tire

Abstract

To provide a tire that is able to improve wet performance without increasing steering force.SOLUTION: At least one row of land portions 30 excluding a shoulder land portion 31 is formed as a bulging rib 32 continuously extending along a tire circumferential direction and including two rows of bulging portions 32a in which a contour line of a tread surface in a tire meridian cross-section bulges outward in a tire radial direction. When a distance between end points W1, W2 of the bulging portions 32a in a tire lateral direction are set as a bulging-rib width W 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, a point PC on a contour line of the bulging rib 32 having the minimum distance from a straight line Q connecting the deepest points of a pair of circumferential main grooves adjacent to the bulging rib 32 are disposed in a range within 15% of the bulging-rib width W on both sides in the tire lateral direction from the center of the bulging rib 32 in the tire lateral direction, in a region A between positions of 5% of the bulging-rib widths W from each of the point W1 and the point W2 toward the center side of the bulging rib 32 in the tire lateral direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire having rib-shaped land portions extending continuously along the tire circumferential direction, and more particularly to a tire that enables improved wet performance without increasing steering force. [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] An object of the present invention is to provide a tire that enables improved wet performance without increasing steering force. [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 the land portions, excluding a pair of shoulder land portions located on the outermost sides in the tire width direction, is a convex rib extending continuously along the tire circumferential direction, the convex rib includes two rows of bulging portions in the tire width direction, in which the outline of the tread surface in the tire meridian cross section is bulged outward in the tire radial direction, and in a tire meridian cross section when mounted on a regular rim and pressurized to a regular internal pressure and in an unloaded state, When an end point on one side in the tire width direction of the bulging portion on one side in the tire width direction is defined as point W1, and an end point on the other side in the tire width direction of the bulging portion on the other side in the tire width direction is defined as point W2, and the distance between point W1 and point W2 is defined as a convex rib width W, in an area A between a position 5% of the convex rib width W from point W1 toward the center of the convex rib in the tire width direction and a position 5% of the convex rib width W from point W2 toward the center of the convex rib in the tire width direction, point PC on the contour line of the convex rib where the distance to a straight line Q connecting the deepest points of a pair of circumferential main grooves adjacent to the convex rib is smallest is located within a range of 15% of the convex rib width W on both sides of the center of the convex rib in the tire width direction. [Effects of the Invention]

[0006] As described above, in the tire of the present invention, at least one row of land portions, excluding a pair of shoulder land portions, is a convex rib having the above-described characteristics. Therefore, the ground pressure is increased in each of the two rows of bulging portions, improving the road contact characteristics when driving on wet roads and improving wet performance. Furthermore, the presence of two rows of bulging portions makes it easier to cut through water films while driving, which is also expected to improve wet performance. Meanwhile, the vicinity of the widthwise center (near point PC) of the convex rib sandwiched between the two rows of bulging portions is relatively recessed compared to the surrounding area, shortening the contact length of the convex rib vicinity (near point PC), thereby enabling steering force to be kept low when steering while stationary. These effects cooperate to improve wet performance while reducing steering force, achieving a good balance between these performance characteristics.

[0007] In the present invention, the arc connecting points W1, W2, and PC is defined as reference profile B, point P1 is defined as the point on the contour line of the convex rib that is the largest in the vertical distance from reference profile B in the region between points W1 and PC, and point P2 is defined as the point on the contour line of the convex rib that is the largest in the vertical distance from reference profile B in the region between points W2 and PC. It is preferable that the vertical distance L1 between point P1 and reference profile B, the vertical distance L2 between point P2 and reference profile B, and the convex rib width W satisfy the relationships 0<(L1 / W)×100≦6 and 0<(L2 / W)×100≦6. By setting the amount of bulge relative to the convex rib width W within an appropriate range in this way, the shape of the two rows of bulges can be maintained favorably, and the effect of easily shearing a water film and improving wet performance can be enhanced.

[0008] In the present invention, it is preferable that the vertical distance L1 and the vertical distance L2 satisfy the relationship 0.8≦L1 / L2≦1.2. By setting the bulging amounts of the two rows of bulging portions to approximately the same level in this way, the ground contact pressure becomes uniform, which is advantageous for reducing the steering force when steering while stationary.

[0009] In the present invention, it is preferable that the convex rib width W, vertical distance L1, vertical distance L2, and hardness Hs of the tread rubber constituting the tread portion satisfy the relationships 0<((L1 / W)×100) / Hs≦0.06 and 0<((L2 / W)×100) / Hs≦0.06, and that the hardness Hs of the tread rubber is 55 or more and 78 or less. By taking the hardness Hs of the tread rubber into consideration in addition to the convex rib width W and the bulge amount (vertical distances L1, L2), the bulge shape of the bulge portion during driving is well maintained, which is advantageous for improving wet performance.

[0010] In the present invention, it is preferable that the convex rib width W satisfies the relationship 10≦(W / TW)×100≦50 with respect to the contact width TW when the tire is mounted on a standard rim, normal internal pressure is applied, and a normal load is applied. When providing two rows of bulges as described above, ensuring a sufficient width of the convex rib makes it possible to ensure the rigidity of the convex rib, and the bulges make it easier to cut through the water film, thereby enhancing the effect of improving wet performance.

[0011] In the present invention, it is preferable that the contour lines of the two rows of bulges are curved so that they always convex outward in the tire radial direction without including any portion that convex inward in the tire radial direction. By smoothly curving each bulge in this way, the flow of drainage that passes through the bulge is improved, which is advantageous for improving wet performance.

[0012] In the present invention, lateral grooves or sipes are formed in one or both of the bulges, one or both ends of which terminate within the convex rib, and the arc connecting points W1, W2, and PC is defined as reference profile B. Point P1 is the point on the contour line of the convex rib that is the shortest in the region between points W1 and PC, and point P2 is the point on the contour line of the convex rib that is the shortest in the region between points W2 and PC, where at least one end of the lateral groove or sipe is preferably positioned within 15% of the convex rib width W on both sides of the position of point PC in the tire width direction, and at least a portion of the lateral groove or sipe is preferably positioned on an extension line that passes through point P1 or point P2 and extends in the tire circumferential direction. When providing lateral grooves or sipes in this manner, appropriately setting the end positions and shapes of the lateral grooves or sipes makes it possible to ensure sufficient drainage by the lateral grooves or sipes, which is advantageous for improving wet performance.

[0013] In the present invention, circumferential narrow grooves extending along the tire circumferential direction are formed in one or both of the bulges, and the arc connecting points W1, W2, and PC is defined as reference profile B. Point P1 is the point on the contour line of the convex rib that is the largest in the region between points W1 and PC and the vertical distance from reference profile B is the greatest, and point P2 is the point on the contour line of the convex rib that is the largest in the region between points W2 and PC and the vertical distance from reference profile B is the greatest. Preferably, the circumferential narrow grooves include a portion located within 15% of the convex rib width W on both sides of point PC in the tire width direction, and a portion located on an extension line extending in the tire circumferential direction through point P1 or point P2. This improves the arrangement and shape of the circumferential narrow grooves, enabling the circumferential narrow grooves to drain water in the relatively recessed portions (near PC) sandwiched between the bulges to the main groove side rather than the bulges (points P1 and P2), which is advantageous for improving wet performance.

[0014] 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]

[0015] [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. 4 is an explanatory diagram schematically showing a convex rib of a tire according to another embodiment of the present invention. [Figure 4] FIG. 4 is an explanatory diagram schematically showing a convex rib of a tire according to another embodiment of the present invention. [Figure 5] FIG. 10 is an explanatory diagram showing an example of a convex rib having a fine groove formed therein. [Figure 6] 10 is an explanatory diagram showing an example of a convex rib having a circumferential narrow groove formed therein; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 on the outer side in the tire width direction of a pair of circumferential main grooves 20 located on the outermost sides 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 convex rib 32, which will be described later.

[0022] As shown in Figures 2 to 4, the convex rib 32 is a land portion including two rows of bulging portions 32a in the tire width direction, where the outline of the tread in a tire meridian cross section bulges outward in the tire radial direction. The convex rib 32 in this invention refers only to a land portion including two rows of bulging portions 32a. A land portion in which the entire tread surface bulges (i.e., a land portion having only one row of bulging portions) does not qualify as a "convex rib" in this invention. Furthermore, although not depicted in Figures 2 to 4 because they are tire meridian cross sections, the convex 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. The provision of such a convex rib 32 increases the ground contact pressure in each of the two rows of bulging portions 32a, improving the road contact characteristics when driving on wet roads and thereby improving wet performance. Furthermore, the two rows of bulging portions 32a facilitate shedding of water film during driving, which is also expected to improve wet performance. On the other hand, since the vicinity of the widthwise center of the convex rib 32 sandwiched between the two rows of bulging portions 32a is relatively recessed from the surrounding area, the contact length of the convex rib 32 near the widthwise center can be shortened, making it possible to keep the steering force low when turning while stationary.

[0023] As described above, the convex 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 provided with the convex ribs 32. This is expected to have the effect of shortening the contact length near the widthwise center of the convex ribs 32 in all land portions 30 excluding the shoulder land portions 31 (convex ribs 32), thereby appropriately shortening the contact length of the entire contact patch, which is advantageous for reducing steering force. Furthermore, since all of the land portions 30 excluding the shoulder land portions 31 are provided with the convex ribs 32, the above-mentioned drainage properties of the convex ribs 32 are ensured, making it possible to improve wet performance.

[0024] The shape of the protruding 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 specified for each tire by a standard, including the standard on which the tire is based. For example, this refers to a standard rim for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO. Furthermore, a "regular internal pressure" refers to the air pressure specified for each tire by a standard, including the standard on which the tire is based. For JATMA, this refers to the maximum air pressure, for TRA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table, and for ETRTO, this refers to the "inflation pressure." Furthermore, a "regular load" refers to the load specified for each tire by a standard, including the standard on which the tire is based. For JATMA, this refers to the maximum load capacity, for TRA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table, and for ETRTO, this refers to the "load capacity."

[0025] As shown enlarged in FIG. 2, the protruding rib 32 has two rows of bulging portions 32a. In such a convex rib 32, when the end point on one side in the tire width direction of the bulging portion 32a on one side in the tire width direction (left side in the figure) is defined as point W1, the end point on the other side in the tire width direction of the bulging portion 32a on the other side in the tire width direction (right side in the figure) is defined as point W2, and the distance between points W1 and W2 is defined as the convex rib width W, in region A between a position 5% of the convex rib width W from point W1 toward the center of the convex rib 32 in the tire width direction and a position 5% of the convex rib width W from point W2 toward the center of the convex rib 32 in the tire width direction, point PC is defined as the point on the contour line of the convex rib 32 where the distance to a straight line Q connecting the deepest points Q1, Q2 of a pair of circumferential main grooves 20 adjacent to the convex rib 32 is the shortest, this point PC is positioned within a range of 15% of the convex rib width W on both sides of the tire width direction from the center of the convex rib 32 in the tire width direction, preferably within 10%, and more preferably within 5%.

[0026] Point PC corresponds to the deepest point of the relatively recessed portion sandwiched between the two rows of bulging portions 32a, and because its position is located approximately in the center of the convex rib 32 in the tire width direction as described above, it is advantageous for reducing the contact length near the widthwise center of the convex rib 32 to reduce the steering force when the tire is turned stationary. If point PC is outside the above range, the contact length at the widthwise center of the convex rib 32 cannot be sufficiently shortened, and the effect of reducing steering force when the tire is turned stationary cannot be expected to be sufficient.

[0027] 2, the location where the two rows of bulging portions 32a are connected has a generally V-shaped cross section, and point PC is located at the apex of this V-shape, but if the two rows of bulging portions 32a are spaced apart as shown in FIG. 3, a plane extending parallel to line Q is included between the two rows of bulging portions 32a, and the distance from line Q to this plane is uniform throughout, point PC is taken to be the center point of that plane in the tire width direction. The two rows of bulging portions 32a may be connected by a smooth arc as shown in the example of FIG. 4, but in this case too, point PC is identified as above, and point PC is located within 15%, preferably within 10%, and more preferably within 5% of the convex rib width W on both sides of the tire width direction center of the convex rib 32.

[0028] 2 to 4, the arc connecting points W1, W2, and PC is defined as reference profile B, and point P1 is the point on the contour line of convex rib 32 at which the vertical distance from reference profile B in the region between points W1 and PC is the largest. Point P2 is the point on the contour line of convex rib 32 at which the vertical distance from reference profile B in the region between points W2 and PC is the largest. The vertical distance L1 between point P1 and reference profile B, the vertical distance L2 between point P2 and reference profile B, and the convex rib width W preferably satisfy the relationships 0<(L1 / W)×100≦6 and 0<(L2 / W)×100≦6, and more preferably 0.1≦(L1 / W)×100≦4 and 0.1≦(L2 / W)×100≦4. By setting the bulge amount (vertical distances L1, L2) relative to the protruding rib width W within an appropriate range in this way, the shape of the two rows of bulging portions 32a can be maintained well, making it easier to shear off water films and improving wet performance. If the ratio L1 / W or L2 / W exceeds the above range, the bulging portions 32a will bulge too much, making it difficult for water that accumulates between the bulging portions 32a to drain, which could result in a decrease in wet performance. If the ratio L1 / W or L2 / W is below the above range, the bulging portions 32a will not bulge, making the rib tread surface essentially flat, and therefore the effect of improving wet performance cannot be expected.

[0029] Furthermore, the vertical distance L1 and the vertical distance L2 preferably satisfy the relationship 0.8≦L1 / L2≦1.2, and more preferably 0.9≦L1 / L2≦1.1. By satisfying this relationship, the two rows of bulging portions 32a will have approximately the same amount of expansion, resulting in uniform ground contact pressure and reduced steering effort when steering while stationary. If the ratio L1 / L2 is outside the above range, one of L1 and L2 will be excessive, resulting in a significant difference in the amount of expansion between the two rows of bulging portions 32a. This will result in a local increase in ground contact pressure at the bulging portion 32a with the larger amount of expansion, potentially increasing steering effort. The individual values ​​of L1 and L2 are not particularly limited, but can be set to, for example, 0.05 mm to 0.4 mm.

[0030] Furthermore, the above-mentioned vertical distance L1 and the vertical distance L2, the convex rib width W, and the hardness Hs of the tread rubber constituting the tread portion 1 (particularly the cap tread layer 11C) preferably satisfy the relationships 0<((L1 / W)×100) / Hs≦0.06 and 0<((L2 / W)×100) / Hs≦0.06, more preferably 0<((L1 / W)×100) / Hs≦0.04 and 0<((L2 / W)×100) / Hs≦0.04, and further the hardness Hs of the tread rubber preferably satisfies the range of 55 to 78, more preferably 58 to 75, and even more preferably 58 to 72. In this way, by taking the hardness Hs of the tread rubber into consideration in addition to the convex rib width W and the bulge amount (vertical distances L1, L2), the bulge shape of the bulge portion during running is maintained well, which is advantageous for improving wet performance. If the hardness Hs is large relative to the ratios L1 / W and L2 / W, the convex ribs 32 (bulges 32a) do not deform sufficiently when in contact with the road, and only the apexes of the bulges 32a (near points P1 and P2) come into contact with the road surface, reducing the actual contact area and potentially resulting in poor wet performance. If the hardness Hs is small relative to the ratios L1 / W and L2 / W, the convex ribs 32 become flexible and are unable to adequately maintain the shape of the bulges 32a, making it difficult to cut off the water film while driving, potentially resulting in poor wet performance. 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.

[0031] When a tire is mounted on a standard rim, pressurized to the standard internal pressure, and placed perpendicularly to a flat plate in a stationary state, the axial length of the contact area between the surface of the tread portion 1 and the flat plate when a standard load is applied is defined as the contact width TW. The convex rib width W preferably satisfies the relationship 10≦(W / TW)×100≦50, more preferably 12≦(W / TW)×100≦45, relative to the contact width TW. When providing the two rows of bulging portions 32a of the present invention, ensuring a sufficient convex rib width W relative to the contact width TW ensures the rigidity of the convex rib 32, thereby enhancing the effect of the bulging portions shedding water film and improving wet performance. A small W / TW ratio results in a narrow convex rib 32, which in turn results in insufficient rib rigidity and potentially reduces handling stability when traveling on wet roads. A large W / TW ratio results in an insufficient groove area, which impairs drainage and potentially reduces wet performance.

[0032] From the viewpoint of drainage, the contour line of each bulge portion 32a is preferably a smooth curve without any irregularities, except for the lateral grooves, sipes, and circumferential narrow grooves described below. That is, the contour line of each bulge portion 32a is preferably curved so as to always convex outward in the tire radial direction, without including any portion that convex inward in the tire radial direction. More specifically, the curve passing through points W1, P1, and PC along the contour line of the convex rib 32 and the curve passing through points W2, P2, and PC along the contour line of the convex rib 32 are preferably curved so as to always convex outward in the tire radial direction. This smooth curvature of each bulge portion 32a improves the flow of drainage water along the bulge portion 32a, which is advantageous for improving wet performance.

[0033] As shown in FIG. 5, the convex rib 32 may be provided with lateral grooves 33 or sipes extending along the tire width direction, as long as the rib is not divided. The lateral grooves 33 are grooves with a width of 1.6 mm or more and 50% or less of the width of the circumferential main grooves 20, and the sipes are fine grooves with a width of 0.4 mm to 1.5 mm. Specifically, lateral grooves 33 or sipes with one or both ends terminating within the convex rib 32 may be formed in one or both of the bulging portions 32a. In this case, it is preferable that at least one end of the lateral grooves 33 or sipes is located within a range of 15% of the convex rib width W on both sides of the position of point PC in the tire width direction. At the same time, it is preferable that at least a portion of the lateral grooves 33 or sipes is located on an extension passing through point P1 or point P2 and extending in the tire circumferential direction. When providing lateral grooves 33 or sipes in this manner, by appropriately setting the end position and shape, it is possible to ensure sufficient drainage by the lateral grooves 33 or sipes, which is advantageous for improving wet performance.

[0034] In the example of FIG. 5(a), lateral grooves 33, one end of which opens into the circumferential main groove 20 and the other end of which terminates at point PC, are provided in each of two rows of bulging portions 32a at intervals in the tire circumferential direction. The lateral grooves 33 in each bulging portion 32a are not connected, so when viewed as a whole, the lateral grooves 33 in one bulging portion 32a and the lateral grooves 33 in the other bulging portion 32a are arranged in a staggered pattern along the tire circumferential direction. In this case, the ends of all lateral grooves 33 on the point PC side terminate within the land portion, so the convex rib 32 is not divided. Furthermore, the ends of the lateral grooves 33 on the point PC side are located within a range of 15% of the convex rib width W on both sides of the point PC in the tire width direction, and a portion of the lateral groove 33 is located on an extension line extending in the tire circumferential direction through point P1 or point P2, so the above-mentioned conditions are satisfied. In the example of Figure 5(b), the lateral grooves 33 curved in an approximately S-shape are provided only on one side of the bulge portion 32a, but in this case too, one end of each lateral groove 33 opens into the circumferential main groove 20 and the other end terminates at the position of point PC, so that the above-mentioned conditions are satisfied as in the case of Figure 5(a).

[0035] In the example of Figure 5(c), the lateral groove 33 provided in the bulge portion 32a on one side (the left side in the figure) is curved in a substantially semicircular shape, with both ends positioned within 15% of the convex rib width W on both sides of the position of point PC in the tire width direction (the position of PC in the illustrated example), but part of the curve is positioned on an extension line passing through point P1 and extending in the tire circumferential direction, so the above-mentioned condition is satisfied. The lateral groove 33 provided in the bulge portion 32a on the other side (the right side in the figure) in the example of Figure 5(c) extends at an angle to the tire width direction, with one end (the end on the side of point PC) positioned within 15% of the convex rib width W on both sides of the position of point PC in the tire width direction (the position of PC in the illustrated example), and the other end is positioned outward in the tire width direction from the extension line passing through point P2 and extending in the tire circumferential direction, and this lateral groove 33 intersects with the extension line passing through point P2 and extending in the tire circumferential direction, so the above-mentioned condition is satisfied.

[0036] In the example of FIG. 5(d), each of the two rows of bulging portions 32a has a lateral groove 33 such that one end (the end on the side of point PC) is located within 15% of the protruding rib width W on both sides of point PC in the tire width direction (the position of PC in the illustrated example), and the other end is located outward in the tire width direction from an extension line passing through point P2 and extending in the tire circumferential direction, and intersects with the extension line passing through point P2 and extending in the tire circumferential direction. In other words, in this case as well, each lateral groove 33 satisfies the above-mentioned conditions. Note that in the example of FIG. 5(d), the end on the side of point PC of the lateral groove 33 provided in one bulging portion 32a and the end on the side of point PC of the lateral groove 33 provided in the other bulging portion 32a are located at the same point, and the series of grooves formed by these lateral grooves 33 are curved so as to be point-symmetrical with respect to the end on the side of point PC (the point where the two are connected).

[0037] As shown in FIG. 6, the protruding rib 32 may be provided with circumferential narrow grooves 34 extending along the tire circumferential direction. The circumferential narrow grooves 34 have a width of 0.4 mm or more and 50% or less of the width of the circumferential main grooves 20. Specifically, the circumferential narrow grooves 34 extending along the tire circumferential direction may be formed in one or both of the bulging portions 32a. In this case, the circumferential narrow grooves 34 preferably include a portion located within 15% of the protruding rib width W on both sides of the tire width direction from the position of point PC, and a portion located on an extension line extending in the tire circumferential direction through point P1 or point P2. This improves the arrangement and shape of the circumferential narrow grooves 34, allowing the circumferential narrow grooves 34 to drain water from the relatively recessed portion (near point PC) sandwiched between the bulging portions 32a toward the main groove 20 rather than the bulging portions 32a (points P1 and P2), which is advantageous for improving wet performance.

[0038] In the example of FIG. 6(a), one of the bulging portions 32a is provided with a circumferential narrow groove 34 that extends linearly in the tire circumferential direction. This circumferential narrow groove 34 is located on an extension that passes through point P2 and extends in the tire circumferential direction, and point P2 is located within 15% of the convex rib width W on both sides of point PC in the tire width direction, thereby satisfying the above-mentioned condition. In the example of FIG. 6(b), one of the bulging portions 32a is provided with a circumferential narrow groove 34 that extends in a wavy curve in the tire circumferential direction. This circumferential narrow groove 34 includes a portion that is located within 15% of the convex rib width W on both sides of point PC in the tire width direction due to its wavy curve, and a portion that is located on an extension that passes through point P1 or point P2 and extends in the tire circumferential direction, thereby satisfying the above-mentioned condition. In the example of FIG. 6(c), one of the bulging portions 32a is provided with a circumferential narrow groove 34 that extends in a zigzag curve in the tire circumferential direction. This circumferential narrow groove 34 is bent in a zigzag shape and includes a portion located within 15% of the protruding rib width W on both sides of the position of point PC in the tire width direction, and a portion located on an extension line extending in the tire circumferential direction through point P1 or point P2, so that the above-mentioned condition is satisfied. Note that in the example of Figures 6(a) to 6(c), the circumferential narrow groove 34 is provided in one bulging portion 32a, while the narrow groove 33 is provided in the other bulging portion 32a, and in this way, the circumferential narrow groove 34 and the narrow groove 33 or sipes can be used together.

[0039] 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]

[0040] Pneumatic tires (test tires) of Conventional Example 1, Comparative Example 1, and Examples 1 to 13 were manufactured, each having a tire size of 235 / 60R18 and the basic structure (cross-sectional structure) illustrated in FIG. 1, with the number of bulging portions, the position of point PC, (L1 / W)×100, (L2 / W)×100, L1 / L2, hardness Hs, ((L1 / W)×100) / Hs, ((L2 / W)×100) / Hs, and W / TW set as shown in Tables 1 and 2, respectively.

[0041] The "Number of bulges" column in Table 1 shows the number of bulges contained in one convex rib. In all test tires, all land portions except for the shoulder land portions are configured as convex ribs. The "Position of point PC" column in Table 1 shows the distance in the tire width direction from the tire width center of the convex rib to point PC (percentage relative to the convex rib width W [unit: %]). A value of "0%" in this column means that point PC is located at the tire width center of the convex rib. In addition, when viewed in meridian section of the tire in an unloaded state with the tire mounted on a regular rim and pressurized to the regular internal pressure, point PC is the point on the contour line of the convex rib where the distance to a straight line Q connecting the deepest points of a pair of circumferential main grooves adjacent to the convex rib is smallest in area A between a position 5% of the convex rib width W from point W1 toward the center of the convex rib in the tire width direction and a position 5% of the convex rib width W from point W2 toward the center of the convex rib in the tire width direction, when point W1 is the end point of the bulge on one side in the tire width direction of the tire, and point W2 is the end point of the bulge on the other side in the tire width direction of the tire, and the distance between point W1 and point W2 is the convex rib width W.Therefore, in Conventional Example 1 in which only one bulge is provided, point PC is located outside area A in the tire width direction (i.e., near the edge of the convex rib).

[0042] The columns "(L1 / W) × 100," "(L2 / W) × 100," "L1 / L2," "((L1 / W) × 100) / Hs," and "((L2 / W) × 100) / Hs" in Table 1 show values ​​calculated from the vertical distance L1 between point P1 and reference profile B, the vertical distance L2 between point P2 and reference profile B, the convex rib width W, and the hardness Hs of the tread rubber that constitutes the tread portion, where the arc connecting points W1, W2, and PC is defined as reference profile B, point P1 is the point on the contour line of the convex rib that has the greatest vertical distance from reference profile B in the region between points W1 and PC, and point P2 is the point on the contour line of the convex rib that has the greatest vertical distance from reference profile B in the region between points W2 and PC. For Conventional Example 1, which includes only one bulge, the numerical values ​​for that bulge are shown as reference values ​​in the "(L1 / W) x 100" and "((L1 / W) x 100) / Hs" columns. The "W / TW" column in Table 1 shows values ​​calculated from the aforementioned convex rib width W and the contact width TW when mounted on a standard rim, with standard internal pressure and load.

[0043] The test tires were evaluated for steering force and wet performance using the following evaluation methods, and the results are shown in Table 1.

[0044] 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 were expressed as an index using the reciprocal of the measured value, with Conventional Example 1's value being set at 100. The higher the index value, the lower the steering force.

[0045] Wet performance Each test tire was mounted on a standard rim (rim size 18 x 7J), inflated to an internal pressure of 230 KPa, and loaded with a load of 6 kN. The tire was then mounted on a test vehicle (a passenger car with an engine displacement of 2000 cc), and a sensory evaluation of the tire's running performance on wet roads was carried out by a test driver on a test course consisting of wet roads. The evaluation results were expressed as an index, with Conventional Example 1 being given a value of 100. The higher the index value, the better the wet performance.

[0046] [Table 1]

[0047] [Table 2]

[0048] As is clear from Table 1, the tires of Examples 1 to 13 improved wet performance while reducing steering force compared to Conventional Example 1. On the other hand, in Comparative Example 1, the position of point PC was positioned far away from the center of the width direction of the convex rib, so although the steering force was suppressed more than in the conventional convex rib with only one bulge portion, a sufficient improvement effect was not obtained.

[0049] The present disclosure encompasses 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 convex rib extending continuously along the tire circumferential direction, The convex rib includes two rows of bulging portions in the tire width direction, in which the outline of the tread surface in the tire meridian cross section bulges outward in the tire radial direction, When viewed from a meridian cross section of a tire mounted on a regular rim and pressurized to a regular internal pressure with no load, the end point of one side in the tire width direction of the bulging portion on one side in the tire width direction is defined as point W1, the end point of the other side in the tire width direction of the bulging portion on the other side in the tire width direction is defined as point W2, and the distance between point W1 and point W2 is defined as a protruding rib width W, a point PC on the contour line of the convex rib that has the shortest distance from a straight line Q connecting the deepest points of a pair of circumferential main grooves adjacent to the convex rib, in a region A between a position 5% of the convex rib width W from the point W1 toward the center of the convex rib in the tire width direction, and a position 5% of the convex rib width W from the point W2 toward the center of the convex rib in the tire width direction, is located within a range of 15% of the convex rib width W on both sides of the tire width direction from the center of the convex rib in the tire width direction. Invention [2] The arc connecting the point W1, the point W2, and the point PC is defined as a reference profile B, When the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W1 and the point PC is defined as point P1, and the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W2 and the point PC is defined as point P2, The tire according to invention [1], wherein the vertical distance L1 between the point P1 and the reference profile B, the vertical distance L2 between the point P2 and the reference profile B, and the convex rib width W satisfy the relationships 0<(L1 / W)×100≦6 and 0<(L2 / W)×100≦6. Invention [3] The tire according to invention [2], wherein the vertical distance L1 and the vertical distance L2 satisfy the relationship 0.8≦L1 / L2≦1.2. Invention [4] A tire according to invention [2] or [3], characterized in that the convex rib width W, the vertical distance L1, the vertical distance L2, and the hardness Hs of the tread rubber constituting the tread portion satisfy the relationships 0<((L1 / W)×100) / Hs≦0.06 and 0<((L2 / W)×100) / Hs≦0.06, and the hardness Hs of the tread rubber is 55 or more and 78 or less. Invention [5] A tire according to any one of inventions [1] to [4], characterized in that when mounted on a standard rim, with standard internal pressure and standard load, the convex rib width W satisfies the relationship 10≦(W / TW)×100≦50 with respect to the contact width TW. Invention [6] A tire according to any one of inventions [1] to [5], characterized in that the contour lines of the two rows of bulging portions are always curved so as to be convex toward the outside in the tire radial direction without including any portion that is convex toward the inside in the tire radial direction. Invention [7] A lateral groove or sipe is formed in one or both of the bulging portions, one end or both ends of which terminate within the convex rib, The arc connecting the point W1, the point W2, and the point PC is defined as a reference profile B, When the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W1 and the point PC is defined as point P1, and the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W2 and the point PC is defined as point P2, A tire according to any one of inventions [1] to [6], characterized in that at least one end of the lateral groove or the sipe is arranged within a range of 15% of the convex rib width W on both sides of the position of point PC in the tire width direction, and at least a part of the lateral groove or the sipe is located on an extension line passing through point P1 or point P2 and extending in the tire circumferential direction. Invention [8] A circumferential narrow groove extending along the tire circumferential direction is formed in one or both of the bulging portions, The arc connecting the point W1, the point W2, and the point PC is defined as a reference profile B, When the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W1 and the point PC is defined as point P1, and the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W2 and the point PC is defined as point P2, The tire according to any one of inventions [1] to [7], characterized in that the circumferential narrow groove includes a portion disposed within a range of 15% of the convex rib width W on both sides of the position of point PC in the tire width direction, and a portion located on an extension line passing through point P1 or point P2 and extending in the tire circumferential direction. [Explanation of symbols]

[0050] 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 32a Bulge 33 Yokomizo 34 Circumferential thin groove 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 at the outermost sides in the tire width direction, among the plurality of land portions is a convex rib extending continuously along the tire circumferential direction, The convex rib includes two rows of bulging portions in the tire width direction, in which the outline of the tread surface in the tire meridian cross section bulges outward in the tire radial direction, When viewed from a meridian cross section of a tire mounted on a regular rim and pressurized to a regular internal pressure in an unloaded state, the end point of one side in the tire width direction of the bulging portion on one side in the tire width direction is defined as point W1, the end point of the other side in the tire width direction of the bulging portion on the other side in the tire width direction is defined as point W2, and the distance between point W1 and point W2 is defined as a protruding rib width W, a point PC on the contour line of the convex rib that has the shortest distance from a straight line Q connecting the deepest points of a pair of circumferential main grooves adjacent to the convex rib, in a region A between a position 5% of the convex rib width W from the point W1 toward the center of the convex rib in the tire width direction, and a position 5% of the convex rib width W from the point W2 toward the center of the convex rib in the tire width direction, is located within a range of 15% of the convex rib width W on both sides of the center of the convex rib in the tire width direction.

2. The arc connecting the point W1, the point W2, and the point PC is defined as a reference profile B, When the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W1 and the point PC is defined as point P1, and the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W2 and the point PC is defined as point P2, 2. The tire according to claim 1, wherein a vertical distance L1 between the point P1 and the reference profile B, a vertical distance L2 between the point P2 and the reference profile B, and the convex rib width W satisfy the relationships 0<(L1 / W)×100≦6 and 0<(L2 / W)×100≦6.

3. 3. The tire according to claim 2, wherein the vertical distance L1 and the vertical distance L2 satisfy the relationship 0.8≦L1 / L2≦1.

2.

4. 4. The tire according to claim 2, wherein the convex rib width W, the vertical distance L1, the vertical distance L2, and a hardness Hs of a tread rubber constituting the tread portion satisfy the relationships 0<((L1 / W)×100) / Hs≦0.06 and 0<((L2 / W)×100) / Hs≦0.06, and the hardness Hs of the tread rubber is 55 or greater and 78 or less.

5. 3. The tire according to claim 1, wherein the width W of the convex rib satisfies the relationship 10≦(W / TW)×100≦50 with respect to the contact width TW when the tire is mounted on a standard rim, is pressurized to a standard internal pressure, and is subjected to a standard load.

6. 3. The tire according to claim 1, wherein the contour lines of the two rows of bulging portions are curved so as to always convex outward in the tire radial direction without including any portion that convex inward in the tire radial direction.

7. A lateral groove or sipe is formed in one or both of the bulging portions, one end or both ends of which terminate within the convex rib, The arc connecting the point W1, the point W2, and the point PC is defined as a reference profile B, When the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W1 and the point PC is defined as point P1, and the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W2 and the point PC is defined as point P2, 3. The tire according to claim 1, wherein at least one end of the lateral groove or the sipe is disposed within a range of 15% of the convex rib width W on both sides of the position of the point PC in the tire width direction, and at least a portion of the lateral groove or the sipe is located on an extension line passing through the point P1 or the point P2 and extending in the tire circumferential direction.

8. A circumferential narrow groove extending along the tire circumferential direction is formed in one or both of the bulging portions, The arc connecting the point W1, the point W2, and the point PC is defined as a reference profile B, When the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W1 and the point PC is defined as point P1, and the point on the contour line of the convex rib that is the largest in the vertical distance from the reference profile B in the region between the point W2 and the point PC is defined as point P2, 3. The tire according to claim 1, wherein the circumferential narrow groove includes a portion disposed within a range of 15% of the protruding rib width W on both sides of the position of the point PC in the tire width direction, and a portion located on an extension line passing through the point P1 or the point P2 and extending in the tire circumferential direction.

Images