Tire

Abstract

To provide a tire that is able to reduce steering force while maintaining wet performance equivalent to the case where a land portion having a swollen tread is provided.SOLUTION: At least one row of land portions 30 excluding a shoulder land portion 31 is formed as a recessed rib 32 continuously extending along a tire circumferential direction and including a recessed portion 32a in which a contour line of a tread surface in a tire meridian cross-section is recessed inward in a tire radial direction. In a tire meridian cross-sectional view in an unloaded state in which the tire is mounted on a normal rim and a normal internal pressure is applied, when a straight line A connecting a point P1 and a point P2 and a straight line B orthogonal to the straight line A and passing through a point P3 are drawn based on the end points P1, P2 in a tire lateral direction of the recessed portion 32a and the deepest portion (the point P3) of the recessed portion 32a, a length L between an intersection of the straight line A and the straight line B and the point P3 satisfies, for a width W of the recessed rib 32 and a hardness Hs of a tread rubber, a relation expressed by 0<(L / W)×100≤6, a relation expressed by 0≤((L / W)×100) / Hs≤0.06, and a relation expressed by Hs is 55 or more and 78 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire having rib-shaped land portions that extend continuously along the tire circumferential direction, and more specifically to a tire that enables improved wet performance without increasing the steering force when stopped (when steering stationary). [Background technology]

[0002] To improve the wet performance of tires, a technology is known in which the contact surface of land portions 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 contact surface of the land portions increases the ground contact pressure of the land portions, improving the contact characteristics between the land portions and the road surface when traveling on wet roads and improving wet performance. However, the bulged contact surface increases the contact length, which causes a problem of increased steering force (especially when steering while stationary). [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] The object of the present invention is to provide a tire that makes it possible to reduce steering force when stopped (when turning at a stationary position) while maintaining wet performance equivalent to that of a tire with a land portion having a bulging tread. [Means for solving the problem]

[0005] In order to achieve the above object, the tire of the present invention has 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 land portions among the plurality of land portions except for a pair of shoulder land portions located at the outermost sides in the tire width direction is a concave rib extending continuously along the tire circumferential direction, the concave rib having a contour line of the tread surface in a tire meridian cross section that includes a recess recessed toward the tire radially inward, and in a no-load state when the tire is mounted on a regular rim and a regular internal pressure is applied, In a tire meridian cross section, when an end point of the recess on one side in the tire width direction is defined as point P1, an end point of the recess on the other side in the tire width direction is defined as point P2, and the deepest part of the recess is defined as point P3, and a line A connecting point P1 and point P2 and a line B perpendicular to line A and passing through point P3 are drawn, a distance L between point P3 and an intersection point of line A and line B satisfies the relationship 0<(L / W)×100≦6 and 0<((L / W)×100) / Hs≦0.06, where W is the width of the recessed rib and Hs is a hardness Hs of tread rubber constituting the tread portion, and the hardness Hs of the tread rubber is 55 or more and 78 or less. [Effects of the Invention]

[0006] In the tire of the present invention, since at least one row of land portions excluding a pair of shoulder land portions has a concave rib having the above-mentioned characteristics, the concave portion exhibits appropriate drainage, ensuring wet performance equivalent to that of land portions having a bulged tread surface, while avoiding the increase in contact length that occurs when land portions having a bulged tread surface are provided, thereby reducing steering force. In particular, the distance L defined by the end point (point P1) of the concave portion on one side in the tire width direction, the end point (point P2) of the concave portion on the other side in the tire width direction, the deepest part of the concave portion (point P3), a line A connecting points P1 and P2, and a line B perpendicular to line A and passing through point P3, the width W of the concave rib, and the hardness Hs of the tread rubber constituting the tread portion satisfy the relationships 0<(L / W)×100≦6 and 0<((L / W)×100) / Hs≦0.06, and the hardness Hs of the tread rubber is 55 to 78, thereby achieving a high level of balance between maintaining wet performance and reducing steering force.

[0007] In the present invention, when point P4 is defined as the intersection point between a line that passes through the midpoint between point P3 and the intersection point of line A and line B and is parallel to line A, and the contour line of the recess, the angle X formed by the line connecting point P4 and point P1 with line A and line A, and the groove wall angle Y of the circumferential main groove adjacent to the recessed rib preferably satisfy the relationship 0.02≦X / Y<1. This provides a good balance between the shape of the recess (degree of depression of the recess) and the overall shape of the recessed rib (degree of inclination of the groove wall of the circumferential main groove adjacent to the recessed rib, i.e., the side surface of the recessed rib on the outer side in the tire width direction), which is advantageous for maintaining wet performance and reducing steering force at the same time.

[0008] In the present invention, it is preferable that point P3 be located within a range of 15% of the width W of the recessed rib on both sides of the tire width direction from the tire width direction center of the recessed rib. This makes the shape of the recessed rib approximately uniform on both sides of the tire width direction center of the recessed rib, making it possible to suppress left-right differences in steering force when steering while stationary, and effectively reducing steering force.

[0009] In the present invention, it is preferable that the contour line of the recessed portion be curved so as to be convex radially inward relative to both the straight line connecting points P1 and P3 and the straight line connecting points P2 and P3. By making the recessed portion curved in this way, the shape of the recessed rib becomes good, which is advantageous for achieving both maintaining wet performance and reducing steering force.

[0010] In the present invention, when a line T is drawn that is parallel to a line M connecting the deepest points of a pair of circumferential main grooves adjacent to the recessed rib and passes through the point P3, it is preferable that the distance T1 between point P1 and the line T and the distance T2 between point P2 and the line T satisfy the relationship 0.7≦T1 / T2≦1.5. This makes the heights of points P1 and P2 from the groove bottoms of the circumferential grooves approximately equal, suppressing the difference in steering force between the left and right sides when steering while stationary, and effectively reducing the steering force.

[0011] In the present invention, the recessed rib may be specified to have chamfered portions on both edges in the tire width direction. In this specification, when the line connecting the tire radially inner end W1 of the chamfered portion on the point P1 side and the tire radially inner end W2 of the chamfered portion on the point P2 side is defined as line W', and the line connecting the deepest points of a pair of circumferential main grooves adjacent to the recessed rib is defined as line M, the distance C between point P1 and line W', the distance D between point P2 and line W', the distance N between the tire radially inner end W1 of the chamfered portion and line M, and the distance U between the tire radially inner end W2 of the chamfered portion and line M preferably satisfy the relationships 0.05≦C / N≦0.98 and 0.05≦D / U≦0.98, and further, the distance Q between point P1 and point P2 and the width W of the recessed rib preferably satisfy the relationship 0.7≦Q / W≦0.97. This improves the shape of the chamfered portion (chamfer width and chamfer depth), which is advantageous for maintaining wet performance while reducing steering force.

[0012] In the present invention, it is preferable that all of the land portions except for a pair of shoulder land portions located at the outermost sides in the tire width direction among the plurality of land portions have concave ribs. This shortens the contact length of the entire ground contact patch, thereby effectively reducing steering force. On the other hand, since all land portions except for the shoulder land portions have concave portions, drainage is ensured, making it possible to maintain good wet performance.

[0013] 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]

[0014] [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 recessed rib of a tire according to an embodiment of the present invention. [Figure 3] FIG. 4 is an explanatory diagram schematically showing a recessed rib of a tire according to another embodiment of the present invention. [Figure 4]FIG. 4 is an explanatory diagram schematically showing a recessed rib of a tire according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] As described below, the present invention relates to the tread portion 1 of the tire (particularly the cross-sectional shape of the recessed ribs described below), and therefore the basic structure of the tire is not limited to the general structure described above. Furthermore, 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) on which land portions (recessed ribs) are formed.

[0020] 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 of the present invention. These at least two circumferential main grooves 20 define a plurality of 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 outward in the tire width direction of a pair of circumferential main grooves 20 located at the outermost positions in the tire width direction are referred to as shoulder land portions 31. In the present invention, at least one row (one row in Fig. 1) of the land portions 30 excluding these shoulder land portions 31 is configured as a recessed rib 32, which will be described later.

[0021] As shown in Figures 2 to 4, the recessed rib 32 is a land portion in which the outline of the tread in a tire meridian cross section includes recesses 32a recessed radially inward. Although not depicted in Figures 2 to 4 because they are tire meridian cross sections, the recessed rib 32 is a land portion that extends continuously in the tire circumferential direction without being interrupted by lateral grooves or sipes extending in the tire width direction. By providing such a recessed rib 32, the recesses 32a ensure adequate drainage, ensuring wet performance equivalent to that of a land portion with a conventional bulged tread, while avoiding the increased contact length that occurs when a land portion with a conventional bulged tread is provided, thereby reducing steering force.

[0022] As described above, the recessed ribs 32 are provided in at least one row in the land portions 30 excluding the shoulder land portions 31, but preferably all of the land portions 30 excluding the shoulder land portions 31 are recessed ribs 32. This shortens the contact length of the entire ground contact surface, effectively reducing steering force. In addition, all of the land portions 30 (recessed ribs 32) excluding the shoulder land portions 31 are provided with recesses 32a, which ensure drainage and make it possible to maintain good wet performance. If the land portions 30 excluding the shoulder land portions 31 include land portions that do not correspond to recessed ribs 32 (land portions with a conventional bulging tread or land portions without recesses or bulges), the contact length at the location of those land portions will be longer, which may increase steering force when steering while stationary.

[0023] The shape of the recessed rib 32 shown in Figures 2 to 4 will be described in detail below. In the following description, a "regular rim" refers to a rim determined for each tire by a standard system including the standard on which the tire is based, such as a standard rim for JATMA, a "Design Rim" for TRA, or a "Measuring Rim" for ETRTO. Also, a "regular internal pressure" refers to the air pressure determined for each tire by a 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, or the "INFLATION PRESSURE" for ETRTO.

[0024] 2 has chamfered portions 32b on both edges of the tread surface in the tire width direction. In a meridian cross section of the tire mounted on a regular rim and pressurized to a regular internal pressure and in an unloaded state, when an end point of one side of the recessed portion 32a in the tire width direction is designated as point P1, an end point of the other side of the recessed portion 32a in the tire width direction is designated as point P2, and the deepest portion of the recessed portion 32a is designated as point P3, a line A connecting points P1 and P2 and a line B perpendicular to line A and passing through point P3 are drawn, the distance L between the intersection of line A and line B and point P3 satisfies the relationships 0<(L / W)×100≦6 and 0<((L / W)×100) / Hs≦0.06 with respect to the width W of the recessed rib 32a and the hardness Hs of the tread rubber constituting the tread rubber layer 11 (particularly the cap tread layer 11C), and the hardness Hs of the tread rubber is set to be 55 or greater and 78 or less.

[0025] The width W of the recessed rib 32a is the distance between point W1 and point W2 (the length of the line segment connecting points W1 and W2), when the radially inner end of the chamfered portion 32b on the point P1 side is point W1 and the radially inner end of the chamfered portion 32b on the point P2 side is point W2, as viewed in a meridian cross section of the tire mounted on a standard rim, with the standard internal pressure applied, and in an unloaded state. If the chamfer is a curved chamfer rather than a linear chamfer as shown in the figure, the starting point of the curved surface that constitutes the chamfered portion 32b is point W1 or point W2. The rubber hardness of the tread rubber refers to the hardness of the rubber measured at 20°C using a type A durometer in accordance with JIS K6253.

[0026] By satisfying the above relationship, the balance between the width W of the recessed rib 32 and the recessed depth (distance L) of the recessed portion 32a, as well as the relationship between these and the rubber hardness of the tread rubber (the degree of deformation when the recessed rib 32 is installed), is favorable, thereby achieving a high level of balance between maintaining wet performance and reducing steering force. If the distance L is small relative to the width W of the recessed rib 32, the recessed portion 32a will not be recessed sufficiently, and drainage will not be ensured. Furthermore, the effect of suppressing an increase in contact length will not be achieved, and there is a risk of increased steering force when steering while stationary. If the distance L is large relative to the width W of the recessed rib 32, water may collect in the recessed portion 32a, impeding drainage and reducing wet performance. If the hardness Hs is small relative to the ratio L / W, the recessed portion 32a will not remain recessed when in contact with the tire and will function as a conventional tread, thereby failing to achieve the effect of reducing steering force. If the hardness Hs is large relative to the ratio L / W, the areas at points P1 and P2 may easily catch on the road surface when the wheel is turned stationary, which may increase the steering force. If the hardness Hs is less than 55, the recess 32a will not remain as a depression when the wheel is in contact with the ground, and will function as a conventional tread, which may not reduce the steering force. If the hardness Hs exceeds 78, the areas at points P1 and P2 may easily catch on the road surface when the wheel is turned stationary, which may increase the steering force.

[0027] The recessed rib 32 illustrated in FIG. 3 differs from the case of FIG. 2 in that no chamfered portions 32b are provided on the edges of the tread on both sides in the tire width direction. In this embodiment, when viewed in meridian section of the tire in an unloaded state with the tire mounted on a regular rim and pressurized to a normal internal pressure, the end point of one side of the recess 32a in the tire width direction is defined as point P1, the end point of the other side of the recess 32a in the tire width direction is defined as point P2, and the deepest part of the recess 32a is defined as point P3. When a line A connecting points P1 and P2 and a line B perpendicular to line A and passing through point P3 are drawn, the distance L between the intersection of line A and line B and point P3 satisfies the relationship 0<((L / W)×100)<6 and 0<((L / W)×100) / Hs<0.06 with respect to the width W of the recessed rib 32a and the hardness Hs of the tread rubber constituting the tread rubber layer 11 (particularly the cap tread layer 11C), and the hardness Hs of the tread rubber is set to be 55 or more and 78 or less.

[0028] In this case, the width W of the recessed rib 32a is the distance between point W1 and point W2 (the length of the line segment connecting points W1 and W2) when the edge (corner) of the recessed rib 32a on the point P1 side is point W1 and the edge (corner) on the point P2 side is point W2 in a meridian cross-section of the tire mounted on a regular rim and pressurized to a regular internal pressure without load. As shown in Figure 4, the end points of the recessed portion 32a and the edge (corner) of the recessed rib 32a may coincide, in which case points P1 and W1, and points P2 and W2, are the same point. The rubber hardness of the tread rubber, as in the case of Figure 2, refers to the hardness of the rubber measured at a temperature of 20°C using a type A durometer in accordance with JIS K6253.

[0029] In the case of the embodiment of Figures 3 to 4, as in the embodiment of Figure 2, by satisfying the above-mentioned relationship, the balance between the width W of the concave rib 32 and the degree of depression of the recess 32a (distance L) and the relationship between these and the rubber hardness of the tread rubber (the degree of deformation when the concave rib 32 is installed) is improved, and it is possible to achieve a high level of balance between maintaining wet performance and reducing steering force.

[0030] The recessed rib 32 is a land portion (rib) having recessed portions 32a, but multiple recessed portions 32a may be provided in one recessed rib 32. In this case, of the multiple recessed portions 32a, the end point located at the outermost position on one side of the recessed rib 32 in the tire width direction is P1, and the end point located at the outermost position on the other side of the recessed rib 32 in the tire width direction is P2. Furthermore, the deepest portion of the multiple recessed portions 32a with the largest recessed amount among the multiple recessed portions 32a is point P3. Even when multiple recessed portions 32a are provided in one recessed rib 32, by setting points P1 to P3 as described above and satisfying the above-mentioned relationship, the balance between the width W of the recessed rib 32 and the recessed degree (distance L) of the recessed portions 32a, as well as the relationship between these and the rubber hardness of the tread rubber (the degree of deformation when the recessed rib 32 is installed), can be improved, thereby achieving a good balance between maintaining wet performance and reducing steering force.

[0031] In any of the cases shown in Figures 2 to 4, the distance L, the width W of the recessed rib 32a, and the hardness Hs of the tread rubber preferably satisfy the relationships 0.1 ≤ (L / W) x 100 ≤ 5 and 0 < ((L / W) x 100) / Hs ≤ 0.04. The distance L is not particularly limited, but can be set, for example, to 0.05 mm to 0.4 mm. The width W of the recessed rib 32a is not particularly limited, but can be set, for example, to 15 mm to 45 mm. The hardness Hs of the tread rubber must always be in the range of 55 to 78, as mentioned above, but can be set preferably to 58 to 75, and more preferably to 58 to 72.

[0032] 2 to 4, when point P4 is defined as the intersection point between a line that passes through the midpoint between point P3 and the intersection point of line A and line B and is parallel to line A, and the contour of recess 32a, angle X formed by a line connecting point P4 and point P1 with line A and groove wall angle Y of circumferential main groove 20 adjacent to recessed rib 32 preferably satisfy the relationship 0.02≦X / Y<1. Note that when a line M connecting deepest points M1 and M2 of a pair of circumferential main grooves 20 adjacent to recessed rib 32 is drawn, and a line N passing through point W1 or point W2 and perpendicular to line M is drawn, groove wall angle Y is defined as the intersection point M4 between the groove wall of circumferential main groove 20 and a line that passes through the midpoint between point W1 and point W3 of line M and line N and is parallel to line M, the line connecting point W1 and point M4 (the groove wall of circumferential main groove 20) with line N.

[0033] By specifying the relationship between the angle X and the groove wall angle Y in this manner, a good balance is achieved between the shape of the recessed portion 32a (the recessed degree of the recessed portion 32a) and the overall shape of the recessed rib 32 (the groove wall of the circumferential main groove 10 adjacent to the recessed rib 32, i.e., the degree of inclination of the side surface of the recessed rib 32 on the outer side in the tire width direction), which is advantageous for maintaining wet performance while reducing steering force. If the groove wall angle Y is smaller than the angle X, the rigidity of the recessed rib 32 may not be sufficiently ensured, which may result in reduced wet performance. If the ratio X / Y is less than 0.02, the recessed portion 32a is not recessed sufficiently, which may result in poor drainage. Furthermore, the effect of suppressing an increase in contact length may not be achieved, which may result in increased steering force when steering while stationary. If the ratio X / Y is 1 or greater, the recessed portion 32a may be recessed to a large extent, which may cause water to collect in the recessed portion 32a, impeding drainage and resulting in reduced wet performance. The angle X is not particularly limited, but may be set to, for example, greater than 0° and less than 15°. The groove wall angle Y is not particularly limited, but can be set to, for example, 5° or more and 40° or less.

[0034] The deepest part (point P3) of the recess 32a is preferably located substantially at the center in the tire width direction of the recess 32a. Specifically, it may be arranged in a range of preferably within 15%, more preferably within 10%, and still more preferably within 5% of the width W of the concave rib 32 from the center in the tire width direction of the concave rib 32 to both sides in the tire width direction. Thereby, the shape of the concave rib 32 becomes substantially uniform on both sides of the center in the tire width direction of the concave rib 32, the difference in steering force between the left and right during installation can be suppressed, and the steering force can be effectively reduced. If point P3 is arranged outside 15% of the width W of the concave rib 32 from the center in the tire width direction of the concave rib 32 to both sides in the tire width direction, the shape of the concave rib 32 will not be uniform left and right, the load will be biased to the end point (point P1 or point P2) on either side in the tire width direction of the recesses 32a, and there is a possibility that the steering force on one side will increase.

[0035] The contour line of the recess 32a is preferably curved so as to protrude inward in the tire diameter direction from both the straight line connecting point P1 and point P3 and the straight line connecting point P2 and point P3. By forming the recess 32a in such a curved shape, the shape of the concave rib 32 is improved, which is advantageous for achieving both maintenance of wet performance and reduction of steering force. In particular, when the length of the line segment connecting point P1 and point P3 is S1, the length of the line segment connecting point P2 and point P3 is S2, the length along the contour line of the recess 32a from point P1 to point P3 is Z1, and the length along the contour line of the recess 32a from point P2 to point P3 is Z2, it is preferable that these lengths satisfy the relationship of 1 < Z1 / S1 < 1.05 and 1 < Z2 / S2 < 1.05. If these lengths are in the relationship of Z1 = S1 or Z2 = S2, the contour line of the recess 32a will be linear, the ground contact pressure cannot be dispersed, the ground contact pressure will be locally high, and there is a possibility that the steering force during installation will increase.

[0036] When a line T is drawn that is parallel to a line M connecting the deepest points of a pair of circumferential main grooves 10 adjacent to the recessed rib 32 and passes through point P3, the distance T1 between point P1 and line T and the distance T2 between point P2 and line T preferably satisfy the relationship 0.7≦T1 / T2≦1.5, more preferably 0.8≦T1 / T2≦1.3. This makes the heights of points P1 and P2 from the groove bottoms of the circumferential grooves 10 approximately equal, suppressing the difference in steering force between the left and right sides when steering while stationary, and effectively reducing steering force. If the ratio T1 / T2 is less than 0.7, a load is likely to be applied to the area at point P2, which may increase the steering force on the point P2 side. If the ratio T1 / T2 is greater than 1.5, a load is likely to be applied to the area at point P1, which may increase the steering force on the point P1 side.

[0037] When the chamfered portion 32b is provided as in the example of FIG. 2, optimizing the chamfer width and chamfer depth is effective in maintaining wet performance and reducing steering force at the same time. Therefore, as shown in Figure 2, when the line connecting the tire radially inner end W1 of the chamfered portion 32b on the point P1 side and the tire radially inner end W2 of the chamfered portion 32b on the point P2 side is defined as line W', and the line connecting the deepest points of a pair of circumferential main grooves 10 adjacent to the recessed rib 32 is defined as line M, it is preferable that the distance C between point P1 and line W', the distance D between point P2 and line W', the distance N between the tire radially inner end W1 of the chamfered portion 32b and line M, and the distance U between the tire radially inner end W2 of the chamfered portion 32b and line M satisfy the relationships 0.05 ≦ C / N ≦ 0.98 and 0.05 ≦ D / U ≦ 0.98, and further the distance Q between point P1 and point P2 and the width W of the recessed rib satisfy the relationship 0.7 ≦ Q / W ≦ 0.97. If C / N or D / U is below the lower limit of the above range, the chamfer depth becomes small and the chamfered portion 32b cannot be expected to drain sufficiently. As a result, water may collect in the recess 32a, preventing drainage and resulting in poor wet performance. If C / N or D / U exceeds the upper limit of the above range, the chamfer depth becomes large, making it difficult to ensure sufficient rigidity of the recessed rib 32, resulting in poor wet performance. If Q / W is less than 0.7, the chamfer width becomes large, narrowing the width of the tread that actually contacts the road surface and increasing ground pressure, which may increase steering force. If Q / W exceeds 0.97, the chamfer width becomes small, preventing drainage to the circumferential main groove 20 and resulting in poor wet performance. The aforementioned distances C, D, N, U, and Q and the width W of the recessed rib more preferably satisfy the relationships 0.06≦C / N≦0.96, 0.06≦D / U≦0.96, and 0.7≦Q / W≦0.95.

[0038] 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]

[0039] Pneumatic tires (test tires) of Conventional Examples 1 and 2, Comparative Examples 1 and 2, and Examples 1 to 28 were manufactured, each having a tire size of 235 / 60R18 and the basic structure (cross-sectional structure) illustrated in FIG. 1 , with the presence or absence of chamfered portions, the number of recessed ribs, (L / W)×100, hardness Hs, (L / W)×100) / Hs, X / Y, position of point P3, T1 / T2, C / N, D / U, and Q / W set as shown in Tables 1 to 4, respectively.

[0040] The "Presence or Absence of Chamfered Portion" column in Tables 1 to 4 indicates whether or not the concave ribs formed on each test tire were chamfered, with "present" indicating cases where chamfered portions were formed and "absent" indicating cases where no chamfered portions were formed. When chamfered portions were present, linear chamfering was performed as in the illustrated example. The "Number of Concave Ribs" column in Tables 1 to 4 indicates the number of concave ribs included in the three rows of land portions excluding the shoulder land portions. Comparative Examples 1 and 2 are examples in which land portions with bulging tread surfaces (convex ribs) were provided instead of concave ribs, and the number of convex ribs is listed in the same column as a reference value.

[0041] The "(L / W) x 100" and "((L / W) x 100) / Hs" columns in Tables 1 to 4 are calculated from the following: when viewed in meridian section of a tire mounted on a regular rim, pressurized to a regular internal pressure, and unloaded, the tire is positioned such that point P1 is the end point of the recess on one side in the tire width direction, point P2 is the end point of the recess on the other side in the tire width direction, and point P3 is the deepest point of the recess; when a line A connecting point P1 and point P2 is drawn and a line B perpendicular to line A and passing through point P3 is drawn, the distance L between point P3 and the intersection of line A and line B; the width W of the recessed rib; and the hardness Hs of the tread rubber constituting the tread. Comparative Examples 1 and 2 are examples in which, as mentioned above, land portions (convex ribs) with a bulged tread surface are provided instead of the recessed ribs. For reference, the values ​​calculated using the bulge amount as the distance L (a negative value) are shown.

[0042] The "X / Y" columns in Tables 1 to 4 show values ​​calculated based on the angle X formed by a line connecting point P4 and point P1 with line A, where point P4 is the intersection point between line A, line B, and point P3, and the contour line of the recess, and line A is the intersection point between line A, line B, and point P3. The "Position of Point P3" column in Tables 1 to 2 shows the distance in the tire width direction from the tire width center of the recess rib to point P3 (proportion to the width W of the recess rib [unit: %]). A value of "0%" in this column means that point P3 is located at the tire width center of the recess rib. Comparative Examples 1 and 2 are examples in which, as described above, land portions (convex ribs) with protruding tread surfaces are provided instead of the recess ribs. For reference, the values ​​shown are those in which the most protruding point of the protruding rib is regarded as point P3. The "T1 / T2" columns in Tables 1 and 2 show values ​​calculated from the distance T1 between point P1 and line T and the distance T2 between point P2 and line T when a line T is drawn that is parallel to a line M connecting the deepest points of a pair of circumferential main grooves adjacent to the concave rib and passes through point P3.

[0043] The columns "C / N," "D / U," and "Q / W" in Tables 1 and 2 show values ​​calculated from the distance C between point P1 and line W', the distance D between point P2 and line W', the distance N between the tire radially inner end W1 of the chamfered portion and line M, the distance U between the tire radially inner end W2 of the chamfered portion and line M, the distance Q between point P1 and point P2, and the width W of the concave rib, where line W' is the line connecting the tire radially inner end W1 of the chamfered portion on the point P1 side and the tire radially inner end W2 of the chamfered portion on the point P2 side, and line M is the line connecting the deepest points of a pair of circumferential main grooves adjacent to the concave rib. Comparative Examples 1 and 2 are examples in which, as described above, land portions (convex ribs) with bulged tread surfaces are provided instead of concave ribs, and reference values ​​are shown based on the values ​​obtained by regarding the end points of the raised convex portions of the convex ribs as P1 and P2.

[0044] The test tires were evaluated for steering force and wet performance using the following evaluation methods, and the results are shown in Tables 1 to 4.

[0045] Steering force Each test tire was mounted on a standard rim (rim size 18x7J), inflated to the standard internal pressure (180KPa), and mounted on a test vehicle (a passenger car with an engine displacement of 2000cc). The front wheels of the test vehicle were placed on a Surf Ty Walk, a steering force meter was attached to the steering wheel, the steering wheel was rotated left and right until it locked, and the steering force was measured at a position where the steering wheel had rotated 70% of its full rotation angle. The evaluation results are shown as an index using the reciprocal of the measured value, with Conventional Example 1 being 100 in Tables 1 and 2, and Conventional Example 2 being 100 in Tables 3 and 4. The higher the index value, the weaker the steering force when stopped (stationary steering).

[0046] Wet 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). A test driver then conducted a sensory evaluation of the running performance on wet roads on a test course consisting of wet roads. The evaluation results are shown as an index in Tables 1 and 2, with Conventional Example 1 being set to 100, and in Tables 3 and 4, with Conventional Example 2 being set to 100. A higher index value indicates better wet performance.

[0047] [Table 1]

[0048] [Table 2]

[0049] [Table 3]

[0050] [Table 4]

[0051] As is clear from Table 1, the pneumatic tires of Examples 1 to 15 reduced steering force while maintaining good wet performance compared to Conventional Example 1. Similarly, as is clear from Table 2, the pneumatic tires of Examples 16 to 28 reduced steering force while maintaining good wet performance compared to Conventional Example 2. On the other hand, in Comparative Examples 1 and 2, the values ​​of (L / W)×100 and ((L / W)×100) / Hs were large and the hardness Hs was small, so the effect of reducing steering force while maintaining wet performance was not sufficiently achieved.

[0052] 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, excluding a pair of shoulder land portions located at the outermost sides in the tire width direction, among the plurality of land portions is a recessed rib extending continuously along the tire circumferential direction, the concave rib includes a recess in which a contour line of the tread surface in a tire meridian cross section is recessed toward the tire radially inward, In a meridian cross section of a tire mounted on a regular rim and with regular internal pressure applied and no load applied, when an end point on one side of the recess in the tire width direction is defined as point P1, an end point on the other side of the recess in the tire width direction is defined as point P2, and the deepest part of the recess is defined as point P3, a straight line A connecting point P1 and point P2 and a straight line B perpendicular to line A and passing through point P3 are drawn, A tire characterized in that the distance L between the intersection of the straight lines A and B and the point P3 satisfies the relationship of 0<(L / W)×100≦6 and 0<((L / W)×100) / Hs≦0.05 with respect to the width W of the recessed rib and the hardness Hs of the tread rubber constituting the tread portion, and the hardness Hs of the tread rubber is 55 or more and 78 or less. Invention [2] The tire according to invention [1], characterized in that when point P4 is defined as the intersection point between a line that passes through the midpoint between point P3 and the intersection point of line A and line B, and is parallel to line A, and the outline of the recess, angle X formed by a line connecting point P4 and point P1 with line A and groove wall angle Y of the circumferential main groove adjacent to the recessed rib satisfies the relationship 0.02≦X / Y<1. Invention [3] A tire according to invention [1] or [2], characterized in that point P3 is located within a range of 15% of the width W of the concave rib on both sides of the tire width direction from the tire width direction center of the concave rib. Invention [4] A tire according to any one of inventions [1] to [3], characterized in that the contour line of the recess is curved so as to be convex radially inward of the tire relative to both the straight line connecting point P1 and point P3 and the straight line connecting point P2 and point P3. Invention [5] A tire according to any one of inventions [1] to [4], characterized in that when a line T is drawn that is parallel to a line M connecting the deepest points of a pair of circumferential main grooves adjacent to the recessed rib and passes through the point P3, the distance T1 between the point P1 and the line T and the distance T2 between the point P2 and the line T satisfy the relationship 0.7≦T1 / T2≦1.5. Invention [6] A chamfered portion is provided on the edges of both sides of the concave rib in the tire width direction, When a straight line connecting the tire radially inner end W1 of the chamfered portion on the point P1 side and the tire radially inner end W2 of the chamfered portion on the point P2 side is defined as a straight line W', and a straight line connecting the deepest points of a pair of circumferential main grooves adjacent to the concave rib is defined as a straight line M, The tire according to any one of inventions [1] to [5], wherein the distance C between the point P1 and the straight line W', the distance D between the point P2 and the straight line W', the distance N between the tire radially inner end W1 of the chamfered portion and the straight line M, and the distance U between the tire radially inner end W2 of the chamfered portion and the straight line M satisfy the relationships of 0.05≦C / N≦0.97 and 0.05≦D / U≦0.98, and further the distance Q between the point P1 and the point P2 and the width W of the recessed rib satisfy the relationship of 0.7≦Q / W≦0.97. Invention [7] A tire according to any one of inventions [1] to [6], characterized in that all of the land portions except for a pair of shoulder land portions located at the outermost sides in the tire width direction among the plurality of land portions are the concave ribs. [Explanation of symbols]

[0053] 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 concave rib 32a Recess 32b Chamfered part 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, excluding a pair of shoulder land portions located outermost in the tire width direction, among the plurality of land portions is a recessed rib extending continuously along the tire circumferential direction, the concave rib includes a recess in which a contour line of the tread surface in a tire meridian cross section is recessed toward the tire radially inward, In a meridian cross section of a tire mounted on a regular rim and with regular internal pressure applied and no load applied, when an end point on one side of the recess in the tire width direction is defined as point P1, an end point on the other side of the recess in the tire width direction is defined as point P2, and the deepest part of the recess is defined as point P3, a straight line A connecting point P1 and point P2 and a straight line B perpendicular to line A and passing through point P3 are drawn, A tire characterized in that a distance L between the intersection of the straight line A and the straight line B and the point P3 satisfies the relationship of 0 < (L / W) × 100 ≦ 6 and 0 < ((L / W) × 100) / Hs ≦ 0.06 with respect to a width W of the recessed rib and a hardness Hs of a tread rubber constituting the tread portion, and the hardness Hs of the tread rubber is 55 or more and 78 or less.

2. 2. The tire according to claim 1, wherein when point P4 is defined as the intersection point between a line that passes through the midpoint between point P3 and the intersection point of line A and line B and is parallel to line A, and the contour line of the recess is intersected by point P4, an angle X formed by a line connecting point P4 and point P1 with line A and point P1, and a groove wall angle Y of a circumferential main groove adjacent to the recessed rib satisfy the relationship 0.02≦X / Y<1.

3. The tire according to claim 1 or 2, wherein the point P3 is located within a range of 15% of the width W of the recessed rib on both sides of the center of the recessed rib in the tire width direction.

4. 3. The tire according to claim 1, wherein a contour line of the recessed portion is curved so as to be convex radially inward relative to both a straight line connecting the point P1 and the point P3 and a straight line connecting the point P2 and the point P3.

5. 3. The tire according to claim 1, wherein when a line T is drawn that is parallel to a line M connecting the deepest points of a pair of circumferential main grooves adjacent to the recessed rib and passes through the point P3, a distance T1 between the point P1 and the line T and a distance T2 between the point P2 and the line T satisfy the relationship 0.7≦T1 / T2≦1.

5.

6. Chamfered portions are provided on both edges of the concave rib in the tire width direction, When a line connecting an inner end W1 of the chamfered portion on the side of point P1 in the tire radial direction and an inner end W2 of the chamfered portion on the side of point P2 in the tire radial direction is defined as a line W', and a line connecting the deepest points of a pair of circumferential main grooves adjacent to the concave rib is defined as a line M, 3. The tire according to claim 1, wherein a distance C between the point P1 and the straight line W', a distance D between the point P2 and the straight line W', a distance N between an inner end W1 of the chamfered portion in the tire radial direction and the straight line M, and a distance U between an inner end W2 of the chamfered portion in the tire radial direction and the straight line M satisfy the relationships of 0.05≦C / N≦0.98 and 0.05≦D / U≦0.98, and further wherein a distance Q between the point P1 and the point P2 and a width W of the recessed rib satisfy the relationship of 0.7≦Q / W≦0.

97.

7. The tire according to claim 1 or 2, wherein all of the plurality of land portions except for a pair of shoulder land portions located outermost in the tire width direction are the concave ribs.

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