Tire and method for manufacturing tire

Abstract

An objective of the present invention is to suppress the occurrence of protrusions on the inner surface of a tire without impairing traction performance. When reference lines La are set extending in a tire width direction from groove width centers O1 of lug grooves 21 at 0.3T positions with respect to a tread width T, centered on a tire equatorial plane CL: for an arbitrarily defined first lug groove 21A disposed on one side in the tire width direction with the tire equatorial plane CL as a boundary, and a second lug groove 21B and a third lug groove 21C disposed on the other side in the tire width direction with the tire equatorial plane CL as a boundary and having reference lines La that are adjacent to each other on both sides in the tire circumferential direction of the reference line La of the first lug groove 21A, a tire circumferential direction distance L1 between the reference line La of the first lug groove 21A and the reference line La of the second lug groove 21B, a tire circumferential direction distance L2 between the reference line La of the first lug groove 21A and the reference line La of the third lug groove 21C, and a maximum groove depth D satisfy the following relationships: 1.0≤L2 / L1≤1.4 and 1.0≤L1 / D≤1.8.

Description

Tire and method for manufacturing a tire

[0001] This invention relates to a tire and a method for manufacturing a tire.

[0002] For example, Patent Document 1 discloses a tire in which a plurality of lug grooves extending in the tire width direction are provided at intervals in the tire circumferential direction in a tread portion, with the inner end in the tire width direction being a closed end and extending from the closed end to the outer side in the tire width direction and opening at a grounding end, and provided on both sides in the tire width direction with an interval across the tire equatorial plane.

[0003] Japanese Patent No. 6720986

[0004] In a tire in which the depth of the lug groove is relatively deep with respect to the thickness in the tire radial direction of the tire equatorial plane, in the manufacture thereof, since the rubber pressed at the portion of the mold corresponding to the lug groove during vulcanization is drawn toward the tire equatorial plane, uneven thickness occurs between the lug groove portion and the vicinity of the tire equatorial plane, and a bulge is likely to occur on the inner surface of the tire near the tire equatorial plane. The bulge on the inner surface of the tire becomes larger as the circumferential distance of the closed end is closer in each lug groove with the tire equatorial plane as a boundary.

[0005] As measures against the occurrence of the bulge on the inner surface of this tire, providing a pre-excavated groove at the position of the lug groove of the green tire during tire manufacture, narrowing the groove width of the lug groove, and making the groove depth near the closed end shallower can be mentioned. However, providing a pre-excavated groove deteriorates productivity, and narrowing the groove width (circumferential groove width in the tire circumferential direction) of the lug groove or making the groove depth near the closed end shallower has problems of deteriorating traction performance.

[0006] An object of this invention is to provide a tire and a method for manufacturing a tire that can suppress the occurrence of a bulge on the inner surface of the tire without impairing the traction performance.

[0007] To achieve the above objective, a tire according to one aspect of the present invention has a tread portion having a lug groove that extends in the tire width direction, with the inner end in the tire width direction being a closed end, and extending outward from the closed end in the tire width direction and opening to the contact end, wherein the lug groove has a maximum groove depth D of 10% or more of the tire cross-sectional height H, is provided in a plurality at intervals in the tire circumferential direction, and is provided on both sides in the tire width direction with respect to the tire equatorial plane, the closed end is located within a range of 0.3T centered on the tire equatorial plane with respect to the tread width T, and the base extending in the tire width direction from the groove width center of the lug groove at the 0.3T position When a reference line is set, for an arbitrary first lug groove located on one side in the tire width direction with respect to the tire equatorial plane, and second and third lug grooves located on the other side in the tire width direction with respect to the tire equatorial plane, the reference line of the first lug groove is adjacent to both sides of the reference line in the tire circumferential direction, the tire circumferential distance L1 between the reference line of the first lug groove and the reference line of the second lug groove, the tire circumferential distance L2 between the reference line of the first lug groove and the reference line of the third lug groove, and the maximum groove depth D satisfy the relationships 1.0 ≤ L2 / L1 ≤ 1.4 and 1.0 ≤ L1 / D ≤ 1.8.

[0008] To achieve the above objective, a tire manufacturing method according to one aspect of the present invention is the tire manufacturing method described above, wherein vulcanization molding is performed using a two-part mold divided in the tire width direction.

[0009] According to this invention, the occurrence of bulges on the inner surface of the tire can be suppressed without impairing traction performance.

[0010] Figure 1 is a partially enlarged meridional section of a pneumatic tire according to the embodiment. Figure 2 is a plan view of the tread portion of a pneumatic tire according to the embodiment. Figure 3 is a plan view of the tread portion of a pneumatic tire according to the embodiment. Figure 4 is a plan view of the tread portion of a pneumatic tire according to the embodiment. Figure 5 is a partially enlarged meridional section of a pneumatic tire according to the embodiment. Figure 6 is a partially enlarged meridional section of a pneumatic tire according to the embodiment. Figure 7 is a meridional cross-sectional view showing the manufacturing method of a pneumatic tire according to the embodiment. Figure 8 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. Figure 9 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. Figure 10 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. Figure 11 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. Figure 12 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. Figure 13 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. Figure 14 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment.

[0011] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited by these embodiments. Furthermore, the components of these embodiments include those that are substituted and obvious for substitution while maintaining the identity of the invention. In addition, the multiple modifications described in these embodiments can be arbitrarily combined within the scope of what is obvious to those skilled in the art.

[0012] In the following description, the tire radial direction refers to the direction perpendicular to the tire rotation axis (not shown), which is the rotation axis of the pneumatic tire 1 of the embodiment. The inner side of the tire radial direction refers to the side toward the tire rotation axis in the tire radial direction, and the outer side of the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side of the tire width direction refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the outer side of the tire width direction refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane perpendicular to the tire rotation axis and passing through the center of the tire width of the pneumatic tire 1. The position of the tire equatorial plane CL in the tire width direction coincides with the tire width direction center line, which is the center position of the pneumatic tire 1 in the tire width direction. The tire equator line refers to a line on the tire equatorial plane CL that runs along the tire circumferential direction of the pneumatic tire 1. Furthermore, a meridional cross-section of a tire (meridian section) refers to the cross-section obtained when the tire is cut along a plane containing the tire's axis of rotation.

[0013] Figure 1 is a meridional cross-section of the pneumatic tire 1 of the embodiment. This embodiment describes an OR tire (Off the Road Tire) mounted on a construction or industrial heavy-duty vehicle, and specifically a radial tire for heavy-duty vehicles.

[0014] The pneumatic tire 1 is formed symmetrically in the tire width direction with respect to the tire equatorial plane CL. Therefore, Figures 1, 5, and 6 show a portion of one side in the tire width direction with respect to the tire equatorial plane CL.

[0015] The pneumatic tire 1 of this embodiment has an annular structure centered on the tire rotation axis and comprises a pair of bead cores 11, a pair of bead fillers 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, and a pair of rim cushion rubbers 17.

[0016] A pair of bead cores 11 are formed by winding one or more bead wires made of steel in a ring-like and multi-layered manner, and are embedded in the bead portions on both sides in the tire width direction to constitute the core of the bead portion.

[0017] A pair of bead fillers 12 are positioned on the outer circumference of a pair of bead cores 11 in the radial direction of the tire to reinforce the bead portion.

[0018] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together. In the pneumatic tire 1 of this embodiment, the carcass layer 13 consists of one carcass ply. The carcass layer 13 is toroidally stretched between the two bead cores 11 to form the framework of the tire. The ends of the carcass layer 13 are also wound back outward in the tire width direction and secured so as to enclose the bead core 11 and the bead filler 12. The carcass layer 13 is constructed by rolling a plurality of carcass cords made of steel covered with a coating rubber, and has a cord angle (defined as the inclination angle of the carcass cord in the longitudinal direction with respect to the tire circumferential direction) of 80° to 90° in absolute value for radial tires. The carcass cords of the carcass layer 13 have a cord diameter in the range of 1.5 mm to 4.5 mm.

[0019] The belt layer 14 is formed by laminating multiple belt plies 141 to 143 and is arranged around the outer circumference of the carcass layer 13. These belt plies 141 to 143 are a combination of belts of various configurations, such as a 0-degree belt or a pair of cross belts. The belt plies are formed by coating multiple belt cords (also called wires) made of steel with a rubber coating and rolling them. The pair of cross belts are formed by coating multiple belt cords made of steel with a rubber coating and rolling them, and have cord angles of opposite signs to each other, and are laminated with the longitudinal directions of the belt cords intersecting each other, thus having a so-called cross-ply structure.

[0020] The tread rubber 15 is arranged on the outer circumference in the tire radial direction of the carcass layer 13 and the belt layer 14 to form the tread portion of the pneumatic tire 1. In the tread portion, the tread rubber 15 forms a tread surface (also called a tread) 15A on the outer surface that comes into contact with the road surface during driving. The outer end of the tread surface 15A in the tire width direction becomes the contact end T0. The distance between the two contact ends T0 in the tire width direction is called the tread width T. In addition, in the tread portion, the tread rubber 15 has buttress surfaces 15B that do not come into contact with the road surface during driving on the side portions on both outer sides in the tire width direction beyond the contact end T0 of the tread surface 15A. The buttress surfaces 15B are provided in the tread rubber 15 from the contact end T0 outward in the tire width direction and inward in the tire radial direction, up to the sidewall rubber 16.

[0021] A pair of sidewall rubbers 16 are positioned on the outer side of the carcass layer 13 in the tire width direction, forming the sidewall portions on both sides of the pneumatic tire 1 in the tire width direction.

[0022] A pair of rim cushion rubbers 17 extend from the inside in the tire radial direction to the outside in the tire width direction of the reversal portion of each bead core 11 and carcass layer 13, forming the rim fitting surface of the bead portion.

[0023] As shown in Figure 2, the pneumatic tire 1 of this embodiment has a tread pattern on the tread portion (tread surface 15A and buttress surface 15B). Here, each dimension of the tread pattern is measured in an unloaded state with the pneumatic tire 1 mounted on a specified rim and filled with a specified internal pressure. The above-mentioned contact edge T0 and tread width T are defined when the tire is mounted on a specified rim, filled with a specified internal pressure, and subjected to a specified load.

[0024] A specified rim refers to a "standard rim" as defined by JATMA, a "Design Rim" as defined by TRA, or a "MEASURING RIM" as defined by ETRTO. Furthermore, specified internal pressure refers to the "maximum air pressure" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "INFLATION PRESSURES" as defined by ETRTO. Furthermore, specified load refers to the "maximum load capacity" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "LOAD CAPACITY" as defined by ETRTO.

[0025] The groove width is measured as the minimum distance between opposing groove walls at the groove opening on the surface of the tread surface 15A when the tire is mounted on a specified rim and filled to a specified internal pressure in an unloaded state. In configurations where the groove opening has a notch or chamfer, the groove width is measured using the intersection of the extension line (profile) of the tread surface 15A and the extension line of the groove wall as the endpoint in a cross section parallel to the tire width direction and tire diameter direction.

[0026] The groove depth is measured as the minimum distance from the surface of the tread surface 15A to the bottom of the groove 21c in an unloaded state with the tire mounted on a specified rim and filled to the specified internal pressure. In addition, if the groove depth has partial irregularities or sipes on the bottom of the groove 21c, these are excluded from the measurement.

[0027] As shown in Figures 1 and 2, the pneumatic tire 1 of the embodiment has lug grooves 21 extending from the tread surface 15A to the buttress surface 15B.

[0028] The lug groove 21 is formed extending along the tire width direction. The lug groove 21 is formed as a closed end 21a, with one end on the inside in the tire width direction terminating at the tread surface 15A. The lug groove 21 extends outward from the closed end 21a in the tire width direction, with the other end on the outside in the tire width direction formed as an open end 21b, opening to the contact end T0 and the buttress surface 15B. In this embodiment, the groove width of the lug groove 21 narrows as it moves from the open end 21b (the other end on the outside in the tire width direction) towards the closed end 21a (the end on the inside in the tire width direction). The lug groove 21 has a maximum groove depth D, where the groove bottom 21c is most recessed 21ca, and a tire cross-sectional height H that is between 10% and 25% (0.1 ≤ D / H ≤ 0.25). The lug groove 21 has a bottom upper portion 21cb located near the outside in the tire width direction of the recess 21ca in the groove bottom 21c.

[0029] These lug grooves 21 are arranged in a row at intervals in the tire circumferential direction on both sides in the tire width direction, with the tire equatorial plane CL as the boundary. Therefore, the lug grooves 21 are provided on one side and the other side in the tire width direction with respect to the tire equatorial plane CL. There are no other lug grooves 21 on the extensions of the lug grooves 21 on one side in the tire width direction with respect to the tire equatorial plane CL and the lug grooves 21 on the other side in the tire width direction. Also, the lug grooves 21 on one side in the tire width direction with respect to the tire equatorial plane CL and the lug grooves 21 on the other side in the tire width direction do not overlap in the tire circumferential direction. In this way, the lug grooves 21 are arranged alternately in a staggered pattern in the tire width direction toward the tire circumferential direction between each contact end T0.

[0030] As described above, the pneumatic tire 1 of this embodiment has a lug groove 21 in the tread portion, the inner end of which extends in the tire width direction is a closed end 21a, and the lug groove 21 extends outward in the tire width direction from the closed end 21a and opens to the contact end T0. As shown in Figure 1, the lug groove 21 has a maximum groove depth D of 10% or more of the tire cross-sectional height H, and as shown in the plan view in Figure 2, a plurality of lug grooves are provided at intervals in the tire circumferential direction and are provided on both sides in the tire width direction with respect to the tire equatorial plane CL, and the closed end 21a is positioned within a range of 30% (0.3T) centered on the tire equatorial plane CL with respect to the tread width T. The closed end 21a may also be positioned within a range of 0.3T on the other side in the tire width direction beyond the equatorial line (tire equatorial plane CL) from the open end 21b. The values ​​of W1, R1, R2, D1, and D2 defined below are values ​​defined on the side of the open end 21b.

[0031] In this embodiment, the pneumatic tire 1 has a maximum groove depth D of the lug groove 21 that is 10% or more of the tire cross-sectional height H, and is included in the category of OR tires that are mounted on construction or industrial heavy-duty vehicles. In this type of pneumatic tire 1, during vulcanization in manufacturing, the rubber pressed by the lug groove corresponding portion of the mold is pushed toward the tire equatorial plane CL, resulting in uneven thickness between the lug groove 21 portion and the area near the tire equatorial plane CL, and making it easy for bulges to occur on the inner surface of the tire near the tire equatorial plane CL. Moreover, in this type of pneumatic tire 1, the closed end 21a is located within a range of 0.3T centered on the tire equatorial plane CL, and because the distance between the closed ends 21a of the lug grooves 21 with respect to the tire equatorial plane CL is relatively short, the above-mentioned uneven thickness is also likely to occur.

[0032] In this regard, in the embodiment, when a reference line La is set in the tire width direction from the groove width center O1 of the lug groove 21 at position 0.3T, the first lug groove 21 (21A) is an arbitrary first lug groove located on one side in the tire width direction with respect to the tire equatorial plane CL, and the second lug groove 21 (21B) and third lug groove 21 (21C) are located on the other side in the tire width direction with respect to the tire equatorial plane CL, and the reference line La of the first lug groove 21 (21A) is adjacent to the reference line La on both sides in the tire circumferential direction. Furthermore, in the embodiment, the pneumatic tire 1 satisfies the following relationships: 1.0 ≤ L2 / L1 ≤ 1.4 and 1.0 ≤ L1 / D ≤ 1.8 for the circumferential distance L1 between the reference line La of the first lug groove 21 (21A) and the reference line La of the second lug groove 21 (21B), the circumferential distance L2 between the reference line La of the first lug groove 21 (21A) and the reference line La of the third lug groove 21 (21C), and the maximum groove depth D of the first lug groove 21 (21A). Note that the relationship between the circumferential distances L1 and L2 applies to all combinations in which the reference line La is adjacent in the lug grooves 21 on one side and the other side in the tire width direction, with respect to the tire equatorial plane CL, regardless of the presence or absence of pitch variation.

[0033] This pneumatic tire 1 satisfies the relationship 1.0 ≤ L2 / L1 ≤ 1.4, thereby optimizing the circumferential distance between lug grooves 21 separated by the tire's equatorial plane CL, suppressing uneven thickness, and preventing the occurrence of bulges on the inner surface of the tire near the tire's equatorial plane CL. For this reason, this pneumatic tire 1 does not require pre-drilled grooves at the positions of the lug grooves 21 of the green tire during manufacturing, thus not impairing productivity. Preferably, the relationship between the circumferential distances L1 and L2 is in the range of 1.0 ≤ L2 / L1 ≤ 1.15, which further optimizes the circumferential distance between lug grooves 21 separated by the tire's equatorial plane CL and further suppresses uneven thickness.

[0034] Furthermore, this pneumatic tire 1 satisfies the relationship 1.0 ≤ L1 / D ≤ 1.8, optimizing the relationship between the circumferential distance between lug grooves 21 separated by the tire equatorial plane CL and the maximum groove depth D, thereby suppressing uneven thickness and preventing the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL. Moreover, this pneumatic tire 1 satisfies the relationship 1.0 ≤ L1 / D ≤ 1.8, optimizing the relationship between the circumferential distance between lug grooves 21 separated by the tire equatorial plane CL and the maximum groove depth D, thereby ensuring traction performance. This pneumatic tire 1 does not require narrowing the groove width of the lug grooves 21 or making the groove depth near the closed end 21a shallower in order to suppress uneven thickness, and thus does not impair traction performance. Preferably, the relationship between the circumferential distance and the maximum groove depth D is in the range of 1.2 ≤ L1 / D ≤ 1.5, which further optimizes the relationship between them and can further suppress uneven thickness without impairing traction performance.

[0035] As a result, this pneumatic tire 1 can suppress the occurrence of bulges on the inner surface of the tire without compromising traction performance.

[0036] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, the groove width W at the position of the maximum groove depth D of the lug groove 21 and the tire circumferential distance L1 satisfy the relationship 1.1 ≤ L1 / W ≤ 1.8.

[0037] This pneumatic tire 1 satisfies the relationship 1.1 ≤ L1 / W ≤ 1.8, optimizing the relationship between the circumferential distance between lug grooves 21 separated by the tire equatorial plane CL and the groove width W at the position of the maximum groove depth D, thereby suppressing uneven thickness and preventing the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL. Furthermore, this pneumatic tire 1 satisfies the relationship 1.1 ≤ L1 / W ≤ 1.8, optimizing the relationship between the circumferential distance between lug grooves 21 separated by the tire equatorial plane CL and the groove width W at the position of the maximum groove depth D, thereby ensuring traction performance. As a result, this pneumatic tire 1 can further suppress uneven thickness without impairing traction performance. It is preferable that the relationship between the groove width W at the position of the maximum groove depth D of the lug groove 21 and the circumferential distance of the tire be in the range of 1.3 ≤ L1 / W ≤ 1.5, further optimizing the relationship between them and further suppressing uneven thickness without impairing traction performance.

[0038] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, the angle α with respect to the tire width direction of the groove center line Lb, which connects the groove width center O1 of the lug groove 21 at the 0.3T position and the groove width center O2 of the lug groove 21 at the 60% (0.6T) position centered on the tire equatorial plane with respect to the tread width T, is in the range of 0° ≤ α ≤ 10° in absolute value.

[0039] As described above, in the pneumatic tire 1, which is included in the OR tire category, the rubber pressed by the lug groove corresponding portion of the mold during vulcanization is pushed toward the tire equatorial plane CL, resulting in uneven thickness between the lug groove 21 portion and the area near the tire equatorial plane CL, and making it easy for bulges to occur on the inner surface of the tire near the tire equatorial plane CL. Furthermore, in the pneumatic tire 1, which is included in the OR tire category, uneven thickness tends to occur more easily the closer the angle α near the 0.3T position of the lug groove 21 is to the tire width direction, such as in the range of 0[°]≦α≦10[°]. For this reason, the pneumatic tire 1 of the embodiment is effective in suppressing uneven thickness without impairing traction performance. It is preferable that the angle α be in the range of 2[°]≦α≦8[°] in order to suppress uneven thickness without impairing traction performance. The angle α includes a lower limit of 0[°], i.e., equal to the tire width direction, but also includes a value of 0.1[°] as a value very close to 0[°].

[0040] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figures 1 and 2, the position of the maximum groove depth D of the lug groove 21 is within a range of 40% (0.4T) to 70% (0.7T) of the tire equator with respect to the tread width T, and the groove width W of the lug groove 21 at the position of the maximum groove depth D, the groove width W1 of the lug groove 21 at the 0.3T position, and the maximum groove depth D satisfy the relationship 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9.

[0041] With this pneumatic tire 1, by satisfying the relationships 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9, the relationship between the groove width W of the lug groove 21 at the position of maximum groove depth D and the groove width W1 of the lug groove 21 at the 0.3T position, and the relationship between the groove width W1 of the lug groove 21 at the 0.3T position and the maximum groove depth D can be made relatively approximate, thereby suppressing uneven thickness without impairing traction performance. Moreover, with this pneumatic tire 1, by satisfying the relationships 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9, the relationship between the groove width W of the lug groove 21 at the position of maximum groove depth D and the groove width W1 of the lug groove 21 at the 0.3T position, and the relationship between the groove width W1 of the lug groove 21 at the 0.3T position and the maximum groove depth D can be made relatively approximate, thereby effectively improving heat dissipation from inside the tire and enhancing heat resistance performance. Furthermore, the relationship between the groove width W of the lug groove 21 at the position of the maximum groove depth D, the groove width W1 of the lug groove 21 at the 0.3T position, and the maximum groove depth D is preferably in the range of 0.7 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.7. By making these relationships more approximate, uneven thickness can be further suppressed without impairing traction performance, and heat resistance can be further improved.

[0042] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, the tire width lengths R1 and R2 of each groove wall 21d facing each other in the tire width direction of the lug groove 21 from the contact end T0 to the 0.3T position satisfy the relationship 0.6 ≤ R1 / R2 ≤ 1.4. The tire width length of the groove wall 21d is measured at the position where the lug groove 21 opens on the tread surface 15A, and if the opening is not a straight line like a zigzag, it is measured as the sum of the lengths when unfolded in a straight line.

[0043] According to this pneumatic tire 1, by satisfying the relationship of 0.6 ≤ R1 / R2 ≤ 1.4, the behavior of the uneven thickness of the rubber can be made relatively uniform, and the uneven thickness can be suppressed. Moreover, according to this pneumatic tire 1, by satisfying the relationship of 0.6 ≤ R1 / R2 ≤ 1.4, the internal surface area of the lug groove 21 becomes relatively uniform and increases, making it easier to dissipate heat, so the heat resistance performance is improved. Note that the relationship between the tire width direction lengths R1 and R2 of each groove wall 21d is preferably in the range of 0.8 ≤ R1 / R2 ≤ 1.2, which can make the behavior of the uneven thickness of the rubber more uniform, further suppress the uneven thickness, and make the internal surface area of the lug groove 21 more uniform and larger, and further make it easier to dissipate heat and further improve the heat resistance performance.

[0044] In addition, in the pneumatic tire 1 of the embodiment, as shown in FIG. 2, the groove width W2 at the grounding end T0 of the lug groove 21 and the groove width W1 at the 0.3T position satisfy the relationship of 0.4 ≤ W1 / W2.

[0045] According to this pneumatic tire 1, by satisfying the relationship of 0.4 ≤ W1 / W2, when the green tire is inserted into the mold, the movement of the rubber from the initial stage to the final stage of insertion becomes more constant, the uneven thickness is suppressed, and the generation of bulges on the inner surface of the tire can be suppressed. Moreover, according to this pneumatic tire 1, by satisfying the relationship of 0.4 ≤ W1 / W2, the groove width near the tire equatorial plane CL is ensured, making it easier to dissipate heat, so the heat resistance performance is improved. The upper limit value of W1 / W2 does not particularly need to be specified. For example, setting the relationship of 0.4 ≤ W1 / W2 ≤ 0.9 is preferable for ensuring the traction performance by the lug groove 21 without making the difference between the groove widths W1 and W2 too large.

[0046] In addition, in the pneumatic tire 1 of the embodiment, as shown in FIG. 3, the groove area ratio S1 within the range of 0.3T and the groove area ratio S2 from the 0.3T position to both outer sides in the tire width direction satisfy the relationship of 2.0 ≤ S2 / S1 ≤ 5.0.

[0047] Here, the groove area ratio is the ratio of the total groove area arranged in a predetermined area of the tread portion to the area of that region. The groove area ratio is defined by groove area / (groove area + ground contact area). The groove area refers to the opening area of the groove on the ground contact surface. The groove refers to the lug groove 21 of the tread portion and does not include sipes or kerfs. Also, the ground contact area refers to the contact area between the tire and the ground contact surface. The groove area and the ground contact area are measured at the contact surface between the pneumatic tire 1 and the flat plate when the tire is mounted on the specified rim, given the specified internal pressure, placed perpendicular to the flat plate in a stationary state, and a load corresponding to the specified load is applied.

[0048] According to this pneumatic tire 1, by satisfying the relationship of 2.0 ≦ S2 / S1 ≦ 5.0, the groove area ratios on the inner and outer sides in the tire width direction with the 0.3T position as the boundary are optimized, and uneven wear can be further suppressed without impairing the traction performance. Specifically, according to this pneumatic tire 1, by setting S2 / S1 to be not less than 2.0, the lug groove 21 is arranged within the range of 0.3T, ensuring the traction performance, and by setting S2 / S1 to be not more than 5.0, the arrangement of the lug groove 21 within the range of 0.3T is restricted to suppress uneven wear. In addition, regarding the relationship between the groove area ratios S1 and S2, it is preferable to be in the range of 3.0 ≦ S2 / S1 ≦ 4.0 in order to suppress uneven wear without impairing the traction performance.

[0049] Also, in the pneumatic tire 1 of the embodiment, as shown in FIG. 4, when mounted on the specified rim, filled with the specified internal pressure, and loaded with the specified load, the number of lug grooves 21 existing in the ground contact region G is 4 or more and 10 or less.

[0050] Here, the ground contact region G is the region where the pneumatic tire 1 and the flat plate contact when the pneumatic tire 1 is mounted on the regular rim, filled with the regular internal pressure, placed perpendicular to the flat plate in a stationary state, and a load corresponding to the specified load is applied.

[0051] With this pneumatic tire 1, having four to ten lug grooves 21 within the contact area G makes the behavior of uneven rubber thickness uniform and suppresses the occurrence of bulges on the inner surface of the tire. Furthermore, with this pneumatic tire 1, having four or more lug grooves 21 within the contact area G ensures sufficient groove area within the contact area G, making heat dissipation easier and thus improving heat resistance.

[0052] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figures 2, 5, and 6, the tread width T and the distance B from the tire equatorial plane CL to the closed end 21a of the lug groove 21 satisfy the relationship 0 ≤ B / 0.5T ≤ 0.2, and the maximum groove depth D of the lug groove 21 and the groove depth D1 at the 0.3T position satisfy the relationship 0 < D1 / D < 0.4. The lug groove 21 has a stepped portion 21cc at the groove bottom 21c at the 0.3T position that is shallower than the recess 21ca of the maximum groove depth D, thereby forming the groove depth D1.

[0053] With this pneumatic tire 1, by satisfying the relationship 0 ≤ B / 0.5T ≤ 0.2, the position of the closed end 21a of the lug groove 21 near the tire equatorial plane CL is defined, and by satisfying the relationship 0 < D1 / D < 0.4, the range of groove depth D1 at the 0.3T position near the tire equatorial plane CL with respect to the maximum groove depth D of the lug groove 21 is defined, thereby ensuring rigidity near the tire equatorial plane CL and ensuring wear resistance. Furthermore, with this pneumatic tire 1, the closer B / 0.5T is to 0 and the closer the closed end 21a of the lug groove 21 is to the tire equatorial plane CL, the better the traction performance can be. Also, with this pneumatic tire 1, the closer D1 / D is to 0.4, the more uneven thickness can be suppressed. As a result, this pneumatic tire 1 can suppress the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL without impairing wear resistance and traction performance. Furthermore, it is preferable for the relationship between the tread width T and the distance B from the tire equatorial plane CL to the closed end 21a of the lug groove 21 to be in the range of 0 ≤ B / 0.5T ≤ 0.15 in order to improve traction performance. This relationship between the tread width T and the distance B from the tire equatorial plane CL to the closed end 21a of the lug groove 21 includes a configuration where 0 = B / 0.5T, that is, as shown in Figure 6, the closed end 21a is on the tire equatorial plane CL, and as described above, the closed end 21a may be positioned on the other side in the tire width direction beyond the tire equatorial plane CL from the open end 21b. It is preferable for the relationship between the tread width T and the distance B from the tire equatorial plane CL to the closed end 21a of the lug groove 21 to be in the range of 0 ≤ B / 0.5T ≤ 0.15 in order to suppress uneven thickness. In addition, the relationship between the groove depths D and D1 of the lug groove 21 includes a lower limit value greater than 0, but also includes a value very close to 0, namely 0.05. The relationship between the groove depths D and D1 of the lug groove 21 includes an upper limit of less than 0.4, but also includes a value of 0.39 as a value very close to 0.4. It is preferable to keep the relationship between the groove depths D and D1 of the lug groove 21 within the range of 0.3 ≤ D1 / D ≤ 0.39 in order to suppress uneven thickness.

[0054] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, the average value Wa of the groove width W1 at the 0.3T position of all lug grooves 21 and the groove width W1 at the 0.3T position of each individual lug groove 21 satisfy the relationship 0.9 ≤ W1 / Wa ≤ 1.1.

[0055] With this pneumatic tire 1, the relationship 0.9 ≤ W1 / Wa ≤ 1.1 is satisfied, that is, the groove width W1 of all lug grooves 21 is the same, which makes it less likely for the balance of uneven thickness to be disrupted and suppresses the unevenness of the bulge on the inner surface of the tire in the circumferential direction of the tire.

[0056] Furthermore, in the pneumatic tire 1 of this embodiment, as shown in Figure 2, the number of pitches P arranged in the circumferential direction of the lug grooves 21 is 40 or less.

[0057] With this pneumatic tire 1, by defining the number of lug grooves 21 in the tire circumferential direction, uneven thickness can be suppressed without impairing traction performance, and the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL can be suppressed. Note that if the number of lug grooves 21 in the tire circumferential direction is small, traction performance tends to decrease, and conversely, if the number is large, bulges tend to occur more easily on the inner surface of the tire near the tire equatorial plane CL. Therefore, it is preferable to set the number of pitches P of the lug grooves 21 arranged in the tire circumferential direction to 20 or more and 30 or less in order to suppress the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL without impairing traction performance.

[0058] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figures 1, 5, and 6, the maximum groove depth D of the lug groove 21 is 80 [mm] or more.

[0059] In pneumatic tires where the maximum groove depth D of the lug grooves 21 is 80 [mm] or more, bulges tend to occur on the inner surface of the tire near the tire equatorial plane CL. For this reason, the pneumatic tire 1 of this embodiment is effective in suppressing uneven thickness.

[0060] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 6, the maximum groove depth D of the lug groove 21 and the groove depth D2 of the lug groove 21 at a position 0.2T centered on the tire equatorial plane CL with respect to the tread width T satisfy the relationship 0 < D2 / D ≤ 0.1.

[0061] According to this pneumatic tire 1, by satisfying the relationship 0 < D2 / D ≤ 0.1, the difference between the maximum groove depth D of the lug groove 21 and the groove depth D2 at position 0.2T is not made too large, thereby suppressing uneven thickness and preventing the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL. The relationship between the groove depths D and D2 of this lug groove 21 includes a lower limit value greater than 0, but also includes a value of 0.05 as a value very close to 0.

[0062] Furthermore, the pneumatic tire 1 of this embodiment has a radial structure, as shown in Figure 1.

[0063] In radial pneumatic tires, bulges tend to occur on the inner surface of the tire near the tire's equatorial plane CL. Therefore, the pneumatic tire 1 of this embodiment is effective in suppressing uneven thickness.

[0064] Furthermore, in the manufacturing method of the pneumatic tire 1 of the embodiment, vulcanization molding is performed using a two-part mold 50 that is divided in the tire width direction, as shown in Figure 7.

[0065] The two-part split mold 50 has one split mold 51A in the tire width direction and the other split mold 51B in the tire width direction, and each split mold 51A, 51B moves toward or toward each other in the tire width direction. Each split mold 51A, 51B has an inner surface for forming the tread portion (tread surface 15A, buttress surface 15B), sidewall portion, and bead portion, and also has a protrusion 52 for forming the lug groove 21. The two-part split mold 50 forms a pneumatic tire 1 by vulcanizing the rubber of the green tire by sandwiching the green tire between the two split molds 51A, 51B.

[0066] In a manufacturing method that uses a two-part mold divided in the tire width direction for vulcanization molding, the protrusions 52 that form the lug grooves 21 sandwich the green tire on the inside in the tire width direction, causing uneven thickness and a tendency for bulges to occur on the inner surface of the tire near the tire equatorial plane CL. For this reason, this manufacturing method is effective in producing the pneumatic tire 1 described above.

[0067] By the way, in this embodiment, as described above, a pneumatic tire 1 was described as an example of a tire. This pneumatic tire 1 can be filled with air, an inert gas such as nitrogen, and other gases. However, the tread pattern configuration of the pneumatic tire 1 described in this embodiment can be arbitrarily applied to other tires within the scope of what is obvious to those skilled in the art. Other tires include, for example, airless tires and solid tires.

[0068] Figures 8 to 14 are charts showing the results of performance tests of the pneumatic tire according to the embodiment. Below, we will describe the performance evaluation tests performed on the comparative example pneumatic tire and the pneumatic tire according to the embodiment. The performance evaluation tests included tests for internal surface bulging, traction performance, heat resistance, and wear resistance. The test tire was a tire size of 29.5R25 L-5.

[0069] The evaluation test for inner surface bulge involves measuring the amount of protrusion on the inner surface of the test tire. Based on this measurement, an index evaluation is performed using the reciprocal of the result, with Comparative Example 1 as the baseline (100). A higher numerical value in this evaluation is preferable.

[0070] The traction performance evaluation test conforms to the TRA standard. The test tire is mounted on a specified rim, filled to the specified internal pressure, and mounted on a construction loader. The time required to reach 10 km / h after starting the drive is measured. Based on this measurement result, an index evaluation is performed using the reciprocal, with Comparative Example 1 as the baseline (100). A higher numerical value in this evaluation is preferable.

[0071] The heat resistance performance evaluation test conforms to the TRA standard. The test tire is mounted on a specified rim, filled to the specified internal pressure, and subjected to a specified load. An indoor drum test is conducted at a test speed of 10 km / h for 24 hours, and the temperature of the belt portion at the center of the tread (tire equator) is measured. Based on this measurement result, an index evaluation is performed using the reciprocal of the result, with Comparative Example 1 as the baseline (100). A higher numerical value in this evaluation is preferable.

[0072] The wear resistance evaluation test involves measuring the tread rubber on the radially outer side of the tire, beyond the maximum groove depth, when the test tire is new. Based on the measurement results, an index evaluation is performed with Comparative Example 1 as the baseline (100). This evaluation indicates that a larger rubber volume in the tread rubber results in a longer wear life, and a higher index value is preferable.

[0073] In the comparative example, the pneumatic tire has L2 / L1 and L1 / D values ​​outside the specified range in the embodiment described above.

[0074] In the embodiment, the pneumatic tire has L2 / L1 and L1 / D within the specified range in the embodiment described above.

[0075] As shown in the test results, the pneumatic tire of the example shows improvements in internal surface bulging, traction performance, heat resistance, and wear resistance compared to the comparative example.

[0076] This disclosure includes the following inventions: [Invention 1] The tread portion has a lug groove that extends in the tire width direction, with the inner end in the tire width direction being a closed end, and extending outward from the closed end in the tire width direction and opening to the contact end, wherein the lug groove has a maximum groove depth D of 10% or more of the tire cross-sectional height H, is provided in a plurality at intervals in the tire circumferential direction, and is provided on both sides in the tire width direction with respect to the tire equatorial plane, and the closed end is located within a range of 0.3T centered on the tire equatorial plane with respect to the tread width T, and when a reference line is set extending in the tire width direction from the groove width center of the lug groove at the 0.3T position, an arbitrary first lug groove is located on one side in the tire width direction with respect to the tire equatorial plane, and a second lug groove and a third lug groove are located on the other side in the tire width direction with respect to the tire equatorial plane, and the reference line is adjacent to both sides of the reference line of the first lug groove in the tire circumferential direction, A tire wherein the tire circumferential distance L1 between the reference line of the first lug groove and the reference line of the second lug groove, the tire circumferential distance L2 between the reference line of the first lug groove and the reference line of the third lug groove, and the maximum groove depth D satisfy the relationships 1.0 ≤ L2 / L1 ≤ 1.4 and 1.0 ≤ L1 / D ≤ 1.8. [Invention 2] The tire according to Invention 1, wherein the groove width W at the position of the maximum groove depth D of the lug groove and the tire circumferential distance L1 satisfy the relationship 1.1 ≤ L1 / W ≤ 1.8. [Invention 3] The tire according to Invention 1 or 2, wherein the angle α of the straight line connecting the groove width center of the lug groove at the 0.3T position and the groove width center of the lug groove at the 0.6T position centered on the tire equatorial plane with respect to the tread width T, with respect to the tire width direction, is in the range of 0 [°] ≤ α ≤ 10 [°] in absolute value. [Invention 4] The position of the maximum groove depth D of the lug groove is within a range of 0.4T to 0.7T centered on the tire equatorial plane with respect to the tread width T, and the groove width W of the lug groove at the position of the maximum groove depth D, the groove width W1 of the lug groove at the 0.3T position, and the maximum groove depth D satisfy the relationship 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9, the tire according to any one of Inventions 1 to 3.[Invention 5] A tire according to any one of Inventions 1 to 4, wherein the tire width lengths R1 and R2 of opposing groove walls in the tire width direction of the lug groove from the contact end to the 0.3T position satisfy the relationship 0.6 ≤ R1 / R2 ≤ 1.4. [Invention 6] A tire according to any one of Inventions 1 to 5, wherein the groove width W2 at the contact end of the lug groove and the groove width W1 at the 0.3T position satisfy the relationship 0.4 ≤ W1 / W2. [Invention 7] A tire according to any one of Inventions 1 to 6, wherein the groove area ratio S1 within the 0.3T range and the groove area ratio S2 on both outer sides in the tire width direction from the 0.3T position satisfy the relationship 2.0 ≤ S2 / S1 ≤ 5.0. [Invention 8] A tire according to any one of Inventions 1 to 7, wherein when mounted on a specified rim, filled with a specified internal pressure, and subjected to a specified load, there are 4 to 10 lug grooves within the contact area. [Invention 9] A tire according to any one of Inventions 1 to 8, wherein the tread width T and the distance B from the tire equatorial plane to the closed end of the lug groove satisfy the relationship 0 ≤ B / 0.5T ≤ 0.2, and the maximum groove depth D of the lug groove and the groove depth D1 at the 0.3T position satisfy the relationship 0 < D1 / D < 0.4. [Invention 10] A tire according to any one of Inventions 1 to 9, wherein the average value Wa of the groove width W1 at the 0.3T position of all the lug grooves and the groove width W1 of each lug groove at the 0.3T position satisfy the relationship 0.9 ≤ W1 / Wa ≤ 1.1. [Invention 11] A tire according to any one of Inventions 1 to 10, wherein the number of pitches arranged in the tire circumferential direction of the lug groove is 40 or less. [Invention 12] A tire according to any one of Inventions 1 to 11, wherein the maximum groove depth D of the lug groove is 80 [mm] or more. [Invention 13] A tire according to any one of Inventions 1 to 12, wherein the maximum groove depth D of the lug groove and the groove depth D2 of the lug groove at a position 0.2T centered on the tire equatorial plane with respect to the tread width T satisfy the relationship 0 < D2 / D ≤ 0.1. [Invention 14] A tire according to any one of Inventions 1 to 13, having a radial structure.[Invention 15] A method for manufacturing a tire according to any one of Inventions 1 to 14, wherein the tire is vulcanized using a two-part mold divided in the tire width direction.

[0077] 1. Pneumatic tire 21. Lug groove 21A. First lug groove 21B. Second lug groove 21C. Third lug groove 21a. Closed end 21d. Groove wall 50. Two-part mold

Claims

1. The tread portion has a lug groove that extends in the tire width direction, with the inner end in the tire width direction being a closed end, and extending outward in the tire width direction from the closed end to open at the contact end, wherein the maximum groove depth D is 10% or more of the tire cross-sectional height H, and a plurality of lug grooves are provided at intervals in the tire circumferential direction, and are provided on both sides in the tire width direction with respect to the tire equatorial plane, and the closed end is positioned within a range of 0.3T centered on the tire equatorial plane with respect to the tread width T, and when a reference line is set extending in the tire width direction from the groove width center of the lug groove at the 0.3T position, an arbitrary first lug groove is provided on one side in the tire width direction with respect to the tire equatorial plane, and a second lug groove and a third lug groove are provided on the other side in the tire width direction with respect to the tire equatorial plane, and the reference line is adjacent to both sides of the reference line of the first lug groove in the tire circumferential direction, A tire in which the circumferential distance L1 between the reference line of the first lug groove and the reference line of the second lug groove, the circumferential distance L2 between the reference line of the first lug groove and the reference line of the third lug groove, and the maximum groove depth D satisfy the relationships 1.0 ≤ L2 / L1 ≤ 1.4 and 1.0 ≤ L1 / D ≤ 1.

8.

2. The tire according to claim 1, wherein the groove width W at the position of the maximum groove depth D of the lug groove and the tire circumferential distance L1 satisfy the relationship 1.1 ≤ L1 / W ≤ 1.

8.

3. The tire according to claim 1, wherein the angle α of the straight line connecting the groove width center of the lug groove at the 0.3T position and the groove width center of the lug groove at the 0.6T position centered on the tire equatorial plane with respect to the tread width T is in the range of 0 [°] ≤ α ≤ 10 [°] in absolute value.

4. The position of the maximum groove depth D of the lug groove is within a range of 0.4T to 0.7T centered on the tire equatorial plane with respect to the tread width T, and the groove width W of the lug groove at the position of the maximum groove depth D, the groove width W1 of the lug groove at the 0.3T position, and the maximum groove depth D satisfy the relationship 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9, as described in claim 1.

5. The tire according to claim 1, wherein the tire widthwise lengths R1 and R2 of each groove wall facing each other in the tire width direction of the lug groove from the contact end to the 0.3T position satisfy the relationship 0.6 ≤ R1 / R2 ≤ 1.

4.

6. The tire according to claim 1, wherein the groove width W2 at the contact end of the lug groove and the groove width W1 at the 0.3T position satisfy the relationship 0.4 ≤ W1 / W2.

7. The tire according to claim 1, wherein the groove area ratio S1 within the range of 0.3T and the groove area ratio S2 on both outer sides in the tire width direction from the 0.3T position satisfy the relationship 2.0 ≤ S2 / S1 ≤ 5.

0.

8. The tire according to claim 1, wherein when mounted on a specified rim, filled to a specified internal pressure, and subjected to a specified load, the number of lug grooves present in the contact area is 4 to 10.

9. The tire according to claim 1, wherein the tread width T and the distance B from the tire equator to the closed end of the lug groove satisfy the relationship 0 ≤ B / 0.5T ≤ 0.2, and the maximum groove depth D of the lug groove and the groove depth D1 at the 0.3T position satisfy the relationship 0 < D1 / D < 0.

4.

10. The tire according to claim 1, wherein the average value Wa of the groove width W1 at the 0.3T position of all the lug grooves and the groove width W1 of each lug groove at the 0.3T position satisfy the relationship 0.9 ≤ W1 / Wa ≤ 1.

1.

11. The tire according to claim 1, wherein the number of pitches of the lug grooves arranged in the circumferential direction of the tire is 40 or less.

12. The tire according to claim 1, wherein the maximum groove depth D of the lug groove is 80 [mm] or more.

13. The tire according to claim 1, wherein the maximum groove depth D of the lug groove and the groove depth D2 of the lug groove at a position 0.2T centered on the tire equator with respect to the tread width T satisfy the relationship 0 < D2 / D ≤ 0.

1.

14. The tire according to claim 1, having a radial structure.

15. A method for manufacturing a tire according to any one of claims 1 to 14, wherein the tire is vulcanized using a two-part mold divided in the tire width direction.

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