JP6648801B1 - Pneumatic tire - Google Patents

Abstract

Provided is a pneumatic tire capable of improving low noise performance while improving traction performance and stone biting performance on an unpaved road. A lug groove (20) comprising first grooves (21, 31) extending in the tire width direction crossing a tire equator (CL) and second grooves (22, 32) extending from one end of the first grooves (21, 31). , 30 are alternately arranged, and the other ends of the first grooves 21, 31 communicate with the second grooves 32, 22 of the lug grooves 30, 20 adjacent in the tire circumferential direction, so that the lug grooves 20, 30 and the circumferential narrow groove are formed. 40 delimits a center block 51 and a shoulder block 52. In each of the lug grooves 20, 30, bottom raising portions 25, 35 are arranged in a part or all of the extending direction of the lug groove center portions 20c, 30c. There is one angle change point on each of the groove walls on the stepping side and the kicking side in the center portions 20c and 30c, and the groove wall angle α on the tread side with respect to the angle change point P is closer to the groove bottom than the angle change point P. Greater than the groove wall angle β. [Selection] Figure 2

Description

  The present invention relates to a pneumatic tire suitable as a heavy-duty pneumatic tire, and more particularly, to a pneumatic tire capable of improving low-noise performance while improving traction performance and stone-biting performance on unpaved roads. Regarding tires.

  Heavy-load pneumatic tires used in construction vehicles such as dump trucks are required to be excellent in traction performance and stone-biting performance mainly on unpaved roads. Therefore, a block-based tread pattern having a large number of lug grooves extending in the tire width direction is adopted (for example, see Patent Document 1).

  On the other hand, in recent years, performance requirements for various tires have been increasing, and even in the above-described tires, not only traction performance on unpaved roads but also tire performance (for example, low noise performance) on paved roads can be improved. It has been demanded. Therefore, there is a need for measures to improve low noise performance while improving traction performance and stone biting performance on unpaved roads.

Japanese Patent No. 4676959

  An object of the present invention is to provide a pneumatic tire capable of improving low noise performance while improving traction performance and stone biting performance on unpaved roads.

A pneumatic tire for achieving the above object has a tread portion that extends in the tire circumferential direction and forms an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a tire diameter of these sidewall portions. A pair of bead portions disposed on the inside in the direction, and in the pneumatic tire in which the rotation direction is designated, on the outer surface of the tread portion, from the tread end on one side with respect to the tire equator, inward in the tire width direction. A lug groove that extends and intersects the tire equator and a lug groove that extends inward in the tire width direction from the tread end on the other side with respect to the tire equator and intersects the tire equator extend in the tire circumferential direction. Each lug groove is arranged alternately, the first groove portion intersecting with the tire equator and extending along the tire width direction, and is smaller than the first groove portion in the tire circumferential direction from one end of the first groove portion. A second groove extending at an angle to the tread end, and the other end of the first groove communicates with the second groove of the lug groove adjacent in the tire circumferential direction, and the first groove has the lug. A circumferential narrow groove that is located closer to the tread end than the tread end of the groove and that connects the second grooves adjacent to each other in the tire circumferential direction on one side or the other side with respect to the tire equator is formed. A plurality of blocks are defined by the lug groove and the circumferential narrow groove, and the blocks are located at a center block located closer to the tire equator than the circumferential narrow groove and a shoulder located at a tread end side relative to the circumferential narrow groove. In each lug groove, a portion sandwiched between the center blocks adjacent to each other in the tire circumferential direction is defined as a lug groove center portion, and the shoulder blocks adjacent to each other in the tire circumferential direction. When the site to be sandwiched between the tooth and the lug groove shoulder portion, the outer side in the tire width direction groove width of the end portion included in said second groove to a tire width direction outer side of the lug groove shoulder portion of the lug groove center portion A bottom raising portion is provided in a part or the whole of the extending direction of the lug groove center portion, and each of the groove walls on the stepping side and the ejection side in the lug groove center portion has a width of 1 mm. And the groove wall angle α formed by the groove wall of the lug groove center portion and the normal to the tread surface of the tread portion on the tread surface side of the angle change point is smaller than the groove change angle of the angle change point. The groove wall angle β is larger than the groove wall angle β formed between the groove wall of the lug groove center portion and the normal to the tread surface of the tread portion on the side.

  In the present invention, since the lug groove including the first groove portion and the second groove portion is provided, low noise performance can be improved while improving traction performance on an unpaved road. That is, the first groove portion extending along the tire width direction is arranged near the tire equator which largely contributes to traction performance, and this first groove portion communicates with another lug groove (second groove portion). Traction performance can be efficiently improved. In addition, by having the circumferential narrow groove, noise is dispersed through the circumferential narrow groove, so that low noise performance can be improved. Furthermore, since a groove component in the tire circumferential direction can be added by the circumferential narrow groove, the tire can be prevented from being laterally displaced at the time of traction, and the stability can be improved. In addition, the groove width at the outer end in the tire width direction at the lug groove center portion is smaller than the groove width at the outer end portion in the tire width direction at the lug groove shoulder portion, and a raised bottom portion is provided at the lug groove center portion. Therefore, the volume of the lug groove does not become excessively large, and low noise performance can be maintained without impairing traction performance. Also, in the lug groove center portion, the groove width is relatively narrowed by making the groove wall angle α on the tread surface side from the angle change point larger than the groove wall angle β on the groove bottom side from the angle change point. Stone biting resistance can be maintained in the center portion.

  In the present invention, the depth from the tread surface of the tread portion to the angle change point is preferably in the range of 35% to 60% with respect to the maximum depth of the lug groove. Thereby, the stone bite resistance can be effectively improved.

  In the present invention, the groove wall angle α on the tread side in the lug groove center portion is preferably 5 ° to 30 °, and the groove wall angle β on the groove bottom side in the lug groove center portion is preferably 3 ° or less. Thereby, the stone bite resistance can be effectively improved while maintaining low noise performance.

  In the present invention, the groove wall angle α1 on the kick-out side and the groove wall angle α2 on the tread side at the groove wall angle α on the tread surface side at the lug groove center portion satisfy the relationship of 0 ° ≦ α1−α2 ≦ 8 °. preferable. Thereby, the stone bite resistance can be effectively improved.

In the present invention, the groove width at the end outside the tire width direction at the lug groove center portion and included in the second groove portion is 38% to 60% of the groove width at the end outside the tire width direction at the lug groove shoulder portion. % Is preferable. Thereby, traction performance can be effectively improved while maintaining low noise performance.

  In the present invention, it is preferable that the depth of the raised bottom in the lug groove center portion is in a range of 65% to 85% with respect to the maximum depth of the lug groove. Thereby, traction performance can be effectively improved while maintaining low noise performance.

In the present invention, it is preferable that the groove wall angle α on the tread side in the lug groove center portion gradually increases from the tire equator toward the outer end in the tire width direction of the lug groove center portion included in the second groove portion . For example, the groove wall angle α on the tread side at the lug groove center portion is 7 ° on the tire equator, while 25 ° at the outer end in the tire width direction of the lug groove center portion included in the second groove portion. preferable. Thereby, traction performance can be effectively improved while maintaining low noise performance.

  In the present invention, the lug groove preferably has a groove depth of 15 mm to 28 mm. The present invention can exhibit particularly excellent performance in traction performance, stone-biting performance, and low noise performance in a heavy-duty pneumatic tire having such characteristics.

  In the present invention, the distance from the tire equator to the tread edge is W, the area between the tire equator and the position 0.5W apart from the tire equator in the tire width direction is the inner area, and 0 is the distance from the tire equator to the tire width direction. When the region between the position separated by 5 W and the tread edge is defined as the outer region, the average angle of the second groove in the inner region with respect to the tire circumferential direction is smaller than the average angle of the second groove in the outer region with respect to the tire circumferential direction. The second groove is curved or bent so that the maximum length of the center block in the tire width direction is preferably 25% to 35% of the tread development width. By bending or bending the second groove portion as described above, the groove length can be increased, traction performance can be improved, and generation of air column resonance can be suppressed. In addition, by securing the maximum width of the center block appropriately, it is possible to sufficiently secure the block rigidity and exhibit good traction performance.

  In the present invention, it is preferable that a shallow groove having at least one bending point is formed on the treads of the center block and the shoulder block. Since the shallow groove has a bending point, the groove component in the tire circumferential direction and the groove component in the tire width direction can be increased in a well-balanced manner, and the traction performance on snow in the tire circumferential direction and the width direction can be efficiently improved. it can.

  In the present invention, when one end of the shallow groove formed in the center block communicates with the circumferential narrow groove, the other end communicates with the second groove, and the shallow groove formed in the center block is projected toward the tire equator. The projection components of the shallow groove do not overlap each other, the shallow groove formed in the shoulder block is terminated at both ends in the block, and is disposed on the step side from the position of the apex on the inner side in the tire width direction of the tread surface of the shoulder block. Is preferred. By providing a suitably shaped shallow groove in the center block located near the tire equator, which greatly contributes to traction performance, traction performance on snow can be effectively improved. In addition, by arranging the shallow grooves so as not to overlap as described above, the block stiffness is prevented from excessively decreasing over the entire circumference of the tire, and the traction performance on snow and the off-road traction performance in the tire circumferential direction are improved. And the performance can be highly compatible. Further, the edge component can be increased toward the stepping side while suppressing the decrease in the rigidity of the shoulder block, and the performance on snow can be effectively improved. On the other hand, since there is no shallow groove on the kick-out side and the block rigidity and the amount of rubber are ensured, uneven wear (heel and toe wear) can be effectively suppressed.

  In the present invention, the “tread ends” are both ends of a tread pattern portion of a tire in a state where the tire is assembled to a regular rim, filled with a regular internal pressure, and no load is applied (no load state). The “distance W in the tire width direction from the tire equator to the tread edge” in the present invention is a tread development width (defined by JATMA) which is a linear distance between the tread edges measured along the tire width direction in the above-described state. "Tread width"). The “regular rim” is a rim defined for each tire in a standard system including a standard on which the tire is based. For example, a standard rim for JATMA, a “Design Rim” for TRA, or an ETRTO In this case, “Measuring Rim” is set. “Normal internal pressure” is the air pressure specified for each tire in a standard system including the standard on which the tire is based. For JATMA, the maximum air pressure is used, and for TRA, the table “TIRE LOAD LIMITS AT VARIOUS” is used. The maximum value described in "COLL INFLASION PRESSURES" is "INFLATION PRESSURE" for ETRTO, but is 180 kPa when the tire is for a passenger car.

1 is a meridional section of a pneumatic tire according to an embodiment of the present invention. 1 is a front view showing a tread surface of a pneumatic tire according to an embodiment of the present invention. FIG. 3 is a sectional view showing a lug groove formed on a tread surface of FIG. 2. It is a front view showing an example of the tread surface of the conventional pneumatic tire. (A)-(c) is sectional drawing which shows the other example of the lug groove formed in the tread surface, respectively.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a tire radially inner side of the sidewall portion 2. And a pair of bead portions 3. In FIG. 1, reference numeral CL indicates a tire equator, and reference numeral E indicates a tread end. In the illustrated example, the tread end E coincides with the outer edge in the tire width direction of the outermost block in the tire width direction (the edge formed by the tread surface of the outermost block in the tire width direction and the outer side surface in the tire width direction). ing. Although FIG. 1 is a meridional cross-sectional view and is not drawn, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape, thereby forming a toroidal pneumatic tire. A basic structure is formed. Hereinafter, the description using FIG. 1 is basically based on the illustrated meridian cross-sectional shape, but each tire constituent member extends in the tire circumferential direction and forms an annular shape.

  A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the inside to the outside of the vehicle around the bead cores 5 arranged in each bead portion 3. Further, a bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped around the main body and the folded portion of the carcass layer 4. On the other hand, a plurality of (four in FIG. 1) belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 60 °. Although not employed in the pneumatic tire of FIG. 1, in the present invention, a belt reinforcing layer (not shown) can be further provided on the outer peripheral side of the belt layer 7. When the belt reinforcing layer is provided, the belt reinforcing layer includes, for example, an organic fiber cord oriented in the tire circumferential direction, and the angle of the organic fiber cord with respect to the tire circumferential direction can be set to, for example, 0 ° to 5 °.

  A tread rubber layer 11 is arranged on the outer peripheral side of the carcass layer 4 and the belt layer 7 in the tread portion 1. A side rubber layer 12 is disposed on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the sidewall portion 2. A rim cushion rubber layer 13 is disposed on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the bead portion 3. The tread rubber layer 11 may have a structure in which two types of rubber layers (cap tread rubber layer and under tread rubber layer) having different physical properties are laminated in the tire radial direction.

  The present invention is applied to such a general pneumatic tire, but its cross-sectional structure is not limited to the basic structure described above.

  As shown in FIG. 2, the surface of the tread portion 1 of the pneumatic tire of the present invention extends inward in the tire width direction from a tread end E on one side (right side in the figure) with respect to the tire equator CL. The lug groove 20 intersecting with the tire equator CL (hereinafter sometimes referred to as “one lug groove 20”) and the tire width from the tread end E on the other side (left side in the figure) with respect to the tire equator CL. A lug groove 30 extending inward in the direction and intersecting with the tire equator CL (hereinafter, may be referred to as “the other lug groove 30”) is provided. The one lug groove 20 and the other lug groove 30 are respectively provided in plural numbers.

  Each lug groove 20, 30 is provided with first groove portions 21, 31 extending along the tire width direction crossing the tire equator CL, and one end of the first groove portions 21, 31 from the first groove portions 21, 31 to the tire. The second groove portions 22 and 32 are inclined at a small angle with respect to the circumferential direction and extend to the tread end E. More specifically, one lug groove 20 crosses the tire equator CL and extends along the tire width direction, and one end of the first groove portion 21 (one side with respect to the tire equator (FIG. And a second groove portion 22 extending from the end portion (right side) of the tire to the tread end E at an angle smaller than the first groove portion 21 with respect to the tire circumferential direction. Similarly, the lug groove 30 on the other side intersects the tire equator CL and extends along the tire width direction, and one end of the first groove 31 (the other side of the tire equator (the other side of the tire equator (in the figure)). The second groove 32 extends to the tread end E at an angle smaller than that of the first groove 31 with respect to the circumferential direction of the tire from the end (left side).

  One lug groove 20 and the other lug groove 30 are alternately arranged one by one in the tire circumferential direction. However, since the lug grooves 20 and 30 basically extend in the opposite directions from the tire equator CL as described above, the first groove 21 of the one lug groove 20 and the other side on the tire equator CL. The first groove portions 31 of the lug grooves 30 are alternately arranged in the tire circumferential direction, but on one side with respect to the tire equator CL, the second groove portions 22 of the one lug groove 20 are spaced apart in the tire circumferential direction. On the other side with respect to the tire equator CL, the second groove portions 32 of the lug grooves 30 on the other side are arranged at intervals in the tire circumferential direction. In the present invention, if the first grooves 21 and 31 are alternately arranged and adjacent to each other on the tire equator CL, it is considered that the lug grooves 20 and 30 are alternately arranged unless otherwise specified. Shall be.

  The other ends of the first grooves 21, 31 of each lug groove 20, 30 communicate with the second grooves 32, 22 of another lug groove 30, 20 adjacent in the tire circumferential direction. That is, the first groove 21 of the one lug groove 20 communicates with the second groove 32 of the other lug groove 30 adjacent in the tire circumferential direction, and the first groove 31 of the other lug groove 30 is in the tire circumferential direction. Is connected to the second groove portion 22 of the one side lug groove 20 adjacent to the lug groove 20.

  The first groove portions 21 and 31 of the lug grooves 20 and 30 are located on the stepping side with respect to the end portions of the lug grooves 20 and 30 on the tread end E side. That is, the pneumatic tire of the present invention is a tire in which the rotation direction R is designated, but each lug groove 20, 30 is defined as a whole with the rotation direction R from the tire equator CL side toward the tire width direction outside. It has a shape inclined in the opposite direction.

  In addition to such lug grooves 20, 30, a circumferential narrow groove 40 is provided. The circumferential narrow groove 40 is formed between the second grooves adjacent to each other in the tire circumferential direction on one side of the tire equator CL, that is, the second lug grooves 20 on the one side adjacent to the tire equator CL in the tire circumferential direction on one side. It extends along the tire circumferential direction so as to connect the groove portions 22 or the second groove portions 32 of the lug grooves 30 on the other side adjacent to the tire equator C on the other side in the tire circumferential direction.

  The circumferential narrow groove 40 is a groove having a smaller groove width than the lug grooves 20 and 30. Specifically, the lug grooves 20 and 30 have a groove width G of, for example, 5 mm to 30 mm and a groove depth of, for example, 8 mm to 25 mm. In particular, when the tire is a heavy-duty pneumatic tire, the groove depth may be, for example, 15 mm to 28 mm. In contrast, the circumferential narrow groove 40 has a groove width of, for example, 7 mm to 11 mm and a groove depth of, for example, 15 mm to 20 mm.

  A plurality of blocks 50 are defined by the lug grooves 20 and 30 and the circumferential narrow groove 40. Of the plurality of blocks 50, those located on the tire equator CL side with respect to the circumferential narrow groove 40 are referred to as a center block 51, and those located on the tread end E side with respect to the circumferential narrow groove 40 are referred to as a shoulder block 52. The center block 51 at least partially exists on the tire equator CL due to the above-described groove shape.

  In each lug groove 20, 30, a portion sandwiched between center blocks 51 adjacent in the tire circumferential direction is defined as lug groove center portions 20c, 30c, and a portion sandwiched between shoulder blocks 52 adjacent in the tire circumferential direction is defined as a lug groove shoulder. Parts 20s and 30s. Specifically, as shown in FIG. 2, the lug groove center portions 20c and 30c are surrounded by a line connecting corners adjacent to each other in the center block 51 adjacent in the tire circumferential direction and an edge line of the center block 51. The lug groove shoulders 20 s and 30 s correspond to slanted lines, and the slanted line is defined by a line connecting adjacent corners of the shoulder blocks 52 adjacent in the tire circumferential direction and an edge of the shoulder block 52. Part. The groove width Gc at the outer end in the tire width direction of the lug groove center portions 20c, 30c is smaller than the groove width Gs at the outer end in the tire width direction of the lug groove shoulders 20s, 30s. Both the groove width Gc and the groove width Gs are widths measured on the tread surface of the tread portion 1. Specifically, the groove width Gc is the length of a line connecting the corners of the center blocks 51 adjacent to each other in the tire circumferential direction, and the groove width Gs is the distance between the corners of the shoulder blocks 52 adjacent to each other in the tire circumferential direction. The length of the connected line.

  As shown in FIG. 3, the lug groove center portions 20c, 30c are provided with raised bottom portions 25, 35 in a part or the whole in the extending direction. The lug groove center portions 20c and 30c have one angle change point P on each groove wall on the stepping side (left side in the figure) and on the kicking side (right side in the figure). Each of the angle change points P on the tread side and the kick side is at the same depth from the tread surface of the tread portion 1. The groove wall angle α is the groove wall angle between the groove walls of the lug groove center portions 20c and 30c and the normal to the tread surface of the tread portion 1 on the tread surface side from the angle change point P. The groove wall angle between the groove walls of the lug groove center portions 20c and 30c and the normal to the tread surface of the tread portion 1 is larger than the groove wall angle β. In other words, at the lug groove center portions 20c, 30c, at least the tire radially outer groove wall is inclined with respect to the normal to the tread surface of the tread portion 1, and the inclination angle of the tire radially outer groove wall is the tire diameter. It is larger than the inclination angle of the groove wall inside in the direction.

  In the above-described pneumatic tire, since the lug grooves 20 and 30 including the first grooves 21 and 31 and the second grooves 22 and 32 are provided, the low noise performance is improved while the traction performance on an unpaved road is improved. can do. That is, the first groove portions 21 and 31 extending along the tire width direction are arranged near the tire equator which greatly contributes to the traction performance, and the first groove portions 21 and 31 are the second groove portions of the other lug grooves 30 and 20. Since it communicates with the grooves 32 and 22, traction performance can be efficiently improved. In addition, by having the circumferential narrow groove 40, noise is dispersed through the circumferential narrow groove 40, so that low noise performance can be improved. Furthermore, since a circumferential groove component can be added by the circumferential narrow groove 40, the tire can be prevented from laterally shifting during traction and stability can be improved. In addition, the groove width Gc of the lug groove center portions 20c, 30c at the outer end in the tire width direction is smaller than the groove width Gs of the lug groove shoulder portions 20s, 30s at the outer end in the tire width direction, and Since the bottom raising portions 25 and 35 are provided in the center portions 20c and 30c, the volume of the lug grooves 20 and 30 does not become excessively large, and low noise performance can be maintained without impairing traction performance. In addition, in the lug groove center portions 20c and 30c, the groove width G is made larger by making the groove wall angle α on the tread surface side than the angle change point P larger than the groove wall angle β on the groove bottom side than the angle change point P. Stone bite resistance can be maintained in the lug groove center portions 20c and 30c that are relatively narrow.

  The depth of the lug groove center portions 20c, 30c can be appropriately set depending on the performance to be emphasized in the tire, but the depth PD from the tread surface of the tread portion 1 to the angle change point P is the same as that of the lug grooves 20, 30. Preferably, it is in the range of 35% to 60% of the maximum depth FD. As described above, by appropriately setting the depth PD of the angle change point P with respect to the maximum depth FD of the lug grooves 20, 30, the stone biting resistance can be effectively improved. Here, if the ratio of the depth PD of the angle change point P to the maximum depth FD of the lug grooves 20, 30 is less than 35% or exceeds 60%, the effect of improving the stone-biting performance cannot be sufficiently obtained. . The depth PD of the angle change point P is preferably maintained at a ratio to the maximum depth FD of the lug grooves 20, 30 in accordance with a change in the depth RD of the raised bottom portions 25, 35, which will be described later. Can also be maintained.

  Further, it is preferable that the depth RD of the raised bottom portions 25, 35 in the lug groove center portions 20c, 30c is in the range of 65% to 85% with respect to the maximum depth FD of the lug grooves 20, 30. By appropriately setting the depth RD of the raised portions 25, 35 with respect to the maximum depth FD of the lug grooves 20, 30, traction performance can be effectively improved while maintaining low noise performance. it can. Here, if the ratio of the depth RD of the raised bottom portions 25, 35 to the maximum depth FD of the lug grooves 20, 30 is less than 65%, the traction performance is reduced, and if it exceeds 85%, the low noise performance is reduced. Tend.

  The groove wall angles of the lug groove center portions 20c and 30c can be appropriately set depending on the performance to be emphasized in the tire, but the groove wall angle α on the tread side is 5 ° to 30 °, and the groove wall on the groove bottom side. Angle β is preferably 3 ° or less. At this time, the groove width G on the groove bottom side of the angle change point P in the lug groove center portions 20c, 30c is preferably 4 mm or more. By appropriately setting the groove wall angle α on the tread surface side and the groove wall angle β on the groove bottom side in this way, it is possible to effectively improve stone biting resistance while maintaining low noise performance. Here, if the groove wall angle α on the tread side is smaller than 5 °, the effect of improving the stone biting performance cannot be sufficiently obtained, and if the groove wall angle α on the tread side is larger than 30 °, the lug grooves 20 and 30 cannot be obtained. Is excessively large, it is difficult to maintain low noise performance.

  Further, the groove wall angle α1 on the kick-out side and the groove wall angle α2 on the tread side at the groove wall angle α on the tread side in the lug groove center portions 20c, 30c satisfy the relationship of 0 ° ≦ α1−α2 ≦ 8 °. Is preferred. More preferably, the groove wall angle α1 on the ejection side is greater than the groove wall angle α2 on the stepping side, and the relationship 0 ° <α1−α2 ≦ 8 ° may be satisfied. By appropriately setting the groove wall angle α1 on the ejection side and the groove wall angle α2 on the stepping side in this way, the stone biting resistance can be effectively improved. Here, when the angle difference (α1−α2) between the groove wall angle α1 and the groove wall angle α2 is larger than 8 °, the stone-biting performance tends to deteriorate.

  In the pneumatic tire, the groove width Gc of the lug groove center portions 20c, 30c at the outer end in the tire width direction is 38 with respect to the groove width Gs of the lug groove shoulder portions 20s, 30s at the outer end in the tire width direction. % To 60%. By appropriately setting the ratio of the groove width Gc to the groove width Gs in this manner, traction performance can be effectively improved while maintaining low noise performance. Here, when the ratio of the groove width Gc to the groove width Gs is less than 38%, the traction performance tends to decrease, and when it exceeds 60%, the low noise performance tends to decrease.

  Further, it is preferable that the groove wall angle α on the tread side in the lug groove center portions 20c, 30c gradually increases from the tire equator CL toward the tire width direction outside. Such a change in the angle of the groove wall angle α starts from the connection point between the first groove portions 21 and 31 of the lug grooves 20 and 30 and the second groove portions 22 and 32, and the lug grooves included in the second groove portions 22 and 32 The ends of the center portions 20c and 30c on the outer side in the tire width direction are defined as end points. Since the groove wall angle α on the tread side gradually increases from the tire equator CL outward in the tire width direction, traction performance can be effectively improved while maintaining low noise performance. The above-mentioned change in the angle of the groove wall angle α can be applied to both the groove wall angle α1 on the ejection side (right side in FIG. 3) and the groove wall angle α2 on the stepping side (left side in FIG. 3). .

  In particular, the above-mentioned groove wall angle α on the tread side is preferably 7 ° on the tire equator CL and 25 ° at the outer end in the tire width direction. By setting the groove wall angle α on the tread side at a specific position in the tire width direction as described above, traction performance can be effectively improved while maintaining low noise performance.

  In FIG. 2, each lug groove 20, 30 is defined as a distance W in the tire width direction from the tire equator CL to the tread end E, and a distance 0.50 W from the tire equator CL in the tire width direction and the tire equator CL. A region between the tread edge E and a position 0.50 W apart from the tire equator CL in the tire width direction is defined as an inner region A, and the second groove portions 22 and 32 in the outer region B are defined as an outer region B. The second grooves 22, 32 are curved or bent such that the average angle θa of the second grooves 22, 32 in the inner region A with respect to the tire circumferential direction is smaller than the average angle θb with respect to the tire circumferential direction. In other words, the second grooves 22, 32 of the lug grooves 20, 30 are smoothly curved or have at least one bend so that the inclination angle with respect to the tire circumferential direction gradually decreases from the tread end E toward the tire equator CL. It is bent with points. In the center block 51, the maximum length L in the tire width direction is set to 25% to 35% of the tread development width TW. As described above, the length of the groove can be increased by bending or bending the second groove portions 22 and 32, thereby improving traction performance and suppressing generation of air column resonance. Further, since the maximum width of the center block 51 is appropriately secured, it is possible to sufficiently secure the block rigidity and exhibit good traction performance.

  The average angle of the second groove portions 22 and 32 of the lug grooves 20 and 30 is the angle formed by a straight line connecting the midpoints of the lug grooves 20 and 30 in the groove width direction at the boundary position of each region with respect to the tire circumferential direction. Can be obtained as However, at the tire equator CL and the tread end E, as shown in the figure, the middle point at the tire equator CL or the tread end E of the extension of the second grooves 22, 32 drawn toward the tire equator CL or the tread end E is used. Shall be.

  As described above, the first groove portions 21 and 31 are provided in order to secure a groove component in the tire width direction mainly in the vicinity of the tire equator CL which largely contributes to traction performance. Therefore, it is preferable that the first groove portions 21 and 31 extend in a direction substantially perpendicular to the tire circumferential direction. Specifically, the angle θc of the first groove portions 21 and 31 with respect to the tire circumferential direction is preferably set to 80 ° to 100 °. Thereby, traction performance can be efficiently improved by the first grooves 21 and 31. When the angle θc of the first groove portions 21 and 31 is less than 80 ° or more than 100 °, the inclination of the first groove portions 21 and 31 with respect to the tire width direction increases, and the groove component in the tire width direction is sufficiently ensured. And the effect of improving traction performance is limited.

  In FIG. 2, a shallow groove 60 having at least one bending point is formed on the tread surface of each block 50. The shallow groove 60 is a groove having a smaller groove depth than the lug grooves 20, 30 and the circumferential narrow groove 40. The groove depth is preferably set to 1 mm to 3 mm, and the groove width is set to, for example, 1 mm to 3 mm. it can. If the depth of the shallow groove 60 is less than 1 mm, the effect of providing the shallow groove 60 is too small to obtain the effect of providing the shallow groove 60. If the depth of the shallow groove 60 exceeds 3 mm, the block rigidity is reduced. The effect is greater. In the following description, the shallow groove 60 formed in the center block 51 is referred to as a center shallow groove 61, and the shallow groove 60 formed in the shoulder block 52 is referred to as a shoulder shallow groove 62. In the illustrated example, both the center shallow groove 61 and the shoulder shallow groove 62 have one bending point. The number of shallow grooves 60 formed in each block 50 is not particularly limited, but it is preferable to provide one shallow groove 60 in each block 50 as shown.

  In the present invention, in order to ensure off-road traction performance, in the tire having a block-based tread pattern in which a plurality of blocks 50 are partitioned by the lug grooves 20, 30 and the circumferential narrow grooves 40 as described above, each block 50 Since the shallow groove 60 having a bending point is provided on the tread surface of the tire, the groove component in the tire circumferential direction and the groove component in the tire width direction can be increased in a well-balanced manner, and the traction performance on snow in the tire circumferential direction and the width direction can be improved. It can be improved efficiently.

  Further, the center shallow groove 61 preferably has one end communicating with the circumferential narrow groove 40 and the other end communicating with the second grooves 22, 32 of the lug grooves 20, 30, as shown in the figure. The center shallow groove 61 is preferably bent along the outer edge of the center block 51 on the stepping side or the kicking side. At this time, the center shallow groove 61 is preferably arranged within a range of ± 5 mm in the tire circumferential direction from the center position of the center block 51 in the tire circumferential direction. Further, it is preferable that projection components of the center shallow groove 61 when the center shallow groove 61 is projected toward the tire equator CL do not overlap. By providing the center block 51 located in the vicinity of the tire equator CL which greatly contributes to the traction performance with the appropriately shaped center shallow groove 61, the traction performance on snow can be effectively improved. Further, since the center shallow grooves 61 do not overlap as described above, the block rigidity is not excessively reduced over the entire circumference of the tire, and the balance between the snow traction performance and the off-road traction performance in the tire circumferential direction is reduced. And these performances can be highly compatible.

  On the other hand, both ends of the shoulder shallow groove 62 are preferably terminated in the shoulder block 52 as shown in the figure. Further, the shoulder shallow groove 62 may be bent along the outer edge of the shoulder block 52 on the stepping side. Furthermore, the shoulder shallow groove 62 may be arranged on the stepping side of the position of the apex of the tread surface of the shoulder block 52 on the inner side in the tire width direction. By providing the shoulder shallow groove 62 in this manner, it is possible to increase the edge component on the stepping side while suppressing a decrease in the rigidity of the shoulder block 52, and it is possible to effectively improve the performance on snow. On the other hand, since there is no shallow groove on the kick-out side and the block rigidity and the amount of rubber are ensured, uneven wear (heel and toe wear) can be effectively suppressed.

  The tire size is 315 / 80R22.5, which has the basic structure illustrated in FIG. 1, and has a base tread pattern, presence or absence of raising at the lug groove center, cross-sectional shape of the lug groove center, and lug groove center. The relationship between the groove wall angle α and the groove wall angle β, the ratio of the depth PD of the angle change point to the maximum depth FD of the lug groove (PD / FD × 100%), and the groove wall on the ejection side of the lug groove center. The angle α1, the groove wall angle α2 on the stepping side of the lug groove center portion, the angle difference (α1−α2) between the groove wall angle α1 and the groove wall angle α2, the groove width of the lug groove center portion relative to the groove width Gs of the lug groove shoulder portion. Table 1 shows the ratio of Gc (Gc / Gs × 100%), the ratio of the depth RD of the raised bottom to the maximum depth FD of the lug groove (RD / FD × 100%), and the presence or absence of an angle change in the lug groove center. And as shown in Table 2. Pneumatic tires of the conventional examples, Comparative Examples 1 and 2, and Examples 1 to 12 were produced.

  Regarding the “tread pattern” in Tables 1 and 2, the numbers of the corresponding drawings are described. The pattern of FIG. 4 of the conventional example is greatly different from the pattern of FIG. 2, but as shown in the figure, the numerical values of each item were obtained by associating the dimensions and the like of each part with FIG. Regarding the “cross-sectional shape at the lug groove center portion” in Tables 1 and 2, the numbers of the corresponding drawings are described. FIG. 5A of the conventional example has a cross-sectional shape in which the groove walls on the stepping side and the kicking side do not have an angle change point, and FIG. 5B of Comparative Example 1 has a notch provided at the edge of the center block. FIG. 5C of Comparative Example 2 is a cross-sectional shape in which the stepped-side groove wall has no angle change point. Comparative Example 1 is a pattern in which the other end of the first groove portion does not communicate with the second groove portion of the lug groove adjacent in the tire circumferential direction. For convenience, the numerical value of each item is assumed to correspond to the pattern of FIG. And so on.

  Regarding “the presence or absence of an angle change in the lug groove center portion” in Tables 1 and 2, it is shown whether or not the groove wall angle α on the tread side in the lug groove center portion gradually increases from the tire equator outward in the tire width direction. In the case of “present”, the angle increases gradually, and in the case of “absent”, it means that there is no angle change.

  With respect to these pneumatic tires, traction performance, low noise performance, and stone bite resistance were evaluated by the following evaluation methods, and the results are shown in Tables 1 and 2.

Traction performance:
A test course consisting of unpaved roads, each test tire being mounted on a wheel with a rim size of 22.5 × 9.00, with an air pressure of 850 kPa, mounted on the drive shaft of a test vehicle (truck having an axle arrangement of 6 × 4). Was used for sensory evaluation by a test driver. The evaluation results were indicated by an index with the value of the conventional example being 100. The larger the index value, the better the traction performance.

Low noise performance:
Each test tire was mounted on a wheel having a rim size of 22.5 × 9.00 and mounted on a drive shaft of a test vehicle (a truck having an axle arrangement of 6 × 4), and ECE R117-02 (ECE Regulation No. 117 Revision 2) )), The sound passing outside the vehicle was measured in accordance with the tire noise test method specified in (1). Specifically, the test vehicle is caused to travel sufficiently short of the noise measurement section, the engine is stopped immediately before the section, and the maximum noise value (dB) in the noise measurement section when the vehicle is coasted (at a frequency of 800 to 1200 Hz). (A noise value in the range) was measured at a plurality of speeds in which a speed range of ± 10 km / h with respect to the reference speed was divided into eight or more at substantially equal intervals, and the average was defined as outside vehicle passing noise. The maximum noise value dB is a sound measured through an A-characteristic frequency correction circuit using a fixed microphone installed at a height of 7.5 m laterally from the traveling center line and 1.2 m from the road surface at an intermediate point in the noise measurement section. Pressure [dB (A)]. The evaluation results were shown as indices using the reciprocal of the measured values and the value of the conventional example as 100. The larger the index value, the smaller the noise passing outside the vehicle and the better the low noise performance.

Stone biting performance:
A test course consisting of unpaved roads, each test tire being mounted on a wheel with a rim size of 22.5 × 9.00, with an air pressure of 850 kPa, mounted on the drive shaft of a test vehicle (truck having an axle arrangement of 6 × 4). After running, the number of stones caught in the lug grooves was measured. The evaluation results were shown as indices using the reciprocal of the measured values and the value of the conventional example as 100. The larger the index value, the more excellent the stone biting performance.

  As is clear from Tables 1 and 2, all of Examples 1 to 12 had improved traction, low noise performance and stone bite resistance as compared with the conventional example.

  On the other hand, in Comparative Example 1, the other end of the first groove portion did not communicate with the second groove portion of the lug groove adjacent in the tire circumferential direction, and did not have a raised portion of the lug groove. Low noise performance deteriorated without improvement. In Comparative Example 2, since there is no angle change point in the groove wall on the stepping side in the lug groove center portion, sufficient off-road traction performance cannot be obtained while maintaining resistance to stone bite.

REFERENCE SIGNS LIST 1 tread portion 2 side wall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 20, 30 lug groove 20c, 30c lug groove center portion 20s, 30s lug groove shoulder portion 21, 31 first groove portion 22, 32 Two grooves 25, 35 Raised bottom part 40 Circumferential narrow groove 51 Center block 52 Shoulder block CL Tire equator E Tread end P Angle change point

Claims (12)

A ring-shaped tread portion extending in the tire circumferential direction, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed inside the tire radial direction of these sidewall portions. In the pneumatic tire with the specified rotation direction,
On the outer surface of the tread portion, a lug groove extending inward in the tire width direction from the tread end on one side with respect to the tire equator and crossing the tire equator, and the tread end on the other side with respect to the tire equator. Lug grooves extending inward in the tire width direction and intersecting the tire equator are alternately arranged in the tire circumferential direction,
Each lug groove intersects the tire equator and extends along the tire width direction, and is inclined at a smaller angle to the tire circumferential direction than the first groove from one end of the first groove. A second groove extending to the tread end, the other end of the first groove communicates with the second groove of the lug groove adjacent in the tire circumferential direction, and the first groove is a tread end side of the lug groove. It is located on the stepping side from the end of
A circumferential narrow groove connecting the second grooves adjacent to each other in the tire circumferential direction on one side or the other side with respect to the tire equator is formed, and a plurality of blocks are defined by the lug grooves and the circumferential narrow grooves. These blocks include a center block located closer to the tire equator than the circumferential narrow groove and a shoulder block located closer to the tread end than the circumferential narrow groove,
In each lug groove, a portion sandwiched between the center blocks adjacent in the tire circumferential direction is defined as a lug groove center portion, and a portion sandwiched between the shoulder blocks adjacent in the tire circumferential direction is defined as a lug groove shoulder portion. The groove width of the end portion included in the second groove portion on the outer side in the tire width direction at the lug groove center portion is smaller than the groove width of the outer end portion in the tire width direction on the lug groove shoulder portion, and the lug groove center portion is provided. A bottom raising portion is provided in a part or the whole of the extending direction of each of the lug groove center portions, and each of the groove walls on the stepping side and the kicking side in the lug groove center portion has one angle change point, and the tread surface is higher than the angle change point. The groove wall angle α formed by the groove wall of the lug groove center portion and the normal to the tread surface of the tread portion on the side of the lug groove center portion is closer to the groove bottom than the angle change point. A pneumatic tire being larger than the groove wall angle β formed between the normal to the tread surface of the wall and the tread portion.   The pneumatic tire according to claim 1, wherein a depth from a tread surface of the tread portion to the angle change point is in a range of 35% to 60% with respect to a maximum depth of the lug groove.   The groove wall angle α on the tread surface side in the lug groove center portion is 5 ° to 30 °, and the groove wall angle β on the groove bottom side in the lug groove center portion is 3 ° or less. Or the pneumatic tire according to 2.   The groove wall angle α1 on the kick-out side and the groove wall angle α2 on the tread side at the groove wall angle α on the tread surface side in the lug groove center portion satisfy a relationship of 0 ° ≦ α1−α2 ≦ 8 °. The pneumatic tire according to claim 1. The groove width of the end portion included in the second groove portion on the outer side in the tire width direction at the lug groove center portion is 38% to 60% with respect to the groove width of the outer end portion in the tire width direction on the lug groove shoulder portion. The pneumatic tire according to any one of claims 1 to 4, wherein:   The pneumatic tire according to any one of claims 1 to 5, wherein a depth of a raised portion in the center portion of the lug groove is in a range of 65% to 85% with respect to a maximum depth of the lug groove. . The groove wall angle α on the tread surface side of the lug groove center portion gradually increases from the tire equator toward the end of the lug groove center portion included in the second groove portion on the outer side in the tire width direction. 7. The pneumatic tire according to any one of to 6. The groove wall angle α on the tread side at the lug groove center portion is 7 ° on the tire equator, while 25 ° at the outer end of the lug groove center portion included in the second groove portion in the tire width direction. The pneumatic tire according to claim 7, wherein:   The pneumatic tire according to any one of claims 1 to 8, wherein a maximum depth of the lug groove is 15 mm to 28 mm. The distance from the tire equator to the tread edge was W, the area between the tire equator and the position 0.5W apart from the tire equator in the tire width direction was the inner area, and the distance from the tire equator was 0.5W in the tire width direction. When the region between the position and the tread end is the outer region, the average angle of the second groove in the inner region with respect to the tire circumferential direction is smaller than the average angle of the second groove in the outer region with respect to the tire circumferential direction. The second groove is curved or bent so that
The pneumatic tire according to any one of claims 1 to 9, wherein a maximum length of the center block in the tire width direction is 25% to 35% of a tread development width.   The pneumatic tire according to any one of claims 1 to 10, wherein a shallow groove having at least one bending point is formed on the tread surfaces of the center block and the shoulder block. One end of the shallow groove formed in the center block communicates with the circumferential narrow groove, the other end communicates with the second groove, and projects the shallow groove formed in the center block toward the tire equator. When the projected components of the shallow groove do not overlap,
12. The shallow groove formed in the shoulder block, both ends of the shallow groove end in the block, and the shallow groove is disposed on a stepping side with respect to a position of a vertex inside a tread surface of the shoulder block in the tire width direction. 13. A pneumatic tire according to claim 1.

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