JP4639776B2 - Heavy duty pneumatic radial tire - Google Patents

Description

  The present invention relates to a heavy duty pneumatic radial tire. In particular, the present invention relates to a heavy-duty pneumatic radial tire capable of suppressing cracks in a groove and improving durability.

  Conventional heavy-duty pneumatic radial tires are often used with a large load during traveling such as trucks and buses, so that the wear of the tread portion is easily different depending on the part, and so-called uneven wear is likely to occur. For this reason, in the conventional heavy-duty pneumatic radial tire, a portion where uneven wear is likely to occur, for example, a secondary groove in a direction along the circumferential groove is provided in a shoulder rib, thereby suppressing uneven wear. However, it is difficult to maintain the effect of suppressing the uneven wear when the wear progresses in the suppression of the uneven wear by the sub-groove. Thus, some conventional heavy-duty pneumatic radial tires maintain the effect of suppressing uneven wear even when wear progresses by devising the shape of the secondary groove. For example, in Patent Document 1, uneven wear is effectively suppressed even when wear progresses by providing irregularities on the groove bottom of the sub-groove. As a result, the uneven wear can be suppressed even at the end of the life of the heavy-duty pneumatic radial tire due to wear, and the uneven wear is more reliably suppressed.

Japanese Patent Laid-Open No. 2001-30716

  However, the heavy-duty pneumatic radial tire as described above is effective in suppressing uneven wear, but the heavy-duty pneumatic radial tire is formed with the circumferential grooves that tend to concentrate stress. In addition, there is a possibility that a problem due to this stress concentration occurs. For example, in a heavy-duty pneumatic radial tire, the tread portion tends to swell outward in the tire radial direction during inflation, but the tread portion is connected to the sidewall portion in the vicinity of the shoulder portion. Tension in the tire width direction is generated near the shoulder portion. A plurality of circumferential grooves are usually formed in the tread portion, but the circumferential groove located closest to the shoulder portion among the plurality of circumferential grooves is deformed in the direction in which the groove width increases due to the tension. It becomes easy to do.

  In particular, in recent heavy-duty pneumatic radial tires, those having an aspect ratio of 70% or less have increased in view of stability and durability during high-speed running. Therefore, the deformation in the direction of opening the groove width of the circumferential groove located closest to the shoulder portion is also remarkable. In this way, when the groove width of the circumferential groove is deformed in the opening direction, stress concentrates on the groove bottom of the circumferential groove, and there is a possibility that cracks may occur in this portion. Cracks generated in the directional grooves have also been a factor that significantly reduces the durability of heavy duty pneumatic radial tires.

  This invention is made in view of the above, Comprising: It aims at providing the pneumatic radial tire for heavy loads which can suppress generation | occurrence | production of the crack of a circumferential groove | channel.

  According to the inventors' research, when a heavy-duty pneumatic radial tire is mounted on a rim and inflated, the tread portion swells outward in the tire radial direction. Is formed in a structure and shape suitable for traveling, the way of swelling differs in each part, and it has been found that there are a part where the way of swelling in the tire radial direction is large and a part where it is small. In addition, the circumferential grooves formed in the tread portion include a circumferential groove that has a wide groove width during inflation and a circumferential groove that does not open very much. As described above, it occurs in a circumferential groove that has a wide groove width during inflation.

  When inflating heavy-duty pneumatic radial tires, the tread bulges in the tire radial direction have large bulges and small bulges. However, as a result of investigating them together, it has been found that the circumferential groove having a large groove width is located in a portion where the swelling method during inflation is large. This is because when the tread portion bulges outward in the tire radial direction, the tire tread portion generates tension in the tire width direction at the same time as the tire diametrically outward direction. Since the tension in the tire width direction is also large, it is considered that when the circumferential groove is located in this portion, the groove width of the circumferential groove is greatly opened by the large tension. As a result of intensive studies, the present inventors have found the cause of the wide opening of the circumferential groove and have completed the present invention.

In order to solve the above-described problems and achieve the object, a heavy-duty pneumatic radial tire according to the present invention is partitioned by a plurality of circumferential grooves formed on a tread surface of a tread portion and the plurality of circumferential grooves. In a heavy-duty pneumatic radial tire having a plurality of land portions, the amount of change in the tire radial direction of the tread surface at a normal internal pressure with respect to the tread surface at an internal pressure of 100 kPa when incorporated in a normal rim A position where the amount of protrusion is the largest is present in a portion other than the center portion of the tread, and some of the plurality of circumferential grooves are located in a protrusion range where the amount of protrusion is substantially the largest. And out of the land portion adjacent to the circumferential groove located in the protruding range at least in the land portion positioned outward in the tire width direction. Range of fine grooves shallower groove depth than the circumferential grooves provided located, the fine grooves, the groove width of the circumferential groove located on the protruding extent when is W, the thin groove is formed The land portion is formed in a range of 0.4 W to 3.0 W on the side where the narrow groove is formed in the tire width direction from the end on the circumferential groove side of the land portion .

  In the present invention, when the amount of bulging outward in the tire radial direction at the time of inflation is defined as the “projection amount” as described above, the land adjacent to the circumferential groove located in the projection range where the projection amount becomes the largest range. A narrow groove having a shallower groove depth than the circumferential groove is provided in the portion. As a result, even if a large tension in the tire width direction acts on the protruding range when inflated, this tension can be absorbed by opening the narrow groove, so the groove width direction of the circumferential groove located in the protruding range The degree of opening is reduced, and the stress at the groove bottom of the circumferential groove is reduced. As a result, the occurrence of cracks in the circumferential groove can be suppressed.

  In the heavy-duty pneumatic radial tire according to the present invention, the protruding amount in the protruding range is 20% or more larger than the protruding amount in the center portion of the tread.

  In this invention, the protruding amount in the protruding range is 20% or more of the protruding amount in the central portion of the tread, and the tension in the tire width direction of the protruding range is surely larger than that in the central portion of the tread. For this reason, by providing the narrow groove in the land portion adjacent to the circumferential groove located in the protruding range, the degree of opening of the circumferential groove in the groove width direction is reduced, and the stress at the groove bottom of the circumferential groove is suppressed. The effect to do becomes large. As a result, the occurrence of cracks in the circumferential groove can be more reliably suppressed.

Also, the heavy duty pneumatic radial tire according to the invention, the narrow groove, the narrow groove is formed in the tire width direction from an end portion of the circumferential groove side of the land portion before KiHosomizo is formed It is formed in the range of 0.5W-2.5W in the side currently performed.

  In the present invention, the occurrence of cracks in the circumferential groove can be more reliably suppressed by setting the range in which the narrow groove is provided to the above range. That is, when the position where the narrow groove is provided is within a range of 0.5 W from the end of the land portion on the circumferential groove side, the circumferential groove and the narrow groove are too close. The width in the tire width direction of the land portion located between the narrow grooves is too narrow, and there is a possibility that damage such as chipping of the land portion is caused by protrusions such as stones on the road surface. In addition, when the position where the narrow groove is provided is more than 2.5 W from the end of the land portion on the circumferential groove side, it is too far from the circumferential groove, so Therefore, it is difficult to absorb the tension in the tire width direction, and the stress at the groove bottom of the circumferential groove cannot be relaxed. Therefore, by providing the position where the narrow groove is provided in the range of 0.5 W to 2.5 W in the tire width direction from the end on the circumferential groove side of the land portion, the tension to the circumferential groove is more reliably absorbed, The stress at the groove bottom of the circumferential groove can be reduced by suppressing the opening of the groove width. As a result, the occurrence of cracks in the circumferential groove can be more reliably suppressed.

  Further, in the heavy-duty pneumatic radial tire according to the present invention, the narrow groove is formed such that the groove depth is within a range of 30% to 70% of the groove depth of the circumferential groove positioned in the protruding range. It is characterized by being.

  In the present invention, by forming the groove depth of the narrow groove within the range of 30% to 70% of the groove depth of the circumferential groove, the occurrence of cracks in the circumferential groove is more reliably suppressed. In other words, when the groove depth of the narrow groove is less than 30% of the groove depth of the circumferential groove, the groove depth of the narrow groove is too shallow, so that the tension in the tire width direction generated with respect to the circumferential groove is absorbed. This may make it difficult to relieve stress at the groove bottom of the circumferential groove. In addition, when the groove depth of the narrow groove is deeper than 70% of the groove depth of the circumferential groove, the groove width of the narrow groove is widened when a tension in the tire width direction is generated. There is a risk that stress concentrates on the bottom and cracks occur in this portion. Therefore, by forming the groove depth of the narrow groove within the range of 30% to 70% of the groove depth of the circumferential groove, the groove of the circumferential groove is more reliably prevented from being damaged. The stress at the bottom can be suppressed. As a result, the occurrence of cracks in the circumferential groove can be more reliably suppressed.

  In the heavy-duty pneumatic radial tire according to the present invention, the narrow groove is formed such that a groove depth is deepened at a position where the protruding amount is large, and a groove depth is shallowed at a position where the protruding amount is small. And

  In the present invention, at a position where the protruding amount is large, for example, at a position where the protruding amount at the position where the narrow groove is formed is 20% or more of the protruding amount at the center of the tread, the tension in the tire width direction is also large. By increasing the depth of the narrow groove, the tension can be more reliably absorbed by the narrow groove, so that the stress at the groove bottom of the circumferential groove can be more reliably reduced. Further, at a position where the protrusion amount is small, for example, at a position where the protrusion amount at the position where the narrow groove is formed is 10% or less of the protrusion amount at the center of the tread, the tension in the tire width direction is also small. Even if the depth is shallow, the tension can be absorbed by the narrow groove. Therefore, by changing the groove depth of the narrow groove in accordance with the protruding amount of the position where the narrow groove is formed, the tension can be absorbed more securely by the narrow groove, and the groove at the bottom of the circumferential groove can be absorbed. Stress can be relieved. As a result, the occurrence of cracks in the circumferential groove can be more reliably suppressed.

  The heavy duty pneumatic radial tire according to the present invention has a flatness ratio of 70% or less.

  In the present invention, by providing the above-mentioned narrow grooves in a heavy-duty pneumatic radial tire having a flatness ratio of 70% or less, occurrence of cracks in the circumferential grooves can be effectively suppressed. In other words, in a heavy-duty pneumatic radial tire with a flatness ratio of 70% or less, the protruding amount in the tire width direction end portion of the tread portion at the time of inflation, that is, the vicinity of the shoulder portion tends to increase. By providing the narrow groove in the vicinity of the circumferential groove located in many portions, the stress at the groove bottom of the circumferential groove can be effectively relieved. As a result, generation of cracks in the circumferential groove can be effectively suppressed.

  Further, in the heavy-duty pneumatic radial tire according to the present invention, a plurality of belt layers are provided on the inner side in the tire radial direction of the tread portion, and the position is located on the outermost side in the tire radial direction among the plurality of belt layers. The belt layer is narrower in the tire width direction than the belt layer adjacent to the inner side in the tire radial direction, and the circumferential groove located in the protruding range is the outermost in the tire radial direction. The belt layer is located on the outer side in the tire width direction than the end of the belt layer in the tire width direction.

  In the present invention, the circumferential groove is positioned at the outer side in the tire width direction, and the circumferential groove is located at the outermost end of the belt layer located at the outermost side in the tire width direction among the plurality of belt layers. By providing the narrow groove in the heavy duty pneumatic radial tire located outward in the tire width direction, occurrence of cracks in the circumferential groove can be effectively suppressed. That is, the amount of protrusion at the time of inflation varies depending on the structure of the heavy-duty pneumatic radial tire. For example, the amount of protrusion varies depending on the position of the end portion of the belt layer. That is, the tread surface of the tread portion is formed by a curved profile line that is generally convex in the tire radial direction, but the belt layer tends to open in the direction parallel to the road surface during inflation, so the belt The amount of protrusion tends to increase toward the end of the layer.

  For this reason, the protrusion amount of the belt layer in the vicinity of the end portion in the tire width direction tends to be large, and the belt layer positioned outwardly in the tire radial direction is closest to the tread surface. The shape of the belt layer located outward in the radial direction is likely to affect the protruding amount, and the position near the end of the belt layer in the tire width direction tends to have the largest protruding amount. For this reason, the circumferential groove located on the outer side in the tire width direction than the end portion in the tire width direction of the belt layer is easily located in the protruding range. By providing the narrow groove, the stress at the groove bottom in the circumferential direction can be effectively reduced. As a result, generation of cracks in the circumferential groove can be effectively suppressed.

  The heavy-duty pneumatic radial tire according to the present invention has an effect that the occurrence of cracks in the circumferential groove can be suppressed.

  Embodiments of a heavy duty pneumatic radial tire according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

  In the following description, the tire width direction refers to a direction parallel to the rotation axis of the heavy-duty pneumatic radial tire, and the inner side in the tire width direction refers to the direction toward the equator in the tire width direction, the outer side in the tire width direction, and Means the direction opposite to the direction of the equatorial plane in the tire width direction. Further, the tire radial direction refers to a direction orthogonal to the rotation axis. The tire circumferential direction is a circumferential direction with the rotation axis as a central axis. FIG. 1 is a meridional sectional view showing the main part of a heavy duty pneumatic radial tire according to the present invention. A heavy-duty pneumatic radial tire 1 shown in FIG. 1 has a tread portion 5 formed on the outermost side in the tire radial direction when viewed in a meridional section, and a tread surface 10 that is a surface of the tread portion 5. Are provided with a plurality of grooves for forming a tread pattern. The groove portion is provided with a plurality of circumferential grooves 21 formed in the tire circumferential direction and a plurality of lug grooves (not shown) formed in the tire width direction. Further, a land portion 17 defined by a groove portion such as a circumferential groove 21 is formed in a portion between the groove portions of the tread portion 5, and the tread surface 10 is a surface of the land portion 17. Is formed. Further, since a plurality of the circumferential grooves 21 are formed, a plurality of the circumferential grooves 21 are formed so as to be arranged substantially parallel to the tire width direction. A narrow groove 40 is formed on the outer side in the tire width direction of the circumferential groove 21 located on the outer side in the width direction.

  Three belt layers 25 are provided on the inner side in the tire radial direction of the tread portion 5. A sidewall portion 30 is provided from an end portion in the tire width direction of the tread portion 5 to a predetermined position on the inner side in the tire radial direction. Further, a carcass 31 is continuously provided on the inner side in the tire radial direction of the belt layer 25 and on the equator plane 45 side of the sidewall portion 30, and the inside of the carcass 31 or the carcass 31 An inner liner 32 is formed along the carcass 31 on the inner side of the heavy-duty pneumatic radial tire 1. The heavy-duty pneumatic radial tire 1 is formed with a flatness ratio of 70% or less. The circumferential groove 21 does not need to be formed accurately in the tire circumferential direction. The circumferential groove 21 is formed in an oblique direction with respect to the tire circumferential direction or formed in a zigzag shape. What is necessary is just to be formed in the direction. Similarly, the lug groove does not need to be accurately formed in the tire width direction, and may be formed substantially in the tire width direction.

  The three belt layers 25 are formed to overlap each other in the tire radial direction, and the three belt layers 25 have different widths in the tire width direction. The width of each belt layer 25 becomes narrower from the inner belt layer 25 in the tire radial direction toward the outer belt layer 25 in the tire radial direction, and is therefore positioned most outward in the tire radial direction. The width of the belt layer 25 is the narrowest.

  Among the circumferential grooves 21, the circumferential groove 21 located most outward in the tire width direction is formed as an outermost circumferential groove 22. The outermost circumferential groove 22 has a tire width that is greater than a belt layer end portion 26 that is an end portion in the tire width direction of the belt layer 25 located on the outermost side in the tire radial direction of the three belt layers 25. Located outside the direction. The narrow groove 40 is located outside the outermost circumferential groove 22 in the tire width direction, that is, is formed in the land portion 17 adjacent to the outermost circumferential groove 22. That is, the narrow groove 40 is formed between the shoulder portion 15 located at the end of the tread portion 5 in the tire width direction and the outermost circumferential groove 22 and extends along the tire circumferential direction. Alternatively, it is provided substantially parallel to the outermost circumferential groove 22. The narrow groove 40 is formed so that the groove width is narrower than the groove width of the outermost circumferential groove 22 and the groove depth is shallower than the groove depth of the outermost circumferential groove 22.

  The groove depth of the narrow groove 40 is preferably in the range of 30% to 70% of the groove depth of the outermost circumferential groove 22. Further, the position where the narrow groove 40 is formed is the outermost circumferential groove 22 side of the land portion 17 where the narrow groove 40 is formed, where W is the groove width of the outermost circumferential groove 22. The narrow groove 40 is formed in the tire width direction from the land portion end portion 18 which is the end portion of the outermost circumferential groove 22 or the end portion of the opening portion of the outermost circumferential groove 22 where the narrow groove 40 is formed. It is preferable that it is formed in the range of 0.5 W to 2.5 W on the side.

  FIG. 2 is a view showing a state of the tread surface during inflation of the heavy duty pneumatic radial tire of FIG. 1. When the pneumatic radial tire 1 for heavy loads is inflated, the tread surface 10 swells outward in the tire radial direction, and this bulging method differs depending on the location in the tire width direction. Specifically, the heavy-duty pneumatic radial tire 1 is incorporated into a normal rim (not shown) suitable for the size of the heavy-duty pneumatic radial tire 1, and in this state, air is injected into the inside, that is, inflated. At that time, the reference internal pressure was set to 100 kPa, and the tread surface 11 at the reference internal pressure, which is the shape of the tread surface 10 when the internal pressure is 100 kPa, and the tread surface 12 at the normal internal pressure, which is the shape of the tread surface 10 at the normal internal pressure, were compared. In this case, the amount of protrusion that is the amount of change in the tire radial direction of the tread surface 12 at the normal internal pressure with respect to the tread surface 11 at the reference internal pressure differs depending on each portion of the tread surface 10 in the tire width direction. The regular rim is “standard rim” defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO. The normal internal pressure is “maximum air pressure” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO.

  FIG. 3 is a diagram showing the relationship between the position in the tire width direction and the protruding amount. In FIG. 3, the vertical axis represents the amount of protrusion, and the horizontal axis represents the position of the tread surface 10 in the tire width direction. The vertical axis shows a state in which the amount of protrusion increases as it goes upward in the figure. In the horizontal axis, the left end of the figure is the equatorial plane 45 side, and the right end of the figure is the shoulder 15 side. The amount of protrusion differs depending on each part in the tire width direction, but the portion where the protrusion amount is the largest is in the tread surface 10 in the vicinity of the equator plane 45, that is, other than the tread central part 14 which is the central part in the tire width direction. More specifically, it is located at a portion slightly inward in the tire width direction or in the direction of the equator plane 45 from the shoulder portion 15. In the shoulder portion 15, the protruding amount is reduced. Therefore, in the protruding amount line 50 indicating the protruding amount, the predetermined range from the tread central portion 14 toward the shoulder portion 15 is substantially constant, and in the vicinity of the shoulder portion 15, the shoulder portion 15 slightly extends from the shoulder portion 15. The amount of protrusion at the portion close to 14 is the largest. In the portion where the amount of protrusion is large, the amount of protrusion changes gently with the maximum portion 52 which is the portion where the amount of protrusion is the largest as the apex. Further, the protruding amount of the maximum portion 52 is 20% or more larger than the protruding amount of the tread central portion 14. Thus, the range in which the protruding amount is larger than the surrounding area with the maximum portion 52 as the apex is the protruding range 51.

  Note that the protrusion range 51 includes not only the maximum portion 52 which is the portion where the protrusion amount is the largest, but also the periphery of the maximum portion 52, so that not only the portion where the protrusion amount is the maximum but also the range where the protrusion amount is substantially the largest. It has become. In addition, since the heavy load pneumatic radial tire 1 is generally symmetric about the equator plane 45, the amount of protrusion is symmetric about the equator plane 45. In this case, the protruding ranges 51 exist at two symmetrical positions with the equator plane 45 as the center when the heavy-duty pneumatic radial tire 1 is viewed in a meridian plane cross section.

  As described above, the protruding range 51 is located at a portion slightly closer to the tread central portion 14 from the shoulder portion 15, and the outermost circumferential groove 22 is formed in this portion. Alternatively, the outermost circumferential groove 22 is located in the protruding range 51. Further, the narrow groove 40 is formed outside the outermost circumferential groove 22 in the tire width direction, and the narrow groove 40 is also located in the protruding range 51.

  When the heavy-duty pneumatic radial tire 1 is mounted on a regular rim and inflated, the tread surface 10 swells outward in the tire radial direction. In the protruding range 51 of the tread surface 10 that changes in this way, the amount of change outward in the tire radial direction changes greatly as compared with other portions of the tread surface 10. When the tread surface 10 changes so as to bulge outward in the tire radial direction, a tension in the tire width direction is generated on the tread surface 10 simultaneously with the change in the tire radial direction outward. In particular, a large tension is generated in the protruding range 51 where the amount of change outward in the tire radial direction is large.

  Thus, the outermost circumferential groove 22 and the narrow groove 40 are formed in the protruding range 51 where a large tension is generated during inflation. A large tension is generated during the inflation in the protruding area 51 where the outermost circumferential groove 22 is formed, but the narrow groove 40 is provided in the protruding area 51 together with the outermost circumferential groove 22. The tension is not concentrated in the outermost circumferential groove 22 and is distributed to the outermost circumferential groove 22 and the narrow groove 40. That is, when the tension in the tire width direction acts on the outermost circumferential groove 22, the outermost circumferential groove 22 is deformed in the direction in which the groove width opens due to this tension, and a large stress is concentrated on the groove bottom 23. For this reason, cracks may occur in the groove bottom 23. However, since the outermost circumferential groove 22 and the narrow groove 40 are provided in the protruding area 51, the large tension generated in the protruding area 51 is the highest. Dispersed in the outer circumferential groove 22 and the narrow groove 40. That is, when the tension is applied, the outermost circumferential groove 22 is deformed in the direction in which the groove width is opened, and at the same time, the narrow groove 40 is also deformed in the direction in which the groove width is opened. Thereby, the deformation amount in the direction in which the groove width of the outermost circumferential groove 22 opens is reduced, and the stress on the groove bottom 23 of the outermost circumferential groove 22 is also reduced. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed.

  Also, the portion where the amount of change in the tire radial direction during inflation is large, the portion close to the shoulder portion 15 is likely to change. Therefore, the protruding range 51 is likely to be located near the shoulder portion 15. As a result, the tension in the tire width direction is likely to act on the land portion 17 located between the outermost circumferential groove 22 and the shoulder portion 15. The directional groove 22 is located outward in the tire width direction. As a result, the tension generated in the protruding range 51 during inflation can be more reliably dispersed, and the stress on the groove bottom 23 of the outermost circumferential groove 22 can be more reliably reduced. As a result, the occurrence of cracks in the circumferential groove 21 can be more reliably suppressed.

  Further, the outermost circumferential groove 22 is located on the outer side in the tire width direction of the belt layer end 26 of the belt layer 25 located on the outermost side in the tire radial direction among the plurality of belt layers 25. . The amount of protrusion during inflation varies depending on the structure of the heavy-duty pneumatic radial tire 1 and also varies depending on the arrangement shape of the belt layer 25. That is, at the time of inflation, the belt layer 25 changes so that the diameter increases outward in the tire radial direction, and the tread surface 10 is affected by this change, but the belt layer 25 positioned most outward in the tire radial direction. Is closest to the tread surface 10 and therefore easily affects the change in the tread surface 10. The belt layer 25 that tends to affect the tread surface 10 tends to open in the direction parallel to the road surface in the state of use of the heavy-duty pneumatic radial tire 1 during inflation. The belt layer end portion 26 of the belt layer 25 located on the side tends to have a large amount of deformation during inflation.

  For this reason, the protruding range 51 is likely to be located in the vicinity of the belt layer end portion 26 of the belt layer 25 in the tire width direction. When the outermost circumferential groove 22, which is a part of the plurality of circumferential grooves 21, is located, the outermost circumferential groove 22 can be located in the protruding range 51. Increases nature. Thus, the land portion adjacent to the outermost circumferential groove 22 positioned outward in the tire width direction than the belt layer end portion 26 of the belt layer 25 positioned most outward in the tire radial direction in this way. By providing the narrow groove 40 in 17, the tension to the outermost circumferential groove 22 can be more reliably dispersed and the stress of the groove bottom 23 can be reduced. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed more reliably.

  The heavy-duty pneumatic radial tire 1 is formed with a flatness ratio of 70% or less. However, in the heavy-duty pneumatic radial tire 1 with a flatness ratio of 70% or less, it protrudes in the vicinity of the shoulder portion 15 during inflation. The amount tends to increase. For this reason, the outermost circumferential groove 22 that is the circumferential groove 21 located in this portion is more likely to be located in the protruding range. Accordingly, by providing the narrow groove 40 in the land portion 17 adjacent to the outermost circumferential groove 22, the stress on the groove bottom 23 due to the tension acting on the outermost circumferential groove 22 can be effectively relieved. . As a result, the occurrence of cracks in the circumferential groove 21 can be effectively suppressed.

  Further, the protruding amount of the maximum portion 52 of the protruding range 51 is 20% or more of the protruding amount of the tread central portion 14, and thus the circumferential groove 21 is located in the protruding range 51 where the protruding amount is large. By providing the narrow groove 40 in the land portion 17 adjacent to the outermost circumferential groove 22, the stress at the groove bottom 23 of the outermost circumferential groove 22 can be more reliably relieved. That is, the large amount of protrusion means that the tension in the tire width direction is also large, so that the land portion 17 adjacent to the outermost circumferential groove 22 located in the portion where the tension in the tire width direction is large is thus described. By providing the narrow groove 40, the effect of suppressing the stress on the groove bottom 23 of the outermost circumferential groove 22 is increased. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed more reliably.

  Further, when the groove width W of the outermost circumferential groove 22 is set, the narrow groove 40 is an end of the land portion 17 where the narrow groove 40 is formed on the outermost circumferential groove 22 side. By providing the narrow groove 40 in the tire width direction from a certain land portion end 18 within a range of 0.5 W to 2.5 W, the groove bottom of the outermost circumferential groove 22 is more reliably provided. 23 stress can be relieved. That is, by forming the narrow groove 40 at a position separated by 0.5 W or more from the land portion end portion 18, the width of the land portion 17 located between the outermost circumferential groove 22 and the narrow groove 40 is narrow. The damage such as chipping of the land portion 17 can be suppressed without becoming too much. Further, by forming the narrow groove 40 at a position of 2.5 W or less from the land end 18, the narrow groove 40 is not too far from the outermost circumferential groove 22. The acting tension can be more reliably absorbed and distributed by the narrow groove 40. Therefore, by providing the narrow groove 40 in the range of 0.5 W to 2.5 W in the tire width direction from the land end 18, the tension acting on the outermost circumferential groove 22 is more reliably absorbed, and the outermost The stress at the groove bottom 23 of the circumferential groove 22 can be relaxed. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed more reliably.

  Further, by forming the groove depth of the narrow groove 40 in the range of 30% to 70% of the groove depth of the outermost circumferential groove 22, the groove bottom of the outermost circumferential groove 22 is more reliably formed. 23 stress can be relieved. That is, by forming the groove depth of the narrow groove 40 at a depth of 30% or more of the outermost circumferential groove 22, the narrow groove 40 is formed with a sufficient depth. When the direction of tension is applied, the narrow groove 40 can be more reliably opened in the groove width direction. Therefore, the deformation acting on the outermost circumferential groove 22 is more reliably caused by the deformation of the narrow groove 40. Can be distributed. Moreover, by forming the groove depth of the narrow groove 40 at a depth equal to or less than 70% of the outermost circumferential groove 22, the groove depth of the narrow groove 40 is suppressed from becoming too deep. When the groove depth of the narrow groove 40 is too deep, when a tension acts on the narrow groove 40, the narrow groove 40 becomes too easy to open, so that the stress at the groove bottom of the narrow groove 40 becomes too large, and the narrow groove 40 is Although there is a possibility of breakage, by forming the groove depth of the narrow groove 40 at a depth of 70% or less of the outermost circumferential groove 22, the breakage of the narrow groove 40 is suppressed. Therefore, by forming the groove depth of the narrow groove 40 in the range of 30% to 70% of the groove depth of the outermost circumferential groove 22, the tension acting on the outermost circumferential groove 22 is Dispersion can be made more reliably, and breakage of the narrow groove 40 can be suppressed, so that the stress at the groove bottom 23 of the outermost circumferential groove 22 can be relaxed more reliably. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed more reliably.

  The narrow groove 40 is formed in the land portion 17 adjacent to the outermost circumferential groove 22. However, if the narrow groove 40 is the land portion 17 adjacent to the circumferential groove 21, You may form in the land part 17 adjacent to the circumferential grooves 21 other than the circumferential groove 22. Since the narrow groove 40 is formed in the land portion 17 adjacent to the circumferential groove 21 positioned in the protruding range 51, the tension acting on the circumferential groove 21 can be dispersed. The acting stress can be relieved. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed.

  The narrow groove 40 has only one narrow groove 40 formed in one land portion 17 of the two land portions 17 adjacent to the circumferential groove 21, but the narrow groove 40 has one circumferential direction. A plurality of grooves 21 may be formed. For example, a plurality of narrow grooves 40 are formed in one land portion 17 of two land portions 17 adjacent to each other in the tire width direction of the circumferential groove 21, or formed in both of the two land portions 17. May be. By forming the narrow groove 40 according to the tension acting on the protruding range 51 or the tension acting on the circumferential groove 21, the stress acting on the groove bottom 23 of the circumferential groove 21 can be relaxed more reliably. As a result, the occurrence of cracks in the circumferential groove 21 can be more reliably suppressed.

  Further, the groove depth of the narrow groove 40 is preferably such that the position where the narrow groove 40 is formed has a deep groove depth at a position where the protrusion amount is large, and a shallow groove depth at a position where the protrusion amount is small. . As a result, the tension can be reliably absorbed by the narrow groove 40. That is, at a position where the amount of protrusion is large, for example, a position where the amount of protrusion is 20% or more of the amount of protrusion of the tread central portion 14, the tension also increases. Therefore, by increasing the groove depth of the narrow groove 40, a large tension can be obtained. Can be distributed. Further, at a position where the amount of protrusion is small, for example, a position where the amount of protrusion is 10% or less of the amount of protrusion of the tread central portion 14, the tension is small, so even if the groove depth of the narrow groove 40 is shallow, the tension in the narrow groove 40 is small. Can be absorbed efficiently. Therefore, the groove depth of the narrow groove 40 is increased when the position where the fine groove 40 is formed is a position where the protrusion amount is large, and the position where the fine groove 40 is formed has a large protrusion amount. In the case of a small position, by reducing the groove depth, the narrow groove 40 can absorb the tension more reliably and efficiently. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed more reliably and efficiently.

  Further, the narrow groove 40 may be continuously formed on the entire circumference, or may be formed discontinuously. If the narrow groove 40 absorbs the tension in the tire width direction acting on the circumferential groove 21 by the narrow groove 40 and can disperse the tension, the narrow groove 40 is formed continuously but discontinuously. It doesn't matter. Dispersing the tension acting on the circumferential groove 21 can alleviate stress concentration at the groove bottom 23 of the circumferential groove 21, and as a result, the occurrence of cracks in the circumferential groove 21 can be suppressed.

  Further, in the heavy-duty pneumatic radial tire 1, the groove portion is provided with the circumferential groove 21 and the lug groove, but the tread pattern formed on the tread surface 10 is provided with the circumferential groove 21. Any tread pattern is acceptable. For example, the narrow groove 40 is provided in the land portion 17 adjacent to the circumferential groove 21 such as a rib pattern in which only the circumferential groove 21 is formed or a block pattern in which the circumferential groove 21 and the lug groove are formed. Also good. When the circumferential groove 21 is provided, the occurrence of cracks in the circumferential groove 21 can be suppressed by providing the narrow groove 40 in the vicinity of the circumferential groove 21 regardless of the shape of the tread pattern. . In particular, in the block pattern, in many cases, the groove depth of the circumferential groove 21 is deep, but when the groove depth of the circumferential groove 21 is thus deep, the circumferential groove 21 Since cracks are easily generated in the groove bottom 23, the effect of suppressing cracks is further increased by providing the narrow grooves 40 in the vicinity of the circumferential grooves 21 in which cracks are likely to occur, and a pneumatic radial tire for heavy loads. 1 can be improved in durability.

  The reference internal pressure for comparing the amount of protrusion is 100 kPa in the heavy-duty pneumatic radial tire 1, but the reference internal pressure may be a pressure other than 100 kPa. By comparing with the normal internal pressure, the amount of protrusion can be derived, and the reference internal pressure is other than 100 kPa as long as it is possible to identify the protrusion range 51 by deriving the difference in the swelling method of each part of the tread surface 10 during inflation. Pressure is also acceptable.

  Hereinafter, with respect to the above-described heavy-duty pneumatic radial tire 1, performance evaluation tests performed on the conventional heavy-duty pneumatic radial tire 1 and the heavy-duty pneumatic radial tire 1 of the present invention will be described. The performance evaluation test was conducted on two items regarding the number of cracks in the circumferential groove 21 and the length of the cracks.

  The test method is as follows. A heavy-duty pneumatic radial tire 1 having a weather pattern of 265 / 60R22.5 size is assembled to a normal rim and set to a normal internal pressure. This heavy-duty pneumatic radial tire 1 is mounted on the front wheel of a 20-ton truck (2, 2-D, D car) and the occurrence of cracks in the circumferential groove 21 is investigated every 40,000 km. The crack length was measured, and the number of cracks and the crack length were evaluated. About the number of the cracks of the circumferential groove | channel 21, it showed with the index | exponent which set the number of the cracks which generate | occur | produced in the circumferential groove | channel 21 of the pneumatic radial tire 1 for heavy loads of the conventional example mentioned later to 100. The smaller the index, the smaller the number of cracks, the harder the cracks are generated, and the better performance against the occurrence of cracks in the groove bottom 23. Regarding the length of the crack in the circumferential groove 21, from the longest crack to the fifth longest crack among the crack lengths generated in the circumferential groove 21 for each heavy-duty pneumatic radial tire 1 to be tested. The average value was calculated, and the average value was shown as an index with the average value of the conventional heavy-duty pneumatic radial tire 1 described later as 100. The smaller the index is, the shorter the crack length is, and even when a crack is generated, it is difficult to increase the crack length, and the performance of the groove bottom 23 against cracks is excellent.

  For the heavy-duty pneumatic radial tire 1 to be tested, the present invention tests five types and one type of conventional example by the above method. Regarding the shapes of the circumferential groove 21 and the narrow groove 40, the circumferential groove 21 has a groove depth of 16 mm and a groove width of 10 mm in both the present inventions 1 to 5 and the conventional example. In addition, in all of the present inventions 1 to 5 and the conventional examples, the amount of protrusion is 63% larger than the amount of protrusion of the tread central portion 14 in which the maximum portion 52, which is the portion of the protrusion range 51 having the largest amount of protrusion, is present. It has become. In the conventional example, the narrow groove 40 is not formed.

  On the other hand, in the first to fifth aspects of the present invention, all the narrow grooves 40 are formed, and all the narrow grooves 40 have a groove depth of 10 mm and a groove width of 3 mm. In the first aspect of the present invention, the narrow groove 40 is formed at the circumferential groove 21 side of the land portion 17 where the narrow groove 40 is formed, where W is the groove width of the circumferential groove 21. Is formed at a position of 0.4 W on the side where the narrow groove 40 is formed from the land portion end portion 18. In the second aspect of the present invention, the narrow groove 40 is formed at a position 0.5 W from the land portion end 18. In the third aspect of the present invention, the narrow groove 40 is formed at a position 1.5 W from the land end 18. In the fourth aspect of the present invention, the narrow groove 40 is formed at a position 2.5 W from the land end 18. In the fifth aspect of the present invention, the narrow groove 40 is formed at a position of 3.0 W from the land end 18. These conventional examples and heavy-duty pneumatic radial tires 1 of the present invention 1 to 5 are subjected to an evaluation test by the above-described method, and the obtained results are shown in Table 1.

  As is apparent from the above test results shown in Table 1, by providing the narrow groove 40 in the vicinity of the circumferential groove 21, cracks in the circumferential groove 21 are reduced, and even if a crack is generated, the length is increased. Becomes shorter. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed.

  In addition, when the narrow groove 40 is too close to the circumferential groove 21, a crack is easily generated in the narrow groove 40 (Invention 1). Further, when the narrow groove 40 is too far from the circumferential groove, the effect of suppressing the occurrence of cracks in the circumferential groove 21 is reduced (Invention 5). For this reason, the position where the narrow groove 40 is provided is 0.5 W to 2... On the side where the narrow groove 40 is formed from the land portion end 18 on the circumferential groove 21 side of the land portion 17 where the narrow groove 40 is formed. By providing in the range of 5 W, generation of cracks in the narrow grooves 40 can be suppressed, cracks in the circumferential grooves 21 can be more reliably reduced, and the length can be shortened even when cracks occur. As a result, the occurrence of cracks in the circumferential groove 21 can be suppressed more reliably.

  As described above, the heavy-duty pneumatic radial tire according to the present invention is useful for a heavy-duty pneumatic radial tire having a circumferential groove, and is particularly suitable for a heavy-duty pneumatic radial tire having a flatness ratio of 70% or less. ing.

1 is a meridional sectional view showing a main part of a heavy-duty pneumatic radial tire according to the present invention. FIG. 2 is a diagram showing a state of a tread surface during inflation of the heavy duty pneumatic radial tire of FIG. 1. It is the figure which showed the relationship between the position in a tire width direction, and the amount of protrusion.

Explanation of symbols

1 Heavy load pneumatic radial tire 5 Tread portion 10 Tread surface 11 Tread surface at normal internal pressure 12 Tread surface at normal internal pressure 14 Tread central portion 15 Shoulder portion 17 Land portion 18 Land portion end portion 21 Circumferential groove 22 Outermost circumferential direction Groove 23 Groove bottom 25 Belt layer 26 Belt layer end 30 Side wall 31 Carcass 32 Inner liner 40 Narrow groove 45 Equatorial surface 50 Projection amount line 51 Projection range 52 Maximum part

Claims (6)

In a heavy-duty pneumatic radial tire having a plurality of circumferential grooves formed on a tread surface of a tread portion and a plurality of land portions defined by the plurality of circumferential grooves,
A position where the protruding amount that is the amount of change in the tire radial direction of the tread surface at the normal internal pressure with respect to the tread surface at the internal pressure of 100 kPa in the state of being incorporated in the normal rim is present in a region other than the tread central portion.
Some of the circumferential grooves of the plurality of circumferential grooves are located in a protruding range that is substantially the largest range of the protruding amount,
Of the land portions adjacent to the circumferential groove positioned in the protruding range, at least the land portion positioned outward in the tire width direction has a groove depth shallower than the circumferential groove positioned in the protruding range. Provided a narrow groove,
When the groove width of the circumferential groove located in the protruding range is W, the narrow groove is in the tire width direction from the end on the circumferential groove side of the land portion where the narrow groove is formed. A heavy-duty pneumatic radial tire characterized by being formed in a range of 0.4 W to 3.0 W on the side where the narrow groove is formed .   2. The heavy-duty pneumatic radial tire according to claim 1, wherein the protruding amount in the protruding range is 20% or more larger than the protruding amount in the tread central portion. The narrow groove is in the range of 0.5W~2.5W on the side the from the circumferential groove side end portion of the land portion before KiHosomizo is formed in the tire width-direction narrow groove is formed The heavy duty pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is heavy.   The narrow groove is formed so that a groove depth is within a range of 30% to 70% of a groove depth of the circumferential groove positioned in the protruding range. The heavy-duty pneumatic radial tire according to any one of the preceding claims.   The flat load pneumatic radial tire according to any one of claims 1 to 4, wherein the flatness ratio is 70% or less. A plurality of belt layers are provided on the inner side in the tire radial direction of the tread portion,
Of the plurality of belt layers, the belt layer positioned most outward in the tire radial direction has a width in the tire width direction narrower than the belt layer adjacently positioned inward in the tire radial direction,
The circumferential groove located in the protruding range is located on the outer side in the tire width direction than the end portion of the belt layer located on the outermost side in the tire radial direction in the tire width direction. The heavy-duty pneumatic radial tire according to any one of 1 to 5.

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