tire

Abstract

To suppress the occurrence of bulges on the inner surface of the tire without compromising traction performance or wear resistance. [Solution] 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 are 0

Description

Technical Field

[0001] This invention relates to a tire.

Background Art

[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. The inner end in the tire width direction of each lug groove is a closed end, and the lug groove extends from the closed end to the outside in the tire width direction and opens at a ground contact end. The lug grooves are provided on both sides in the tire width direction with an interval across the tire equatorial plane.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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, during manufacturing, the rubber pushed by the lug groove corresponding portion of the mold in the vulcanization process is drawn toward the tire equatorial plane. As a result, 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 in each lug groove across the tire equatorial plane is shorter.

[0005] As countermeasures against the occurrence of the bulge on the inner surface of the tire, there are providing a pre - dug groove at the position of the lug groove of the green tire during tire manufacturing, narrowing the groove width of the lug groove, and making the groove depth near the closed end shallower. However, providing a pre - dug groove in advance deteriorates productivity, and narrowing the groove width (the 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 the present invention is to provide a tire capable of suppressing the generation of ridges on the inner surface of the tire without impairing the traction performance and wear resistance.

Means for Solving the Problems

[0007] To achieve the above object, a tire according to an aspect of the present invention has, in a tread portion, a lug groove in which an end on the inner side in the tire width direction extending in the tire width direction is a closed end, and which extends from the closed end to the outside in the tire width direction and opens at a grounding end. The lug groove has a maximum groove depth D of 10% or more of the tire section height H, and a plurality of the lug grooves are provided at intervals in the tire circumferential direction and are provided on both sides in the tire width direction with the tire equatorial plane as a boundary. The closed end is disposed within a range of 0.3T centered on the tire equatorial plane with respect to the tread width T. The tread width T and the distance B from the tire equatorial plane to the closed end of the lug groove satisfy the relationship of 0 ≦ B / 0.5T ≦ 0.2. The maximum groove depth D of the lug groove and the groove depth D1 at the 0.3T position satisfy the relationship of 0 < D1 / D < 0.4.

Effects of the Invention

[0008] According to this invention, the generation of ridges on the inner surface of the tire can be suppressed without impairing the traction performance and wear resistance.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is an enlarged partial meridional cross-sectional view of a pneumatic tire according to an embodiment. [Figure 2] FIG. 2 is a plan view of a tread portion of a pneumatic tire according to an embodiment. [Figure 3] FIG. 3 is a plan view of a tread portion of a pneumatic tire according to an embodiment. [Figure 4] FIG. 4 is a plan view of a tread portion of a pneumatic tire according to an embodiment. [Figure 5] FIG. 5 is an enlarged partial meridional cross-sectional view of a pneumatic tire according to an embodiment. [Figure 6]Figure 6 is a partially enlarged meridional cross-sectional view of a pneumatic tire according to the embodiment. [Figure 7] Figure 7 is a meridional cross-sectional view showing a method for manufacturing a pneumatic tire according to an embodiment. [Figure 8] Figure 8 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 9] Figure 9 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 10] Figure 10 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 11] Figure 11 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 12] Figure 12 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 13] Figure 13 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Modes for carrying out the invention]

[0010] 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.

[0011] In the following description, the tire radial direction refers to the direction orthogonal to the tire rotation axis (not shown) which is the rotation axis of the pneumatic tire 1 of the embodiment. The inner side in the tire radial direction refers to the side facing the tire rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. Also, the tire circumferential direction refers to the circumferential direction around the tire rotation axis as the central axis. Further, the tire width direction refers to the direction parallel to the tire rotation axis. The inner side in the tire width direction refers to the side facing the tire equatorial plane (tire equatorial line) CL in the tire width direction, and the outer side in 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 that is orthogonal to the tire rotation axis and passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL coincides with the center line in the tire width direction which is the central position in the tire width direction of the pneumatic tire 1. The tire equatorial line refers to a line on the tire equatorial plane CL and along the tire circumferential direction of the pneumatic tire 1. Also, the cross-section in the tire meridian direction (meridian cross-sectional view) refers to the cross-section when the tire is cut by a plane including the tire rotation axis.

[0012] FIG. 1 is a meridian cross-section of the pneumatic tire 1 of the embodiment. In this embodiment, an OR tire (Off the Road Tire) mounted on a construction or industrial heavy-duty vehicle, and a radial tire for heavy-duty vehicles will be described.

[0013] The pneumatic tire 1 is formed symmetrically in the tire width direction with the tire equatorial plane CL as the boundary. For this reason, in FIGS. 1, 5, and 6, a part of one side in the tire width direction with the tire equatorial plane CL as the boundary is shown.

[0014] The pneumatic tire 1 of the embodiment has an annular structure centered on the tire rotation axis, and includes 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.

[0015] A pair of bead cores 11 are formed by winding one or more bead wires made of steel in a circular and multiple manner, and are respectively embedded in the bead portions on both sides in the tire width direction to constitute the cores of the bead portions.

[0016] A pair of bead fillers 12 are respectively arranged on the outer periphery in the tire radial direction of the pair of bead cores 11 to reinforce the bead portions.

[0017] The carcass layer 13 has a single-layer structure composed of one carcass ply or a multi-layer structure formed by laminating a plurality of carcass plies. In the pneumatic tire 1 of the embodiment, the carcass layer 13 is composed of one carcass ply. The carcass layer 13 is bridged in a toroidal shape between both bead cores 11 to constitute the skeleton of the tire. Further, both ends of the carcass layer 13 are wound back and locked outward in the tire width direction so as to wrap the bead core 11 and the bead filler 12. Further, the carcass layer 13 is formed by covering a plurality of carcass cords made of steel with a coat rubber and performing rolling processing. In the case of a radial tire, it has a cord angle (defined as the inclination angle of the longitudinal direction of the carcass cord with respect to the tire circumferential direction) of 80° or more and 90° or less in absolute value. Further, the carcass layer 13 has a cord diameter of the carcass cord in the range of 1.5 [mm] or more and 4.5 [mm] or less.

[0018] The belt layer 14 is formed by laminating a plurality of belt plies 141 to 143 and is disposed by being wound around the outer periphery of the carcass layer 13. These belt plies 141 to 143 are combined with belts of various configurations, such as a 0-degree belt or a pair of cross belts. The belt ply is formed by covering a plurality of belt cords (also referred to as wire materials) made of steel with a coat rubber and performing rolling processing. A pair of cross belts is formed by covering a plurality of belt cords made of steel with a coat rubber and performing rolling processing, has cord angles of opposite signs to each other, and has a so-called cross ply structure in which the longitudinal directions of the belt cords cross each other and are laminated.

[0019] 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.

[0020] 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.

[0021] A pair of rim cushion rubbers 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of the folded portion of each bead core 11 and carcass layer 13, forming the rim fitting surface of the bead portion.

[0022] 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.

[0023] 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. Finally, 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.

[0024] 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 the 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.

[0025] The groove depth is measured as the minimum distance from the surface of the tread surface 15A to the groove bottom 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 a configuration with partial irregularities or sipes on the groove bottom 21c, these are excluded from the measurement.

[0026] 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.

[0027] 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 inner side 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 outer side in the tire width direction formed as an open end 21b, opening to the contact end T0 and the buttress surface 15B. In the embodiment, the groove width of the lug groove 21 is formed to narrow from the open end 21b (the other end on the outer side in the tire width direction) toward the closed end 21a (the inner end in the tire width direction). The lug groove 21 has a maximum groove depth D, where the groove bottom 21c is the most recessed recess 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 part 21cb located near the outer side in the tire width direction of the recess 21ca of the groove bottom 21c.

[0028] 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.

[0029] Thus, the pneumatic tire 1 of the embodiment has, in the tread portion, a lug groove 21 that extends in the tire width direction, with the inner end in the tire width direction being a closed end 21a, and extends from the closed end 21a to the outside in the tire width direction and opens at a grounding end T0. As shown in FIG. 1, the lug groove 21 has a maximum groove depth D that is 10% or more of the tire section height H. As shown in the plan view of FIG. 2, a plurality of the lug grooves 21 are provided at intervals in the tire circumferential direction, and are provided on both sides in the tire width direction with the tire equatorial plane CL as a boundary. The closed end 21a is disposed within a range of 30% (0.3T) centered on the tire equatorial plane CL with respect to the tread width T. Note that the closed end 21a may be disposed within a range of 0.3T on the other side in the tire width direction beyond the equator line (tire equatorial plane CL) from the open end 21b. The values of W1, R1, R2, D1, and D2 defined hereinafter are the values defined on the side of the open end 21b.

[0030] In the pneumatic tire 1 of such an embodiment, the maximum groove depth D of the lug groove 21 is 10% or more of the tire section height H, and it is included in the category of OR tires mounted on construction or industrial heavy-duty vehicles. And in this type of pneumatic tire 1, since the rubber pushed at the lug groove corresponding portion of the mold during vulcanization at the time of manufacture is drawn toward the tire equatorial plane CL, uneven thickness occurs between the lug groove 21 portion and the vicinity of the tire equatorial plane CL, and a bulge is likely to occur on the inner surface of the tire near the tire equatorial plane CL. Moreover, in this type of pneumatic tire 1, due to the closed end 21a being disposed within a range of 0.3T centered on the tire equatorial plane CL, the distance between the closed ends 21a of the lug grooves 21 with the tire equatorial plane CL as a boundary is relatively short, so the above-mentioned uneven thickness is likely to occur.

[0031] In this regard, as shown in FIGS. 2, 5, and 6, in the pneumatic tire 1 of the embodiment, 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 of 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 of 0 < D1 / D < 0.4. The lug groove 21 forms the groove depth D1 by having a step portion 21cc that is shallower than the recess 21ca of the maximum groove depth D at the groove bottom 21c at the 0.3T position.

[0032] According to this pneumatic tire 1, by satisfying the relationship of 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 of 0 < D1 / D < 0.4, the range of the 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, so that the rigidity near the tire equatorial plane CL can be ensured and the wear resistance performance can be ensured. And according to 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 improved. Also, according to this pneumatic tire 1, the closer D1 / D is to 0.4, the more the uneven wear can be suppressed. Therefore, this pneumatic tire 1 does not need to provide an excavation groove in advance at the position of the lug groove 21 of the green tire during manufacturing, so the productivity is not impaired.

[0033] 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 the traction performance and wear resistance performance.

[0034] 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, such as 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 it is 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.

[0035] 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.

[0036] 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 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.

[0037] Furthermore, in the pneumatic tire 1 of the 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.

[0038] According to this pneumatic tire 1, by defining the number of lug grooves 21 in the tire circumferential direction, it is possible to suppress uneven tire wear and the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL without impairing the traction performance. Note that if the number of lug grooves 21 in the tire circumferential direction is small, the traction performance tends to decrease, and conversely, if it is large, bulges are likely to occur on the inner surface of the tire near the tire equatorial plane CL. Therefore, it is preferable that the number of pitches P arranged in the tire circumferential direction of the lug grooves 21 is 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 the traction performance.

[0039] Also, in the pneumatic tire 1 of the embodiment, as shown in FIGS. 1, 5, and 6, the maximum groove depth D of the lug groove 21 is 80 [mm] or more.

[0040] In a pneumatic tire with a maximum groove depth D of the lug groove 21 of 80 [mm] or more, bulges are likely to occur on the inner surface of the tire near the tire equatorial plane CL. Therefore, the pneumatic tire 1 of the embodiment is effective in suppressing uneven tire wear.

[0041] Also, in the pneumatic tire 1 of the embodiment, as shown in FIG. 6, the maximum groove depth D of the lug groove 21 and the groove depth D2 of the lug groove 21 at the 0.2T position centered on the tire equatorial plane CL with respect to the tread width T satisfy the relationship of 0 < D2 / D ≤ 0.1.

[0042] According to this pneumatic tire 1, by satisfying the relationship of 0 < D2 / D ≤ 0.1, the difference between the maximum groove depth D of the lug groove 21 and the groove depth D2 at the 0.2T position is not made too large, so uneven tire wear can be suppressed and the occurrence of bulges on the inner surface of the tire near the tire equatorial plane CL can be suppressed. The relationship between the groove depths D and D2 of this lug groove 21 includes that the lower limit value exceeds 0, but includes 0.05 as a value approaching 0 infinitely.

[0043] 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) centered on the tire equatorial plane 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.

[0044] 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.

[0045] 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.

[0046] With this pneumatic tire 1, by satisfying the relationship 0.6 ≤ R1 / R2 ≤ 1.4, the behavior of uneven rubber thickness can be made relatively uniform and uneven thickness can be suppressed. Moreover, with this pneumatic tire 1, by satisfying the relationship 0.6 ≤ R1 / R2 ≤ 1.4, the internal surface area of ​​the lug groove 21 becomes relatively uniform and larger, making it easier to dissipate heat and thus improving heat resistance performance. Furthermore, 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 makes the behavior of uneven rubber thickness even more uniform and suppresses uneven thickness, and makes the internal surface area of ​​the lug groove 21 more uniform and larger, making it easier to dissipate heat and further improving heat resistance performance.

[0047] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, the groove width W2 at the contact end T0 of the lug groove 21 and the groove width W1 at the 0.3T position satisfy the relationship 0.4 ≤ W1 / W2.

[0048] With this pneumatic tire 1, by satisfying the relationship 0.4 ≤ W1 / W2, the movement of the rubber becomes more consistent from the initial to the final stages of insertion when inserting the green tire into the mold, suppressing uneven thickness and preventing the occurrence of bulges on the inner surface of the tire. Moreover, with this pneumatic tire 1, by satisfying the relationship 0.4 ≤ W1 / W2, the groove width near the tire's equatorial plane CL is secured, making heat dissipation easier and thus improving heat resistance. The upper limit of W1 / W2 does not need to be specifically defined, but for example, setting the relationship to 0.4 ≤ W1 / W2 ≤ 0.9 is preferable in order to ensure traction performance by the lug grooves 21 without making the difference between groove widths W1 and W2 too large.

[0049] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 3, 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.

[0050] Here, the groove area ratio is the ratio of the total groove area in a predetermined region of the tread to the area of ​​that region. The groove area ratio is defined as groove area / (groove area + contact area). Groove area refers to the opening area of ​​the grooves on the contact surface. Grooves refer to the lug grooves 21 of the tread and do not include sipes or calves. Contact area refers to the contact area between the tire and the contact surface. The groove area and contact area are measured at the contact surface between the pneumatic tire 1 and the flat plate when the tire is mounted on a specified rim, subjected to a specified internal pressure, placed perpendicular to a flat plate in a stationary state, and subjected to a load corresponding to a specified load.

[0051] With this pneumatic tire 1, by satisfying the relationship 2.0 ≤ S2 / S1 ≤ 5.0, the ratio of groove area between the inner and outer sides in the tire width direction with the 0.3T position as the boundary is optimized, and thickness variation can be further suppressed without impairing traction performance. Specifically, with this pneumatic tire 1, by setting S2 / S1 to 2.0 or more, traction performance can be ensured by positioning the lug grooves 21 within the 0.3T range, and by setting S2 / S1 to 5.0 or less, thickness variation can be suppressed by restricting the positioning of the lug grooves 21 within the 0.3T range. Furthermore, it is preferable that the relationship between the groove area ratios S1 and S2 be in the range of 3.0 ≤ S2 / S1 ≤ 4.0 in order to suppress thickness variation without impairing traction performance.

[0052] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 4, when mounted on a specified rim, filled with a specified internal pressure, and subjected to a specified load, the number of lug grooves 21 within the contact area G is between 4 and 10.

[0053] Here, the contact area G is the area in contact between the pneumatic tire 1 and the flat plate when the pneumatic tire 1 is mounted on a regular rim, filled to the regular internal pressure, and placed perpendicular to the flat plate in a stationary state, with a load corresponding to the specified load applied.

[0054] With this pneumatic tire 1, having 4 to 10 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 4 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.

[0055] Furthermore, in the pneumatic tire 1 of the embodiment, when a reference line La is set extending in the tire width direction from the groove width center O1 of the lug groove 21 at the 0.3T position, 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 where the reference line La is adjacent in the lug grooves 21 on one side and the other side in the tire width direction, with the tire equatorial plane CL as the boundary, regardless of the presence or absence of pitch variation.

[0056] According to this pneumatic tire 1, by satisfying the relationship 1.0 ≤ L2 / L1 ≤ 1.4, the circumferential distance between the lug grooves 21 with respect to the tire's equatorial plane CL is optimized, thickness variation is suppressed, and the occurrence of bulges on the inner surface of the tire near the tire's equatorial plane CL can be suppressed. 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 the lug grooves 21 with respect to the tire's equatorial plane CL and further suppresses thickness variation.

[0057] 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's 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's 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's 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 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, further optimizing the relationship and suppressing uneven thickness without impairing traction performance.

[0058] 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.

[0059] 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's 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's 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's 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.

[0060] 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.

[0061] 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 0.1[°] 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 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), the sidewall portion, and the bead portion, and also has a protrusion 52 for forming the lug groove 21. The two-part 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, which causes uneven thickness and tends to result in bulges 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, or 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. [Examples]

[0068] Figures 8 to 13 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, and wear resistance. The test tire was a 29.5R25 L-5 tire size.

[0069] The evaluation test for inner surface bulge involves measuring the amount of bulge 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 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 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). In this evaluation, a larger rubber volume in the tread rubber results in a longer wear life, and a higher index value is preferable.

[0072] In the comparative example, the pneumatic tire has B / 0.5T and D1 / D values ​​outside the specified range for the embodiment described above.

[0073] The pneumatic tire of the embodiment has B / 0.5T and D1 / D within the specified range as described above.

[0074] As shown in the test results, the pneumatic tire of the example shows improved internal surface bulging, traction performance, and wear resistance compared to the comparative example.

[0075] This disclosure includes the following inventions: [Invention 1] The tread portion has lug grooves that extend 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. The lug grooves have a maximum groove depth D that is 10% or more of the tire section height H, are provided in a plurality at intervals in the tire circumferential direction, are provided on both sides in the tire width direction with the tire equatorial plane as a boundary, and the closed ends are arranged within a range of 0.3T centered on the tire equatorial plane with respect to the tread width T. 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, 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. Tire. [Invention 2] The average value Wa of the groove widths W1 at the 0.3T position of all the lug grooves and the groove width W1 at the 0.3T position of each individual lug groove satisfy the relationship 0.9 ≦ W1 / Wa ≦ 1.1. The tire according to Invention 1. [Invention 3] The number of pitches of the lug grooves arranged in the tire circumferential direction is 40 or less. The tire according to Invention 1 or 2. [Invention 4] The maximum groove depth D of the lug groove is 80 [mm] or more. The tire according to any one of Inventions 1 to 3. [Invention 5] The maximum groove depth D of the lug groove and the groove depth D2 of the lug groove at the 0.2T position centered on the tire equatorial plane with respect to the tread width T satisfy the relationship 0 < D2 / D ≦ 0.1. The tire according to any one of Inventions 1 to 4. [Invention 6] The position of the maximum groove depth D of the lug groove exists within a range of 0.4T to 0.7T centered on the tire equatorial plane with respect to the tread width T. 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 following conditions are met: 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9. A tire according to any one of inventions 1 to 5. [Invention 7] The tire width lengths R1 and R2 of the opposing groove walls in the tire width direction of the lug groove from the ground contact end to the 0.3T position are The relationship 0.6 ≤ R1 / R2 ≤ 1.4 is satisfied. A tire according to any one of inventions 1 to 6. [Invention 8] The groove width W2 at the contact end of the lug groove and the groove width W1 at the 0.3T position are The relationship 0.4 ≤ W1 / W2 is satisfied. A tire according to any one of inventions 1 to 7. [Invention 9] The groove area ratio S1 within the aforementioned 0.3T range and the groove area ratio S2 on both outer sides in the tire width direction from the 0.3T position are, The relationship 2.0 ≤ S2 / S1 ≤ 5.0 is satisfied. A tire according to any one of inventions 1 to 8. [Invention 10] When mounted on a specified rim, filled with the specified internal pressure, and subjected to the specified load, the number of lug grooves within the contact area is between 4 and 10. A tire according to any one of inventions 1 to 9. [Explanation of Symbols]

[0076] 1. Pneumatic tire 21 lug grooves 21a Closed end 21d groove wall

Claims

1. The tread portion has lug grooves that extend 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. The lug grooves have a maximum groove depth D of 10% or more of the tire cross-sectional height H, are provided in multiple locations spaced apart in the circumferential direction of the tire, and are provided on both sides in the tire width direction with respect to the tire equatorial plane, and the closed ends are positioned within a range of 0.3T centered on the tire equatorial plane with respect to the tread width T. The tread width T and the distance B from the tire's equatorial plane to the closed end of the lug groove are, The relationship 0 ≤ B / 0.5T ≤ 0.2 is satisfied, The maximum groove depth D of the lug groove and the groove depth D1 at the 0.3T position are The relationship 0 < D1 / D < 0.4 is satisfied. tire.

2. 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 are The relationship 0.9 ≤ W1 / Wa ≤ 1.1 is satisfied. The tire according to claim 1.

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

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

5. 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 are, The relationship 0 < D² / D ≤ 0.1 is satisfied. The tire according to claim 1.

6. The position of the maximum groove depth D of the lug groove lies within a range of 0.4T to 0.7T centered on the tire equatorial plane with respect to the tread width T. 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 are Satisfying the relationships 0.5 ≤ W1 / W ≤ 0.9 and 0.5 ≤ W1 / D ≤ 0.9, The tire according to claim 1.

7. The tire width lengths R1 and R2 of the opposing groove walls in the tire width direction of the lug groove from the ground contact end to the 0.3T position are The relationship 0.6 ≤ R1 / R2 ≤ 1.4 is satisfied. The tire according to claim 1.

8. The groove width W2 at the contact end of the lug groove and the groove width W1 at the 0.3T position are The relationship 0.4 ≤ W1 / W2 is satisfied. The tire according to claim 1.

9. 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 are The relationship 2.0 ≤ S2 / S1 ≤ 5.0 is satisfied. The tire according to claim 1.

10. When mounted on a specified rim, filled with the specified internal pressure, and subjected to the specified load, the number of lug grooves within the contact area is between 4 and 10. The tire according to claim 1.

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