Pneumatic tire

Abstract

To provide a pneumatic tire which can achieve both wear performance and wet performance.SOLUTION: A pneumatic tire 1 includes a tread part 2 having a contact surface 2s, and is used while being mounted on a rim. The rim diameter RD of the rim is 10 to 18 inches, and the rim width RW is 78% to 99% of a cross-sectional width SW of the tire. A ratio SH / SW of the cross-sectional height SH of the tire to the cross-sectional width SW is 30% to 45%. The tread part 2 has at least two circumferential direction grooves 6 continuously extending in a tire circumferential direction, and a plurality of land parts 7 partitioned by the circumferential direction grooves 6. A sum Sc1 of contact areas of the land parts 7 at the time of brand-new is 80% to 95% of the total area S of a virtual contact surface filling all the grooves including the circumferential groove 6. The maximum groove width W1 of the circumferential groove 6 at the time of brand-new is 1.0% to 5.3% of the maximum contact length L1 in the tire circumferential direction when a normal load is loaded on the tire in a normal state, and a maximum contact length L1 in the tire circumferential direction when being contacted to a plane at a camber angle of 0°.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire that is mounted on a rim when used. [Background technology]

[0002] Small-diameter pneumatic tires suitable for use on small shuttle buses, etc. For example, Patent Document 1 below proposes a pneumatic tire with improved durability in the bead portion where strain is concentrated due to the small diameter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-102627 Summary of the Invention [Problem to be solved by the invention]

[0004] However, small-diameter pneumatic tires used on heavy vehicles, such as those described in Patent Document 1, have a short contact patch length and a wide contact patch width, meaning that they have a wide contact patch shape, making it difficult to achieve both good wear performance and good wet performance.

[0005] The present invention was devised in consideration of the above-described circumstances, and its main object is to provide a pneumatic tire that is wide and small in diameter, and that can achieve both good wear performance and good wet performance. [Means for solving the problem]

[0006] The present invention provides a pneumatic tire that is mounted on a rim and used, the pneumatic tire having a tread portion with a contact patch, the rim diameter RD of the rim being 10 to 18 inches, the rim width RW of the rim being 78% to 99% of the tire's section width SW, and a ratio SH / SW of the tire's section height SH to the section width SW being 30% to 45%, the tread portion having at least two circumferential grooves extending continuously in the tire circumferential direction and a plurality of land portions separated by the at least two circumferential grooves, the sum Sc1 of the contact areas of the plurality of land portions in a new state being 80% to 95% of the total area S of a virtual contact patch that fills all grooves including the at least two circumferential grooves, and the maximum groove width W1 of the at least two circumferential grooves in a new state being 1.0% to 5.3% of the maximum contact length L1 in the tire circumferential direction when the tire is in a normal state, is loaded with a normal load, and contacts the ground on a flat surface with a camber angle of 0°. [Effects of the Invention]

[0007] By having the above-described configuration, the pneumatic tire of the present invention can achieve both good wear performance and good wet performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an embodiment of a pneumatic tire of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the shape of the contact surface when new. [Figure 3] FIG. 1 is a schematic diagram showing the contact patch shape at 80% wear. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a tire meridian cross-sectional view showing a new pneumatic tire 1 in a normal state according to this embodiment. Here, the "normal state" refers to a state in which the pneumatic tire 1 is mounted on a normal rim, and is adjusted to a normal internal pressure and is unloaded. Unless otherwise specified below, the dimensions of each part of the pneumatic tire 1 are values ​​measured in this normal state. Furthermore, the "new state" refers to a state in which the tread portion 2, which will be described later, is not worn.

[0010] If there is a standard system including the standard on which the pneumatic tire 1 is based, a "genuine rim" is a rim defined for each tire by that standard, for example, a "standard rim" for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO. If there is no standard system including the standard on which the pneumatic tire 1 is based, a "genuine rim" is a rim that can be assembled and does not cause air leakage, and has the smallest rim diameter RD and the smallest rim width RW among those rims.

[0011] "Normal internal pressure" is the air pressure set for each tire by a standard set by the JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for the TRA, and the "INFLATION PRESSURE" for the ETRTO. If there is no standard set that includes the standard set by the pneumatic tire 1, "normal internal pressure" is the air pressure set for each tire by the manufacturer, etc.

[0012] 1, the pneumatic tire 1 of this embodiment is mounted on a rim for use, and has a small diameter, a short contact length, and a wide contact width, i.e., a wide contact patch. When used in a small bus, a low-floor electric vehicle, or the like, this pneumatic tire 1 can increase the interior space and the space inside the rim, thereby improving transportation efficiency and accommodating larger diameter brakes, larger in-wheel motors, and the like.

[0013] The rim diameter RD of the rim on which the pneumatic tire 1 of this embodiment is mounted is 10 to 18 inches. A rim diameter RD of 10 inches or more ensures sufficient space inside the rim. A rim diameter RD of 18 inches or less helps to increase the interior space of a minibus, low-floor electric vehicle, etc.

[0014] The rim width RW of the rim in this embodiment is 78% to 99% of the tire cross-sectional width SW. Here, the rim width RW of the rim corresponds to the width between a pair of outer surfaces 4s in the tire axial direction on the inner side in the tire radial direction of the pneumatic tire 1 in a normal state. The cross-sectional width SW is the width in the tire axial direction between a pair of tire maximum width positions in the profile of the pneumatic tire 1 excluding partially protruding portions.

[0015] By making the rim width RW 78% or more of the cross-sectional width SW, it is possible to maintain sufficient air volume to support the total vehicle weight. By making the rim width RW 99% or less of the cross-sectional width SW, it is useful for supporting high loads such as those of small buses and low-floor electric vehicles.

[0016] The ratio SH / SW of the tire's section height SH to its section width SW of the pneumatic tire 1 of this embodiment is 30% to 45%. Here, the tire's section height SH is the height in the tire radial direction from the bead base line BL to the tire equator C. The bead base line BL is an imaginary line corresponding to the rim diameter RD of the rim. The ratio SH / SW is a value generally known as the aspect ratio.

[0017] A SH / SW ratio of 30% or more allows sufficient air volume to be maintained to support the total vehicle weight. A SH / SW ratio of 45% or less prevents the tire's outer diameter SD from becoming excessively large, which helps to increase the interior space of minibuses, low-floor electric vehicles, etc.

[0018] The pneumatic tire 1 of this embodiment includes a tread portion 2 having a contact surface 2s. The pneumatic tire 1 preferably includes a pair of sidewall portions 3 extending radially inward from both axial sides of the tread portion 2, and bead portions 4 located radially inward of each of the pair of sidewall portions 3.

[0019] Each of the pair of bead portions 4 has, for example, an annular bead core 5 extending in the tire circumferential direction. The bead core 5 is formed of, for example, a steel wire. Here, the axially outer surface 4s of the bead portion 4 on the radially inner side of the pneumatic tire 1 described above is the axially outer surface 4s of the bead portion 4.

[0020] The tread portion 2 of this embodiment has at least two circumferential grooves 6 extending continuously in the tire circumferential direction, and a plurality of land portions 7 separated by the at least two circumferential grooves 6. When new, the circumferential grooves 6 desirably have a maximum groove width W1 at the opening on the outer side in the tire radial direction smaller than a maximum groove width W4 near the groove bottom on the inner side in the tire radial direction.

[0021] Such circumferential grooves 6 can secure a contact area when new and improve the wear performance of the pneumatic tire 1. Furthermore, such circumferential grooves 6 can improve the wet performance of the pneumatic tire 1 at the end of wear by increasing the maximum groove width W4 near the groove bottom.

[0022] Fig. 2 is a schematic diagram showing the contact patch shape when a new, normal tire is loaded with a normal load and contacts the ground on a flat surface with a camber angle of 0°. In Fig. 2, two circumferential grooves 6 are formed in a straight line, but this is not limited to this. As long as there are two or more circumferential grooves 6, there may be three or four circumferential grooves 6, or the circumferential grooves 6 may extend in a zigzag pattern. Also, although Fig. 2 shows only circumferential grooves 6 as grooves, the tread portion 2 may have lateral grooves or sipes extending in a direction intersecting the tire circumferential direction.

[0023] Here, the "normal load" is the load determined for each tire by a standard system that includes the standard on which the pneumatic tire 1 is based, if such a system exists; for example, it is the "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and the "LOAD CAPACITY" for ETRTO. If there is no standard system that includes the standard on which the pneumatic tire 1 is based, the "normal load" is the load determined for each tire by the manufacturer or the like as the maximum load that can be applied when using the pneumatic tire 1.

[0024] 1 and 2, the sum Sc1 of the contact areas of the multiple land portions 7 when new is preferably 80% to 95% of the total area S of the virtual contact patch that fills all grooves, including at least two circumferential grooves 6. When the sum Sc1 of the contact areas when new is 80% or more of the total area S of the virtual contact patch, the wear performance of the pneumatic tire 1 when new can be improved. When the sum Sc1 of the contact areas when new is 95% or less of the total area S of the virtual contact patch, it helps to ensure the wet performance of the pneumatic tire 1 when new.

[0025] The maximum groove width W1 of the at least two circumferential grooves 6 in a new state is preferably 1.0% to 5.3% of the maximum contact length L1 in the circumferential direction of the tire when the tire is in a normal state, is subjected to a normal load, and is in contact with a flat surface with a camber angle of 0°.

[0026] When the maximum groove width W1 of the circumferential grooves 6 in a new state is 1.0% or more of the maximum contact length L1, it is possible to improve the wet performance of the pneumatic tire 1 in a new state. When the maximum groove width W1 of the circumferential grooves 6 in a new state is 5.3% or less of the maximum contact length L1, it is possible to improve the wear performance of the pneumatic tire 1 in a new state. Therefore, the pneumatic tire 1 of this embodiment can achieve both good wear performance and good wet performance.

[0027] In a more preferred embodiment, the maximum groove width W2 of the at least two circumferential grooves 6 at 20% wear is 1.0% to 5.3% of the maximum contact length L1. Here, 20% wear refers to an initial state of wear where the tire has worn 20% when the amount of wear from a new tire to the wear limit is taken as 100%.

[0028] By making the maximum groove width W2 of the circumferential grooves 6 at 20% wear 1.0% or more of the maximum contact length L1, it is possible to improve the wet performance in the early stage of wear of the pneumatic tire 1. By making the maximum groove width W2 of the circumferential grooves 6 at 20% wear 5.3% or less of the maximum contact length L1, it is possible to improve the wear performance in the early stage of wear of the pneumatic tire 1.

[0029] It is desirable that the maximum groove width W2 of the circumferential groove 6 at 20% wear is equal to the maximum groove width W1 of the circumferential groove 6 when new. Such a pneumatic tire 1 can maintain equivalent wear performance and wet performance from when new to the initial stage of wear.

[0030] The sum Sc2 of the contact areas of the multiple land portions 7 at 20% wear is preferably 80% to 95% of the total area S of the virtual contact patch. When the sum Sc2 of the contact areas at 20% wear is 80% or more of the total area S of the virtual contact patch, the wear performance of the pneumatic tire 1 in the early stage of wear can be improved. When the sum Sc2 of the contact areas at 20% wear is 95% or less of the total area S of the virtual contact patch, it helps to ensure the wet performance of the pneumatic tire 1 in the early stage of wear.

[0031] The maximum groove width W3 of the at least two circumferential grooves 6 at 50% wear is preferably 1.5% to 6.8% of the maximum contact length L1. Here, 50% wear refers to a state in the middle of wear where the tire has worn 50% when the amount of wear from a new tire to the wear limit is taken as 100%.

[0032] By making the maximum groove width W3 of the circumferential groove 6 at 50% wear 1.5% or more of the maximum contact length L1, it is possible to improve wet performance when the groove depth becomes smaller in the middle stage of wear of the pneumatic tire 1. By making the maximum groove width W3 of the circumferential groove 6 at 50% wear 6.8% or less of the maximum contact length L1, it is possible to maintain good wear performance in the middle stage of wear of the pneumatic tire 1.

[0033] The sum Sc3 of the contact areas of the multiple land portions 7 at 50% wear is preferably 75% to 95% of the total area S of the virtual contact patch. When the sum Sc3 of the contact areas at 50% wear is 75% or more of the total area S of the virtual contact patch, the wear performance of the pneumatic tire 1 in the middle stage of wear can be improved. When the sum Sc3 of the contact areas at 50% wear is 95% or less of the total area S of the virtual contact patch, it helps to ensure the wet performance of the pneumatic tire 1 in the middle stage of wear.

[0034] The maximum groove width W4 of the at least two circumferential grooves 6 at 80% wear is preferably 5.8% to 10.5% of the maximum contact length L1. Here, 80% wear refers to the final stage of wear where the tire has worn 80% when the amount of wear from a new tire to the wear limit is taken as 100%.

[0035] By making the maximum groove width W4 of the circumferential groove 6 at 80% wear 5.8% or more of the maximum contact length L1, it is possible to improve wet performance when the groove depth becomes extremely small at the end of wear of the pneumatic tire 1. By making the maximum groove width W4 of the circumferential groove 6 at 80% wear 10.5% or less of the maximum contact length L1, it is possible to maintain good wear performance even at the end of wear of the pneumatic tire 1.

[0036] The sum Sc4 of the contact areas of the multiple land portions 7 at 80% wear is preferably 70% to 85% of the total area S of the virtual contact patch. When the sum Sc4 of the contact areas at 80% wear is 70% or more of the total area S of the virtual contact patch, the wear performance of the pneumatic tire 1 can be maintained even in the final stage of wear. When the sum Sc4 of the contact areas at 80% wear is 85% or less of the total area S of the virtual contact patch, the wet performance of the pneumatic tire 1 can be maintained in the final stage of wear.

[0037] Fig. 3 is a schematic diagram showing the shape of the contact patch when a tire in a normal state at 80% wear is loaded with 40% of the normal load and contacts the ground on a flat surface with a camber angle of 0°. As shown in Fig. 3, the maximum groove width W4 of the circumferential groove 6 at 80% wear is preferably 50% to 75% of the tire circumferential contact length L2 when a tire in a normal state is loaded with 40% of the normal load and contacts the ground on a flat surface with a camber angle of 0°.

[0038] By making the maximum groove width W4 of the circumferential grooves 6 at 80% wear 50% or more of the contact length L2 at 40% load, it is possible to suppress hydroplaning, which is likely to occur when driving at high speeds with no load, and improve the wet performance at the end of wear of the pneumatic tire 1. By making the maximum groove width W4 of the circumferential grooves 6 at 80% wear 75% or less of the contact length L2 at 40% load, it is possible to maintain the rigidity of the tread portion 2 and ensure the braking performance at the end of wear of the pneumatic tire 1.

[0039] 1, the pneumatic tire 1 preferably includes a carcass 8 extending from a tread portion 2 to a pair of bead portions 4, and a belt layer 9 disposed in the tread portion 2. The carcass 8 includes at least one carcass ply 8A, 8B, and in this embodiment, two carcass plies.

[0040] The two carcass plies 8A, 8B include, for example, a first carcass ply 8A located on the radially inner side of the tire in the tread portion 2, and a second carcass ply 8B located on the radially outer side of the first carcass ply 8A in the tire. Such a carcass 8 can exhibit strength suitable for supporting a heavy load of a minibus, a low-floor electric vehicle, etc.

[0041] At least one of the carcass plies 8A, 8B preferably includes a main body portion 8a extending from the tread portion 2 through the pair of sidewall portions 3 to the bead cores 5 of the pair of bead portions 4, and a pair of turned-up portions 8b continuing to the main body portion 8a. Each of the pair of turned-up portions 8b is, for example, a portion that is turned up around each of the pair of bead cores 5 from the axially inner side to the axially outer side of the tire.

[0042] In this embodiment, each of the first carcass ply 8A and the second carcass ply 8B includes a main body portion 8a and a turned-up portion 8b. The first carcass ply 8A and the second carcass ply 8B have improved side strength due to the turned-up portions 8b, and are suitable for supporting high loads in vehicles such as minibuses and low-floor electric vehicles.

[0043] The carcass plies 8A, 8B include carcass cords (not shown) made of, for example, organic fiber cords, such as cords made of one or more hybrid fibers selected from the group consisting of polyethylene terephthalate fiber, polyethylene naphthalate fiber, nylon fiber, aramid fiber, and rayon fiber.

[0044] The carcass cords are preferably arranged at an angle of 25 to 90° with respect to the circumferential direction of the tire. Here, the angle of the carcass cords is the angle in a tire in a normal state, and can be confirmed, for example, by partially peeling off the tread portion 2.

[0045] When the carcass cords are inclined at an angle of less than 90° with respect to the tire circumferential direction, it is desirable that the carcass cords of the first carcass ply 8A and the carcass cords of the second carcass ply 8B be inclined in opposite directions with respect to the tire circumferential direction. For example, a bias structure may be employed for the carcass 8. Such carcass plies 8A, 8B are suitable for supporting a heavy load in vehicles such as minibuses and low-floor electric vehicles.

[0046] The belt layer 9 includes at least one, preferably two or more, and in this embodiment, two belt plies 9A and 9B. The two belt plies 9A and 9B include, for example, a first belt ply 9A located on the radially inner side of the tire and a second belt ply 9B located on the radially outer side of the first belt ply 9A. Such a belt layer 9 can improve the rigidity of the tread portion 2 and is suitable for supporting a heavy load.

[0047] The belt plies 9A and 9B include, for example, belt cords (not shown) made of steel cords. The belt cords may be, for example, solid steel wires or twisted wires made by twisting together a plurality of steel filaments.

[0048] The belt cords are arranged at an angle of, for example, 10 to 30° with respect to the tire circumferential direction. The belt cords of the first belt ply 9A and the belt cords of the second belt ply 9B are preferably inclined in opposite directions with respect to the tire circumferential direction.

[0049] Such a belt layer 9 can increase the rigidity of the tread portion 2 and maintain good wear performance of the pneumatic tire 1. Here, the angle of the belt cord is the angle in a tire in a normal state, and can be confirmed by, for example, partially peeling off the tread portion 2.

[0050] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment and can be modified and practiced in various ways.

[0051] [Note] The present invention is as follows.

[0052] [Invention 1] A pneumatic tire that is mounted on a rim and used, a tread portion having a contact surface, The rim diameter RD of the rim is 10 to 18 inches, The rim width RW of the rim is 78% to 99% of the tire cross-sectional width SW, a ratio SH / SW of the tire's section height SH to the section width SW is 30% to 45%, The tread portion has at least two circumferential grooves extending continuously in the tire circumferential direction and a plurality of land portions separated by the at least two circumferential grooves, The sum Sc1 of the contact areas of the plurality of land portions when new is 80% to 95% of the total area S of the virtual contact surface that fills all grooves including the at least two circumferential grooves, The maximum groove width W1 of the at least two circumferential grooves in a new state is 1.0% to 5.3% of the maximum contact length L1 in the tire circumferential direction when the tire is in a normal state, is loaded with a normal load, and is in contact with a flat surface with a camber angle of 0°. Pneumatic tires.

[0053] [Invention 2] The pneumatic tire according to invention 1, wherein the maximum groove width W2 of the at least two circumferential grooves at 20% wear is 1.0% to 5.3% of the maximum contact length L1.

[0054] [Invention 3] The pneumatic tire according to invention 2, wherein the sum Sc2 of the contact areas of the plurality of land portions at 20% wear is 80% to 95% of the total area S.

[0055] [Invention 4] 4. The pneumatic tire according to any one of claims 1 to 3, wherein the maximum groove width W3 of the at least two circumferential grooves at 50% wear is 1.5% to 6.8% of the maximum contact length L1.

[0056] [Invention 5] The pneumatic tire according to invention 4, wherein a sum Sc3 of the contact areas of the plurality of land portions at 50% wear is 75% to 95% of the total area S.

[0057] [Invention 6] 6. The pneumatic tire according to any one of Inventions 1 to 5, wherein the maximum groove width W4 of the at least two circumferential grooves at 80% wear is 5.8% to 10.5% of the maximum contact length L1.

[0058] [Invention 7] 7. The pneumatic tire according to claim 6, wherein a sum Sc4 of the contact areas of the plurality of land portions at 80% wear is 70% to 85% of the total area S.

[0059] [Invention 8] The pneumatic tire according to Invention 6 or 7, wherein the maximum groove width W4 at 80% wear is 50% to 75% of the circumferential contact length L2 of the tire when the tire is in a normal state and is subjected to 40% of a normal load and is in contact with a flat surface with a camber angle of 0°. [Explanation of symbols]

[0060] 1 pneumatic tire 2 Tread section 2s ground plane 6 Circumferential groove 7 Land

Claims

1. A pneumatic tire that is mounted on a rim and used, a tread portion having a contact surface, The rim diameter RD of the rim is 10 to 18 inches, The rim width RW of the rim is 78% to 99% of the tire cross-sectional width SW, a ratio SH / SW of the tire section height SH to the section width SW is 30% to 45%, The tread portion has at least two circumferential grooves extending continuously in the tire circumferential direction and a plurality of land portions separated by the at least two circumferential grooves, The sum Sc1 of the ground contact areas of the plurality of land portions when new is 80% to 95% of the total area S of the virtual ground contact surface that fills all grooves including the at least two circumferential grooves, The maximum groove width W1 of the at least two circumferential grooves in a new state is 1.0% to 5.3% of the maximum contact length L1 in the tire circumferential direction when the tire is in a normal state, is loaded with a normal load, and is in contact with a flat surface with a camber angle of 0°. Pneumatic tires.

2. 2. The pneumatic tire according to claim 1, wherein a maximum groove width W2 of the at least two circumferential grooves at 20% wear is 1.0% to 5.3% of the maximum contact length L1.

3. 3. The pneumatic tire according to claim 2, wherein a sum Sc2 of the contact areas of the plurality of land portions at 20% wear is 80% to 95% of the total area S.

4. 2. The pneumatic tire according to claim 1, wherein a maximum groove width W3 of the at least two circumferential grooves at 50% wear is 1.5% to 6.8% of the maximum contact length L1.

5. 5. The pneumatic tire according to claim 4, wherein a sum Sc3 of the contact areas of the plurality of land portions at 50% wear is 75% to 95% of the total area S.

6. 6. The pneumatic tire according to claim 1, wherein a maximum groove width W4 of the at least two circumferential grooves at 80% wear is 5.8% to 10.5% of the maximum contact length L1.

7. 7. The pneumatic tire according to claim 6, wherein a sum Sc4 of the contact areas of the plurality of land portions at 80% wear is 70% to 85% of the total area S.

8. 7. The pneumatic tire according to claim 6, wherein the maximum groove width W4 at 80% wear is 50% to 75% of the tire circumferential contact length L2 when the tire is in a normal state and is subjected to 40% of a normal load and is in contact with a flat surface with a camber angle of 0°.

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