JP3398730B2 - Pneumatic radial tire for heavy loads - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty pneumatic radial tire mainly used for trucks, buses and the like.

[0002]

2. Description of the Related Art When an unused radial tire is filled with a prescribed air pressure in a normal use condition (outer diameter growth of the tire at this time is referred to as inflation gloss, hereinafter referred to as INF gloss). 7) is a cross-sectional view in the tire width direction of FIG. Where 101
Is a carcass, 102 is a belt, 103 is a bead wire,
104 is a rim flange, 105 is a tread (tread)
The part 106 is a sidewall part.

The tread portion 105 sandwiches a tire center line (equator line) 109 and extends on both sides of the center region 107.
And the sidewall portions 10 on both sides of the central region 107.
6 and a shoulder region 108 that is connected to the belt 6.

[0004] In the conventional radial tire, the tread tread 105 in the above-mentioned cross section is formed with one radius of curvature during vulcanization molding. However, in such a tire, at the time of INF gloss, the radius of curvature R12 of the shoulder region 108 of the tread portion 105 is
The radius of curvature R11 of the central region 107 is smaller than that of the central region 107, and the shoulder region 1 is in contact with the boundary 110 between the two regions.
The ground contact surface 08 has a shape that is depressed radially inward of the tire.

In order to compensate for this drop during the INF gloss, as shown in FIG. 8, in the tread molding shape during tire vulcanization molding, the shoulder region 108 is centered at a point 111 in the tread tread 105. A so-called shoulder-raising is performed so that the curved surface is in contact with the curved surface of the region 107 and has a curvature radius R22 larger than the curvature radius R21.

[0006] With such a tire with shoulders raised,
As shown in FIG. 9B, the tread contact surface 105 in the cross section in the tire width direction can be formed with one radius of curvature during INF gloss. However, as shown in FIG. 10B, the central region 1 is caused by the outer diameter growth (hereinafter referred to as service gloss) when the tire is used (for example, when the truck is mounted and the vehicle travels about 10,000 km).
07, which is a boundary between the shoulder region 108 and the shoulder region 108
05 1/4 point 1/4 of tread width from both ends
10 is protruding. This is a phenomenon similarly occurring in a conventional tire that does not raise the shoulder. This phenomenon occurs because the tire receives a load during use and is further rotated at a high speed to receive heat and strain to deform the shape of the carcass, and is also called shoulder drop. As a result, as shown in FIGS. 9A and 10A, also in the ground contact shape of the tire, the ground contact length of the central region 107 is further longer than the ground contact length of the shoulder region 108.

Conventionally, in the domestic market of trucks, buses, etc., driving is relatively frequent in urban areas. In urban areas, steering wheel operation is frequently performed during starting, stopping, and traveling, so that the tread tread wears out. It was accelerated, and the influence of the shoulder drop on the worn shape of the tire was relatively small.

However, due to recent changes in transportation conditions, long-distance and high-speed traveling has become frequent,
This shoulder drop is a big problem. In particular, in buses and trucks that perform such traveling, since radial tires having a rib pattern or rib / lug pattern with good straight running stability are used, the problem is more serious. This is usually the case with such tires, 1/4 point 11 above.
Since the groove 112 is continuously provided in the vicinity of 0 in the tire circumferential direction, the shoulder rib 108 on the outer side of the groove 112 is dropped, and the groove 112 has a shape protruding (FIG. 10 ( See b)).

During such running, forced wear of the tread surface is not promoted as in running in urban areas,
Since the wear rate decreases extremely, the tire front-rear pressure in the tread surface (drive, drive,
Braking force), lateral force (side force), ground contact shape, tread crown shape. In particular, at the ¼ point protrusion, lateral wear is generated in the ground contact surface, and river wear, which is uneven wear that occurs in the tire circumferential direction along the groove, occurs. Further, as a result of the contact length of the contact shape, that is, the shoulder region having a short outer circumference rolling at the same speed as the central region, a large slip occurs at the shoulder end, the tread is scraped off, and uneven wear of the shoulder wear or the like occurs. Appears prominently.

Due to the various problems caused by the decrease in the wear rate and the vibrations caused by the uneven wear, the tires must be replaced at an early stage, and the life of the tires is short.

In order to solve these problems, it is necessary to delay the occurrence time of the shoulder drop as much as possible so as not to occur at least during the service gloss as described above.

In view of this point, as a result of intensive studies, it is possible to significantly delay the generation time by improving the ground contact property of the tread tread and the distribution of wear energy consumed by the tread during tire rolling. It was also found that the ground contact property and wear energy distribution depend on the tread crown shape and the belt shape.

The reason will be described below.

In high-speed steady running with a low wear rate, the running condition is mainly straight ahead or a running condition close to that, and the slip angle is fixed for a long time. In such a state, in-plane stress is constantly applied to a portion in the tread tread portion where stress is likely to be concentrated, for example, the 1/4 point protrusion 110 of FIG. 10B, which may be a cause of uneven wear. . Further, in such a straight running state where the number of steering wheel operations is small, the ground contact shape or the deformation in the tread tread portion is fixed while being uneven, which further causes stress concentration in the tread tread portion.

On the other hand, a tire having a higher grounding property has a higher cornering power (hereinafter referred to as CP) and a higher C.
A tire having P has a smaller steering angle, that is, a higher cornering force with a slip angle (hereinafter referred to as CF).
Exert. If the slip angle required for a tire with a high CP is reduced, naturally, the addition of the slip angle leads to the reduction of deformation in the ground contact surface and, in the strongest case, the concentration of in-plane stress. That is, a tire having a higher grounding property is less likely to be deformed in the tread tread portion and less susceptible to stress concentration. Furthermore, since a high CP is exhibited, a small slip angle can be added to the required CF and the tread portion can be deformed. In order to improve the grounding property, the point is how the tread rubber is uniformly grounded on the entire tread portion by the belt layer body.

This is as shown in FIG. 6 (a).
At the time of gloss, the belt 102 has an appropriate curvature, and
As shown in (b), when the belt 102 is deformed so as to be flattened at the time of grounding (load state), the tread 1
This is because a strong reaction force is obtained in the central region 107 of 05, the ground contact property is improved, and the price tear, which is said to be mainly due to the outermost belt layer, is also increased. An ideal tire belt layer body 102 for obtaining such a high grounding property is a belt radius (curvature radius in the tread width direction of the outer surface of the outermost belt) and a crown radius (tread of the tread tread portion at the time of INF gloss). Radius of curvature in the width direction) has almost the same value.

However, the belt layer body has not only the above-mentioned ground contact but also the effect as a hoop for maintaining the shape of the radial tire case, and the functions of the two belt layer bodies have contradictory characteristics. . That is, in order to secure a high ground contact property, it is necessary to have flexibility instead of a belt layer body having high rigidity, while rigidity is required for the hoop effect.

In other words, considering the function of the belt layer body as a hoop, the rigidity of the belt 102, which receives tension generated by the internal pressure during INF gloss, increases in proportion to the internal pressure.
The radius on the belt tries to expand. On the other hand, both ends of the tread 105 are pulled inward in the radial direction of the tire, and the crown radius tends to be reduced. As a result, reverse warp deformation of the belt occurs as shown in FIG.

In a tire having a flatness ratio (H / W =) of 80% or more, the bearing of the internal pressure of the belt portion is not so high and the shape of the tire case can be easily maintained. In this case, the on-belt radius expands (inverse warp deformation of the belt) by filling with internal pressure, but the problem is relatively small because it has an absolute value close to the tread crown radius.

However, for tires with an aspect ratio of less than 80%,
Since the shortage of the air volume is compensated by the high internal pressure filling, the burden on the belt is large, and the belt radius already exceeds the crown radius at the initial point as shown in FIG. 11 (a). Therefore, at the time of grounding, as shown in FIG. 11B, both ends of the rising belt 102 have a shape (projection of the crown ¼ point) as if the shoulder region 108 were pulled out. Therefore, in the tread central area 107,
The reaction force of the belt 102 is not sufficiently obtained, the ground contact property is impaired, and the uneven wear resistance of the tread is lowered together with the shoulder drop deformation. As described above, when the ground contact pressure of the central region 107 of the tread 105 is low and the ground contact pressure of the shoulder region 108 is high, a load is applied when the tire rolls, and thus the belt 1
The strain concentrates on both ends of 02, and the tread rubber and belt 10
2 causes separation and peeling phenomenon.

When a belt layer body (excluding a winding belt) composed only of a low-angle belt (cured 15 ° or less) is used, the reverse warp deformation of the belt is more remarkable, and the grounding property of the belt central region is exhibited. The deterioration of the price tear significantly deteriorates, and adversely affects various characteristics such as CP within a minute steering angle during traveling.

Since the restraint force of the belt is increased in the case of only the low-angle belt, the CP in the excessive steering angle (practically a low speed traveling range such as turning) is increased due to the improvement of the rigidity in the tread surface. However, since the belt is deformed in the reverse warp and the grounding property is impaired, the CF required for straight traveling
Therefore, it becomes necessary to increase the slip angle to compensate for this. When the slip angle is increased, the deformation in the tread contact surface increases, which hinders the consumption of uniform wear energy over the entire tread, which is considered to be essential for uniform wear and uneven wear resistance. Stress concentration in the plane causes the generation of river wear and the like.

As described above, the shape of the belt layer body is
It has a great influence on the ground contact property and various cornering characteristics of the tire, and has a strong influence on the uneven wear resistance that influences the wear life of the pneumatic radial tire for heavy loads.

Here, since the conventional shoulder raising described above is a shoulder raising by the contact circle, the thickness of the tread on the belt of the shoulder portion 108 when the internal pressure is not filled is equal to the central region 107.
Not much larger than the tread thickness on the belt. Therefore, at the time of INF gloss, the reverse warp deformation of the belt cannot be sufficiently suppressed because the thicknesses of the both are reversed. Therefore, at the time of INF gloss,
Compared with the one in which the shape of this belt layer body does not raise the shoulder,
There has been little improvement, and as a result, 1/4 point stands out during service gloss. If the shoulder raising is increased to prevent this, as shown in FIG. 8, the contact point 111 that is the starting point of the shoulder raising reaches the central region 107 of the tread 105. In this case, since both ends of the groove 112 sandwiched between the shoulder rib 108 and the central region 107 are also raised, the 1/4 point further protrudes, and there is a problem that river wear is particularly likely to occur.

In view of the above points, the present invention improves the grounding property so as to exert a high cornering power, minimizes the deformation in the tread grounding surface and the necessary slip angle during high-speed steady running, and prevents uneven wear. To provide a tire having improved The present invention is particularly suitable for a tire having an aspect ratio of less than 80%, but can be applied to a tire having an aspect ratio of 80% or more.

[0026]

A pneumatic radial tire for heavy load according to the present invention is a shoulder rib which is located at both ends of a tread in the tire width direction and is formed by grooves continuously provided in the tire circumferential direction. A region and a radial tire having a tread central region sandwiched in the groove as a contact surface, wherein the molding shape of the tread outer periphery at the time of vulcanization molding is a cross section in the tire width direction, the tread central region and the shoulder The rib region has an arc shape having a predetermined radius of curvature, and the intersection point of the arc forming the tread central region and the arc forming the shoulder rib region is in the groove, and, The circular arc forming the shoulder rib region is in the radial direction of the tire rather than the circular arc forming the tread central region in the shoulder rib region. The one in which such have been so positioned outside.

In the above tire, the intersection point of the arc forming the tread central area and the arc forming the shoulder rib area is divided into two equal parts in the width direction of the tire within the groove. It is preferable that it is located between the center line of the groove, which is a line to be formed, and the wall surface of the groove on the outer side in the tire width direction.

Further, in the above-mentioned tire, the intersection point of the arc forming the tread central region and the arc forming the shoulder rib region is at the tire radial outer end of the outer wall surface of the groove. Is preferred.

[0029]

In the radial tire of the present invention described above, the thickness of the tread from the belt end portion in the shoulder area of the tread is sufficiently larger than the thickness of the tread on the belt in the central area of the tread. Therefore, I
Even when the shoulder region is pulled inward in the tire radial direction at the time of NF gloss, the belt upper radius and the crown radius can be made substantially the same value, and the above-mentioned reverse warp deformation of the belt can be suppressed. Therefore, when a load is applied, the ground contact property of the tread central portion is improved by the reaction force of the deformation that flattens the belt. With this improved grounding,
The outermost belt layer causes an increase in plysteer, which is thought to be the main cause, while uniform grounding of the tread also increases cornering power. A tire with high cornering power means that the combined force of price tear and conicity , which must be canceled to keep the tire straight, can be dealt with by adding a minimum slip angle, which reduces deformation in the contact surface and the entire tread surface. It enables uniform consumption of wear energy.

Further, the intersection of the arc forming the tread central region and the arc forming the shoulder rib region is a line that divides the groove into two equal parts in the tire width direction, and the center line of the groove and the tire of the groove. If it is between the outer wall surface in the width direction, the tire width direction outer end of the groove in the tire ground contact surface, because it is easier to form in the tire radial direction inward than the tire width direction inner end of the groove, Only the shoulder rib area is raised more effectively.

Furthermore, when the intersection is located at the outer end of the outer wall surface of the groove in the tire radial direction, both ends of the groove on the tread contact surface are formed on the same arc, and only the shoulder rib region is formed. Since the shoulder is raised more effectively, a more uniform grounding property can be obtained.

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged sectional view of an essential part showing the structure of a tread portion of an inner wall surface of a vulcanizing mold used for manufacturing a radial tire according to an embodiment of the present invention. A so-called green tire before vulcanization molding is put in this mold, and heat and pressure are applied. The shape of the tire at this time is the shape at the time of vulcanization molding and has the same shape as the inner wall surface of the mold. Therefore,
The structure of the radial tire 10 during vulcanization molding will be described with reference to FIGS. 1 and 2.

The tread portion 12 of the tire 10 has four grooves 14 continuous in the tire circumferential direction. Each groove 14 has a depth of 15 mm and a width of 12 mm, and is linearly formed along the tire circumferential direction. These four grooves 14
Of these, shoulder ribs 16 are formed at both ends of the tread 12 by the two grooves 14a close to both ends of the tread 12, respectively. A quarter point rib 18 is formed between the groove 14a and the groove 14b from the center of the tread 12,
A center rib 20 through which a tire center line (equatorial line) 22 passes is formed between the two grooves 14b from the center. Here, from this tire center line 22 on the ground contact surface of the tire to the inner end 24 of the groove 14a, that is, the 1/4 point rib 1
The length to the outer edge of 8 is 1/4 of the tread width (TW)
It is set to (1 / 4TW).

In the cross section in the tire width direction, the central region 19 composed of the 1/4 point rib 18 and the center rib 20 is
The ground contact surface is formed in an arc shape having a radius of curvature R1. The center of the circle forming the arc is on the tire center line 22, and R1 is 300R ≦ R1 ≦ 2000R.
It is set in the range of (mm).

On the other hand, the shoulder rib 16 has its ground contact surface formed in an arc shape having a radius of curvature R2. This R2 is set in the range of R1 ≦ R2 <4000R (mm). When R2 is 4000R or more, the shoulder ribs 16 due to thermal contraction of the tread rubber after vulcanization molding.
It is not preferable because the center of the tread 12 is depressed and the end of the tread 12 is projected. The arc of the shoulder rib 16 is located further outward in the tire radial direction than the extension line 21 that extends the arc of the central region 19 to the region of the shoulder rib 16.
In the outer wall in the tire width direction of No. 6, the shoulder rib 16 is formed to be thicker by d. Further, the arc of the shoulder rib 16 and the arc of the central region 19 are different from each other in the groove 14
They intersect at an outer end 26 of the ground contact surface of a. That is, the outer end 26 of the groove 14a on the tire contact surface has the intersection 30 of the above two arcs, and the shoulder is raised from this point.

The starting point 30 for raising the shoulder is the above-mentioned groove 14a.
Is not limited to the outer end 26 of the ground plane of
It only needs to be in the groove 14a. That is, as shown in FIG. 14A, the tire width direction outer side wall 2 of the quarter point rib 18 is formed.
5, that is, the wall surface 25 of the groove 14a on the inner side in the tire width direction,
The tire width direction inner side wall 27 of the shoulder rib 16, that is,
It suffices to be in a region (TW1) sandwiched between the groove 14a and the wall surface 27 on the outer side in the tire width direction.

When the intersection point 30 exists in the area of the TW1, it is not necessary to provide an inflection point in the shoulder rib 16 such as the intersection point where the arc changes greatly.

The intersection 30 is preferably the groove 1 described above.
It is better to be located between the center line 28 of 4a and the wall surface 27 of the groove 14a on the outer side in the tire width direction. That is, FIG.
As shown in (b), a region (TW2) between the center line 28 of the groove 14a, which is a line that divides the groove 14a into two equal parts in the tire width direction, and the tire width direction inner side wall 27 of the shoulder rib 16.
Is preferred.

If there is an intersection 30 in this TW2 area,
It is easy to form an appropriate level difference between both ends 24 and 26 on the ground plane of the groove 14a.

This step is, as shown in FIG.
The inner end 24 of the groove 14a on the ground contact surface is formed so as to be located further outward in the radial direction of the tire than the outer end 26 thereof. Then, if the distance between the perpendiculars from the both ends 24, 26 on the ground contact surface of the groove 14a to the tire center line 22 is h, this step h is 0 <h ≦ 3 (mm).
It is formed in the range of. The step h is 0 mm, or
When the outer end 26 is located radially outward of the tire,
The 1 / 4-point rib 18 has a low ground contact property, and a rib punch that is largely worn unevenly is likely to occur. On the other hand, if it is 3 mm or more, the outer peripheral length near the inner end of the shoulder rib 16 is too short, and uneven wear is likely to occur. Here, the step h is preferably 0.1 ≦ h ≦ 0.5 (mm).

As shown in FIG. 14C, the above intersection 3
It is preferable that 0 is provided at the outer end 26 of the outer wall surface 27 of the groove 14a in the tire radial direction, that is, the outer end 26 of the groove 14a on the ground contact surface, because this appropriate step h can be formed more easily.

Reference numeral 32 is a side wall portion connected to the shoulder rib 16, reference numeral 34 is a belt, and reference numeral 36 is a carcass. This belt 34
At the time of vulcanization molding, it is arranged so as to have the same curvature as the central region 19 of the tread.

FIG. 3 shows a part of the rib pattern of the tread tread portion 12 according to another embodiment of the radial tire 10 manufactured according to FIG. Each groove 14a, 14b
Are provided in a zigzag shape along the tire circumferential direction. In the case of having such a rib pattern, the intersection point 30 which is the starting point of the shoulder raising is where the groove 14a adjacent to the shoulder rib 16 swings most toward the tire center line 22, and the above-mentioned starting point 30 is configured. Should be applied. However, at other portions in the tire circumferential direction, the quarter point ribs 18
It is preferred that there is no intersection 30 above. In a tire having a zigzag rib pattern, it is most preferable to provide the intersection point 30 at the inner end 38 of the ground contact surface of the shoulder rib 16 when the groove 14a is located closest to the center of the tread.

The tread pattern according to the present invention is not limited to the patterns shown in FIGS. 2 and 3 and may be any pattern having a groove 14a forming the shoulder rib, and for example, a linear rib. The pattern may be a combination of ribs and zigzag ribs, or a rib / lug pattern. However, the swinging of the zigzag rib in the tire width direction is preferably not so large for wear resistance.

FIG. 4 is an enlarged view of a main part of a cross section in the tire width direction of a heavy duty pneumatic radial tire 10 according to an embodiment of the present invention, in which an internal pressure of 0.5 kg / cm ² is filled. Since the shape of the radial tire when it is filled with the internal pressure of 0.5 kg / cm ² is almost the same as the shape at the time of vulcanization molding, the shape of the belt 34 and the tread tread 12 is further shown in FIG. Detailed description. The same reference numerals as those in FIG. 1 have the same structure unless otherwise specified.

The belt 34 is composed of three sheets 34a, 34b and 34c from the outside in the outer diameter direction of the tire. Here, the number of belts 34 is preferably three or more. The belt 34b in the middle is the widest belt having the widest width. The thickness A of the tread 12 at the tire center line 22 from the outermost belt 34a, which is one outermost side of the maximum width belt 34b, and the length of the normal line from the both ends of the outermost belt 34a to the shoulder ribs 16, Belt 34
There is a relationship of A <B with the thickness B of the tread 12 on the end a.

Due to the relationship of A <B, as shown in FIG. 5, in the INF gloss, the belt radius has a radius of curvature which is substantially the same as the crown radius of the belt radius. That is, the radius on the belt is formed to be rounder than when the radius on the belt has the relationship of A = B as shown by the dotted line in FIG.

As described above, in order to prevent reverse warp deformation of the belt layer body, in the belt positioned above the maximum width belt, A
The relationship of <B is provided, and the belt is forcibly formed into a round shape. In order to secure the belt thickness of A <B, shoulder raising is performed by using the intersection point, which is limited to the shoulder ribs located at the belt end. This can also contribute to prevention of shoulder drop of the tread crown shape. Further, if the shoulder is raised using such an intersection, the thickness of B can be easily formed in an effective range.

With the round shape of the belt layer body, the outward convex shape of the tread center portion is emphasized, and the strong repulsive force due to the depression of the belt center portion within the ground contact surface improves the ground contact performance of the tire center portion. The improved grounding of the belt leads to an increase in plysteer, which is thought to be mainly due to the outermost belt layer, while the uniform grounding of the tread also increases the cornering power (CP).

This high CP must be canceled in order to keep the tire straight, but in the above case, the resultant force of the price tear and conicity can be dealt with by adding a minimum slip angle, and the deformation in the ground contact surface can be dealt with. It enables reduction and uniform consumption of wear energy over the entire tread. As a result, a high CP is realized by improving the ground contact property, the uneven wear resistance performance, which is said to be the most important in heavy-duty tires, can be improved, and the wear resistance is also improved by uniform in-plane ground contact.

In order to confirm the above effects, various characteristics of the tire of the example of the present invention and the tire of the comparative example were evaluated. The results are shown in Table 1 below, FIG. 12 and FIG.
3 shows. Here, with the tire of the embodiment, the intersection 30 that is the starting point for raising the shoulder as shown in FIG. 1 is the outer end 26 of the groove 14a on the tire ground contact surface, that is, the shoulder rib 16.
It is the tire 10 with the shoulder raised at the inner end of the. On the other hand, the tires of Comparative Examples 1 and 2 are tires in which the tread tread portion is formed with a single radius of curvature at the time of vulcanization molding without raising the shoulder.

[0053]

[Table 1] The tire size is 285/75 in both the example and the comparative example.
R24.5 14PR, and the tread pattern is
A tire having five straight rib patterns separated by four straight grooves as shown in FIG. 2 was used. The belt structure of each tire is 4 as shown in item 1 of Table 1.
The number # 1B is a belt located on the innermost side in the radial direction of the tire, and the belts # 2B, # 3B, and # 4B are sequentially arranged outward. Further, 20 ° L means that the cords that form the belt form an angle of 20 ° with the tire circumferential direction on the development surface of the tread portion of the tire, and are arranged at the upper left of the traveling direction. . The configuration of each belt of the tire is the same as that of the example and the comparative example 1,
In Comparative Example 2, the belt angle of # 2B to # 4B was set to a lower angle (17 °) than the other two examples.

These tires were mounted on a rim of 8.25 × 24.5 and filled with an internal pressure of 7.7 kg / cm ² . The three-point radius on the belt during this filling is shown in Table 1.
As shown in item 2 of the above, the tire 10 of the present embodiment is 200
0R (mm) was the smallest, and Comparative Example 1 was 4000R. Thus, despite the same belt configuration,
In the tire 10 of the present embodiment, the belt at the time of INF gloss is formed to be more round because the shoulder is raised by the above-mentioned intersection. On the other hand, the tire of Comparative Example 2 had a flat belt and did not have a curved shape. When the belt angle is small in this way, the rigidity of the belt is high, the outer diameter growth is suppressed, and the above-mentioned reverse warp deformation of the belt occurs. The three-point radius on the belt is the radius that passes through the center and both ends of the outermost belt, and is measured with an R ruler.

Price tire (PS) and conicity (CO), which are the uniformity (U / F) of each tire, and cornering power (CP) as cornering characteristics,
Table 1 shows the cornering force (CF) and the slip angle required for going straight.

These values are the lateral force (F _y ) and the braking force generated on the tire when a load is applied to the tire on the drum tester and the tire is rolled with the radius kept constant. (F _x ) is measured and obtained. Where Pricetea (P
S) and conicity (CO) are defined as F _{y +} is the lateral force generated during forward rotation and F _y− is the lateral force generated during reverse rotation.
It is calculated by the following formula.

PS = (F _{y +} −F _y− ) / 2 CO = (F _{y +} + F _y− ) / 2 The cornering force (CF) rolls the tire with the slip angle θ and F _y , F _x is measured and calculated by the following calculation formula.

CF = F _y cos θ−F _x sin θ The cornering power (CP) is obtained from CP = CF / θ. The slip angle required for straight traveling is an actual measured value of the slip angle required for rolling the tire straight on the drum.

Regarding the U / F characteristic, the absolute value of the plysteer of the tire 10 of this embodiment is the largest, and the plysteer is smaller in the order of Comparative Example 1 and Comparative Example 2. Further, the absolute value of the conicity of the tire 10 of the present embodiment is the smallest, and the conicity is larger in the order of Comparative Example 1 and Comparative Example 2.

As shown in FIG. 12, regarding the cornering power (CP) rising curve of each tire, the tire 10 of this example has the sharpest rising curve and is excellent in ground contact. In Comparative Example 1 and Comparative Example 2, the rising is slower and the grounding property is worse than in the Examples.

As described above, the larger the belt radius associated with the internal pressure filling is, the more the belt warp deformation in the tire ground contact surface increases, so that the belt lifting phenomenon at the center of ground contact becomes more prominent (see FIG. 11 ( See b)). As a result, the ground contact property of the tire tread portion is deteriorated, and thus the price tear, which is mainly caused by the expansion and contraction of the outermost belt layer, decreases as the ground contact decreases. Further, the cornering characteristics are deteriorated due to the impaired ground contactability of the tire. In item 4, the cornering power (CP) has a slip angle of θ = 1 ° / 2.
This is the value at ° / 3 °, and the cornering force (C
F) is the value when the slip angle is θ = 13 °.

Due to the U / F and the cornering characteristics as described above, the tire 10 of the present embodiment is capable of canceling the price tear, conicity, and residual cornering force and adding a slip angle for generating the cornering force required for straight traveling. Decrease. As shown in Item 5, Comparative Examples 1 and 2
It is understood that the tire of No. 2 requires a slip angle corresponding to 2 to 3.5 times that of the example product in order to generate sufficient cornering force. In other words, by reducing the radius on the belt when filling the internal pressure, the grounding performance at the center of the grounding is improved, the cornering power is increased, and the additional amount of slip angle required during running and the deformation in the grounding surface due to steering are generated. It contributes to the occurrence of uneven wear and the reduction of its growth.

The value in parentheses in item 5 is the value of the slip angle of the comparative example when the slip angle of the example is 100.

FIG. 13 shows the distribution of wear energy consumed in the ground contact surface. This wear energy distribution is a distribution state of wear energy measured at each of three points of five ribs by giving a tire a slip angle assuming a straight running state (in the figure, SH is a shoulder rib and 1/4 is 1). / 4 point rib, CE indicates center rib). Here, the wear energy is data obtained by integrating the inner product of the in-plane pressure vector and the displacement vector measured at a constant sampling interval from the start to the end of contact with the ground. The in-plane pressure is corrected by the tire vertical pressure and road mu.

Further, if the wear energy distribution in the ground contact surface of the tire or in the ribs is uniform, uneven wear is unlikely to occur.

The slip angle added to each tire was 0.05 ° for the tire 10 of this example, and 0.12 ° for the comparative example 1,
Comparative Example 2 is 0.20 °. The tire of the example is shown in FIG.
As shown in FIG. 3 (a), the addition of the slip angle was the smallest and the in-plane wear energy distribution was the most uniform. For this reason,
Uniform wear occurs on the entire surface of the tread.

In the tire of Comparative Example 1, as shown in FIG. 13 (b), the shoulder rib has reduced wear energy. Further, in the tire of Comparative Example 2, as shown in FIG. 13 (c), the addition of the slip angle is maximum, and the variation of the in-plane wear energy distribution is large. In the tire of the comparative example, as shown in FIG. 11 (b), this means that the belt has the tread tread portion 1
This is because the / 4 point is strongly extruded, and the ground contact pressure at the shoulder portion and the central portion of the tread is low. As described above, in Comparative Examples 1 and 2, the above-mentioned 1/4 point is likely to occur.

It should be noted that the shoulder ribs on the side of the cereal have a reduced wear energy, but since this side of the cerial is mounted on the outside of the vehicle when it is mounted on the vehicle, it is uniform during actual running. Wear energy. This is because the ground contact pressure at that portion increases due to the large load at the tire rotation shaft end. That is, this decrease in wear energy is compensated by this ground pressure.

[0069]

According to the radial tire for heavy load of the present invention, the slip angle can be reduced in order to keep the tire straight, and it is possible to reduce the deformation in the tread surface and consume the uniform wear energy of the entire tread surface. The uneven wear resistance is improved. In particular, uneven wear resistance during high-speed steady running is improved, and tire life is extended.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a main part of an inner wall surface of a vulcanization molding die for molding a radial tire according to an embodiment of the present invention.

FIG. 2 is an enlarged plan view of an essential part of a tread tread portion during vulcanization molding of a radial tire according to an embodiment of the present invention.

FIG. 3 is an enlarged plan view of an essential part of a tread tread portion during vulcanization molding of a radial tire according to another embodiment of the present invention.

FIG. 4 shows a radial tire according to an embodiment of the present invention.
It is a principal part expanded sectional view at the time of internal pressure filling of 5 kg / cm < ² >.

FIG. 5 is an enlarged cross-sectional view of a main part of the radial tire according to one embodiment of the present invention when the radial tire is used and the internal pressure is regulated.

6A and 6B are diagrams illustrating the shapes of a belt and a tread of a radial tire according to the present invention, in which FIG. 6A is an enlarged cross-sectional view of a main part at the time of filling to a prescribed internal pressure, and FIG. FIG.

FIG. 7 is a cross-sectional view when a conventional radial tire is filled with a specified internal pressure during use.

FIG. 8 is an enlarged cross-sectional view of an essential part showing a tread shape at the time of vulcanization molding of a conventional radial tire with shoulders raised.

FIG. 9 is a view for explaining the shape of a conventional radial tire when it is filled with a prescribed internal pressure during use, (a)
Is the plane shape of the tread contact surface when the tire touches the ground, and (b) is the cross-sectional shape of the tread when not touching the ground.

FIG. 10 is a diagram for explaining the shape of the conventional radial tire at the time of service gloss when used, in which (a) is
It is the plane shape of the tread contact surface when the tire touches the ground, and (b) is the cross-sectional shape of the tread when not touching the ground.

11A and 11B are views for explaining the shapes of a belt and a tread of a conventional radial tire, FIG. 11A is an enlarged cross-sectional view of an essential part at the time of filling to a prescribed internal pressure, and FIG. FIG.

FIG. 12 is a graph showing the relationship between slip angle and cornering power for a radial tire according to an example of the present invention and a conventional radial tire.

FIG. 13 is a diagram showing the distribution of wear energy consumed over the entire tread during straight running (slip angle added) for a radial tire according to an embodiment of the present invention and a conventional radial tire.

FIG. 14 is a schematic cross-sectional view of a main part of a tread for explaining the position of an intersection point 30 which is the starting point of shoulder raising of the radial tire of the present invention, where (a) is in the groove 14a, (b) is
Is in the center line 28 of the groove 14a and the outer wall surface 27 of the groove 14a, and (c) is in the outer end 26 of the groove 14a in the ground contact surface.

[Explanation of symbols]

10 ... Radial tire 12 ... tread 14a ... groove 16 ... Shoulder rib 19 ... Tread central area 26 ... Outer end of groove 14a on ground contact surface 27: Wall surface of groove 14a outside in the tire width direction 28: center line of groove 14a 30 ... intersection R1 ... Radius of curvature of the tread central area R2: Radius of curvature of shoulder ribs

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-95909 (JP, A) JP-A-5-77608 (JP, A) JP-A-4-59401 (JP, A) JP-A-2- 185807 (JP, A) JP 64-1608 (JP, A) JP 54-70501 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 11 / 00,11 / 01

Claims (6)

(57) [Claims] 1. A tread located at both ends in the tire width direction,
A radial tire in which a shoulder rib region formed by a groove continuously provided in a circumferential direction of each tire and a tread central region sandwiched by the groove as a grounding surface is a tread outer periphery during vulcanization molding. The molded shape of, in the cross section in the tire width direction, the tread central region and the shoulder rib region each have an arc shape having a predetermined radius of curvature, and the arc forming the tread central region and the shoulder rib region. An intersection that intersects with the arc forming the inner side of the groove, and the arc forming the shoulder rib region is more outward in the radial direction of the tire than the arc forming the tread central region in the shoulder rib region. A heavy-duty pneumatic radial tire characterized by being positioned at. 2. An intersection of an arc forming the tread central area and an arc forming the shoulder rib area is a line that divides the groove into two equal parts in the width direction of the tire within the groove. The heavy-duty pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is located between a center line of the groove and a wall surface of the groove on the outer side in the tire width direction. 3. An intersection of an arc forming the central region of the tread and an arc forming the shoulder rib region is located at an outer end in the tire radial direction of the outer wall surface of the groove. The pneumatic radial tire for heavy loads according to claim 2. 4. The inner end of the groove on the ground plane is the outer end.
Characterized by being located outward in the radial direction of the tire
A heavy duty pneumatic radial tie according to claim 2 or 3.
Ya. 5. A tire center line comprising three or more belts
The thickness of the tread (A) from the outermost belt in the
Lowered from both ends of the outer belt to the shoulder rib area
Tread thickness on the outermost belt edge, which is the length of the normal
(B) means that A <B during vulcanization molding
Heavy load air according to any one of claims 1 to 4
Radial tires with. 6. The tread width direction of the outer surface of the outermost belt
Radius on the belt, which is the radius of curvature in the
Crown that is the radius of curvature of the surface portion in the tread width direction
Radius is almost the same as inflation gloss
A heavy load according to claim 5, characterized in that they have the same value.
Pneumatic radial tire.