JP5852686B2 - Heavy duty tire - Google Patents

Description

  The present invention relates to a heavy duty tire capable of enhancing wet performance while maintaining wear resistance and uneven wear resistance.

  Conventionally, in heavy-duty tires used for trucks and buses, for example, as shown in Patent Document 1 below, a plurality of main grooves extending continuously in the tire circumferential direction, and between the main grooves and the main grooves There has been proposed a tread pattern in which a plurality of blocks are formed by a lateral groove that connects a tire and a ground contact end.

JP 2011-195045 A

  In heavy duty tires, excellent wet performance is required. In order to improve the wet performance, it is effective to increase the groove volume of the tread portion.

  However, when the groove volume of the tread portion is increased, the rubber volume of the tread portion is decreased and the wear resistance performance may be lowered. Furthermore, the rigidity of the tread portion may be reduced, and the uneven wear resistance performance may be reduced.

  The present invention has been devised in view of the above circumstances, and a main object of the present invention is to provide a heavy-duty tire capable of obtaining excellent wet performance without impairing wear resistance and uneven wear resistance. It is said.

  The present invention provides a tread portion having a pair of center main grooves extending zigzag continuously in the tire circumferential direction on both sides of the tire equator, and a zigzag between the center main groove and the tread grounding end in the tire circumferential direction. A pair of shoulder main grooves extending continuously, a plurality of center lateral grooves connecting between the pair of center main grooves, and a plurality of middle lateral grooves connecting between the center main groove and the shoulder main grooves are provided. Thus, a center block sectioned by the pair of center main grooves and the center lateral grooves is a center land portion in which the center blocks are arranged in the tire circumferential direction, and the middle block sectioned by the center main grooves, the shoulder main grooves, and the middle lateral grooves. A heavy load comprising a pair of middle land portions arranged in the tire circumferential direction, and a shoulder land portion divided by the shoulder main groove and the tread ground contact end A tire, wherein the center main groove and the shoulder main groove are inclined at an angle of 3 ° to 9 ° with respect to a tire circumferential direction, and the long side portion is inclined in the opposite direction, and the tire Short side portions having a circumferential length smaller than the long side portion are alternately provided, and the middle lateral groove has a tire equator of an outer zigzag top portion protruding toward the grounding end side of the center main groove and the shoulder main groove. The inner side zigzag top part protruding to the side is provided inclined with respect to the tire axial direction, the center lateral groove is connected between the long side parts of the pair of center main grooves, and the middle lateral groove and Is provided so as to be inclined in the opposite direction.

  In the heavy duty tire according to the present invention, the center main groove has a first groove edge on the tire equator side and a second groove edge on the tread ground end side, and the most tread ground end of the first groove edge. The first apex on the side is preferably on the tire equator side than the second apex on the most tire equator side of the second groove edge.

  In the heavy duty tire according to the present invention, a ratio W11 / TW of a tire axial direction distance W11 from the first top to the second top and a tread contact width TW is 0.005 to 0.02. It is desirable.

  In the heavy duty tire according to the present invention, the shoulder main groove has a third groove edge on the tire equator side and a fourth groove edge on the tread ground end side, and the most tread ground end of the third groove edge. It is desirable that the third top portion on the side is located closer to the tire equator than the fourth top portion closest to the tire equator of the fourth groove edge.

  In the heavy duty tire according to the present invention, a ratio W21 / TW of the tire axial distance W21 from the third top to the fourth top and the tread contact width TW is 0.005 to 0.02. It is desirable.

  In the heavy duty tire according to the present invention, it is preferable that the zigzag amplitude W12 of the center main groove in the tire axial direction is 10% to 18% of the maximum length WA of the center block in the tire axial direction.

  In the heavy duty tire according to the present invention, it is preferable that the maximum length WB of the middle block in the tire axial direction is 95% to 105% of the maximum length WA of the center block in the tire axial direction.

  In the heavy duty tire according to the present invention, it is desirable that the maximum length WC of the shoulder land portion in the tire axial direction is 95% to 105% of the maximum length WA of the center block in the tire axial direction.

  In the heavy duty tire according to the present invention, it is desirable that the middle block has an inclined slot whose depth gradually increases toward the center main groove at a position facing the center lateral groove across the center main groove. .

  In the heavy duty tire according to the present invention, it is preferable that a land ratio of the tread portion is 70% or more.

  In the heavy duty tire of the present invention, the center main groove and the shoulder main groove are inclined with respect to the tire circumferential direction, the long side part is inclined in the opposite direction to the long side part, and the tire circumferential direction Short sides having a length smaller than the long sides are alternately provided. Thereby, the edge component in the tire axial direction is increased, and the traction performance on the wet road surface is improved. The inclination angle of the long side portion with respect to the tire circumferential direction is defined as 3 ° to 9 °. Such center main grooves and shoulder main grooves exhibit excellent drainage performance and edge effect, and improve the wet performance of heavy duty tires.

  The middle land portion is provided with a middle lateral groove that is connected to the outer zigzag top of the center main groove and the inner zigzag top of the shoulder main groove and is inclined with respect to the tire axial direction. Such a middle lateral groove exhibits excellent drainage and edge effects between the center main groove and the shoulder main groove, and improves the wet performance of the heavy duty tire. Further, the center land portion is provided with a center lateral groove that connects the long sides of the pair of center main grooves and inclines in a direction opposite to the middle lateral groove. Such a center lateral groove exhibits excellent drainage and edge effect between the pair of center main grooves, and improves the wet performance of the heavy duty tire.

  Due to these synergistic effects, the heavy-duty tire of the present invention can obtain sufficient wet performance without increasing the groove volume, and has excellent wet performance without impairing wear resistance and uneven wear resistance. Can be obtained.

It is an expanded view of the tread part which shows one embodiment of the tire for heavy loads of the present invention. It is an AA line sectional view of the tread part of Drawing 1. FIG. 2 is an enlarged development view of a crown land portion of FIG. 1. FIG. 2 is an enlarged development view of a middle land portion of FIG. 1. It is the perspective view which expanded a part of tread part of FIG. It is the perspective view which expanded the middle block of FIG. FIG. 2 is an enlarged development view of a shoulder land portion of FIG. 1.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a development view of the tread portion 2 of the heavy duty tire (not shown) of the present embodiment. FIG. 2 shows a cross section taken along line AA of the tread portion 2. As shown in FIG. 1, a pair of center main grooves 3 that are arranged on both sides of the tire equator C and extend in a zigzag manner continuously in the tire circumferential direction in the tread portion 2, and the tire axial direction of the center main grooves 3 A pair of shoulder main grooves 4 extending outwardly in a tire circumferential direction and extending in a zigzag shape are formed.

  In the center main groove 3, long side portions 3a that are inclined with respect to the tire circumferential direction and short side portions 3b that are shorter in the tire circumferential direction than the long side portions 3a are alternately provided. A zigzag center main groove 3 is formed by inclining the short side portion 3b in the direction opposite to the long side portion 3a with respect to the tire circumferential direction.

  The inclination angle α1 of the long side portion 3a with respect to the tire circumferential direction is preferably 3 ° or more, more preferably 5 ° or more, preferably 9 ° or less, more preferably 7 ° or less. When the inclination angle α1 is less than 3 °, the edge component in the tire axial direction is insufficient, and sufficient traction performance may not be obtained on a wet road surface. On the other hand, when the inclination angle α1 exceeds 9 °, the zigzag amplitude W12 of the center main groove 3 is increased, so that the drainage performance of the center main groove 3 is deteriorated and sufficient wet performance may not be obtained.

  Similarly, the shoulder main groove 4 is provided with long side portions 4a and short side portions 4b whose length in the tire circumferential direction is smaller than that of the long side portion 4a. A zigzag shoulder main groove 4 is formed by inclining the short side portion 4b in the direction opposite to the long side portion 4a with respect to the tire circumferential direction.

  Similar to the center main groove 3, the inclination angle α2 of the long side portion 4a of the shoulder main groove 4 with respect to the tire circumferential direction is preferably 3 ° or more, more preferably 5 ° or more, preferably 9 ° or less, more preferably. Is 7 ° or less. In the heavy load tire of this embodiment, the long side portion 3a inclination angle α1 of the center main groove 3 and the inclination angle α2 of the long side portion 4a of the shoulder main groove 4 are defined within an appropriate range. Have

  The center main groove 3 has an inner zigzag top portion 3i that protrudes most toward the tire equator C side, that is, the inner side in the tire axial direction, and an outer zigzag top portion 3o that protrudes most toward the ground contact end Te side, ie, the outer side in the tire axial direction. Similarly, the shoulder main groove 4 has an inner zigzag top 4i that protrudes most toward the tire equator C side, that is, the inner side in the tire axial direction, and an outer zigzag top 4o that protrudes most toward the ground contact end Te side, that is, the outer side in the tire axial direction. Yes.

  The groove width W1 of the center main groove 3 and the groove width W2 of the shoulder main groove 4 are set according to, for example, the ground contact width TW of the tread portion 2. Here, the contact width TW of the tread portion 2 is the length in the tire axial direction between the tread contact ends Te and Te.

  The tread ground contact Te means the ground contact end on the outermost side in the tire axial direction when a normal load is loaded on a normal tire and grounded on a flat surface with a camber angle of 0 °. Here, the normal state is a no-load state in which the tire is assembled on a normal rim (not shown) and filled with a normal internal pressure. Hereinafter, unless otherwise specified, dimensions and the like of each part of the tire are values measured in the normal state.

  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, “Standard Rim” for JATMA, “Design Rim” for TRA, ETRTO If so, use "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. “JAMATA” is the “maximum air pressure”, TRA is the table “TIRE LOAD LIMITS” The maximum value described in "AT VARIOUS COLD INFLATION PRESSURES". If ETRTO, "INFLATION PRESSURE".

  “Regular load” is the load that each standard defines for each tire in the standard system including the standard on which the tire is based. “JATMA” is the “maximum load capacity”, TRA is the table “TIRE LOAD” The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in the case of ETRTO.

  The groove width W1 of the center main groove 3 is preferably 1.5% to 5% of the ground contact width TW of the tread portion 2, for example. When the groove width W1 is less than 1.5% of the ground contact width TW, the drainability of the tread portion 2 may be deteriorated. When the groove width W1 exceeds 5% of the ground contact width TW, the rubber volume is insufficient, and the wear resistance and uneven wear resistance may be deteriorated.

  As shown in FIG. 2, the groove depth D1 of the center main groove 3 is preferably, for example, 10 mm to 20 mm. When the said groove depth D1 is less than 10 mm, there exists a possibility that the drainage of the tread part 2 may fall. When the groove depth D1 exceeds 20 mm, the rigidity of the tread portion 2 is insufficient, and the wear resistance and uneven wear resistance may be deteriorated.

  Similarly, the groove width W2 of the shoulder main groove 4 is desirably 1.5% to 5% of the ground contact width TW of the tread portion 2, for example, and the groove depth D2 of the shoulder main groove 4 is, for example, 10 mm to 20 mm. desirable.

  FIG. 3 shows the central region of the tread portion 2 including the pair of center main grooves 3 and 3. The center main groove 3 has a first groove edge 3c on the tire equator C side and a second groove edge 3d on the tread ground contact Te side. The first groove edge 3c has a first apex 3j closest to the tread ground end Te. The second groove edge 3d has a second apex 3p closest to the tire equator C side.

  The first top 3j is located closer to the tire equator C than the second top 3p. That is, as indicated by hatching in FIG. 3, the center main groove 3 has a groove direct passage portion 3E that communicates linearly in the tire circumferential direction between the first top portion 3j and the second top portion 3p. In the present embodiment, since the groove direct passage portion 3E is provided in the center main groove 3, the drainage performance of the center main groove 3 is improved, and the wet performance of the heavy load tire is improved.

  The width of the groove direct portion 3E is represented by a distance W11 in the tire axial direction from the first top 3j to the second top 3p. The ratio W11 / TW between the distance W11 and the tread contact width TW is, for example, preferably 0.005 or more, more preferably 0.01 or more, preferably 0.02 or less, more preferably 0.015 or less. It is.

  When the ratio W11 / TW is less than 0.005, the width of the groove direct portion 3E is insufficient, and the drainage performance of the center main groove 3 may not be sufficiently improved. On the other hand, when the ratio W11 / TW exceeds 0.02, the rubber volume in the central region of the tread portion 2 is insufficient, and there is a possibility that the wear resistance performance and uneven wear resistance performance may be deteriorated.

  FIG. 4 shows an intermediate region of the tread portion 2 including the center main groove 3 and the shoulder main groove 4. The shoulder main groove 4 has a third groove edge 4c on the tire equator C side and a fourth groove edge 4d on the tread ground contact Te side. The third groove edge 4c has a third top portion 4j closest to the tread ground contact Te. The fourth groove edge 4d has a fourth apex portion 4p closest to the tire equator C side.

  The third top 4j is located closer to the tire equator C than the fourth top 4p. That is, as indicated by hatching in FIG. 4, the shoulder main groove 4 has a groove direct portion 4E that communicates linearly in the tire circumferential direction between the third top portion 4j and the fourth top portion 4p. In the present embodiment, since the straight groove portion 4E is provided in the shoulder main groove 4, the drainage performance of the shoulder main groove 4 is improved, and the wet performance of the heavy duty tire is enhanced.

  The width of the groove direct portion 4E is represented by a distance W21 in the tire axial direction from the third top portion 4j to the fourth top portion 4p. The ratio W21 / TW between the distance W21 and the tread contact width TW is, for example, preferably 0.005 or more, more preferably 0.01 or more, preferably 0.02 or less, more preferably 0.015 or less. It is.

  When the ratio W21 / TW is less than 0.005, the width of the groove direct portion 4E is insufficient, and the drainage performance of the shoulder main groove 4 may not be sufficiently improved. On the other hand, when the ratio W21 / TW exceeds 0.02, the rubber volume in the intermediate region of the tread portion 2 is insufficient, and the uneven wear resistance may be deteriorated.

  As shown in FIGS. 1 to 4, the tread portion 2 is divided into a plurality of land portions by the center main groove 3 and the shoulder main groove 4. That is, the tread portion 2 includes a tire shaft of a pair of middle land portions 6 and a shoulder main groove 4 sandwiched between a center land portion 5 sandwiched between a pair of center main grooves 3 and 3, a crown main groove 3 and a shoulder main groove 4. The region is divided into a pair of shoulder land portions 7 located on the outer side in the direction.

  As shown in FIG. 3, the center land portion 5 is provided with a plurality of center lateral grooves 51 that connect between the pair of center main grooves 3 and 3. The center lateral groove 51 connects the long side portions 3a, 3a of the pair of center main grooves 3, 3. Such a center lateral groove 51 exhibits excellent drainage and edge effect between the pair of center main grooves 3 and 3 and improves the wet performance of the heavy duty tire.

  The center land portion 5 is divided into a plurality of center blocks 52 by a plurality of center lateral grooves 51. Thereby, the center land portion 5 is a center block row 53 in which a plurality of center blocks 52 are spaced apart in the tire circumferential direction.

  The center block 52 is formed in an octagonal shape including the step portion 54 by the zigzag center main groove 3. The zigzag amplitude W12 in the tire axial direction of the center main groove 3 is, for example, preferably 10% or more, more preferably 13% or more, preferably 18% or less of the maximum length WA of the center block 52 in the tire axial direction. More preferably, it is 16% or less.

  When the zigzag amplitude W12 is less than 10% of the maximum length WA, the edge component in the tire axial direction is insufficient, and sufficient traction performance may not be obtained on a wet road surface. On the other hand, when the zigzag amplitude W12 exceeds 18% of the maximum length WA, the drainage performance of the center main groove 3 may be deteriorated, and sufficient wet performance may not be obtained.

  A pair of chamfered portions 55 are formed at the acute block top portion located diagonally to the center block 52 among the block top portions where the center main groove 3 and the center lateral groove 51 intersect. The chamfered portion 55 promotes the flow of water between the center main groove 3 and the center lateral groove 51. Further, the chamfered portion 55 relaxes stress concentration at the block top and suppresses damage such as chipping. Instead of the chamfered portion 55, a rounded corner portion may be formed at the block vertex.

  As shown in FIG. 4, the middle land portion 6 is provided with a plurality of middle lateral grooves 61 that connect between the center main groove 3 and the shoulder main groove 4. The middle lateral groove 61 is inclined in the direction opposite to the center lateral groove 51, and connects between the outer zigzag top part 3 o of the center main groove 3 and the inner zigzag top part 4 i of the shoulder main groove 4. Such a middle lateral groove 61 exhibits excellent drainage and edge effect between the center main groove 3 and the shoulder main groove 4, and improves the wet performance of the heavy load tire.

  The middle land portion 6 is divided into a plurality of middle blocks 62 by a plurality of middle lateral grooves 61. Accordingly, the middle land portion 6 is a middle block row 63 in which a plurality of middle blocks 62 are spaced apart in the tire circumferential direction.

  As shown in FIGS. 3 and 4, the maximum length WB of the middle block 62 in the tire axial direction is, for example, preferably 95% or more, more preferably 98 of the maximum length WA of the center block 52 in the tire axial direction. % Or more, preferably 105% or less, more preferably 102% or less.

  When the maximum length WB is less than 95% of the maximum length WA, the rubber volume of the middle block 62 is insufficient, so that there is a possibility that the middle block 62 is unevenly worn. On the other hand, when the maximum length WB exceeds 105% of the maximum length WA, the rubber volume of the center block 52 is insufficient.

  FIG. 5 shows an enlarged part of the tread portion 2 viewed from the side of the ground contact Te. In FIG. 6, the middle block 62 viewed from the tire equator C side is shown enlarged. As shown in FIG. 4 to FIG. 6, an inclined slot 64 whose depth gradually increases toward the center main groove 3 is provided on the center main groove 3 side of the middle block 62.

  The inclined slot 64 is provided at a position facing the center lateral groove 51 across the center main groove 3. Such an inclined slot 64 promotes the flow of water from the middle block 62 toward the center lateral groove 51 and improves the drainage of the middle block 62.

  In the present embodiment, a chamfered portion 55 is formed at the top of the center block 52 that faces the inclined slot 64 across the center main groove 3, so that the flow of water from the middle block 62 toward the center lateral groove 51 flows. It is further promoted.

  As shown in FIG. 4, the center lateral groove 51 and the inclined slot 64 facing each other across the center main groove 3 overlap in a region 65 indicated by hatching in the tire circumferential direction. The tire circumferential direction length L1 of the region 65 is desirably 25% to 50% of the tire circumferential direction length L2 of the center lateral groove 51, for example. That is, the inclined slot 64 and the center lateral groove 51 opposed to the inclined slot 64 are in the region of 25% to 50% of the tire circumferential direction length L2 of the center lateral groove 51 in the opening length in the center main groove 3. It is desirable to overlap.

  When the length L1 is less than 25% of the length L2, the effect of promoting the flow of water from the middle block 62 toward the center lateral groove 51 by the inclined slot 64 may be reduced. On the other hand, when the length L1 exceeds 50% of the length L2, the flow of water from the middle block 62 on one side to the center lateral groove 51 across the tire equator C becomes excessively strong, and the middle block on the other side The flow of water from 62 toward the center lateral groove 51 is obstructed, and the drainage performance of the tread portion 2 as a whole may be reduced.

  As shown in FIG. 4, the inclined slot 64 extends from the center main groove 3 toward the crown main groove 4 and terminates in the middle block 62 without communicating with the crown main groove 4. The length L3 from the opening 64a in the center main groove 3 of the inclined slot 64 to the end 64b of the inclined slot 64 is preferably, for example, 55% to 65% of the groove width W1 of the center main groove 3.

  When the length L3 is less than 55% of the groove width W1, the volume of the inclined slot 64 is insufficient, and the effect of promoting the flow of water from the middle block 62 toward the center lateral groove 51 may be reduced. On the other hand, when the length L3 exceeds 65% of the groove width W1, the rubber volume of the middle block 62 is insufficient, and the wear resistance may be deteriorated. Furthermore, the rigidity of the middle block 62 may be reduced, and the uneven wear resistance performance may be reduced.

  As shown in FIGS. 2B and 6, the depth D3 of the inclined slot 64 in the opening 64a, that is, the depth of the deepest portion of the inclined slot 64 is, for example, the groove depth D1 of the center main groove 3. It is desirable to be 50% to 100%.

  When the depth D3 is less than 50% of the groove depth D1, the effect of promoting the flow of water from the middle block 62 to the center lateral groove 51 by the inclined slot 64 may be reduced.

  As shown in FIGS. 2B and 6, the inclined slot 64 has an inclined surface 64 c that is inclined inward in the tire radial direction from the tread surface 62 s of the middle block 62 at the bottom. The angle θ formed by the inclined surface 64c and the tread surface 62s of the middle block 62 is preferably 50 ° to 70 °, for example.

  When the angle θ is less than 50 °, the volume of the inclined slot 64 is insufficient, and the effect of promoting the flow of water from the middle block 62 toward the center lateral groove 51 may be reduced. On the other hand, when the angle θ exceeds 70 °, the rubber volume of the middle block 62 is insufficient, and the wear resistance may be lowered. Furthermore, the rigidity of the middle block 62 may be reduced, and the uneven wear resistance performance may be reduced.

  As shown in FIGS. 4 to 6, among the block tops at which the center main groove 3 and the shoulder main groove 4 intersect with the middle lateral groove 61, the acute block tops located diagonally to the middle block 62 have a pair of A chamfered portion 66 is formed. The chamfered portion 66 promotes the flow of water between the center main groove 3 and the shoulder main groove 4 and the middle lateral groove 61. Further, the chamfered portion 66 relaxes stress concentration at the block top and suppresses damage such as chipping. Instead of the chamfer 66, a rounded corner may be formed at the top of the block.

  FIG. 7 shows an enlarged view of the shoulder main groove 4 and the shoulder land portion 7. The shoulder land portion 7 is formed continuously in the tire circumferential direction. Such a shoulder land portion 7 has high rigidity, and effectively suppresses uneven wear such as so-called shoulder drop wear. Furthermore, since the rubber volume in the vicinity of the tread ground contact Te is secured by the shoulder land portion 7 continuous in the tire circumferential direction, the wear resistance performance and the uneven wear resistance performance are improved.

  As shown in FIGS. 3 and 7, the maximum length WC in the tire axial direction of the shoulder land portion 7 is, for example, preferably 95% or more, more preferably the maximum length WA in the tire axial direction of the center block 52. It is 98% or more, preferably 105% or less, more preferably 102% or less.

  If the maximum length WC is less than 95% of the length WA, the shoulder land portion 7 has insufficient rubber volume, which may cause uneven wear on the shoulder land portion 7. On the other hand, if the maximum length WC exceeds 105% of the maximum length WA, the rubber volume of the center block 52 is insufficient, which may cause uneven wear in the center block 52.

  In this embodiment, the land ratio of the tread portion 2 is sufficiently ensured by the shoulder land portion 7 continuous in the tire circumferential direction, and wear resistance performance and uneven wear resistance performance are enhanced. More specifically, the land ratio of the tread portion 2 is desirably 70% or more, for example.

  When the land ratio of the tread portion 2 is less than 70%, the rubber volume of the tread portion 2 is insufficient, the rigidity of the tread portion 2 is lowered, and wear resistance performance and uneven wear resistance performance may be lowered. Furthermore, the center block 52 and the middle block 62 may be damaged due to a decrease in rigidity of the tread portion 2.

  While the heavy duty tire of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be implemented in various forms.

   A heavy duty tire of size 215 / 75R17.5 having the basic structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1 and tested for wet performance and uneven wear resistance. The test method is as follows.

<Wet performance>
Each sample tire was mounted on the rear wheel of a truck (2-D vehicle) having a maximum loading capacity of 4 tons under the conditions of a rim of 17.5 × 6.00 and an internal pressure of 700 kPa. The above vehicle is brought into a wet road surface with a water film with a thickness of 5 mm in a half-loading state, passing through 10 m from the moment when the clutch is engaged with the transmission gear fixed at 2nd speed and the engine speed fixed at 1500 rpm. Time was measured and indexed. The result is the reciprocal of each passing time, and is represented by an index with the value of Example 1 being 100. The evaluation shows that the larger the value, the better the drainage performance.

<Uneven wear resistance>
The tire of Example 1 is mounted on one rear wheel of the vehicle, and the other tires are mounted on the other rear wheel, and the vehicle is run until 50% of any tire is worn on a general road. It was confirmed by visual inspection. The result is expressed by a score of 5 as Example 1. The larger the numerical value, the better the uneven wear resistance.

  As is apparent from Table 1, it was confirmed that the heavy load tires of the examples had significantly improved wet performance without impairing the uneven wear resistance as compared with the comparative examples.

2 tread portion 3 center main groove 3a long side portion 3b short side portion 3c first end edge 3d second end edge 3i inner zigzag top portion 3j first top portion 3o outer zigzag top portion 3p second top portion 4 shoulder main groove 4a long side portion 4b Short side part 4c 3rd edge 4d 4th edge 4i Inner zigzag top part 4j 3rd top part 4o Outer zigzag top part 4p 4th top part 5 Center land part 6 Middle land part 7 Shoulder land part 51 Center lateral groove 52 Center block 61 Middle lateral groove 62 Middle block 64 Inclined slot

Claims (10)

A pair of center main grooves extending in a zigzag manner on both sides of the tire equator in the tire circumferential direction on the tread portion, and extending in a zigzag manner in the tire circumferential direction between the center main groove and the tread ground contact end. By providing a pair of shoulder main grooves, a plurality of center lateral grooves connecting between the pair of center main grooves, and a plurality of middle lateral grooves connecting between the center main groove and the shoulder main grooves,
A center land section in which the center blocks divided by the pair of center main grooves and the center lateral grooves are arranged in the tire circumferential direction, and a middle block divided by the center main grooves, the shoulder main grooves, and the middle lateral grooves are tire circumferences. A heavy-duty tire comprising a pair of middle land portions arranged in a direction, and a shoulder land portion divided by the shoulder main groove and the tread grounding end,
The center main groove and the shoulder main groove have a long side portion inclined at 3 ° to 9 ° with respect to the tire circumferential direction, an inclination opposite to the long side portion, and a length in the tire circumferential direction. Are alternately provided with short sides smaller than the long sides,
The middle lateral groove is connected to an outer zigzag top portion protruding toward the ground end of the center main groove and an inner zigzag top portion protruding toward the tire equator of the shoulder main groove, and is inclined with respect to the tire axial direction. Provided,
The center lateral groove is provided between the long side portions of the pair of center main grooves, and is inclined in a direction opposite to the middle lateral groove. The center main groove has a first groove edge on the tire equator side and a second groove edge on the tread grounding end side,
2. The heavy duty tire according to claim 1, wherein a first apex of the first groove edge closest to the tread ground contact end is located closer to the tire equator than a second apex of the second groove edge closest to the tire equator.   The heavy duty tire according to claim 2, wherein a ratio W11 / TW between a distance W11 in the tire axial direction from the first top portion to the second top portion and a tread ground contact width TW is 0.005 to 0.02. The shoulder main groove has a third groove edge on the tire equator side and a fourth groove edge on the tread ground end side,
4. The third apex of the third groove edge closest to the tread grounding end side is closer to the tire equator than the fourth apex of the fourth groove edge closest to the tire equator. 5. Heavy duty tire.   The heavy duty tire according to claim 4, wherein a ratio W21 / TW of a distance W21 in the tire axial direction from the third top portion to the fourth top portion and a tread ground contact width TW is 0.005 to 0.02.   6. The heavy-duty tire according to claim 1, wherein a zigzag amplitude W <b> 12 of the center main groove in the tire axial direction is 10% to 18% of a maximum length WA of the center block in the tire axial direction. The heavy duty tire according to any one of claims 1 to 6, wherein the shoulder land portion is formed continuously in a tire circumferential direction . The heavy load according to any one of claims 1 to 7, wherein the middle block has an inclined slot whose depth gradually increases toward the center main groove at a position facing the center lateral groove across the center main groove. tire. The inclined slot and the center lateral groove facing the inclined slot overlap in an area of 25% to 50% of the tire circumferential direction length of the center lateral groove in the opening length of the center main groove. The heavy duty tire according to claim 8 . The heavy duty tire according to claim 8 or 9, wherein a depth of a deepest portion of the inclined slot is 50% to 100% of a depth of the center main groove .

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