Tire

Abstract

To provide a tire capable of improving turning performance on a wet road surface and suppressing generation of squeal noise while maintaining good straight running performance on the wet road surface.SOLUTION: At least one row of the land portions 30 formed in the tread portion 1 is a convex rib 32 having a shape in which a contour line of a tread surface bulges outward in a tire radial direction, the contour line of the tread surface of the convex rib 32 is constituted by a plurality of arcs, and a line segment connecting end portions (point p1, point p2) of the convex rib 32 is a straight line P, A vertical distance p3 between the straight line P and the contour line of the convex rib 32 at a position of 80% of a length ap between the point p4 and the point p4 and a length b between the point p1 and the point p3 satisfy a relationship of 0.3 ≤ p4 / b <1, and a length W of the straight line P and the length b satisfy a relationship of 0.001 ≤ b / W ≤ 0.25, where the point b1 is an intersection point of the straight line P and a perpendicular line of the straight line P passing through the point on the contour line of the convex rib having a maximum length from the straight line P. b1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

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

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

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

[0005] In order to achieve the above object, the tire of the present invention provides a tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, the tread portion having at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions partitioned by the circumferential main grooves, at least one row of the plurality of land portions extending continuously along the tire circumferential direction, a convex rib having a shape in which the outline of the tread surface in a meridian cross section of the tire mounted on a normal rim and applied with normal internal pressure and in an unloaded state bulges outward in the tire radial direction, when one end of the convex rib in the tire width direction is defined as point p1, the other end of the convex rib in the tire width direction as point p2, the line segment connecting point p1 and point p2 as straight line P, the point on the outline of the convex rib that is the greatest distance from the straight line P as point p3, and the intersection of the perpendicular to the straight line P passing through point p3 and the straight line P as point p4, On one side of point p3 in the tire width direction of the contour line of the tread surface, 80% or more of the length of the portion of the contour line of the tread surface of the convex rib on that side of point p3 in the tire width direction is composed of a plurality of circular arcs, and when the perpendicular distance between the straight line P and the contour line of the convex rib at a position 80% of the distance ap between point p4 and point p1, moving from point p4 to point p1, is defined as distance b1, and the perpendicular distance between the straight line P and the contour line of the convex rib at a position 80% of the distance ap' between point p4 and point p2, moving from point p4 to point p2, is defined as distance b1', the distance b1 or distance b1' on the contour line composed of a plurality of circular arcs satisfies the relationship 0.3≦b1 / b<1 or 0.3≦b1' / b<1 with respect to the distance b between point p3 and point p4, and the length W of the straight line P and the distance b satisfy the relationship 0.001≦b / W≦0.25. [Effects of the Invention]

[0006] To improve wet performance, the tire of the present invention includes a convex rib in which the contour line of the tread in a tire meridian cross section bulges outward in the tire radial direction. Because the convex rib has the above-described characteristics, the bulging shape of the convex rib is favorable, enabling a good balance between straight-line running performance and cornering performance on wet roads while suppressing the generation of squealing. That is, the tire improves straight-line running performance on wet roads by increasing the contact pressure at the bulging portion of the convex rib (near point p3), while preventing the tire widthwise ends of the convex rib (near points p1 and p2) from bulging outward relative to point p3, thereby suppressing a decrease in contact pressure and ensuring good cornering performance on wet roads. Furthermore, the uniform distribution of contact pressure on the convex rib contact surface can suppress squealing at low speeds.

[0007] In the present invention, when the contour line of the tread of the convex rib is viewed as a curve on an XY coordinate system with the line connecting points p3 and p4 as the Y axis, the line connecting points 1 and p2 as the X axis, and point p4 as the origin, the contour line made up of the plurality of circular arcs is preferably approximated to a function curve on the XY coordinate system selected from an elliptic function, a super elliptic function, a cycloid function, an epicycloid function, an involute function, and a power function, and the distance between the function curve and the contour line made up of the plurality of circular arcs in the direction perpendicular to the line P is preferably 5% or less of the distance b. This improves the bulging shape of the convex rib, which is advantageous for suppressing squealing while providing a good balance between straight-line running performance and cornering performance on wet roads.

[0008] In particular, it is preferable that the function curve be defined by the following formula (1) or (2): The function of the following formula (1) or (2) is a so-called super elliptic function, and the resulting tread contour line has a shape in which point p3 is sufficiently bulging, while points p1 and p2 do not drop excessively relative to point p3, which is advantageous for suppressing squealing while achieving a good balance between straight-line performance and cornering performance on wet roads.

[0009]

number

[0010]

number

[0011] (In the above formulas (1) and (2), a is a radius of the major axis of the curve defined by the function of formula (1) on the X-axis closer to point p1 than point p4, and satisfies the relationship ap≦a≦ap×1.5 with respect to the distance ap between point p1 and point p4, a' is a radius of the major axis of the curve defined by the function of formula (2) on the X-axis closer to point p2 than point p4, and satisfies the relationship ap'≦a'≦ap'×1.5 with respect to the distance ap' between point p2 and point p4, b is a radius of the minor axis of the curve defined by the function of formula (1) or (2) on the Y axis closer to point p3 than point p4, and is equal to the distance between point p3 and point p4, satisfying the relationship 0.001≦b / a≦0.45 or 0.001≦b / a′≦0.45; The relationships n≧1.5, m≧1.5, and y>0 are satisfied.)

[0012] In the present invention, the N-th arc from the point p3 side among the plurality of arcs is R N (N is an integer between 1 and k, and k is an integer between 4 and 5), and the arc R N and arc R N+1 The point connecting these points is point T N Then, the arc R N and arc R N+1 is point T N and the point T N The intersection point of the perpendicular line of the line P passing through the line P and the line P is the point x N , point p4 to point x N Distance to ap N , the kth arc R from the point p3 side k The intersection of the perpendicular line of the line P passing through the outer end of the tire width direction and the line P is the point x k , point p4 to point x kDistance to ap k When the distance ap1 and the distance ap k 0.1≦ap1 / ap k ≦0.7 and point x N and point x N+1 The distance d on the line P N and point x N+1 and point x N+2 The distance d on the line P N+1 Toga d N ≧d N+1 This satisfies the following relationship: The curved shape of the contour line of the convex rib is favorable, which is advantageous for suppressing the occurrence of squealing while improving straight-line running performance and cornering performance on wet road surfaces in a balanced manner.

[0013] At this time, the distance d N and the distance d N+1 When N=1, 0.5≦d N+1 / d N ≦0.9, and when N≧1, 0.5≦d N+1 / d N It is preferable to satisfy the relationship < 1. This improves the curved shape of the contour line of the convex rib, which is advantageous for suppressing the occurrence of squealing while improving straight-line running performance and cornering performance on wet road surfaces in a balanced manner.

[0014] At this time, the arc R N The radius of curvature of r N When defined as follows, the radius of curvature r N and the radius of curvature r N+1 Toga r N >r N+1 This satisfies the following relationship: The curved shape of the contour line of the convex rib is favorable, which is advantageous for suppressing the occurrence of squealing while improving straight-line running performance and cornering performance on wet road surfaces in a balanced manner.

[0015] In the present invention, it is preferable that the number k of circular arcs constituting the contour line of the tread surface of the convex rib on one side of point p3 in the tire width direction satisfies the relationship 4≦k≦10. This improves the curved shape of the contour line of the convex rib, which is advantageous for suppressing the generation of squealing while improving straight-line running performance and cornering performance on wet roads in a balanced manner.

[0016] In the present invention, it is preferable that point p3 be located within a range of 30% of the length W of said straight line P on both sides in the tire width direction from the midpoint of said straight line P. This causes the central portion of the convex rib to bulge the most (point PC at which the convex rib bulges the most is located near the center of the convex rib in the tire width direction), which promotes drainage above the rib and is advantageous for improving wet performance.

[0017] In the present invention, the hardness Hs of the tread rubber constituting the tread portion is preferably 55 or more and 78 or less. By having such an appropriate hardness, the bulging shape of the convex ribs is well maintained during running, and the effects of the convex ribs described above can be efficiently exhibited.

[0018] 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]

[0019] [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. 3 is an explanatory diagram showing an enlarged view of a main part of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] As shown in FIG. 1, at least two circumferential main grooves 20 (four in the example of FIG. 1) extending linearly along the tire circumferential direction are provided on the surface of the tread portion 1 of the tire. The circumferential main grooves 20 are grooves that perform the main drainage function and have a maximum groove width of, for example, 3 mm to 30 mm and a maximum groove depth of, for example, 4 mm to 10 mm. These at least two circumferential main grooves 20 define multiple rows (five in the example of FIG. 1) of land portions 30 extending along the tire circumferential direction. In the following description, a pair of land portions 30 located on the tire widthwise outer side of a pair of circumferential main grooves 20 located on the outermost sides in the tire widthwise direction may be referred to as shoulder land portions 31. In the present invention, at least one row of these land portions 30 (one row in FIG. 1) is configured as a convex rib 32, which will be described later. When the land portion 30 excluding the shoulder land portion 31 is a convex rib 32, this land portion 30 (convex rib 32) is defined by a pair of circumferential main grooves 20, and therefore a profile shape described below is applied to the top surface (tread surface) of the land portion 30 (convex rib 32) sandwiched between the pair of circumferential main grooves 20. When the shoulder land portion 31 is a convex rib 32, the shoulder land portion 31 (convex rib 32) is defined on the outer side of the circumferential main groove 20 in the tire width direction, and therefore a profile shape described below is applied to the top surface (tread surface) of the shoulder land portion 31 (convex rib 32) sandwiched between the circumferential main groove 20 and the ground contact edge.

[0026] The convex ribs 32 are land portions having a shape in which the outline of the tread bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim, normal internal pressure is applied, and no load is applied, as shown in Figures 2 to 4. Furthermore, although not depicted in Figures 2 to 4 because they are tire meridian cross sections, the convex ribs 32 have a shape that extends continuously in the tire circumferential direction without being interrupted by lateral grooves extending in the tire width direction.

[0027] "Regular rim" refers to the rim specified for each tire by the standard system, including the standard on which the tire is based, such as the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. "Regular internal pressure" refers to the air pressure specified for each tire by the standard system, including the standard on which the tire is based, such as the maximum air pressure for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and the "INFLATION PRESSURE" for ETRTO.

[0028] 2, the end of this convex rib 32 on one side in the tire width direction is defined as point p1, the end of the convex rib 32 on the other side in the tire width direction is defined as point p2, the line segment connecting points p1 and p2 is defined as line P, the point on the contour line of the convex rib 32 that is the longest from line P is defined as point p3, and the intersection of line P and a perpendicular to line P passing through point p3 is defined as point p4. When defined in this way, at least on one side in the tire width direction of point p3 of the contour line of the tread surface of the convex rib 32, 80% or more of the length of the portion of the contour line of the tread surface of the convex rib 32 on one side in the tire width direction of point p3 is always composed of multiple circular arcs. In other words, of the contour lines of the tread surface of the convex rib 32 of the present invention, either the contour line from point p3 to point p1 or the contour line from point p3 to point p2 or both are always composed of multiple circular arcs. The area formed by multiple arcs does not have to be the entire contour line from point p3 to point p1 or the entire contour line from point p3 to point p2, but may be 80% or more of the length along the contour line from point p3 to point p1 starting from point p3 or 80% or more of the length along the contour line from point p3 to point p2.

[0029] Further, when the perpendicular distance between the straight line P and the contour line of the convex rib, moving from point p4 to point p1 at a position 80% of the distance ap between point p4 and point p1, is defined as distance b1, and when the perpendicular distance between the straight line P and the contour line of the convex rib, moving from point p4 to point p1 at a position 80% of the distance ap' between point p4 and point p2, is defined as distance b1', the distance b1 or distance b1' on the contour line made up of multiple arcs satisfies the relationship 0.3≦b1 / b<1 or 0.3≦b1' / b<1 with respect to the distance b between point p3 and point p4, and the length W of the straight line P and the distance b satisfy the relationship 0.001≦b / W≦0.25.

[0030] Such a bulging shape increases the ground contact pressure at the bulging portion of the convex rib 32 (near point p3) and improves straight-line running performance when traveling on wet roads, while preventing the tire width direction ends of the convex rib 32 (near points p1 and p2) from bulging out relative to the vicinity of point p3 prevents a decrease in ground contact pressure and ensures good cornering performance on wet roads. In addition, the above-mentioned bulging shape makes it possible to even out the ground contact pressure distribution on the tread surface of the convex rib 32, thereby suppressing squealing at low speeds.

[0031] When the contour line between points p3 and p1 is composed of multiple arcs, the ratio b1 / b of the distance b1 to the distance b satisfies the relationship 0.3≦b1 / b<1 as described above, but preferably satisfies the relationship 0.4≦b1 / b≦0.9. When the contour line between points p3 and p2 is composed of multiple arcs, the ratio b1' / b of the distance b1' to the distance b satisfies the relationship 0.3≦b1' / b<1 as described above, but preferably satisfies the relationship 0.4≦b1' / b≦0.9. This allows the amount of drop in the tire near point p1 or point p2 relative to point p3 to be set within an appropriate range, which is advantageous for suppressing squealing while improving straight-line performance and cornering performance on wet roads in a balanced manner. If the ratios b1 / b and b1' / b are less than 0.3, the effect of suppressing the drop in the tire widthwise outer side of the convex rib 32 is limited. If the ratios b1 / b and b1' / b are 1 or greater, point p3 will not substantially bulge out relative to point p1 or point p2, making it difficult for the convex rib 32 to maintain its shape.

[0032] The ratio b / W of the length W of the straight line P to the distance b indicates the degree of bulging relative to the width of the convex rib 32. When this ratio satisfies the relationship 0.001≦b / W≦0.25, preferably 0.001≦b / W≦0.20, the bulging shape of the convex rib 32 is improved, resulting in a balanced improvement in straight-line running performance and cornering performance on wet roads while suppressing squealing. If the ratio b / W is less than 0.001, the bulging amount relative to the width of the convex rib 32 becomes too small, resulting in a performance equivalent to no bulging, and thus the effect of improving wet performance is limited. If the ratio b / W exceeds 0.25, the bulging amount relative to the width of the convex rib 32 becomes too large, making it difficult to ensure a sufficient contact area, and the effect of improving wet performance is limited. The length W of the straight line P is the distance between points p1 and p2 and essentially corresponds to the width of the convex rib 32. Therefore, the length W can be appropriately set according to the tire size and tread pattern. The range is not particularly limited, but the length W can be set to, for example, 10 mm to 50 mm.

[0033] In the present invention, it is sufficient that at least one of the plurality of land portions is a convex rib 32 that satisfies the above-mentioned conditions, and therefore the other land portions 30 may be land portions (conventional general land portions) having a shape in which the outline of the tread does not bulge outward in the tire radial direction in a meridian cross section of the tire when mounted on a regular rim and under normal internal pressure and in an unloaded state. Also, the land portions may have a bulging shape that is not composed of multiple arcs (for example, an arc-shaped outline having a single radius of curvature).

[0034] As shown in Figure 3, the above-described convex rib 32 is depicted in an XY coordinate system with the line connecting points p3 and p4 as the Y axis, the line connecting points 1 and p2 as the X axis, and point p4 as the origin. When the contour of the tread of the convex rib 32 is viewed as a curve on this XY coordinate system, the contour composed of multiple arcs preferably has a shape that approximates a function curve selected from elliptic functions, superelliptic functions, cycloid functions, epicycloid functions, involute functions, and power functions on this XY coordinate system. That is, the distance between these function curves (see the dashed lines in the figure) and the contour composed of multiple arcs in the direction perpendicular to the line P (error E from the function curve) is preferably 5% or less, more preferably 2% or less, of the distance b. This improves the bulging shape of the convex rib 32, which is advantageous for suppressing squealing while providing a good balance of straight-line running performance and cornering performance on wet roads. If the error E from the function curve exceeds 5% of the distance b, the contour line of the tread surface of the convex rib 32 will not approximate the above-mentioned function curve, and the effect of improving the bulging shape of the convex rib 32 will be limited. Note that the error E from the function curve is the distance between the function curve (see the dashed lines in the figure) measured on perpendicular lines to a straight line P drawn every 5% of the distance ap or the distance ap' and the contour line made up of multiple arcs, all of which must fall within the above-mentioned range. Note that for the sake of explanation, the error E from the function curve is exaggerated in Figure 3.

[0035] In particular, it is preferable that the contour line of the convex rib 32 of the present invention approximates the function of the following formula (1) or (2) among the above-mentioned functional curves. That is, the function of the following formula (1) or (2) is a so-called super elliptic function, and the contour line of the tread obtained thereby has a shape in which point p3 is sufficiently bulging, while points p1 and p2 do not drop excessively relative to point p3, which is advantageous for suppressing the generation of squealing while achieving a good balance between straight-line performance and cornering performance on wet roads.

[0036]

number

[0037]

number

[0038] In the above formulas (1) and (2), a is the radius of the major axis of the curve defined by the function of formula (1) on the X-axis on the side of point p1 relative to point p4, and satisfies the relationship ap≦a≦ap×1.5, where ap is the distance between points p1 and p4; a' is the radius of the major axis of the curve defined by the function of formula (2) on the X-axis on the side of point p2 relative to point p4, and satisfies the relationship ap'≦a'≦ap'×1.5, where ap' is the distance between points p2 and p4; b is the radius of the minor axis of the curve defined by the function of formula (1) or (2) on the Y-axis on the side of point p3, and matches the distance between points p3 and p4, and satisfies the relationship 0.001≦b / a≦0.45 or 0.001≦b / a'≦0.45; and n≧1.5, m≧1.5, and y>0.

[0039] In the above formulas (1) and (2), if a or a' is less than ap or ap', sufficient ground contact pressure cannot be obtained at the tire width direction ends of the convex ribs 32, and the effect of improving cornering performance on wet road surfaces will be limited. If a or a' exceeds ap × 1.5 or ap' × 1.5, the convex ribs 32 will not expand sufficiently and sufficient ground contact pressure cannot be obtained at the tire width direction ends of the convex ribs 32, and the effect of improving cornering performance on wet road surfaces will be limited. The above a, a', ap, and ap' preferably satisfy the relationships ap≦a≦ap × 1.2 and ap'≦a'≦ap' × 1.2.

[0040] In the above formulas (1) and (2), if b / a or b / a' is less than 0.001, the bulging amount of the convex rib 32 becomes excessive, the contact area decreases, and straight-line running performance and cornering performance on wet roads cannot be sufficiently ensured. If b / a or b / a' exceeds 0.45, the bulging amount of the convex rib 32 becomes too small, and sufficient contact pressure cannot be obtained at the tire width direction ends of the convex rib 32, limiting the effect of improving cornering performance on wet roads. Furthermore, sufficient contact pressure cannot be maintained at the center of the convex rib 32, resulting in reduced drainage, which may also reduce straight-line running performance on wet roads. Preferably, the above b / a or b / a' satisfies the relationship 0.002≦b / a≦0.40 or 0.002≦b / a'≦0.40.

[0041] In the above formulas (1) and (2), n and m satisfy the relationships n≧1.5 and m≧1.5, preferably 1.5≦n≦5 and 1.5≦m≦5, more preferably 2≦n≦4 and 2≦m≦4, and even more preferably 2≦n≦3 and 2≦m≦3. In the above formulas (1) and (2), the larger n and m are, the smaller the difference in the amount of expansion between the center and the tire widthwise ends of the convex rib 32. This allows for improved contact pressure at the tire widthwise ends of the convex rib 32, thereby improving cornering performance on wet roads while maintaining straight-line performance on wet roads. In particular, setting n and m within the above-described ranges improves the expansion shape of the convex rib 32, which is advantageous for achieving a balanced improvement in straight-line performance and cornering performance on wet roads. If n and m are less than 1.5, the tire widthwise ends of the convex rib 32 will sag significantly, limiting the effect of improving contact pressure at the tire widthwise ends of the convex rib 32. If n and m exceed 5, the difference in the amount of expansion between the center of the convex rib 32 and the tire widthwise end portion becomes too small, the expansion of the center of the convex rib 32 becomes insufficient, and it becomes difficult to maintain sufficient ground contact pressure at the center of the convex rib 32.

[0042] In addition to the above-mentioned n and m satisfying the above-mentioned ranges, the ratio n / m preferably satisfies the relationship 0.8≦n / m≦1.2, more preferably 0.9≦n / m≦1.1. This improves the bulging shape of the convex rib 32, which is advantageous for improving straight-line running performance and cornering performance on wet roads in a balanced manner. If the ratio n / m is below the above-mentioned range, the contact pressure at the tire widthwise ends of the convex rib 32 increases, limiting the effect of improving straight-line running performance on wet roads. If the ratio n / m exceeds the above-mentioned range, the difference in the amount of bulging between the center portion of the convex rib 32 and the tire widthwise ends becomes too small, resulting in insufficient bulging at the center portion of the convex rib 32 and making it difficult to maintain sufficient contact pressure at the center portion of the convex rib 32.

[0043] When the contour line of the tread surface of the convex rib 32 is composed of multiple arcs, the number of arcs constituting the contour line of the tread surface of the convex rib 32 on one side of point p3 in the tire width direction is defined as k. The number of arcs k preferably satisfies the relationship 4≦k, more preferably 4≦k≦10, and even more preferably 4≦k≦8. This improves the curved shape of the contour line of the convex rib, which is advantageous for suppressing squealing while improving straight-line running performance and cornering performance on wet roads in a balanced manner. If k<4, the effect of improving the bulging shape of the convex rib 32 as described above is limited. If k>10, the shape of the tread surface of the convex rib becomes complex, making it difficult to manufacture a mold for manufacturing a tire with a convex rib 32 that satisfies the above-mentioned conditions.

[0044] As shown in Figure 4, among the multiple arcs, the Nth arc from the point p3 side is R N (N is an integer between 1 and k, and k is an integer between 4 and 5), and the arc R N and arc R N+1 The point connecting these points is point T N Then, the arc R N and arc R N+1 is point T N The example in FIG. 4 is for the case where k=4, i.e., the case where four arcs R1 to R4 are included, and points T1 to T3 are included as points connecting the arcs, and arcs R1 and R2 have a common tangent L (see the broken line in the figure) at point T1, arcs R2 and R3 have a common tangent (not shown) at point T2, and arcs R3 and R4 have a common tangent (not shown) at point T3. Furthermore, N The intersection point of the perpendicular line of the line P passing through the point x N , point p4 to point x N Distance to ap N , the kth arc R from point p3 k The intersection of the perpendicular line of the line P passing through the outer end of the tire width direction and the line P is the point x k , point p4 to point x k Distance to ap k When the distance ap1 and the distance ap k Preferably, 0.1≦ap1 / ap k ≦0.7, more preferably 0.2≦ap1 / apk ≦0.6. In addition, point x N and point x N+1 Distance d on the line P N and point x N+1 and point x N+2 Distance d on the line P N+1 Toga d N ≧d N+1 This satisfies the relationship:

[0044] This improves the curved shape of the contour line of the convex rib 32, which is advantageous for suppressing the occurrence of squealing while improving straight-line running performance and cornering performance on wet road surfaces in a balanced manner.

[0045] In particular, the ratio ap1 / ap k The relationship of d is satisfied. N ≧d N+1 By satisfying the above relationship, the first arc R1 from point p3 to the arc R furthest from point p3 k As the ratio ap1 / ap becomes smaller, the length of the arc in the tire width direction gradually decreases, and the difference in the length of the arc in the tire width direction decreases, so the curved shape of the contour line of the convex rib 32 becomes good. k If the radius of the arc R is outside the above range, k The balance between the distance d and the arc R1 cannot be improved, and the effect of suppressing squealing while improving straight-line performance and cornering performance on wet roads in a balanced manner is limited. N and d N+1 If the above-mentioned magnitude relationship is not satisfied, the effect of improving the shape of the contour line of the convex rib 32 will be limited.

[0046] The "arc R" in the above explanation N and arc R N+1 is point T N "Having a common tangent at" means that the arc R N Point T N Tangent to arc R N+1 Point T N This means that the difference in angle between the tangents at the arc R is within 5°. If the difference in angle between these tangents exceeds 5°, N and arc R N+1 and point T NTherefore, it becomes difficult to obtain a good shape for the convex rib 32.

[0047] For the sake of explanation, Figure 4 shows an enlarged view of the point p1 side of point p3, but the contour line on the point p2 side of point p3 can also have a similar shape. In other words, at least one or both contour lines on each side of point p3 in the tire width direction can be configured with multiple arcs as described above and below. When the above-described structure is applied to both sides of point p3, the contour lines on both sides do not need to be symmetrical with respect to the perpendicular line to line P passing through point p3, and the contour lines on each side can independently satisfy the various conditions described above.

[0048] The above distance d N and distance d N+1 When N=1, preferably 0.5≦d N+1 / d N ≦0.9, more preferably 0.6≦d N+1 / d N ≦0.8, and when N≧2, preferably 0.5≦d N+1 / d N <1, more preferably 0.5≦d N+1 / d N It is desirable to satisfy the relationship of <0.9. This improves the curved shape of the contour line of the convex rib, which is advantageous in suppressing the occurrence of squealing while improving the straight-line running performance and cornering performance on wet roads in a balanced manner. In either case, the ratio d N+1 / d N If the ratio d is smaller than the above range, the arc becomes too small toward the end of the protruding rib 32, and the effect of improving the shape of the contour line of the protruding rib 32 is limited. N+1 / d N If is larger than the above range, the effect of improving the shape of the contour line of the protruding rib 32 will be limited.

[0049] As described above, the contour line of the tread surface of the convex rib 32 of the present invention is formed by a plurality of arcs R N The radius of curvature is r N When defined as follows, the radius of curvature r N and the radius of curvature r N+1 What is rN >r N+1 It is preferable that the relationship be satisfied. That is, it is preferable that the radii of curvature of the multiple circular arcs gradually decrease with increasing distance from point p3. For example, the example in Figures 2 and 4 includes circular arcs R1 to R4, and these radii of curvature r1 to r4 satisfy the relationship r1>r2>r3>r4. This improves the curved shape of the contour line of the convex rib 32, which is advantageous for suppressing squealing while improving straight-line performance and cornering performance on wet roads in a balanced manner.

[0050] In addition to the above relationship, the distance b preferably satisfies the relationship 0.05 mm≦b≦2.0 mm, more preferably 0.05 mm≦b≦1.5 mm, and even more preferably 0.05 mm≦b≦1.2 mm. This improves the bulging shape of the convex rib, which is advantageous for balanced improvement of straight-line running performance and cornering performance on wet roads. If the distance b is less than 0.05 mm, the bulge at the center of the convex rib 32 is insufficient, making it difficult to maintain sufficient ground contact pressure at the center of the convex rib 32. If the distance b exceeds 2.0 mm, the bulge amount of the convex rib 32 becomes excessive, making it impossible to ensure a sufficient contact area, limiting the effect of improving cornering performance and straight-line running performance on wet roads.

[0051] As described above, point p3 is the point on the contour of the protruding rib 32 where the distance to the line P connecting points p1 and p2 is greatest, and corresponds to the point of maximum expansion of the protruding rib 32. This point p3 should be located within a range of preferably 30%, more preferably 25%, and even more preferably 20% of the length W of line P on both sides of the midpoint of line P in the tire width direction. This allows the central portion of the protruding rib 32 to expand most (point p3 where the protruding rib 32 expands most is located near the center of the protruding rib 32 in the tire width direction), which promotes drainage on the protruding rib 32 and is advantageous for improving wet performance. If point p3 is located outside the above range, the point where the protruding rib 32 expands most (point p3) will be unevenly located at the end of the protruding rib in the tire width direction, making it difficult to ensure good drainage performance.

[0052] In the above-mentioned convex rib 32, the groove depth of a pair of adjacent circumferential main grooves 20 is preferably 80% or more of the groove depth of the deepest circumferential main groove 20. Since land portions where the groove depth of adjacent circumferential main grooves 20 is large (i.e., land portions that protrude from the groove bottom to a large extent) are greatly affected by ground contact pressure, application of the above-mentioned convex rib 32 can effectively improve straight-line running performance and cornering performance on wet road surfaces.

[0053] The convex rib 32 has a shape that extends continuously in the tire circumferential direction without being interrupted by lateral grooves extending in the tire width direction, but may also have narrow grooves or sipes with a groove width of less than 3 mm. The provision of these narrow grooves or sipes ensures the drainage and edge effects of the narrow grooves and sipes, which is advantageous for improving straight-line performance and cornering performance on wet roads. Note that, because the narrow grooves and sipes have a small groove width as described above, the provision of these narrow grooves and sipes means that the convex rib 32 is considered to be uninterrupted.

[0054] Regarding the tread portion 1 configured as described above, the hardness Hs of the tread rubber (rubber constituting the tread rubber layer 11) constituting the tread portion 1 is preferably 55 or more and 78 or less, more preferably 58 or more and 75 or less, and even more preferably 58 or more and 72 or less. When the tread rubber layer includes a cap tread layer 11C and an undertread layer 11U as shown in FIG. 1 , at least the cap tread layer 11C is preferably made of rubber having the above-mentioned hardness. Having the tread portion 1 with an appropriate hardness allows the protruding shape of the convex ribs 32 to be well maintained during running, allowing the above-described effects of the convex ribs 32 to be efficiently exhibited. If the hardness Hs is less than 55, the tread rubber is too soft, and therefore the protruding shape of the convex ribs 32 cannot be adequately maintained when deformed by lateral force during running, limiting the effect of uniforming ground pressure. If the hardness Hs exceeds 78, the tread rubber is too hard, and the ground pressure of the convex ribs 32 may increase locally, limiting the effect of uniforming ground pressure. The rubber hardness of the tread rubber is determined in accordance with JIS K6253 and is measured at a temperature of 20°C using a durometer type A.

[0055] 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]

[0056] Pneumatic tires (test tires) of Conventional Example 1, Comparative Example 1, and Examples 1 to 31 were manufactured, each having a tire size of 235 / 60R18 and the basic structure (cross-sectional structure) illustrated in FIG. 1 , with the following items set as shown in Tables 1 to 3 based on the outline of the tread surface of the convex rib in a meridian cross section of the tire when mounted on a regular rim and pressurized to a regular internal pressure in an unloaded state.

[0057] The "number of arcs" in Tables 1 to 3 refers to the number of arcs that make up the contour line on one side in the tire width direction relative to point p3, where point p1 is the end of the raised rib on one side in the tire width direction, point p2 is the end of the raised rib on the other side in the tire width direction, point P is the line segment connecting points p1 and p2, point p3 is the point on the contour line of the raised rib that is the longest from line P, and point p4 is the intersection of line P and the perpendicular to line P that passes through point p3. "b / W" and "b1 / b" refer to the ratio b1 / b of the distance b between points p3 and p4 and the perpendicular distance b1 between line P and line P at a position 80% of the distance ap between point p4 and point p1, moving from point p4 to point p1, and b / W is the ratio b / W of the length W of line P to the distance b.

[0058] The "Error from Function Curve" in Tables 1 to 3 indicates the error between the curve defined by the function of Equation (1) above and the contour of the convex rib when viewed as a curve on an XY coordinate system with the line connecting points p3 and p4 as the Y axis, the line connecting points 1 and p2 as the X axis, and point p4 as the origin. It is the maximum value of the distance between the function curve and the contour line made up of multiple arcs, measured on perpendicular lines to a line P drawn every 5% of the distance ap between points p1 and p4. The "Relationship to Equation (1)" column indicates the ratio a / ap of the radius a on the side of point p1 closer to point p4 on the X axis of the major axis of the curve defined by the function of Equation (1) above to the distance ap between points p1 and p4, the ratio b / a of the distance b between points p3 and p4 and the radius a, m in Equation (1) above, and n in Equation (1) above.

[0059] "ap1 / ap" in Tables 1 to 3 k ", "d N+1 / d N " is the Nth arc from point p3 side among multiple arcs, R N (N is an integer between 1 and k, and k is an integer between 4 and 5), and the arc R N and arc R N+1 The point connecting these points is point T N Let T be the point N The intersection point of the perpendicular line of the line P passing through the point x N , point p4 to point x N Distance to ap N , the kth arc R from point p3 k The intersection of the perpendicular line of the line P passing through the outer end of the tire width direction and the line P is the point x k , point p4 to point x k Distance to ap k When the distance ap1 and the distance ap k The ratio of ap1 / ap k , point x N and point x N+1 Distance d on the line P N and point x N+1 and point x N+2 Distance d on the line P N+1 Relative to d N+1 / d N is.

[0060] The "relationship of curvature radius" in Tables 1 to 3 is N The radius of curvature of r N The radius of curvature r when defined as N and the radius of curvature r N+1 The "position of p3" is the ratio of the distance from the midpoint of line P to point p3 to the length W of line P. "Hardness Hs" is the hardness of the tread rubber (cap tread rubber) that makes up the tread portion, and is a value measured at a temperature of 20°C using a durometer type A in accordance with JIS K6253.

[0061] These test tires were evaluated for straight running performance, cornering performance and squeal reduction performance on wet road surfaces using the following evaluation methods. The results are shown in Tables 1 to 3.

[0062] Straight-line performance on wet roads Each test tire was mounted on a standard rim (rim size 18 x 7J), inflated to an internal pressure of 250 KPa (standard internal pressure for passenger cars), and fitted to all wheels of a test vehicle (a passenger car with an engine displacement of 2000 cc). The vehicle was driven on a test course consisting of a wet road at a speed of 60 km / h, and five test drivers performed a sensory evaluation of the driving performance when driving on a straight road. The evaluation results were calculated by adding up the scores of the five drivers and are shown in the "Wet straight-line performance" column in the table as an index, with Conventional Example 1's value set at 100. A higher index value indicates better straight-line performance on wet roads.

[0063] Turning performance on wet roads Each test tire was mounted on a standard rim (rim size 18x7J), inflated to an internal pressure of 250 KPa (standard internal pressure for passenger cars), and fitted to all wheels of a test vehicle (a passenger car with an engine displacement of 2000 cc). The vehicle was driven on a test course consisting of a wet road surface at a speed of 60 km / h, and five test drivers performed a sensory evaluation of the cornering performance when entering a corner. The evaluation results were calculated by adding up the scores of the five drivers and are shown in the "Wet cornering performance" column in the table as an index, with Conventional Example 1's value set at 100. A higher index value indicates better cornering performance on wet roads.

[0064] 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.

[0065] [Table 1]

[0066] [Table 2]

[0067] [Table 3]

[0068] As is clear from Tables 1 to 3, the tires of Examples 1 to 31 improved the turning performance and squeal reduction performance on wet roads, achieving a good balance between these performances, while maintaining the straight-line running performance on wet roads at the same level as Conventional Example 1. On the other hand, in Comparative Example 1, the turning performance and squeal reduction performance on wet roads deteriorated because the convex ribs did not have an appropriate bulging shape.

[0069] 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 among the plurality of land portions extends continuously along the tire circumferential direction, and is a convex rib having a shape in which the outline of the tread surface bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim and has a regular internal pressure applied and is in an unloaded state, When the end of one side of the convex rib in the tire width direction is defined as point p1, the end of the other side of the convex rib in the tire width direction is defined as point p2, the line segment connecting point p1 and point p2 is defined as a straight line P, the point on the contour line of the convex rib that is the longest from the straight line P is defined as point p3, and the intersection of the straight line P and the perpendicular line to the straight line P that passes through point p3 is defined as point p4, On one side in the tire width direction of point p3 of the contour line of the tread surface of the convex rib, 80% or more of the length of the portion on the one side in the tire width direction of point p3 of the contour line of the tread surface of the convex rib is made up of a plurality of circular arcs, a vertical distance between the straight line P and the contour line of the protruding rib at a position that is 80% of the distance ap between the point p4 and the point p1 from the point p4 toward the point p1 is defined as a distance b1; When the perpendicular distance between the straight line P and the contour line of the protruding rib at a position that is 80% of the distance ap' between the point p4 and the point p2 from the point p4 toward the point p2 is defined as a distance b1', a distance b1 or a distance b1' on the contour line formed by the plurality of circular arcs satisfies the relationship of 0.3≦b1 / b<1 or 0.3≦b1' / b<1 with respect to the distance b between the point p3 and the point p4, and a length W of the straight line P and the distance b satisfy the relationship of 0.001≦b / W≦0.25. Invention [2] When the outline of the tread surface of the convex rib is viewed as a curve of XY coordinates with the line connecting the point p3 and the point p4 as the Y axis, the line connecting the point 1 and the point p2 as the X axis, and the point p4 as the origin, The tire according to invention [1], characterized in that the contour line formed by the plurality of circular arcs is approximated to a function curve selected from an elliptic function, a super elliptic function, a cycloid function, an epicycloid function, an involute function, and a power function on the XY coordinate system, and the distance between the function curve and the contour line formed by the plurality of circular arcs in a direction perpendicular to the straight line P is 5% or less of the distance b. Invention [3] The tire according to invention [2], characterized in that the function curve is defined by a function of the following formula (1) or (2):

number

number

[0070] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Belt reinforcement layer 11 Tread rubber layer 11C cap tread rubber layer 11U Undertread rubber layer 12 Side rubber layer 13 Rim cushion rubber layer 20 Circumferential main groove 30 Land 31 Shoulder Land Section 32 Convex rib CL Tire Equator

Claims

1. A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion includes at least two circumferential main grooves extending along the tire circumferential direction and a plurality of rows of land portions defined by the circumferential main grooves, At least one row of land portions among the plurality of land portions extends continuously along the tire circumferential direction, and is a convex rib having a shape in which the outline of the tread surface bulges outward in the tire radial direction in a meridian cross section of the tire when the tire is mounted on a regular rim and has a regular internal pressure applied and is in an unloaded state, When one end of the convex rib in the tire width direction is defined as point p1, the other end of the convex rib in the tire width direction is defined as point p2, the line segment connecting point p1 and point p2 is defined as a straight line P, the point on the contour line of the convex rib that is the greatest distance from the straight line P is defined as point p3, and the intersection of the straight line P and a perpendicular line to the straight line P that passes through point p3 is defined as point p4, On one side in the tire width direction of point p3 of the contour line of the tread surface of the convex rib, a portion of 80% or more of the length of the portion on the one side in the tire width direction of point p3 of the contour line of the tread surface of the convex rib is made up of a plurality of circular arcs, a distance b1 is a perpendicular distance between the straight line P and the contour line of the convex rib at a position that is 80% of a distance ap between the point p4 and the point p1 from the point p4 toward the point p1, When the perpendicular distance between the straight line P and the contour line of the convex rib at a position that is 80% of the distance ap′ between the point p4 and the point p2 from the point p4 toward the point p2 is defined as a distance b1′, a distance b1 or a distance b1' on the contour line formed by the plurality of circular arcs satisfies a relationship of 0.3≦b1 / b<1 or 0.3≦b1' / b<1 with respect to a distance b between the point p3 and the point p4, and a length W of the straight line P and the distance b satisfy a relationship of 0.001≦b / W≦0.

25.

2. When the outline of the tread surface of the convex rib is viewed as a curve of XY coordinates with the line connecting the points p3 and p4 as the Y axis, the line connecting the points 1 and p2 as the X axis, and the point p4 as the origin, 2. The tire according to claim 1, wherein the contour line formed by the plurality of circular arcs is approximated to a function curve selected from an elliptic function, a superelliptic function, a cycloid function, an epicycloid function, an involute function, and a power function on the XY coordinate system, and the distance between the function curve and the contour line formed by the plurality of circular arcs in a direction perpendicular to the straight line P is 5% or less of the distance b.

3. 3. The tire according to claim 2, wherein the function curve is defined by a function of the following formula (1) or (2): [Equation 1] [Equation 2] (In the above formulas (1) and (2), a is a radius of the major axis of the curve defined by the function of formula (1) on the X-axis closer to point p1 than point p4, and satisfies the relationship ap≦a≦ap×1.5 with respect to the distance ap between point p1 and point p4, a' is a radius of the major axis of the curve defined by the function of formula (2) on the X-axis closer to point p2 than point p4, and satisfies the relationship ap'≦a'≦ap'×1.5 with respect to the distance ap' between point p2 and point p4, b is a radius of the minor axis of the curve defined by the function of formula (1) or (2) on the Y axis closer to point p3 than point p4, and b coincides with the distance between point p3 and point p4, and satisfies the relationship 0.001≦b / a≦0.45 or 0.001≦b / a′≦0.45; The relationships n ≧ 1.5, m ≧ 1.5, and y > 0 are satisfied.

4. Among the plurality of circular arcs, the Nth circular arc from the point p3 side is R N (N is an integer between 1 and k, and k is an integer between 4 and 5), and the arc R N and arc R N+1 The point connecting these points is point T N Then, the arc R N and arc R N+1 That is, point T N have a common tangent at Said point T N The intersection point of the perpendicular line of the line P passing through the line P and the line P is the point x N , point p4 to point x N Distance to ap N , the kth arc from the point p3 side is R k The intersection of the perpendicular line of the straight line P passing through the outer end of the tire in the width direction and the straight line P is the point x k , point p4 to point x k Distance to ap k When the distance ap is defined as 1 and distance ap k That is, 0.1≦ap 1 / ap k ≦0.7 and the point x N and point x N+1 The distance d on the line P N and point x N+1 and point x N+2 The distance d on the line P N+1 Togad N ≧d N+1 3. The tire according to claim 1, wherein the following relationship is satisfied:

5. The distance d N and the distance d N+1 When N=1, 0.5≦d N+1 / d N ≦0.9, and when N≧1, 0.5≦d N+1 / d N 5. The tire according to claim 4, wherein the relationship: .lambda.<1 is satisfied.

6. The circular arc R N The radius of curvature of r N When defined as above, the radius of curvature r N and the radius of curvature r N+1 Togar N >r N+1 5. The tire according to claim 4, wherein the following relationship is satisfied:

7. 3. The tire according to claim 1, wherein the number k of the arcs constituting the contour line of the tread surface of the convex rib on one side of the point p3 in the tire width direction satisfies the relationship 4≦k≦10.

8. 3. The tire according to claim 1, wherein the point p3 is located within a range of 30% of the length W of the straight line P on both sides of the midpoint of the straight line P in the tire width direction.

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

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