JP6790841B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire having improved wandering performance while suppressing shoulder drop wear.

For pneumatic tires for heavy loads and light trucks, so-called single radius tires in which the tread contour shape is formed by a single arc having a center on the equatorial plane of the tire have been widely adopted. However, in such a single radius tire, the difference in tire radius between the tire equatorial surface side and the tread end side is large. Therefore, there is a problem that slippage occurs between the tread surface on the tread end side and the road surface, and so-called shoulder drop wear occurs.

Therefore, it has been proposed to form the tread contour shape with an arc portion on the equator side and an arc portion on the shoulder side having a radius of curvature larger than that of the arc portion on the equator side (see Patent Document 1 below). However, in the case of the tire of this proposal, when the tread end comes into contact with the unevenness in the rut when traveling on a road surface having a rut, a large reaction force acts and the vehicle sways, resulting in poor straightness of the rut. Further, when getting out of the rut, the camber thrust required to get over the slope of the rut is small and the reaction force against the slope is large, so that there is a problem that the rut escape performance (rut riding performance) is also poor. As described above, the wandering performance, which is the rut straightness and the rut escape performance, and the shoulder drop wear are in a trade-off relationship.

In Patent Document 2 below, in order to improve wandering performance while suppressing shoulder drop wear, the tread end is formed by a small arc portion (so-called round shoulder) having a small radius of curvature, or the tire circumference is near the tread end. It has been proposed to form a vertical tread that extends continuously in the direction, or to form a sipe that extends in the tire axial direction outside the vertical tread.

However, in view of the recent demand for higher performance tires, it is strongly desired to achieve both shoulder drop wear resistance and wandering performance at a higher level.

Japanese Unexamined Patent Publication No. 2004-203343 JP-A-S63-258203

Therefore, an object of the present invention is to provide a pneumatic tire capable of achieving both shoulder drop wear resistance and wandering performance at a higher level.

According to the present invention, the tread portion is provided with a center main groove that extends continuously in the tire circumferential direction and a pair of shoulder main grooves that continuously extend in the tire circumferential direction on both sides of the center main groove. A pneumatic tire divided into a pair of center land portions between the shoulder main groove and the center main groove and a pair of shoulder land portions between the shoulder main groove and the tread ground contact end.
The shoulder land portion includes a plurality of shoulder slots extending across the tread ground contact end from the inner end portion that is interrupted in the shoulder land portion to the outer end portion that is interrupted in the buttress portion.
The width Wa in the tire circumferential direction of each shoulder slot is 18 to 28% of the tire circumferential pitch Pa of the shoulder slot.
In the tire meridional cross section in the 5% internal pressure state where the rim is assembled to the regular rim and the internal pressure is 5% of the regular internal pressure
The tread contour line on the surface of the tread portion intersects the first arc portion of the radius of curvature R1 having the center of the arc on the equatorial plane of the tire at the intersection Q with the first arc portion, and is 5 to 15% of the radius of curvature R1. It consists of a second arc with a radius of curvature R2.
The tire axial distance LQ from the tire equatorial plane to the intersection Q is 75 to 85% of the ground contact half width Tw, which is the tire axial distance from the tire equatorial plane to the tread ground contact end.
The tire radial distance L2 from the tire equatorial point where the tread contour line and the tire equatorial plane intersect to the intersection Q is 1 to 3% of the ground contact half width Tw.
Moreover, the tire radial distance L1 from the tire equator point to the tread ground contact end is 4 to 6% of the ground contact half width Tw.

In the pneumatic tire of the present invention, the maximum depth of the shoulder slot is preferably 18 to 22% of the groove depth of the shoulder main groove.

In the pneumatic tire of the present invention, the shoulder land portion has two or three shoulders extending across the tread ground contact end between the shoulder slots from the inner end portion interrupted in the shoulder land portion to the outer end portion interrupted in the buttress portion. It is preferable to have a buttress.

The tire shape in the "5% internal pressure state" is usually substantially the same as the tire shape in the vulcanization die. Then, by specifying the shape of the mold surface of the vulcanization mold, the tire shape in the 5% internal pressure state can be controlled. In the present specification, unless otherwise specified, the dimensions and the like of each part of the tire are set to the values specified in the 5% internal pressure state.

Further, the "tread ground contact end" is defined as the position of the outermost end in the tire axial direction of the tread tread that touches the road surface when a regular load is applied to the tire in a state where the rim is assembled to the regular rim and the regular internal pressure is applied. Defined.

The "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, JATTA is a standard rim, TRA is "Design Rim", or ETRTO. If so, it means "Measuring Rim". The "regular internal pressure" is the air pressure defined for each tire by the standard. If it is JATMA, it is the maximum air pressure, if it is TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", ETRTO. If so, it means "INFLATION PRESSURE", but in the case of passenger car tires, it is 180 kPa. The "regular load" is the load defined by the standard for each tire, and is the maximum load capacity for JATMA and the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA. If it is ETRTO, it is "LOAD CAPACITY".

Since the present invention is configured as described above, it is possible to achieve both shoulder drop wear resistance and wandering performance at a higher level, as described in the embodiment for carrying out the invention.

It is sectional drawing which shows one Example of the pneumatic tire of this invention. It is a developed view which shows the surface of the tread part developed in a plane. It is a diagram which shows the tread outline.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, the pneumatic tire 1 of the present embodiment has a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and inside the tread portion 2 and in the radial direction of the carcass 6. It includes a belt layer 7 arranged on the outside. In this example, the case where the pneumatic tire 1 is a tire for a light truck is shown.

The carcass 6 is formed of at least one carcass cord arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator C, and in this example, a total of two carcass plies 6A and 6B arranged inside and outside the radial direction. Will be done. The carcass ply 6A inside has folded portions 6A2 folded around the bead core 5 at both ends of the main body portion 6A1 straddling between the bead cores 5 and 5. Further, the outer carcass ply 6B is terminated so as to overlap the outer surface of the folded portion 6A2 without being folded around the bead core 5.

The belt layers 7 have at least two belt cords arranged at an angle of, for example, 15 to 75 ° with respect to the tire equator C, and in this example, the first to third belt plies 7A to which are arranged in order from the inside in the radial direction. Formed from 7C. In this example, the angle of the belt cord of the first belt ply 7A is, for example, 45 to 75 °, and the angle of the belt cords of the second and third belt plies 7B and 7C is, for example, 10 to 35 ° and the direction of inclination. Are different from each other. As a result, the belt cords intersect each other between the plies, and the belt rigidity is increased.

If necessary, the number of belt plies may be increased or decreased in the belt layer 7, and a band ply in which, for example, a band cord is spirally wound in the tire circumferential direction is provided on the outside of the belt layer 7. You can also do it.

Reference numeral 8 in FIG. 1 is a bead apex rubber for reinforcing the bead, which passes between the main body portion 6A1 and the folded portion 6A2 and extends radially outward from the bead core 5. Reference numeral 9 is a reinforcing cord layer for bead reinforcement, for example, one or more reinforcing cords in which steel reinforcing cords are arranged at an angle of, for example, 30 to 60 ° with respect to the tire circumferential direction, or two reinforcements in this example. Formed from ply.

As shown in FIG. 2, the tread portion 2 includes a center main groove 10 continuously extending in the tire circumferential direction and a pair of shoulder main grooves 11 extending continuously in the tire circumferential direction on both sides of the center main groove 10. To prepare. As a result, the tread portion 2 is divided into a pair of center land portions 12 between the shoulder main groove 11 and the center main groove 10, and a pair of shoulder land portions 13 between the shoulder main groove 11 and the tread ground contact end TE. Tread.

In this example, the case where the center land portion 12 and the shoulder land portion 13 are rib bodies that continuously extend in the tire circumferential direction is shown.

Width _{W 12} of the center land portion 12, 36 to 40% of the range of the ground half width Tw (shown in FIG. 1), the width _{W 13} of the shoulder land portion 13 is preferably 45 to 50% range of the ground half width Tw. Further, the sum (W ₁₂ + W ₁₃ ) of the width W ₁₂ and the width W ₁₃ is preferably in the range of 80 to 85% of the ground contact half width Tw. As a result, the balance between wet performance and steering stability performance on a dry road surface is optimized. When the sum (W ₁₂ + W ₁₃ ) is less than 80% of the ground contact half width Tw, the tread rigidity is reduced and the steering stability performance tends to be insufficient. On the contrary, if it exceeds 85%, the drainage property is reduced and the wet performance tends to be insufficient. Further, when the width W ₁₂ deviates from 36 to 40% of the ground contact half width Tw, and when the width W ₁₃ deviates from 45 to 50% of the ground contact half width Tw, the rigidity balance between the center land portion 12 and the shoulder land portion 13 is poor. As a result, the steering stability performance tends to deteriorate, and center wear and shoulder wear tend to be induced.

The "ground contact half width Tw" is defined by the tire axial distance from the tire equatorial plane Co to the tread ground contact end TE.

As the center main groove 10 and the shoulder main groove 11, a straight groove in which the groove side edges on both sides extend linearly and a zigzag groove in which at least one groove side edge extends in a zigzag shape (including a wavy shape) can be adopted. In the case of a zigzag groove, the width of the groove and the width of each land portion are defined with the center of amplitude at the side edge of the zigzag groove as the side edge of the virtual groove. The groove widths W ₁₀ and W ₁₁ of the center main groove 10 and the shoulder main groove 11 are appropriately set based on the range of the sum (W ₁₂ + W ₁₃ ). Further, the groove depths D ₁₀ and D ₁₁ (shown in FIG. 1) can be variously determined according to the custom. In this example, the groove depth D ₁₀ and the groove depth D ₁₁ are the same and are set in the range of 8 to 15 mm (for example, 10.5 mm).

A horizontal sipe 15 that crosses the center land portion 12 and a vertical sipe 16 that extends continuously in the tire circumferential direction are arranged in the center land portion 12. However, when the sipe 15 and 16 close their openings at the time of touchdown, the center land portion 12 substantially constitutes a rib body. The depth of the sipes 15 and 16 is preferably 40 to 60% of the groove depth D ₁₀ .

Further, the shoulder land portion 13 is provided with a plurality of wide shoulder slots 20 extending across the tread ground contact end TE.

The inner end 20a of the shoulder slot 20 is interrupted in the shoulder land portion 13, and the outer end 20b is interrupted in the buttress portion 21. The width Wa of the shoulder slot 20 in the tire circumferential direction is in the range of 18 to 28% of the tire circumferential pitch Pa of the shoulder slot 20. The shoulder slot 20 of this example extends along the tire axial direction line with a constant width Wa.

As shown in FIG. 1, the shoulder slot 20 has a maximum depth D ₂₀ near the tread ground contact end TE, and the depth gradually decreases from this maximum depth position toward the inner end portion 22a and the outer end portion 22b. .. The maximum depth D ₂₀ is preferably 18 to 22% of the groove depth D ₁₁ of the shoulder main groove 11.

As shown in FIG. 2, in the shoulder land portion 13, two or three (three in this example) shoulder sipes extending in parallel with the shoulder slot 20 across the tread grounding end TE between the shoulder slots 20 and 20. 22 is arranged. The inner end 22a of the shoulder sipe 22 is interrupted in the shoulder land portion 13, and the outer end 22b is interrupted in the buttress portion 21. The depth of the shoulder sipe 22 is also the same as that of the shoulder slot 20, and the maximum depth D ₂₂ (not shown) is preferably 18 to 22% of the groove depth D ₁₁ of the shoulder main groove 11.

Further, as shown in FIG. 3, in the tire meridional cross section under the 5% internal pressure state, the tread contour line on the surface of the tread portion 2 is the first arc portion J1 having a radius of curvature R1 having an arc center on the tire equatorial plane Co and the arc portion J1. It intersects the first arc portion at an intersection Q and is composed of a second arc portion J2 having a radius of curvature R2 of 5 to 15% of the radius of curvature R1.

The tire axial distance LQ from the tire equatorial plane Co to the intersection Q is 75 to 85% of the ground contact half width Tw. Further, the tire radial distance L2 (sometimes referred to as “camber amount L2”) from the tire equatorial point Cp where the tread contour line and the tire equatorial surface Co intersect to the intersection Q is 1 to 3% of the ground contact half width Tw. Moreover, the tire radial distance L1 (sometimes referred to as “camber amount L1”) from the tire equatorial point Cp to the tread ground contact end TE is 4 to 6% of the ground contact half width Tw.

Such a pneumatic tire 1 is
(A) The shoulder land portion 13 is provided with a shoulder slot 20 having a width Wa of 18 to 28% of the circumferential pitch Pa;
(B) The tread contour line includes a second arc portion J2 at which the first arc portion J1 intersects the first arc portion J1 at the intersection Q, and the second arc portion J2 has a radius of curvature R2 of 5 to 15% of the radius of curvature R1. Formed by an arc;
(C) The tire axial distance LQ of the intersection Q is 75 to 85% of the ground contact half width Tw;
(D) The camber amount L2 at the intersection Q is 1 to 3% of the ground contact half width Tw;
(E) The camber amount L1 of the tread grounding end TE is 4 to 6% of the grounding half width Tw:
By cooperating with each other, it becomes possible to achieve both shoulder drop wear resistance and wandering performance at a high level.

Specifically, it is a premise that a large camber thrust is generated by making the second arc portion J2 a small arc. At this time, if the radius of curvature R2 of the second arc portion J2 is too small, the camber amount L1 of the tread ground contact end TE becomes large, which causes a tendency for shoulder drop wear to occur.

Therefore, while restricting the radius of curvature R2 to a range of 5 to 15% of the radius of curvature R1, the camber amount L1 is set to 4 to 6% of the ground contact half width Tw, which is lower than the conventional one. As a result, the ground contact length on the shoulder side is increased to reduce the amount of slippage, and the shoulder drop wear resistance is improved, while the camber thrust is increased by the second arc portion J2 of the small arc to improve the wandering performance. Becomes possible. When the radius of curvature R2 is out of the range of 5 to 15% of the radius of curvature R1, the effect of increasing the camber thrust is small, and it becomes difficult to sufficiently improve the wandering performance. From this point of view, the lower limit of the radius of curvature R2 is preferably 7% or more of the radius of curvature R1, and the upper limit is preferably 12% or less. Further, when the camber amount L1 exceeds 6% of the ground contact half width Tw, the shoulder drop wear resistance tends to decrease, and when it is less than 4%, the wandering performance is adversely affected.

Further, the tire axial distance LQ of the intersection Q is set to 75 to 85% of the ground contact half width Tw, and the second arc portion J2 of the small arc is provided only in the vicinity of the ground contact end. As a result, the influence of the second arc portion J2 on the ground contact length on the shoulder side, that is, the influence on the shoulder drop wear resistance can be suppressed. When the tire axial distance LQ is less than 75% of the contact half width Tw, the second arc portion J2 tends to worsen shoulder drop wear. On the contrary, if it exceeds 85%, the second arc portion J2 becomes local, so that the effect of improving the wandering performance is reduced. From such a viewpoint, the lower limit of the tire axial distance LQ is preferably 78% or more of the ground contact half width Tw, and the upper limit is preferably 82% or less.

Further, if the camber amount L2 itself at the intersection Q is large, the ground contact length on the shoulder side is reduced. Therefore, it is necessary to regulate this camber amount L2 to a range of 1 to 3% of the ground contact half width Tw.

On the other hand, since there are restrictions on shoulder drop wear resistance, there is a limit to improving wandering performance only with the second arc portion J2. Therefore, the shoulder slot 20 is provided in the shoulder land portion 13, and the width Wa thereof is set as wide as 18 to 28% of the circumferential pitch Pa.

As a result, the rigidity of the peripheral portion of the ground contact end including the tread ground contact end TE can be reduced. As a result, the reaction force when the vehicle comes into contact with the slope or unevenness in the rut during rut running can be reduced, and the rut straightness can be improved. In addition, the camber thrust is increased, and the rut escape performance can be improved in combination with the decrease in the reaction force. The shoulder sipe 22 also functions in the same manner as the shoulder slot 20, and can further improve the wandering performance.

If the width Wa of the shoulder slot 20 is less than 18% of the circumferential pitch Pa, the rigidity of the peripheral portion of the ground contact end is not sufficiently lowered, which causes a tendency of insufficient wandering performance. On the contrary, if it exceeds 28%, the steering stability tends to decrease. Similarly, when the maximum depth D ₂₀ of the shoulder slot 20 is less than 18% of the groove depth D ₁₁ , the rigidity of the peripheral portion of the ground contact end is not sufficiently lowered, which causes a tendency of insufficient wandering performance. On the contrary, if it exceeds 22%, the steering stability tends to decrease.

By cooperating with each other in this way (A) to (E), it becomes possible to achieve both shoulder drop wear resistance and wandering performance at a high level.

The tire axial distance Lb (shown in FIG. 2) from the tread ground contact end TE of the inner end portion 20a of the shoulder slot 20 is preferably in the range of 4 to 7 of the ground contact half width Tw. If it exceeds 7%, the steering stability tends to decrease, and if it exceeds 4%, the wandering performance tends to be insufficient.

Although the particularly preferable embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be modified into various embodiments.

The light truck tires (205 / 85R16) shown in FIGS. 1 to 3 were prototyped with the specifications shown in Tables 1 to 3. Then, the wandering performance, steering stability, and shoulder drop wear resistance of each prototype tire were tested. Except for Table 1, the specifications are substantially the same.

(1) Wandering performance:
The prototype tires are mounted on all wheels of a light truck (loading capacity 3 tons) with a rim (16 x 5.5J) and internal pressure (600kPa), and run on a road surface with ruts to improve rut straightness and rut escape. It was displayed by the 10-point method by the sensory evaluation of the driver. The result is better as the numerical value is larger than 6 points.

(2) Steering stability:
Using the above vehicle, the test course on a dry asphalt road surface was run, and the steering stability was displayed by the 10-point method by the sensory evaluation of the driver. The result is better as the numerical value is larger than 6 points.

(3) Shoulder drop wear resistance:
Using the above vehicle, travel 15,000 km on a general road (100% of the general road) in the area west of Kanto, and for the tire mounted on the front, the amount of wear δc in the center main groove and the outer wall surface of the shoulder main groove in the tire axial direction. The amount of wear δs was measured. Then, it was evaluated by the value of the ratio δc / δs of the amount of wear. As a result, the closer the value is to 1.0, the more uniform the wear is, and the lower the value is, the worse the shoulder drop wear resistance is.

As shown in the table, it can be confirmed that the example product can achieve both shoulder drop wear resistance and wandering performance at a high level.

1 Pneumatic tire 2 Tread part 10 Center main groove 11 Shoulder main groove 12 Center land part 13 Shoulder land part 21 Buttless part 20 Shoulder slot 20a Inner end 20b Outer end 22 Shoulder sipe 22a Inner end 22b Outer end Co tire Equatorial surface Cp Tire equatorial point J1 1st arc part J2 2nd arc part TE tread ground contact end

Claims (3)

By providing the tread portion with a center main groove that extends continuously in the tire circumferential direction and a pair of shoulder main grooves that extend continuously in the tire circumferential direction on both sides of the center main groove, the tread portion becomes the shoulder main groove. A pneumatic tire divided into a pair of center land portions between the groove and the center main groove and a pair of shoulder land portions between the shoulder main groove and the tread ground contact end.
The shoulder land portion includes a plurality of shoulder slots extending across the tread ground contact end from the inner end portion that is interrupted in the shoulder land portion to the outer end portion that is interrupted in the buttress portion.
The width Wa in the tire circumferential direction of each shoulder slot is 18 to 28% of the tire circumferential pitch Pa of the shoulder slot.
In the tire meridional cross section in the 5% internal pressure state where the rim is assembled to the regular rim and the internal pressure is 5% of the regular internal pressure.
The tread contour line on the surface of the tread portion intersects the first arc portion of the radius of curvature R1 having the center of the arc on the equatorial plane of the tire at the intersection Q with the first arc portion, and is 5 to 15% of the radius of curvature R1. It consists of a second arc with a radius of curvature R2.
The tire axial distance LQ from the tire equatorial plane to the intersection Q is 75 to 85% of the ground contact half width Tw, which is the tire axial distance from the tire equatorial plane to the tread ground contact end.
The tire radial distance L2 from the tire equatorial point where the tread contour line and the tire equatorial plane intersect to the intersection Q is 1 to 3% of the ground contact half width Tw.
A pneumatic tire characterized in that the tire radial distance L1 from the tire equatorial point to the tread ground contact end is 4 to 6% of the ground contact half width Tw. The pneumatic tire according to claim 1, wherein the maximum depth of the shoulder slot is 18 to 22% of the groove depth of the shoulder main groove. The shoulder land portion is characterized by having two or three shoulder sipes extending across the tread ground contact end between the shoulder slots from the inner end portion that is interrupted in the shoulder land portion to the outer end portion that is interrupted in the buttress portion. The pneumatic tire according to claim 1 or 2.

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