JP2014073804A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly durable pneumatic tire for a heavy load, capable of effectively preventing the partial separation of tread rubber, which is caused by extension of cracking occurring from a width direction end part of an outermost belt layer to a circumferential groove provided on a tread surface.SOLUTION: A belt 3 is arranged on an outer circumferential side of a crown area of a toroidally arranged carcass 1. At least two circumferential grooves 1G to 3G extending in a tire circumferential direction are provided in a tread surface 4a. In a tire width direction cross section, when an intersection point P of a perpendicular line vertically extended from the outermost circumferential groove 3G to a sixth belt layer 6B which is the outermost layer among belt layers is defined, the relationship between a distance Y between the lower end of the outermost circumferential groove 3G and the intersection point P and a distance X between the tire width direction end part of the sixth belt layer 6B and the intersection point P is set so as to satisfy: X<Y×3. Further, the width direction end part of a fourth belt layer 4B is arranged in a range of 50% to 75% of a width dimension of the tread surface 4a.

Description

  The present invention relates to a heavy duty pneumatic tire used for construction vehicles such as a dump truck and an excavator loader.

  Conventionally, as this type of heavy-duty pneumatic tire, for example, the one shown in Patent Document 1 is known.

  In such a heavy-duty pneumatic tire, in order to achieve both durability and transportation efficiency (high speed), the surface layer of the tread portion of the tire is formed of rubber having high wear resistance, and the inner layer on the inner peripheral side of the surface layer Is made of a low heat-generating rubber to improve wear resistance while suppressing the occurrence of cracks in the belt due to thermal degradation.

JP 2007-22424 A

  With the above conventional structure, it is possible to suppress the occurrence of cracks from the belt layers, but on the other hand, when a large load acts on the tire when the vehicle travels, and the lug provided on the tread surface is crushed, A large distortion is generated at the width direction end of the outermost belt layer, and a crack is generated from the width direction end of the belt layer toward the outer side in the radial direction of the belt layer. When the circumferential groove extending in the tire circumferential direction is formed on the tread surface, depending on the formation position, the crack is connected to the circumferential groove, and in particular, the outer portion in the width direction of the tread portion is peeled off ( Separation) may occur, and measures to avoid this have been required.

  An object of the present invention is to solve such problems of heavy-duty pneumatic tires, and the object of the present invention is that cracks generated from the widthwise ends of the outermost belt layer are tread surfaces. An object of the present invention is to provide a heavy-duty pneumatic tire excellent in durability that can effectively prevent partial peeling of the tread rubber caused by being connected to a circumferential groove provided in the tire.

The heavy-duty pneumatic tire according to claim 1 is a cross-section in the tire width direction, and a circumferentially arranged groove arranged on the outermost side in the width direction of the tread surface is an outermost circumferential groove, and is an outermost layer of belt layers. When the intersection of the perpendicular line perpendicular to the outermost circumferential groove and the sixth belt layer is placed, the distance Y between the lower end of the outermost circumferential groove and the intersection, the sixth belt layer Since the relationship between the tire width direction end and the distance X between the intersections is set as X <Y × 3 ^1/2 , from the width direction end of the No. 6 belt layer to the surface of the belt layer Even if a crack extending toward the center in the width direction of the tread surface occurs at an angle of about 30 degrees, this crack is connected to the outermost circumferential groove to prevent the tread rubber from partially peeling, The durability performance of the heavy duty pneumatic tire can be improved. Also, according to the heavy duty pneumatic tire of the present invention, the widthwise end of the No. 4 belt layer is arranged in the range of 50% to 75% of the width dimension of the tread surface. The width direction end of the No. 4 belt layer is suppressed by suppressing deformation of the No. 4 belt layer during load rolling of the tire, even if the end portions in the width direction are arranged so as to satisfy the relationship of X <Y × 3 ^1/2 The occurrence of cracks from the portion can be suppressed, and the growth of the tire diameter (internal pressure diameter growth) that occurs when the internal pressure is applied to the tire can be suppressed. That is, if the width direction end of the No. 6 belt layer is arranged so as to satisfy a relationship of X <Y × 3 ^1/2 , the deformation of the width direction end of the No. 4 belt layer during the rolling load of the tire is large. However, by arranging the width direction end of the No. 4 belt layer in the range of 50% to 75% of the width dimension of the tread surface, the width direction end of the No. 4 belt layer is made inward in the width direction than before. It can arrange | position and can suppress the deformation | transformation and can suppress the generation | occurrence | production of the crack from the width direction edge part of the 4th belt layer. Also, if the width of the No. 4 belt layer is too narrow, there is a risk that tire diameter growth (internal pressure diameter growth) may occur when internal pressure is applied to the tire. By disposing in the range of 50% to 75% of the width dimension of the surface, it is possible to suppress the growth of the inner pressure diameter while suppressing the occurrence of cracks from the end in the width direction of the fourth belt layer.

  In the heavy duty pneumatic tire according to claim 2, the width direction end of the No. 6 belt layer is arranged directly below the outermost circumferential groove or on the outer side in the tire width direction with respect to the outermost circumferential groove. Thus, the rigidity in the radial direction of the tire in the portion on the outer side in the tire width direction with respect to the outermost circumferential direction groove can be increased, and the wear resistance performance of the tread surface in the portion can be increased.

  The heavy duty pneumatic tire according to claim 3 is configured such that the end in the width direction of the No. 6 belt layer is disposed on the outer side in the tire width direction than the end in the width direction of the No. 4 belt layer. During rolling, the expansion and contraction in the circumferential direction of the width direction end of the No. 4 belt layer with respect to the width direction end of the No. 6 belt layer is reduced, and cracks from the width direction end of the No. 4 belt layer are reduced. Occurrence and progress can be suppressed. In addition, by arranging the width direction end of the No. 6 belt layer on the outer side in the tire width direction than the width direction end of the No. 4 belt layer, cracks generated from the width direction end of the No. 4 belt layer are tread. Transmission to the surface can be prevented by the No. 6 belt layer, and cracks generated from the width direction end of the No. 4 belt layer can be prevented from continuing to the outermost circumferential groove. Thereby, the tread cut by the crack from the 4th belt layer etc. can be prevented, and durability of a tire can be improved.

  In the above, the “tread surface” is to be in contact with the road surface when rolling a heavy-duty pneumatic tire that is assembled to the applicable rim and filled with the specified internal pressure while applying a load corresponding to the maximum load capacity. Means the outer peripheral surface over the entire circumference of the tire. Here, “applicable rim” refers to a rim (standard rim) defined in the following standards according to the tire size, and “specified internal pressure” is defined in accordance with the maximum load capacity in the following standards. The “maximum load capacity” refers to the maximum mass allowed to be applied to the tire according to the following standards. The standard is determined by an industrial standard effective in the region where the tire is produced or used. For example, in the United States, “THE TIRE AND RIM ASSOCIATION INC. (TRA) is YEAR BOOK”. In Europe, it is “The European Tire and Rim Technical Organization's STANDARDS MANUAL”, and in Japan it is “JAMATA YEAR BOOK of Japan Automobile Tire Association”.

  In the above, the position of the end in the width direction of the No. 6 belt layer, the position of the end of the No. 4 belt layer in the width direction, the position of the outermost circumferential groove, the width dimension of the outermost circumferential groove, the distance X, the distance Y, the tread surface The width dimension of each of the belt layers and the width dimension of each belt layer are measured in a no-load state in which the tire is assembled to the applicable rim and filled with the specified internal pressure.

  In the above, the “outermost circumferential direction groove” is not only a groove having such a width that the opposing groove walls are open to the tread surface without contacting each other in the tread ground surface, but also the tread ground surface. Among them, a sipe-like structure in which opposing groove walls contact each other is included. Here, the “tread contact surface” means a part of the tread surface in the circumferential direction that comes into contact with the road surface when the maximum load capacity is applied under the condition that the tire is assembled to the adaptive rim and filled with the specified internal pressure. Say.

  According to the heavy-duty pneumatic tire of the present invention, it is possible to prevent the progress of cracks from the end in the belt layer width direction (of 6 belts and 4 belts) to the circumferential groove, and to improve the tire durability.

It is a width direction sectional view showing a half part of a tread part of a heavy-duty pneumatic tire which is one embodiment of the present invention. It is a figure similar to FIG. 1 which shows the positional relationship of each belt layer shown in FIG. 1, and an outermost periphery direction groove | channel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view in the width direction showing a half portion of a tread portion of a heavy duty pneumatic tire according to an embodiment of the present invention. In this figure, a heavy duty pneumatic tire is applied to an application rim (not shown). It is assembled and is in a no-load state filled with the specified internal pressure.

  Reference numeral 1 in the figure denotes a carcass. This carcass 1 which is a radial carcass is folded back around a corresponding bead core (not shown) embedded in each of the pair of bead portions, and extends from the bead core to the tread portion 2 through the sidewall portion. Arranged in an extending toroid. This heavy duty pneumatic tire has a radial structure in which two carcass ply cords constituting the carcass 1 are extended in the radial direction. Note that the carcass 1 is not limited to two carcass plies, and may be composed of one or three or more carcass plies.

  A belt 3 is disposed on the outer peripheral side of the crown region 1a of the carcass 1, that is, on the outer side in the tire radial direction. The belt 3 includes six belt layers 1B to 6B arranged in a stacked manner, and these belt layers 1B to 6B are arranged in order from the innermost layer, that is, the inner layer in the tire radial direction, in order from the first belt layer 1B, 2B. No. belt layer 2B, No. 3 belt layer 3B, No. 4 belt layer 4B, No. 5 belt layer 5B and No. 6 belt layer 6B, and No. 6 belt layer 6B is the outermost layer. Each of the belt layers 1B to 6B is an inclined belt in which the belt cord is inclined with respect to the tire equatorial plane, and is laminated so that the inclination directions of the belt cords of adjacent belt layers inside and outside the tire in the radial direction intersect each other. The That is, each belt layer 1B-6B is directed to the direction in which the respective belt cords cross each other, preferably the belt cords of odd-numbered belt layers 1B, 3B, 5B with respect to the tire equator plane, The belt cords of the even-numbered belt layers 2B, 4B, and 6B are inclined to one side in the width direction with respect to the tire equator plane, and the odd-numbered belt layers 1B, 3B, and 5B are opposite to the tire equator plane. It arrange | positions so that it may incline to a certain width direction other side. The belt layers 1B to 6B constituting the belt 3 are not limited to the inclined belt, and various belt layers such as a belt cord parallel to the tire equator plane can be used.

  A tread rubber 4 constituting the tread portion 2 is disposed on the outer peripheral side of the belt 3. Among the tread rubbers 4, low heat-generating rubber is used as the rubber of the inner layer side portion on the belt 3 side, whereas the rubber on the surface side portion on the tread surface 4 a side is compared with the rubber on the belt 3 side. Rubber with good wear resistance is used.

  The outer peripheral surface of the tread rubber 4 is a tread surface 4a, and five (only three are shown in the drawing) circumferential grooves 1G to 3G are provided on the tread surface 4a. These circumferential grooves 1G to 3G extend continuously in a straight line along the tire circumferential direction, and divide the tread surface 4a into a plurality of land portions in the width direction. The circumferential groove 1G provided at the center position in the tire width direction is the center groove 1G, and the circumferential groove 3G disposed on the outermost side in the width direction of the tread surface 4a is the outermost circumferential groove 3G. The outermost circumferential groove 3G is spaced from the tire equatorial plane to the outer side in the tire width direction by a quarter point that is a quarter of the width dimension of the tread surface 4a and 3/8 of the width dimension of the tread surface 4a. It is provided between 3/8 points. Note that the number of circumferential grooves can be arbitrarily set as long as at least two circumferential grooves are provided. Moreover, each circumferential groove | channel is not restricted to the form continuously extended straightly, For example, it is good also as a form extended zigzag or a wave shape.

  The tread surface 4a is provided with a plurality of lug grooves 4G extending in the tire width direction, arranged at equal intervals in the circumferential direction. These lug grooves 4G open toward the tire side at the tread end, which is the widthwise end of the tread surface 4a, as indicated by broken lines in FIG. A plurality of lugs 5 arranged in the circumferential direction are partitioned by the lug grooves 4G. And these lugs 5 are divided into the tire width direction inner side and the outer side part from the outermost periphery direction groove | channel 3G.

  As shown in FIG. 2, the width dimension of the tread surface 4a, that is, the width in the tire width direction is W0, the width dimension of the first belt layer 1B is W1, the width dimension of the second belt layer 2B is W2, and the third belt layer 3B. W3 is the width dimension of the 4th belt layer 4B, W4 is the width dimension of the 5th belt layer 5B, and W6 is the width dimension of the 6th belt layer 6B. The width dimensions W1 to W6 of the belt layers 1B to 6B have a relationship of W0> W5> W3> W6> W4> W1> W2. Each of the belt layers 1B to 6B is arranged with the center in the width direction aligned with the center of the tread surface 4a, that is, the center in the tire width direction, and the belt layer having a larger width dimension has an end in the width direction at the outer side in the tire width direction. It is supposed to be located in. The width dimensions W0 to W6 are all measured in parallel with the tire width direction.

  In addition, the width direction end of the No. 6 belt layer 6B and the width direction end of the No. 4 belt layer 4B are shifted to the outer side in the tire width direction with respect to the outermost circumferential groove 3G in the vicinity immediately below the outermost circumferential groove 3G. Has been placed. Moreover, the width direction edge part of the 6th belt layer 6B is arrange | positioned rather than the width direction edge part of the 4th belt layer 4B on the tire width direction outer side.

Here, as shown in FIG. 2, the width direction end of the No. 6 belt layer 6B is the cross section of the tire width direction, and an intersection P between the perpendicular line dropped from the outermost circumferential groove 3G and the No. 6 belt layer 6B. When placed, the distance Y between the lower end of the outermost circumferential groove 3G and the intersection point P and the distance X between the tire width direction end of the No. 6 belt layer 6B and the intersection point P ^satisfy X <Y × 3 ^1/2 . It is arranged at a position that satisfies the relationship. Here, the distance X between the end in the tire width direction of the No. 6 belt layer 6B and the intersection P is the outermost circumferential groove 3G between the end in the width direction of the No. 6 belt layer 6B and the outermost circumferential groove 3G. On the other hand, it should just be prescribed | regulated as the distance to the tire width direction outer side along the 6th belt layer 6B.

In this heavy-duty pneumatic tire, the center of the tread surface 4a in the width direction at an angle of about 30 degrees with respect to the surface of the belt layer 6B from the end in the width direction of the No. 6 belt layer 6B when the tire rolls. There is a risk of cracks extending toward the surface. On the other hand, in the present invention, the end in the width direction of the No. 6 belt layer 6B is set at the intersection P between the vertical line and the No. 6 belt layer 6B, which are perpendicular to the outermost circumferential groove 3G in the cross section in the tire width direction. Then, the relationship between the distance Y between the lower end of the outermost circumferential groove 3G and the intersection point P and the distance X between the end portion in the tire width direction of the sixth belt layer 6B and the intersection point P is X <Y × 3 ^{1 /} Since the crack is arranged at a position satisfying the relationship of ^2, the crack does not reach the outermost circumferential groove 3G, and is directed to the center in the width direction of the tread surface 4a below the outermost circumferential groove 3G. The inside of the tread rubber 4 is developed. That is, the crack generated from the end portion in the width direction of the No. 6 belt layer 6B extends toward the center in the width direction of the tread surface 4a at an angle of about 30 degrees with respect to the No. 6 belt layer 6B. Is arranged at a position satisfying the relationship of X <Y × 3 ^1/2 with respect to the outermost circumferential groove 3G, even if the crack from the No. 6 belt layer 6B greatly develops. However, the crack does not reach the outermost circumferential groove 3G. Therefore, in the structure of the present invention, the crack generated from the end portion in the width direction of the No. 6 belt layer 6B is connected to the outermost circumferential groove 3G, and the tread rubber 4 (lug 5) constituting the tread portion 2 is partially peeled off. Can be prevented, thereby improving the durability of the heavy-duty pneumatic tire. Further, since the end in the width direction of the No. 6 belt layer 6B is arranged on the outer side in the tire width direction with respect to the outermost circumferential groove 3G, the tire radial direction in the portion on the outer side in the tire width direction with respect to the outermost circumferential groove 3G. The wear resistance performance of the tread surface 4a in the portion can be enhanced.

In the present embodiment, the end in the width direction of the 6th belt layer 6B is arranged at a position satisfying the relationship of X <Y × ^31/2 , but more preferably, the 6th belt layer The end in the width direction of the layer 6B can also be arranged at a position that satisfies the relationship X <Y.

  Here, when measuring the distance X between the width direction end of the No. 6 belt layer 6B and the outermost circumferential groove 3G, the deepest portion (the lowest) of the outermost circumferential groove 3G closest to the No. 6 belt layer 6B. Point) can be used as a measurement reference position, but when the bottom of the outermost circumferential groove 3G is flat, the groove wall on the inner side in the tire width direction can be used as a measurement reference. In addition, when the outermost circumferential groove 3G is formed in a zigzag or wavy form, the measurement reference position can be based on the innermost portion of the groove in the tire width direction.

  In addition, the width direction edge part of the 6th belt layer 6B can also be arrange | positioned directly under the outermost periphery direction groove | channel 3G.

Here, in this heavy duty pneumatic tire, the end in the width direction of the fourth belt layer 4B, which is the fourth from the innermost layer, is arranged in the range of 50% to 75% of the width dimension of the tread surface 4a. . That is, the width dimension W4 of the fourth belt layer 4B is set to be in the range of 50% to 75% of the width dimension W0 of the tread surface 4a. If the width direction end of the No. 6 belt layer 6B is arranged so as to satisfy the relationship of X <Y × 3 ^1/2 , the width dimension of the No. 6 belt layer 6B becomes smaller, so that the 4 in the load rolling of the tire is reduced. The deformation of the end portion in the width direction of the number belt layer 4B becomes larger, but by arranging the end portion in the width direction of the number 4 belt layer 4B in the above range, the end portion in the width direction of the number 4 belt layer 4B is wider than before. It can arrange | position inside a direction and can suppress the deformation | transformation. Thereby, generation | occurrence | production of the crack from the width direction edge part of the 4th belt layer 4B can be suppressed. On the other hand, if the position of the end portion in the width direction of the No. 4 belt layer 4B is arranged too much inside, there is a possibility that the tire diameter grows (internal pressure diameter growth) when an internal pressure is applied to the tire. By arranging the width direction end portion of the layer 4B in the above range, it is possible to suppress the inner diameter growth while suppressing the occurrence of cracks from the width direction end portion of the fourth belt layer 4B.

Thus, in the heavy-duty pneumatic tire of the present invention, the widthwise end of the No. 6 belt layer 6B is arranged so as to satisfy the relationship X <Y × 3 ^1/2 and the width of the No. 4 belt layer 4B. Since the end in the direction is arranged in the range of 50% to 75% of the width dimension of the tread surface 4a, the crack generated from the end in the width direction of the No. 6 belt layer 6B is connected to the outermost groove in the tread. It is possible to prevent the rubber from partially peeling, and to suppress the occurrence of cracks from the No. 4 belt layer 4B while suppressing the tire inner diameter growth, thereby improving the durability performance of the heavy duty pneumatic tire. Can be made.

  Further, as described above, in the present embodiment, the width direction end portion of the sixth belt layer 6B is arranged on the outer side in the tire width direction than the width direction end portion of the fourth belt layer 4B. . Thereby, the elastic deformation in the circumferential direction of the width direction end portion of the No. 4 belt layer 4B with respect to the width direction end portion of the No. 6 belt layer 6B at the time of load rolling of the tire is reduced, and the No. 4 belt layer 4B. It is possible to suppress the occurrence and development of cracks from the end in the width direction. Moreover, even if a crack occurs from the end in the width direction of the fourth belt layer 4B, the progress of the crack into the belt 3 can be suppressed.

  Here, the outermost circumferential grooves 3G and the widthwise ends of the sixth belt layer can be arranged in the range of 50% to 75% of the width dimension of the tread surface 4a on the tread surface 4a. That is, the width dimension W6 of the 6th belt layer 6B can be set in the range of 50% to 75% of the width dimension W0 of the tread surface 4a. In the case shown in the drawing, the outermost circumferential groove 3G has a 1/4 point that is a point that is 1/4 of the width dimension of the tread surface 4a on the outer side in the tire width direction from the tire equatorial plane, and the width dimension of the tread surface 4a. The width dimension W6 of the sixth belt layer 6B is set to about 60% of the width dimension W0 of the tread surface 4a, corresponding to being provided between 3/8 points that are 3/8 points away. ing.

  By setting the width dimension W6 of the No. 6 belt layer 6B within the above range, when the tire is subjected to load point movement, expansion and contraction in the circumferential direction of the end portion in the width direction of the No. 6 belt layer 6B is achieved. Compared with the case where the width 4 is set to 75% or more of the width dimension W0 of the surface 4a, it can be made sufficiently small, and sufficient wear resistance can be ensured in the outer portion of the tread surface 4a in the tire width direction. Thereby, while being able to suppress the generation | occurrence | production of the crack from the width direction edge part of the 6th belt layer 6B, the progress of the generated crack can be suppressed and the durable performance of this heavy duty pneumatic tire can be further enhanced. it can.

  Further, the width direction end portion of the No. 6 belt layer 6B is disposed on the outer side in the tire width direction than the width direction end portion of the No. 4 belt layer 4B, that is, the width direction end portion of the No. 4 belt layer 4B is No. 6. Since it is arranged on the inner side in the tire width direction than the end portion in the width direction of the belt layer 6B, occurrence of cracks from the end portion in the width direction of the No. 4 belt layer 4B is further suppressed, and the width of the No. 4 belt layer 4B. The progress of cracks generated from the end portions in the direction into the belt 3 is further suppressed.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, in this embodiment, the widthwise end portion of the sixth belt layer 6B, X <a position that satisfies Y × 3 ^1/2 relationship, the tire width direction than the outermost groove 3G However, the present invention is not limited to this, and the end in the width direction of the 6th belt layer 6B is a position satisfying the relationship of X <Y × 3 ^1/2 and the outermost circumferential groove It may be arranged on the inner side in the tire width direction than 3G. Further, the end in the width direction of the sixth belt layer 6B can be disposed at a position satisfying the relationship of X <Y × 3 ^1/2 and directly below the outermost circumferential groove 3G.

Further, the width direction end portion of the sixth belt layer 6B is, if the position that satisfies X <Y × 3 ^1/2 relationship, the magnitude relationship of the width of each belt 1B~6B is be variously changed Can do.

  Next, examples of the heavy duty pneumatic tire of the present invention will be described.

  As test tires, two types of example tires and four types of comparative tires were prepared. These test tires have a tire size of 53 / 80R63.

  Example tire 1 is a heavy-duty pneumatic tire shown in FIG. 1, and the distance X from the outermost circumferential groove 3G at the widthwise end of the sixth belt layer 6B is 10 mm, and the outermost circumferential groove of the sixth belt layer 6B. The upper distance Y up to 3G is 60 mm, the width dimension W6 of the sixth belt layer 6B is 61% of the width dimension W0 of the tread surface 4a, and the width dimension W4 of the fourth belt layer 4B is 64% of the width dimension W0 of the tread surface 4a. . Example tire 2 is a heavy-duty pneumatic tire shown in FIG. 1, and the distance X from the outermost circumferential groove 3G of the widthwise end of the sixth belt layer 6B is 10 mm, and the outermost circumferential groove of the sixth belt layer 6B. The upper distance Y to 3G is 60 mm, the width dimension W6 of the sixth belt layer 6B is 61% of the width dimension W0 of the tread surface 4a, and the width dimension W4 of the fourth belt layer 4B is 74 of the width dimension W0 of the tread surface 4a. %.

  In comparison with the example tire, the comparative example tire 1 has a width dimension W6 of the sixth belt layer 6B of 76% of the width dimension W0 of the tread surface 4a and a width dimension W4 of the fourth belt layer 4B of the width dimension of the tread surface 4a. In Comparative Example Tire 2, the width dimension W6 of the sixth belt layer 6B is set to 83% of the width dimension W0 of the tread surface 4a, and the width dimension W4 of the fourth belt layer 4B is set to the tread surface 4a. The comparative tire 3 has a width dimension W6 of the sixth belt layer 6B of 76% of the width dimension W0 of the tread surface 4a and a width dimension W4 of the fourth belt layer 4B. The width of the tread surface 4a is 64% of the width dimension W0. In the comparative example tire 4, the width dimension W6 of the sixth belt layer 6B is 61% of the width dimension W0 of the tread surface 4a, and the width of the fourth belt layer 4B. Dimension W4 of the tread surface 4a It is obtained by the 69% size W0. In addition, the width dimension of each belt layer 1B, 2B, 3B, 5B except the 6th belt layer 6B and the 4th belt layer 4B is the same as an Example tire and a comparative example tire.

  These test tires were assembled on a rim having a rim width of 36 inches, filled with a specified internal pressure of 600 kPa, and using an indoor drum tester having a diameter of 5 m, under a load condition of load 82.5 ton and side force 12.4 ton. A drum test with a running time of 500 hours was conducted. And the length of the crack from the width direction edge part of the No. 6 belt layer 6B of the test tire after the test (the length of the crack from the belt layer end of the No. 6 belt layer), the width of the No. 6 belt layer 6B Distance from which the crack generated from the end in the direction reaches the outermost circumferential groove 3G and the length of the crack from the end in the width direction of the 4th belt layer 4B (the length of the crack from the belt layer end of the 4th belt layer) ) Was measured. The test is shown in Table 1.

  As is clear from the results shown in Table 1, in Comparative Example Tires 1 to 3, the length of the crack generated from the end portion in the width direction of the No. 6 belt layer 6B is longer than that of Example Tires 1 and 2, and No. 6 The distance until the crack generated from the end in the width direction of the belt layer 6B reaches the outermost circumferential groove 3G is 50 mm to 65 mm, and the crack may reach the outermost circumferential groove 3G and be connected. On the other hand, in the example tires 1 and 2, the length of the crack generated from the end in the width direction of the sixth belt layer 6B is shorter than that of the comparative example tires 1 to 3, and the crack is the outermost circumferential groove 3G. Never reach. Therefore, in Example Tires 1 and 2, the partial cracking of the tread rubber 4 that is caused by the crack generated from the width direction end of the sixth belt layer 6B being connected to the outermost circumferential groove 3G of the tread surface 4a is effectively performed. It can be understood that the durability performance of the tire can be improved by preventing.

  On the other hand, in the comparative example tire 4, the length of the crack generated from the end portion in the width direction of the sixth belt layer 6B is as short as that of the example tires 1 and 2, and the crack reaches the outermost circumferential groove 3G. There is no. However, in this comparative example tire 4, the width dimension W4 of the No. 4 belt layer 4B is larger than the width dimension W4 of the No. 4 belt layer 4B in the Example tires 1 and 2, so the No. 4 belt layer The crack length from the end in the width direction of 4B is increased, and this crack propagates into the belt 3. On the other hand, in Example tires 1 and 2 in which the width dimension W4 of the 4th belt layer 4B is equal to the width dimension W6 of the 6th belt layer 6B, cracks from the end in the width direction of the 4th belt layer 4B are observed. It turns out that progress can be suppressed and the durability performance of a tire can be improved.

  1 carcass ply, 1a crown area, 2 tread part, 3 belt, 4 tread rubber, 4a tread surface, 5 lugs, 1B to 6B belt layer, 1G circumferential groove (center groove), 2G circumferential groove, 3G circumferential groove (Outermost circumferential direction groove) 4G lug groove, W0 tread surface width dimension, W1 to W6 width dimension of each belt layer, X, Y distance

Claims (3)

A carcass composed of one or more carcass plies disposed in a toroidal manner between a pair of bead portions, a belt disposed on the outer peripheral side of the crown region of the carcass, and an outer peripheral side of the belt. A heavy duty pneumatic tire having a tread rubber forming a tread surface, and provided with at least two circumferential grooves extending in a tire circumferential direction on the tread surface,
The belt includes six belt layers,
In the cross section in the tire width direction, among the circumferential grooves, those arranged on the outermost side in the width direction of the tread surface are outermost grooves, and among the belt layers, the outermost layer is a sixth belt layer, The distance Y between the lower end of the outermost circumferential groove and the intersection, and the end of the sixth belt layer in the tire width direction when the intersection of the perpendicular line perpendicular to the outermost circumferential groove and the sixth belt layer is placed. The relationship between the distance X between the part and the intersection is set as X <Y × 3 ^1/2 ,
A heavy-duty pneumatic tire characterized in that the end in the width direction of the fourth belt layer, the fourth from the innermost layer, is arranged in a range of 50% to 75% of the width dimension of the tread surface.   2. The heavy duty pneumatic tire according to claim 1, wherein an end in the width direction of the No. 6 belt layer is disposed directly below the outermost circumferential groove or on the outer side in the tire width direction with respect to the outermost circumferential groove.   The heavy duty pneumatic tire according to claim 1 or 2, wherein an end in the width direction of the No. 6 belt layer is disposed on an outer side in the tire width direction than an end in the width direction of the No. 4 belt layer.

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