JP2020066305A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire allowing for improvement of traction performance thereof and anti-stone-biting performance thereof on an unpaved road and furthermore allowing for improvement low noise performance thereof.SOLUTION: Lug grooves 20 and 30 constituted of first groove portions 21 and 31 crossing a tire equator CL and extending in a tire width direction and second groove portions 22 and 32 extending from one ends of the first groove portions 21 and 31 are alternately arranged, and the other ends of the first groove portions 21 and 31 are communicated with the second groove portions 32 and 22 of the lug grooves 30 and 20 adjacent to each other in a tire circumferential direction. The lug grooves 20 and 30 and a narrow groove 40 in a circumferential direction section a center block 51 and a shoulder block 52. In the lug grooves 20 and 30, bottom-raised portions 25 and 35 are arranged in parts or the whole in an extending direction of lug groove center portions 20c and 30c. One angle variation points are provided at groove walls at a tread-in side and at a kick-out side in the lug center portions 20c and 30c, where an angle α of the groove wall closer to a tread-face side than the angle variation point P is larger than an angle β of the groove wall closer to a groove-bottom side than the angle variation point P.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire suitable as a heavy duty pneumatic tire, and more specifically, a pneumatic tire capable of improving low noise performance while improving traction performance and anti-stone trapping performance on an unpaved road. Regarding tires.

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

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

Japanese Patent No. 4676959

  It is an object of the present invention to provide a pneumatic tire capable of improving low noise performance while improving traction performance and stone trapping resistance performance on an unpaved road.

  A pneumatic tire for achieving the above object is a tread portion which extends in the tire circumferential direction and forms an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a tire diameter of these sidewall portions. A pair of beads arranged on the inner side in the direction, and in a pneumatic tire with a designated rotation direction, on the outer surface of the tread portion, from the tread end on one side with respect to the tire equator to the inner side in the tire width direction. A lug groove that extends across the tire equator and a lug groove that extends inward in the tire width direction from the tread end on the other side of the tire equator and intersects the tire equator in the tire circumferential direction. Alternately arranged, each lug groove is smaller than the first groove portion extending from the one end of the first groove portion in the tire circumferential direction, the first groove portion extending along the tire width direction so as to intersect the tire equator. It is composed of a second groove portion that is inclined at an angle and extends to the tread end, the other end of the first groove portion communicates with the second groove portion of the lug grooves that are adjacent in the tire circumferential direction, and the first groove portion is the lug. Located on the stepping side of the tread end side of the groove, a circumferential narrow groove is formed that connects the second groove portions adjacent to each other in the tire circumferential direction on one side or the other side with respect to the tire equator. A plurality of blocks are defined by the lug groove and the circumferential narrow groove, and the blocks are located on the tire equator side of the circumferential narrow groove and the shoulder located on the tread end side of the circumferential narrow groove. In each lug groove including a block, a portion sandwiched between the center blocks adjacent to each other in the tire circumferential direction is a lug groove center portion, and the shoulder blocks such as adjacent to each other in the tire circumferential direction. When the lug groove shoulder portion is a portion sandwiched by the groove, the groove width of the tire width direction outer end portion of the lug groove center portion is narrower than the tire width direction outer end portion of the lug groove shoulder portion. A bottom raised part is provided in a part or all of the extending direction of the lug groove center part, and each groove wall on the stepping side and the kicking side in the lug groove center part has one angle change point, The groove wall angle α formed by the groove wall of the lug groove center portion on the tread side from the angle change point and the normal to the tread portion of the tread portion is the groove of the lug groove center portion on the groove bottom side from the angle change point. It is characterized in that it is larger than the groove wall angle β formed by the wall and the normal to the tread surface of the tread portion.

  In the present invention, since the lug groove including the first groove portion and the second groove portion is provided, it is possible to improve the low noise performance while improving the traction performance on the unpaved road. That is, the first groove portion extending along the tire width direction is arranged in the vicinity of the tire equator, which greatly contributes to the traction performance, and the first groove portion communicates with another lug groove (second groove portion). The traction performance can be efficiently improved. Further, since the noise is dispersed through the circumferential narrow groove by having the circumferential narrow groove, the low noise performance can be improved. Furthermore, since the groove component in the tire circumferential direction can be added by the circumferential fine groove, the tire can be prevented from laterally shifting during traction and stability can be improved. In addition to this, the groove width of the end portion on the tire width direction outer side in the lug groove center portion is narrower than the groove width of the tire width direction outer end portion on the lug groove shoulder portion, and the raised bottom portion is arranged in the lug groove center portion. Therefore, the volume of the lug groove does not become excessively large, and the low noise performance can be maintained without impairing the traction performance. Further, in the lug groove center portion, the groove wall angle α on the tread side from the angle change point is made larger than the groove wall angle β on the groove bottom side from the angle change point, so that the groove width relatively narrows. Stone chewing 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 biting resistance can be effectively improved.

  In the present invention, it is preferable that the tread surface side groove wall angle α in the lug groove center portion is 5 ° to 30 °, and the groove bottom side groove wall angle β in the lug groove center portion is 3 ° or less. As a result, it is possible to effectively improve stone entrapment resistance while maintaining low noise performance.

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

  In the present invention, the groove width at the tire width direction outer end of the lug groove center portion is preferably in the range of 38% to 60% of the groove width at the tire width direction outer end of the lug groove shoulder portion. . As a result, it is possible to effectively improve the traction performance while maintaining the low noise performance.

  In the present invention, the depth of the raised bottom portion in the lug groove center portion is preferably in the range of 65% to 85% with respect to the maximum depth of the lug groove. As a result, it is possible to effectively improve the traction performance while maintaining the 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 tire width direction outer side. For example, it is preferable that the groove wall angle α on the tread side of the lug groove center portion is 7 ° on the tire equator while being 25 ° at the end portion on the tire width direction outer side. As a result, it is possible to effectively improve the traction performance while maintaining the low noise performance.

  In the present invention, the groove depth of the lug groove is preferably 15 mm to 28 mm. INDUSTRIAL APPLICABILITY The present invention can exhibit particularly excellent traction performance, anti-stone trapping 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 region between the tire equator and the position 0.5 W away from the tire equator in the tire width direction is the inner region, and the tire equator has a width of 0 in the tire width direction. The average angle of the second groove portion in the inner region with respect to the tire circumferential direction is smaller than the average angle of the second groove portion in the outer region with respect to the tire circumferential direction when the region between the position separated by 5 W and the tread end is the outer region. It is preferable that the second groove is curved or bent so that the maximum length of the center block in the tire width direction is 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, the traction performance can be improved, and the generation of air column resonance noise can be suppressed. Further, by appropriately securing the maximum width of the center block, it is possible to secure sufficient 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 snow traction performance in the tire circumferential direction and the width direction can be efficiently improved. it can.

  In the present invention, one end of the shallow groove formed in the center block communicates with the circumferential narrow groove and the other end communicates with the second groove portion, and the shallow groove formed in the center block is projected toward the tire equator. The projected components of the shallow groove do not overlap with each other, and the shallow groove formed on the shoulder block ends at both ends within the block, and is arranged on the stepping side from the position of the apex on the tire width direction inner side of the tread surface of the shoulder block. Is preferred. As described above, the traction performance on snow can be effectively improved by providing the appropriately shaped shallow groove in the center block located near the equator of the tire, which greatly contributes to the traction performance. Further, by arranging so that the shallow grooves do not overlap as described above, avoiding excessive decrease in block rigidity over the entire circumference of the tire, and snow traction performance and off-road traction performance in the tire circumferential direction and It is possible to achieve a good balance between the above and these performances at a high level. Further, it is possible to increase the edge component on the stepping side while suppressing the deterioration of the rigidity of the shoulder block, and it is possible to effectively improve the snow performance. On the other hand, since there is no shallow groove on the kicking side and the block rigidity and the amount of rubber are secured, uneven wear (heel and toe wear) can be effectively suppressed.

  In the present invention, the “tread ends” are both ends of the tread pattern portion of the tire in a state where the tire is assembled on a regular rim, filled with regular internal pressure, and no load is applied (no load). 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 (specified by JATMA) which is a linear distance between the tread edges measured along the tire width direction in the above state. "Tread width"). The “regular rim” is a rim that is defined for each tire in a standard system including a standard on which the tire is based. For example, JATMA is a standard rim, TRA is “Design Rim”, or ETRTO. If so, it is set to “Measuring Rim”. "Regular internal pressure" is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. In the case of JATMA, the maximum air pressure, and in the case of TRA, the table "TIRE LOAD LIMITS AT VARIOUS". The maximum value described in "COLD INFORMATION PRESSSURES" is "INFLATION PRESSURE" for ETRTO, but 180 kPa for tires for passenger cars.

It is a meridian sectional view of the pneumatic tire which consists of 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. It is sectional drawing which shows the lug groove formed in the tread surface of FIG. It is a front view which shows an example of the tread surface of the pneumatic tire of a prior art example. (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, a pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a sidewall portion 2 which is disposed inside a tire radial direction. And a pair of bead portions 3. In FIG. 1, reference symbol CL indicates the tire equator, and reference symbol E indicates the tread edge. 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 not drawn because it is a meridional sectional view, 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, whereby the toroidal of the pneumatic tire. The basic structure of the shape is constructed. Hereinafter, although the description with reference to FIG. 1 is basically based on the illustrated meridian cross-sectional shape, each of the tire constituent members extends in the tire circumferential direction to form 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 back from the vehicle inner side to the outer side around the bead cores 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4. On the other hand, a plurality of layers (four layers in FIG. 1) of 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 that are inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect 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 the range of, for example, 10 ° to 60 °. Although not used in the pneumatic tire of FIG. 1, a belt reinforcing layer (not shown) may be further provided on the outer peripheral side of the belt layer 7 in the present invention. 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 organic fiber cord can be set at an angle of 0 ° to 5 ° with respect to the tire circumferential direction.

  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. The side rubber layer 12 is arranged on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2. A rim cushion rubber layer 13 is arranged on the outer peripheral side (outer side 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 having different physical properties (cap tread rubber layer and undertread rubber layer) are laminated in the tire radial direction.

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

  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 drawing) with respect to the tire equator CL. And a tire width from a tread end E on the other side (left side in the drawing) with respect to the tire equator CL, and a lug groove 20 that intersects with the tire equator CL (may be referred to as "one side lug groove 20" in the following description). A lug groove 30 (which may be referred to as “the other side lug groove 30” in the following description) that extends inward in the direction and intersects with the tire equator CL is provided. A plurality of lug grooves 20 on one side and a plurality of lug grooves 30 on the other side are provided.

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

  One lug groove 20 and the other lug groove 30 are alternately arranged 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 portion 21 and the other side of the lug groove 20 on one 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 the one side with respect to the tire equator CL, the second groove portions 22 of the one side lug groove 20 are spaced in the tire circumferential direction. On the other side of 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 groove portions 21 and 31 are alternately arranged and are 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. I shall.

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

  The first groove portions 21 and 31 of the lug grooves 20 and 30 are located closer to the step-in side than 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 specified, but the lug grooves 20 and 30 as a whole have a rotation direction R from the tire equator CL side toward the tire width direction outer side. It has a shape inclined in the opposite direction.

  In addition to such lug grooves 20 and 30, circumferential narrow grooves 40 are provided. The circumferential narrow groove 40 is formed between the second groove portions adjacent to each other in the tire circumferential direction on one side of the tire equator CL, that is, the second lug groove 20 on one side adjacent to the tire equator CL on the one side in the tire circumferential direction. The groove portions 22 extend in 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 that are 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. On the other hand, 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, 30 and the circumferential narrow groove 40. Among the plurality of blocks 50, one located closer to the tire equator CL side than the circumferential narrow groove 40 is called a center block 51, and one located closer to the tread end E side than the circumferential narrow groove 40 is called a shoulder block 52. At least a part of the center block 51 exists on the tire equator CL due to the groove shape described above.

  In each of the lug grooves 20, 30, a portion sandwiched between center blocks 51 adjacent to each other in the tire circumferential direction is a lug groove center portion 20c, 30c, and a portion sandwiched between shoulder blocks 52 adjacent in the tire circumferential direction is a lug groove shoulder. The parts are 20s and 30s. Specifically, as shown in FIG. 2, the lug groove center portions 20c and 30c are surrounded by a line connecting adjacent corner portions of adjacent center blocks 51 in the tire circumferential direction and an edge line of the center block 51. The lug groove shoulder portions 20 s and 30 s, which correspond to the slanted line portion, are surrounded by the edge line of the shoulder block 52 and the line that connects the corner portions that are adjacent to each other in the tire circumferential direction. It corresponds to the department. The groove width Gc at the tire width direction outer end of the lug groove center portions 20c and 30c is smaller than the groove width Gs of the tire width direction outer end of the lug groove shoulder portions 20s and 30s. The groove width Gc and the groove width Gs are both measured on the tread surface of the tread portion 1. Specifically, the groove width Gc is the length of a line connecting the corner portions of the center blocks 51 adjacent to each other in the tire circumferential direction, and the groove width Gs is the corner portion of the shoulder blocks 52 adjacent to each other in the tire circumferential direction. It is the length of the connected line.

  As shown in FIG. 3, the lug groove center portions 20c and 30c are provided with bottom raised portions 25 and 35 at some or all of their extending directions. 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 the kicking side (right side in the figure). The angle changing points P on the stepping side and the kicking side are both at the same depth from the tread surface of the tread portion 1. The groove wall angle α is a groove wall angle formed by the groove walls of the lug groove center portions 20c and 30c and the normal line to the tread surface of the tread portion 1 on the tread side from the angle change point P. The groove wall angle formed by 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, in the lug groove center portions 20c and 30c, at least the groove wall on the tire radial outer side is inclined with respect to the normal to the tread surface of the tread portion 1, and the inclination angle of the groove wall on the tire radial outer side is the tire diameter. It is larger than the inclination angle of the groove wall on the inner side in the direction.

  In the pneumatic tire described above, since the lug grooves 20 and 30 including the first groove portions 21 and 31 and the second groove portions 22 and 32 are provided, the low noise performance is improved while improving the traction performance on the unpaved road. 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 groove portions 32 and 22, the traction performance can be efficiently improved. Further, since the circumferential narrow groove 40 is provided, noise is dispersed through the circumferential narrow groove 40, so that low noise performance can be improved. Furthermore, since the groove component in the tire circumferential direction can be added by the circumferential narrow groove 40, it is possible to prevent the tire from laterally shifting during traction and improve the stability. In addition to this, the groove width Gc at the tire width direction outer end of the lug groove center portions 20c and 30c is narrower than the groove width Gs of the tire width direction outer end of the lug groove shoulder portions 20s and 30s. Since the raised bottom portions 25 and 35 are arranged 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. Further, in the lug groove center portions 20c and 30c, the groove width G is set so that the groove wall angle α on the tread side from the angle change point P is larger than the groove wall angle β on the groove bottom side from the angle change point P. The stone trapping resistance can be maintained in the lug groove center portions 20c and 30c which are relatively narrowed.

  The depth 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 depth PD from the tread surface of the tread portion 1 to the angle change point P is equal to that of the lug grooves 20 and 30. It is preferably in the range of 35% to 60% with respect to the maximum depth FD. In this way, by appropriately setting the depth PD of the angle change point P with respect to the maximum depth FD of the lug grooves 20 and 30, the stone entrapment 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 and 30 is less than 35% or more than 60%, the effect of improving the anti-stone bite performance cannot be sufficiently obtained. . The depth PD of the angle change point P is preferably maintained at a ratio with respect to the maximum depth FD of the lug grooves 20 and 30 as the depth RD of the bottom raised portions 25 and 35 described later changes. You can also keep it.

  Further, the depth RD of the raised bottom portions 25, 35 in the lug groove center portions 20c, 30c is preferably in the range of 65% to 85% with respect to the maximum depth FD of the lug grooves 20, 30. Thus, by appropriately setting the depth RD of the raised bottom portions 25, 35 with respect to the maximum depth FD of the lug grooves 20, 30, it is possible to effectively improve the traction performance while maintaining the 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 conversely, 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. The 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 and 30c is preferably 4 mm or more. By appropriately setting the groove wall angle α on the tread side and the groove wall angle β on the groove bottom side in this way, it is possible to effectively improve the stone trapping 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 anti-stone bite performance cannot be sufficiently obtained, and if the groove wall angle α on the tread side is larger than 30 °, the lug grooves 20, 30 are formed. It becomes difficult to maintain the low noise performance because the volume of the above becomes excessively large.

  Furthermore, in the groove wall angle α on the tread side of the lug groove center portions 20c and 30c, the groove wall angle α1 on the kicking side and the groove wall angle α2 on the stepping side must satisfy the relation of 0 ° ≦ α1−α2 ≦ 8 °. Is preferred. More preferably, the groove wall angle α1 on the kicking side is larger than the groove wall angle α2 on the stepping side, and the relationship of 0 ° <α1−α2 ≦ 8 ° may be satisfied. In this way, by appropriately setting the groove wall angle α1 on the kicking side and the groove wall angle α2 on the stepping side, the stone trapping resistance can be effectively improved. Here, if the angle difference (α1-α2) between the groove wall angle α1 and the groove wall angle α2 is larger than 8 °, the stone entrapment resistance tends to deteriorate.

  In the pneumatic tire, the groove width Gc of the tire width direction outer end of the lug groove center portions 20c and 30c is 38 with respect to the groove width Gs of the tire width direction outer end of the lug groove shoulder portions 20s and 30s. It may be in the range of 60% to 60%. By properly setting the ratio of the groove width Gc to the groove width Gs in this way, it is possible to effectively improve the traction performance while maintaining the 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 deteriorate, and conversely, when it exceeds 60%, the low noise performance tends to deteriorate.

  In addition, the groove wall angle α on the tread side of the lug groove center portions 20c and 30c preferably gradually increases from the tire equator CL toward the outer side in the tire width direction. Such an angle change of the groove wall angle α starts from the connecting portion between the first groove portions 21 and 31 and the second groove portions 22 and 32 of the lug grooves 20 and 30, and is a lug groove included in the second groove portions 22 and 32. The end portions of the center portions 20c and 30c on the outer side in the tire width direction are set as end points. In this way, the groove wall angle α on the tread side gradually increases from the tire equator CL toward the outer side in the tire width direction, so that it is possible to effectively improve the traction performance while maintaining the low noise performance. The above-mentioned change in the groove wall angle α can be applied to both the groove wall angle α1 on the kicking 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 tread side groove wall angle α is preferably 7 ° on the tire equator CL and 25 ° at the end portion on the tire width direction outer side. As described above, by setting the groove wall angle α on the tread side at a specific position in the tire width direction, it is possible to effectively improve the traction performance while maintaining the low noise performance.

  In FIG. 2, the lug grooves 20 and 30 have a distance in the tire width direction from the tire equator CL to the tread end E as W, and a position apart from the tire equator CL by 0.50 W in the tire width direction and the tire equator CL. When a region between the tread end E and a position spaced from the tire equator CL in the tire width direction by 0.50 W is defined as an inner region A, the second groove portions 22, 32 in the outer region B are defined. The second groove portions 22, 32 are curved or bent so that the average angle θa of the second groove portions 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 groove portions 22, 32 of the lug grooves 20, 30 are smoothly curved so that the inclination angle with respect to the tire circumferential direction gradually decreases from the tread end E side toward the tire equator CL side, or at least one bend. It has a point and is bent. The maximum length L of the center block 51 in the tire width direction is set to 25% to 35% of the tread development width TW. As described above, by bending or bending the second groove portions 22 and 32, the groove length can be increased, the traction performance can be improved, and the generation of air column resonance noise can be suppressed. Further, since the maximum width of the center block 51 is appropriately secured, it is possible to secure sufficient 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 an angle formed by a straight line connecting the midpoints of the groove width directions of the lug grooves 20 and 30 at the boundary positions of the regions with respect to the tire circumferential direction. Can be asked as However, at the tire equator CL and the tread end E, as shown in the figure, the midpoint at the tire equator CL or the tread end E of the extension line of the second groove portions 22, 32 drawn toward the tire equator CL or the tread end E is used. I shall.

  As described above, the first groove portions 21 and 31 are provided to secure the groove component in the tire width direction mainly in the vicinity of the tire equator CL that largely contributes to the 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 80 ° to 100 °. As a result, the first groove portions 21 and 31 can efficiently improve the traction performance. 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 becomes large, and a sufficient groove component in the tire width direction is ensured. Cannot be achieved, and the effect of improving traction performance is limited.

  Further, 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, and 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 groove depth of the shallow groove 60 is less than 1 mm, the effect of providing the shallow groove 60 is not obtained because the shallow groove 60 is too shallow, and if the groove depth of the shallow groove 60 exceeds 3 mm, the block rigidity is increased. The impact will increase. In the following description, the shallow groove 60 formed in the center block 51 is called a center shallow groove 61, and the shallow groove 60 formed in the shoulder block 52 is called 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 for each block 50 as shown in the figure.

  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 divided by the lug grooves 20, 30 and the circumferential narrow grooves 40 as described above, each block 50 is 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 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, as shown, the center shallow groove 61 preferably has one end communicating with the circumferential narrow groove 40 and the other end communicating with the second groove portions 22, 32 of the lug grooves 20, 30. 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 the projection components of the center shallow groove 61 when the center shallow groove 61 is projected toward the tire equator CL do not overlap. Thus, by providing the center shallow groove 61 having an appropriate shape in the center block 51 located near the tire equator CL, which greatly contributes to the traction performance, it is possible to effectively improve the snow traction performance. Further, since the center shallow grooves 61 do not overlap as described above, the block rigidity is prevented from being 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 avoided. Can be improved, and these performances can be highly compatible.

  On the other hand, the shoulder shallow groove 62 is preferably terminated at both ends within 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. Further, the shoulder shallow groove 62 is preferably arranged on the stepping side with respect to 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 way, it is possible to increase the edge component on the stepping side while suppressing the decrease in rigidity of the shoulder block 52, and it is possible to effectively improve the snow performance. On the other hand, since there is no shallow groove on the kicking side and the block rigidity and the amount of rubber are secured, uneven wear (heel and toe wear) can be effectively suppressed.

  The tire size is 315 / 80R22.5, has the basic structure illustrated in FIG. 1, and has a basic tread pattern, whether or not the lug groove center portion has a bottom raised, cross-sectional shape of the lug groove center portion, and lug groove center portion. The magnitude 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 kick side of the lug groove center portion Angle α1, groove wall angle α2 on the stepping side of the lug groove center, angle difference between groove wall angle α1 and groove wall angle α2 (α1−α2), groove width of the lug groove center with respect to groove width Gs of the lug groove shoulder 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 determined conventional example, comparative examples 1-2, and examples 1-12 were produced.

  For the "tread patterns" in Tables 1 and 2, the corresponding drawing numbers are described. The pattern of FIG. 4 of the conventional example is significantly different from the pattern of FIG. 2, but as described in the figure, the numerical values of each item were obtained by associating the dimensions and the like of each part with FIG. Regarding "Cross-sectional shape at center of lug groove" in Tables 1 and 2, the corresponding drawing numbers are described. FIG. 5 (a) 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. 5 (b) of Comparative Example 1 has a notch at the edge portion of the center block 5C of Comparative Example 2 is a cross-sectional shape in which the groove wall on the stepping side does not have an angle change point. In addition, 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 that is adjacent in the tire circumferential direction, but for convenience sake, the numerical values of each item correspond to the pattern of FIG. Etc. were displayed.

  Regarding “presence or absence of angle change in 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 toward the tire width direction outer side. Yes, the case of “present” means that the angle gradually increases, and the case of “no” means that the angle does not change.

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

Traction performance:
Each test tire was mounted on a wheel with a rim size of 22.5 × 9.00, the air pressure was set to 850 kPa, the tire was mounted on the drive shaft of a test vehicle (a truck with an axle arrangement of 6 × 4), and the test course consisted of an unpaved road. A sensory evaluation was conducted by a test driver. The evaluation results are shown 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 with a rim size of 22.5 × 9.00, mounted on the drive shaft of a test vehicle (a truck with an axle arrangement of 6 × 4), and ECE R117-02 (ECE Regulation No. 117 Revision 2). The noise passing through the vehicle was measured in accordance with the tire noise test method specified in (4). Specifically, the test vehicle is run sufficiently before the noise measurement section, the engine is stopped immediately before the section, and the maximum noise value (dB) in the noise measurement section when coasting is performed (frequency of 800 to 1200 Hz). The noise value in the range) was measured at a plurality of speeds at which the speed range of ± 10 km / hour with respect to the reference speed was divided into eight or more at substantially equal intervals, and the average was taken as the outside passing noise. The maximum noise value dB is the sound measured through the A characteristic frequency correction circuit using a stationary microphone installed at a height of 7.5 m laterally from the running center line and 1.2 m from the road surface at the midpoint in the noise measurement section. Pressure [dB (A)]. The evaluation result was shown by an index with the value of the conventional example being 100, using the reciprocal of the measured value. The larger the index value, the smaller the passing noise outside the vehicle and the better the low noise performance.

Stone bite resistance:
Each test tire was mounted on a wheel with a rim size of 22.5 × 9.00, the air pressure was set to 850 kPa, the tire was mounted on the drive shaft of a test vehicle (a truck with an axle arrangement of 6 × 4), and the test course consisted of an unpaved road. After running, the number of stones bitten in the lug groove was measured. The evaluation result was shown by an index with the value of the conventional example being 100, using the reciprocal of the measured value. The larger this index value is, the better the stone biting resistance is.

  As is clear from Table 1 and Table 2, in each of Examples 1 to 12, the traction property, the low noise performance, and the anti-stone trapping performance were improved as compared with the conventional example.

  On the other hand, in Comparative Example 1, since the other end of the first groove portion is not in communication with the second groove portion of the lug groove that is adjacent in the tire circumferential direction and does not have the raised bottom portion of the lug groove, the off-road traction performance is low. 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 center portion of the lug groove, sufficient off-road traction performance cannot be obtained while maintaining stone trapping resistance.

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

A pneumatic tire for achieving the above object is a tread portion which extends in the tire circumferential direction and forms an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a tire diameter of these sidewall portions. A pair of beads arranged on the inner side in the direction, and in a pneumatic tire with a designated rotation direction, on the outer surface of the tread portion, from the tread end on one side with respect to the tire equator to the inner side in the tire width direction. A lug groove that extends across the tire equator and a lug groove that extends inward in the tire width direction from the tread end on the other side of the tire equator and intersects the tire equator in the tire circumferential direction. Alternately arranged, each lug groove is smaller than the first groove portion extending from the one end of the first groove portion in the tire circumferential direction, the first groove portion extending along the tire width direction so as to intersect the tire equator. It is composed of a second groove portion that is inclined at an angle and extends to the tread end, the other end of the first groove portion communicates with the second groove portion of the lug grooves that are adjacent in the tire circumferential direction, and the first groove portion is the lug. Located on the stepping side of the tread end side of the groove, a circumferential narrow groove is formed that connects the second groove portions adjacent to each other in the tire circumferential direction on one side or the other side with respect to the tire equator. A plurality of blocks are defined by the lug groove and the circumferential narrow groove, and the blocks are located on the tire equator side of the circumferential narrow groove and the shoulder located on the tread end side of the circumferential narrow groove. In each lug groove including a block, a portion sandwiched between the center blocks adjacent to each other in the tire circumferential direction is a lug groove center portion, and the shoulder blocks such as 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 Is narrower than the groove width of the end portion of the lug groove, a bottom raised portion is provided in a part or all of the extending direction of the lug groove center portion, and each of the groove walls on the stepping side and the kicking side of the lug groove center portion is 1 There are two angle change points, 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 side from the angle change point is the groove bottom from the angle change point. On the side, the groove wall angle β is larger than the groove wall angle β formed by the groove wall of the lug groove center portion and the normal to the tread surface of the tread portion.

In the present invention, the groove width at the tire width direction outer side in the lug groove center portion and the end portion included in the second groove portion is 38% to 60 with respect to the groove width at the tire width direction outer end portion in the lug groove shoulder portion. It is preferably in the range of%. As a result, it is possible to effectively improve the traction performance while maintaining the low noise performance.

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

Claims (12)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on the tire radial inner side of these sidewall portions. In a pneumatic tire with a specified rotation direction,
On the outer surface of the tread portion, a lug groove that extends inward in the tire width direction from the tread end on one side with respect to the tire equator and intersects with the tire equator, and from the tread end on the other side with respect to the tire equator. A lug groove extending inward in the tire width direction and intersecting with the tire equator is alternately arranged in the tire circumferential direction,
Each lug groove is a first groove portion that extends along the tire width direction and intersects the tire equator, and is inclined from one end of the first groove portion at a smaller angle with respect to the tire circumferential direction than the first groove portion. The second groove portion extending to the tread end, the other end of the first groove portion communicates with the second groove portion of the lug groove adjacent in the tire circumferential direction, the first groove portion is the tread end side of the lug groove. It is located on the stepping side from the end of
A circumferential narrow groove that connects the second groove portions 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 groove and the circumferential narrow groove. These blocks include a center block located on the tire equator side of the circumferential narrow groove and a shoulder block located on the tread end side of 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 a lug groove center portion, and a portion sandwiched between the shoulder blocks adjacent to each other in the tire circumferential direction is a lug groove shoulder portion, The groove width of the tire width direction outer end portion of the lug groove center portion is narrower than the tire width direction outer end portion of the lug groove shoulder portion, and part or all of the lug groove center portion extending direction. Is provided with a bottom raised portion, each groove wall on the stepping side and the kicking side in the lug groove center portion has one angle change point, and the groove of the lug groove center portion on the tread side from the angle change point. The groove wall angle α formed by the wall and the normal to the tread surface of the tread portion is on the groove wall of the lug groove center portion and the tread surface of the tread portion on the groove bottom side with respect to the angle change point. A pneumatic tire and greater than the groove wall angle β formed between the normal line to.   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 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 tread side in the center portion of the lug groove and the groove wall angle α1 on the kicking side and the groove wall angle α2 on the stepping side satisfy the relation of 0 ° ≦ α1−α2 ≦ 8 °. The pneumatic tire according to claim 1.   The groove width at the tire width direction outer end of the lug groove center portion is in the range of 38% to 60% of the groove width at the tire width direction outer end of the lug groove shoulder portion. The pneumatic tire according to any one of claims 1 to 4.   The pneumatic tire according to any one of claims 1 to 5, wherein a depth of the raised bottom portion in the lug groove center portion is in a range of 65% to 85% with respect to a maximum depth of the lug groove. .   The pneumatic tire according to any one of claims 1 to 6, wherein a groove wall angle α on the tread side in the lug groove center portion gradually increases from the tire equator toward the tire width direction outer side.   The pneumatic tire according to claim 7, wherein the groove wall angle α on the tread side of the lug groove center portion is 7 ° on the tire equator and is 25 ° at the end portion on the tire width direction outer side. .   The pneumatic tire according to any one of claims 1 to 8, wherein the maximum depth of the lug groove is 15 mm to 28 mm. The distance from the tire equator to the tread edge is W, the region between the tire equator and the tire equator at a distance of 0.5 W in the tire width direction is the inner region, and the tire equator is at a distance of 0.5 W in the tire width direction. When the region between the position and the tread end is the outer region, the average angle with respect to the tire circumferential direction of the second groove portion in the inner region is smaller than the average angle with respect to the tire circumferential direction of the second groove portion in the outer region. So that the second groove portion is curved or bent,
The maximum length of the center block in the tire width direction is 25% to 35% of the tread development width, and the pneumatic tire according to any one of claims 1 to 9.   The pneumatic tire according to claim 1, wherein a shallow groove having at least one bending point is formed on a tread surface 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 and the other end communicates with the second groove portion, and the shallow groove formed in the center block is projected toward the tire equator. When the projection components of the shallow groove do not overlap,
The shallow groove formed in the shoulder block has both ends terminating within the block, and is arranged on the stepping side with respect to the position of the apex of the tread surface of the shoulder block on the inner side in the tire width direction. Pneumatic tire described in.

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