Pneumatic tire

Abstract

To provide a pneumatic tire that can improve wet handling stability while maintaining excellent dry handling stability.SOLUTION: In a pneumatic tire of which an installation direction to a vehicle is designated, at least one row of a plurality of land parts 20 formed on a tread part 1 is a convex rib in which a contour line of a tread in a tire meridian cross section projects to a tire radial direction outer side, and when a position of a ground contact end E on the contour line of the tread part 1 is represented by a point PA, a position at 5% of a nominal tire width W from the ground contact end E to a tire width direction inner side is represented by a point PB, and a position at 10% of the tire nominal tire width W from the ground contact end E to the tire width direction inner side is represented by a point PC, a curvature radius SRin of a circular arc passing three points of the point PA, the point PB, and the point PC inside a vehicle, and a curvature radius SRout of a circular arc passing three points of the point PA, the point PB, and the point PC outside the vehicle satisfy the relationship of 1.1≤SRout / SRin≤2.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire having a specified mounting direction on a vehicle, and more particularly to a pneumatic tire that enables steering stability on both dry road surfaces and wet road surfaces. [Background technology]

[0002] It is known that the aspect ratio of pneumatic tires is set low (for example, an aspect ratio of approximately 30% to 50%) to improve handling stability on dry roads (dry handling stability) (see, for example, Patent Document 1). However, tires with low aspect ratios have a shorter contact length than tires with high aspect ratios (for example, tires with an aspect ratio of approximately 55% to 80%), which tends to make it difficult to ensure handling stability on wet roads (wet handling stability). Furthermore, pneumatic tires generally set to a negative camber have a shorter contact length on the outer side of the vehicle than on the inner side, which makes it difficult to prevent hydroplaning during cornering, making it difficult to ensure wet handling stability. Furthermore, when a vehicle rolls (when the vehicle tilts laterally during a turn) and the load shifts from the inner side of the vehicle to the outer side of the vehicle, the difference in contact length between the inner and outer sides of the vehicle results in insufficient drainage on the outer side of the vehicle, which can lead to sudden oversteer and other unstable vehicle behavior during cornering. Therefore, there is a demand for improving wet handling stability (particularly cornering performance on wet roads) while maintaining excellent dry handling stability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP Patent Publication No. 2008-126945 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a pneumatic tire that can improve wet steering stability while maintaining excellent dry steering stability. [Means for solving the problem]

[0005] In order to achieve the above object, a pneumatic tire of the present invention includes a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on the radially inner sides of the sidewall portions, and the pneumatic tire has at least one carcass layer mounted between the pair of bead portions, a plurality of belt layers arranged on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer arranged on the outer peripheral side of the belt layer, and the tire is fitted in a specified direction to a vehicle. In the pneumatic tire, at least three main grooves extending in a circumferential direction of the tire are formed in the tread portion, and at least four rows of land portions are defined by these main grooves, and at least one row of these land portions is a convex rib extending continuously around the entire circumference of the tire, and the convex rib has a contour line of the tread surface in a tire meridian cross section that includes a bulge portion protruding radially outward, and in the tire meridian cross section, the position of a ground contact edge on the contour line of the tread portion is designated as point P A , the position 5% of the nominal tire width inward from the contact edge in the tire width direction is point P B , the position 10% of the nominal tire width inward from the contact edge in the tire width direction is point P C When the vehicle is mounted, the point P A , said point P B , and said point P C The radius of curvature of the arc passing through these three points is SRin, and the point P is the outer side of the vehicle when the vehicle is installed. A , said point P B , and said point P C The radius of curvature SRout of the arc passing through these three points satisfies the relationship 1.1≦SRout / SRin≦2.0. [Effects of the Invention]

[0006] The inventors of the present invention conducted extensive research into the cross-sectional shape (profile) of pneumatic tires and discovered that while typical methods for improving wet performance, such as increasing groove area, result in a decrease in dry handling stability, the adoption of the above-described convex ribs with bulges increases ground pressure at the bulges, improving road contact characteristics when driving on wet roads and thereby improving wet performance. Furthermore, the provision of convex ribs maintains dry performance because increased groove area does not result in a decrease in land rigidity, thereby maintaining dry performance. Furthermore, the inventors of the present invention discovered that, while pneumatic tires typically have a negative camber, the contact length on the outer side of the vehicle tends to be shorter than the contact length on the inner side of the vehicle. By making the radius of curvature SRout on the outer side larger than the radius of curvature SRin on the inner side of the vehicle and lowering the vertical spring of the outer sidewall, the difference in contact length between the inner and outer sides of the vehicle (i.e., increasing the contact length on the outer side of the vehicle) can be reduced, thereby suppressing hydroplaning during cornering and improving wet handling stability. In addition, it was found that by reducing the difference in contact patch length between the inside and outside of the vehicle as described above, oversteer behavior during cornering can also be reduced, and in this respect, wet handling stability can also be improved. The present invention is based on these findings, and by making at least one row of land portions into a convex rib and ensuring that the curvature radius of the aforementioned portion satisfies the relationship 1.1≦SRout / SRin≦2.0, the aforementioned effects can be exerted in a balanced manner, improving wet handling stability while maintaining excellent dry handling stability, and achieving a high degree of compatibility between these performances.

[0007] In the present invention, the radius of curvature SRin on the vehicle inner side is preferably 30 mm to 200 mm, which is advantageous for improving wet steering stability because it ensures a sufficient contact patch length on the vehicle inner side and also ensures a sufficient contact patch length on the vehicle outer side due to the aforementioned ratio SRout / SRin.

[0008] In the present invention, it is preferable that the land portion disposed on the vehicle outer side and on the tire equator side of the tire among the land portions be a convex rib. By forming the land portion on the vehicle outer side as a convex rib in this way, it is advantageous for effectively preventing hydroplaning during cornering and improving wet handling stability.

[0009] In the present invention, it is preferable that the protrusion amount L of the convex rib satisfies the relationship 0.1%≦L / W×100≦5.0% relative to the width W of the convex rib, which allows the convex rib to bulge appropriately, which is advantageous for improving wet steering stability.

[0010] In the present invention, it is preferable that the land portion includes at least two rows of convex ribs adjacent in the tire width direction, and that the difference ΔL in the protrusion amounts of adjacent convex ribs in the tire width direction satisfies the relationship 0.1 mm≦ΔL≦0.8 mm. This reduces the difference in contact patch length between adjacent convex ribs and makes the contact patch lengths of adjacent convex ribs approximately uniform, thereby suppressing performance changes when load is transferred during cornering.

[0011] In the present invention, the tire section height is preferably 150 mm or less. Since a tire with such a small section height (low aspect tire) tends to have a shorter contact patch length in the shoulder region of the tread than a tire with a large section height (high aspect tire), application of the present invention makes it possible to effectively improve wet steering stability.

[0012] In the present invention, it is preferable that the groove area ratio Gin in the vehicle-inner region, which is located on the vehicle inner side of the tire equator, and the groove area ratio Gout in the vehicle-outer region, which is located on the vehicle outer side of the tire equator, satisfy the relationship Gin > Gout. By increasing the groove area ratio on the vehicle-inner side in this way, high drainage performance is achieved, which is advantageous for improving wet steering stability.

[0013] In the present invention, the cover cord constituting the belt cover layer is preferably a hybrid cord made of nylon fiber and aramid fiber. Such hybrid cords tend to have excellent cornering power, and therefore, by combining them with the present invention, wet steering stability at high speeds can be improved.

[0014] In the present invention, the carcass cords constituting the carcass layer are preferably rayon fiber cords. When the carcass layer is made of rayon fiber cords, it is desirable that the carcass layer has excellent vertical spring characteristics. Since excellent vertical spring characteristics can be obtained due to the relationship of the ratio SRout / SRin described above, wet steering stability at high speeds can be improved.

[0015] In the present invention, when the point where the outer surface of the bead portion separates from the rim flange in a rim-assembled state is defined as the rim separation point P1, the point where the sidewall portion protrudes furthest outward in the tire width direction at the tire's widest position is defined as the tire maximum protrusion point P2, and the angle formed by a line passing through rim separation point P1 and tire maximum protrusion point P2 with respect to the tire width direction is defined as the backlash angle, it is preferable that the backlash angle θin on the vehicle inner side and the backlash angle θout on the vehicle outer side satisfy 1.05≦θin / θout≦1.3. By setting the backlash angles in this way and making the backlash angle θin on the vehicle inner side greater than the backlash angle θout on the vehicle outer side, the vertical spring on the vehicle outer side can be increased, thereby improving ground contact pressure on the vehicle outer side, which is advantageous for improving drainage and wet performance.

[0016] In this invention, the term "tread edge" refers to the axial end of the contact area formed when a tire is mounted on a standard rim, inflated to the standard internal pressure, placed vertically on a flat surface, and subjected to a standard load. The term "standard rim" refers to the rim specified for each tire by the standard system, including the standard on which the tire is based. For example, the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. The term "standard internal pressure" refers to the air pressure specified for each tire by the standard system, including the standard on which the tire is based. For JATMA, the maximum air pressure is specified, for TRA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" table, and for ETRTO, the "INFLATION PRESSURE" is specified. However, if the tire is for a passenger car, the term is 180 kPa. "Normal load" is the load specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the maximum load capacity, for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "LOAD CAPACITY." However, if the tire is for a passenger car, it is a load equivalent to 88% of the above load.

[0017] In the present invention, the "rim-mounted state" when defining the "rim separation point" refers to a state in which the tire is mounted on the aforementioned "regular rim" and inflated to "regular internal pressure." The "tire maximum protrusion point" is the point at which the outer surface of the tire protrudes most outward in the tire width direction at the tire radial position (maximum tire width position) where the total tire width (tire cross-sectional width including patterns and lettering on the side of the tire) is at its maximum in the "rim-mounted state" similar to the "rim separation point." [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2]FIG. 2 is an explanatory diagram showing an enlarged view of a main part of the tread portion of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0020] As shown in Fig. 1, the pneumatic tire of the present invention includes a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on either side 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, and the symbol E indicates the ground-contact edge. 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 the 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.

[0021] A carcass layer 4 is mounted between a pair of left and right bead portions 3. This carcass layer 4 includes multiple reinforcing cords (carcass cords) extending in the tire radial direction and folded back from the inner side to the outer side in the tire width direction around bead cores 5 arranged in each bead portion 3. The material of the carcass cords constituting the carcass layer 4 is not particularly limited, and various materials commonly used in pneumatic tires can be used. However, when the carcass cords are rayon fiber cords, it is preferable to supplement the vertical spring characteristics by the tire structure, so this can be suitably combined with the present invention described below. A bead filler 6 is arranged on the outer periphery of the bead core 5, and this bead filler 6 is enclosed by the main portion and folded back portion of the carcass layer 4. The bead filler 6 has a generally triangular cross section, for example, as shown in the figure, and is made of a rubber composition.

[0022] Multiple belt layers 7 are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords (belt cords) inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between layers. In these belt layers 7, the reinforcing cords have an inclination angle with respect to the tire circumferential direction, for example, in the range of 10° to 40°. At least one belt cover layer 8 is provided on the outer periphery of the belt layer 7 for the purpose of improving high-speed durability. The belt cover layer 8 includes reinforcing cords (cover cords) oriented in the tire circumferential direction. In the belt cover layer 8, the reinforcing cords have an angle with respect to the tire circumferential direction, for example, in the range of 0° to 5°. The material of the cover cords constituting the belt cover layer 8 is not particularly limited, and various organic fiber cords commonly used in pneumatic tires can be used. However, when the cover cords are hybrid cords made of nylon fiber and aramid fiber, such hybrid cords tend to have excellent cornering power. Therefore, by applying them in combination with the present invention described below, wet steering stability at high speeds can be improved.

[0023] The pneumatic tire of the present invention is a tire for which the mounting direction of the front and back of the tire when mounted on a vehicle is specified. In Fig. 1, "IN" indicates the inside of the vehicle when mounted on the vehicle, and "OUT" indicates the outside of the vehicle when mounted on the vehicle. A tire for which the mounting direction on a vehicle is specified has a mounting direction indicator (not shown) formed, for example, on at least the sidewall portion 2 on the outside of the vehicle, which indicates the mounting direction on the vehicle. The mounting direction indicator displays, for example, the character string "OUTSIDE" along the tire circumferential direction on the outside of the vehicle, and displays, for example, the character string "INSIDE" along the tire circumferential direction on the inside of the vehicle.

[0024] As shown in FIG. 1 , the tire of the present invention has a tread portion 1 formed with at least three (four in the illustrated example) main grooves 10 extending in the tire circumferential direction, and these main grooves 10 define at least four (five in the illustrated example) rows of land portions 20. The main grooves 10 are grooves that perform the primary drainage function, and their groove widths are set in the range of 5.0 mm to 20.0 mm, and their groove depths are set in the range of 5.0 mm to 10.0 mm. In the following description, the pair of main grooves 10 located on both sides of the tire equator CL will be referred to as inner main grooves 11, the pair of main grooves 10 located on the outermost sides in the tire width direction will be referred to as outer main grooves 12, the land portion 20 defined between the pair of inner main grooves 11 will be referred to as center land portion 21, the land portion 20 defined between the inner main groove 11 and the outer main groove 12 will be referred to as intermediate land portion 22, and the land portion 20 defined on the outer side of the outer main groove 12 in the tire width direction will be referred to as shoulder land portion 23. Since the present invention mainly relates to the cross-sectional shape of the tire (the profile line from the shoulder land portion 23 to the bead portion 3 and the bulging shape of the convex rib A described below), the basic structure (internal structure) of the tire is not limited to the general structure described above.

[0025] In the present invention, at least one row of the at least four rows of land portions 20 described above is a convex rib A that extends continuously around the entire circumference of the tire. As shown enlarged in Fig. 2, the convex rib A is a rib whose tread contour in a tire meridian cross section includes a bulge that protrudes radially outward in the tire radial direction. Fig. 2 shows an enlarged view of the tread portion 1 on the vehicle outer side of the tire equator, depicting three rows of land portions: a part of the center land portion 21, an intermediate land portion 22 on the vehicle outer side, and a shoulder land portion 23 on the vehicle outer side. Of these, the intermediate land portion 22 and the shoulder land portion 23 on the vehicle outer side are configured as the convex rib A.

[0026] In addition to the above, in the present invention, as shown in FIG. 1, the position of the ground contact edge E on the contour line of the tread portion 1 in the tire meridian cross section is defined as point P A , point P at a position 5% of the tire nominal width NW inward in the tire width direction from the ground contact edge E B , the point P is 10% of the tire nominal width NW inward from the ground contact edge E in the tire width direction. C At this time, point P A , point PB , and point P C The radius of curvature of the arc passing through these three points is SRin, and point P A , point P B , and point P C The radius of curvature of the arc passing through these three points is SRout, and the ratio SRout / SRin of the radius of curvature SRin to the radius of curvature SRout satisfies the relationship 1.1≦SRout / SRin≦2.0, preferably 1.1≦SRout / SRin≦1.5. A , point P B , and point P C It is the radius of curvature of the arc drawn based on these three points, and depending on the tire shape, it may not completely match the contour line of the actual tire meridian cross section of the tread portion 1. Note that the tire nominal width W is a value generally displayed as the tire size, and is a different value from the cross section width SW used when determining the back angle (rim separation point) described below.

[0027] By employing the convex rib A as described above, the contact pressure at the bulging portion of the convex rib A increases, improving road contact characteristics when driving on wet roads and improving wet performance. Furthermore, by making the radius of curvature SRout on the vehicle outer side larger than the radius of curvature SRin on the vehicle inner side, the vertical spring of the vehicle outer sidewall portion 2 is lowered to reduce the difference in contact length between the vehicle inner side and the vehicle outer side (i.e., the contact length on the vehicle outer side, which tends to be shorter in pneumatic tires generally set to negative camber, is increased), thereby suppressing hydroplaning during cornering and improving wet handling stability. In addition, the aforementioned relationship between the ratio SRout / SRin reduces the difference in contact length between the vehicle inner side and the vehicle outer side, thereby suppressing oversteer behavior during cornering, further improving wet handling stability. Furthermore, because the above-described structure (convex rib A and ratio SRout / SRin) improves wet performance, for example, there is no reduction in the rigidity of the land portion 20 due to an increase in groove area, and dry performance can be maintained.

[0028] If the ratio SRout / SRin is less than 1.1, the difference in contact length between the inside and outside of the vehicle cannot be suppressed, and the effect of improving wet handling stability cannot be expected. If the ratio SRout / SRin exceeds 2.0, a sufficient contact length cannot be secured on the inside of the vehicle, and handling stability on both dry and wet roads decreases. If the convex rib A is not provided, the effect of improving ground pressure by the convex rib A (bulge portion) cannot be expected, and wet handling stability cannot be improved.

[0029] At least one row of the land portions 20 may be a convex rib A, but as shown in Figure 2, it is preferable that the land portion 20 on the vehicle outer side of the tire equator be a convex rib A. Furthermore, when multiple rows of land portions (for example, the illustrated intermediate land portion 22 and shoulder land portion 23) are included on the vehicle outer side, it is preferable that at least the land portion arranged on the tire equator CL side (i.e., the illustrated intermediate land portion 22) be a convex rib A, and more preferably, all land portions on the vehicle outer side (i.e., both the illustrated intermediate land portion 22 and the shoulder land portion 23) be a convex rib A. In this way, making the land portions on the vehicle outer side a convex rib A effectively suppresses hydroplaning during cornering and is advantageous for improving wet handling stability.

[0030] The protrusion amount L of the convex rib A, relative to the width W of the convex rib A, preferably satisfies the relationship 0.1%≦L / W×100≦5.0%, more preferably 0.3%≦L / W×100≦2.0%. This allows the convex rib A to bulge appropriately, which is expected to fully improve the ground contact pressure of the convex rib A (bulging portion), advantageously improving wet handling stability. If the L / W ratio is less than 0.1%, the convex rib A will not be able to ensure sufficient contact length, and drainage will not be sufficiently improved. If the L / W ratio exceeds 5.0%, the contact length of the convex rib A will be too long, preventing it from efficiently transmitting lateral force to the road surface during steering, making it difficult to maintain good dry handling stability. Furthermore, excessive contact pressure may result, reducing high-speed durability. Note that, when the protruding rib A has main grooves 10 on both sides in the tire width direction of the protruding rib A (for example, when the width Wm of the illustrated intermediate land portion 22 is shown), the width W of the protruding rib A is the length measured along the tire width direction between the edges p on both sides in the tire width direction of the protruding rib A. When the protruding rib A has main grooves 10 only on the inner side in the tire width direction of the protruding rib A (for example, when the width Ws of the illustrated shoulder land portion 23 is shown), the width W of the protruding rib A is the length measured along the tire width direction between the inner edge p of the protruding rib A in the tire width direction and the ground contact edge W. When the protruding rib A has main grooves 10 on both sides in the tire width direction of the protruding rib A (for example, when the protruding rib A has a protruding amount Lm of the illustrated intermediate land portion 22), the protruding amount L of the protruding rib A is the vertical distance from the reference line (see the dashed line in FIG. 2 ) to the most protruding point in a meridian cross section, the reference line passing through at least three of the four edges p at the openings of the two main grooves 10 adjacent to both sides in the tire width direction of the protruding rib A, having its center on the inner side in the tire radial direction, and having the maximum radius of curvature. Furthermore, when the main groove 10 is present only on the inner side of the convex rib A in the tire width direction (for example, in the case of the protrusion amount Ls of the shoulder land portion 23 shown in the figure), in the meridian cross section, the reference line (see the dashed line in Figure 2) is an arc with the maximum radius of curvature that passes through three points, the two edges p and the ground contact edge E at the opening of one main groove 10 adjacent to the inner side of the convex rib A in the tire width direction, and has its center on the inner side of the tire radial direction, and the distance is the vertical distance from this reference line to the most bulging point.The actual range of the protrusion amount L (protrusion amount Lm of the intermediate land portion 22, protrusion amount Ls of the shoulder land portion 23) is not particularly limited as it varies depending on the above ratio L / W depending on conditions such as tire size, but can be set to, for example, 0.1 mm to 1.0 mm.

[0031] When the land portions 20 include at least two rows of convex ribs A adjacent to each other in the tire width direction, for example, when the intermediate land portion 22 and the shoulder land portion 23 adjacent to each other in the tire width direction as shown in FIG. 2 are convex ribs A, the protrusion amount L (Lm, Ls) of each convex rib A may be the same, but preferably the protrusion amount L is larger for the land portion 20 closer to the tire equator CL (the intermediate land portion 22 in the illustrated example). For example, in the illustrated example, the protrusion amount Lm of the intermediate land portion 22 is preferably larger than the protrusion amount Ls of the shoulder land portion 23. When the protrusion amounts of the convex ribs A adjacent to each other in the tire width direction are different, the difference ΔL between the protrusion amounts of these convex ribs A (the difference between the protrusion amounts Lm and Ls in the illustrated example) preferably satisfies the relationship 0.1 mm≦ΔL≦0.8 mm, and more preferably satisfies the relationship 0.3 mm≦ΔL≦0.5 mm. This reduces the difference in contact length between adjacent convex ribs A and makes the contact lengths of adjacent convex ribs A approximately uniform, thereby suppressing performance changes during load transfer during cornering. If the difference in protrusion amount ΔL is less than 0.1 mm, the protrusion amounts are essentially the same, and the effect of reducing the difference in contact length between adjacent convex ribs A cannot be expected. If the difference in protrusion amount ΔL exceeds 0.8 mm, the contact length of the convex rib A on the side with the relatively larger protrusion amount becomes excessive, preventing efficient transmission of lateral force to the road surface during steering, making it difficult to maintain good dry handling stability. There is also a risk of excessive ground pressure and reduced high-speed durability.

[0032] The radius of curvature SRin on the vehicle inner side is preferably 30 mm to 200 mm, more preferably 30 mm to 100 mm. This ensures a sufficient contact length on the vehicle inner side, and also ensures a sufficient contact length on the vehicle outer side due to the aforementioned SRout / SRin ratio, which is advantageous for improving wet handling stability. If the radius of curvature SRin is less than 30 mm, the contact length on the vehicle inner side may not be sufficient, which may result in a decrease in handling stability on both dry and wet road surfaces. If the radius of curvature SRin exceeds 200 mm, the longer contact length may cause heat to accumulate in the shoulder area, which may worsen high-speed durability. The radius of curvature SRout on the vehicle outer side is not particularly limited, but may be set to, for example, 35 mm to 220 mm.

[0033] In addition to the above structure, in the present invention, in the rim-assembled state shown in Fig. 1, the point where the outer surface of the bead portion 3 separates from the rim flange of the rim R is defined as the rim separation point P1, and the point where the sidewall portion 2 protrudes furthest outward in the tire width direction at the tire's widest position (the position in the tire radial direction where the tire cross-sectional width SW is greatest) is defined as the tire maximum protrusion point P2. If the backlash angle is defined as the angle formed by a line passing through the rim separation point P1 and the tire maximum protrusion point P2 with respect to the tire width direction, the backlash angle θin on the vehicle-inboard side and the backlash angle θout on the vehicle-outboard side preferably satisfy the relationship 1.05≦θin / θout≦1.3, and more preferably 1.05≦θin / θout≦1.2. By setting the backlash angles in this way and making the backlash angle θin on the vehicle-inboard side greater than the backlash angle θout on the vehicle-outboard side, the vertical spring on the vehicle-outboard side can be increased, thereby improving ground contact pressure on the vehicle-outboard side, which is advantageous for improving drainage and wet performance. If the ratio θin / θout is less than 1.05, the rearward facing angles on the inside and outside of the vehicle will be substantially the same, making it impossible to expect the aforementioned effect of improving wet performance.If the ratio θin / θout exceeds 1.3, the difference in vertical spring strength of the sidewall portion 2 between the inside and outside of the vehicle will be large, resulting in a decrease in handling stability.

[0034] The rearward facing angle θin on the vehicle inner side is preferably 65° to 90°, and more preferably 70° to 80°. This ensures sufficient vertical spring in the sidewall portion 2 on the vehicle inner side, which is advantageous for improving load durability. If the rearward facing angle θin is less than 65°, sufficient vertical spring cannot be ensured, and the effect of improving load durability will be limited. The rearward facing angle θout on the vehicle outer side is not particularly limited, but can be set to, for example, 62° to 85°. Note that, due to the structure, the rearward facing angles θin and θout of a rim-mounted pneumatic tire will not exceed 90°.

[0035] The present invention described above can be applied to various pneumatic tires. While tires with a small cross-sectional height (low aspect tires) have excellent dry handling stability, they tend to have a shorter contact length in the shoulder region (shoulder land portion 21) of the tread portion 1 compared to tires with a large cross-sectional height (high aspect tires). Therefore, applying the present invention can effectively improve wet handling stability. Specifically, the tire cross-sectional height of a pneumatic tire to which the present invention is applied is preferably 150 mm or less. Furthermore, from the viewpoint of improving dry handling stability, the aspect ratio of a pneumatic tire to which the present invention is applied is preferably 20% to 55%, more preferably 35% to 55%.

[0036] While the tread pattern in the tread portion 1 of a pneumatic tire to which the present invention is applied is not particularly limited, it is preferable that the groove area ratio Gin in the vehicle-inner region, which is on the vehicle inner side of the tire equator CL, and the groove area ratio Gout in the vehicle-outer region, which is on the vehicle outer side of the tire equator CL, satisfy the relationship Gin > Gout. In particular, it is preferable that the difference (Gin - Gout) between the groove area ratio Gin in the vehicle-inner region and the groove area ratio Gout in the vehicle-outer region be 1% or more. With a tread pattern having a high groove area ratio on the vehicle-inner side, high drainage performance is achieved on the vehicle-inner side, which has a long contact length, and wet handling stability based on the tread pattern can be further improved.

[0037] 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]

[0038] The tire has the basic structure (internal structure) illustrated in FIG. 1, and the tire cross-sectional shape (profile line) in the tire meridian cross section is A ) and a point 5% of the nominal tire width inward from the contact edge E in the tire width direction (point P B ) and a position 10% of the nominal tire width inward from the contact edge E in the tire width direction (point P C ) and SRout (vehicle exterior) are the radius of curvature of the arc passing through these three points. The ratio SRout / SRin, radius of curvature SRout, radius of curvature SRin, presence or absence of convex ribs, arrangement of convex ribs, relationship between the protrusion amount Lm and width Wm of the intermediate land portion when the intermediate land portion is a convex rib (Lm / Wm × 100%), relationship between the protrusion amount Ls and width Ws of the shoulder land portion when the shoulder land portion is a convex rib (Ls / Ws × 100%), difference in protrusion amount ΔL (= Lm Pneumatic tires (test tires) of Conventional Examples, Comparative Examples 1 and 2, and Examples 1 to 11 were manufactured with the following settings as shown in Tables 1 and 2: the groove area ratio (θin / θout), the cover cord material, the carcass cord material, the ratio of the rear angle θin (inner side of the vehicle) and the rear angle θout (outer side of the vehicle) when the angle formed by a straight line passing through the rim separation point P1 and the tire maximum protrusion point P2 in the rim-assembled state with respect to the tire width direction, the rear angle θout, and the rear angle θin. The test tires had front tire sizes of 275 / 45R21 110Y and rear tire sizes of 315 / 40R21 115Y.

[0039] The "Positive Rib Arrangement" columns in Tables 1 and 2 indicate whether the land area is on the vehicle's inner or outer side, and whether the center land area, intermediate land area, or shoulder land area has a positive rib. For example, "Vehicle Outer Side, Intermediate + Shoulder" indicates that the two rows of land areas on the vehicle's outer side, the intermediate land area, and the shoulder land area, have positive ribs. The "Groove Area Ratio Magnitude Relationship" columns in Tables 1 and 2 indicate the magnitude relationship between the groove area ratio Gin in the inner region of the tread, which is located on the inner side of the tire equator, and the groove area ratio Gout in the outer region of the tread, which is located on the outer side of the tire equator, using equal or inequality signs. The "Cover Cord Material" and "Carcass Cord Material" columns in Tables 1 and 2 list the type of organic fiber that makes up each cord. Note that hybrid cords made of nylon and aramid fibers are listed as "Nylon + Aramid."

[0040] These test tires were evaluated for dry steering stability, wet steering stability, and high-speed durability by the following test methods, and the results are shown in Tables 1 and 2.

[0041] Dry steering stability Each test tire was mounted on a 21x9.5J rim wheel for the front tire and a 21x11.5J rim wheel for the rear tire, and mounted on a 4000cc SUV (4WD). Both the front and rear tires were inflated to an air pressure of 250kPa, and a test driver conducted a sensory evaluation of handling stability (especially straight-line stability and linearity) on a test course consisting of a dry paved surface (dry road surface). The evaluation results were expressed as an index with the conventional example being 100. The higher the index value, the better the dry handling stability.

[0042] Wet driving stability Each test tire was mounted on a 21x9.5J rim wheel for the front tire and a 21x11.5J rim wheel for the rear tire, and mounted on a 4000cc SUV (4WD). Both the front and rear tires were inflated to an air pressure of 250kPa, and a test driver conducted a sensory evaluation of handling stability (particularly the ability to suppress hydroplaning during cornering and linearity) on a test course consisting of a wet paved road surface (wet road surface). The evaluation results were expressed as an index, with the conventional example being set at 100. The higher the index value, the better the wet handling stability.

[0043] fast durability Each test tire was mounted on a wheel with a rim size of 21 x 9.5J for the front tires and 21 x 11.5J for the rear tires, and then mounted on an indoor drum testing machine (drum diameter: 1707mm). The tire was inflated to 360kPa, subjected to 68% of the maximum load specified by the ETRTO standard, and tested at a camber angle of -3°. The speed was increased by 10km / h every 10 minutes, and the maximum speed reached when the tire broke was measured. The evaluation results were expressed as an index, with the value of the conventional tire being 100. The higher the index value, the higher the maximum speed reached when the tire broke, indicating better high-speed durability.

[0044] [Table 1]

[0045] [Table 2]

[0046] As can be seen from Tables 1 and 2, the tires of Examples 1 to 11 improved dry steering stability, wet steering stability, and high-speed durability compared to the conventional tires, achieving a high degree of compatibility between these performances. On the other hand, in Comparative Example 1, the ratio SRout / SRin did not satisfy the conditions of the present invention, so wet steering stability could not be sufficiently improved, and the effect of improving high-speed durability could not be obtained. In Comparative Example 2, since no convex ribs were provided, wet steering stability could not be sufficiently improved.

[0047] The present disclosure encompasses the following inventions. Invention [1] A pneumatic tire having a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on the tire radially inward side of the sidewall portions, and having at least one carcass layer mounted between the pair of bead portions, a plurality of belt layers arranged on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer arranged on the outer peripheral side of the belt layer, and having a specified mounting direction on a vehicle, At least three main grooves extending in the tire circumferential direction are formed in the tread portion, and at least four rows of land portions are defined by these main grooves, and at least one row of these land portions is a convex rib that extends continuously around the entire tire circumference, and the convex rib includes a bulge portion where the outline of the tread surface in a tire meridian cross section protrudes outward in the tire radial direction, In the tire meridian cross section, the contact edge position on the contour line of the tread portion is defined as point P A , the position 5% of the nominal tire width inward from the contact edge in the tire width direction is point P B , the position 10% of the nominal tire width inward from the contact edge in the tire width direction is point P C When the vehicle is mounted, the point P A , said point P B , and said point P C The radius of curvature of the arc passing through these three points is SRin, and the point P is the outer side of the vehicle when the vehicle is installed. A , said point P B , and said point P Cand a radius of curvature SRout of an arc passing through the three points satisfy the relationship 1.1≦SRout / SRin≦2.0. Invention [2] The pneumatic tire according to invention [1], wherein the radius of curvature SRin on the inner side of the vehicle is 30 mm to 200 mm. Invention [3] A pneumatic tire according to invention [1] or [2], characterized in that the land portion arranged on the vehicle outer side and on the tire equator side from the tire equator among the land portions is the convex rib. Invention [4] A pneumatic tire according to any one of inventions [1] to [3], characterized in that the protrusion amount L of the convex rib satisfies the relationship 0.1%≦L / W×100≦5.0% with respect to the width W of the convex rib. Invention [5] A pneumatic tire according to any one of inventions [1] to [4], characterized in that the land portion includes at least two rows of convex ribs adjacent in the tire width direction, and the difference ΔL in the protrusion amount of the convex ribs adjacent in the tire width direction satisfies the relationship 0.1 mm≦ΔL≦0.8 mm. Invention [6] The pneumatic tire according to any one of inventions [1] to [5], characterized in that the tire cross-sectional height is 150 mm or less. Invention [7] A pneumatic tire according to any one of inventions [1] to [6], characterized in that in the tread portion, a groove area ratio Gin in a vehicle inner region that is on the vehicle inner side of the tire equator and a groove area ratio Gout in a vehicle outer region that is on the vehicle outer side of the tire equator satisfy the relationship Gin > Gout. Invention [8] The pneumatic tire according to any one of inventions [1] to [7], wherein the cover cord constituting the belt cover layer is a hybrid cord made of nylon fiber and aramid fiber. Invention [9] The pneumatic tire according to any one of inventions [1] to [8], wherein the carcass cords constituting the carcass layer are rayon fiber cords. Invention

[10] A pneumatic tire according to any one of inventions [1] to [9], characterized in that, when the point at which the outer surface of the bead portion separates from the rim flange in a rim-assembled state is defined as a rim separation point P1, the point at which the sidewall portion protrudes furthest outward in the tire width direction at the tire's widest position is defined as a tire maximum protrusion point P2, and the angle formed by a line passing through the rim separation point P1 and the tire maximum protrusion point P2 with respect to the tire width direction is defined as a rearward angle, the rearward angle θin on the vehicle inner side and the rearward angle θout on the vehicle outer side satisfy 1.05≦θin / θout≦1.3. [Explanation of symbols]

[0048] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Belt cover layer 10 Main groove 11 Inner main groove 12 Outer main groove 20 Land 21 Center Land Division 22 Intermediate land area 23 Shoulder land area A Convex rib CL Tire Equator E Ground end R rim

Claims

1. A pneumatic tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, the pneumatic tire having at least one carcass layer mounted between the pair of bead portions, a plurality of belt layers disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer disposed on the outer peripheral side of the belt layer, the pneumatic tire having a specified mounting direction on a vehicle, At least three main grooves extending in the tire circumferential direction are formed in the tread portion, and at least four rows of land portions are defined by these main grooves, and at least one row of these land portions is a convex rib that extends continuously around the entire tire circumference, and the convex rib includes a bulge portion where the outline of the tread surface in a tire meridian cross section protrudes outward in the tire radial direction, In the tire meridian cross section, the contact edge position on the contour line of the tread portion is defined as point P A , the position 5% of the nominal tire width inward from the ground edge in the tire width direction is set to point P B , the position 10% of the nominal tire width inward from the ground edge in the tire width direction is set to point P C When the vehicle is mounted, the point P A , said point P B , and said point P C The radius of curvature SRin of the arc passing through these three points is the point P A , said point P B , and said point P C and a radius of curvature SRout of an arc passing through the three points satisfies the relationship 1.1≦SRout / SRin≦2.

0.

2. 2. The pneumatic tire according to claim 1, wherein the radius of curvature SRin on the vehicle inner side is 30 mm to 200 mm.

3. 3. The pneumatic tire according to claim 1, wherein the land portion disposed on the vehicle outer side and on the tire equator side of the tire equator is the convex rib.

4. 3. The pneumatic tire according to claim 1, wherein a protrusion amount L of the convex rib satisfies the relationship 0.1%≦L / W×100≦5.0% with respect to a width W of the convex rib.

5. 3. The pneumatic tire according to claim 1, wherein the land portion includes at least two rows of convex ribs adjacent to each other in the tire width direction, and a difference ΔL in the protrusion amounts of the convex ribs adjacent to each other in the tire width direction satisfies the relationship 0.1 mm≦ΔL≦0.8 mm.

6. 3. The pneumatic tire according to claim 1, wherein the tire cross section height is 150 mm or less.

7. 3. The pneumatic tire according to claim 1, wherein in the tread portion, a groove area ratio Gin in a vehicle inner region that is on the vehicle inner side of the tire equator and a groove area ratio Gout in a vehicle outer region that is on the vehicle outer side of the tire equator satisfy the relationship Gin > Gout.

8. 3. The pneumatic tire according to claim 1, wherein the cover cord constituting the belt cover layer is a hybrid cord made of nylon fiber and aramid fiber.

9. 3. The pneumatic tire according to claim 1, wherein the carcass cords constituting the carcass layer are rayon fiber cords.

10. 3. The pneumatic tire according to claim 1, wherein the point at which the outer surface of the bead portion separates from the rim flange in a rim-mounted state is defined as a rim separation point P1, the point at which the sidewall portion protrudes furthest outward in the tire width direction at the tire's widest position is defined as a tire maximum protrusion point P2, and the angle formed by a straight line passing through the rim separation point P1 and the tire maximum protrusion point P2 with respect to the tire width direction is defined as a rearward facing angle θin on the vehicle inner side and the rearward facing angle θout on the vehicle outer side satisfy 1.05≦θin / θout≦1.3.

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