Tire

Abstract

To provide a tire capable of improving wet performance while suppressing generation of squeal noise.SOLUTION: At least one row of the plurality of rows of land portions 30 formed in the tread portion 1 is a convex rib 32 that continuously extends along the tire circumferential direction, includes a first bulging portion side 32a in which a contour line of a tread surface in a tire meridian cross section bulges outward in the tire radial direction, and includes a second bulging portion side 32a that bulges further outward in the tire radial direction from the contour line side 32a of the first bulging portion at least at one end portion of the first bulging portion side 32b in the tire lateral direction.SELECTED DRAWING: Figure 3

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 specifically to a tire that can improve wet performance while suppressing the generation of squealing noise. [Background technology]

[0002] To improve wet tire performance, a known technology is to shape the contact surface of land portions formed in the tread portion so that they partially bulge radially outward 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 thereby improving wet tire performance. However, the bulged contact surface of the land portions reduces the ground contact pressure at the tire width direction ends (non-bulged portions) of the land portions, resulting in an uneven contact pressure distribution on the tread surface, which is a concern as it can easily cause squealing at low speeds. Therefore, there is a need for a solution that improves wet tire performance while suppressing squealing. [Prior art documents] [Patent documents]

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

[0004] An object of the present invention is to provide a tire that can improve wet performance while suppressing the generation of squealing noise. [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 being a convex rib extending continuously along the tire circumferential direction, the convex rib including a first bulge portion where a contour line of the tread surface in a tire meridian cross section bulges outward in the tire radial direction, and including a second bulge portion at at least one end in the tire width direction that bulges further outward in the tire radial direction from the contour line of the first bulge portion. [Effects of the Invention]

[0006] In order to improve wet performance, the tire of the present invention is provided with a convex rib in which the outline of the tread in a tire meridian cross section bulges outward in the tire radial direction. Because this convex rib has the above-described characteristics, wet performance can be improved while suppressing the generation of squealing. Specifically, the provision of the first bulge portion promotes drainage on the convex rib, thereby improving wet performance, and the provision of the second bulge portion improves the contact pressure at the tire width direction end of the convex rib, thereby making the contact pressure uniform and reducing squealing. These cooperations improve wet performance while suppressing the generation of squealing, achieving a good balance between these performances.

[0007] In the present invention, 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, if a line segment Q is defined as being parallel to a line segment X1 connecting both ends of the tread surface of the convex rib and passing through the deepest point of the circumferential main groove adjacent to the convex rib, it is preferable that point PC on the contour line of the first bulge portion that is the greatest distance from the line segment Q be located within a range of 20% of the length W1 of the line segment X1 on both sides of the midpoint of the line segment X1 in the tire width direction. In this way, by bulging the center of the convex rib (by positioning the part where the first bulge portion bulges most near the center of the convex rib in the tire width direction), drainage over the rib can be promoted, which is advantageous for improving wet performance.

[0008] In the present invention, an arc passing through points PH1 and PH2 on the contour line of the first bulging portion at positions 20% of the length W1 from the point PC to both sides in the tire width direction and the point PC is defined as a reference profile. When a point p on the contour line of the second bulging portion where the normal direction distance from the reference profile is maximized is defined, it is preferable that the point p is arranged within 30% of the length W2 of a line segment X2 connecting the intersection on the point p side of the reference profile and the contour line of the convex rib to the intersections on both sides in the tire width direction of the reference profile and the contour line of the convex rib. Thereby, since the point (point p) where the second bulging portion bulges most is arranged at an appropriate position in the tire width direction (the tire width direction end portion of the convex rib), it is advantageous for equalizing the ground contact pressure and reducing the skid noise.

[0009] In the present invention, when the normal direction distance from the reference profile of the point p is L1 and the distance between the line segment X2 and the point PC is L3, it is preferable that the distances L1 and L3 satisfy the relationship of 0.10 ≦ L1 / L3 ≦ 0.90. Thus, since the bulging amount (distance L3) of the first bulging portion is larger than the bulging amount (distance L1) of the second bulging portion, the central portion of the convex rib bulges most, which is advantageous for promoting drainage on the convex rib and improving wet performance. Also, since the balance between the bulging amount (distance L3) of the first bulging portion and the bulging amount (distance L1) of the second bulging portion becomes good, it is advantageous for equalizing the ground contact pressure and reducing the skid noise.

[0010] In the present invention, it is preferable that the distance L1 and the length W2 satisfy the relationship of 0 < L1 / W2 × 100 ≦ 4. Thereby, since the bulging amount (distance L1) of the second bulging portion is set within an appropriate range, it is advantageous for equalizing the ground contact pressure and reducing the skid noise.

[0011] In the present invention, it is preferable that the distance L3 and the length W2 satisfy the relationship of 0 < L3 / W2 × 100 ≦ 6. Thereby, since the bulging amount (distance L3) of the first bulging portion is set within an appropriate range, it is advantageous for equalizing the ground contact pressure and reducing the skid noise.

[0012] In the present invention, the second bulging portion is provided at both end portions in the tire width direction of the first bulging portion. The point p in the second bulging portion on one side in the tire width direction is defined as point p1, and the point p in the second bulging portion on the other side in the tire width direction is defined as point p2. The point on the contour line of the convex rib where the distance from the point PC to the line segment T1 connecting the point PC and the point p1 is maximized is defined as point T1'. The point on the contour line of the convex rib where the distance from the point PC to the line segment T2 connecting the point PC and the point p2 is maximized is defined as point T2'. When the intersection point of the line passing through the point T1' and perpendicular to the straight line Q and the line segment X2 is defined as point W3, and the intersection point of the line passing through the point T2' and perpendicular to the straight line Q and the line segment X2 is defined as point W4, it is preferable that the distance WA from the intersection point on the p1 side of the reference profile and the contour line of the convex rib to the point W3, the distance WB from the intersection point on the p2 side of the reference profile and the contour line of the convex rib to the point W4, and the distance WC between the point W3 and the point W4 satisfy the relationship of 0.33 < WC / (WA + WB + WC) ≤ 0.9 and 0.7 ≤ WA / WB ≤ 1.5. Thereby, the relationship between the widths of the first bulging portion and the second bulging portion becomes good, which is advantageous for equalizing the ground contact pressure and reducing the skid noise.

[0013] In the present invention, when the second bulging portion is provided at both end portions in the tire width direction of the first bulging portion, the point p in the second bulging portion on one side in the tire width direction is defined as point p1, and the point p in the second bulging portion on the other side in the tire width direction is defined as point p2, it is preferable that the distance H1 between the straight line Q and the point p1 and the distance H2 between the straight line Q and the point p2 satisfy the relationship of 0.7 ≤ H1 / H2 ≤ 1.5. Thereby, when a pair of second bulging portions are provided at both end portions in the tire width direction of the convex rib, the balance of the bulging amounts of these pair of second bulging portions becomes good, which is advantageous for equalizing the ground contact pressure and reducing the skid noise.

[0014] In the present invention, it is preferable that the hardness Hs of the tread rubber constituting the tread portion is 55 or more and 78 or less. By having such an appropriate hardness, the bulging shapes of the first bulging portion and the second bulging portion are well maintained during running, and the above-described effects of the convex rib can be efficiently exhibited.

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

[0016] [Figure 1] 1 is a meridian cross-sectional view of a tire according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram schematically showing a convex rib of a tire according to an embodiment of the present invention. [Figure 3] FIG. 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. 4 is an explanatory diagram schematically showing a convex rib of a tire according to another embodiment of the present invention. [Figure 6] FIG. 4 is an explanatory diagram schematically showing a convex rib of a tire according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

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

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

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

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

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

[0023] As shown in FIGS. 2 to 6 , the convex rib 32 is a land portion in which the outline of the tread in a tire meridian cross section includes a first bulge portion 32a that bulges outward in the tire radial direction, and includes a second bulge portion 32b that bulges further outward in the tire radial direction from the outline of the first bulge portion 32a at at least one end of the first bulge portion 32a in the tire width direction. The convex rib 32 in the present invention refers only to a land portion that includes the first bulge portion 32a and the second bulge portion 32b described above. A land portion in which the entire tread surface bulges (i.e., a land portion having only one row of bulges) does not qualify as a "convex rib" in the present invention. However, since it is sufficient for at least one of the multiple land portions to be a convex rib 32, the tread surfaces of land portions other than the convex rib 32 may have a bulge shape different from the "convex rib" in the present invention (for example, the entire tread surface of the land portion bulges). 2 to 6 are tire meridian cross sections and are therefore not depicted, the convex ribs 32 are land portions that extend continuously in the tire circumferential direction without being interrupted by lateral grooves or sipes extending in the tire width direction. By providing such convex ribs 32, the first bulging portions 32a promote drainage above the convex ribs 32, improving wet performance, and the second bulging portions 32b increase and equalize the ground contact pressure at the tire width direction ends of the convex ribs 32, thereby reducing squealing.

[0024] As described above, the convex rib 32 is provided in at least one row of the multiple land portions 30. Any of the multiple land portions 30 may be provided with the convex rib 32. However, if at least one row of the land portions 30, excluding the shoulder land portions 31, is provided with the convex rib 32, the effects of the convex rib 32, as described below, can be efficiently achieved. In other words, the groove depth of a pair of circumferential main grooves 20 adjacent to the convex rib 32 is preferably 80% or more of the groove depth of the deepest circumferential main groove 20. Land portions with a large groove depth of the adjacent circumferential main groove 20 (i.e., land portions with a large protrusion height from the groove bottom) are significantly affected by ground contact pressure. Therefore, applying the convex rib 32 described above is advantageous for equalizing ground contact pressure and reducing squealing. More preferably, all of the land portions 30, excluding the shoulder land portions 31, are provided with the convex rib 32. This ensures that the effects of the convex rib 32 described above are achieved in all land portions 30 (convex ribs 32) excluding the shoulder land portions 31, thereby effectively improving wet performance and reducing squealing.

[0025] The shape of the protruding rib 32 shown in Figures 2 to 6 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.

[0026] As shown enlarged in FIGS. 2 and 3, the convex rib 32 includes a first bulge portion 32a and a second bulge portion 32b. In particular, FIG. 2 illustrates an embodiment in which one second bulge portion 32b is provided at one end of the first bulge portion 32a, and FIG. 3 illustrates an embodiment in which a second bulge portion 32b is provided at each end of the first bulge portion 32a. Regarding such a convex rib 32, in a meridian cross section of the tire mounted on a standard rim and pressurized to a standard internal pressure in an unloaded state, a line segment parallel to a line segment X1 connecting both ends of the tread surface of the convex rib 32 and passing through the deepest point of the circumferential main groove adjacent to the convex rib 32 is defined as a straight line Q. Furthermore, a point on the contour of the first bulge portion 32a that is the greatest distance from the line segment Q is defined as a point PC. Point PC, defined in this manner, is preferably located within a range of 20%, more preferably 15%, and even more preferably 10% of the length W1 of line segment X1 on both sides of the midpoint of line segment X1 in the tire width direction. By placing point PC in this position, the central portion of the convex rib 32 is bulged (the portion where the first bulging portion 32a bulges most is located near the center of the convex rib 32 in the tire width direction), which promotes drainage over the rib and is advantageous for improving wet performance.

[0027] Note that, when the groove depths of a pair of circumferential main grooves adjacent to the convex rib 32 are different as shown in FIG. 2, the line Q is defined based on the deepest point of the circumferential main groove with the larger groove depth. Furthermore, even if the groove depths are the same, when the distances from line X1 to the deepest points of the pair of circumferential main grooves are different due to the curved shape of the tread portion 1, the line Q is drawn by selecting the deepest point of the circumferential main groove so that the distance from line X1 is greater. The two ends of the tread surface of the convex rib 32, which are the base points of line segment X1, are the points where the side surfaces of the convex rib 32 (wall surfaces of the adjacent circumferential main grooves) and the tread surface of the convex rib 32 connect (the edges of the convex rib 32). If the edges of the convex rib 32 are chamfered, the base point of line segment X1 is the end point of the chamfer on the tread surface side. If point PC is located outside the above-mentioned range, the ground contact pressure cannot be sufficiently uniform, and the squeal reduction effect is limited.

[0028] Using point PC as defined above as a reference, in the present invention, as shown in Figures 4 and 5, the reference profile is defined as an arc (see the dashed line in the figures) passing through points PH1 and PH2 on the contour line of the first bulge portion 32a, which are located 20% of the length W1 on both sides of point PC in the tire width direction. The reference profile corresponds to the general bulging shape of the entire protruding rib 32 excluding the second bulge portion 32b. The second bulge portion 32b is a portion that bulges further from the first bulge portion 32a, or in other words, a portion that bulges further from the reference profile. When point p is defined as the point on the contour line of the second bulge portion 32b that is the longest normal distance from the reference profile, point p should be located preferably within 30%, and more preferably within 20%, of the length W2 of the line segment X2 that connects the intersection of the reference profile and the contour line of the protruding rib 32 on the side of point p with the intersection of the reference profile and the contour line of the protruding rib 32 on both sides in the tire width direction. This positions the point (point p) at which the second bulging portion 32b bulges most in the tire width direction (at the tire widthwise end of the convex rib 32), which is advantageous for equalizing the ground contact pressure and reducing squealing. If point p is positioned outside the above-mentioned range, the ground contact pressure cannot be sufficiently equalized, and the effect of reducing squealing will be limited. Note that FIG. 4 shows an embodiment in which one second bulging portion 32b is provided at one end of the first bulging portion 32a, and FIG. 5 shows an embodiment in which second bulging portions 32b are provided at both end portions of the first bulging portion 32a, but in the case of FIG. 5 as well, it is preferable that point p (points p1 and p2) be positioned within the above-mentioned range.

[0029] Let L1 and L2 be the distances in the normal direction from the reference profile of points p1 and p2 defined above (the expansion amount of the second bulging portion 32b), and let L3 be the distance between line segment X2 and point PC (the expansion amount of the first bulging portion 32a). The distances L1 to L3 preferably satisfy the relationship 0.10≦L1 / L3<0.90, more preferably 0.12≦L1 / L3≦0.90, and also satisfy the relationship 0.10≦L2 / L3<0.90, more preferably 0.12≦L2 / L3≦0.90. In this way, the expansion amount of the first bulging portion 32a (distance L3) is greater than the expansion amount of the second bulging portion 32b (distances L1 and L2), so that the central portion of the protruding rib 32 expands the most, which is advantageous for promoting drainage on the protruding rib 32 and improving wet performance. Furthermore, a good balance is achieved between the expansion amount of the first bulging portion 32a (distance L3) and the expansion amount of the second bulging portion 32b (distances L1 and L2), which is advantageous for equalizing ground pressure and reducing squealing. If L1 / L3 or L2 / L3 is less than 0.10, the expansion amount of the second bulging portion 32b is small, which limits the effect of equalizing ground pressure. If L1 / L3 or L2 / L3 exceeds 0.90, the expansion amount of the second bulging portion 32b is large, which limits the effect of equalizing ground pressure.

[0030] The individual ranges of the distances L1 to L3 are not particularly limited as long as they satisfy the above relationship, but the distances L1 and L2 corresponding to the amount of expansion of the second bulging portion 32b may be set to, for example, 0.05 mm or more and 0.2 mm or less, and the distance L3 corresponding to the amount of expansion of the first bulging portion 32a may be set to, for example, 0.1 mm or more and 0.5 mm or less.

[0031] As described above, the distances L1 and L2 correspond to the bulging amounts of the second bulging portion 32b. These distances L1 and L2 preferably satisfy the relationships of 0 < L1 / W2×100 ≦ 4, more preferably 0 < L1 / W2×100 ≦ 3 with respect to the length W2, and preferably 0 < L2 / W2×100 ≦ 4, more preferably 0 < L2 / W2×100 ≦ 3. Thereby, since the bulging amounts (distances L1 and L2) of the second bulging portion 32b are set within an appropriate range, it is advantageous for equalizing the ground pressure and reducing the skid noise. When L1 / W2×100 or L2 / W2×100 is below the above range, the bulging amount of the second bulging portion 32b is too small with respect to the width of the convex rib, so the effect of equalizing the ground pressure becomes limited. When L1 / W2×100 or L2 / W2×100 exceeds the above range, the bulging amount of the second bulging portion 32b is too large with respect to the width of the convex rib, so the effect of equalizing the ground pressure becomes limited.

[0032] Similar to the aforementioned distances L1 and L2, the distance L3 is also preferably within an appropriate range with respect to the length W2, and the distance L3 and the length W2 preferably satisfy the relationship of 0 < L3 / W2×100 ≦ 6, more preferably 0 < L3 / W2×100 ≦ 4. Thereby, since the bulging amount (distance L3) of the first bulging portion 32a is set within an appropriate range, it is advantageous for equalizing the ground pressure and reducing the skid noise. When L3 / W2×100 is below the above range, the bulging amount of the first bulging portion 32a is too small with respect to the width of the convex rib, so the effect of equalizing the ground pressure becomes limited. When L3 / W2×100 exceeds the above range, the bulging amount of the first bulging portion 32a is too large with respect to the width of the convex rib, so the effect of equalizing the ground pressure becomes limited.

[0033] As shown in FIG. 6, when the second bulging portion 32b is provided at both ends of the first bulging portion 32a in the tire width direction, a point on the contour line of the convex rib where the distance from the line segment T1 connecting the point PC and the point p1 is maximized is defined as the point T1', and a point on the contour line of the convex rib where the distance from the line segment T2 connecting the point PC and the point p2 is maximized is defined as the point T2'. Further, an intersection point of a line passing through the point T1' and perpendicular to the straight line Q and the line segment X2 is defined as the point W3, and an intersection point of a line passing through the point T2' and perpendicular to the straight line Q and the line segment X2 is defined as the point W4. Regarding each point defined in this way, the distance WA from the intersection point on the p1 side between the reference profile and the contour line of the convex rib 32 to the point W3, the distance WB from the intersection point on the p2 side between the reference profile and the contour line of the convex rib 32 to the point W4, and the distance WC between the point W3 and the point W4 preferably satisfy the relationship of 0.33 < WC / (WA + WB + WC) ≦ 0.9, more preferably 0.45 ≦ WC / (WA + WB + WC) ≦ 0.9, and preferably satisfy the relationship of 0.7 ≦ WA / WB ≦ 1.5, more preferably 0.8 ≦ WA / WB ≦ 1.3. Thereby, the relationship between the widths of the first bulging portion 32a and the second bulging portion 32b becomes good, which is advantageous for equalizing the contact pressure and reducing the skid noise. When WC / (WA + WB + WC) is less than 0.33 as described above, the second bulging portion 32b may bulge more than the first bulging portion 32a and the contact pressure at the end of the convex rib 32 may increase, and the effect of equalizing the contact pressure becomes limited. When WC / (WA + WB + WC) exceeds 0.9 as described above, the second bulging portion 32b does not bulge sufficiently, so the effect of equalizing the contact pressure becomes limited. When WA / WB is out of the above range, the bulging positions of the pair of second bulging portions 32b become asymmetric with respect to the center in the width direction of the convex rib 32, so the effect of equalizing the contact pressure becomes limited.

[0034] As shown in Figure 6, when the second bulging portions 32b are provided at both ends of the first bulging portion 32a in the tire width direction, the distance H1 between the line Q and point p1 and the distance H2 between the line Q and point p2 preferably satisfy the relationship 0.7 ≤ H1 / H2 ≤ 1.5, and more preferably 0.8 ≤ H1 / H2 ≤ 1.3. This ensures a good balance of the bulging amounts of the pair of second bulging portions 32b when a pair of second bulging portions 32b is provided at both ends of the protruding rib 32 in the tire width direction, which is advantageous for equalizing ground pressure and reducing squealing. If H1 / H2 is outside the above range, a load is likely to be applied to one of the pair of second bulging portions 32b (the one with the larger distance H1 or H2), limiting the effect of equalizing ground pressure.

[0035] With respect to the tread portion 1 configured as described above, the hardness Hs of the tread rubber (the rubber constituting the tread rubber layer 11) constituting the tread portion 1 is preferably 55 or more and 78 or less, more preferably 58 or more and 75 or less, and even more preferably 58 or more and 72 or less. When the tread rubber layer includes a cap tread layer 11C and an under tread layer 11U as shown in FIG. 1 , at least the cap tread layer 11C is preferably made of rubber having the above-mentioned hardness. Having the tread portion 1 with an appropriate hardness in this manner allows the bulged shapes of the first bulge portion 32a and the second bulge portion 32b to be well maintained during running, thereby efficiently demonstrating the effects of the convex ribs 32 described above. If the hardness Hs is less than 55, the tread rubber is too soft and therefore the bulged shape of the convex ribs 32 cannot be adequately maintained when the convex ribs 32 are deformed by lateral force during running, limiting the effect of uniforming ground pressure. If the hardness Hs exceeds 78, the tread rubber is too hard, which may cause localized increases in ground contact pressure at the convex ribs 32, limiting the effect of uniforming the ground contact pressure. The rubber hardness of the tread rubber is measured at 20°C using a type A durometer in accordance with JIS K6253.

[0036] 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]

[0037] Pneumatic tires (test tires) of Conventional Example 1 and Examples 1 to 34 were produced, each having a tire size of 235 / 60R18 and the basic structure (cross-sectional structure) illustrated in FIG. 1 , with the convex ribs having the presence or absence of a second bulge portion, the position of point PC, the position of point p1, the position of point p2, L1 / L3, L2 / L3, L1 / W2×100, L2 / W2×100, L3 / W2×100, hardness Hs, WC / (WA+WB+WC), WA / WB, and H1 / H2 set as shown in Tables 1 to 4, respectively.

[0038] The "Presence or Absence of Second Bulge Portion" column in the table indicates whether or not the tire includes a second bulge portion that bulges radially outward from the outline of the first bulge portion at the end of the first bulge portion in the tire width direction. "Absent" for Conventional Example 1 means that the land tread bulges in the same way as the first bulge portion, but does not include a second bulge portion. When the second bulge portion is "present," the number in parentheses indicates the number of second bulge portions, with "1" meaning that a second bulge portion is present at one end of the first bulge portion and "2" meaning that a second bulge portion is present at both ends of the first bulge portion.

[0039] In the table, the "Position of Point PC" column indicates the tire widthwise distance from the midpoint of line segment X1 to point PC on the contour line of the first bulge portion at which the distance from line Q is greatest, when the tire is mounted on a standard rim, pressurized to the standard, and unloaded. When line Q is defined as a line segment parallel to line segment X1 connecting both ends of the tread surface of the convex rib and passing through the deepest point of the circumferential main groove adjacent to the convex rib, the distance is expressed as a percentage (unit: %) of the length of line segment X1. The "Position of Point p1" and "Position of Point p2" columns in the table indicate the distance from the intersection of point p1 or p2 between the reference profile and the contour line of the convex rib on either side of point p1 or p2 on the contour line of the second bulge portion at which the distance from the reference profile in the normal direction is greatest. The distance is expressed as a percentage (unit: %) of the length of line segment X2 connecting the intersections of the reference profile and the contour line of the convex rib on both sides of the tire widthwise direction. If the second bulge portion is provided on only one side of the convex rib, the value is shown in the "Position of Point p1" column.

[0040] The "L1 / L3" and "L2 / L3" columns in the table show the relationship between L1, the normal distance from the reference profile of point p1, L2, the normal distance from the reference profile of point p2, and L3, the distance between line segment X2 and point PC. The "L1 / W2×100", "L2 / W2×100", and "L3 / W2×100" columns in the table show the relationship between the above distances L1 to L3 and the aforementioned length W2.

[0041] The "Hardness Hs" column in the table indicates the hardness Hs of the tread rubber (cap tread rubber) that constitutes the tread portion, and is a value measured at a temperature of 20°C using a durometer type A in accordance with JIS K6253.

[0042] The columns "WC / (WA+WB+WC)" and "WA / WB" in the table show the relationship between the distance WA from the intersection of the reference profile and the contour of the convex rib on the side of point p1 to point W3, the distance WB from the intersection of the reference profile and the contour of the convex rib on the side of point p2 to point W4, and the distance WC between point W3 and point W4, where T1' is the point on the contour of the convex rib where the distance to the line segment T1 connecting point PC and point p1 is the longest, T2' is the point on the contour of the convex rib where the distance to the line segment T2 connecting point PC and point p2 is the longest, W3 is the intersection of a line passing through point T1' and perpendicular to line Q with line segment X2, and W4 is the intersection of a line passing through point T2' and perpendicular to line Q with line segment X2. The column "H1 / H2" in the table shows the relationship between the distance H1 between line Q and point p1 and the distance H2 between line Q and point p2.

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

[0044] Squeal reduction performance Each test tire was mounted on a standard rim (rim size 18x7J), inflated to standard internal pressure (180KPa), and mounted on a test vehicle (a passenger car with an engine displacement of 2000cc). Five test drivers then conducted a sensory evaluation of the squealing noise at a traveling speed of 4km / h. The evaluation results were calculated by averaging each test driver's 10-point evaluation (the higher the score, the better), and expressed as an index with Conventional Example 1 being given a value of 100. The higher this index value, the greater the reduction in squealing noise, indicating excellent squealing noise reduction performance.

[0045] Wet performance Each test tire was mounted on a standard rim (rim size 18x7J), inflated to an internal pressure of 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 tire's running performance on wet roads on a test course consisting of wet roads. The evaluation results were expressed as an index, with Conventional Example 1's value being 100. The higher the index value, the better the wet performance.

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] [Table 4]

[0050] As is clear from Tables 1 to 4, the tires of Examples 1 to 34 were improved in squeal noise and wet performance compared to Conventional Example 1.

[0051] 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 the land portions among the plurality of land portions is a convex rib extending continuously along the tire circumferential direction, The convex rib includes a first bulge portion in which a contour line of the tread in a tire meridian cross section bulges outward in the tire radial direction, and includes a second bulge portion at at least one end of the first bulge portion in the tire width direction, bulging further outward in the tire radial direction from the contour line of the first bulge portion. Invention [2] In a meridian cross section of a tire mounted on a regular rim and with regular internal pressure applied and no load, When a line segment that is parallel to a line segment X1 that connects both ends of the tread surface of the convex rib and that passes through the deepest point of the circumferential main groove adjacent to the convex rib is defined as a line segment Q, a point PC on the contour line of the first bulge portion that is the greatest distance from the line segment Q is located within a range of 20% of the length W1 of the line segment X1 on both sides in the tire width direction from the midpoint of the line segment X1. Invention [3] A reference profile is defined as a circular arc passing through points PH1 and PH2 on the contour line of the first bulge portion at positions 20% of the length W1 on both sides of the point PC in the tire width direction, and the point PC, When the point on the contour line of the second bulge portion at which the distance in the normal direction from the reference profile is maximum is defined as point p, The tire according to invention [2], characterized in that point p is located within 30% of the length W2 of line segment X2 that connects the intersection of the reference profile and the contour line of the raised rib on the side of point p with the intersection of the reference profile and the contour line of the raised rib on both sides in the tire width direction. Invention [4] The tire according to invention [3], characterized in that when the distance in the normal direction from the reference profile of the point p is L1 and the distance between the line segment X2 and the point PC is L3, the distance L1 and the distance L3 satisfy the relationship 0.10≦L1 / L3<0.90. The invention [5] The tire according to the invention [4], characterized in that the distance L1 and the length W2 satisfy the relationship of 0 < L1 / W2 × 100 ≦ 4. The invention [6] The tire according to the invention [4] or [5], characterized in that the distance L3 and the length W2 satisfy the relationship of 0 < L3 / W2 × 100 ≦ 6. The invention [7] The second bulging portion is provided at both ends in the tire width direction of the first bulging portion. Let the point p in the second bulging portion on one side in the tire width direction be point p1, and the point p in the second bulging portion on the other side in the tire width direction be point p2. Let the point on the contour line of the convex rib where the distance from the line segment T1 connecting the point PC and the point p1 is maximized be point T1', and the point on the contour line of the convex rib where the distance from the line segment T2 connecting the point PC and the point p2 is maximized be point T2'. When the intersection of the line passing through the point T1' and perpendicular to the line Q and the line segment X2 is point W3, and the intersection of the line passing through the point T2' and perpendicular to the line Q and the line segment X2 is point W4. The distance WA from the intersection on the point p1 side between the reference profile and the contour line of the convex rib to the point W3, the distance WB from the intersection on the point p2 side between the reference profile and the contour line of the convex rib to the point W4, and the distance WC between the point W3 and the point W4 satisfy the relationships of 0.33 < WC / (WA + WB + WC) ≦ 0.9 and 0.7 ≦ WA / WB ≦ 1.5. The tire according to any one of the inventions [4] to [6]. The invention [8] The second bulging portion is provided at both ends in the tire width direction of the first bulging portion. When the point p in the second bulging portion on one side in the tire width direction is point p1, and the point p in the second bulging portion on the other side in the tire width direction is point p2. The tire according to any one of the inventions [3] to [7], characterized in that the distance H1 between the line Q and the point p1 and the distance H2 between the line Q and the point p2 satisfy the relationship of 0.7 ≦ H1 / H2 ≦ 1.​​​[Explanation of symbols]

[0052] 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 First bulge 32b Second bulge 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 the land portions among the plurality of land portions is a convex rib extending continuously along the tire circumferential direction, The convex rib includes a first bulge portion in which a contour line of the tread in a tire meridian cross section bulges outward in the tire radial direction, and includes a second bulge portion at at least one end of the first bulge portion in the tire width direction, bulging further outward in the tire radial direction from the contour line of the first bulge portion.

2. When mounted on a standard rim and under normal internal pressure, the tire is in a no-load state.

2. The tire according to claim 1, wherein when a line segment that is parallel to a line segment X1 connecting both ends of the tread surface of the convex rib and that passes through the deepest point of the circumferential main groove adjacent to the convex rib is defined as a line segment Q, a point PC on the contour line of the first bulge portion that is the greatest distance from the line segment Q is located within a range of 20% of a length W1 of the line segment X1 on both sides in the tire width direction from the midpoint of the line segment X1.

3. a reference profile is defined as a circular arc passing through points PH1 and PH2 on the contour line of the first bulge portion at positions 20% of the length W1 on both sides of the point PC in the tire width direction, and the point PC; When a point on the contour line of the second bulge portion at which the distance from the reference profile in the normal direction is maximum is defined as point p, The tire according to claim 2, characterized in that the point p is located within 30% of a length W2 of a line segment X2 that connects an intersection point between the reference profile and the contour line of the convex rib on the side of point p and an intersection point between the reference profile and the contour line of the convex rib on both sides in the tire width direction.

4. 4. The tire according to claim 3, wherein when a distance in a normal direction from the reference profile to the point p is defined as L1 and a distance between the line segment X2 and the point PC is defined as L3, the distance L1 and the distance L3 satisfy a relationship of 0.10≦L1 / L3≦<0.

90.

5. 5. The tire according to claim 4, wherein the distance L1 and the length W2 satisfy the relationship: 0<L1 / W2×100≦4.

6. The tire according to claim 4 or 5, wherein the distance L3 and the length W2 satisfy the relationship: 0<L3 / W2×100≦6.

7. the second bulging portions are provided at both end portions in the tire width direction of the first bulging portion, The point p in the second bulge portion on one side in the tire width direction is defined as point p1, and the point p in the second bulge portion on the other side in the tire width direction is defined as point p2, a point on the contour line of the convex rib where the distance between the line segment T1 connecting the point PC and the point p1 is maximum is defined as point T1', and a point on the contour line of the convex rib where the distance between the line segment T2 connecting the point PC and the point p2 is maximum is defined as point T2', When the intersection of the line passing through the point T1' and perpendicular to the straight line Q with the line segment X2 is defined as point W3, and the intersection of the line passing through the point T2' and perpendicular to the straight line Q with the line segment X2 is defined as point W4, The tire according to claim 4 or 5, characterized in that a distance WA from a point of intersection between the reference profile and the contour line of the convex rib on the side of point p1 to point W3, a distance WB from a point of intersection between the reference profile and the contour line of the convex rib on the side of point p2 to point W4, and a distance WC between point W3 and point W4 satisfy the relationships 0.33<WC / (WA+WB+WC)≦0.9 and 0.7≦WA / WB≦1.

5.

8. the second bulging portions are provided at both end portions in the tire width direction of the first bulging portion, When the point p in the second bulge portion on one side in the tire width direction is defined as point p1 and the point p in the second bulge portion on the other side in the tire width direction is defined as point p2, The tire according to any one of claims 3 to 5, characterized in that a distance H1 between the straight line Q and the point p1 and a distance H2 between the straight line Q and the point p2 satisfy the relationship 0.7≦H1 / H2≦1.

5.

9. The tire according to any one of claims 1 to 5, characterized in that the hardness Hs of the tread rubber constituting the tread portion is 55 or more and 78 or less.

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