JP7024360B2 - Heavy-duty tires and methods for manufacturing heavy-duty tires - Google Patents

Description

The present invention relates to a heavy-duty tire having improved center wear resistance and a method for manufacturing a heavy-duty tire.

Life is one of the most important performances of heavy-duty tires because they are used for commercial vehicles.

Since the tire mounted on the drive shaft travels only in the straight direction, a high contact pressure continues to be applied to the center region. Therefore, center wear is likely to occur, and tires are often replaced due to this center wear. Therefore, improving the center wear resistance performance leads to an improvement in the life of heavy-duty tires.

The following have been proposed as general means for improving center wear resistance. For example, the contour line on the circumferential direction of the ground contact shape (footprint shape) under a normal load is flattened (flattened). As a result, the ground contact shape is made closer to a rectangular shape, and the ground contact pressure in the center region is lowered.

However, depending on the destination (for example, North America region, etc.), the heavy load tire mounted on the drive shaft may be used under light load usage conditions due to load regulation or the like. Specifically, in North America and the like, tires mounted on drive shafts are subject to light load usage conditions of 60% or less of the road index. In such a case, when the ground is touched, the grounding area on the shoulder side is reduced and the grounding shape is not flat. Therefore, there is a problem that the center wear becomes large as compared with the usage condition of a heavy load close to the load index.

As related prior art documents, for example, the following Patent Documents 1 and 2 are known.

Japanese Unexamined Patent Publication No. 08-002210 Japanese Unexamined Patent Publication No. 2007-331439

An object of the present invention is to provide a heavy load tire capable of satisfactorily exhibiting center wear resistance even under a light load, and a method for manufacturing the heavy load tire.

The first invention of the present application is from a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and three or four belt plies arranged outside the carcass in the tire radial direction and inside the tread portion. Including the belt layer
In addition, the tread portion has a center land portion most arranged on the equator side of the tire, a shoulder land portion arranged on the most tread end side, and the center land portion and the shoulder land arranged by a plurality of main grooves extending in the tire circumferential direction. It is a heavy load tire divided into the middle land area between the parts.
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 of 5% of the regular internal pressure is filled.
The contour line on the surface of the tread portion intersects the arc portion in the radius of curvature R1 having the center of the arc on the equator of the tire at the turning point P and the radius of curvature R2 smaller than the radius of curvature R1. It consists of an arc outside the
The inflection point P is located on the middle land portion and is located on the middle land portion.
The distance Lp in the tire axial direction from the tire equatorial line to the inflection point P is characterized by being 0.35 to 0.50 times the tread half width Wt, which is the tire axial distance from the tire equatorial line to the tread end. ..

In the heavy load tire according to the present invention, the ratio R2 / R1 of the radius of curvature R1 and the radius of curvature R2 is preferably 0.14 to 0.20.

In the heavy load tire according to the present invention, the belt ply includes the first to third belt plies arranged in order from the inner side in the radial direction of the tire, and the second belt ply has the widest width.
The ply half width of the second belt ply from the tire equator is preferably 0.8 to 0.95 times the tread half width.

In the heavy load tire according to the present invention, the flatness of the tire is preferably 80% or less.

In the heavy load tire according to the present invention, it is preferable that the shoulder land portion includes a plurality of shoulder lateral grooves that cross the shoulder land portion, and the groove depth of the shoulder lateral grooves is 3.0 mm or less.

The second invention of the present application is from a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and three or four belt plies arranged outside the tire radial direction of the carcass and inside the tread portion. Including the belt layer
In addition, the tread portion has a center land portion most arranged on the equator side of the tire, a shoulder land portion arranged on the most tread end side, and the center land portion and the shoulder land arranged by a plurality of main grooves extending in the tire circumferential direction. It is a method of manufacturing heavy-duty tires divided into middle land areas between the parts.
Includes a vulcanization process that vulcanizes raw tires with a mold
In addition, in the mold, the contour line of the tread forming surface for forming the tread portion is transformed into a mold arc portion within a radius of curvature R1 _K having an arc center on the tire equatorial line and a mold arc portion within the arc center. It _{consists of an arc portion of a mold outside the radius of curvature R2 K ,} which intersects at the point PK and is smaller than the radius of curvature R1 _K.
The inflection point _PK is located on the middle land portion forming surface portion for molding the middle land portion.
The distance Lp _K in the tire axial direction from the tire equatorial line to the turning point _{PK is 0.35 to 0.50 times the mold tread half width Wt K ,} which is the tire axial distance from the tire equatorial line to the tread end forming position. It is characterized by being.

In the method for manufacturing a heavy-duty tire according to the present invention, the ratio R2 _K / R1 _K of the radius of curvature R1 _K and the radius of curvature R2 _K is preferably 0.14 to 0.20.

In the method for manufacturing a heavy-duty tire according to the present invention, the mold has a ratio WE / WF of the mold clip width WF and the width WE between the maximum width positions of the sidewall forming surface for forming the sidewall portion. It is preferably 1.27 to 1.37.

In the method for manufacturing a heavy-duty tire according to the present invention, the mold has a radial distance HB from the maximum width position of the sidewall molding surface for molding the sidewall portion to the bead baseline, and a mold clip. The ratio HB / WF to the width WF is preferably 0.45 to 0.5.

In the method for manufacturing a heavy load tire according to the present invention, the radial distance HB from the maximum width position of the sidewall forming surface for forming the sidewall portion to the bead baseline by the mold, and the heavy load tire. In the vulcanized state in the mold, the ratio HB / HA to the radial distance HA from the inner surface of the carcass on the tire equatorial line to the bead baseline is preferably in the range of 0.4 to 0.6. ..

A "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 there is, it means "Measuring Rim". "Regular internal pressure" is the air pressure specified for each tire by the above standard. If it is JATTA, 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".

In the present invention, the contour shape of the tire in the 5% internal pressure state is close to the profile of the molded surface of the vulcanization die, and can be regarded as the tire shape intended in the tire design. In the present invention, in the tire meridional cross section under the 5% internal pressure state, the contour line of the surface of the tread portion includes an arc portion inside the radius of curvature R1 and an arc portion outside the radius of curvature R2 smaller than the radius of curvature R1. It is formed of a so-called double radius consisting of. By setting R1> R2, a tread profile with a flat tire equatorial side can be obtained.

The inflection point P at which the inner arc portion and the outer arc portion intersect is located on the middle land portion, not at the position of the main groove. Therefore, even after inflating, the connection between the inner and outer arc portions is maintained smoothly, and the above-mentioned change in the tread profile is suppressed. As a result, even when the load fluctuates, the flatness of the circumferential contour line of the ground contact shape is maintained from the center land portion to the middle land portion.

Moreover, the distance Lp in the tire axial direction from the tire equator to the inflection point P is 0.35 to 0.50 times the tread half width Wt. That is, the position of the inflection point P is closer to the equator of the tire as compared with the conventional double radius tire. As a result, even when the load fluctuates, the contour line on the circumferential side of the ground contact shape is maintained flat from the center land portion to the middle land portion. As a result, it is possible to improve the center wear resistance performance while suppressing shoulder drop wear (shoulder wear) even under a light load.

It is sectional drawing which shows one Example of the heavy load tire of this invention. It is a development view of a tread pattern. It is a diagram which shows the outline of the tread surface. It is sectional drawing which shows the mold. It is a conceptual diagram of the profile of the carcass ply explaining the effect by a ratio WE / WF. It is sectional drawing of the tire for heavy load in the vulcanized state in a die.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, the heavy-duty 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 the carcass 6 outside the carcass 6 in the radial direction and the tread portion 2. It is provided with a belt layer 7 arranged inside the carcass. In this example, the heavy load tire 1 is formed as a flat tire having a flatness ratio of 80% or less.

The carcass 6 is formed of, for example, one or more carcass cords made of steel arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction, in this example, one carcass ply 6A. The carcass ply 6A is provided with folded portions 6b that are folded back from the inside to the outside in the tire axial direction around the bead core 5 at both ends of the main body portion 6a straddling between the bead cores 5 and 5.

The belt layer 7 is formed of three or four belt plies including the first, second, and third belt plies 7A, 7B, and 7C arranged in order from the carcass 6 side toward the outer side in the radial direction. In this example, the case where the fourth belt ply 7D is arranged on the outer side in the radial direction of the third belt ply 7C is shown.

The angle α1 (not shown) of the belt cord of the first belt ply 7A with respect to the tire circumferential direction is, for example, 45 to 75 °. The angle α2 (not shown) of the belt cords of the second to fourth belt plies 7B to 7D with respect to the tire circumferential direction is, for example, 10 to 35 °. The inclination directions of the belt cords of the second belt ply 7B and the third belt ply 7C are different from each other. As a result, the belt cords intersect each other between the belt plies 7B and 7C, and the belt rigidity is increased. In particular, in order to make the ground pressure uniform, it is preferable to limit the angle α2 to 16 degrees or less (for example, 15 degrees), further increase the binding force by the belt layer 7, and suppress the dimensional change of the tread portion.

Of the belt plies, the second belt ply 7B is the widest. The ply half width Wb from the tire equator C of the second belt ply 7B is preferably in the range of 0.8 to 0.95 times the tread half width Wt which is the distance in the tire axial direction from the tire equator C to the tread end Te.

Reference numeral 8 in FIG. 1 is a bead apex rubber for reinforcing the bead, which passes between the main body portion 6a and the folded-back portion 6b of the carcass 6 and extends radially outward from the bead core 5. Reference numeral 9 is a reinforcing cord layer for reinforcing the bead, 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 one reinforcement in this example. Formed from plies.

As shown in FIG. 2, the tread portion 2 includes a plurality of main grooves 10 that continuously extend in the tire circumferential direction. As a result, the tread portion 2 is located between the center land portion 11c located closest to the tire equator C side, the shoulder land portion 11s arranged closest to the tread end Te side, and the center land portion 11c and the shoulder land portion 11s. It is divided into the middle land area of 11m. In this example, the case where the center land portion 11c is one and is arranged on the tire equator C is shown. However, there are two center land portions 11c, which may be arranged on both sides of the tire equator C.

In this example, the case where the main groove 10 is a zigzag groove (including a wavy groove) is shown, but it may be a straight groove extending linearly. The groove width and groove depth of the main groove 10 can be variously determined according to the custom. In this example, the case where the groove depth D1 (shown in FIG. 1) of the main groove 10 is 25 mm is shown.

The center land portion 11c is divided into a plurality of center blocks Bc by a lateral groove 12c that crosses the center land portion 11c. Similarly, the middle land portion 11m is divided into a plurality of middle blocks Bm by a lateral groove 12m that crosses the middle land portion 11m. Further, the shoulder land portion 11s is divided into a plurality of shoulder blocks Bs by a lateral groove 12s that crosses the shoulder land portion 11s. In this example, the groove depths D2 (shown in FIG. 1) of the lateral grooves 12c and 12 m are 0.6 to 1.0 times (20.5 mm in this example) the groove depth D1 of the main groove 10, respectively. Deep enough. On the other hand, the groove depth D3 (shown in FIG. 1) of the lateral groove 12s is 3.0 mm or less. As a result, the shoulder land portion 11s has increased rigidity and wear resistance.

FIG. 3 shows a tire meridional cross section under 5% internal pressure. As shown in FIG. 3, in the 5% internal pressure state, the contour line of the surface of the tread portion 2 changes to the arc portion J1 in the radius of curvature R1 having the arc center on the tire equatorial line C and the arc portion J1 in this. It is composed of an arc portion J2 outside the radius of curvature R2 that intersects at the curved point P.

The radius of curvature R2 is smaller than the radius of curvature R1, and the ratio R2 / R1 is preferably in the range of 0.14 to 0.20. This provides a tread profile with a flat tire equatorial side.

The inflection point P is located on the middle land portion 11 m. The distance Lp of the inflection point P from the tire equator C in the tire axial direction is in the range of 0.35 to 0.50 times the tread half width Wt.

In the heavy load tire 1 of the present invention, the inflection point P is not located at the position of the main groove 10, but is located on the middle land portion 11 m. Therefore, even after inflating, the connection between the inner and outer arc portions J1 and J2 is maintained smoothly, and the above-mentioned change in the tread profile is suppressed. As a result, even when the load fluctuates, the flatness of the circumferential contour line of the ground contact shape is maintained from the center land portion 11c to the middle land portion 11m.

Further, the distance Lp of the inflection point P is 0.35 to 0.50 times the tread half width Wt, and the position of the inflection point P is closer to the tire equatorial line C as compared with the conventional double radius tire. As a result, even when the load fluctuates, the flatness of the circumferential contour line of the ground contact shape is maintained from the center land portion 11c to the middle land portion 11m. As a result, even under a light load, the ground contact pressure can be made uniform, and the center wear resistance performance can be improved while suppressing shoulder drop wear (shoulder wear).

When the distance Lp is smaller than 0.35 times the tread half width Wt, the region range of the arc portion J1 inside becomes narrow. Therefore, in the load fluctuation, the ground contact pressure from the center land portion 11c to the middle land portion 11m becomes non-uniform, and the effect of suppressing the center wear is not sufficiently exhibited. On the contrary, when the distance Lp exceeds 0.50 times the tread half width Wt, the ground contact length of the shoulder land portion 11s becomes relatively short with respect to the ground contact length of the middle land portion 11m. Therefore, under a light load, shoulder drop wear tends to occur. From such a viewpoint, the lower limit of the distance Lp is preferably 0.375 times or more of the tread half width Wt, and the upper limit is preferably 0.475 times or less.

As described above, the ratio R2 / R1 of the radii of curvature of the inner and outer arc portions J1 and J2 is in the range of 0.14 to 0.20. Therefore, in the center land portion 11c, the contour line on the circumferential direction of the ground contact shape becomes flat, and the ground contact pressure can be suppressed low. When the ratio R2 / R1 is smaller than 0.14, the ground contact length of the shoulder land portion 11s becomes relatively short with respect to the ground contact length of the middle land portion 11m, and shoulder drop wear tends to occur under a light load. .. On the contrary, when it is larger than 0.20, the ground contact length of the shoulder land portion 11s becomes relatively longer than the ground contact length of the middle land portion 11m, and the ground contact pressure of the shoulder land portion 11s becomes high. By that amount, the ground pressure of the middle land portion 11 m becomes low. As a result, the ground contact pressure from the center land portion 11c to the middle land portion 11m becomes non-uniform, and center wear is likely to occur under a light load. From this point of view, the lower limit of the ratio R2 / R1 is preferably 0.16 or more, and the upper limit is preferably 0.18 or less.

Further, in the heavy load tire 1, as described above, the ply half width Wb of the second belt ply 7B is 0.8 to 0.95 times the tread half width Wt. When the ply half-width Wb is less than 0.8 times the tread half-width Wt, the binding force of the belt layer 7 on the shoulder land portion 11s side becomes small, and after inflating, the contact pressure of the shoulder land portion 11s becomes high. By that amount, the ground pressure of the middle land portion 11 m becomes low. As a result, the ground contact pressure from the center land portion 11c to the middle land portion 11m becomes non-uniform, and center wear is likely to occur under a light load. If the ply half-width Wb exceeds 0.95 times the tread half-width Wt, the belt end will be too close to the side surface of the tire, making it difficult to manufacture the tire. From such a viewpoint, the lower limit of the ply half width Wb is preferably 0.825 times or more the tread half width Wt, and the upper limit is preferably 0.925 times or less.

A tire with a high flatness (a tire having a large flatness) tends to have a longer contact length on the equator C side of the tire due to the characteristics of the profile than a tire with a low flatness. Therefore, when the distance Lp is set to 0.35 to 0.50 times the tread half width Wt and the inflection point P is brought closer to the tire equatorial line C as in the present invention, the ground contact length of the center land portion 11c becomes the ground contact of the shoulder land portion 11s. It becomes relatively long with respect to the length, which is disadvantageous to center wear and tends to prevent the effect of the invention from being effectively exerted. Therefore, the heavy load tire 1 of the present invention is preferably a low flatness tire having a flatness ratio of 80% or less.

Next, a method of manufacturing the heavy-duty tire 1 will be described.
As shown in FIG. 4, the manufacturing method includes a vulcanization step of vulcanizing the raw tire T by the mold 20. The raw tire T can be formed by the same method as before. Further, the vulcanization step can also be performed by the same method except for the mold 20 used.

The mold 20 has a tread forming surface _2SK for forming the tread portion 2, a sidewall forming surface _3SK for forming the sidewall portion 3, and a bead forming surface 4S for forming the bead portion 4. It has a cavity surface containing _K.

The contour shape of the tread forming surface _2SK has a turning point _PK at the mold arc portion J1 _K in the radius of curvature R1 _K having an arc center at the tire equatorial line C and the mold arc portion J1 _K in this. It is composed of a mold arc portion J2 _K outside the intersecting radius of curvature R2 _K.

The radius of curvature R2 _K is smaller than the radius of curvature R1 _K , and the ratio R2 _K / R1 _K is preferably in the range of 0.14 to 0.20.

The inflection point _PK is located on the middle land portion molding surface portion _mSK for molding the middle land portion 11 m. Further, the distance Lp _K in the tire axial direction from the tire equatorial line C of the inflection point _PK is 0.35 to 0.50 times the mold tread half width Wt _K. The mold tread half width Wt _K is the distance in the tire axial direction from the tire equator C to the tread end forming position Te _K.

Such a mold 20 can form the above-mentioned heavy-duty tire 1 by vulcanization. In the mold 20, the reason for restricting R2 _K / R1 _K to the range of 0.14 to 0.20 and the reason for restricting Lp _K / Wt _K to 0.35 to 0.50 is the heavy load tire 1. The reason for restricting R2 / R1 to the range of 0.14 to 0.20 and the reason for restricting Lp / Wt to 0.35 to 0.50 are the same.

Further, the mold 20 has a ratio WE / WF of the mold clip width WF and the width WE between the maximum width position _QK of the sidewall forming surface _3SK (sometimes referred to as the mold mold width WE). It is preferably 27 to 1.37. In the conventional heavy load tire mold, the ratio WE / WF is smaller than 1.27, for example, 1.25 or less. In this example, the mold mold width WE is large and the mold clip width WF is small as compared with the conventional case, so that the ratio WE / WF is 1.27 to 1.37.

FIG. 5 conceptually shows the profile of the carcass ply 6A. As shown in FIG. 5, in the tire formed by the mold 20, the code path of the carcass ply 6A (indicated by the solid line) is the carcass ply of the tire formed by the conventional mold (indicated by the alternate long and short dash line). Longer than the code path. Therefore, when inflated, the carcass ply 6A is lifted outward in the radial direction on the shoulder side due to the long cord path, which has the effect of suppressing shoulder drop wear. This is useful for suppressing the tendency of shoulder drop wear due to the double radius of the contour line of the tread portion 2.

When the ratio WE / WF is less than 1.27, the effect of suppressing the shoulder drop wear cannot be expected. In particular, when the ratio WE / WF is less than 1.27 due to the large mold clip width WF, the distortion generated in the bead portion 4 at the time of rim assembly becomes large and the bead durability tends to decrease.

Further, when the ratio WE / WF exceeds 1.37 due to the large mold mold width WE, there is a concern that the total width of the tire deviates from the tire standard. On the contrary, when the ratio WE / WF exceeds 1.37 due to the small mold clip width WF, the mold clip width WF gets too close to the rim width, which causes deterioration of the air-in performance.

Further, in order to further improve the wear life of the heavy load tire mounted on the drive shaft, it is also preferable to enhance the center wear resistance performance under an ultra-light load close to an empty state.

In order to improve the center wear resistance performance under ultra-light load in addition to under light load, as shown in FIG. 4, in the mold 20, from the maximum width position Q of the sidewall forming surface _3SK to the bead baseline BL. The ratio HB / WF of the radial distance HB to the mold clip width WF is preferably 0.45 to 0.5.

Further, as shown in FIG. 6, in the vulcanized state of the heavy-duty tire 1 in the mold 20, the radial distance HA and the maximum width position Q from the inner surface of the carcass 6 at the tire equatorial line C to the bead baseline BL. The ratio HB / HA to the radial distance HB is preferably 0.4 to 0.6.

By restricting the ratio HB / WF and the ratio HB / HA to the above ranges, the carcass line can be brought closer to the natural equilibrium shape. Therefore, when inflated, the entire tire swells, and a tread profile close to the tread molded surface _2SK of the mold 20 can be obtained. As a result, it is possible to obtain a ground contact shape in which the circumferential contour line is flattened.

When the ratio HB / WF exceeds 0.5 and HB / HA exceeds 0.6, the carcass line tends to deviate from the natural equilibrium shape. Therefore, when inflated, the tread profile is deformed from the shape of the tread forming surface _2SK of the mold 20, and a flat ground contact shape cannot be obtained.

Specifically, when the ratio HB / WF exceeds 0.5 and the HB / HA exceeds 0.6, the carcass line in the bead portion 4 rises in the radial direction (in the radial direction). The posture is such that the angle with respect is small). Therefore, the change in the carcass line in the bead portion 4 when inflated becomes large. As a result, the carcass line in the tread portion 2 is pulled toward the bead portion 4, and the ground contact shape (contour line on the circumferential direction side) becomes round.

When the ratio HB / WF is less than 0.45 and the HB / HA is less than 0.4, the volume of the bead portion 4 becomes small and the durability performance tends to decrease.

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

Using the mold shown in FIG. 4, the heavy-duty tire (295 / 75R22.5) shown in FIG. 1 was prototyped with the specifications shown in Tables 1 to 3. Then, the center wear resistance, shoulder drop wear resistance, durability, total tire width (pass / fail of the standard), air-in performance, and tire manufacturability of each prototype tire were tested.

(A) In Table 1, the ratio of the radius of curvature of the tread contour line (R2 / R1, R2 _K / R1 _K ), the ratio of the half width of the belt ply (Wb / Wt), and the ratio of the clip width (WE / WF) are the optimum values. The ratio of the distances of the inflection points (Lp / Wt, Lp _K / Wt _K ) is changed. The specifications are substantially the same except those listed in the table.

(B) In Table 2, the ratio of the radius of curvature of the tread contour line (R2 / R1, R2 _K / R1 _K ), with the ratio of the distances of the inflection points (Lp / Wt, Lp _K / Wt _K ) as the optimum value, The half-width ratio of the belt ply (Wb / Wt) and the ratio of the clip width (WE / WF) are changed. The specifications are substantially the same except those listed in the table.

(1) Center wear resistance and shoulder drop wear resistance:
The test tire was mounted on the first axle of the drive shaft of the trailer head with a rim (8.25 x 22.5) and internal pressure (750 kPa). In Tables 1 and 2, the load on the test tire is 60% of the load index (light load state). Further, in Table 3, the load on the test tire is 30% of the load index (empty state).

Then, the actual vehicle traveled 50,000 km on a general road, and the amount of center wear and the amount of shoulder drop wear after traveling were measured. Based on the measurement results, the evaluation was made with an index of Example 1 as 100. The larger the value, the better the wear performance.

(2) Durability:
Using a drum tester, the test tires are rimmed (8.25 x 22.5), internal pressure (750 kPa), running speed of 45 km / h, from 100% load of road index, every 24 hours. The load was increased by 10%, and the mileage until the bead portion of the tire was damaged was measured. Based on the measurement results, the evaluation was made with an index of Example 1 as 100. The larger the number, the better the durability.

(3) Air-in performance:
After assembling the rim, the ease of inflating the tire was evaluated by an index with Example 1 as 100. The larger the value, the better the air-in performance.

(4) Total tire width (pass / fail of standard):
It was determined whether the total tire width was within the standard.

(5) Tire manufacturability Judgment was made based on the presence or absence of troubles due to the width of the belt layer during raw tire manufacturing and vulcanization.

As shown in Tables 1 and 2, the example products exhibit good center wear resistance even in a light load state (load of 60% of the load index) while suppressing an excessive decrease in shoulder wear resistance. You can see that it is irritated. As for the center wear resistance and shoulder drop wear resistance, an evaluation value of 90 or more is acceptable under a light load.

(C) In Table 3, the ratio of the distances of the turning points (Lp / Wt, Lp _K / Wt _K ), the ratio of the radius of curvature of the tread contour line (R2 / R1, R2 _K / R1 _K ), and the half width of the belt ply. The ratio (Wb / Wt) and the ratio of the clip width (WE / WF) are set as the optimum values, and the ratio (HB / WF) and the ratio (HB / HA) of the radial distance of the maximum width position of the sidewall forming surface are changed. is doing. The specifications are substantially the same except those listed in the table. In Table 3, the center wear resistance, shoulder drop wear resistance, and durability were tested.

As shown in Table 3, by regulating the ratio HB / WF and the ratio HB / HA, even in an empty state (load of 30% of the load index), the shoulder wear resistance is not excessively deteriorated and the shoulder wear resistance is suppressed. It can be confirmed that the center wear performance can be exhibited well. As for the center wear resistance and shoulder drop wear resistance, an evaluation value of 90 or more is acceptable under a light load.

1 Heavy load tire 2 Tread part 2S _K tread molding surface 3 Side wall part 3S _K sidewall molding surface 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 7A-7D Belt ply 10 Main groove 11c Center land part 11m Middle land part 11s Shoulder Land part 12s Shoulder lateral groove 20 Arc part in mold J1 Arc part in _K1 Mold arc part J2 Outer arc part J2 _K Outer mold arc part mS _K Middle Land part Molded surface part Q _K Maximum width position T Raw tire Te Tread end Te _K Tread end molding position Wb ply half width Wt tread half width

Claims (10)

It includes a carcass from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer composed of 3 or 4 belt plies arranged on the outer side of the carcass in the radial direction of the tire and inside the tread portion.
In addition, the tread portion has a center land portion most arranged on the equator side of the tire, a shoulder land portion arranged on the most tread end side, and the center land portion and the shoulder land arranged by a plurality of main grooves extending in the tire circumferential direction. It is a heavy load tire divided into the middle land area between the parts.
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 of 5% of the regular internal pressure is filled.
The contour line on the surface of the tread portion intersects the arc portion in the radius of curvature R1 having the center of the arc on the equator of the tire at the turning point P and the radius of curvature R2 smaller than the radius of curvature R1. It consists of an arc outside the
The inflection point P is located on the middle land portion and is located on the middle land portion.
The distance Lp in the tire axial direction from the tire equatorial line to the inflection point P is 0.35 to 0.50 times the tread half width Wt, which is the tire axial distance from the tire equatorial line to the tread end. Tires for heavy loads. The heavy-duty tire according to claim 1, wherein the ratio R2 / R1 of the radius of curvature R1 and the radius of curvature R2 is 0.14 to 0.20. The belt ply includes the first to third belt plies arranged in order from the inner side in the radial direction of the tire, and the second belt ply is the widest and has the widest width.
The heavy load tire according to claim 1 or 2, wherein the ply half width from the tire equator of the second belt ply is 0.8 to 0.95 times the tread half width. The heavy-duty tire according to any one of claims 1 to 3, wherein the flatness of the tire is 80% or less. The invention according to any one of claims 1 to 4, wherein the shoulder land portion includes a plurality of shoulder lateral grooves that cross the shoulder land portion, and the groove depth of the shoulder lateral grooves is 3.0 mm or less. Heavy load tires. A carcass extending from the tread portion to the bead core of the bead portion through the sidewall portion and a belt layer composed of three or four belt plies arranged outside the tire radial direction of the carcass and inside the tread portion are included.
In addition, the tread portion has a center land portion most arranged on the equator side of the tire, a shoulder land portion arranged on the most tread end side, and the center land portion and the shoulder land arranged by a plurality of main grooves extending in the tire circumferential direction. It is a method of manufacturing heavy-duty tires divided into middle land areas between the parts.
Includes a vulcanization process that vulcanizes raw tires with a mold
Further, in the mold, the contour line of the tread forming surface for forming the tread portion is formed on the arc portion of the mold within the radius of curvature _R1K having the center of the arc on the equatorial line of the tire and the arc portion of the mold. It _{consists of an arc portion of a mold outside the radius of curvature R2 K ,} which intersects at the turning point PK and is smaller than the radius of curvature R1 _K.
The inflection point _PK is located on the middle land portion forming surface portion for forming the middle land portion.
The distance Lp _K in the tire axial direction from the tire equatorial line to the turning point _{PK is 0.35 to 0.50 times the tire axial half width Wt K ,} which is the tire axial distance from the tire equatorial line to the tread end forming position. A method for manufacturing a heavy-duty tire, which is characterized by being. The method for manufacturing a heavy-duty tire according to claim 6, wherein the ratio R2 _K / R1 _K of the radius of curvature R1 _K and the radius of curvature R2 _K is 0.14 to 0.20. The mold has a ratio WE / WF of 1.27 to 1.37 between the mold clip width WF and the width WE between the maximum width positions of the sidewall molding surface for molding the sidewall portion. The method for manufacturing a heavy-duty tire according to claim 6 or 7. The mold has a ratio HB / WF of the radial distance HB from the maximum width position of the sidewall forming surface for forming the sidewall portion to the bead baseline and the mold clip width WF of 0.45. The method for manufacturing a heavy-duty tire according to any one of claims 6 to 8, wherein the weight is 0.5. The tire is in a radial distance HB from the maximum width position of the sidewall forming surface for forming the sidewall portion to the bead baseline and the vulcanized state of the heavy load tire in the mold. The manufacture of a heavy-duty tire according to any one of claims 6 to 9, wherein the ratio HB / HA to the radial distance HA from the inner surface of the carcass to the bead baseline at the equator is in the range of 0.4 to 0.6. Method.

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