JP4707861B2 - Heavy duty tire - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a heavy load tire having a stepped land portion provided at a groove bottom of a circumferential groove for suppressing uneven wear.
[0002]
[Prior art]
Tires used in heavy-duty vehicles such as trucks and buses that run at high speeds usually have a tread pattern with a plurality of grooves in the circumferential direction, but these tires have a bias around the ribs before reaching their wear life. There is a problem that the tire life is reduced due to wear, and in response to this, a step land portion is provided at the bottom of the circumferential groove, and a load in the sliding direction is loaded on this, thereby promoting the accelerated progress of uneven wear. It is known that it can be effectively suppressed. FIG. 4A is a plan view of a stepped land portion in this prior art, and FIG. 4B is a cross-sectional view along the line BB. The circumferential groove 91 defines a land portion 92 and has a step land portion 93 that protrudes from the groove bottom. The top surface 95 of the step land portion is located slightly inward in the tire radial direction from the land portion 92. When the tire rolls, the top surface 95 is dragged by the road surface and shear force in the braking direction is concentrated here. In addition, the shearing force on the surrounding land is reduced and uneven wear is suppressed.
[0003]
[Problems to be solved by the invention]
The step land portion 93 divides the original circumferential groove 91 into side grooves 94R and 94L and reduces the groove volume, resulting in a decrease in wet performance. In order to suppress the volume drop due to the step land portion 93, a circumferential groove 91 with a side groove wall is usually used. However, when the groove wall stands and the groove wall angle becomes small, a so-called stone biting phenomenon that stones cannot be caught in the side grooves easily occurs. If stone biting occurs, there will be a problem of cracks in the tire and tire destruction. In order to prevent this, if an attempt is made to widen the groove width, the land area is reduced and the wear resistance of the tire is reduced.
[0004]
The above will be described in detail with reference to FIG. 3 showing the relationship between the groove shape and the stone bite. In FIG. 3, the vertical axis indicates the ratio of the groove width to the groove depth, and the horizontal axis indicates the groove wall angle. The groove wall angle is smaller on the left side of the horizontal axis, and the groove wall stands. Moreover, the groove | channel represented by the point on the straight line L means that it becomes a triangular shape without a groove bottom, The area | region where a groove | channel becomes reverse trapezoid shape above this line, and the groove | channel below this line is a groove | channel. This is a non-existent area. The area above the straight line L further includes a safe area A where little stone biting occurs, a rough road danger area B where stone biting may occur when traveling on rough roads, and the risk of stone biting even during normal driving. Divided into a risk zone C. If the groove width is reduced with the same groove wall angle and the same groove depth, stone biting will not occur at the first point X, but it will be in the safe area A, but it will pass the rough road dangerous area and be in the dangerous area C. At point Y, stone biting is likely to occur. As the groove wall angle is smaller and the groove width is narrower, the frequency of stone biting is more likely to occur. Therefore, the boundary lines of the respective regions in FIG.
[0005]
In FIG. 3, in the circumferential groove having the conventional stepped land portion, as described above, the groove wall has to be set at a steep angle to secure the groove volume, and the groove width has not been increased. It was difficult to get out of danger zone C.
[0006]
The present invention has been made in view of such problems, and without impairing the uneven wear resistance effect of the stepped land portion provided in the groove, and by reducing the land area, the wear resistance is improved. An object of the present invention is to provide a heavy-duty tire in which occurrence of stone biting in the side grooves on both sides thereof is suppressed without sacrificing.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has been made, and the gist configuration and operation thereof will be described below.
The heavy-duty tire according to claim 1 has, on the surface of the tread portion of the tire, a groove portion including a circumferential groove extending in the circumferential direction with a constant width, and a land portion partitioned by these groove portions, A step extending in the circumferential direction, having a top surface that has a height that touches the surface at the time of rolling, inwardly in the tire radial direction from the contour line of the tread portion, in one circumferential groove provided with a land portion, of the top surface, at least one of the edges extending in the circumferential direction, by meandering along the circumferential direction to form a boundary between the circumferential groove and the land portion land The interval between the edge and the edge of the top surface is changed in the circumferential direction, and narrow portions having a narrow interval and wide portions having a wide interval are alternately formed in the circumferential direction .
[0008]
According to this tire, the edge of the step land portion meanders, and the side groove on both sides formed by providing the step land portion in the original circumferential groove alternately has a narrow portion and a wide portion. become. Although the stone biting occurs more frequently in the narrow part, the narrow part is limited to a short range in the circumferential direction. The tire can be discharged from the side groove immediately without causing damage to the tire. Further, since the wide portion is originally a safe area against stone chewing, stone chewing does not occur.
[0009]
The tire according to claim 2 is the tire according to claim 1, wherein the width of the top surface of the step land portion is constant.
[0010]
According to this, since the top surface is provided with a constant width, the step land portion functions uniformly in the circumferential direction, and uneven wear can be effectively suppressed.
[0011]
A tire according to a third aspect is the tire according to any one of the first and second aspects, wherein the edge of the top surface of the step land portion meanders at a constant period.
[0012]
According to this, since the edge of the top surface of the step land portion meanders at a constant cycle, the uneven wear suppression effect due to the provision of the step land portion can be exhibited uniformly over the entire circumference, and the side The discharging effect of the stones biting into the narrow part of the groove can be obtained over the entire circumference.
[0013]
A tire according to a fourth aspect is the tire according to any one of the first to third aspects, wherein the circumferential groove includes a boundary line between the circumferential groove and the land portion in a cross section including the axis of the tire. The ratio between the maximum value and the minimum value of the distance along the tire axial direction between one land edge and the step land top surface edge on the side close to the land edge is 1.2 or more.
[0014]
According to this, the ratio of the maximum value and the minimum value of the distance along the tire axial direction between the land edge and the step land top surface edge on the side close to the land edge is set to 1.2 or more. It is possible to effectively discharge the stones biting into the narrow part of the.
[0015]
A tire according to a fifth aspect is the tire according to any one of the first to fourth aspects, wherein the land edge is aligned with a tire axial direction between a land edge and a step land top edge near the land edge. The ratio between the maximum value and the minimum value of the interval is 15.0 or less.
[0016]
If the ratio between the maximum value and the minimum value of the distance along the tire axial direction between the land edge and the step land top surface edge on the side close to this land edge exceeds 15.0, it is due to the provision of the step land This tire having a ratio of 15.0 or less is suitable because the effect of suppressing uneven wear cannot be sufficiently exerted, but rather, the occurrence of new uneven wear due to a large meandering amplitude.
[0017]
A tire according to a sixth aspect is the tire according to any one of the first to fifth aspects, wherein the circumferential meander cycle of the edge of the top surface of the step land portion is set to 1/30 to 1/1 of the tire circumferential length. It will be 100.
[0018]
If the circumferential meandering cycle at the edge of the top surface of the stepped land exceeds 1/30 of the tire circumferential length, the change in the circumferential direction of the side groove width will be gradual. If the meander cycle is less than 1/100 of the tire circumference, the uneven wear suppression effect due to the provision of the stepped land portion cannot be fully exerted, but rather the meander cycle is short. Since this will cause new uneven wear, this tire having a meandering period of 1/30 to 1/100 of the tire circumference is suitable.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a heavy duty tire according to the present invention will be described with reference to FIGS. FIG. 1 is a plan view of a step land portion when a tread portion of a tire according to the present invention is viewed from the outside in the radial direction. 2A is a cross-sectional view taken along the line aa ′ in FIG. 1, and FIG. 2B is a cross-sectional view taken along the line bb ′ in FIG.
[0020]
As shown in FIG. 1, this tire has a stepped land portion that extends in the circumferential direction and extends in the circumferential direction by meandering in a wavy shape at a meandering pitch P in a circumferential groove 11 that partitions the land portion 12. 13 is provided. The step land portion 13 divides the circumferential groove into a right side groove 14R and a left side groove 14L.
[0021]
And as shown to FIG. 2 (a), FIG.2 (b), the level | step difference land part 13 has the top surface 15 provided in the radial direction low by D from the land part, The slip component is borne, and the function of suppressing the progression of uneven wear of the land portion 12 is brought about.
[0022]
In FIG. 1, the step land portion 13 meanders so that a land edge 21 that forms a boundary between the land portion 12 and the circumferential groove 11 and a top surface edge 22 of the top surface 15 of the step land portion 13. The interval along the tire axial direction changes periodically, and narrow portions Rn and wide portions Rw are alternately arranged in the side grooves 14R and 14L, respectively. The narrow width portion Rn of the side groove has a cross-sectional shape represented by a point belonging to the danger zone C shown in FIG. 3, so that it is easy to bite the stone, but the narrow width portion Rn is short in the circumferential direction. Since it is limited to the range, the stones bitten by the deformation of the step land portion 13 during rolling can be easily discharged. Further, since the wide portion Rw of the side groove has a cross-sectional shape represented by a point belonging to the safety zone A shown in FIG. 3, the probability of biting a stone even when traveling on a rough road is extremely low.
[0023]
In FIG. 1, examples of specific dimensions are as follows. The tire size is 295 / 75R225, the groove width W of the circumferential groove 11 is 30 mm, the groove depth H is 15.5 mm, the groove angle α is 2.5 degrees, the step D of the step land portion 13 with the land portion 12 is 2.5 mm, and The width T of the top surface 15 is 8 mm. Further, the step land portion 13 meanders in a sine wave shape, and its period P is 70 mm, and the interval between the land portion edge 21 and the top surface edge 22 of the top surface 15 of the step land portion 13 is along the tire axial direction. The maximum value Zmax is 18 mm and the minimum value Zmin is 4 mm. Therefore, the ratio of the maximum value to this minimum value is 4.5.
[0024]
【Example】
The tire of the example of FIG. 1 was compared with the tire of the conventional example shown in FIG. The dimension specifications of the tires of the examples are as described above, and the tires of the conventional examples are obtained by extending the step land portions of the tires of the examples straight in the circumferential direction and extending in the center of the circumferential grooves, Accordingly, other dimensions such as the groove width and groove depth of the circumferential groove, the width of the top surface of the step land portion, the step height of the top surface, and the like are the same as those of the embodiment.
[0025]
The method of stone biting evaluation is as follows. In other words, in the United States, a highway including both an interstate and a local road was actually run, and the number of stone bites after running for 5000 miles was counted and evaluated. As a result, assuming that the number of stone bites of the conventional tire was 100, the number of stone bites of the tire of the example was 20, and the stone biting performance could be greatly improved.
[0026]
【The invention's effect】
As is clear from the above description, according to the present invention, the step land portion is provided meandering in the circumferential groove, so that the stone bite is not impaired without impairing the wear resistance performance or the uneven wear resistance performance. It is possible to provide a tire that does not easily occur.
[Brief description of the drawings]
FIG. 1 is a plan view of a circumferential groove of a tire according to the present invention.
FIG. 2 is an arrow view showing the aa ′ arrow view and the bb ′ arrow view of FIG. 1;
FIG. 3 is a relationship diagram schematically showing a relationship between a groove shape and a stone bite.
FIG. 4 is a plan view of a circumferential groove of a conventional tire.
[Explanation of symbols]
11 circumferential groove 12 land part 13 step land part 14L, 14R side groove part 15 top surface 21 of step land part land edge 22 step land part top surface edge Rn narrow part Rw of side groove wide part of side groove

Claims (6)

On the surface of the tread portion of the tire, it has a groove portion including a circumferential groove extending in the circumferential direction with a constant width, and a land portion partitioned by these groove portions,
At least one circumferential groove, which protrudes from the groove bottom , has a top surface having a height to contact with the ground when rolling , extending in the tire radial direction from the outline of the tread portion, and extends in the circumferential direction. While providing a stepped land,
The top surface, at least one of the edges extending in the circumferential direction, by meandering along the circumferential direction, and land edges forming the boundary between the circumferential groove and the land portion, said top A heavy-duty tire in which a gap between a surface edge is changed in a circumferential direction, and a narrow part with a narrow gap and a wide part with a wide gap are alternately formed in a circumferential direction . The heavy duty tire according to claim 1, wherein the width of the top surface of the step land portion is constant. The heavy-duty tire according to any one of claims 1 to 2, wherein an edge of a top surface of the step land portion meanders at a constant cycle. In the cross section including the axis of the tire, one land portion edge of the circumferential groove, which forms the boundary line between the circumferential groove and the land portion, and the step land portion top surface edge on the side close to the land portion edge The heavy-duty tire according to any one of claims 1 to 3, wherein a ratio between a maximum value and a minimum value of the interval along the tire axial direction is 1.2 or more. The ratio between the maximum value and the minimum value of the distance along the tire axial direction between the land edge and the step land top surface edge on the side close to the land edge is 15.0 or less. Heavy duty tires as described in 1. The heavy-duty tire according to any one of claims 1 to 5, wherein a meandering cycle in the circumferential direction of the edge portion of the top surface of the stepped land portion is 1/30 to 1/100 of the tire circumferential length.

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