JP4710938B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that improves the rigidity of a land portion while maintaining snow performance and drainage performance.

  Pneumatic tires, especially studless tires, receive water and snow between the tread surface and the road surface in the groove by arranging a block-shaped land portion consisting of a circumferential groove and a width direction groove in the tread portion. It is common to improve drainage effect and edge effect, and to provide drainage performance and performance on snow. In this type of pneumatic tire, it is preferable to dispose the width direction grooves with respect to the tire width direction in order to further improve drainage performance. However, when the width direction groove is inclined with respect to the tire width direction, an acute angle portion and an obtuse angle portion are generated in the tread shape of the land portion, and the rigidity of the land portion at the acute angle portion is reduced with respect to the obtuse angle portion. As a result, abnormal wear (for example, heel and toe wear) is caused.

  Therefore, some conventional pneumatic tires attempt to increase the rigidity of land portions defined by widthwise grooves inclined with respect to the tire width direction. For example, in the pneumatic tire described in Patent Literature 1, the inclination angle of the groove wall surface with respect to the tread surface normal is set to the inclination angle continuous with the end portion on the first arrival side (acute angle side) in the tire rotation, and the rear arrival side (obtuse angle side). It is larger than the inclination angle connected to the end portion. Further, in the pneumatic tire described in Patent Document 2, the inclination angle of the side wall (groove wall) of the land portion facing at least one of the circumferential groove and the width direction groove is set at the acute corner portion of the land portion. It is larger than the obtuse corner.

JP-A-11-147407 Japanese Patent Publication No.7-115569

  With the conventional pneumatic tire, it is possible to increase the rigidity of the land portion defined by the widthwise grooves inclined with respect to the tire width direction while maintaining drainage performance and on-snow performance. However, in recent years, further improvement in the rigidity of the land has been desired in order to cope with higher performance of vehicles.

  This invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can improve rigidity, maintaining drainage performance and performance on snow.

In order to achieve the above object, in the pneumatic tire according to the present invention, at least three circumferential main grooves extending in the tire circumferential direction and linear with respect to the tire width direction in a mode communicating with the circumferential main groove. In a pneumatic tire having a tread portion in which a block-shaped land portion is defined by a plurality of sub-grooves extending inclined to each other, each groove wall of the sub-grooves facing each other in the tire circumferential direction includes the sub-grooves The tire width of the tread surface of the land portion in plan view, including an overlapping portion formed by changing the inclination angle with respect to the normal line of the tread portion of the tread portion in a partially overlapping manner without contacting in the extending direction of A second line connecting at least two midpoints in the tire circumferential direction between the first dividing line passing through the center of the tire along the tire circumferential direction and the groove center of the tread side opening in each of the sub-grooves sandwiching the land portion. Virtually four land parts by dividing line The area Sa of the land surface on the acute angle side, the area Sb of the land surface on the obtuse angle side, the area Sb of the land surface on the obtuse angle side, and the acute angle side are divided into two areas, the acute angle side and the obtuse angle side along one of the sub grooves. The area La of the groove bottom expanded from the tread of the land portion to the groove bottom of the sub-groove due to the inclination of the groove wall of the sub-groove, and the land portion of the land portion due to the inclination of the groove wall of the sub-groove on the obtuse angle side The relationship of the area Lb at the groove bottom expanded from the tread surface to the groove bottom of the sub groove is Lb <La, 0.05 ≦ La / Sa, 1.1 ≦ (La / Sa) ÷ (Lb / Sb). With respect to the angle Ga1 at the acute angle portion of the tread surface of the land portion, the groove wall of the sub-groove is 0 with respect to the normal line of the tread surface of the land portion. A hypothetical side at the bottom of the sub-groove that overlaps the side of the tread surface of the land portion and the groove wall of the sub-groove The angle Ga2 formed by the side at the groove bottom that is wide-angled from the virtual side due to the actual inclination is set in a range of 0.1 ≦ Ga2 / Ga1 ≦ 0.4 .

According to this pneumatic tire, since the groove wall of the sub groove is overlapped by the overlapping portion in the extending direction of the sub groove, deformation of the land portion is suppressed. For this reason, the rigidity of the land portion in the tire circumferential direction can be improved. Further, the overlapping portion suppresses the opening of the groove starting from the secondary groove during inflation, and the deformation of the tread portion during tire rolling can be suppressed. Further, since the land portions adjacent to each other in the tire circumferential direction are supported by the overlapping portion, deformation of the land portion can be suppressed even with respect to the load in the tire width direction. Furthermore, the overlapping portion is formed without contact of each groove wall, and the groove depth of the sub-groove does not change in the extending direction, so that the drainage performance and on-snow performance can be maintained. Moreover, according to this pneumatic tire, the relationship between the areas Sa, Sb, La, and Lb is set in the above range, so that the rigidity improvement effect of the land portion, the drainage performance after wear and the performance on snow are maintained. The effect can be achieved as appropriate. Moreover, according to this pneumatic tire, if the ratio of the angle Ga2 to the angle Ga1 is less than 0.1, the rigidity improvement effect of the land portion 24 is deteriorated. On the other hand, if the ratio of the angle Ga2 to the angle Ga1 exceeds 0.4, the effect of maintaining drainage performance after wear and on-snow performance deteriorates. Therefore, it is preferable to set the ratio of the angle Ga2 to the angle Ga1 within the above range in terms of improving the rigidity of the land portion and maintaining the drainage performance after wear and the performance on snow.

  In the pneumatic tire according to the present invention, the overlapping portion has a bent portion in which a groove bottom of the sub-groove is bent in an extending direction of the sub-groove.

  According to this pneumatic tire, the effect that the land portions adjacent in the tire circumferential direction support each other with respect to the load in the tire width direction is further improved, so that the rigidity of the land portion can be further improved. The bent part may be bent at at least one point. Moreover, the bending part may be provided curvedly. If the bent part is curved, the occurrence of cracks at the groove bottom can be suppressed.

  Further, in the pneumatic tire according to the present invention, the circumferential land portion row that is divided by extending five or more circumferential main grooves along the tire circumferential direction is arranged on the outer side in the tire width direction from the central portion in the tire width direction. R1, R2, R3,... Rn, and the circumferential grooves R1, R2, R3,... Rn are divided into block shapes, and the secondary grooves S1, S2, S3,. 55 [deg.] Where D1 is an acute angle formed by the tire equator line, D2 is an acute angle formed by the inclination of the minor groove S2 and the tire equator line, and D3 is an acute angle formed by the inclination of the minor groove S3 and the tire equator line. ≦ D1 ≦ 70 [degree], 65 [degree] ≦ D2 ≦ 80 [degree], and D1 <D2 <D3.

  According to this pneumatic tire, the displacement of the tread portion outward in the tire width direction at the center portion in the tire width direction during inflation is reduced with respect to the outer portion in the tire width direction (the portion closest to the shoulder portion). Suppresses deformation of the tread when the tire is in contact with the ground. For this reason, the rigidity of a land part can further be improved.

  In the pneumatic tire according to the present invention, at least one of the circumferential main grooves is formed by changing the inclination angle of each groove wall with respect to the normal line of the tread surface in the tire circumferential direction. It is characterized by that.

  According to this pneumatic tire, since the deformation of the land portion partitioned by the circumferential main groove is suppressed, the rigidity of the land portion can be further improved.

  In the pneumatic tire according to the present invention, the reinforcing material in the outermost belt in the tire radial direction disposed in the tread portion and the groove bottom of the circumferential main groove disposed closest to the tire equator line. The rubber thickness T is set in the range of 3.0 [mm] ≦ T ≦ 5.5 [mm].

  According to this pneumatic tire, when the rubber thickness T is less than 3.0 [mm], the occurrence of cracks at the bottom of the circumferential main groove is a concern. On the other hand, when the rubber thickness T exceeds 5.5 [mm], the distortion of the tread portion at the time of tire contact increases, the land portion falls down, and the rigidity of the tread portion cannot be increased. The rubber thickness T is preferably set in the above range.

  The pneumatic tire according to the present invention is characterized in that tan δ when the rubber of the tread portion is heated at 100 [° C.] is set in a range of tan δ ≦ 0.10.

  According to this pneumatic tire, when tan δ exceeds 0.10, the amount of heat generated by the rubber in the tread portion increases, and the rolling resistance of the tire increases. Therefore, tan δ is preferably set in the above range.

  The pneumatic tire according to the present invention is characterized by being applied to a heavy duty pneumatic tire.

  According to this pneumatic tire, in a heavy duty pneumatic tire, the rolling resistance of the tire tends to increase. Therefore, there is an advantage that the effect of reducing the rolling resistance can be obtained more remarkably by making the heavy duty pneumatic tire applicable.

  The pneumatic tire according to the present invention corresponds to a land portion having a sub-groove inclined with respect to the tire width direction and having an acute angle portion, and can improve rigidity while maintaining drainage performance and on-snow performance.

  Embodiments of a pneumatic 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. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention, FIG. 2 is a plan view showing a tread portion of the pneumatic tire shown in FIG. 1, and FIG. 3 is a view of the tread portion shown in FIG. 4 is an enlarged perspective view of the main portion of the tread portion shown in FIG. 2, FIGS. 5 and 6 are enlarged views of the main portion of the tread portion shown in FIG. 2, and FIG. 7 is a bent portion where the overlapping portion is bent. FIG. 8 is an enlarged plan view showing a bent portion where the overlapping portion is curved, FIG. 9 is a plan view showing another form of the land portion, and FIG. 10 is an embodiment of the present invention. It is a graph which shows the result of the performance test of a pneumatic tire.

  In the following description, the tire radial direction refers to a direction orthogonal to the rotation axis (not shown) of the pneumatic tire 1, and the tire radial direction inner side refers to the side toward the rotation axis in the tire radial direction, the tire diameter The direction outer side means the side away from the rotation axis in the tire radial direction. Further, the tire circumferential direction refers to a direction around the rotation axis as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction is the side toward the tire equatorial plane C in the tire width direction, and the outer side in the tire width direction is the tire equatorial plane C in the tire width direction. The side away from.

  The pneumatic tire 1 described below is configured to be substantially symmetric with respect to the tire equatorial plane C. The tire equatorial plane C is a plane that is orthogonal to the rotational axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. The tire width is the width in the tire width direction between the portions located outside in the tire width direction, that is, the distance between the portions farthest from the tire equatorial plane C in the tire width direction. Further, the tire equator line is a line on the tire equator plane C and along the circumferential direction of the pneumatic tire 1. And since the pneumatic tire 1 demonstrated below is comprised so that it may become substantially symmetrical centering on the tire equator surface C, when cutting a pneumatic tire in the plane which passes along the rotating shaft of the pneumatic tire 1 In the meridional sectional view (FIG. 1), one side centered on the tire equatorial plane C is shown and only the one side is described, and the description on the other side is omitted.

  As shown in FIG. 1, a pneumatic tire 1 according to the present embodiment includes a tread portion 2, shoulder portions 3 on both outer sides in the tire width direction, sidewall portions 4 and beads that are sequentially continuous from the shoulder portions 3. Part 5. The pneumatic tire 1 includes a carcass 6 and a belt layer 7.

  The tread portion 2 is exposed to the outside of the pneumatic tire 1, and the surface thereof is the contour of the pneumatic tire 1. On the outer peripheral surface of the tread portion 2, that is, the tread surface 21 that is in contact with the road surface during traveling, as shown in FIGS. 1 and 2, at least three (in this embodiment) formed extending in the tire circumferential direction. A plurality of block-shaped land portions 24 are defined by five circumferential main grooves 22 and a plurality of sub-grooves 23 that extend in an inclined manner with respect to the tire width direction in a manner in which the circumferential main grooves 22 communicate with each other. Has been. In addition, it is preferable that the angle of the groove wall 22a with respect to the normal line of the tread portion 21 of the tread portion 2 is set to about 5 [degrees] in the circumferential main groove 22. Moreover, it is preferable that the groove width of the sub groove 23 is narrower than the circumferential main groove 22 and is 5 [mm] or more and 10 [mm] or less. Further, the sub-groove 23 may or may not be the same as the groove depth of the circumferential main groove 22. For example, the groove depth of the circumferential main groove 22 is set to 20 [mm], and the groove depth of the sub-groove 23 is set to 15 [mm].

  The shoulder portion 3 is a portion on both outer sides in the tire width direction of the tread portion 2. Further, the sidewall portion 4 is exposed at the outermost side in the tire width direction of the pneumatic tire 1. The bead unit 5 includes a bead core 51 and a bead filler 52. The bead core 51 is formed by winding a bead wire 51a, which is a steel wire, in a ring shape. The bead filler 52 is disposed in a space formed by folding the end of the carcass 6 outward in the tire width direction at the position of the bead core 51.

  The carcass 6 is configured such that each tire width direction end portion is folded with respect to the pair of bead portions 5 and is wound around in a toroidal shape in the tire circumferential direction to constitute a tire skeleton. The carcass 6 is a carcass cord made of organic fibers (such as nylon or polyester) or steel covered with rubber.

  The belt layer 7 is provided on the outer side in the tire radial direction than the carcass 6 in the tread portion 2. The belt layer 7 is a belt in which a cord (reinforcing material) such as organic fiber (nylon, polyester, etc.) or steel is covered with rubber, and a plurality of these belts are laminated. The belt layer 7 in the present embodiment is laminated in the order of the first belt 71, the second belt 72, the third belt 73, and the fourth belt 74 from the outer side in the tire radial direction of the carcass 6 toward the outer side in the tire radial direction. It has a four-layer structure.

  An overlapping portion 25 is formed in the sub-groove 23 that extends over the pneumatic tire 1 and extends between the land portions 24 adjacent to each other in the tire circumferential direction.

  The overlapping portion 25 is a normal line of the tread portion 21 of the tread portion 2 in such a manner that the groove walls 23a and 23a facing each other in the tire circumferential direction of the sub groove 23 do not contact in the extending direction of the sub groove 23 and partially overlap. The inclination angle with respect to is changed.

  As shown in FIGS. 3 (a), 3 (b), and 4, the overlapping portion 25 is formed so that the groove walls 23 a and 23 a of the sub-groove 23 facing each other in the tire circumferential direction are from The inclination angle θ is changed with respect to the normal line 21 a of the tread surface 21 so as to expand toward the groove bottom of the sub-groove 23. Further, the groove walls 23a are not in contact with each other so that when the inclination angle of one groove wall 23a opposed in the tire circumferential direction gradually increases, the inclination angle of the other groove wall 23a gradually decreases. The grooves 23 are provided symmetrically at the groove center. With this configuration, as shown in FIG. 3B, when the groove depth D of the sub-groove 23 is constant in the extending direction and the sub-groove 23 is viewed in the extending direction, each groove has an overlap width Lp. Overlapping portions 25 are formed where the walls 23a do not contact each other and overlap each other.

Further, as shown in FIG. 5, in plan view, in the first dividing line C <b> 1 passing through the tire width direction center of the tread surface 21 of the land portion 24 along the tire circumferential direction, and in each of the sub grooves 23 sandwiching the land portion 24. The land portion 24 is virtually divided into four regions by a second dividing line C2 connecting at least two midpoints α and β in the tire circumferential direction between the groove centers Ca and Ca of the tread side opening. Of the two areas on the acute angle side and the obtuse angle side along one sub groove 23, the area Sa of the tread surface 21 of the land portion 24 on the acute angle side, the area Sb of the tread surface 21 of the land portion 24 on the obtuse angle side, and the sub groove on the acute angle side. 23, the area La of the groove bottom that has expanded from the tread 21 of the land portion 24 to the groove bottom of the sub-groove 23 due to the inclination of the groove wall 23a of the land portion 24, and the inclination of the groove wall 23a of the sub-groove 23 on the obtuse angle side. The relationship of the area Lb at the groove bottom expanded from the tread 21 to the groove bottom of the sub-groove 23 is
Lb <La,
0.05 ≦ La / Sa,
1.1 ≦ (La / Sa) ÷ (Lb / Sb)
Is set in the range.

  In the pneumatic tire 1 configured as described above, since the overlapping portion 25 is provided and each groove wall 23a of the sub groove 23 (the wall portion of the land portion 24) is overlapped in the extending direction of the sub groove 23, Since the deformation of the land portion 24, in particular, the deformation on the acute angle side of the land portion 24 is suppressed, the rigidity of the land portion 24 in the tire circumferential direction can be improved. For this reason, rolling resistance can be reduced and heel and toe wear can be suppressed. Moreover, since the groove wall 23a (wall part of the land portion 24) of the sub-groove 23 is overlapped in the extending direction of the sub-groove 23, the situation where the sub-groove 23 opens from the sub-groove 23 at the time of inflation is suppressed. Therefore, it becomes possible to suppress the deformation of the tread portion 2 at the time of tire rolling. Furthermore, since the groove wall 23a (wall portion of the land portion 24) of the sub-groove 23 is overlapped in the extending direction of the sub-groove 23, the adjacent land portions 24 in the tire circumferential direction act to support each other. Therefore, it is possible to suppress the deformation of the land portion 24 even with respect to the load in the tire width direction. Furthermore, the overlapping portion 25 is formed without contact with each groove wall 23a, and the groove depth D of the sub-groove 23 does not change in the extending direction, so that drainage performance and on-snow performance are maintained. Is possible.

  Moreover, in this pneumatic tire 1, the area Sa of the tread surface 21 of the land portion 24 on the acute angle side, the area Sb of the tread surface 21 of the land portion 24 on the obtuse angle side, and the inclination of the groove wall 23 a of the sub-groove 23 on the acute angle side. From the tread surface 21 of the land portion 24 to the groove bottom of the sub-groove 23 due to the area La at the groove bottom expanded from the tread surface 21 to the bottom of the sub-groove 23 and the inclination of the groove wall 23a of the sub-groove 23 on the obtuse angle side. The relationship of the area Lb at the groove bottom that is extremely enlarged is set in the above range. For this reason, it is possible to appropriately achieve the effect of improving the rigidity of the land portion 24 and the effect of maintaining drainage performance and on-snow performance after wear.

  The relationship between the areas Sa, Sb, La, and Lb is set in the range of Lb <La, 0.08 ≦ La / Sa, 1.3 ≦ (La / Sa) ÷ (Lb / Sb) ≦ 2.5. It is further preferable in terms of improving the rigidity of the land portion 24 and maintaining the drainage performance after wear and the performance on snow.

  Thus, in the pneumatic tire 1 of the present embodiment, it is possible to improve rigidity while maintaining drainage performance and performance on snow, corresponding to a land portion having an acute angle portion.

  By the way, in the pneumatic tire 1 of the present embodiment, the groove wall 23a of the auxiliary groove 23 with respect to the angle Ga1 at the acute angle portion of the tread surface 21 of the land portion 24 in the plan view shown in FIG. The angle Ga2 at the groove bottom that is expanded from the tread surface 21 of the land portion 24 to the groove bottom of the sub-groove 23 due to the inclination is set in a range of 0.1 ≦ Ga2 / Ga1 ≦ 0.4. Specifically, the angle Ga1 is an acute angle formed by the sides 21b and 21c of the tread surface 21 of the land portion 24 in the plan view shown in FIG. Further, the angle Ga2 is the land portion 24 when the groove wall 23a of the auxiliary groove 23 is set to 0 degree with respect to the normal of the tread surface 21 of the land portion 24 in the plan view shown in FIG. The angle formed by the virtual side at the groove bottom of the sub-groove 23 that overlaps the side 21b of the tread surface 21 and the side 23b at the groove bottom widened from the virtual side by the actual inclination of the groove wall 23a of the sub-groove 23 is there. In the plan view shown in FIG. 6, the vertices O of the angles Ga1 and Ga2 overlap. In addition, when the groove bottom of the sub-groove 23 is curved due to a change in the inclination angle of the groove wall 23a of the sub-groove 23, that is, when the side 23b is curved, the angle Ga2 is curved in plan view. The angle formed by the tangent line passing through the vertex O of the side 23b and the virtual side.

  If the ratio of the angle Ga2 to the angle Ga1 is less than 0.1, the rigidity improvement effect of the land portion 24 is deteriorated. On the other hand, if the ratio of the angle Ga2 to the angle Ga1 exceeds 0.4, the effect of maintaining drainage performance after wear and on-snow performance deteriorates. Therefore, it is preferable to set the ratio of the angle Ga2 to the angle Ga1 within the above range in order to achieve the effect of improving the rigidity of the land portion 24 and the effect of maintaining drainage performance after wear and performance on snow.

  Further, in the pneumatic tire 1 of the present embodiment, the overlapping portion 25 has a bent portion 25 a in which the groove bottom is bent in the extending direction of the sub-groove 23. As shown in FIG. 7, the bent portion 25a is provided by bending the groove bottom of the sub-groove 23 at at least one point (two points in the present embodiment) due to the change in the inclination angle of the groove wall 23a of the sub-groove 23. As shown in FIG. 8, there is a form in which the groove bottom of the sub-groove 23 is curved by changing the inclination angle of the groove wall 23 a of the sub-groove 23.

  According to such a configuration, each land portion 24 adjacent in the tire circumferential direction further improves the effect of supporting each other against the load in the tire width direction, so that the rigidity of the land portion 24 can be further improved. Become. Further, if the bent portion 25a is provided to be curved, it is possible to suppress the occurrence of cracks at the groove bottom of the sub-groove 23.

Moreover, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 1, the circumferential land portion row partitioned by extending five or more circumferential main grooves 22 along the tire circumferential direction, R1, R2, R3,... Rn from the center in the tire width direction (the portion closest to the tire equatorial plane C) to the outside in the tire width direction. The sub-grooves 23 that partition each circumferential land portion row R1, R2, R3,... Rn into block shapes are denoted by S1, S2, S3,. Furthermore, the acute angle that the inclination of the secondary groove S1 makes with the tire equator line is D1, the acute angle that the inclination of the auxiliary groove S2 makes with the tire equator line, and the acute angle that the inclination of the auxiliary groove S3 makes with the tire equator line is D3. if you did this,
55 [degrees] ≦ D1 ≦ 70 [degrees],
65 [degree] ≦ D2 ≦ 80 [degree],
D1 <D2 <D3
Have the relationship.

  According to such a configuration, the displacement of the tread portion 2 toward the outer side in the tire width direction at the center portion in the tire width direction during inflation is reduced with respect to the outer portion in the tire width direction (the portion closest to the shoulder portion 3). The deformation of the tread portion 2 at the time of tire contact is suppressed. For this reason, the rigidity of the land portion 24 can be further improved.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 9, at least one circumferential main groove 22 has an inclination angle of each groove wall 22 a with respect to the normal line of the tread surface 21 of the tread portion 2. It is formed by changing in the circumferential direction.

  According to such a configuration, deformation of the land portion 24 partitioned by the circumferential main groove 22 is suppressed. For this reason, the rigidity of the land portion 24 can be further improved.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 1, the reinforcing material in the outermost fourth belt 74 of the belt layer 7 in the tire radial direction and the circumference disposed closest to the tire equator line. The rubber thickness T between the direction main groove 22 and the groove bottom 22b is set in a range of 3.0 [mm] ≦ T ≦ 5.5 [mm].

  When the rubber thickness T is less than 3.0 [mm], there is a concern about the generation of cracks at the groove bottom 22b. On the other hand, when the thickness T of the rubber exceeds 5.5 [mm], the distortion of the tread portion 2 at the time of tire contact increases, and the land portion 24 falls and the rigidity of the tread portion 2 cannot be increased. The effect of reducing rolling resistance is reduced. Therefore, the rubber thickness T between the reinforcing material in the fourth belt 74 and the groove bottom 22b of the circumferential main groove 22 disposed closest to the tire equator line is 3.0 [mm] ≦ T. It is preferable to be set in a range of ≦ 5.5 [mm].

  Further, in the pneumatic tire 1 of the present embodiment, tan δ when the rubber of the tread portion 2 is heated at 100 [° C.] is set in a range of tan δ ≦ 0.10.

  When tan δ exceeds 0.10, the amount of heat generated by the rubber in the tread portion 2 increases and the rolling resistance of the tire increases. Therefore, it is preferable that tan δ when the rubber of the tread portion 2 is heated at 100 [° C.] is set in a range of tan δ ≦ 0.10.

  Moreover, it is preferable that the pneumatic tire 1 of the present embodiment is a heavy load pneumatic tire. In a heavy duty pneumatic tire, the rolling resistance of the tire tends to increase. Therefore, there is an advantage that the effect of reducing the rolling resistance can be obtained more remarkably by making the heavy duty pneumatic tire applicable. Further, the pneumatic tire 1 of the present embodiment is not clearly shown in the figure, but it is preferable that a sipe or a narrow groove is formed on the tread surface 21 of the tread portion 2 and a studless tire is applied.

  In the pneumatic tire 1 of the above-described embodiment, the sub-groove 23 is illustrated and described in a linearly inclined manner with respect to the tire width direction, but this is not restrictive. For example, although not clearly shown in the drawing, the sub-groove 23 may be bent and provided with the above-described configuration, the same effect can be obtained.

[Example]
In this example, performance tests on rolling resistance performance, uneven wear resistance performance, on-snow performance (at 50% wear), drainage performance (at 50% wear), and crack resistance performance for multiple types of pneumatic tires with different conditions. (See FIG. 10).

  In this performance test, a pneumatic tire having a tire size of 275 / 80R22.5 was assembled to a regular rim and filled with a regular internal pressure. The regular rim here refers to an “applied rim” defined in JATMA, a “Design Rim” defined in TRA, or a “Measuring Rim” defined in ETRTO. The normal internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO.

  In the rolling resistance performance test, a load of 30.89 [kN] is applied to the pneumatic tire, and the rolling resistance at a speed of 80 [km / h] is measured with a drum type rolling resistance tester. And index evaluation is performed based on this measurement result. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable the rolling resistance tends to decrease.

  In the uneven wear resistance test, a pneumatic tire is mounted on a heavy load test vehicle having a total vehicle weight of 25 [t] (6 × 2) and travels on a general pavement for 30,000 [km]. After this travel, the degree of heel and toe wear is observed and index evaluation is performed. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  In the performance test on snow, the braking distance from the traveling speed of 40 [km / h] on the road surface on the snow is evaluated by the heavy load test vehicle. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  In the drainage performance test, the braking distance from the traveling speed of 40 [km / h] is evaluated on the wet road surface by the heavy load test vehicle. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  In the crack resistance test, the vehicle is run on a general pavement for 30,000 [km] with the heavy load test vehicle. And after this driving | running | working, a crack generation rate (crack generation block / total number of blocks) is measured. And index evaluation is performed based on this measurement result. This evaluation is indicated by an index value based on a conventional pneumatic tire (conventional example) as a reference (100), and the larger the index value, the more preferable.

  The pneumatic tire of the conventional example has a tread portion in which a block-shaped land portion is defined by a circumferential main groove and a sub-groove, but does not have an overlapping portion and has areas Sa and Sb. , La, Lb, the ratio of angle Ga2 to angle Ga1, and the relationship of acute angles D1, D2, D3 to the tire equator line are not optimized.

  On the other hand, the pneumatic tires of Examples 1 to 5 have overlapping portions, and the relationship among the areas Sa, Sb, La, and Lb is optimized. In the pneumatic tire of Example 3, the ratio of the angle Ga2 to the angle Ga1 is optimized in addition to the pneumatic tires of Example 1 and Example 2. Furthermore, in addition to the pneumatic tire of Example 3, the pneumatic tire of Example 4 has a bent portion. Furthermore, in the pneumatic tire of Example 5, in addition to the pneumatic tire of Example 4, the relationship between the acute angles D1, D2, and D3 with respect to the tire equator line is optimized.

  As shown in the test results of FIG. 10, in the pneumatic tires of Examples 1 to 5, the rolling resistance performance, the uneven wear resistance and the anti-wear performance are improved by improving the rigidity while maintaining the drainage performance and the performance on snow, respectively. It can be seen that the crack performance is improved.

  As described above, the pneumatic tire according to the present invention is suitable for improving rigidity while maintaining drainage performance and performance on snow.

1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention. It is a top view which shows the tread part of the pneumatic tire shown in FIG. FIG. 3 is an enlarged view of a main part of a tread portion shown in FIG. 2. FIG. 3 is an enlarged perspective view of a main part of a tread portion shown in FIG. 2. FIG. 3 is an enlarged view of a main part of a tread portion shown in FIG. 2. FIG. 3 is an enlarged view of a main part of a tread portion shown in FIG. 2. It is an enlarged plan view which shows the bending part which the overlapping part bends. It is an enlarged plan view which shows the bending part which the overlap part curves. It is a top view which shows the other form of a land part. It is a graph which shows the result of the performance test of the pneumatic tire concerning the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 21 Tread surface 22 Circumferential main groove 22a Groove wall 22b Groove bottom 23 Subgroove 23a Groove wall 24 Land part 25 Overlapping part 25a Bending part 3 Shoulder part 4 Side wall part 5 Bead part 6 Carcass 7 Belt layer 71, 72, 73, 74 Belt Lp Overlapping width of overlapping portion C Tire equatorial plane C1 First dividing line C2 Second dividing line Ca Groove center α, β Midpoint between groove centers Sa Area of the tread Sb Area of the tread on the land on the obtuse angle side La Area on the groove bottom that extends from the tread to the groove bottom of the secondary groove on the acute angle side Lb Groove bottom that extends from the tread to the groove bottom of the sub groove on the obtuse angle side Area Ga1 Angle at the acute angle of the tread surface of the land portion Ga2 Angle at the groove bottom expanded from the tread surface of the land portion to the groove bottom of the sub groove due to the inclination of the groove wall of the sub groove R1, R2, R3 Circumferential land portion Row S1, S2, S 3 Sub-grooves in each circumferential land row D1, D2, D3 Acute angle formed by the inclination of the sub-grooves and the tire equator line

Claims (9)

Block-shaped by at least three circumferential main grooves extending in the tire circumferential direction and a plurality of sub-grooves extending in a straight line with respect to the tire width direction in a mode communicating with the circumferential main groove. In a pneumatic tire having a tread portion in which a land portion is defined,
The groove walls of the sub grooves facing each other in the tire circumferential direction are formed by changing the inclination angle with respect to the normal line of the tread portion in such a manner that they partially overlap without contacting in the extending direction of the sub grooves. With overlapping parts,
The tire between the first dividing line passing through the tire width direction center of the tread surface of the land portion along the tire circumferential direction and the groove center of the tread side opening in each of the sub grooves sandwiching the land portion in plan view The land portion is virtually divided into four regions by a second dividing line that connects at least two middle points in the circumferential direction, of which two regions on the acute angle side and the obtuse angle side along one sub-groove, An area Sa of the tread surface of the land portion on the acute angle side, an area Sb of the tread surface of the land portion on the obtuse angle side, and an inclination of the groove wall of the sub groove on the acute angle side lead from the tread surface of the land portion to the groove bottom of the sub groove. The relationship between the area La at the expanded groove bottom and the area Lb at the groove bottom expanded from the tread of the land portion to the groove bottom of the subsidiary groove due to the inclination of the groove wall of the subsidiary groove on the obtuse angle side,
Lb <La,
0.05 ≦ La / Sa,
1.1 ≦ (La / Sa) ÷ (Lb / Sb)
Is set in a range of,
And, in plan view, when the groove wall of the secondary groove is set to 0 degree with respect to the normal of the tread surface of the land portion with respect to the angle Ga1 at the acute angle portion of the tread surface of the land portion with respect to the region on the acute angle side An angle Ga2 formed by a virtual side at the groove bottom of the sub-groove that overlaps a side of the tread surface of the land portion and a side at the groove bottom that is wide-angled from the virtual side by the actual inclination of the groove wall of the sub-groove Is set in the range of 0.1 ≦ Ga2 / Ga1 ≦ 0.4 . 2. The pneumatic tire according to claim 1, wherein the overlapping portion has a bent portion in which a groove bottom of the auxiliary groove is bent in an extending direction of the auxiliary groove. The pneumatic tire according to claim 2 , wherein the bent portion is bent at at least one point. The pneumatic tire according to claim 2 , wherein the bent portion is provided to be curved. A circumferential land portion row that is divided by extending five or more circumferential main grooves along the tire circumferential direction is defined as R1, R2, R3,... Rn from the tire width direction central portion to the tire width direction outer side,
The sub-grooves partitioning each circumferential land portion row R1, R2, R3,... Rn into block shapes are designated as S1, S2, S3,.
The acute angle formed by the inclination of the sub-groove S1 with the tire equator line is D1, the acute angle formed by the inclination of the sub-groove S2 with the tire equator line is D2, and the acute angle formed by the inclination of the sub-groove S3 with the tire equator line is D3. If
55 [degrees] ≦ D1 ≦ 70 [degrees],
65 [degree] ≦ D2 ≦ 80 [degree],
D1 <D2 <D3
The pneumatic tire according to any one of claims 1-4, characterized in that it has a relationship. The circumferential main grooves of the at least one the of claims 1 to 5, characterized in that the inclination angle of each groove wall with respect to the normal line of the tread surface of the tread portion is formed by changing the tire circumferential direction The pneumatic tire according to any one of the above. The rubber thickness T between the reinforcing material in the outermost belt in the tire radial direction arranged in the tread portion and the groove bottom of the circumferential main groove arranged closest to the tire equator line is 3 The pneumatic tire according to any one of claims 1 to 6 , wherein the pneumatic tire is set in a range of 0.0 [mm] ≤ T ≤ 5.5 [mm]. The pneumatic tire according to any one of claims 1 to 7 , wherein tan δ at the time of 100 [° C.] heating of the rubber in the tread portion is set in a range of tan δ ≦ 0.10. The pneumatic tire according to any one of claims 1-8, characterized in that it is applied to heavy-duty pneumatic tire.

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