JP2017056781A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve travel performance on an ice road while maintaining travel performance on a dry road and a snow road.SOLUTION: The present invention relates to a pneumatic tire characterized in that each block provided to a tread part 2 is provided with at least one siping; the ratio Smax/Smin of area Smax of a tread of a maximum block and area Smin of a tread of a minimum block is 1.0-1.2, and the ratio Emax/Emin of a total edge component Emax of a maximum edge block and a total edge component Emin of a minimum edge block is 1.0-1.3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire in which siping is formed on a block.

  Conventionally, in order to improve the frictional force on an icy road, for example, a pneumatic tire in which siping is provided in a block provided in a tread portion has been proposed. Such a pneumatic tire has improved frictional force on an icy road due to the edge effect of siping.

  However, since the rigidity of the block provided with siping is lowered, there is a problem that the running performance of the tire on a dry road and a snow road is lowered.

  In order to deal with such problems, Patent Documents 1 and 2 below limit the length of the siping and the length of the lateral edge to a predetermined range, thereby maintaining the running performance on the dry road and the snow road while maintaining the ice performance. Proposing pneumatic tires that can improve road performance. However, even with such a pneumatic tire, there is not enough compatibility between running performance on dry roads and snowy roads and running performance on ice roads, and there is room for further improvement.

JP 2009-190677 A JP 2012-101719 A

  The inventors have conducted extensive research and found that the difference between the maximum value and the minimum value of the tread edge area of each block and the total edge component that is the sum of the edge components of each block increases mainly. It was found that only the block having the value exerted the frictional force, and the other blocks did not exhibit the effective frictional force. The inventors have also found that the entire block can be effectively used by limiting the ratio between the maximum value and the minimum value of the tread area and total edge component of each block to a certain range.

  The present invention has been devised in view of the actual situation as described above, and is based on defining the ratio between the maximum value and the minimum value of the tread area and total edge component of each block within a certain range. The main object of the present invention is to provide a pneumatic tire capable of improving driving performance on ice roads while maintaining driving performance on dry roads and snow roads.

  Among the present inventions, the invention according to claim 1 is a tire tread portion having a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and a tire circumferential direction outside the center main groove in the tire axial direction. A pair of middle main grooves extending continuously, a pair of shoulder narrow grooves extending continuously in the tire circumferential direction on the outer side in the tire axial direction of the middle main groove, and a plurality of center lateral grooves crossing between the center main grooves, , A plurality of middle lateral grooves crossing between the center main groove and the middle main groove, a plurality of inner shoulder lateral grooves crossing between the middle main groove and the shoulder narrow groove, the shoulder narrow groove and the tread. By providing a plurality of outer shoulder lateral grooves that cross between the ends, a center block row in which a plurality of center blocks are arranged in the tire circumferential direction between the center main grooves, A pair of middle block rows in which a plurality of middle blocks are arranged in the tire circumferential direction between the main main groove and the middle main groove, and a plurality of inner shoulder blocks are arranged between the middle main groove and the shoulder narrow groove. A pair of inner shoulder block rows arranged in the circumferential direction, and a pair of outer shoulder block rows arranged in the tire circumferential direction on the outer side of the shoulder narrow groove are provided, the center block, the middle block, The inner shoulder block and the outer shoulder block have different shapes, and the center block, the middle block, the inner shoulder block, and the block including the outer shoulder block have a tread area. The largest block with the largest and the smallest block with the smallest tread area The ratio Smax / Smin between the area Smax of the tread of the largest block and the area Smin of the tread of the smallest block is 1.0 to 1.2, and each block is at least 1 A siping of a book is formed, and among the blocks, there are a maximum edge block having the largest sum edge component, which is a sum of edge components projected in the tire axial direction, and a minimum edge block having the smallest sum edge component. The ratio Emax / Emin between the sum edge component Emax of the largest edge block and the sum edge component Emin of the smallest edge block is 1.0 to 1.3.

  Further, in the invention according to claim 2, the block includes a maximum circumferential direction rigidity block having the largest rigidity in the tire circumferential direction and a minimum circumferential direction rigidity block having the smallest rigidity in the tire circumferential direction. 2. The air according to claim 1, wherein a ratio Fmax / Fmin between a tire circumferential direction rigidity Fmax of the maximum circumferential direction rigid block and a tire circumferential direction rigidity Fmin of the minimum circumferential direction rigid block is 1.0 to 1.3. This is a tire.

  According to a third aspect of the present invention, the center block is provided with two sipings whose both ends are opened in the pair of center main grooves, respectively, so that a central block piece between the sipings and the central block are provided. The tire block is divided into a pair of end block pieces on both sides in the tire circumferential direction, and the center block piece of the center block has a larger width in the tire axial direction than the end block piece of the center block. This is a pneumatic tire.

  According to a fourth aspect of the present invention, the middle block is provided with two sipings having one end opened in the center main groove and the other end opened in the middle main groove. The central block piece of the middle block is divided into a block piece and a pair of end block pieces on both sides in the tire circumferential direction of the central block piece. 4. The pneumatic tire according to claim 1, wherein the pneumatic tire has a substantially trapezoidal shape gradually decreasing toward the other side, and the end block piece of the middle block has a substantially rectangular shape. 5.

  According to a fifth aspect of the present invention, the middle block includes: a first middle block in which a length in the tire circumferential direction of the substantially trapezoidal central block piece gradually decreases toward an outer side in the tire axial direction; A second middle block in which the length in the tire circumferential direction of the central block piece of the shape gradually decreases toward the inside in the tire axial direction, the middle block row includes the first middle block, the second middle block, The pneumatic tire according to claim 4, wherein are alternately arranged in the tire circumferential direction.

  The center block, middle block, inner shoulder block, and outer shoulder block of the pneumatic tire of the present invention have different shapes. Thereby, each block can be formed in the shape according to each arrangement | positioning. For this reason, traveling performance on dry roads and snowy roads and traveling performance on icy roads are compatible.

  In the pneumatic tire of the present invention, the ratio Smax / Smin between the area Smax of the tread of the largest block and the area Smin of the tread of the smallest block is 1.0 to 1.2. The ratio Emax / Emin between the sum edge component Emax of the largest edge block having the largest sum edge component and the sum edge component Emin of the smallest edge block having the smallest sum edge component is 1.0 to 1.3. Such a pneumatic tire reduces the difference in frictional force exerted by each block, and exerts an effective frictional force on the entire block that is in contact with the ground. For this reason, traveling performance on ice roads is improved while traveling performance on dry roads and snowy roads is maintained.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an expanded sectional view of the AA part of FIG. It is the elements on larger scale of a center block row. (A) is BB sectional drawing of FIG. 3, (b) is CC sectional drawing of FIG. It is the elements on larger scale of a middle block row. (A) is DD sectional drawing of FIG. 5, (b) is EE sectional drawing of FIG. It is the elements on larger scale of an inner side shoulder block row | line | column. (A) is FF sectional drawing of FIG. 7, (b) is GG sectional drawing of FIG. It is the elements on larger scale of an outer side shoulder block row | line | column. (A) is HH sectional drawing of FIG. 9, (b) is II sectional drawing of FIG. It is explanatory drawing explaining an edge component. It is explanatory drawing explaining the rigidity of the circumferential direction of a block.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire (hereinafter sometimes simply referred to as “tire”) 1 of the present embodiment is suitably used as a heavy duty pneumatic tire for winter, for example. The tread portion 2 of the tire 1 has a pair of center main grooves 3 and 3 extending zigzag continuously on both sides of the tire equator C, and a tire circumferential direction outside the center main groove 3 in the tire axial direction. A pair of middle main grooves 4 and 4 extending in a zigzag manner are provided.

  FIG. 2 is a cross-sectional view taken along the line AA in FIG. As shown in FIG. 2, the groove width W1 of the center main grooves 3 and 3 (meaning the groove width perpendicular to the center line of the groove) and the groove depth D1, and the groove width W2 of the middle main groove 4 and The groove depth D2 is variously determined according to the custom. However, when these groove widths or groove depths are small, the running performance on snowy roads may be deteriorated. On the contrary, when these groove widths or groove depths are large, the contact area and rigidity of the tread portion 2 may be reduced, and the steering stability may be deteriorated. For this reason, the groove width W1 of the center main groove 3 and the groove width W2 of the middle main groove 4 are preferably 3 to 7% of the tread grounding width TW (shown in FIG. 1), for example. The groove depth D1 of the center main groove 3 and the groove depth D2 of the center main groove 3 are preferably 14.5 to 24.5 mm, for example.

  The tread contact width TW is the tread end Te on the outermost side in the tire axial direction when the tire 1 that is assembled to the normal rim and filled with the normal internal pressure is contacted to the plane with a normal load and a camber angle of 0 °. , And means the distance in the tire axial direction between Te.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, the standard rim for JATMA, “Design Rim” for TRA, or ETRTO If present, it means "Measuring Rim".

  “Regular internal pressure” is the air pressure defined by the standard for each tire. The maximum air pressure for JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” for TRA, If so, use "INFLATION PRESSURE".

  “Regular load” is the load that the standard defines for each tire. If it is JATMA, it is the maximum load capacity. If so, it is "LOAD CAPACITY".

  In the present specification, unless otherwise specified, the size of each part of the tire is a value specified in a normal state with no load loaded with a normal rim and filled with a normal internal pressure.

  As shown in FIGS. 1 and 2, the tread portion 2 is further provided with a pair of shoulder narrow grooves 5, 5 extending linearly continuously in the tire circumferential direction outside the middle main groove 4 in the tire axial direction. It is done.

  As shown in FIG. 2, the groove width W3 and the groove depth D3 of the shoulder narrow groove 5 are determined from the viewpoint of securing rigidity at both ends in the tire axial direction of the tread portion 2 and the groove width W1 of the center main groove 3 and It is set smaller than the groove depth D1. The groove width W3 of the shoulder narrow groove 5 is desirably set to 0.8 to 2.0% of the tread ground contact width TW, for example. The depth D3 of the shoulder narrow groove 5 is set to 11.5 to 21.5 mm, for example.

  As shown in FIG. 1, the tread portion 2 further includes a plurality of center lateral grooves 6 that cross between the center main grooves 3 and 3, and a plurality of middle that crosses between the center main groove 3 and the middle main groove 4. A lateral groove 7, a plurality of inner shoulder lateral grooves 8 that cross between the middle main groove 4 and the shoulder narrow groove 5, and a plurality of outer shoulder lateral grooves 9 that intersect between the shoulder narrow groove 5 and the tread end Te are provided. .

  As shown in FIGS. 1 and 2, the groove width W4 of the center lateral groove 6, the groove width W5 of the middle lateral groove 7, and the groove width W6 of the inner shoulder lateral groove 8 are, for example, the groove width W1 of the center main groove 3. It is set to 0.95 to 1.05 times. The groove depth D4 of the center lateral groove 6, the groove depth D5 of the middle lateral groove 7, and the groove depth D6 of the inner shoulder lateral groove 8 are, for example, 0.65 to 0 of the groove depth D1 of the center main groove 3 .85 times is set. Each of these lateral grooves inclines at a small angle θ1 of 5 to 10 ° with respect to the tire axial direction and extends substantially linearly. Each such lateral groove ensures drainage while maintaining the rigidity of the tread portion 2.

  The outer shoulder lateral groove 9 includes a first outer shoulder lateral groove 10 extending in the tire axial direction with a constant groove width W7, and a second outer shoulder lateral groove 11 having a widened portion 59 in which the groove width gradually increases outward in the tire axial direction. Are alternately provided in the tire circumferential direction. The groove depth D7 of the outer shoulder lateral groove 9 is set to 9.5 to 19.5 mm, for example. Such outer shoulder lateral grooves 9 improve wet performance and drainage performance.

  As shown in FIG. 1, the tread portion 2 is provided with a center block row 20 on the tire equator C. The center block row 20 includes a plurality of center blocks 21 divided by a pair of center main grooves 3 and 3 and a center lateral groove 6. Each center block 21 has the same shape.

  The tread portion 2 is provided with a pair of middle block rows 30 and 30 on both sides of the center block row 20 in the tire axial direction. The middle block row 30 includes a plurality of middle blocks 31 divided by a center main groove 3, a middle main groove 4, and a middle lateral groove 7. The middle block 31 of the present embodiment has a first middle block 32 in which the block length in the tire circumferential direction gradually decreases toward the outer side in the tire axial direction, and a block length in the tire circumferential direction gradually increases toward the outer side in the tire axial direction. The second middle blocks 33 are alternately provided in the tire circumferential direction.

  In the tread portion 2, a pair of inner shoulder block rows 40, 40 are provided on the outer side of the middle block row 30 in the tire axial direction. The inner shoulder block row 40 includes a plurality of inner shoulder blocks 41 divided into a middle main groove 4, a shoulder narrow groove 5, and an inner shoulder lateral groove 8. Each inner shoulder block 41 has the same shape.

  The tread portion 2 is provided with a pair of outer shoulder block rows 50, 50 outside the inner shoulder block row 40 in the tire axial direction. The outer shoulder block row 50 includes a plurality of outer shoulder blocks 51 divided by the shoulder narrow grooves 5 and the outer shoulder lateral grooves 9. In the outer shoulder block 51, for example, first outer shoulder blocks 52 and second outer shoulder blocks 53 having different shapes are provided alternately in the tire circumferential direction.

  Each block 13 provided in the tread portion 2 has an optimum shape depending on the formation position thereof. Therefore, the center block 21, the middle block 31, the inner shoulder block 41, and the outer shoulder block 51 of the present invention have different shapes. Thereby, each block 13 is made into the shape according to each arrangement | positioning, and dry road performance, snowy road performance, and icy road performance are compatible.

  The block 13 includes a maximum block 14 having the largest tread area and a minimum block 15 having the smallest tread area. In the tire 1 of the present embodiment, the second middle block 33 is the maximum block 14. The center block 21 is the minimum block 15. However, the present invention is not limited to such an embodiment.

  In the tire 1 of the present invention, the ratio Smax / Smin between the area Smax of the tread of the largest block 14 and the area Smin of the tread of the smallest block 15 is 1.0 to 1.2. Such a tire 1 has a small difference in frictional force exerted by each block, and exerts an effective frictional force on each of the blocks that are in contact with the ground. When the ratio Smax / Smin is larger than 1.2, a block having a relatively small tread area does not exhibit an effective frictional force, and the frictional force of the entire tire decreases.

  In order to further exert the above-described effects, the ratio Smax / Smin is preferably 1.15 or less, more preferably 1.10 or less, and further preferably 1.05 or less.

  Each block 13 of the present invention is provided with at least one siping. Two sipings are formed in each block 13 of the present embodiment. Such a block 13 exhibits a large frictional force due to the edge effect of siping.

  The block 13 includes a maximum edge block 16 having the largest sum edge component, which is the sum of the edge components projected in the tire axial direction, and a minimum edge block 17 having the smallest sum edge component. In the present embodiment, the maximum edge block 16 is the center block 21, and the minimum edge block 17 is the outer shoulder block 51. However, the present invention is not limited to such an embodiment.

  As shown in FIG. 11, when the block a has an edge b having a length L5 that is inclined by α with respect to the tire axial direction C, the edge component projected in the tire axial direction of the edge b is , L5cosα. The sum edge component is the sum of the edge components projected in the tire axial direction for the entire edge of the block a. In the case where siping c is provided in block a, the total edge component of block a as a whole is the edge component projected in the tire axial direction of edges d and d of siping c onto the total edge component of the edge of block a. Is added and calculated.

  As shown in FIG. 1, in the tire 1 of the present invention, the ratio Emax / Emin between the total edge component Emax of the maximum edge block 16 and the total edge component Emin of the minimum edge block 17 is 1.0 to 1.3. is there. In such a tire 1, the difference in frictional force due to the edge effect exhibited by each block 13 is small, and the effective frictional force is exhibited in the entire grounded block. When the ratio Emax / Emin is greater than 1.3, the block having a relatively small total edge component does not exhibit an effective frictional force, and the frictional force of the entire tire decreases.

  In order to further exhibit the above-described effect, the ratio Emax / Emin is preferably 1.15 or less, more preferably 1.10 or less, and further preferably 1.05 or less.

  The land ratio Lr of the tread portion 2 is preferably 65% or more, more preferably 70% or more, preferably 80% or less, more preferably 75% or less. As a result, traveling performance on icy roads and snowy roads is improved while maintaining steering stability on dry roads. The “land ratio” is a ratio Sb / Sa of the actual total ground contact area Sb to the total area Sa of the virtual ground contact surface in which each groove and siping are filled between the tread ground contact Te and Te. .

  The total edge component Et of the entire tire 1 is preferably 30000 mm or more, more preferably 32000 mm or more, preferably 35000 mm or less, more preferably 33000 mm or less. When the total edge component Et is small, the running performance on icy roads and snowy roads may be deteriorated. On the contrary, when the total edge component Et is large, the steering stability on the dry road may be lowered.

  The number N of blocks included in each block row is preferably 70 or more, more preferably 75 or more, preferably 85 or less, more preferably 80 or less. When the number N of blocks in each block row is small, there is a possibility that the edge component cannot be secured. On the other hand, when the number N of blocks is large, the rigidity of the tread portion 2 is lowered, and the steering stability may be lowered.

  Among each block 13, the tire circumferential direction rigidity Fmax of the maximum circumferential direction rigidity block 18 having the largest tire circumferential direction rigidity, and the tire circumferential direction rigidity Fmin of the minimum circumferential direction rigidity block 19 having the smallest tire circumferential direction rigidity. The ratio Fmax / Fmin is preferably 1.0 or more, more preferably 1.1 or more, preferably 1.3 or less, more preferably 1.2 or less. In the present embodiment, the first middle block 32 is the maximum circumferential direction rigid block 18, and the center block 21 is the minimum circumferential direction rigid block 19. However, the present invention is not limited to such an embodiment.

  The rigidity F in the tire circumferential direction of the block is indicated by a load in the tire circumferential direction per unit deformation amount. Specifically, as shown in FIG. 12, a load f in the tire circumferential direction D was applied in a state where the longitudinal load was 0 using a contact plate (not shown) bonded to the entire surface of the tread surface b of the block a. At this time, the amount of displacement t in the tire circumferential direction D of the tread b of the block a is measured. The rigidity F in the tire circumferential direction of the block is specified by a ratio f / t (N / mm) between the load f in the tire circumferential direction and the positional deviation amount t.

  In order to further exhibit the above-described effect, the ratio Fmax / Fmin is preferably 1.15 or less, more preferably 1.10 or less, and further preferably 1.05 or less.

  FIG. 3 shows a partially enlarged view of the center block row 20. As shown in FIG. 3, the center block 21 is formed in, for example, a substantially hexagonal shape having a maximum width near the center in the tire circumferential direction.

  The maximum block width W8 of the center block 21 in the tire axial direction is set to 0.12 to 0.14 times the tread ground contact width TW (shown in FIG. 1), for example. The maximum block length L1 of the center block 21 is set to, for example, 1.0 to 1.3 times the block width W8. Such a center block 21 exhibits an edge effect with a good balance in the tire circumferential direction and the tire axial direction.

  The center block 21 is provided with two sipings 22 and 22 having both ends opened in the pair of center main grooves 3 and 3, respectively. Thus, the center block 21 is divided into a central block piece 23 and a pair of end block pieces 24 and 24 arranged on both sides in the tire circumferential direction. Such a center block 21 increases an edge component extending in the tire axial direction, and particularly improves traction performance and braking performance on an icy road.

  For example, the center block piece 23 is located in the center portion of the center block 21 in the tire circumferential direction, and is formed in a substantially rectangular shape including the maximum width portion 21 e of the center block 21 in the tire axial direction. The central block piece 23 increases the edge component extending in the tire axial direction while maintaining the rigidity of the center block 21 in the tire axial direction. Therefore, the traction performance and the steering stability performance on the icy road of the tire are improved.

  The pair of end block pieces 24 and 24 are formed in a substantially trapezoidal shape in which the width in the tire axial direction gradually decreases toward both outer sides of the block in the tire circumferential direction, for example. Such an end block piece 24 suppresses a decrease in rigidity of the center block 21 while increasing an edge component, and improves traveling performance on ice roads while maintaining traveling performance on dry roads and snow roads. .

  The siping 22 is inclined at an angle θ2 of 5 to 10 ° in the tire axial direction, for example. The two sipings 22 extend parallel to each other in the tire axial direction. Each siping 22 extends in a zigzag manner. Such a siping 22 increases the rigidity of the center block 21 by engaging the central block piece 23 and the end block piece 24 when a load in the tire circumferential direction acts on the center block 21. Thereby, the handling stability on an icy road is improved.

  As shown in FIG. 4A, the depth d1 of the siping 22 is desirably set to 0.35 to 0.45 times the block height h1 of the center block 21, for example.

  As shown in FIG. 4B, it is desirable that the depth d1 of the siping 22 is larger on the outer side in the tire axial direction than the center portion. Such a siping 22 improves the steering stability on dry roads and ice roads in order to ensure the rigidity of the center portion of the center block 21 in the tire axial direction.

  As shown in FIG. 3 and FIG. 4A, it is desirable to provide sub-sipes 25 extending in the tire axial direction at a depth smaller than that of the siping 22 on both sides of the siping 22 in the tire circumferential direction. Such a secondary siping 25 complements the edge effect of the siping 22 and improves the running performance on icy roads and snowy roads.

  FIG. 5 shows a partially enlarged view of the middle block row 30. As shown in FIG. 5, the middle block row 30 includes a plurality of middle blocks 31 provided in the tire circumferential direction.

  The maximum block width W9 in the tire axial direction of the middle block 31 is set to 0.12 to 0.14 times the tread ground contact width TW (shown in FIG. 1), for example. Further, the maximum block length L2 in the tire circumferential direction of the middle block 31 is set to, for example, 1.0 to 1.3 times the block width W9. Thereby, traveling performance on dry roads and snowy roads and traveling performance on icy roads are compatible.

  The middle block 31 is provided with two sipings 34 and 34 having one end opened at the center main groove 3 and the other end opened at the middle main groove 4, whereby a central block piece 35 between the sipings 34 and 34, The central block piece 35 is divided into a pair of end block pieces 36 on both sides in the tire circumferential direction. Such a middle block 31 improves traction performance on ice roads.

  The central block piece 35 of the middle block 31 has, for example, a substantially trapezoidal shape in which the length of the tread surface in the tire circumferential direction gradually decreases from one side to the other side in the tire axial direction. Such a middle block 31 can diversify the directions of the edges, and is useful for improving the running performance on snowy roads and ice roads.

  The pair of end block pieces 36, 36 of the middle block 31 are preferably formed in, for example, a substantially rectangular shape that is line-symmetric with respect to the center line 35c of the center block piece 35. Such an end block piece 36 improves the traction performance and the braking performance on a dry road, an icy road, and a snowy road in a well-balanced manner.

  The middle block 31 includes a first middle block 32 and a second middle block 33 having different shapes. The first middle block 32 and the second middle block 33 are provided alternately in the tire circumferential direction.

  The first middle block 32 has, for example, a polygonal shape in which the block length in the tire circumferential direction gradually decreases toward the outer side in the tire axial direction. An edge 32 i extending in the tire circumferential direction on the inner side in the tire axial direction of the first middle block 32 is formed by a curve or an arc that is convex with respect to the center main groove 3. Furthermore, the edge 32 o extending in the tire circumferential direction on the outer side in the tire axial direction of the first middle block 32 is formed by a curved line or an arc that is concave with respect to the middle main groove 4. In the central block piece 35 of the first middle block 32, the length of the tread surface in the tire circumferential direction gradually decreases from the inner side A in the tire axial direction toward the outer side B. Such a first middle block 32 increases the rigidity on the inner side in the tire axial direction, and improves the steering stability on dry roads and snowy roads.

  The second middle block 33 has, for example, a polygonal shape in which the block length in the tire circumferential direction gradually increases toward the outer side in the tire axial direction. Further, the edge 33 i extending in the tire circumferential direction on the inner side in the tire axial direction of the second middle block 33 is formed in a substantially zigzag shape. Further, the edge 33 o extending in the tire circumferential direction on the outer side in the tire axial direction of the second middle block 33 is formed by a curved line or an arc that is concave with respect to the middle main groove 4. Further, in the central block piece 35 of the second middle block 33, the length of the tread surface in the tire circumferential direction gradually decreases from the outer side B in the tire axial direction toward the inner side A. Such a second middle block 33, combined with the first middle block 33, increases edge components extending in multiple directions and improves steering stability on ice roads.

  The two sipings 34, 34 of the present embodiment are, for example, a first siping 34a inclined at an angle θ3 of 5 to 10 ° in the tire axial direction and zigzag in the tire axial direction, and opposite to the first siping 34a. And a second siping 34b that is inclined in the direction and zigzags in the tire axial direction. Such a siping 34 improves the rigidity of the central block piece 35 in the tire axial direction when a load in the tire circumferential direction acts on the middle block 31. For this reason, the handling stability especially on an icy road is improved.

  As shown in FIG. 6A, the depth d2 of the siping 34 is preferably set to 0.35 to 0.45 times the block height h2 of the middle block 31, for example.

  As shown in FIG. 6B, it is desirable that the depth d2 of the siping 34 is larger at the tire axial direction outer side B than at the tire axial direction inner side A. Such a siping 34 effectively drains the absorbed water to the outer side in the tire axial direction, and maintains the rigidity of the middle block 31 on the inner side in the tire axial direction. For this reason, driving stability on dry roads is improved while traveling performance on icy roads and snowy roads is improved.

  As shown in FIG. 5 and FIG. 6A, it is desirable that auxiliary sipings 37 extending in the tire axial direction at a depth smaller than that of the siping 22 are provided on both sides of the siping 22 in the tire circumferential direction. Such a secondary siping 37 complements the edge effect of the siping 22 and improves the running performance on icy and snowy roads.

  FIG. 7 shows a partially enlarged view of the inner shoulder block row 40. The maximum block width W10 in the tire axial direction of the inner shoulder block 41 is set to 0.11 to 0.13 times the tread ground contact width TW, for example. The maximum block length L3 of the center block of the inner shoulder block 41 is set to, for example, 1.0 to 1.3 times the block width W10. Such an inner shoulder block 41 achieves both running performance on dry roads and snowy roads and running performance on ice roads.

  The edge 41 i extending in the tire circumferential direction on the inner side in the tire axial direction of the inner shoulder block 41 of the present embodiment is formed by a curved line or an arc that is concave with respect to the middle main groove 4. In addition, an end edge 41o extending in the tire circumferential direction on the outer side in the tire axial direction of the inner shoulder block 41 extends in a substantially straight line parallel to the tire circumferential direction. The inner shoulder block 41 having the end edges 41i and 41o improves the steering stability on the snow road because the end edge 41i presses and hardens the snow when running on the snow road.

  The inner shoulder block 41 of the present embodiment is provided with two sipings 42, 42 having one end opened by the middle main groove 4 and the other end opened by the shoulder narrow groove 5, whereby the center between the sipings 42, 42 is provided. The block piece 43 is divided into a pair of end block pieces 44 and 44 on both sides in the tire circumferential direction of the central block piece 43. Such an inner shoulder block 41 improves steering stability on dry roads and snowy roads.

  The central block piece 43 of the inner shoulder block 41 has, for example, a substantially rectangular shape whose width in the tire axial direction is smaller than the adjacent end block piece 44. Further, the end block piece 44 of the inner shoulder block 41 has, for example, a substantially rectangular shape whose width in the tire axial direction gradually increases from the central block piece 43 side toward the inner shoulder lateral groove 8 side. The inner shoulder block 41 including the central block piece 43 and the end block pieces 44 and 44 increases the edge component extending in the tire axial direction, improves the rigidity on both sides in the tire circumferential direction, and provides traction performance on ice roads. And improve the braking performance.

  The two sipings 42 and 42 provided on the inner shoulder block 41 are inclined at an angle θ4 of 5 to 10 ° in the tire axial direction and extend parallel to each other in the tire axial direction, for example. Further, the siping 42 of the present embodiment extends in a zigzag shape. Such a siping 42 increases the rigidity of the inner shoulder block 41 by closely contacting the central block piece 43 and the end block piece 44 when a load in the tire circumferential direction acts on the inner shoulder block 41. Improve the handling stability of the.

  As shown in FIG. 8A, the depth d3 of the siping 42 is preferably set to 0.35 to 0.45 times the block height h3 of the inner shoulder block 41, for example.

  As shown in FIG. 8B, it is desirable that the depth d3 of the siping 42 is larger on the outer side B in the tire axial direction than on the inner side A in the tire axial direction. Such a siping 42 effectively drains the absorbed moisture outward in the tire axial direction, and maintains the rigidity of the inner shoulder block 41 on the tire axial direction side. For this reason, driving stability on dry roads is improved while traveling performance on icy roads and snowy roads is improved.

  As shown in FIG. 7 and FIG. 8A, it is desirable to provide auxiliary sipings 45 extending in the tire axial direction at a depth smaller than the siping 22 on both sides of the siping 22 in the tire circumferential direction. Such a secondary siping 45 complements the edge effect of the siping 22 and improves the running performance on icy and snowy roads.

  FIG. 9 shows a partially enlarged view of the outer shoulder block row 50. As shown in FIG. 9, in the outer shoulder block row 50, first outer shoulder lateral grooves 10 and second outer shoulder lateral grooves 11 having different shapes are alternately provided in the tire circumferential direction. For example, the first outer shoulder lateral groove 10 has a constant width and extends substantially parallel to the tire axial direction and linearly. Further, the second outer shoulder lateral groove 11 is continuous with the shoulder narrow groove 5, and has a linear width 58 extending linearly in the tire axial direction with a larger groove width than the first outer shoulder lateral groove 10, and continuous with the linear portion 58. And a widened portion 59 that gradually increases the width in the tire circumferential direction and extends outward in the tire axial direction. The first outer shoulder lateral groove 10 and the second outer shoulder lateral groove 11 improve the drainage performance while maintaining the rigidity of the outer shoulder block row 50.

  As shown in FIG. 2, the outer shoulder lateral groove 9 is preferably provided with a tie bar 57 in which a part of the groove bottom 9d is raised. The tie bar 57 of the present embodiment is provided in the first outer shoulder lateral groove 10. Such a tie bar 57 improves the rigidity of the outer shoulder block row 50 in the tire circumferential direction, and in particular, improves steering stability on a dry road.

  In the outer shoulder block 51, first outer shoulder blocks 52 and second outer shoulder blocks 53 having different shapes are provided alternately in the tire circumferential direction.

  The maximum block width W11 in the tire axial direction of the outer shoulder block 51 is set to, for example, 0.10 to 0.12 times the tread contact width TW (shown in FIG. 1). The maximum block length L4 of the outer shoulder block 51 is set to 1.0 to 1.3 times the block width W11, for example. Such an outer shoulder block 51 achieves both driving performance on dry roads and snowy roads and driving performance on ice roads.

  An edge 51i extending in the tire circumferential direction on the inner side in the tire axial direction of the outer shoulder block 51 of the present embodiment extends substantially linearly in parallel with the tire circumferential direction. Further, the outer edge 51o of the outer shoulder block 51 on the outer side in the tire axial direction extends in the tire circumferential direction while being bent. The outer shoulder block 51 having such end edges 51i and 51o increases the edge component while improving the wandering performance, and improves the steering stability on the icy road.

  The outer shoulder block 51 of the present embodiment is provided with a siping 54 having one end connected to the outer edge 51o in the tire axial direction and the other end interrupted in the outer shoulder block 51. As a result, the edge component increases while maintaining the rigidity of the outer shoulder block 51 on the inner side A in the tire axial direction.

  The siping 54 includes, for example, a first siping 54a and a second siping 54b having different shapes. The first siping 54a is inclined from the edge 51o in the tire axial direction at an angle θ5 of 5 to 10 °, linearly extends toward the edge 51i, and is bent along the tire circumferential direction inside the outer shoulder block 51. In addition, the outer shoulder block 51 is interrupted. The second siping 54b is inclined in a direction opposite to the first siping 54a with respect to the tire axial direction and extends linearly, and is bent in the tire circumferential direction in the direction opposite to the first siping 54a. It breaks inside. Further, the first and second sipings 54a and 54b extend linearly while approaching each other toward the inner side in the tire axial direction, and bend while being separated from each other in the middle. Such a siping 54 facilitates deformation of the end edge 51o and improves wandering performance.

  As shown in FIG. 10A, it is desirable that a chamfered portion 55 in which a step surface 51 s and a groove wall 54 w of the siping 54 are cut out is formed in the opening 54 o on the tread surface of the siping 54. Such a chamfered portion 55 improves the water absorption of the siping 54, and in particular, improves snow road performance.

  The depth d4 of the siping 54 is preferably set to 0.35 to 0.45 times the block height h4 of the outer shoulder block 51, for example.

  As shown in FIG. 10B, it is desirable that the depth d7 of the siping 54 gradually increase from the inner side in the tire axial direction toward the outer side. Such a siping 54 effectively drains the absorbed water to the outer side in the tire axial direction and maintains the rigidity of the outer shoulder block 51 on the inner side in the tire axial direction. For this reason, driving stability on dry roads is improved while traveling performance on icy roads and snowy roads is improved.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, it cannot be overemphasized that this invention can be changed into various aspects, without being limited to said specific embodiment.

A heavy duty pneumatic tire of size 11R22.5 based on the specifications in Table 1 was prototyped based on the specifications in Table 1. In addition, the traction performance of each sample tire on icy roads and the running performance on dry and snowy roads were tested.
The common specifications and test methods for tires are as follows.
Land ratio Lr = 75.0%
Total edge component for the entire tire Et = 32000mm

<Traction performance on icy roads>
The following test vehicle was used to test the traction performance on icy roads. The traction performance was measured by measuring the running time when a test vehicle in a stopped state was suddenly started on a icy road test course and allowed to travel a certain distance. The result is an index in which the reciprocal of the traveling time of Comparative Example 1 is 100, and the larger the value, the greater the traction performance on the icy road.
Test vehicle: 10t truck Sample tire mounting position: mounted on all wheels Loading capacity: 50% of standard loading capacity

<Driving performance on dry and snowy roads>
Using the test vehicle, the overall driving performance including driving stability, riding comfort, turning performance, etc. when driving on dry and snowy road test courses was evaluated by the driver's sensuality. A result is a score which sets the comparative example 1 to 100, and shows that driving performance is excellent, so that a numerical value is large.
The test results are shown in Table 1.

  As is clear from Table 1, it was confirmed that the pneumatic tires of the examples had significantly improved running performance on icy roads while maintaining running performance on dry roads and snowy roads.

DESCRIPTION OF SYMBOLS 1 Tire 2 Tread part 3 Center main groove 4 Middle main groove 5 Shoulder narrow groove 6 Center lateral groove 7 Middle lateral groove 8 Inner shoulder lateral groove 9 Outer shoulder lateral groove 13 Block 20 Center block row 21 Center block 22 Siping 30 Middle block row 31 Middle block 40 Inner shoulder block row 41 Inner middle block 50 Outer shoulder block row 51 Outer shoulder block

Claims (5)

A pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator in the tread portion; a pair of middle main grooves extending continuously in the tire circumferential direction outside the center main groove in the tire axial direction; and A pair of shoulder narrow grooves extending continuously in the tire circumferential direction on the outer side in the tire axial direction of the middle main groove, a plurality of center lateral grooves crossing between the center main grooves, and between the center main groove and the middle main groove A plurality of middle transverse grooves across the middle main grooves and the shoulder narrow grooves, a plurality of inner shoulder transverse grooves across the middle groove, and a plurality of outer shoulder lateral grooves across the shoulder narrow grooves and the tread ends. By providing
A center block row in which a plurality of center blocks are arranged in the tire circumferential direction between the center main grooves,
A pair of middle block rows in which a plurality of middle blocks are arranged in the tire circumferential direction between the center main groove and the middle main groove,
A pair of inner shoulder block rows in which a plurality of inner shoulder blocks are arranged in the tire circumferential direction between the middle main groove and the shoulder narrow groove, and
A pair of outer shoulder block rows are provided outside the shoulder narrow groove, and a plurality of outer shoulder blocks are arranged in the tire circumferential direction.
The center block, the middle block, the inner shoulder block, and the outer shoulder block have different shapes,
Among the blocks including the center block, the middle block, the inner shoulder block, and the outer shoulder block, the largest block having the largest tread area and the smallest block having the smallest tread area are included.
The ratio Smax / Smin between the area Smax of the tread of the largest block and the area Smin of the tread of the smallest block is 1.0 to 1.2,
Each of the blocks is formed with at least one siping,
The block includes a maximum edge block having the largest sum edge component that is the sum of the edge components projected in the tire axial direction, and a minimum edge block having the smallest sum edge component,
The pneumatic tire according to claim 1, wherein a ratio Emax / Emin between a sum edge component Emax of the maximum edge block and a sum edge component Emin of the minimum edge block is 1.0 to 1.3. The block includes a maximum circumferential rigidity block having the largest rigidity in the tire circumferential direction and a minimum circumferential rigidity block having the smallest rigidity in the tire circumferential direction.
2. The air according to claim 1, wherein a ratio Fmax / Fmin between a tire circumferential direction rigidity Fmax of the maximum circumferential direction rigid block and a tire circumferential direction rigidity Fmin of the minimum circumferential direction rigid block is 1.0 to 1.3. Enter tire. The center block is provided with two sipings whose both ends are opened in the pair of center main grooves, respectively, so that a center block piece between the sipings and a pair of ends on both sides in the tire circumferential direction of the center block piece Divided into block pieces,
The pneumatic tire according to claim 1 or 2, wherein the central block piece of the center block has a larger width in the tire axial direction than the end block piece of the center block. The middle block is provided with two sipings having one end opened in the center main groove and the other end opened in the middle main groove, whereby a central block piece between the sipings and a tire of the central block piece It is divided into a pair of end block pieces on both sides in the circumferential direction,
The central block piece of the middle block has a substantially trapezoidal shape in which the length in the tire circumferential direction of the tread gradually decreases from one side in the tire axial direction toward the other side,
The pneumatic tire according to any one of claims 1 to 3, wherein the end block piece of the middle block has a substantially rectangular shape. The middle block includes a first middle block in which a tire circumferential direction length of the substantially trapezoidal central block piece gradually decreases toward an outer side in a tire axial direction, and a tire circumferential direction of the substantially trapezoidal central block piece. A second middle block whose length gradually decreases inward in the tire axial direction,
The pneumatic tire according to claim 4, wherein in the middle block row, the first middle block and the second middle block are alternately arranged in a tire circumferential direction.

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