JPH0648109A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To improve the eccentric abrasion resistance by suppressing the reduction of the crown R due to traveling, maintaining the bead durability of a pneumatic radial tire for heavy load. CONSTITUTION:In the filled state with the internal pressure of 10% of a prescribed internal pressure through the rim assembly, if the radius of curvature of carcass line is set to R2 directly under the belt edge part having the max. width, R3 at the carcass max. width position, and R4 at the position in 70% of the height at the max. width position from the innermost position in the tire radial direction of the carcass ply, 1>R3/R2>0.55, R4>R3. As for the carcass line in the case when the regular internal pressure is filled, the carcass max. width position R3 is recessed to the inside in the tire width direction, and the vicinity of the tread edge part having the radius of curvature of R3 larger than R2 is projected towards the tire outside, and the shape of a crown is made flat, and the difference of the radius on the shoulder side of the tread and the radius on the equator plane becomes small, and the part on the shoulder side of the tread is prevented from being dragged for a road surface, and the generation of the eccentric abrasion is suppressed.

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, and more particularly to a heavy-duty pneumatic radial tire with improved wear resistance and bead durability of the shoulder portion.

[0002]

2. Description of the Related Art Different from general passenger cars, heavy-duty pneumatic radial tires having excellent bead durability are used for vehicles having a large load such as trucks and construction vehicles.

In this type of heavy duty pneumatic radial tire, the ride comfort on rough roads and the envelope property are good, and the durability against belt cut separation is good. A flattening ratio of 90 S or more is mainly suitable for running on a bad road and is frequently used.

[0004]

By the way, in a pneumatic tire, the shape of the carcass changes before and after the internal pressure is filled, and the widthwise central portion of the tread has a slightly larger radius due to the internal pressure filling.

By the way, the carcass shape of the tire has generally been a so-called natural equilibrium shape in which a change in the shape of the tire before and after the internal pressure is filled shows a uniform bulging deformation in order to obtain various performances of the tire.

On the other hand, the conventional flatness ratios 90S and 100
The carcass shape in a heavy-duty pneumatic radial tire such as S is set with an emphasis on preventing the carcass ply end from breaking at the bead portion and the separation of the belt end.
When the radius of curvature of the carcass line of the carcass is R1 at the center of the tread and R2 is just below the end of the belt having the maximum width, the relationship between R1 and R2 is set to R1> R2.

As the carcass line is filled with internal pressure, the carcass line is deformed so that the vicinity of the center of the arc of the large radius of curvature is convex toward the outside of the tire, and the adjacent small radius of curvature is inside the tire. It tends to deform so as to be depressed. That is, in the conventional heavy-duty pneumatic radial tire, when the internal pressure is filled, the carcass line is radially outward in the vicinity of the equatorial plane, the carcass line maximum width position and the bead portion are outwardly of the tire, and The area immediately below the belt edge moves inward of the tire.

As a result, an appropriate compressive stress can be applied to the folded end of the carcass ply under the filling internal pressure, failure of the ply end can be prevented, and at the tread portion, the belt tension is increased to increase the belt tension between the belt layers. It was attempted to reduce the distortion and prevent the separation at the belt end.

In such a tread of a conventional pneumatic radial tire for heavy load, the diameter on the shoulder side tends to be smaller than the diameter on the equatorial plane at the time of filling with internal pressure, but not so much when new. There was no problem.

However, the crown radius is gradually reduced according to the running amount, and accordingly, the rectangular ratio of the ground contact shape is reduced, and the shoulder side portion of the tread is dragged against the road surface, which is called shoulder drop wear. It was found that uneven wear occurs.

In consideration of the above facts, the present invention provides a heavy-duty pneumatic radial tire capable of suppressing the diameter reduction of the crown radius due to running and improving the uneven wear resistance while maintaining the bead durability. That is the purpose.

[0012]

The present invention has an aspect ratio of 90.
For heavy-duty pneumatic radial tires of the above series, with the rim assembled and filled with 10% of the specified internal pressure, the radius of curvature of the carcass line is R at the center of the tread.
1, R2 immediately below the end of the belt having the maximum width, R3 at the carcass maximum width position, and R4 at 70% of the carcass maximum width position height h from the carcass radial innermost position, R1 The relationship with R2 is R1> R2, R2 and R
3 is 1> R3 / R2> 0.55, the relationship between R4 and R3 is R4> R3, and H is the carcass height from the innermost position in the tire radial direction of the carcass, H and h Is characterized in that the relation of 0.45 ≦ h / H ≦ 0.65 is satisfied.

[0013]

The pneumatic radial tire for heavy loads of the present invention is
With the rim assembled and filled with 10% of the specified internal pressure, the radius of curvature of the carcass line is R at the center of the tread.
1, R2 immediately below the end of the belt having the maximum width, R3 at the carcass maximum width position, and R4 at 70% of the carcass maximum width position height h from the carcass radial innermost position, R1 The relationship with R2 is R1> R2, R2 and R
3 is 1> R3 / R2> 0.55, the relationship between R4 and R3 is R4> R3, and H is the carcass height from the innermost position in the tire radial direction of the carcass, H and h Since the relationship of 0.45 ≤ h / H ≤ 0.65 is set, when the normal internal pressure is filled, the carcass line has a carcass maximum width position having a curvature of R3 that hardly changes or is dented inward in the tire width direction. As a result, a force to push the tread end outward in the tire radial direction is exerted, and further, the vicinity of the maximum width belt end having a radius of curvature R2 larger than R3 is convex toward the tire outer side. Deform.

Therefore, when the heavy duty pneumatic radial tire of the present invention is filled with the regular internal pressure, the crown shape is flattened, and the crown shape is also apt to be flattened even when the running amount is increased. In actual running, the diameter of the shoulder side of the tread and the difference between the diameter of the equatorial surface are suppressed from increasing, and the shoulder side portion of the tread is suppressed from being dragged with respect to the road surface, Occurrence of uneven wear is suppressed. That is, the rectangular ratio of the ground contact shape of the tread is suppressed, and the uneven wear resistance is improved as compared with the conventional pneumatic radial tire for heavy load.

Further, the carcass maximum width position is recessed inward in the tire width direction, and 70% of the height h of the carcass maximum width position from the tire radial innermost position of the carcass having a curvature radius R4 larger than R3. When the position tries to project and deform to the outside of the tire, a force in the direction of falling to the outside of the tire acts on the bead portion, so that the durability of the bead portion can be maintained as in the conventional case.

When h / H is less than 0.45,
The carcass maximum width position that displaces to the inside of the tire approaches the bead part, and the part that displaces to the outside of the tire (the part of R4) due to internal pressure filling on the tire shaft side approaches the ply end too much, so that tensile strain is applied to the ply end. , It is easy to cause damage due to separation at the ply end. Further, when h / H exceeds 0.65, the carcass shape of the conventional pneumatic radial tire for heavy load approaches, and the displacement of the tread shoulder side to the tire radial direction outer side due to internal pressure filling is insufficient, resulting in shoulder drop. The effect of suppressing wear cannot be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

In the heavy-duty pneumatic radial tire 10 of the present invention shown in FIG. 1, the carcass ply 12 extending radially is a carcass cord arranged in a direction orthogonal to the tire circumferential direction. It is composed of a coating rubber covering this.

Both ends of the carcass ply 12 in the tire width direction are folded back around the pair of bead cores 14 from the inner side to the outer side in the tire axial direction, and are respectively formed as folded back end portions 12A.

In the bead portion 16 near the bead core 14, a steel cord protective layer 18 is adjacently arranged on the side opposite to the carcass ply 12. The steel protective layer 18 is a steel cord covered with a coating rubber.

Further, an organic fiber protective layer 20 and an organic fiber protective layer 22 are arranged adjacent to each other on the side opposite to the carcass ply 12 of the steel cord layer 18. The organic fiber protective layers 20 and 22 are formed by coating an organic fiber cord such as nylon with a coating rubber.

On the other hand, on the outer side in the tire radial direction of the carcass ply 12, at least three belt layers 24 are formed.
Is provided, and a tread 26 is provided on the outer side of the belt layer 24 in the tire radial direction. A predetermined tread pattern (not shown) is formed on the tread 26.

In the heavy-duty pneumatic radial tire 10 having such a structure, the radius of curvature of the carcass line is R1 at the center of the tread 24 (the center of curvature is the tire with the internal pressure being 10% of the normal internal pressure). (On the equator plane), R2 immediately below the end of the belt having the maximum width, R3 at the carcass maximum width position, and R4 at a position 70% of the carcass maximum width position height h from the innermost position of the carcass ply 12 in the tire radial direction. Sometimes, the relationship between R1 and R2 is R1> R
2, the relationship between R2 and R3 is 1> R3 / R2> 0.55,
Further, the relation between R4 and R3 is R4> R3, and further, when the carcass height from the innermost position of the carcass ply 12 in the tire radial direction is H, the relation between H and h is 0.45 ≦ h. /H≦0.65.

Further, the relation w / W between the distance w of the boundary point a of R1 and R2 from the tire equatorial plane and the tread maximum width W is
The condition is 0.6 ≦ w / W ≦ 0.9. The maximum tread width W as used herein refers to the dimension in the direction along the tire axis from the tire equatorial plane to the shoulder end on one side in the tire axial direction.

The heavy duty pneumatic radial tire 10 of this embodiment has a tire size of TBR-10.00R20 and an aspect ratio of 100.

In the heavy duty pneumatic radial tire 10 of this embodiment, the radius of curvature of the carcass line is R1.
360mm, R2 130mm, R3 90mm, R4 1
The carcass height H is 278 mm and the carcass maximum width position height h is 166 mm. Therefore,
In the heavy duty pneumatic radial tire 10 of the present embodiment,
h / H becomes 0.597.

Further, in the heavy duty pneumatic radial tire 10 of this embodiment, the dimension w from the tread center CL at the intersection a of the radius of curvature R1 and the radius of curvature R2 is 140 mm, and the maximum width dimension W of the tread is 200 mm. Is. Therefore, the heavy-duty pneumatic radial tire 1 of the present embodiment
At 0, w / W is 0.7.

When the maximum width of the carcass is S,
The maximum width dimension W of the tread, W / S, is 0.6.
It is preferable that ≦ W / S ≦ 0.75.

Next, the operation of this embodiment will be described. In the heavy duty pneumatic radial tire 10 of the present embodiment, the radius of curvature of the carcass line is R1 (the center of curvature is on the tire equatorial plane) at the center of the tread 24 in a state of being filled with 10% of the normal internal pressure. R2 immediately below the belt end having a large width, R3 at the carcass maximum width position, and 7 of the carcass maximum width position height h from the carcass ply 12 innermost position in the tire radial direction.
When R4 is set at the 0% position, the relationship between R1 and R2 is R1> R2, and the relationship between R2 and R3 is 1> R3 / R2>.
0.55, the relationship between R4 and R3 is R4> R3, and when the carcass height from the innermost position in the tire radial direction of the carcass ply 12 is H, H and h
Since the relationship of 0.45 ≦ h / H ≦ 0.65 is satisfied, the carcass ply 12 has a curvature of R3 smaller than R2 as shown in FIG. 1 when the normal internal pressure is filled. Significant position is in the axial direction of the tire (direction of arrow A in Figure 1)
The concave portion causes a force to push the tread end portion outward in the tire radial direction (arrow B direction in FIG. 1), and the vicinity of the tread end portion having a radius of curvature R2 larger than R3 is outside the tire. It deforms so that it becomes convex toward.

Therefore, in the heavy duty pneumatic radial tire 10 of the embodiment, the crown shape in the tire cross section, that is, the tread 2 is filled by filling the normal internal pressure.
The tread shape of 6 is flattened in the tire cross section, and
By suppressing the diameter reduction of the crown radius due to running growth, the diameter difference between the center side portion and the shoulder side portion from the tire axis is small on the tread surface of the tread 26, and the diameter difference on the shoulder portion side of the tread 26 is small. The uneven wear at both ends of the tread 26 due to the above can be largely suppressed as compared with the conventional pneumatic radial tire for heavy load.

70% of the height h of the carcass maximum width position from the tire radial innermost position of the carcass ply 12 having a carcass maximum width position recessed inward in the tire width direction and a curvature radius R4 larger than R3. Due to the force of the projecting deformation toward the outside of the tire, a force in the direction of falling toward the outside of the tire (direction of arrow C in FIG. 1) acts on the bead portion.

Further, since the shape change of the bead portion due to the filling of the internal pressure can be maintained as in the conventional case, the durability of the bead portion can be maintained as in the conventional case.

If the relationship h / H between the carcass height H and the carcass maximum width position height h is less than 0.45, the portion displaced outward in the tire axial direction (the portion R4) is the ply end 12.
Since it gets too close to B, a tensile strain is applied to the ply end 12B, so that the ply end 12B is likely to be damaged by the ply end separation. On the other hand, the tread with h / H exceeding 0.65 approaches the carcass shape of the conventional pneumatic radial tire for heavy load, and the change of the shoulder portion to the outer side in the tire radial direction due to the internal pressure filling is insufficient, and the shoulder drop wear is caused. Not effectively improved.

Further, when the distance w of the boundary point a between R1 and R2 from the equatorial plane of the tire and the maximum width W of the tread are w and W, if w / W is less than 0.6, the radius of curvature R2 is large. The area is too wide and the tension is dispersed, the change of the shoulder portion to the outer side in the tire radial direction due to the internal pressure filling cannot be effectively reached, and the reduction of the radius of curvature of the crown radius due to running cannot be sufficiently suppressed. On the other hand, when w / W exceeds 0.9, the carcass shape of the conventional pneumatic radial tire for heavy load approaches the carcass shape, and the change of the shoulder portion to the outer side in the radial direction of the tire due to the internal pressure filling is insufficient, resulting in shoulder drop wear. Not effectively improved.

[Test Example] The heavy-duty pneumatic radial tire 10 of the present embodiment and a conventional heavy-duty pneumatic radial tire were assembled into rims respectively, and the crown radius change rate, the step-down amount at the shoulder side end of the tread, and The durability of the bead portion was tested.

The conventional pneumatic radial tire for heavy load used in the test has a tire size of TBR-10.00R2.
0 and the flatness rate is 100%. Further, in the conventional pneumatic radial tire for heavy load, the radius of curvature of the carcass line at an internal pressure of 10% is R1 of 400 mm and R2 of
Is 100 mm, R3 is 120 mm, R4 is 80 mm, carcass height H is 278, carcass maximum width position height h is 1
It is 66 mm. Also, the radius of curvature R1 and the radius of curvature R
The dimension w from the tread center CL at the intersection a with 2 is
130 mm, belt layer 2 from tread center CL
The dimension W up to the end of No. 4 is 190 mm.

The rate of change in crown radius is determined by assembling each test tire on the rim, filling the tire with a normal internal pressure, and mounting the tire on an actual vehicle to run the load at 100% of the specified load. The curvature of the Earl was measured. The relationship between the change rate of the crown radius and the traveling distance is shown in the graph of FIG. The vertical axis of the graph represents the rate of change of crown radius (100 when the product is new), and the horizontal axis represents the traveling distance. Also, tread 2 after the test
The running growth amount in the cross section of No. 6 is shown in the graph of FIG.

As for the step-down amount, similarly, each test tire was assembled on a rim, filled with a normal internal pressure, and mounted on an actual vehicle, and the load was run at 100% of the specified load.
The amount of wear of both ends of the tread from the time of new article was measured for each predetermined traveling distance. The relationship between the step-down amount and the traveling distance is shown in the graph of FIG. The vertical axis of the graph is the step-down amount from the time of new article at both ends of the tread, and the horizontal axis of the graph is the travel distance.

Further, regarding the durability of the bead portion, similarly, each test tire was assembled on a rim, filled with a regular internal pressure, and mounted on an actual vehicle to run, and the traveling distance up to damage to the bead portion (ply end separation) was measured. However, it is an index display with the mileage when the conventional pneumatic radial tire for heavy load causes damage to the bead portion as 100. The test results are shown in Table 1 below. In addition, in Table 1, the traveling distance is 0 km.
The crown radius at the time point and at the time of 20,000 km, and the step-down amount (wear amount) of the tread end portion at the time of the traveling distance of 50,000 km are also described.

[0040]

[Table 1]

From the test results shown in the graphs of FIGS. 2 to 4, the change rate of the crown radius of the pneumatic radial tire for heavy load of the present invention is smaller than that of the conventional pneumatic radial tire for heavy load, and the tread of the tread It is clear that the shoulder side end has a small step down amount.

[0042]

As described above, since the pneumatic radial tire for heavy loads of the present invention has the above-mentioned constitution, while maintaining the bead durability, it is possible to suppress the diameter reduction of the crown radius due to running and to prevent uneven wear. It has an excellent effect that the property can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a heavy duty pneumatic radial tire according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a change rate of crown radius and a traveling distance.

FIG. 3 is a graph showing a running growth amount in a cross section of a tread.

FIG. 4 is a graph showing a relationship between a step-down amount and a traveling distance.

[Explanation of symbols]

 10 Pneumatic radial tire for heavy load 12 Carcass ply 26 Tread

Claims (1)

[Claims] 1. A pneumatic radial tire for heavy loads having an aspect ratio of 90 series or more, the radius of curvature of the carcass line is R at the center of the tread with the rim assembled and filled with an internal pressure of 10% of the specified internal pressure.
1. R1 immediately below the belt end having the maximum width, R3 at the carcass maximum width position, and R4 at 70% of the carcass maximum width position height h from the carcass radial innermost position, R1 The relationship between R2 and R2 is R1> R2, the relationship between R2 and R3 is 1> R3 / R2> 0.55, and the relationship between R4 and R3 is R4> R3. Where H is h, the relation between H and h is 0.45 ≦ h / H ≦
A pneumatic radial tire for heavy loads, which has a size of 0.65.