JP2017061322A - Heavy load pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve snow road performance with good balance while maintaining uneven wear resistance.SOLUTION: A heavy load pneumatic tire 1 includes a center land part 6 formed to extend in a tire peripheral direction while a width in a tire axial direction is repeatedly increased/decreased between a center main groove 3 and a middle main groove 4. The center main groove 3 includes a first inclined part 3A and a second inclined part 3B inclined oppositely to the first inclined part 3A and at an angle smaller than that of the first inclined part 3A to the tire peripheral direction. The center land part 6 has treads, which are arrayed in the tire peripheral direction, sectioned into hexagonal center blocks 11 by a plurality of center lateral grooves 9 connecting the zig zag top part of the center main groove 3 and the zig zag top part of the middle main groove 4 to each other where the width of the center land part 6 in the tire axial direction is smallest. The center lateral groove 9 and the first inclined part 3A incline in the same direction with respect to the tire axial direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heavy duty pneumatic tire that maintains snow road performance in a well-balanced manner while maintaining uneven wear resistance.

  A heavy duty pneumatic tire having a block pattern having a plurality of blocks divided into main grooves and lateral grooves in a tread portion is known. Such a block pattern tends to cause uneven wear such as heel and toe wear in each block. In order to improve the uneven wear resistance performance, for example, a heavy duty pneumatic tire has been proposed in which the groove volume of the lateral groove is reduced to increase the rigidity of the block in the circumferential direction of the tire.

  However, the heavy duty pneumatic tire as described above has a reduced snow column shear force due to the lateral grooves. For this reason, the heavy-duty pneumatic tire as described above has a problem that snow road performance is deteriorated.

JP 2012-51504 A

  The present invention has been devised in view of the actual situation as described above. Based on the improvement of the center land portion and the center lateral groove, a heavy load that improves the snow road performance in a well-balanced manner while maintaining uneven wear resistance performance. The main purpose is to provide heavy duty pneumatic tires.

  In the present invention, one center main groove extending continuously in the tire circumferential direction on the tire equator in a zigzag shape on the tire equator, one on each side of the center main groove, and continuing in a zigzag shape in the tire circumferential direction. And a heavy duty pneumatic tire in which a center land portion extending in the tire circumferential direction is formed between the center main groove and the middle main groove while the tire axial width repeatedly increases and decreases. The center main groove has a first inclined portion inclined to one side with respect to the tire circumferential direction, and an angle opposite to the first inclined portion and an angle of the first inclined portion with respect to the tire circumferential direction. The center land portion includes a zigzag top portion of the center main groove and a zigzag top portion of the middle main groove that have a minimum width in the tire axial direction of the center land portion. And The ingredients plurality of center lateral grooves, tread is divided into hexagonal center block, wherein the center lateral grooves and said first inclined portion, and being inclined in the same direction with respect to the tire axial direction.

  In the heavy duty pneumatic tire according to the present invention, the center block is provided with a center sipe that connects the second inclined portion and a zigzag top portion that protrudes outward in the tire axial direction of the middle main groove. Is desirable.

  In the heavy duty pneumatic tire according to the present invention, a distance in a tire circumferential direction between an opening end of the center sipe in the center main groove and a protruding end on an inner side in a tire axial direction of the center block is the center block. It is desirable that it is 10% to 20% of the maximum length (LC) in the tire circumferential direction.

  In the heavy duty pneumatic tire according to the present invention, it is desirable that an angle of each inclined component of the middle main groove with respect to the tire circumferential direction is smaller than an angle of the second inclined portion with respect to the tire circumferential direction.

  In the heavy duty pneumatic tire according to the present invention, the groove width of the center main groove is preferably smaller than the groove width of the middle main groove.

  In the heavy duty pneumatic tire according to the present invention, it is desirable that the groove width of the center lateral groove is larger than the groove width of the center main groove.

  In the heavy duty pneumatic tire according to the present invention, it is desirable that the length of the center lateral groove in the tire axial direction is 9% to 17% of the tread width.

  In the heavy duty pneumatic tire according to the present invention, it is desirable that an angle of the middle main groove with respect to a tire circumferential direction is 1 to 9 degrees.

  In the heavy duty pneumatic tire according to the present invention, the angle of the first inclined portion with respect to the tire circumferential direction is 4 to 13 degrees, and the angle of the second inclined portion with respect to the tire circumferential direction is 1 to 9 degrees. Is desirable.

  The heavy duty pneumatic tire according to the present invention has a center block aspect ratio (LC / WC) which is a ratio of a maximum length (LC) in the tire circumferential direction of the center block and a maximum width (WC) in the tire axial direction. 2.0 to 2.6 is desirable.

  The heavy-duty pneumatic tire of the present invention includes a center land portion extending in the tire circumferential direction while the width in the tire axial direction repeatedly increases and decreases between the center main groove and the middle main groove. The center land portion has a tread surface divided into hexagonal center blocks by a center lateral groove provided at a position where the width in the tire axial direction is minimized. Since the width in the tire axial direction of such a center block decreases from the central portion in the tire circumferential direction toward both ends, the both ends of the block are appropriately deformed when the block is stepped on and kicked out, Slip on the road surface is suppressed. As a result, during straight running, the wear energy acting on both ends of the center block where a large contact pressure acts is reduced.

  The center main groove has a first inclined portion inclined to one side with respect to the tire circumferential direction, and a second inclined portion that is opposite to the first inclined portion and inclined at an angle smaller than the angle of the first inclined portion with respect to the tire circumferential direction. And an inclined portion. The first inclined portion having a large angle with respect to the tire circumferential direction forms a strong snow column. Further, the first inclined portion moves in a direction in which the groove walls on both sides are closed by the force in the tire circumferential direction during straight traveling. Thereby, the deformation | transformation of the tire circumferential direction of the center land part of the both sides of a 1st inclination part is suppressed. For this reason, the slip with respect to a road surface is further suppressed. Moreover, the 2nd inclination part of a small angle maintains the pattern rigidity of the center land part of the both sides large. Therefore, the center main groove defined in this way suppresses slipping on the road surface while increasing the rigidity of the center land portion where a large contact pressure acts during straight traveling, and further exerts a snow column shear force. It can improve the straight running stability on snowy roads.

  The first inclined portion having an angle larger than that of the second inclined portion has high snow drain resistance at the connection position with the second inclined portion, and therefore, it is difficult to discharge the snow in the first inclined portion to the second inclined portion side. For this reason, in the present invention, by inclining the center lateral groove and the first inclined portion in the same direction with respect to the tire axial direction, using the rolling of the tire, the snow in the first inclined portion is removed from the center lateral groove. Through the middle main groove. For this reason, snowy road performance further improves.

  As described above, the heavy duty pneumatic tire of the present invention sets the tread surface of the center block to a hexagonal shape, and makes the direction of the inclination of the center lateral groove the same as the direction of the inclination of the first inclined portion. Uneven wear performance and snow road performance can be improved.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an enlarged view of the middle land part and shoulder land part of the right side of FIG. It is an enlarged view of the center land part of FIG. It is an enlarged view of the center land part of FIG. It is an enlarged view of the middle land part and shoulder land part of the right side of FIG. It is an expanded view of the tread part of a comparative example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a development view of a tread portion 2 of a heavy duty pneumatic tire 1 showing an embodiment of the present invention. The heavy-duty pneumatic tire (hereinafter sometimes simply referred to as “tire”) 1 according to the present embodiment is suitably used for, for example, trucks and buses.

  As shown in FIG. 1, the tread portion 2 is provided with a main groove extending continuously in the tire circumferential direction.

  The main groove of the present embodiment includes one center main groove 3 provided on the tire equator C, middle main grooves 4 and 4 disposed on both sides of the center main groove 3, and the middle main groove 4. It includes a pair of shoulder main grooves 5, 5 arranged between the tread end Te.

  The “tread end” Te is an edge that can be identified by a clear edge in appearance. However, when the edge cannot be identified, when the normal load is loaded on the normal rim that is assembled to the normal rim and filled with the normal internal pressure, the normal load is applied and the tire is grounded to the plane with a camber angle of 0 degrees. Is defined as the ground contact position on the outermost side in the tire axial direction. In the normal state, the distance in the tire axial direction between the tread ends Te and Te is determined as the tread width TW. Unless otherwise noted, the dimensions and the like of each part of the tire are values measured in a 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 Then "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”, “INFLATION PRESSURE” in the case of ETRTO.

  “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. “JATMA” is “maximum load capacity”, TRA is “TIRE LOAD” The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” in the case of ETRTO.

  The center main groove 3 extends in a zigzag shape. The center main groove 3 of the present embodiment has a first inclined portion 3A inclined to one side with respect to the tire circumferential direction and a direction opposite to the first inclined portion 3A and an angle of the first inclined portion 3A with respect to the tire circumferential direction. And a second inclined portion 3B inclined at a small angle. The first inclined portions 3A and the second inclined portions 3B are provided alternately. The first inclined portion 3A having a large angle with respect to the tire circumferential direction forms a strong snow column. Further, the first inclined portion 3A moves in a direction in which the groove walls on both sides are closed by the force in the tire circumferential direction during straight traveling. Thereby, the deformation | transformation of the tire circumferential direction of the land part of the both sides of 3 A of 1st inclination parts is suppressed. For this reason, the slip with respect to a road surface is suppressed. Further, the second inclined portion 3B having a small angle maintains the tire circumferential rigidity of the land portions on both sides of the second inclined portion 3B. Therefore, the center main groove 3 suppresses slipping on the road surface while increasing the tire circumferential rigidity of the land portion on both sides of the center main groove 3 on which a large contact pressure acts during straight traveling, and further exhibits a snow column shear force. Therefore, in particular, straight running stability and uneven wear resistance performance on snowy roads can be improved.

  The center main groove 3 has a zigzag top 3h that is convex toward one side in the tire axial direction (right side in FIG. 1) and a zigzag top 3k that is convex toward the other side in the tire axial direction (left side in FIG. 1). ing. The zigzag apex 3h that protrudes toward one side in the tire axial direction is a portion that protrudes toward one side in the tire axial direction at the intersection of the first inclined portion 3A and the second inclined portion 3B. The zigzag apex 3k that protrudes toward the other side in the tire axial direction is a portion that protrudes toward the other side in the tire axial direction at the intersection of the first inclined portion 3A and the second inclined portion 3B.

  The angle θ1 of the first inclined portion 3A with respect to the tire circumferential direction is preferably 4 to 13 degrees. The angle θ2 of the second inclined portion 3B with respect to the tire circumferential direction is preferably 1 to 9 degrees. When the angle θ1 of the first inclined portion 3A exceeds 13 degrees, or when the angle θ2 of the second inclined portion 3B exceeds 9 degrees, the rigidity of the land portion near the top portions 3h and 3k of the zigzag of the center main groove 3 is increased. May decrease excessively. In addition, when the angle θ1 of the first inclined portion 3A is less than 4 degrees, or when the angle θ2 of the second inclined portion 3B is less than 1 degree, the axial component of each of the inclined portions 3A and 3B becomes small, and the snow column Shear force may be reduced. The angle θ2 of the second inclined portion 3B is more preferably 2 degrees or more.

  The length L1 in the tire circumferential direction of the first inclined portion 3A is 5% to 17% of the tread width TW from the viewpoint of increasing the pattern rigidity and the snow column shearing force of the land portions on both sides of the center main groove 3 in a balanced manner. Is desirable.

  The center main groove 3 is formed with a uniform width. Such center main groove 3 maintains high rigidity on both sides thereof. Although not particularly limited, the groove width W1 of the center main groove 3 is preferably 0.5% to 3% of the tread width TW.

  FIG. 2 is an enlarged view of the middle main groove 4 and the shoulder main groove 5 on the right side of FIG. As shown in FIG. 2, the middle main groove 4 extends in a zigzag shape. That is, since the middle main groove 4 has a tire axial direction component, it exerts a snow column shearing force. The middle main groove 4 of the present embodiment alternately includes middle first portions 4A that are inclined to one side with respect to the tire circumferential direction and middle second portions 4B that are inclined in a direction opposite to the middle first portion 4A. It is out.

  The middle main groove 4 has a zigzag apex 4h that protrudes outward in the tire axial direction at the intersection of the middle first portion 4A and the middle second portion 4B, and the intersection of the middle first portion 4A and the middle second portion 4B. And a zigzag apex 4k that protrudes inward in the tire axial direction.

  The tire circumferential direction length of the middle first portion 4A of the present embodiment is the same as the tire circumferential direction length of the middle second portion 4B. Such a middle main groove 4 equalizes the pattern rigidity of the land portions on both sides of the middle first portion 4A and the middle second portion 4B, so that the wear is made uniform. The land portion near the middle main groove 4 has a lower ground pressure when traveling straight ahead than the land portion near the center main groove 3. Therefore, priority is given to equalizing the rigidity of the land portion over suppressing deformation of the land portion. Therefore, it is desirable to improve the wear resistance. The middle first portion 4A and the middle second portion 4B may have different tire circumferential lengths.

  In order to effectively exhibit the above-described action, the angle θ3 of the inclined component (middle first portion 4A and middle second portion 4B) of the middle main groove 4 with respect to the tire circumferential direction is greater than the angle θ2 of the second inclined portion 3B. It is desirable to be smaller. That is, it is desirable that the angle θ3 of the middle main groove 4 is smaller than the angles (θ1 and θ2) of the center main groove 3. When the angle θ3 of the middle main groove 4 is excessively small, the snow column shear force by the middle main groove 4 may be reduced. When the angle θ3 of the middle main groove 4 is large, the tire circumferential rigidity of the land portion in the vicinity of both sides of the middle main groove 4 is reduced, and the wear of the land portions on both sides of the center main groove 3 and both sides of the middle main groove 4 are reduced. There is a risk that the difference with the wear of the land portion of the tsunami increases. For this reason, the angle θ3 of the middle main groove 4 is preferably 1 to 9 degrees, and more preferably 8 degrees or less.

  It is desirable that the groove width W2 of the middle main groove 4 is larger than the groove width W1 of the center main groove 3. As a result, it is possible to increase the pattern rigidity of the land portion near the tire equator C where a large contact pressure acts during straight traveling, and thus the uneven wear resistance is improved. The groove width W2 of the middle main groove 4 is preferably 1.5 of the groove width W1 of the center main groove 3 in order to smoothly discharge the snow in each of the main grooves 3 and 4 while exhibiting such an action. -3.0 times. In the present embodiment, the middle main groove 4 is formed with a uniform width.

  The shoulder main groove 5 extends in a zigzag shape. That is, the shoulder main groove 5 has an inclined component. The shoulder main groove 5 of the present embodiment alternately includes a shoulder first portion 5A inclined to one side with respect to the tire circumferential direction and a shoulder second portion 5B inclined to the other side with respect to the tire circumferential direction. Yes. Such a shoulder main groove 5 can also improve snow road performance. Although not particularly limited, the angle θ4 of the shoulder main groove 5 is preferably 1 to 7 degrees.

  The shoulder main groove 5 has a zigzag apex 5h that protrudes outward in the tire axial direction and a zigzag apex 5k that protrudes inward in the tire axial direction. The zigzag apex 5h that protrudes outward in the tire axial direction is an intersection of the shoulder first portion 5A and the shoulder second portion 5B, and is a portion that protrudes outward in the tire axial direction. The zigzag apex 5k that protrudes inward in the tire axial direction is the intersection of the shoulder first portion 5A and the shoulder second portion 5B, and is the portion that protrudes inward in the tire axial direction.

  The width W3 of the shoulder main groove 5 is desirably larger than the width W2 of the middle main groove 4. Such a shoulder main groove 5 secures a groove volume in the entire tread portion 2, and thus effectively exerts a snow column shearing force. The groove width W3 of the shoulder main groove 5 is preferably 2.0 to 4.0 times the groove width W1 of the center main groove 3.

  The groove depth (not shown) of each of the main grooves 3 to 5 can be variously determined according to the custom. The groove depth of each of the main grooves 3 to 5 is preferably 10 to 16.5 mm, for example.

  As shown in FIG. 1, each of the main grooves 3 to 5 causes the tread portion 2 to have a pair of center land portions 6 and 6, middle land portions 7 and 7, and shoulder land portions 8 and 8. Is provided.

  The center land portion 6 is formed between the center main groove 3 and the middle main groove 4. The middle land portion 7 is formed between the middle main groove 4 and the shoulder main groove 5. The shoulder land portion 8 is formed between the shoulder main groove 5 and the tread end Te.

  FIG. 3 is an enlarged view of the center land portion 6 of FIG. As shown in FIG. 3, in the present embodiment, the center land portion 6 increases or decreases the width in the tire axial direction in the tire circumferential direction by shifting the zigzag phase of the center main groove 3 and the middle main groove 4 by about a half pitch. Is repeated. That is, the center land portion 6 alternately has a maximum width portion 6A having a maximum width in the tire axial direction and a minimum width portion 6B having a minimum width in the tire circumferential direction. The maximum width portion 6A is a portion that joins the top portion 4h outside the zigzag of the middle main groove 4 and the zigzag top portions 3h, 3k of the center main groove 3 facing the top portion 4h. The minimum width portion 6B is a portion connecting the top portion 4k inside the zigzag of the middle main groove 4 and the zigzag top portions 3h, 3k of the center main groove 3 opposed to the top portion 4k.

  The center land portion 6 is provided with a plurality of center lateral grooves 9 extending in the tire circumferential direction extending over the minimum width portion 6B of the center land portion 6. Since the center lateral groove 9 has a large tire axial component, it exerts a snow column shear force. Since the center lateral groove 9 is provided in the minimum width portion 6B where a larger ground pressure acts, it can form a strong snow column.

  The center lateral groove 9 extends linearly. Thereby, since the rigidity of the center land part 6 of the both sides of the tire circumferential direction of the center lateral groove 9 becomes high, heel and toe wear can be suppressed.

  The center lateral groove 9 is inclined with respect to the tire axial direction. Since the center lateral groove 9 has a tire circumferential direction component, the snow in the center lateral groove 9 can be discharged to the main grooves 3 and 4 on both sides by using rolling of the tire.

  The center lateral groove 9 is inclined in the same direction with respect to the first inclined portion 3A and the tire axial direction. Thereby, the snow in the 1st inclination part 3A of an angle larger than the 2nd inclination part 3B can be smoothly discharged | emitted to the middle main groove 4 side via the center lateral groove 9 by rolling of a tire. For this reason, snowy road performance further improves.

  When the angle θ5 of the center lateral groove 9 with respect to the tire axial direction is large, the rigidity of the center land portion 6 in the vicinity of the center lateral groove 9 may be reduced. For this reason, the angle θ5 of the center lateral groove 9 with respect to the tire axial direction is preferably 5 to 15 degrees.

  The length L2 (shown in FIG. 1) of the center lateral groove 9 in the tire axial direction is preferably 9% to 17% of the tread width TW. When the tire axial direction length L2 of the center lateral groove 9 is less than 9% of the tread width TW, the rigidity of the center land portion 6 in the vicinity of the center lateral groove 9 may be lowered. When the length L2 of the center lateral groove 9 in the tire axial direction exceeds 17% of the tread width TW, the snow in the center lateral groove 9 becomes difficult to be discharged, and the snow road performance may be deteriorated.

  The groove width W4 of the center lateral groove 9 is preferably larger than the groove width W1 of the center main groove 3. Thereby, a large snow column shear force is exhibited while the pattern rigidity of the center land portion 6 is maintained. For this reason, the groove width W4 of the center lateral groove 9 is preferably 1.2 to 2.4 times the groove width W1 of the center main groove 3. The center lateral groove 9 is formed with a uniform width in this embodiment.

  In order to improve snow road performance and uneven wear resistance in a well-balanced manner, the groove depth (not shown) of the center lateral groove 9 is desirably 90% to 98% of the groove depth of the middle main groove 4.

  As shown in FIG. 4, the center land portion 6 is divided into hexagonal center blocks 11 by treads arranged in the tire circumferential direction by center lateral grooves 9. Since the width W10 of the center block 11 in the tire axial direction decreases from the center portion 11c in the tire circumferential direction toward both end portions 11t, the both end portions 11t of the center block 11 are pushed and kicked when the center block 11 is stepped on. By appropriately deforming at the time of starting, slipping on the road surface is suppressed. Thereby, since wear energy acting on both end portions 11t of the center block 11 is reduced, uneven wear resistance is greatly improved. The “hexagonal shape” does not need to be a strict hexagonal shape, and the width W10 of the center block 11 in the tire axial direction from the center portion 11c side in the tire circumferential direction toward the both end portions 11t. Should be smaller.

  The center block aspect ratio (LC / WC), which is the ratio of the maximum length LC in the tire circumferential direction of the center block 11 to the maximum width WC in the tire axial direction, is preferably 2.0 to 2.6. Thereby, the tire circumferential direction rigidity of the center block 11 is enhanced, and the groove width W4 (shown in FIG. 2) of the center lateral groove 9 is ensured, and snow road performance can be maintained.

  In the present embodiment, the center block 11 is provided with an open type center sipe 13 that connects between the center main groove 3 and the middle main groove 4. Such a center sipe 13 exhibits an edge effect and improves snow and ice road performance. The center block 11 of the present embodiment is divided by a center sipe 13 into a pair of center block pieces 11a and 11a on both sides thereof.

  The center sipe 13 extends in a zigzag shape. Thereby, since the deformation | transformation to the tire axial direction of the center block pieces 11a and 11a is suppressed, the suppression effect of the slip with respect to a road surface becomes still larger. In addition, the center sipe 13 is not limited to such an aspect, For example, what extends in a wave form, a sine wave form, or a linear form may be sufficient.

  In the present embodiment, the center sipe 13 is connected to the second inclined portion 3B of the center main groove 3 and the top 4h outside the middle main groove 4. That is, the center sipe 13 is not opened at the tops 3 h and 3 k of the center main groove 3 adjacent to the tire equator C. For this reason, the rigidity of the protruding end 11k on the inner side in the tire axial direction of the center block 11 is maintained high, and a large ground pressure acts on this portion, so that the snow column by the center lateral groove 9 and the first inclined portion 3A near the protruding end 11k. Can be pressed more firmly. Further, the center sipe 13 is opened at the top 4 h on the outer side of the middle main groove 4, thereby appropriately reducing the rigidity of the protruding end 11 n on the outer side in the tire axial direction of the center block 11. As a result, the contact pressure at the intersection of the middle first portion 4A and the middle second portion 4B is reduced, and the opening and closing of the groove wall of the middle main groove 4 is promoted, so that the snow in the middle main groove 4 is rotated in the direction of rotation. It is possible to discharge smoothly to the rear. Therefore, snow road performance can be further improved.

  The distance L3 in the tire circumferential direction between the opening end 13e in the center main groove 3 of the center sipe 13 and the protruding end 11k on the inner side in the tire axial direction of the center block 11 is the maximum circumferential length LC of the center block 11 in the tire circumferential direction. It is desirable that it is 10% to 20%. When the distance L3 is less than 10% of the maximum length LC of the center block 11, the rigidity of the projecting end 11k of the center block 11 is excessively lowered, the snow cannot be pressed and the snow column shear force is small. There is a risk. When the distance L3 exceeds 20% of the maximum length LC of the center block 11, the rigidity balance between the pair of center block pieces 11a and 11a is deteriorated, and the difference in wear between the block pieces 11a and 11a may be increased. is there.

  The center sipe 13 is preferably inclined in the same direction as the center lateral groove 9. Thereby, since the rigidity of the center block piece 11a in the tire circumferential direction can be ensured evenly along the tire axial direction, the difference in wear can be reduced. In order to further enhance such an effect, it is desirable that the angle θ6 of the center sipe 13 with respect to the tire circumferential direction is inclined at the same angle as the angle θ5 of the center lateral groove 9. The sipe angle extending in a zigzag manner as in this embodiment is defined by the zigzag amplitude center line.

  Although not particularly limited, the depth (not shown) of the center sipe 13 is preferably 80% or more of the groove depth of the middle main groove 4 in order to effectively exhibit the above-described action. Is 84% or more, preferably 96% or less, more preferably 92% or less.

  As shown in FIG. 5, in the present embodiment, in the middle land portion 7, the zigzag phase of the middle main groove 4 and the shoulder main groove 5 is shifted by about a half pitch, whereby the width in the tire axial direction increases or decreases in the tire circumferential direction. Is repeated. That is, the middle land portion 7 alternately has a maximum width portion 7A having a maximum width in the tire axial direction and a minimum width portion 7B having a minimum width in the tire axial direction in the tire circumferential direction. The maximum width portion 7 </ b> A is a portion that joins the inner top portion 4 k of the middle main groove 4 and the outer top portion 5 h of the shoulder main groove 5. The minimum width portion 7 </ b> B is a portion that connects the outer top portion 4 h of the middle main groove 4 and the inner top portion 5 k of the shoulder main groove 5.

  The middle land portion 7 is provided with a plurality of middle lateral grooves 15 extending in the tire circumferential direction extending over the minimum width portion 7B of the middle land portion 7. Since the middle lateral groove 15 has a large tire axial component, it improves snow road performance. Further, the middle lateral groove 15 provided in the minimum width portion 7B where a larger ground pressure acts can form a strong snow column.

  The middle lateral groove 15 extends linearly. Thereby, the rigidity of the middle land portion 7 on both sides of the middle lateral groove 15 is ensured to be high, and the slip on the road surface is suppressed.

  The middle lateral groove 15 is inclined with respect to the tire axial direction. Since such a middle lateral groove 15 has a tire circumferential direction component, snow in the middle lateral groove 15 can be discharged to the main grooves 4 and 5 on both sides by utilizing rolling of the tire.

  The angle θ7 of the middle lateral groove 15 with respect to the tire axial direction is preferably smaller than the angle θ5 of the center lateral groove 9 (shown in FIG. 3). In general, the lateral force generated during cornering is greater at the outer land portion in the tire axial direction. Therefore, in order to reduce the wear difference between the center land portion 6 and the middle land portion 7, the tire of the middle land portion 7 is used. It is also desirable to make the axial rigidity larger than the rigidity of the center land portion 6 in the tire axial direction. For this reason, the angle θ7 of the middle lateral groove 15 is desirably 4 to 14 degrees.

  The groove width W5 of the middle lateral groove 15 is preferably larger than the groove width W4 (shown in FIG. 3) of the center lateral groove 9. Thereby, the tire circumferential direction rigidity of the middle land portion 7 is made smaller than the tire circumferential direction rigidity of the center land portion 6, and the wear based on the difference in the contact pressure generated in the center land portion 6 and the middle land portion 7 is made to approach evenly. be able to. For this reason, the groove width W5 of the middle lateral groove 15 is desirably 1.5 to 2.5 times the groove width W4 of the center lateral groove 9.

  The middle land portion 7 is divided into hexagonal middle blocks 17 by treads arranged in the tire circumferential direction by middle lateral grooves 15. The width W11 of the middle block 17 in the tire axial direction decreases from the central portion 17c in the tire circumferential direction toward both end portions 17t. For this reason, the both ends 17t of the middle block 17 are appropriately deformed when the middle block 17 is stepped on and kicked out, thereby suppressing slippage on the road surface. As a result, the wear energy acting on both end portions 17t of the middle block 17 is reduced, so that the wear resistance performance is greatly improved. The “hexagonal shape” is defined similarly to the case of the center block 11.

  The middle block 17 of the present embodiment is a plain block in which grooves and sipes are not provided on the tread surface 17n. Since such a middle block 17 has a large rigidity, uneven wear is suppressed.

  The middle block aspect ratio (LM / WM) is preferably smaller than the center block aspect ratio (LC / WC). The middle block aspect ratio (LM / WM) is a ratio between the maximum length (LM) of the middle block 17 in the tire circumferential direction and the maximum width (WM) in the tire axial direction. The center block aspect ratio (LC / WC) is a ratio between the maximum length (LC (shown in FIG. 3)) of the center block 11 in the tire circumferential direction and the maximum width (WC) in the tire axial direction. That is, based on the profile of the tread portion 2 and the like, the contact pressure of the center block 11 is generally larger than the contact pressure of the middle block 17 during straight traveling. The aspect ratio correlates with the overall tire circumferential rigidity of the block, and the block having a larger aspect ratio has a greater tire circumferential rigidity. Accordingly, by defining the middle block aspect ratio to be smaller than the center block aspect ratio, it is possible to adjust the tire circumferential rigidity of the block in accordance with the contact pressure distribution. Thereby, especially the wear difference of heel and toe wear can be eliminated between the center block 11 and the middle block 17, and it can approach uniform wear. The middle block aspect ratio (LM / WM) is preferably 1.9 to 2.5 from the viewpoint of effectively exhibiting the above-described action.

  In the present embodiment, the shoulder land portion 8 is repeatedly increased and decreased in the tire circumferential direction by the zigzag shoulder main groove 5 in the tire axial direction. That is, the shoulder land portion 8 alternately has a maximum width portion 8A having a maximum width in the tire axial direction and a minimum width portion 8B having a minimum width in the tire axial direction in the tire circumferential direction. The maximum width portion 8A is a portion that connects the top portion 5k inside the shoulder main groove 5 and the tread end Te. The minimum width portion 8B is a portion that connects the top portion 5h outside the shoulder main groove 5 and the tread end Te.

  The shoulder land portion 8 is provided with a plurality of shoulder lateral grooves 21 extending in the tire circumferential direction extending over the minimum width portion 8B of the shoulder land portion 8. Such a shoulder lateral groove 21 can smoothly discharge the snow in the shoulder main groove 5 and the snow in the shoulder lateral groove 21 to the outside of the tread end Te.

  The shoulder lateral groove 21 of the present embodiment includes a shoulder inner portion 21A and a shoulder outer portion 21B. The shoulder inner portion 21A terminates in the shoulder land portion 8 extending outward from the shoulder main groove 5 in the tire axial direction. The shoulder outer portion 21B joins the shoulder inner portion 21A and the tread end Te, and the groove width gradually increases outward in the tire axial direction. Such a shoulder outer portion 21B further improves snow removal performance.

  In the shoulder land portion 8 of the present embodiment, the shoulder treads arranged in the tire circumferential direction are divided into pentagonal shoulder blocks 23 by shoulder lateral grooves 21. Since the width W12 in the tire axial direction of the shoulder block 23 decreases from the central portion in the tire circumferential direction toward both ends, the effect of suppressing slipping on the road surface is exhibited as in the middle block 17.

  The shoulder block 23 of the present embodiment is a plain block in which no groove or sipe is provided on the tread surface 23n. Since such a shoulder block 23 has great rigidity, uneven wear is suppressed.

  The shoulder block aspect ratio (LS / WS), which is the ratio of the maximum length (LS) in the tire circumferential direction of the shoulder block 23 and the maximum width (WS) in the tire axial direction, is obtained from the middle block aspect ratio (LM / WM). It is desirable that it is also small. As a result, the tire circumferential rigidity of the block can be adjusted in accordance with the contact pressure distribution, so that a wear difference such as heel and toe wear can be reduced between the middle block 17 and the shoulder block 23. In addition, a greater lateral force acts on the shoulder block 23 than on the middle block 17. A block having a smaller aspect ratio has a greater tire axial rigidity. For this reason, it is possible to reduce shoulder wear and the like that are likely to occur in the shoulder block 23. The shoulder block aspect ratio (LS / WS) is preferably 1.2 to 1.8 from the viewpoint of effectively exhibiting the above-described action.

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

Tires of size 275 / 80R22.5 having the basic pattern of FIG. 1 were prototyped based on the specifications in Table 1, and the uneven wear resistance and drainage performance of each sample tire was tested. The common specifications and test methods for each sample tire are as follows.
Tread width TW: 231mm
Groove depth of each main groove: 16.5mm
L3: Distance in the tire circumferential direction between the opening end in the center main groove of the center sipe and the protruding end on the inner side in the tire axial direction of the center block LC: Maximum length in the tire circumferential direction of the center block (constant)
WC: Maximum width of center block in the tire axial direction Center main groove width W1 / TW: 1.8% (constant)
The test method is as follows.

<Uneven wear resistance (heel and toe wear)>
Each test tire was mounted on all wheels of a 10-car load 2-D vehicle under the following conditions, and the test driver ran the vehicle on a dry asphalt road test course for 60000 km. And the difference of the abrasion amount of the tire peripheral direction both sides of the center block of a rear wheel, a middle block, and a shoulder block was measured. For the measurement, eight blocks having a substantially equal pitch in the tire circumferential direction were used for each block. The results are displayed as the average value of all measured values. The smaller the value, the better.
Rim (all wheels): 7.50 x 22.5
Internal pressure (all wheels): 900 kPa
Load capacity: 5 tons (loading in front of loading platform)

<Snow road performance>
A test driver made the vehicle run on a test course on a snowy road surface, and the driving characteristics at this time, such as steering stability, traction, and grip, were evaluated based on the test driver's sensuality. The results are displayed with a score of 100 as an example. The larger the value, the better. A test driver with a noticeable performance difference was given a 10 point difference, and a test driver with a clear performance difference was given a 5 point difference. Differences of 3 points or less are differences that are difficult for passengers to notice, although test drivers can recognize performance differences. The larger the value, the better.
The test results are shown in Table 1.

  As a result of the test, it can be confirmed that the uneven tire wear performance and snow road performance of the tires of the examples are improved in a balanced manner as compared with the comparative example. In addition, the test was performed while changing the tire size, and the test result was the same.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire for heavy loads 3 Center main groove 3A 1st inclination part 3B 2nd inclination part 4 Middle main groove 6 Center land part 9 Center side groove 11 Center block

Claims (13)

One center main groove extending continuously in the tire circumferential direction in the tire circumferential direction on the tire equator on the tread portion, and one middle on each side of the center main groove and extending continuously in the tire circumferential direction in a zigzag shape Main groove and
Between the center main groove and the middle main groove is a heavy duty pneumatic tire formed with a center land portion extending in the tire circumferential direction while repeatedly increasing and decreasing the width in the tire axial direction,
The center main groove is inclined to one side with respect to the tire circumferential direction, and is inclined in an opposite direction to the first inclined portion and at an angle smaller than an angle of the first inclined portion with respect to the tire circumferential direction. Alternately including second inclined portions that
The middle main groove alternately includes middle first portions that are inclined toward the one side with respect to a tire circumferential direction, and middle second portions that are inclined in a direction opposite to the middle first portion,
The center land portion has a hexagonal tread surface formed by a plurality of center lateral grooves that connect a zigzag top portion of the center main groove and a zigzag top portion of the middle main groove where the width in the tire axial direction of the center land portion is the smallest. Divided into shape center blocks,
One of the center lateral grooves that divide the center block includes the first middle portion on the outer side in the tire axial direction, and the second inclined portion on the tire equator side that is inclined in the direction opposite to the first middle portion. Each connected,
The center lateral groove and the first inclined portion are inclined in the same direction with respect to the tire axial direction.   2. The heavy-duty pneumatic tire according to claim 1, wherein the center block is provided with a center sipe that connects the second inclined portion and a zigzag top portion that protrudes outward in the tire axial direction of the middle main groove.   The distance in the tire circumferential direction between the opening end of the center sipe in the center main groove and the projecting end of the center block in the tire axial direction is the maximum length (LC) of the center block in the tire circumferential direction. The heavy-duty pneumatic tire according to claim 2, wherein the pneumatic tire is 10% to 20%.   The heavy duty pneumatic tire according to any one of claims 1 to 3, wherein an angle of each inclination component of the middle main groove with respect to a tire circumferential direction is smaller than an angle of the second inclined portion with respect to the tire circumferential direction.   5. The heavy duty pneumatic tire according to claim 1, wherein a groove width of the middle main groove is larger than a groove width of the center main groove.   The heavy tire for a heavy load according to any one of claims 1 to 5, wherein a groove width of the center lateral groove is larger than a groove width of the center main groove.   The heavy tire for a heavy load according to any one of claims 1 to 6, wherein a length in the tire axial direction of the center lateral groove is 9% to 17% of a tread width.   The heavy tire for heavy loads according to any one of claims 1 to 7, wherein an angle of the middle main groove with respect to a tire circumferential direction is 1 to 9 degrees. The angle of the first inclined part with respect to the tire circumferential direction is 4 to 13 degrees,
The heavy duty pneumatic tire according to any one of claims 1 to 8, wherein an angle of the second inclined portion with respect to a tire circumferential direction is 1 to 9 degrees.   A center block aspect ratio (LC / WC), which is a ratio of a maximum length (LC) in the tire circumferential direction of the center block and a maximum width (WC) in the tire axial direction, is 2.0 to 2.6. Item 10. The heavy duty pneumatic tire according to any one of Items 1 to 9.   11. The heavy duty pneumatic tire according to claim 1, wherein a tire circumferential direction length of the middle first portion is the same as a tire circumferential direction length of the middle second portion.   The heavy tire for a heavy load according to any one of claims 1 to 11, wherein a groove width of the middle main groove is 1.5 to 3.0 times a groove width of the center main groove.   The heavy duty pneumatic tire according to any one of claims 1 to 12, wherein the middle main groove is formed with an equal width.

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