions having a bulging shape that is not composed of multiple arcs (an arc-shaped outline having a single radius of curvature).

[0030] The number of arcs that make up the contour line is preferably 2 to 4, and more preferably 2 to 3. If the number of arcs that make up the contour line is less than 2 (i.e., a single arc), it is not possible to improve the bulging shape of the convex rib 32 as described above. If the number of arcs that make up the contour line exceeds 4, the shape of the tread surface of the convex rib becomes complex, making it difficult to manufacture a mold for manufacturing a tire equipped with the convex rib 32 that satisfies the above-mentioned conditions.

[0031] As shown in FIG. 2 , if the intersection of the perpendicular line of a line P passing through point T1 and the line P is defined as point x1, point x1 should be located from point x0 to point p within a range of preferably 40% to 90%, more preferably 40% to 85%, and even more preferably 40% to less than 80% of the distance ap between point x0 and point p. This provides a good balance between the first circular arc from point PC and the second and subsequent circular arcs, which is advantageous for suppressing squealing while improving straight-line running performance and cornering performance on wet roads in a balanced manner. If point x1 is located closer to point x0 than the above range, point T1 will be closer to point PC, which will not sufficiently increase the contact pressure at the tire widthwise end of the convex rib 32. This will limit the effectiveness of improving cornering performance on wet roads and squealing at low speeds. If point x1 is located closer to point p than the above range, point T1 will be closer to point p, and the second and subsequent circular arcs will become thinner, making it difficult to maintain the shape of the convex rib 32.

[0032] As shown in Fig. 3, when the perpendicular distance between the straight line P and the contour line of the convex rib 32 at the position of 80% of the aforementioned distance ap is defined as the distance b1, the ratio b1 / b of the distance b to the distance b1 preferably satisfies the relationship of 0.40 < b1 / b ≤ 0.90, more preferably 0.40 ≤ b1 / b ≤ 0.85, and even more preferably 0.40 < b1 / b ≤ 0.80. Thereby, it is possible to prevent the outer side of the convex rib 32 in the tire width direction from significantly dropping below the point PC, which is advantageous for suppressing the generation of skid noise while improving the straight-ahead performance and turning performance on a wet road surface in a balanced manner. When the ratio b1 / b is less than 0.40, the effect of suppressing the drop of the outer side of the convex rib 32 in the tire width direction is limited. When the ratio b1 / b exceeds 0.90, the bulging amount also becomes large on the outer side of the convex rib 32 in the tire width direction, making it difficult to maintain the shape of the convex rib 32.

[0033] In addition to the above relationship of the ratio b1 / b, further, as shown in Fig. 3, when the perpendicular distance between the straight line P and the contour line of the convex rib 32 at the position of 60% of the distance ap is defined as the distance b2, the ratio b2 / b of the distance b to the distance b2 preferably satisfies the relationship of 0.40 ≤ b2 / b ≤ 0.90, more preferably 0.40 ≤ b2 / b ≤ 0.88, and even more preferably 0.45 ≤ b2 / b ≤ 0.88. Also, this distance b2 preferably satisfies the relationship of b > b2 > b1 with respect to the aforementioned distance b1 and distance b. Thereby, the curved shape of the contour line of the convex rib when moving from the point PC toward the outer side of the convex rib in the tire width direction becomes good, which is advantageous for suppressing the generation of skid noise while improving the straight-ahead performance and turning performance on a wet road surface in a balanced manner. When the ratio b2 / b is less than 0.40, the effect of suppressing the drop of the outer side of the convex rib 32 in the tire width direction is limited. When the ratio b2 / b exceeds 0.90, the bulging amount also becomes large on the outer side of the convex rib 32 in the tire width direction, making it difficult to maintain the shape of the convex rib 32.

[0034] As described above, the tread contour line of the convex rib 32 of the present invention is composed of a plurality of arcs R N When its radius of curvature is defined as r N When the radius of curvature r N And the radius of curvature rN+1 What is r N >r N+1 It is preferable that the relationship be satisfied. In other words, it is preferable that the radii of curvature of the multiple circular arcs gradually decrease with increasing distance from point PC. For example, the example in FIG. 2 includes circular arcs R1 and R2, and the radii of curvature r1 and r2 of these arcs satisfy the relationship r1>r2. This improves the curved shape of the contour line of the convex rib 32, which is advantageous for suppressing squealing while improving straight-line performance and cornering performance on wet roads in a balanced manner.

[0035] In particular, when focusing on the first circular arc R1 and the second circular arc R2 from the point PC, the radii of curvature r1 and r2 preferably satisfy the relationship 2≦r1 / r2≦200, more preferably 2≦r1 / r2≦150, and even more preferably 2≦r1 / r2≦130. This results in a well-balanced curve between the first circular arc R1 and the second circular arc R2 from the point PC, which is advantageous for suppressing squealing while improving straight-line running performance and cornering performance on wet roads in a balanced manner. If the ratio r1 / r2 is less than 2, the tire widthwise end of the convex rib 32 becomes flat, limiting the effect of increasing the ground contact pressure at the tire widthwise end. If the ratio r1 / r2 exceeds 200, it becomes difficult to ensure the bulging shape of the convex rib 32. It is also preferable that the above relationship be satisfied for the circular arcs R1 and R2 when the third or subsequent circular arcs are included.

[0036] In addition to the above relationship, the distance b preferably satisfies the relationship 0.05 mm≦b≦2.0 mm, more preferably 0.05 mm≦b≦1.5 mm, and even more preferably 0.05 mm≦b≦1.2 mm. This improves the bulging shape of the convex rib, which is advantageous for balanced improvement of straight-line running performance and cornering performance on wet roads. If the distance b is less than 0.05 mm, the bulge at the center of the convex rib 32 is insufficient, making it difficult to maintain sufficient ground contact pressure at the center of the convex rib 32. If the distance b exceeds 2.0 mm, the bulge amount of the convex rib 32 becomes excessive, making it impossible to ensure a sufficient contact area, limiting the effect of improving cornering performance and straight-line running performance on wet roads.

[0037] As described above, point PC is the point on the contour of the convex rib 32 where the distance to the line P connecting the pair of points p is greatest, and corresponds to the maximum bulge point of the convex rib 32. This point PC should be located within a range of preferably 30%, more preferably 25%, and even more preferably 20% of the length W of line P on both sides of the midpoint of line P in the tire width direction. This allows the central portion of the convex rib 32 to bulge the most (point PC where the convex rib 32 bulges the most is located near the center of the convex rib 32 in the tire width direction), which promotes drainage on the convex rib 32 and is advantageous for improving wet performance. If point PC is located outside the above range, the point where the convex rib 32 bulges the most (point PC) will be unevenly located at the end of the convex rib in the tire width direction, making it difficult to ensure good drainage performance.

[0038] In the above-mentioned convex rib 32, the groove depth of a pair of adjacent circumferential main grooves 20 is preferably 80% or more of the groove depth of the deepest circumferential main groove 20. Since land portions where the groove depth of adjacent circumferential main grooves 20 is large (i.e., land portions that protrude from the groove bottom to a large extent) are greatly affected by ground contact pressure, application of the above-mentioned convex rib 32 can effectively improve straight-line running performance and cornering performance on wet road surfaces.

[0039] The convex rib 32 has a shape that extends continuously in the tire circumferential direction without being interrupted by lateral grooves extending in the tire width direction, but may also have narrow grooves or sipes with a groove width of less than 3 mm. The provision of these narrow grooves or sipes ensures the drainage and edge effects of the narrow grooves and sipes, which is advantageous for improving straight-line performance and cornering performance on wet roads. Note that, because the narrow grooves and sipes have a small groove width as described above, the provision of these narrow grooves and sipes means that the convex rib 32 is considered to be uninterrupted.

[0040] Regarding the tread portion 1 configured as described above, the hardness Hs of the tread rubber (rubber constituting the tread rubber layer 11) constituting the tread portion 1 is preferably 55 or more and 78 or less, more preferably 58 or more and 75 or less, and even more preferably 58 or more and 72 or less. When the tread rubber layer includes a cap tread layer 11C and an undertread layer 11U as shown in FIG. 1 , at least the cap tread layer 11C is preferably made of rubber having the above-mentioned hardness. Having the tread portion 1 with an appropriate hardness allows the protruding shape of the convex ribs 32 to be well maintained during running, allowing the above-described effects of the convex ribs 32 to be efficiently exhibited. If the hardness Hs is less than 55, the tread rubber is too soft, and therefore the protruding shape of the convex ribs 32 cannot be adequately maintained when deformed by lateral force during running, limiting the effect of uniforming ground pressure. If the hardness Hs exceeds 78, the tread rubber is too hard, and the ground pressure of the convex ribs 32 may increase locally, limiting the effect of uniforming ground pressure. The rubber hardness of the tread rubber is determined in accordance with JIS K6253 and is measured at a temperature of 20°C using a durometer type A.

[0041] In the above explanation using Figures 2 and 3, the structure of the present invention has been described mainly with reference to the contour line on one side of point PC in the tire width direction, but the same structure as on one side can also be adopted for the other side (the side not indicated with symbols R1, R2, etc. in the figures). In other words, at least one or both contour lines on each side of point PC in the tire width direction can be configured with multiple arcs as described above. When the present invention is applied to both sides of point PC, the contour lines on both sides do not need to be symmetrical with respect to the perpendicular line to line P passing through point PC, and the contour lines on each side can independently satisfy the various conditions described above.

[0042] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0043] The tire size is 235 / 60R18, and it has the basic structure (cross-sectional structure) illustrated in FIG. 1, and for the convex rib, when both ends of the convex rib in the tire width direction are defined as points p, the line segment connecting the pair of points p is defined as a straight line P, the point on the contour of the convex rib that is the longest from the straight line P is defined as point PC, and the intersection of the perpendicular to the straight line P that passes through point PC and the straight line P is defined as point x0, the number of arcs that make up the contour from point p to point PC on one side of point PC, the ratio b / W of the length W of the straight line P to the distance b from point x0 to point PC, the position of the intersection x1 of the perpendicular to the straight line P that passes through point T1 where the first arc R1 and the second arc R2 from the point PC side are connected and the straight line P (the ratio of the distance ap from point x0 to x1 Tables 1 to 3 show the relationship between the distance from the midpoint of the line P to point PC and the length W of the line P (the "position of p3" in the table, units: %). Tables 1 to 3 show the relationship between the distance W from the midpoint of the line P to point PC and the length W of the line P (the "position of p3" in the table, units: %). Tables 1 to 3 show the relationship between the distance W from the midpoint of the line P to point PC and the length W of the line P (the "position of p3" in the table, units: %). Tables 1 to 3 show the relationship between the distance W from the midpoint of the line P to point PC and the length W of the line P (the "position of p3" in the table, units: %). Tables 1 to 3 show the relationship between the distance W from the midpoint of the line P to point PC and the length W of the line P (the "position of p3" in the table, units: %). Tables 1 to 3 show the relationship between the distance W from the midpoint of the line P to point PC and the length W of the line P (the "cap tread rubber"). Tables 1 to 3 show the relationship between the distance W from the midpoint of the line P to point PC and the length W of the line P (the "position of p3" in the table, units: %) ...

[0044] The values ​​in the table are based on the contour line of the tread surface of the convex rib in a meridian cross section of a tire mounted on a standard rim and pressurized to the standard internal pressure, without load. "Hardness Hs" is a value measured at 20°C using a durometer type A in accordance with JIS K6253.

[0045] In addition, Conventional Example 1 is an example in which the contour line of the tread surface of the convex rib is composed of a single arc with a radius of curvature of 18 mm, and Comparative Example 1 is an example in which the contour line of the tread surface of the convex rib is composed of a single arc with a radius of curvature of 63 mm.

[0046] The straight running performance and cornering performance on wet road surfaces of these test tires were evaluated by the following evaluation methods, and the results are shown in Tables 1 to 3.

[0047] Straight-line performance on wet roads Each test tire was mounted on a standard rim (rim size 18 x 7J), inflated to an internal pressure of 250 KPa (standard internal pressure for passenger cars), and fitted to all wheels of a test vehicle (a passenger car with an engine displacement of 2000 cc). The vehicle was driven on a test course consisting of a wet road at a speed of 60 km / h, and five test drivers performed a sensory evaluation of the driving performance when driving on a straight road. The evaluation results were calculated by adding up the scores of the five drivers and are shown in the "Wet straight-line performance" column in the table as an index, with Conventional Example 1's value set at 100. A higher index value indicates better straight-line performance on wet roads.

[0048] Turning performance on wet roads Each test tire was mounted on a standard rim (rim size 18x7J), inflated to an internal pressure of 250 KPa (standard internal pressure for passenger cars), and fitted to all wheels of a test vehicle (a passenger car with an engine displacement of 2000 cc). The vehicle was driven on a test course consisting of a wet road surface at a speed of 60 km / h, and five test drivers performed a sensory evaluation of the cornering performance when entering a corner. The evaluation results were calculated by adding up the scores of the five drivers and are shown in the "Wet cornering performance" column in the table as an index, with Conventional Example 1's value set at 100. A higher index value indicates better cornering performance on wet roads.

[0049] Squeal reduction performance Each test tire was mounted on a standard rim (rim size 18x7J), inflated to standard internal pressure (180KPa), and mounted on a test vehicle (a passenger car with an engine displacement of 2000cc). Five test drivers then conducted a sensory evaluation of the squealing noise at a traveling speed of 4km / h. The evaluation results were calculated by averaging each test driver's 10-point evaluation (the higher the score, the better), and expressed as an index with Conventional Example 1 being given a value of 100. The higher this index value, the greater the reduction in squealing noise, indicating excellent squealing noise reduction performance.

[0050] [Table 1]

[0051] [Table 2]

[0052] [Table 3]

[0053] As is clear from Tables 1 to 3, the tires of Examples 1 to 21 maintained straight-line running performance on wet roads at the same level as Conventional Example 1, while improving cornering performance and squeal reduction on wet roads, achieving a good balance between these performances. On the other hand, in Comparative Example 1, the contour line of the tread surface of the convex rib was composed of a single arc, as in Conventional Example 1, and therefore did not achieve the effect of improving straight-line running performance, cornering performance, or squeal reduction on wet roads. In Comparative Example 2, although the contour line of the tread surface of the convex rib was composed of multiple arcs, the ratio b / W (amount of bulge relative to the width of the convex rib) was too large, resulting in a reduced contact area and therefore a decrease in cornering performance and straight-line running performance on wet roads.

[0054] The present disclosure includes the following inventions. Invention [1] A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion includes at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions defined by the circumferential main grooves, At least one row of land portions among the plurality of land portions extends continuously along the tire circumferential direction, and is a convex rib having a shape in which the outline of the tread surface bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim and has a regular internal pressure applied and is in an unloaded state, Let both ends of the convex rib in the tire width direction be point p respectively, a line segment connecting the pair of points p be line P, a point on the contour line of the convex rib where the distance from line P is maximized be point PC, and when an intersection point of a perpendicular line to line P passing through point PC and line P is defined as point x0, The contour line from point p on one side to point PC with respect to point PC is composed of a plurality of arcs, Among the plurality of arcs, the Nth arc from the point PC side is R N (N is an integer of 1 or more), and the arc R N and the arc R N+1 When the connection point is point T N Then, the arc R N and the arc R N+1 and the arc R have a common tangent at point T N And, A tire, characterized in that the length W of the line P and the distance b from the point x0 to the point PC satisfy the relationship of 0.001 ≦ b / W ≦ 0.25. Invention [2] When an intersection point of a perpendicular line to the line P passing through the point T1 and the line P is defined as point x1, The tire according to invention [1], characterized in that the point x1 is arranged in a range of 40% or more and 90% or less of the distance ap between the point x0 and the point p from the point x0 toward the point p. Invention [3] When the perpendicular distance between the line P and the contour line of the convex rib at a position of 80% of the distance ap between the point x0 and the point p from the point x0 toward the point p is defined as distance b1, The tire according to invention [1] or [2], characterized in that the ratio b1 / b of the distance b and the distance b1 satisfies the relationship of 0.40 < b1 / b ≦ 0.90. Invention [4] When the perpendicular distance between the line P and the contour line of the convex rib at a position of 60% of the distance ap between the point x0 and the point p from the point x0 toward the point p is defined as distance b2, The tire according to invention [3], characterized in that the ratio b2 / b of the distance b and the distance b2 satisfies the relationship of 0.40 ≦ b2 / b ≦ 0.90, and satisfies the relationship of b > b2 > b1. Invention [5] The arc R NThe radius of curvature of r N When defined as follows, the radius of curvature r N and the radius of curvature r N+1 Toga r N >r N+1 The tire according to any one of inventions [1] to [4], characterized in that the following relationship is satisfied. Invention [6] The arc R N The radius of curvature of r N The tire according to any one of inventions [1] to [5], wherein the radius of curvature r1 and the radius of curvature r2 satisfy the relationship 2≦r1 / r2≦200 when defined as follows: Invention [7] The tire according to any one of inventions [1] to [6], wherein the distance b satisfies the relationship 0.05 mm≦b≦2.0 mm. Invention [8] A tire according to any one of inventions [1] to [7], characterized in that the point PC is located within a range of 30% of the length W of the straight line P on both sides of the midpoint of the straight line P in the tire width direction. Invention [9] The tire according to any one of inventions [1] to [8], characterized in that the hardness Hs of the tread rubber constituting the tread portion is 55 or more and 78 or less. [Explanation of symbols]

[0055] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Belt reinforcement layer 11 Tread rubber layer 11C cap tread rubber layer 11U Undertread rubber layer 12 Side rubber layer 13 Rim cushion rubber layer 20 Circumferential main groove 30 Land 31 Shoulder Land Section 32 Convex rib CL Tire Equator

Claims

1. A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion includes at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions defined by the circumferential main grooves, At least one row of land portions among the plurality of land portions extends continuously along the tire circumferential direction, and is a convex rib having a shape in which the outline of the tread surface bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim and has a regular internal pressure applied and is in an unloaded state, When both ends of the protruding rib in the tire width direction are defined as points p, a line segment connecting the pair of points p is defined as a straight line P, a point on the contour line of the protruding rib that is the longest distance from the straight line P is defined as point PC, and the intersection of the perpendicular to the straight line P that passes through point PC and the straight line P is defined as point x0, The contour line from point p on one side of point PC to point PC is made up of a plurality of arcs, Among the plurality of circular arcs, the Nth circular arc from the point PC side is R N (N is an integer of 1 or more), and the arc R N and arc R N+1 The point where and are connected is point T N Then, the arc R N and arc R N+1 That is, point T N have a common tangent at A tire characterized in that the length W of the straight line P and the distance b from the point x0 to the point PC satisfy the relationship 0.001≦b / W≦0.

25.

2. Said point T 1 When the intersection point of the perpendicular line of the line P passing through the line P and the line P is defined as point x1, 2. The tire according to claim 1, wherein the point x1 is located in a range from the point x0 toward the point p that is 40% to 90% of the distance ap between the point x0 and the point p.

3. When the perpendicular distance between the straight line P and the contour line of the convex rib at a position 80% of the distance ap between the point x0 and the point p toward the point x0 is defined as a distance b1, 3. The tire according to claim 1, wherein a ratio b1 / b of the distance b to the distance b1 satisfies the relationship: 0.40<b1 / b≦0.

90.

4. When the perpendicular distance between the straight line P and the contour line of the convex rib at a position 60% of the distance ap between the point x0 and the point p toward the point x0 is defined as a distance b2, 4. The tire according to claim 3, wherein a ratio b2 / b of the distance b to the distance b2 satisfies the relationship of 0.40≦b2 / b≦0.90, and satisfies the relationship of b>b2>b1 with the distance b1.

5. The circular arc R N The radius of curvature of r N When defined as above, the radius of curvature r N and the radius of curvature r N+1 Togar N >r N+1 3. The tire according to claim 1, wherein the following relationship is satisfied:

6. The circular arc R N The radius of curvature of r N When defined as above, the radius of curvature r 1 and the radius of curvature r 2 and 2≦r 1 / r 2 3. The tire according to claim 1, wherein the relationship of ≦200 is satisfied.

7. 3. The tire according to claim 1, wherein the distance b satisfies the relationship 0.05 mm≦b≦2.0 mm.

8. 3. The tire according to claim 1, wherein the point PC is located within a range of 30% of the length W of the straight line P on both sides of the midpoint of the straight line P in the tire width direction.

9. 3. The tire according to claim 1, wherein the hardness Hs of the tread rubber constituting the tread portion is 55 or more and 78 or less.

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