Tire

Abstract

To provide a tire whose cut separation is suppressed while maintaining an abrasion life sufficiently.SOLUTION: A tire 10 according to the present invention comprises, on a tread surface 11, width-directional narrow grooves 8 having tire width-directional constituents and extending. The width-directional narrow grooves 8 have center-side narrow groove parts 8a positioned inside in a tire width direction and shoulder-side narrow groove parts 8b leading to outside in the tire width direction of the center-side narrow groove parts. The center-side narrow groove part 8a is formed in a shape in which a narrow width part 8au including a groove opening, a taper-shape part 8at whose groove width gradually becomes larger as going toward a groove bottom, a wide straight part 8as extending in a groove depth direction with a constant groove width larger than a groove width of the narrow width part and a circular-arc shape part 8ab including a groove bottom line up continuously, from the groove opening side towards the groove bottom side. The shoulder-side narrow groove part 8b is formed in a shape in which a narrow width part 8bu including a groove opening, a taper-shape part 8bt whose groove width gradually becomes larger as going toward a groove bottom and a circular-arc-shape part 8bb including a groove bottom line up continuously, from the groove opening side towards the groove bottom side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] Conventionally, particularly for tires for construction and mining vehicles that transport ores and topsoil in mines and the like, especially for tires for construction and mining vehicles for good roads suitable for work on relatively firm road surfaces that mainly mine copper ores, iron ores, etc., in order to increase the rubber volume in the tread portion and improve the wear life, only relatively narrow grooves may be mainly provided in the tread portion. For example, Patent Document 1 discloses a construction vehicle tire (OR) provided with relatively narrow grooves extending in the tire width direction in the tread portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, generally, when the groove width in the tread portion is narrowed, separation between the tread rubber and the belt due to road surface cuts, called cut separation, tends to increase, and as a result, the total life of the tire may not be sufficiently improved, and there is still room for improvement in the above - mentioned conventional technology.

[0005] Therefore, an object of the present invention is to provide a tire that suppresses cut separation while sufficiently maintaining the wear life.

Means for Solving the Problems

[0006] The tire of the present invention is A tire having a widthwise narrow groove extending in a tire width direction component on a tread surface, wherein the widthwise narrow groove has a center side groove portion located on the inner side in the tire width direction and a shoulder side groove portion continuous with the outer side in the tire width direction of the center side groove portion, in a cross-sectional view perpendicular to the extending direction of the center side groove portion, the center side groove portion has, from the groove opening side toward the groove bottom side, a narrow width portion including the groove opening, a tapered portion whose groove width increases toward the groove bottom side, a wide width straight portion extending in the groove depth direction with a constant groove width larger than that of the narrow width portion, and an arcuate portion including the groove bottom, and is formed in a shape in which they are continuously connected, in a cross-sectional view perpendicular to the extending direction of the shoulder side groove portion, the shoulder side groove portion is characterized in that it is formed in a shape in which, from the groove opening side toward the groove bottom side, a narrow width portion including the groove opening, a tapered portion whose groove width increases toward the groove bottom side, and an arcuate portion including the groove bottom are continuously connected. According to the tire of the present invention, cut separation can be suppressed while sufficiently maintaining the wear life.

[0007] In the tire of the present invention, in a developed view of the tread surface, when a tire width direction position separated from the tire equatorial plane by 1 / 8 of the tread width divided into eight equal parts is referred to as a 1 / 8 point, it is preferable that the center side groove portion is disposed in a tire width direction region between both the 1 / 8 points. In this case, the wear life is more effectively maintained.

[0008] In the tire of the present invention, in a cross-sectional view in the tire width direction, when the maximum groove depth in the tread portion is referred to as OTD and the position where the groove bottoms of the maximum groove depth portions having the maximum groove depth are connected in a direction parallel to the tread surface is referred to as the OTD position, it is preferable that the groove depth direction distance between the boundary position between the narrow width portion and the tapered portion in the center side groove portion and the OTD position is 2 / 3 or less of the OTD. In this case, the wear life is more effectively maintained..

[0009] In the tire of the present invention, in a cross-sectional view in the tire width direction, when the maximum groove depth in the tread portion is referred to as OTD, and the position connecting the groove bottoms of the maximum groove depth portions having the maximum groove depth in a direction parallel to the tread surface is referred to as the OTD position, the groove depth direction distance between the boundary position between the tapered portion and the wide-width straight portion in the center side narrow groove portion and the OTD position is preferably 1 / 6 or more of the OTD. In this case, cut separation is more effectively suppressed.

[0010] In the tire of the present invention, in a cross-sectional view in the tire width direction, when the maximum groove depth in the tread portion is referred to as OTD, and the position connecting the groove bottoms of the maximum groove depth portions having the maximum groove depth in a direction parallel to the tread surface is referred to as the OTD position, the groove depth direction distance between the groove bottom of the center side narrow groove portion and the OTD position is preferably 1 / 12 or less of the OTD. In this case, cut separation is more effectively suppressed.

[0011] In the tire of the present invention, the groove depth of the shoulder side narrow groove portion is preferably shallower than the groove depth of the center side narrow groove portion. In this case, maintenance of wear life and suppression of cut separation can be more effectively achieved simultaneously.

[0012] In the tire of the present invention, the tire is preferably a tire for construction and mining vehicles. In this case, the effects of the present invention can be more effectively exerted.

Effects of the Invention

[0013] According to the present invention, it is possible to provide a tire that suppresses cut separation while sufficiently maintaining the wear life.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] The tire according to the present invention can be suitably used for any type of tire, and in particular, for pneumatic tires for construction and mining vehicles that transport ores and overburden in mines and the like. Among them, it can be suitably used for tires for construction and mining vehicles for good roads that are suitable for working on relatively firm road surfaces mainly for mining copper ores, iron ores, etc.

[0016] Hereinafter, embodiments of the tire according to the present invention will be illustrated and described with reference to the drawings. The same reference numerals are given to the members and parts common to each figure. In this specification, the "tire circumferential direction" refers to the direction in which the tire rotates around the rotation axis of the tire, the "tire radial direction" refers to the direction orthogonal to the rotation axis of the tire, and the "tire width direction" refers to the direction parallel to the rotation axis of the tire. In some drawings, the tire circumferential direction is indicated by the symbol "CD", the tire radial direction is indicated by the symbol "RD", and the tire width direction is indicated by the symbol "CD". Also, in this specification, the side closer to the tire equatorial plane CL along the tire width direction is referred to as the "inner side in the tire width direction", and the side farther from the tire equatorial plane CL along the tire width direction is referred to as the "outer side in the tire width direction".

[0017] Figs. 1 to 3 are drawings for explaining a tire 10 according to an embodiment of the present invention. Fig. 1 is a developed view showing the tread surface of a tire according to an embodiment of the present invention. Fig. 2(a) is a cross-sectional view taken along line A-A of Fig. 1, and Fig. 2(b) is a cross-sectional view taken along line B-B of Fig. 1. Fig. 3 is a partial cross-sectional view in the tire width direction of a tire half (more specifically, a cross-sectional view of one side of the tire half with respect to the tire equatorial plane CL viewed from the tire circumferential direction CD side, cut along the center lines of the widthwise narrow grooves 81 and lug grooves 91 in Fig. 1) taken along line X-X of Fig. 1. The tire of the present invention may be configured as any type of tire, but the tire of this embodiment is configured as a tire for construction and mining vehicles.

[0018] Hereinafter, unless otherwise specified, the positional relationship, dimensions, etc. of each element are measured in a reference state where the tire is mounted on an application rim, filled with a specified internal pressure, and is unloaded. Also, in a state where the tire is mounted on an application rim, filled with a specified internal pressure, and loaded with a maximum load, the width in the tire width direction of the ground contact surface in contact with the road surface is referred to as the "tread width (TW)", and the end in the tire width direction of the ground contact surface is referred to as the "tread end (TE)".

[0019] As used herein, the "applicable rim" refers to the standard rim (Measuring Rim in the ETRTO STANDARDS MANUAL and Design Rim in the TRA YEAR BOOK) for the applicable size, which is an industrial standard effective in the region where the tire is produced and used, and is described in the JATMA YEAR BOOK of JATMA (Japan Automobile Tire Association) in Japan, the STANDARDS MANUAL of ETRTO (The European Tyre and Rim Technical Organisation) in Europe, the YEAR BOOK of TRA (The Tire and Rim Association, Inc.) in the United States, etc. or will be described in the future. In the case of a size not described in these industrial standards, it refers to a rim with a width corresponding to the bead width of a pneumatic tire. The "applicable rim" includes sizes that will be described in the above-mentioned industrial standards in the future in addition to the current sizes. Examples of "sizes that will be described in the future" may include sizes described as "FUTURE DEVELOPMENTS" in the 2013 edition of ETRTO.

[0020] As used herein, the "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel for the applicable size and ply rating described in industrial standards such as the JATMA YEAR BOOK mentioned above. In the case of a size not described in the above-mentioned industrial standards, it refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted. Also, as used herein, the "maximum load" means the load corresponding to the maximum load capacity of a tire of the applicable size described in the above-mentioned industrial standards, or, in the case of a size not described in the above-mentioned industrial standards, the load corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted.

[0021] In this specification, the "groove width" is measured in a direction parallel to the tread surface in a cross-section perpendicular to the extending direction of the groove on the tread surface in the reference state. The groove width may vary in a direction perpendicular to the tread surface. Also, in this specification, the "groove depth direction" refers to the direction perpendicular to the tread surface in the reference state, and the "groove depth" in this specification is measured in a direction perpendicular to the tread surface in the reference state.

[0022] As shown in FIG. 3, a tire 10 according to an embodiment of the present invention includes a tread portion 1, a pair of sidewall portions 2 extending radially inward in the tire width direction from both ends of the tread portion 1 in the tire width direction, and a pair of bead portions 3 provided at the radially inner ends of the respective sidewall portions 2. Further, the tire 10 includes a pair of bead cores 3a, a carcass 4, a belt 5, a wire chafer 6, and tread rubber 1a. The tire 10 may have an inner liner (not shown) on its innermost surface. Note that FIG. 3 shows one tire half of the tire 10, but the other tire half of the tire 10 has an equivalent configuration. However, the other tire half of the tire 10 may have a configuration different from that of the one tire half.

[0023] Each bead core 3a is embedded in the corresponding bead portion 3. The bead core 3a includes a plurality of bead wires surrounded by rubber. However, the bead core 3a may be composed of a single bead wire. The bead wire is preferably made of a metal (e.g., steel). The bead wire can be made of, for example, a monofilament or a stranded wire. Note that the bead wire may be made of an organic fiber or a carbon fiber.

[0024] The carcass 4 spans between a pair of bead cores 3a and extends toroidally through a pair of sidewall portions 2 and a tread portion 1. The carcass 4 is composed of at least one (in this example, one) carcass ply formed by rubber-coating a carcass cord. The carcass cord can be formed of, for example, a monofilament or a twisted wire. In this embodiment, the carcass cord is composed of metal (for example, steel), but the carcass cord may be composed of organic fibers such as polyester, nylon, rayon, and aramid. Also, in this embodiment, the carcass 4 is a radial carcass, but the carcass 4 may be a bias carcass. Further, in this embodiment, the carcass 4 has a ply main body portion located between a pair of bead cores 3a and a ply folded-back portion that is folded back from both ends of the ply main body portion from the inner side in the tire width direction to the outer side in the tire width direction around the bead core 3a. However, the folding form of the carcass 4 is not particularly limited. For example, the carcass 4 may be wound around the bead core 3a or may not have a ply folded-back portion. Note that a chafer or the like (not shown) for protecting the carcass 4 may be provided in the bead portion 3.

[0025] The belt 5 is disposed on the outer side in the tire radial direction with respect to the crown portion of the carcass 4. The belt 5 includes at least one belt layer formed by rubber-coating belt cords arranged at a predetermined angle with respect to the tire circumferential direction. As shown in FIG. 3, in this example, the belt 5 is composed of six belt layers 5a, 5b, 5c, 5d, 5e, and 5f. In this embodiment, among the six belt layers 5a to 5f, the two belt layers 5a and 5b closest to the carcass 4 are formed with a relatively narrow width in the tire width direction (for example, 34 to 63% of the tread width TW). Further, the belt cords constituting the two belt layers 5a and 5b intersect with each other and are inclined at a relatively small cord angle (for example, 4 to 10°) with respect to the tire circumferential direction. As a result, the belt 5 (more specifically, the belt layers 5a and 5b) exhibits a so-called tag effect and can sufficiently bear the tension in the tire circumferential direction, thereby suppressing the diameter growth of the tread portion 1. Also, in this embodiment, among the six belt layers 5a to 5f, the four belt layers 5c, 5d, 5e, and 5f closest to the tread surface 11 are formed with a relatively wide width in the tire width direction (for example, 75 to 100% of the tread width TW). Further, the belt cords constituting the four belt layers 5c, 5d, 5e, and 5f intersect with each other at least between any two layers and are inclined at a relatively large cord angle (for example, 18 to 35°) with respect to the tire circumferential direction. Thereby, it is possible to suppress the concentration of stress at the tire width direction ends of the two belt layers 5a and 5b closest to the above-described carcass 4 and the occurrence of separation, and thus suppress the deterioration of the durability of the tire 10. In this embodiment, the belt cord is made of metal (for example, steel), but the belt cord may be made of organic fibers such as polyester, nylon, rayon, and aramid.

[0026] The tread rubber 1a is located on the outer side in the tire radial direction of the belt 5 in the tread portion 1. The tread rubber 1a constitutes the tread surface 11 which is the outer surface in the tire radial direction of the tread portion 1. A tread pattern as shown in FIG. 1 (to be described later) is formed on the tread surface 11.

[0027] Hereinafter, the tread pattern of the tire 10 according to an embodiment of the present invention will be described. As shown in Fig. 1, the tire 10 of the present embodiment has, on the tread surface 11, three circumferential grooves 7 (71, 72, 73) that extend with a tire circumferential direction component (in this example, along the tire circumferential direction (i.e., without inclination with respect to the tire circumferential direction)) (hereinafter also referred to as "extending in the tire circumferential direction" or "extending in the tire circumferential direction"), widthwise grooves 8 (81, 82, 83, 84) that extend with a tire width direction component (hereinafter also referred to as "extending in the tire width direction" or "extending in the tire width direction"), and lug grooves 9 (91, 92) that also extend with a tire width direction component. The tread pattern of the tread surface 11 has a block pattern having blocks partitioned by these circumferential grooves 7, widthwise grooves 8, and lug grooves 9. Further, as shown in Fig. 1, the tread patterns of both halves sandwiching the tire equatorial plane CL are slightly offset from each other in the tire circumferential direction, but are substantially the same in other respects. That is, in the developed view of the tread surface, the patterns of both halves can be overlapped with each other by translating one in parallel and performing a line-symmetric movement. However, in the present embodiment, as long as the tread surface 11 has the widthwise grooves 8, the tread pattern is not particularly limited.

[0028] In the present embodiment, as shown in Fig. 1, the circumferential groove 72 extends on the tire equatorial plane CL along the tire equatorial plane CL. The circumferential grooves 71 and 73 are respectively on both sides in the tire width direction of the circumferential groove 72 and are arranged at intervals in the tire width direction from the circumferential groove 72.

[0029] As shown in Fig. 1, the widthwise grooves 81 to 84 each extend in the tire width direction so as to communicate with the circumferential grooves between the circumferential grooves 72 and 71 or so as to communicate with the circumferential grooves between the circumferential grooves 72 and 73. In this example, the width-direction groove 81 differs from the width-direction groove 82 only in that it has a second shoulder-side groove portion 81c, which will be described later. The width-direction grooves 81 and 82 are alternately arranged at substantially equal intervals in the tire circumferential direction in one tire half portion across the tire equatorial plane CL. Also, in this example, the width-direction groove 83 differs from the width-direction groove 84 only in that it has a second shoulder-side groove portion 83c, which will be described later. The width-direction grooves 83 and 84 are alternately arranged at substantially equal intervals in the tire circumferential direction in the other tire half portion across the tire equatorial plane CL. As shown in FIG. 1, the width-direction grooves 81 to 84 extend in the tire width direction in a curved shape that is approximately S-shaped in the developed view of the tread surface 11. However, the width-direction grooves 81 to 84 do not necessarily have to extend in a curved shape and may extend linearly, for example. Here, in this specification, a "groove" such as a circumferential-direction groove or a width-direction groove refers to a groove in which the groove walls come into contact with each other and close at least in part in the groove depth direction in a state where the tire is mounted on an application rim, filled with a specified internal pressure, and loaded with a maximum load. In particular, when the tire 10 is an extra-large pneumatic tire for construction and mining vehicles as in this embodiment, for example, the groove width at the groove opening of the width-direction groove 8 (81 to 84) is preferably, for example, 3 to 18 mm, and more preferably 5 to 15 mm, from the viewpoint of ensuring both sufficient drainage and cooling performance and ensuring the rubber volume of the tread portion 1 and suppressing a decrease in rigidity.

[0030] As shown in FIG. 1, the lug grooves 91 and 92 are in the shoulder portions on the outer side in the tire width direction of the tread surface 11, extend outward in the tire width direction from the circumferential-direction groove 71 or 72, and reach the tread edge TE. The lug groove 91 communicates with the circumferential-direction groove 71 and the width-direction groove 81. Also, the lug groove 92 communicates with the circumferential-direction groove 73 and the width-direction groove 83.

[0031] In this embodiment, as shown in FIGS. 1 and 2, each of the width-direction grooves 8 (81 to 84) has a center-side groove portion 8a (81a to 84a) located on the inner side in the tire width direction and a shoulder-side groove portion 8b (81b to 84b) connected to the outer side in the tire width direction of the center-side groove portion 8a (81a to 84a). Here, the phrase "the center-side groove portion 8a is located on the inner side in the tire width direction" means that the center-side groove portion 8a is located on the inner side in the tire width direction compared to the shoulder-side groove portion 8b. In this example, as shown in FIGS. 1 and 3, the boundary positions in the tire width direction between the center-side groove portions 8a (81a to 84a) and the shoulder-side groove portions 8b (81b to 84b) on the tread surface 11 are respectively the 1 / 8 points P1 / 8 described later. However, the boundary positions in the tire width direction do not have to be the 1 / 8 points P1 / 8. In this example, as shown in FIG. 3, between the center-side groove portion 8a (81a) and the shoulder-side groove portion 8b (81b), there is substantially no transition portion, and they switch almost abruptly.

[0032] As shown in FIG. 2(a), the center-side groove portions 8a (81a to 84a) of the width-direction grooves 8 (81 to 84) are, in a cross-sectional view perpendicular to the extending direction of the center-side groove portion 8a on the tread surface 11, from the groove opening side to the groove bottom side, a narrow-width portion 8au including the groove opening, a tapered portion 8at where the groove width W2 increases as it goes toward the groove bottom side, a wide-width straight portion 8as extending in the groove depth direction with a constant groove width W3 larger than the narrow-width portion 8au, and an arc-shaped portion 8ab including the groove bottom, and are formed in a continuously connected shape. In other words, in the above cross-sectional view, the center-side groove portion 8a is formed in a paddle (oar used for rowing a canoe, etc.) shape. The narrow-width portion 8au includes the groove opening, that is, it is located at the position closest to the tread surface 11. As shown in FIG. 2(a), in this example, the narrow-width portion 8au is formed such that both groove walls are linear along the groove depth direction in a cross-sectional view, and extends in the groove depth direction with a constant relatively small groove width W1. In this example, the narrow-width portion 8au is formed with a groove width W1 such that at least some of the groove walls come into contact with each other and close in a state where the tire is mounted on the application rim, filled with the specified internal pressure, and loaded with the maximum load. However, the cross-sectional shape of the narrow-width portion 8au is not particularly limited to the above shape. The tapered portion 8at is continuously connected to the groove bottom side in the groove depth direction of the narrow-width portion 8au. The tapered portion 8at is formed such that the groove width W2 increases toward the groove bottom side, that is, such that both groove walls are substantially tapered in a cross-sectional view. As shown in FIG. 2(a), in this example, the tapered portion 8at has both groove walls extending linearly in the groove depth direction in a cross-sectional view, but both groove walls may extend curvilinearly (e.g., in an arc shape) in the groove depth direction in a cross-sectional view. Also, in this example, the tapered portion 8at is formed such that the groove width W2 gradually (i.e., continuously) increases toward the groove bottom side, but it may be formed such that the groove width W2 increases intermittently (i.e., discontinuously at predetermined positions in the groove depth direction) toward the groove bottom side. The wide-width straight portion 8as is continuously connected to the groove bottom side in the groove depth direction of the tapered portion 8at. The wide-width straight portion 8as has both groove walls formed linearly (more specifically, extending linearly along the groove depth direction, that is, extending linearly parallel to the groove depth direction) in a cross-sectional view and extends in the groove depth direction with a constant relatively large groove width W3. The groove width W3 of the wide-width straight portion 8as is larger than the groove width (more specifically, the maximum groove width) W1 of the narrow-width portion 8au. The arc-shaped portion 8ab includes the groove bottom, that is, is located at the position closest to the groove bottom. The arc-shaped portion 8ab is continuously connected to the groove bottom side in the groove depth direction of the wide-width straight portion 8as. As shown in FIG. 2(a), in this example, the arc-shaped portion 8ab is formed by substantially a semi-circular arc in a cross-sectional view, but it does not necessarily have to be formed by a strictly single arc in a cross-sectional view and may be formed, for example, in a shape where a plurality of arcs are connected (and thus a smooth curved shape).

[0033] In the present embodiment, as shown in FIG. 2(a), the boundary portions between the narrow-width portion 8au, the tapered portion 8at, and the wide-width straight portion 8as of the center-side narrow groove portion 8a are each formed angularly in a cross-sectional view, but the boundary portions between the narrow-width portion 8au, the tapered portion 8at, the wide-width straight portion 8as, and the arc-shaped portion 8ab may each be formed with rounded corners in a cross-sectional view from the viewpoint of suppressing stress concentration at the boundary portions.

[0034] As shown in Fig. 2(b), in a cross-sectional view perpendicular to the extending direction of the shoulder-side groove portion 8b (81b to 84b) of the width-direction grooves 8 (81 to 84) on the tread surface 11, from the groove opening side toward the groove bottom side, a narrow-width portion 8bu including the groove opening, a tapered portion 8bt where the groove width W2 increases toward the groove bottom side, and an arcuate portion 8bb including the groove bottom are continuously connected. In other words, in the above cross-sectional view, the shoulder-side groove portion 8b is formed in a flask shape. The cross-sectional shape of the shoulder-side groove portion 8b is different from that of the center-side groove portion 8a only in that it does not have a portion corresponding to the wide-width straight portion 8as in the center-side groove portion 8a described above. In other respects, it is substantially the same as the center-side groove portion 8a. That is, the narrow-width portion 8bu of the shoulder-side groove portion 8b is the same as the narrow-width portion 8au of the center-side groove portion 8a described above, the tapered portion 8bt of the shoulder-side groove portion 8b is the same as the tapered portion 8at of the center-side groove portion 8a described above, and the arcuate portion 8bb of the shoulder-side groove portion 8b is the same as the arcuate portion 8ab of the center-side groove portion 8a described above. Since their cross-sectional shapes are substantially the same, their descriptions are omitted.

[0035] In the present embodiment, as shown in Fig. 2(b), the boundary portion between the narrow-width portion 8bu and the tapered portion 8bt of the shoulder-side groove portion 8b is formed angularly in a cross-sectional view. However, the boundary portions between the narrow-width portion 8bu, the tapered portion 8bt, and the arcuate portion 8bb may be formed with rounded corners in a cross-sectional view from the viewpoint of suppressing stress concentration at the boundary portion.

[0036] In addition, in the present embodiment, as shown in FIGS. 1 and 3, the width-direction grooves 81 and 83 each further have second shoulder-side groove portions 81c and 83c that are continuous with the outside in the tire width direction of the shoulder-side groove portions 81b and 83b. The cross-sectional shapes of the second shoulder-side groove portions 81c and 83c are not particularly limited, and for example, they may be grooves that extend with a substantially constant groove width from the groove opening to the vicinity of the groove bottom. Also, in the illustrated example, the second shoulder-side groove portions 81c and 83c are formed as grooves, but they do not have to be formed as grooves. Furthermore, the width-direction groove 8 does not have to have the second shoulder-side groove portions 81c and 83c, such as the width-direction grooves 82 and 84.

[0037] Hereinafter, while explaining the causes of cut separation and the like with reference to FIG. 4, the effects of the above-described embodiment will be described.

[0038] FIG. 4 is a schematic diagram (which may be regarded as a schematic cross-sectional view) for explaining the cause of cut separation. Cut separation is the separation between the tread rubber and the belt due to road surface cuts. More specifically, cut separation is a phenomenon in which when the tread surface is cut by a foreign object or the like on the road surface and it reaches the boundary between the tread rubber and the belt, it further spreads over a wider range along the belt due to the shear strain between the tread rubber and the belt, causing a wide range of separation between the tread rubber and the belt. FIG. 4 is a schematic view of the tire 10 in contact with the road surface GR when the tire 10 is rolling, as viewed from the side of the tire 10. It is assumed that the tire 10 is rotating in the tire circumferential direction indicated by the reference symbol CD in the figure. In this state, since the tire 10 is in contact with the road surface GR while receiving the load F, the tread rubber 1a at the contact portion is crushed between the belt 5 (more specifically, the belt layer 5f closest to the tread surface 11) (see FIG. 3) and the road surface GR, and bulges outward in the tire circumferential direction as shown by the two-dot chain line in FIG. 4 (generally referred to as crushing deformation). Therefore, a large circumferential shear strain occurs between the tread rubber 1a and the belt 5. If there is a cut wound that has reached the belt 5, it will spread along the belt 5 and may cause cut separation. Here, for example, as shown in FIG. 4, even if a groove with a relatively small groove width is provided in the tread surface 11, the outward bulge (crushing deformation) of the tread rubber 1a in the tire circumferential direction cannot be suppressed. However, when a groove with a large groove width is provided, the groove wall of the groove bulges inward, so that the crushing deformation of the tread rubber 1a can be absorbed and suppressed. As a result, the circumferential shear strain between the tread rubber 1a and the belt 5 can be reduced, and cut separation can be suppressed. On the other hand, increasing the groove width of the groove provided in the tread portion 1 is effective in suppressing cut separation as described above, but the wear life of the tire is reduced due to the decrease in the rubber volume of the tread portion and the decrease in the tread rigidity (block rigidity).

[0039] Also, for example, tires for construction and mining vehicles (for example, tires for mining dump trucks) are often mounted on the front axle when new and rotated to the rear axle during wear. However, cut separation often occurs in the rear axle-mounted tires in the middle of wear. This is because the rear axle-mounted tires are often damaged by cuts when they run over foreign objects such as rocks on the road surface that are not visible to the driver, especially when backing up. Furthermore, cut marks that serve as the starting point of cut separation often occur near the center in the tire width direction of the tread surface 11. As described above, in the vicinity of the center in the tire width direction of the tread surface 11, relatively narrow-belt layers in the tire width direction that exhibit the so-called tag effect (for example, belt layers 5a and 5b in FIG. 5) are often arranged, and the tag effect by the belt attracts deep cut marks conversely.

[0040] In view of the above analysis, according to the tire 10 of the present embodiment, the circumferential groove 8 provided in the tread surface 11 has a center-side groove portion 8a located on the inner side in the tire width direction, and the center-side groove portion 8a has a wide-width straight portion 8as extending in the groove depth direction with a constant groove width larger than the narrow-width portion 8au. Therefore, in the vicinity of the center in the tire width direction of the tread surface 11 where cut separation is likely to occur, the crushing deformation of the tread rubber 1a can be sufficiently absorbed by the wide-width straight portion 8as, and thus cut separation can be effectively suppressed. Moreover, according to the tire 10 of the present embodiment, since the wide-width straight portion 8as is located at an intermediate position in the groove depth direction of the center-side groove portion 8a sandwiched between the narrow-width portion 8au, the tapered portion 8at, and the arc-shaped portion 8ab, at the initial stage of wear, while ensuring the rubber volume of the tread portion 1 and thus suppressing a decrease in wear life, around the middle stage of wear when cut separation is likely to occur, the wide-width straight portion 8as appears, and cut separation can be effectively suppressed. Furthermore, according to the tire 10 of the present embodiment, since the shoulder-side groove portion 8b continuous to the outer side in the tire width direction of the center-side groove portion 8a does not have a wide-width straight portion similar to the center-side groove portion 8a, it does not cause a decrease in rubber volume and a decrease in tread rigidity (block rigidity) due to that, and sufficient maintenance of wear life can be achieved. Moreover, according to the tire 10 of the present embodiment, both the center-side groove portion 8a and the shoulder-side groove portion 8b of the circumferential groove 8 have an arc-shaped portion 8ab or 8bb including the groove bottom (that is, located at the groove bottom portion), so that groove bottom cracks can be suppressed. As described above, according to the tire 10 of the present embodiment, cut separation can be suppressed while sufficiently maintaining the wear life.

[0041] Hereinafter, a preferred configuration and the like of the tire 10 of the present embodiment will be described.

[0042] In the tire 10 of the present embodiment, in the developed view of the tread surface, when the tire width direction position separated from the tire equator plane CL by 1 / 8 of the tread width TW ((1 / 8)TW) which divides the tread width TW into eight equal parts is referred to as the 1 / 8 point (in FIGS. 1 and 3, indicated by reference sign P1 / 8), it is preferable that the center side groove portion 8a is disposed in the tire width direction region between both 1 / 8 points (that is, the 1 / 8 points on both sides sandwiching the tire equator plane CL) (that is, the tire width direction region including the 1 / 8 point and inside the 1 / 8 point in the tire width direction). Since a fatal cut injury that becomes a starting point of cut separation is likely to occur in the tire width direction region between both 1 / 8 points, it is sufficient to dispose the center side groove portion 8a effective for suppressing cut separation in the region. On the other hand, a shoulder side groove portion 8b having no wide-width straight portion and effective for maintaining the wear life is disposed outside the tire width direction of the region, so that the wear life is more effectively maintained. Here, as described above, in the present embodiment, the boundary positions in the tire width direction between the center side groove portions 8a (81a to 84a) and the shoulder side groove portions 8b (81b to 84b) in the tread surface 11 are respectively the 1 / 8 points. In other words, the center side groove portion 8a extends over the entire tire width direction region inside the 1 / 8 point including the 1 / 8 point in each of the width direction grooves 8. However, the center-side groove portion 8a does not have to be arranged over the entire tire width direction region on the inner side in the tire width direction of the 1 / 8 point including the 1 / 8 point in the width direction groove 8. The center-side groove portion 8a may be arranged in a part of the tire width direction region on the inner side in the tire width direction of the 1 / 8 point including the 1 / 8 point in the width direction groove 8. From the viewpoint of sufficiently suppressing cut separation, for example, when a tire width direction position separated from the tire equator plane CL by a width of 3 / 32 of the tread width TW ((3 / 32)TW) is referred to as the 3 / 32 point, the center-side groove portion 8a is preferably arranged from the inner end in the tire width direction of the width direction groove 8 to the tire width direction outer side up to the tire width direction position between the 3 / 32 point and the 1 / 8 point. However, the arrangement range of the center-side groove portion 8a in the tire width direction does not have to be as described above.

[0043] In the tire 10 of the present embodiment, in a tire width direction cross-sectional view, the maximum groove depth in the tread portion 1 is referred to as OTD, and when a position where the groove bottoms BOTD (see FIG. 3) of the maximum groove depth portions having the maximum groove depth are connected in a direction parallel to the tread surface 11 is referred to as the OTD position (indicated by the symbol POTD in FIGS. 2 and 3), the groove depth direction distance D1 (see FIG. 2(a)) between the boundary position between the narrow width portion 8au and the tapered portion 8at in the center-side groove portion 8a and the OTD position POTD is preferably 2 / 3 or less of the OTD. In the above-described tire rotation, generally, until the tire wears to a groove depth direction position where the groove depth direction distance from the OTD position POTD is about 2 / 3 of the OTD, the tire is often used on the front axle where the occurrence frequency of cut separation is low. Therefore, as described above, by setting the groove depth direction distance D1 between the boundary position between the narrow width portion 8au and the tapered portion 8at in the center-side groove portion 8a and the OTD position POTD to 2 / 3 or less of the OTD, it is possible to greatly secure the groove depth direction length and thus the rubber volume of the narrow width portion 8au without significantly impairing the cut separation resistance, and the wear life can be more effectively maintained. In addition, in the present embodiment, as shown in FIG. 3, the maximum groove depth portion (and thus the groove bottom BOTD of the maximum groove depth portion) is within the second shoulder side groove portion 81c (or 83c) of the narrow groove 81 (or 83) in the width direction, but the maximum groove depth portion may be in other locations of the tread portion 1. Also, the OTD position POTD, in other words, is the position in the direction perpendicular to the tread surface 11 of a virtual surface (including a curved surface) parallel to the tread surface 11 passing through the groove bottom BOTD of the maximum groove depth portion. However, for simplicity of explanation, in FIGS. 2(a) and (b), it is shown as a straight line together with the tread surface 11. The OTD, in other words, is the distance between the POTD and the tread surface 11 that are parallel to each other.

[0044] From the same perspective as above, the groove depth direction distance D1 (see FIG. 2(b)) between the boundary position of the narrow width portion 8bu and the tapered portion 8bt in the shoulder side groove portion 8b and the OTD position POTD is preferably 2 / 3 or less of the OTD, similar to the groove depth direction distance D1 (see FIG. 2(a)) between the boundary position of the narrow width portion 8au and the tapered portion 8at in the center side groove portion 8a and the OTD position POTD.

[0045] In the tire 10 of the present embodiment, the groove depth direction distance D2 (see FIG. 2(a)) between the boundary position of the tapered portion 8at and the wide width straight portion 8as in the center side groove portion 8a and the OTD position POTD is preferably 1 / 6 or more of the OTD. Generally, when the tire wears to near the groove depth direction position where the groove depth direction distance from the OTD position POTD is about 1 / 3 of the OTD (at that time, near the groove depth direction position where the groove depth direction distance from the OTD position POTD is about 1 / 6 of the OTD, which is half of the groove depth at that time, the groove wall bulges most greatly toward the inner side of the groove under load), the occurrence rate of cut separation is particularly high, and thereafter, the occurrence of cut separation decreases. Therefore, as described above, by setting the groove depth direction distance D2 between the boundary position of the tapered portion 8at and the wide width straight portion 8as in the center side groove portion 8a and the OTD position POTD to be 1 / 6 or more of the OTD, cut separation can be more effectively suppressed.

[0046] From the viewpoint of sufficiently absorbing the crashing deformation of the tread rubber 1a described above and effectively suppressing cut separation, when the narrow-width part 8au and the tapered part 8at are polished and the wide-width straight part 8as appears on the tread surface 11, the tire is mounted on the application rim, filled with the specified internal pressure, and loaded with the maximum load, it is preferable that the groove widths W3 and the groove depth direction lengths D4 (see FIG. 2(a)) of the wide-width straight part 8as are set so that the groove walls of the wide-width straight part 8as do not contact each other (that is, the wide-width straight part 8as does not close). Also, regarding the wide-width straight part 8as, from the viewpoint of achieving both suppression of cut separation and maintenance of wear life, the groove depth direction length D4 thereof is preferably 0.15 to 0.5 times that of the OTD. Also, from the same viewpoint, the groove width W3 thereof is preferably 1.5 to 3.0 times the groove width (more specifically, the maximum groove width) W1 of the narrow-width part 8au.

[0047] In the tire 10 of the present embodiment, the groove depth direction distance D3 (see FIG. 2(a)) between the groove bottom of the center side narrow groove part 8a and the OTD position POTD is preferably 1 / 12 or less of the OTD. Thereby, it is possible to ensure a large groove depth direction length of the wide-width straight part 8as that can contribute to the suppression of cut separation, and cut separation is more effectively suppressed.

[0048] In the tire 10 of the present embodiment, the groove depth of the shoulder side narrow groove part 8b is shallower than the groove depth of the center side narrow groove part 8a. In other words, the groove depth direction distance D3 (see FIG. 2(b)) between the groove bottom of the shoulder side narrow groove part 8b and the OTD position POTD is preferably larger than the groove depth direction distance D3 (see FIG. 2(a)) between the groove bottom of the center side narrow groove part 8a and the OTD position POTD. As a result, compared with the case where the groove depth of the shoulder-side groove portion 8b and the groove depth of the center-side groove portion 8a are at a predetermined same depth, the groove depth of the shoulder-side groove portion 8b becomes shallower, and thus, the wear life is improved due to the increase in the rubber volume, or the groove depth of the center-side groove portion 8a becomes deeper, and thus, the effect of suppressing cut separation is enhanced. That is, with the above configuration, it is possible to more effectively achieve both the maintenance of the wear life and the suppression of cut separation.

[0049] In the tire 10 of the present embodiment, as in the present embodiment, the tire 10 is preferably a tire for construction and mining vehicles. Tires for construction and mining vehicles have a high frequency of cut separation occurring, and it is particularly likely to be a problem to achieve both the wear life and the cut separation. Therefore, each of the effects according to the above-described present embodiment can be more effectively exhibited.

[0050] What has been described above is an illustrative embodiment of the present invention, and various modifications can be made without departing from the scope of the claims.

Examples

[0051] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0052] Regarding a comparative example tire and an inventive example tire having a configuration substantially equivalent to the tire shown in FIGS. 1 to 3 except for the configuration of the width-direction groove 8, the transition of the shear strain in the tire circumferential direction (circumferential shear strain) during tire rolling was obtained by FEM calculation. The FEM conditions were as follows. Tire size: 50 / 80R57 Rim size: 32.00 / 6.0 Internal pressure: 700 KPa Load: 73 ton Wear state: After 50 mm wear out of 95 mm OTD Shape of the width-direction groove and groove depth after the above wear (each +50 mm is the groove depth at the time of new product): (Comparative Example Tire) It has a uniform cross-sectional shape shown in Fig. 2(b) and a uniform groove depth of 23 mm. (Inventive Example Tire) As an embodiment, it has the shape shown in Figs. 1 to 2 above, with a groove depth of 40 mm from the tire equatorial plane CL to the 1 / 8 point P1 / 8 and a groove depth of 23 mm on the outer side in the tire width direction from the 1 / 8 point P1 / 8. Under the above FEM conditions, referring to Fig. 4, the transition of the circumferential shear strain (circumferential shear strain) on the belt layer 5f closest to the tread surface 11 in the tire configuration of Fig. 3 (more specifically, between the belt layer 5f and the tread rubber 1a in the vicinity of the tire equatorial plane CL) was obtained. The results are shown in Figs. 5(a) and (b).

[0053] In Figs. 5(a) and (b), the symbol PSI represents the indentation position, the symbol PKO represents the kick-out position, and the symbol DS represents the strain difference. That is, the graphs in Figs. 5(a) and (b) show how the circumferential shear strain changes when the tire rolls including the range from the indentation side to the kick-out side. In each figure, the circumferential shear strain (vertical axis) is shown in exponential form. Here, the smaller the strain difference DS between the indentation position PSI and the kick-out position PKO, the less likely separation is to progress. According to the results in Figs. 5(a) and (b), when the strain difference DS in the comparative example tire shown in Fig. 5(a) is set to 100, the strain difference DS of the inventive example tire shown in Fig. 5(b) is 95, and the strain difference DS is reduced by 5%. From this, it can be seen that the inventive example tire can sufficiently suppress cut separation.

Industrial Applicability

[0054] The tire according to the present invention can be suitably used for any type of tire, and in particular, it can be suitably used for pneumatic tires for construction and mining vehicles, especially pneumatic tires for construction and mining vehicles mainly for good roads.

Explanation of Signs

[0055] 1: Tread part, 1a: Tread rubber, 2: Sidewall part, 3: Bead part, 3a: Bead core, 4: Carcass, 5: Belt, 5a - 5f: Belt layer 7, 71 - 73: Circumferential fine grooves, 8, 81 - 84: Width - direction fine grooves, 8a, 81a - 84a: Center - side fine - groove part, 8b, 81b - 84b: Shoulder - side fine - groove part, 81c, 83c: Second - shoulder - side fine - groove part, 8au, 8bu: Narrow - width part, 8at, 8bt: Tapered part, 8as: Wide - width straight part, 8ab, 8bb: Arc - shaped part, 9, 91 - 92: Lug grooves 10: Tire, 11: Tread tread surface BOTD: Groove bottom of the maximum groove depth part, CD: Tire circumferential direction, CL: Tire equatorial plane, D1 - D3: Groove - depth - direction distance, D4: Groove - depth - direction length, DS: Distortion difference, F: Load, GR: Road surface, OTD: Maximum groove depth in the tread part, POTD: OTD position, PKO: Kicking - out position, PSI: Depression position, P1 / 8: 1 / 8 point, RD: Tire radial direction, TE: Tread end, TW: Tread width, W1 - W3: Groove width, WD: Tire width direction

Claims

1. A tire having a widthwise narrow groove extending with a tire width direction component on a tread surface, The widthwise narrow groove has a center side narrow groove portion located on the inner side in the tire width direction and a shoulder side narrow groove portion continuous with the outer side in the tire width direction of the center side narrow groove portion, In a cross-sectional view perpendicular to the extending direction of the center side narrow groove portion, the center side narrow groove portion has, from the groove opening side toward the groove bottom side, a narrow width portion including the groove opening, a tapered portion whose groove width increases toward the groove bottom side, a wide width straight portion extending in the groove depth direction with a constant groove width larger than that of the narrow width portion, and an arcuate portion including the groove bottom, and is formed in a shape in which they are continuously connected, The shoulder side narrow groove portion is formed in a shape in which, in a cross-sectional view perpendicular to the extending direction of the shoulder side narrow groove portion, from the groove opening side toward the groove bottom side, a narrow width portion including the groove opening, a tapered portion whose groove width increases toward the groove bottom side, and an arcuate portion including the groove bottom are continuously connected. A tire characterized by this.

2. In a developed view of the tread surface, when a tire width direction position separated from the tire equatorial plane by 1 / 8 of the tread width divided into eight equal parts is referred to as a 1 / 8 point, the center side narrow groove portion is arranged in a tire width direction region between the two 1 / 8 points. The tire according to claim 1.

3. In a cross-sectional view in the tire width direction, when the maximum groove depth in the tread portion is referred to as OTD and the position connecting the groove bottoms of the maximum groove depth portions having the maximum groove depth in a direction parallel to the tread surface is referred to as the OTD position, the groove depth direction distance between the boundary position between the narrow width portion and the tapered portion in the center side narrow groove portion and the OTD position is 2 / 3 or less of OTD. The tire according to claim 1 or 2.

4. In a cross-sectional view in the tire width direction, when the maximum groove depth in the tread portion is referred to as OTD and the position where the groove bottoms of the maximum groove depth portions having the maximum groove depth are connected in a direction parallel to the tread surface is referred to as the OTD position, the groove depth direction distance between the boundary position between the tapered portion and the wide straight portion in the center side narrow groove portion and the OTD position is 1 / 6 or more of the OTD. The tire according to any one of claims 1 to 3.

5. In a cross-sectional view in the tire width direction, when the maximum groove depth in the tread portion is referred to as OTD and the position where the groove bottoms of the maximum groove depth portions having the maximum groove depth are connected in a direction parallel to the tread surface is referred to as the OTD position, the groove depth direction distance between the groove bottom of the center side narrow groove portion and the OTD position is 1 / 12 or less of the OTD. The tire according to any one of claims 1 to 4.

6. The groove depth of the shoulder side narrow groove portion is shallower than the groove depth of the center side narrow groove portion. The tire according to any one of claims 1 to 5.

7. The tire is a tire for construction and mining vehicles. The tire according to any one of claims 1 to 6.

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