JP2016107884A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire with suppressed uneven wear and furthermore with improved wet performance.SOLUTION: A center land portion 5 comprises center lateral grooves 10 inclined at an angle of 20-40° and terminating in the center land portion 5. The center lateral grooves 10 include first center lateral grooves 10A and second center lateral grooves 10B. The first center lateral grooves 10A and the second center lateral grooves 10B are inclined in a same orientation, and are alternately arranged in a tire circumferential direction. The first center lateral grooves 10A and the second center lateral grooves 10B each comprise an overlap portion 15 and a non-overlap portion 16. Average groove width of the overlap portion 15 is smaller than that of the non-overlap portion 16. A middle land portion 6 comprises middle lateral grooves 30. The middle lateral grooves 30 comprise a pair of main portions 34 and a joint portion 35. The main portions 34 are inclined at an angle of 20-40° to a tire axial direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire with improved center lateral grooves and middle lateral grooves.

  There has been proposed a pneumatic tire having a tread portion having a lateral groove extending incline with respect to the tire axial direction. The lateral grooves effectively discharge the water film between the tread portion and the road surface to the outside in the tire axial direction during wet running, thereby improving the wet performance of the tire.

  However, in a pneumatic tire having a lateral groove, the pattern rigidity of the tread portion is nonuniform in the circumferential direction. Therefore, such a pneumatic tire has a problem that uneven wear of the tread portion is likely to occur.

  In order to solve such a problem, the following Patent Document 1 discloses a pneumatic tire that improves wet performance while suppressing uneven wear of the middle land portion by providing siping of a specific shape in the middle land portion. is suggesting. However, even in such a pneumatic tire, there is room for further improvement in suppressing uneven wear and improving wet performance.

JP 2010-179827 A

  The present invention has been devised in view of the actual situation as described above, and provides a pneumatic tire with improved wet performance while suppressing uneven wear on the basis of improving the shape of the center lateral groove and the middle lateral groove. The main purpose is to do.

  According to the first aspect of the present invention, the tread portion includes a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and in the tire circumferential direction outside the center main groove in the tire axial direction. By providing a pair of shoulder main grooves extending continuously, a center land portion between the pair of center main grooves and a pair of middle land portions between the center main groove and the shoulder main grooves are provided. In the divided pneumatic tire, the center land portion has one end communicating with the center main groove, inclined at an angle of 20 to 40 ° with respect to the tire axial direction, and the other end A center lateral groove that terminates in the center land portion is provided, and the center lateral groove extends from the center main groove on one side toward the center main groove on the other side and terminates beyond the tire equator. And a second center lateral groove extending from the other side center main groove toward the one side center main groove and ending beyond the tire equator, the first center lateral groove and the second center groove The lateral grooves are inclined in the same direction and are alternately provided in the tire circumferential direction, and the first center lateral groove and the second center lateral groove adjacent in the tire circumferential direction are overlapped with each other in the tire circumferential direction. A non-overlapping portion that does not overlap with each other in the tire circumferential direction, the average groove width of the overlapping portion is smaller than the average groove width of the non-overlapping portion, and one end of the middle land portion is the center main groove A middle lateral groove that communicates and the other end communicates with the shoulder main groove is provided, and the middle lateral groove extends from the one end and the other end to the center of the middle land portion and inclines in the same direction. And a joint portion that is continuous with the pair of main portions and is inclined in a direction opposite to the main portions, and the pair of main portions is inclined at an angle of 20 to 40 ° with respect to a tire axial direction. It is characterized by including the inclined part.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the length of the overlapping portion in the tire axial direction is 0.10 to 0.40 times the width of the center land portion in the tire axial direction. It is.

  According to a third aspect of the present invention, the middle land portion includes a middle block divided by the middle lateral groove, and each middle block has a groove depth larger than the middle lateral groove and has a groove width. 3. The pneumatic tire according to claim 1, wherein a middle siping of 0.5 to 1.0 mm is provided, and the middle siping is a pneumatic tire according to claim 1, wherein both ends are terminated in the middle land portion.

  Further, the middle sipe includes a pair of main sipe portions extending in the same direction as the main portion, and a sub sipe portion extending in the same direction as the joint portion and connecting between the pair of main sipe portions. It is a pneumatic tire of Claim 3 containing.

  The center lateral groove of the pneumatic tire of the present invention has one end communicating with the center main groove, inclined at an angle of 20 to 40 ° with respect to the tire axial direction, and the other end terminating in the center land portion. Such a center lateral groove makes the center land portion into a rib shape continuous in the tire circumferential direction while improving the wet performance. For this reason, the rigidity in the tire circumferential direction of the center land portion is maintained, and consequently uneven wear of the center land portion is suppressed.

  The center lateral groove extends from the center main groove on one side to the center main groove on the other side and terminates beyond the tire equator, and the center main groove on the one side from the center main groove on the other side. And a second center lateral groove extending beyond the tire equator. Since the first center lateral groove and the second center lateral groove are provided so as to intersect the tire equator having a large contact pressure, a large edge effect is exhibited and wet performance is improved. Further, the first center lateral grooves and the second center lateral grooves are inclined in the same direction and are alternately provided in the tire circumferential direction. Such a 1st center horizontal groove and a 2nd center horizontal groove make the fall of the rigidity of a center land part uniform, and suppress uneven wear.

  The first center lateral groove and the second center lateral groove adjacent to each other in the tire circumferential direction include overlapping portions that overlap with each other in the tire circumferential direction and non-overlapping portions that do not overlap with each other in the tire circumferential direction. The average groove width of the overlapping portion is smaller than the average groove width of the non-overlapping portion. Thereby, the fall of the rigidity of the center land part by an overlapping part and a non-overlapping part becomes uniform, and uneven wear is suppressed.

  The middle lateral groove of the pneumatic tire of the present invention has one end communicating with the center main groove and the other end communicating with the shoulder main groove. The middle lateral groove includes a pair of main portions extending in the same direction from the one end and the other end toward the center of the middle land portion, and a joint portion connected to the pair of main portions and inclined in the direction opposite to the main portion. Including. The pair of main portions is inclined at an angle of 20 to 40 ° with respect to the tire axial direction. Such a middle lateral groove, when a load in the tire axial direction is applied to the tread surface of the tread portion, such as during turning, brings the groove walls on both sides of the joint portion into contact with each other and suppresses deformation of the middle land portion. For this reason, the rigidity of a middle land part becomes large and by extension, uneven wear is suppressed. Further, such a joint portion increases the length of the middle lateral groove, increases the edge component, and improves the wet performance.

It is an expanded view of the tread part of the pneumatic tire for heavy loads of this embodiment. It is AA sectional drawing of FIG. It is an enlarged view of the center land part of FIG. It is an enlarged view of the middle land part of FIG.

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

  The center main groove 3 and the shoulder main groove 4 extend linearly, for example. The groove width W1 of the center main groove 3 and the groove width W2 of the shoulder main groove 4 are, for example, 2.0 to 6.0% of the tread grounding width TW. Such center main groove 3 and shoulder main groove 4 effectively drain the water film generated between the tread surface 2s of the tread portion 2 and the road surface during wet running, and improve the wet performance.

  The tread ground contact width TW is a distance in the tire axial direction between the tread ground contact ends Te and Te in a normal state in which the rim is assembled on a regular rim (not shown) and filled with a regular internal pressure. When there is no notice in particular, the dimension of each part of a tire is the value measured in the said normal state.

  The “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. “Standard Rim” for JATMA, “Design Rim” for TRA For ETRTO, "Measuring Rim".

  The “regular internal pressure” is the air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. “JATMA” indicates “highest air pressure”, and TRA indicates “TIRE LOAD”. The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO.

  The tread ground contact end Te is an outer end of the ground contact surface in the tire axial direction when the normal tire 1 is loaded with a normal load and grounded to a plane with a camber angle of 0 °.

  The “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. “JAMATA” indicates “maximum load capacity”, and TRA indicates “TIRE” The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in the case of ETRTO.

  FIG. 2 shows an AA cross section of FIG. As shown in FIG. 2, the groove depth D1 of the center main groove 3 and the groove depth D2 of the shoulder main groove 4 can be variously determined according to common practice. The groove depths D1 and D2 are set to, for example, 10 to 20 mm in order to improve the wet performance while maintaining the rigidity of the tread portion 2.

  As shown in FIG. 1, the tread portion 2 includes a center land portion 5 between the pair of center main grooves 3 and 3, and a pair of middle land portions 6 and 6 between the center main groove 3 and the shoulder main grooves 4. , And a pair of shoulder land portions 7, 7 on the outer side in the tire axial direction of the shoulder main groove 4.

  FIG. 3 shows an enlarged view of the center land portion 5 of FIG. As shown in FIG. 3, the center land portion 5 has a rib shape extending continuously in the tire circumferential direction. The center land portion 5 extends with a substantially constant width W3. The width W3 of the center land portion 5 in the tire axial direction is preferably, for example, 0.10 to 0.20 times the tread ground contact width TW (shown in FIGS. 1 and 2 and the same applies hereinafter).

  A center lateral groove 10 is provided in the center land portion 5. The center lateral groove 10 extends linearly. The center lateral groove 10 has one end 11 communicating with the center main groove 3 (shown in FIG. 1) and the other end 12 terminating in the center land portion 5. The center lateral groove 10 extends at an angle of 20 to 40 ° with respect to the tire axial direction. Such a center lateral groove 10 makes the center land portion 5 into a rib shape continuous in the tire circumferential direction while improving wet performance. For this reason, the rigidity in the tire circumferential direction of the center land portion 5 is maintained, and consequently uneven wear of the center land portion 5 is suppressed.

  When the angle θ1 of the center lateral groove 10 with respect to the tire axial direction is less than 20 °, the rigidity in the tire circumferential direction of the center land portion 5 is reduced, and heel and toe wear may occur around the center lateral groove 10. On the other hand, when the angle θ1 is larger than 40 °, the drainage of the center lateral groove 10 is lowered, and the wet performance may be lowered. For this reason, the angle θ1 is preferably 25 ° or more, more preferably 28 °, preferably 35 ° or less, more preferably 32 ° or less.

  The length L1 of the center lateral groove 10 in the tire axial direction is preferably 0.55 times or more, more preferably 0.60 times or more, preferably 0.70 times the width W3 of the center land portion 5 in the tire axial direction. Hereinafter, it is more preferably 0.65 times or less. When the length L1 of the center lateral groove 10 in the tire axial direction is smaller than 0.55 times the width W3 of the center land portion 5, the wet performance may not be improved. On the contrary, when the length L1 is larger than 0.65 times the width W3 of the center land portion 5, the rigidity of the center land portion 5 may be reduced, and uneven wear may occur.

  As shown in FIG. 2, the groove depth D3 of the center lateral groove 10 is preferably 1.0 mm or more, more preferably 1.5 mm or more, preferably 3.0 mm or less, more preferably 2.5 mm or less. is there. When the groove depth D3 of the center lateral groove 10 is smaller than 1.0 mm, the wet performance may not be improved. On the contrary, when the groove depth D3 of the center lateral groove 10 is larger than 3.0 mm, the rigidity of the center land portion 5 is lowered, and there is a possibility that uneven wear occurs.

  As shown in FIG. 3, the center lateral groove 10 includes a first center lateral groove 10A and a second center lateral groove 10B. The first center lateral groove 10A extends from the center main groove 3A on one side toward the center main groove 3B on the other side and ends beyond the tire equator C. The second center lateral groove 10B extends from the center main groove 3B on the other side toward the center main groove 3A on the one side and terminates beyond the tire equator C.

  The first center lateral groove 10A and the second center lateral groove 10B are inclined in the same direction. The angle difference | θ2-θ3 | between the angle θ2 of the first center lateral groove 10A with respect to the tire axial direction and the angle θ3 of the second center lateral groove 10B with respect to the tire axial direction is preferably 10 ° or less, more preferably 5 ° or less. . When the angle difference | θ2−θ3 | is larger than 10 °, the rigidity of the center land portion 5 becomes non-uniform, which may cause uneven wear. In the present embodiment, the angle difference | θ2−θ3 | is 0 °.

  The first center lateral grooves 10A and the second center lateral grooves 10B are alternately provided on the tire equator C in the tire circumferential direction.

  On the tire equator C, the first center lateral groove 10A and the second center lateral groove 10B of the present embodiment are provided at equal intervals. The first center lateral groove 10A and the second center lateral groove 10B as described above make the lowering of the rigidity of the center land portion 5 more uniform and effectively suppress uneven wear.

  The first center lateral groove 10A and the second center lateral groove 10B adjacent in the tire circumferential direction include an overlapping portion 15 that overlaps with each other in the tire circumferential direction and a non-overlapping portion 16 that does not overlap with each other in the tire circumferential direction.

  The overlapping portion 15 and the non-overlapping portion 16 of the first center lateral groove 10A are separated by a tire circumferential direction line 17 passing through the other end 12 of the second center lateral groove 10B adjacent in the tire circumferential direction. The overlapping portion 15 and the non-overlapping portion 16 of the second center lateral groove 10B are separated by a tire circumferential line 18 passing through the other end 12A of the first center lateral groove 10A adjacent in the tire circumferential direction.

  In each lateral groove, the average groove width of the overlapping portion 15 is smaller than the average groove width of the non-overlapping portion 16. Thereby, the difference in rigidity between the land portion 24 between the overlapping portions 15 and 15 adjacent in the tire circumferential direction and the land portion 25 between the non-overlapping portions 16 and 16 adjacent in the tire circumferential direction is reduced. For this reason, the fall of the rigidity of the center land part 5 by the overlapping part 15 and the non-overlapping part 16 becomes uniform, and uneven wear is suppressed.

  In this specification, the “average groove width” means, for convenience, a value S / L obtained by dividing the area S of the groove opening by the length L of the center line of the groove in the tire axial direction.

  The length L2 of the overlapping portion 15 in the tire axial direction is preferably 0.10 times or more, more preferably 0.20 times or more, preferably 0.40 times the width W3 of the center land portion 5 in the tire axial direction. Hereinafter, it is more preferably 0.30 times or less. When the length L2 of the overlapping portion 15 in the tire axial direction is smaller than 0.10 times the width W3, the wet performance may be deteriorated. On the contrary, when the length L2 of the overlapping portion 15 in the tire axial direction is larger than 0.40 times the width W3, the rigidity of the center land portion 5 is lowered, and uneven wear may occur.

  Each overlapping portion 15 gradually increases the groove width W6 from the other end 12 to the one end 11 of each center lateral groove 10. Such an overlapping portion 15 effectively drains the water film in the center lateral groove 10 to the outer side in the tire axial direction during wet running, thereby improving drainage.

  The groove width W6 of the overlapping portion 15 is preferably 0.8 mm or more, more preferably 1.0 mm or more, preferably 1.5 mm or less, more preferably 1.3 mm or less. If the groove width W6 of the overlapping portion 15 is less than 0.8 mm, the wet performance may not be improved. When the groove width W6 of the overlapping portion 15 is larger than 1.5 mm, the rigidity of the center land portion 5 is reduced, and there is a possibility that uneven wear occurs.

  The non-overlapping portion 16 includes a first portion 20 and a second portion 21 that is continuous with the first portion 20 and communicates with the center main groove 3 while increasing the groove width.

  The first portion 20 is smoothly connected to the overlapping portion 15 and extends outward in the tire axial direction. The groove width W7 of the first portion 20 gradually increases from the tire equator C side toward the tire axial direction outer side.

  When the groove width W7 of the first portion is large, the rigidity of the center land portion 5 may be reduced and uneven wear may occur. Conversely, when the groove width W7 of the first portion is small, the wet performance may be reduced. For this reason, the groove width W7 of the first portion is preferably 1.5 mm or more, more preferably 1.8 mm or more, preferably 2.5 mm or less, more preferably 2.2 mm or less.

  The second portion 21 includes a groove edge 22 on one side inclined in the same direction as the first portion 20, and a groove edge 23 on the other side extending inclined in the opposite direction to the first portion 20. As a result, the center lateral groove 10 increases in width and communicates with the center main groove 3 (shown in FIG. 1). For this reason, the water film in the center lateral groove 10 is effectively drained during wet running.

  The ratio W8 / W7o of the groove width W8 at the outer end 21o in the tire axial direction of the second portion 21 and the groove width W7o at the outer end 20o in the tire axial direction of the first portion 20 is preferably 2.5 or more. More preferably, it is 2.8 or more, preferably 3.5 times or less, more preferably 3.2 times or less. When the ratio W8 / W7o between the groove width W8 and the groove width W7o is less than 2.5, the wet performance may not be improved. On the contrary, there is a possibility that uneven wear may occur at the edge 5e of the center land portion 5 where the ratio W8 / W7o is greater than 3.5.

  From the same viewpoint, the ratio L3 / W7o between the length L3 of the second portion 21 in the tire axial direction and the groove width W7o at the outer end 20o of the first portion 20 in the tire axial direction is preferably 1.0. Preferably it is 1.3 or more, Preferably it is 2.0 or less, More preferably, it is 1.7 or less.

  As shown in FIG. 1, a middle lateral groove 30 is provided in the middle land portion 6. The middle lateral groove 30 has one end 32 communicating with the center main groove 3 and the other end 33 communicating with the shoulder main groove 4. Thereby, the middle land portion 6 is composed of a block row including middle blocks 31 divided by middle lateral grooves 30. The middle land portion 6 has a substantially constant width W4. The width W4 of the middle land portion 6 in the tire axial direction is, for example, 0.10 to 0.20 times the tread ground contact width TW.

  FIG. 4 shows an enlarged view of the middle land portion 6. As shown in FIG. 4, the middle lateral groove 30 includes a pair of main portions 34, 34 extending from each of one end 32 and the other end 33 toward the center of the middle land portion 6 in the same direction, and a pair of main portions 34, 34. It includes a joint portion 35 that connects between the main portions 34 and 34 and is inclined in the opposite direction to the main portion 34. The pair of main portions 34 is inclined at an angle θ4 of 20 to 40 ° with respect to the tire axial direction.

  Such a middle lateral groove 30 is configured such that when a load in the tire axial direction is applied to the tread surface 2s (shown in FIG. 1) of the tread portion 2 during turning, the groove walls on both sides of the joint portion 35 are brought into contact with each other. The deformation of the part 6 is suppressed. For this reason, although it is a block row | line | column, the middle land part 6 has big rigidity, and by extension, uneven wear is suppressed. Further, such a joint 35 provides a large middle lateral groove 30 length, thereby increasing edge components and improving wet performance.

  When the angle θ4 of the main portion 34 is less than 20 °, heel and toe wear may occur. On the other hand, when the angle θ4 is larger than 40 °, the drainage of the middle lateral groove 30 is lowered, and the wet performance may be lowered. For this reason, the angle θ4 of the main portion 34 with respect to the tire axial direction is preferably 25 ° or more, more preferably 28 ° or more, preferably 35 ° or less, more preferably 32 ° or less.

  The main part 34 includes an inclined part 36 and a widened part 37. The inclined portion 36 is inclined with respect to the tire axial direction and has a substantially constant groove width. The widened portion 37 is continuous with the inclined portion 36 and expands the groove width to communicate with the center main groove or the shoulder main groove. Such a main portion 34 effectively drains the water film in the middle lateral groove 30 during wet running, and improves wet performance.

  The joint portion 35 extends linearly. When the angle θ5 between the joint portion 35 and the main portion 34 is small, there is a possibility that uneven wear may occur at the groove edge of the middle lateral groove 30. On the other hand, when the angle θ5 is large, the length of the middle lateral groove 30 is not increased, and the effect of improving the wet performance may not be obtained. For this reason, the angle θ5 between the joint portion 35 and the main portion 34 is preferably 75 ° or more, more preferably 80 ° or more, preferably 90 ° or less, more preferably 85 ° or less.

  The middle lateral groove 30 extends with a substantially constant groove width. When the groove width W9 of the middle lateral groove 30 is small, the wet performance may be deteriorated. On the contrary, when the groove width W9 of the middle lateral groove 30 is large, there is a possibility that the rigidity of the middle land portion 6 is lowered and uneven wear occurs. For this reason, the groove width W9 of the middle lateral groove 30 is preferably 1.5 mm or more, more preferably 1.8 mm or more, preferably 2.5 mm or less, more preferably 2.2 mm or less.

  From the same viewpoint, the groove depth D4 (shown in FIG. 2) of the middle lateral groove 30 is preferably 1.0 mm or more, more preferably 1.5 mm or more, preferably 3.0 mm or less, more preferably 2. 5 mm or less.

  When the number Nm of the middle horizontal grooves 30 per tire in each middle land portion 6 is small, the water film between the middle land portion 6 and the road surface cannot be sufficiently discharged during wet traveling, and the wet performance may be deteriorated. There is. On the contrary, when the number Nm is large, the length of the middle block 31 in the tire circumferential direction is small, and there is a possibility that uneven wear occurs in the middle land portion 6. For this reason, the number Nm of the middle lateral grooves 30 per tire circumference in each middle land portion 6 is preferably 0.30 times or more, more preferably 0.45 times or more, the number Nc of tires per center lateral groove per tire circumference. It is preferably 0.70 times or less, more preferably 0.55 times or less.

  The middle block 31 is provided with a middle siping 38 having a groove width W10 of 0.5 to 1.0 mm. In the middle siping 38, both ends 38e, 38e are terminated in the middle land portion 6. The middle siping 38 includes a pair of main sipe portions 39 and 39 extending in the same direction as the main portion 34 and a sub sipe portion 40 extending in the same direction as the joint portion 35 and connecting between the pair of main sipe portions 39 and 39. Including. The main sipe part 39 and the sub sipe part of this embodiment are parallel to the main part 34 and the joint part 35, respectively. Such middle siping 38 suppresses a decrease in local rigidity of the middle block 31. For this reason, the wet performance is improved while uneven wear of the middle block 31 is suppressed.

  As shown in FIG. 2, the middle siping 38 has a groove depth D <b> 5 that is larger than the middle lateral groove 30. The groove depth D5 of the middle siping 38 is preferably 5 mm or more, more preferably 7 mm or more, preferably 10 mm or less, more preferably 8 mm or less. Such a middle siping 38 improves wet performance without significantly reducing the rigidity of the middle block 31.

  As shown in FIG. 1, the shoulder land portion 7 has a rib shape in which a lateral groove extending from the shoulder main groove 4 to the tread ground contact Te is not provided. The width W5 of the shoulder land portion 7 in the tire axial direction is, for example, 0.15 to 0.25 times the tread ground contact width TW.

  The shoulder land portion 7 of the present embodiment is provided with a small siping 45 having one end 43 communicating with the main groove and the other end 44 terminating in the shoulder land portion. The small siping 45 has a length L4 in the tire axial direction of 2.0 to 5.0 mm. Such a small siping 45 can suppress stone biting of the main groove.

  The small siping 45 may be provided in the center land portion 5 and the middle land portion 6. Thereby, the stone biting in the center main groove 3 and the shoulder main groove 4 is effectively suppressed.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

A pneumatic tire having a tread pattern shown in FIG. 1 was prototyped based on the specifications shown in Table 1. Further, as Comparative Examples 1 to 3, a pneumatic tire having a tread pattern that does not include the center lateral groove and the middle lateral groove, a tread pattern that includes only the center lateral groove, and a tread pattern that includes only the middle lateral groove was prototyped. . The wet performance and uneven wear resistance performance of each test tire was tested. The common specifications for each test tire are as follows.
Tire size: 11R22.5
Rim size: 22.5 × 7.5
Tire internal pressure: 900 kPa
Tread width TW: 210mm
Shoulder main groove:
Groove width W1: 11mm
Groove depth D1: 14 mm
Center main groove:
Groove width W2: 10 mm
Groove depth D2: 14 mm
The test method is as follows.

<Wet performance>
The braking distance when each test tire was mounted on the following test vehicle and fully braked on a wet road surface was measured. Detailed conditions are as follows. The result is the reciprocal of the braking distance, and is displayed as an index with the value of Comparative Example 1 being 100. The larger the value, the smaller the braking distance and the better.
Test vehicle: Load capacity 8t, 2-D vehicle Road surface: Wet road surface with water depth of 1.0mm Traveling speed: 60km / h

<Uneven wear resistance>
After traveling 10,000 km with the test vehicle, the wear amount on the edge of the center land and on the tire equator was measured, and the uneven wear amount was calculated. The uneven wear amount is a difference between the wear amount at the edge of the center land portion and the wear amount on the tire equator. The result is the reciprocal of the amount of uneven wear, and is displayed as an index with the value of Comparative Example 1 being 100. The larger the value, the smaller the uneven wear amount and the better. The test results are shown in Table 1.

  As a result of the test, it can be confirmed that the wet performance and the uneven wear resistance performance of the tire of the example are significantly improved as compared with the comparative example.

DESCRIPTION OF SYMBOLS 1 Tire 2 Tread part 3 Center main groove 4 Shoulder main groove 5 Center land part 6 Middle land part 10 Center horizontal groove 10A 1st center horizontal groove 10B 2nd center horizontal groove 15 Overlapping part 16 Non-overlapping part 30 Middle horizontal groove 34 Main part 35 Joint part

Claims (4)

The tread portion is provided with a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and a pair of shoulder main grooves extending continuously in the tire circumferential direction outside the center main groove in the tire axial direction. By being
A pneumatic tire in which a center land portion between the pair of center main grooves and a pair of middle land portions between the center main groove and the shoulder main grooves are divided,
The center land portion has a center lateral groove with one end communicating with the center main groove, extending at an angle of 20 to 40 ° with respect to the tire axial direction, and the other end terminating in the center land portion. Provided,
The center lateral groove extends from the center main groove on one side toward the center main groove on the other side and terminates beyond the tire equator;
A second center lateral groove extending from the other side center main groove toward the one side center main groove and terminating beyond the tire equator;
The first center lateral groove and the second center lateral groove are inclined in the same direction and are alternately provided in the tire circumferential direction,
The first center lateral groove and the second center lateral groove adjacent in the tire circumferential direction include an overlapping portion that overlaps with each other in the tire circumferential direction, and a non-overlapping portion that does not overlap with each other in the tire circumferential direction,
The average groove width of the overlapping portion is smaller than the average groove width of the non-overlapping portion,
The middle land portion is provided with a middle lateral groove having one end communicating with the center main groove and the other end communicating with the shoulder main groove.
The middle lateral groove is connected to the pair of main portions inclined in the same direction from the one end and the other end toward the center of the middle land portion, and is connected to the pair of main portions and opposite to the main portion. Including a sloped joint,
The pair of main portions includes an inclined portion that is inclined at an angle of 20 to 40 ° with respect to the tire axial direction.   The pneumatic tire according to claim 1, wherein a length of the overlapping portion in the tire axial direction is 0.10 to 0.40 times a width of the center land portion in the tire axial direction. The middle land portion includes a middle block divided by the middle lateral groove,
Each of the middle blocks is provided with a middle siping having a groove depth larger than the middle lateral groove and a groove width of 0.5 to 1.0 mm,
The pneumatic tire according to claim 1 or 2, wherein both ends of the middle siping are terminated in the middle land portion.   The middle siping includes a pair of main sipe portions extending in the same direction as the main portion, and a sub sipe portion extending in the same direction as the joint portion and connecting between the pair of main sipe portions. The described pneumatic tire.

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