JPH0446805A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To keep the stability of a tread part shape and enhance durability on bad roads by disposing a first belt layer almost in the whole range of a tread part, crossing second and third belt layer cords in the tire circumference direction, and interposing an intermediate rubber layer between an outmost belt layer and the other belt layer. CONSTITUTION:One layer or more of carcass plies 2 are disposed in the direction of a radial and passed from a tread part 1 to a side wall part, and both their ends are wound up around a beat part and hooked Steel belt layers 3 tighten the carcass plies 2 and consist of a first belt layer 3A, second 3B, third 3C and an outmost belt layer 4 nearest the surface of the tread part 1, which layers 3A 4 layer in that order counted from the carcass ply 2 in the tread part direction. An intermediate rubber layer 5 lies between the outmost belt layer 4 and third belt layer 3C, and makes a belt structure separating the outmost belt 4 from the belt layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to improvements in the belt structure of pneumatic radial tires used for large vehicles.

[Prior Art] In conventional heavy-duty pneumatic radial tires, the steel belt layer is usually closest to one or more carcass plies 6, as shown in FIG. 3, and the angle of the cord with respect to the tire circumferential direction is Consisting of a first belt layer 7 with a large diameter, a second belt layer 8, a third belt layer 9, and an outermost belt layer 10, which are laminated on the upper surface of the first belt layer and whose cords have a small angle with respect to the tire circumferential direction and intersect with each other. has been done. In such a tire, the first belt layer 7 is arranged over almost the entire tread portion 11 as shown in the figure, so the carcass ply 6 and the second Not only does it serve as a buffer layer with the belt layer 8 or the third belt layer 9, but it also serves as reinforcement against internal pressure, increasing the rigidity of the entire belt and contributing to dimensional stability. Note that 12 is a side wall portion, and 13 is a bead portion.

On the other hand, as shown in FIG. 4, there is a belt layer having a split structure in which the first belt layer 7 is removed from the center of the tread portion and is divided into parts of both shoulders.

[Problems to be Solved by the Invention] However, in the radial tire of the type shown in FIG. 3 in which the first belt layer 7 is arranged over almost the entire tread portion 11,
Due to the high belt rigidity, there is little deformation of the belt layer, and the deformation of the tread rubber within the contact surface and internal friction caused by deflection due to load are reduced, resulting in excellent shape retention and improved wear resistance. Due to the belt's high rigidity, it has poor ability to follow irregularities such as protrusions on the road surface, and the central part of the tread is easily damaged due to stress concentration due to protrusions, leading to internal cord breakage.

In the radial tire shown in FIG. 4 in which the chaste No. 1 belt layer has a split structure, the tread portion 11, which is easily susceptible to stress concentration, has low rigidity and is made flexible. It is preferable in terms of reducing damage, and has traditionally been used mainly for rough roads, but on the other hand,
As the reinforcing effect of the second belt layer 7 decreases, the outer diameter of the crown portion increases with use, and the shape of the central part of the tread becomes unstable.
This also contributed to the increase in strain at each end of the belt layer 9. Therefore, tires with this structure are suitable for use on rough roads with a short running life, but when adopted as tires for general use, high-speed durability, There was a problem with updateability.

The purpose of this invention is to satisfy both of these characteristics, and to provide a tire that maintains the stability of the tread shape without reducing belt rigidity, and at the same time has excellent tread durability on rough roads against uneven road surfaces. It is in the point of providing.

[Means for Solving the Problems] As explained above, the tire shown in Figure 3 has high belt rigidity because the No. 1 belt is arranged over almost the entire tread area, and the shape of the tread area is Although stable,
Due to its high rigidity, the tread has the disadvantage of being difficult to follow changes in the road surface, and is easily damaged by stress concentration caused by uneven road surfaces.
In the tire shown in Figure 4, the No. 1 belt is divided into left and right parts to reduce the rigidity of the central part of the tread, which is prone to stress concentration, and to provide flexibility and relieve stress. There is a drawback that the increase in outer diameter growth due to the decrease in reinforcing effect induces instability of the tread shape, and the shear strain at the end between the No. 2 and No. 3 belt layers also increases.
The belt and tread durability on rough roads have contradictory characteristics.

Therefore, the present invention proposes a carcass ply having at least one layer arranged in a radial direction, which passes through the tread portion and sidewall portion of the tire, and winds up and locks both ends around the bead portion of the tire, and a carcass ply which is tightened by the carcass ply and has at least three layers. In the heavy-duty pneumatic radial tire having the steel belt layer constructed as described above, the belt layer is further configured to satisfy the following requirements.

■The first belt layer, which is the first belt layer counting from the carcass ply layer in the tread direction, is placed over almost the entire tread area, and the angle of the cord with respect to the tire circumferential direction is 2. It is larger than the cord angle with respect to the tire circumferential direction of the belt of more than one layer.

■Second and third counting from the carcass ply layer in the tread direction
The cords of the second belt layer and the third belt layer are made to cross each other in the tire circumferential direction.

■Among the belt layers, between the outermost belt layer located at the outermost side in the tread direction from the carcass ply layer and the other belt layers, there is an intermediate rubber layer that separates the outermost belt layer from the other belt layers. intervene.

[Function] As described above, in the steel belt layer, the first belt layer counted from the carcass ply layer in the tread direction is arranged over almost the entire tread area, and the cord angle with respect to the circumferential direction of the first belt layer is adjusted as described above. In addition to making the cord angle larger than the cord angle with respect to the circumferential direction of the two or more layers of steel belts laminated on the top surface, the cords of the second belt layer and the third belt layer, counting from the carcass ply layer in the tread direction, are respectively placed around the tire circumference. Since they intersect with each other in the direction, the outer diameter of the crown part increases with use, unlike conventional split structures, and the shape of the central part of the tread does not become unstable, and the belt rigidity does not decrease. without high speed durability,
Updateability is good.

Furthermore, the belt layer of the tire according to the present invention has a structure in which an intermediate rubber layer is interposed between the outermost belt layer and the other belt layers, and the outermost belt layer is separated from the other belt layers. Similar to structural tires, the central part of the tread is made flexible, allowing it to better track bumps and other irregularities on the road surface, helping to alleviate stress.

Therefore, it can be used with durability on both rough roads and general roads.

The thickness of the intermediate rubber layer is preferably approximately uniform in the belt width direction, and the thickness T is preferably set to 3 to 20%, particularly 4 to 10%, of the total tire thickness H in the tire equatorial plane. If the thickness T of the intermediate rubber layer exceeds 20%, the durability will be poor, and if it is less than 3%, a sufficient stress relaxation effect will not be obtained.

Embodiment FIGS. 1 and 2 are a half-sectional view of a heavy-duty pneumatic radial tire according to an embodiment of the present invention, and a conceptual diagram showing a developed state of the belt structure of the tire.

In the drawings, 1 is a tread portion, and 2 is a carcass ply arranged in one or more layers in the radial direction.

Although not shown, the carcass ply 2 passes from the tread portion 1 through the sidewall portion, and both ends thereof are wound up and locked around the bead portion. 3 is this carcass ply 2
In this embodiment, the first steel belt layer tightens the
It is composed of a No. 4 belt layer 3A, a No. 2 belt layer 3B, a No. 3 belt layer 3c, and an outermost belt layer 4 corresponding to the No. 4 belt layer closest to the tread portion 1 surface.

As shown in the figure, the first belt layer 3A is arranged over almost the entire area of the tread portion 1, and the cord angle with respect to the tire circumferential direction is the same as that of the second belt layer 3B and the third belt layer 3C arranged on the upper surface of the tire circumference. The angle is larger than the cord angle with respect to the direction. The second belt layer 3B and the third belt layer 3c are arranged to cross each other in the circumferential direction.

5 is an intermediate rubber layer interposed between the outermost belt layer 4 and the third belt layer 3c, and has a belt structure in which the outermost belt layer 4 is separated from the other belt layers 3. Note that T is the thickness of the intermediate rubber layer in the tire's equatorial plane, and H is the total thickness H of the tread portion in the tire's equatorial plane.

Example 1.2 Next, tires with different intermediate rubber layer thicknesses were made as trial tires with tire sizes of 11R24, 516PR, and tested and compared with tires of conventional structure. Table 1 shows the results.

Table 1 (Note 1) Thickness T of intermediate rubber layer Dimensions (m/m) in the tire equatorial plane.

(Note 2) Durability Durability is load 3189 kg, internal pressure 8.4 kg/cm
2 rims 8.25 x 24.5, after 24 hours of break-in running at 48/h + e/h on a drum testing machine, the drum speed was increased in 8/1/h steps every 12 hours, leading to failure. It was evaluated based on speed and time.

(Note 3) Outer diameter growth In the above durability test, the drum tester was used at 481v/h.
The outer diameter dimension was measured after running for 24 hours at /H.

(Note 4) Belt rigidity 38ψ Belt rigidity was determined by measuring the drag force when the plunger reached four times the total tire thickness at the tread equatorial plane.

(Note 5) Envelope characteristics: On top of a cylindrical projection with a diameter of 16 m/ya and a height of 8 Il/111, a load of 2800 kg and an internal pressure of 7.7 kg/
Load the tire under the specified conditions of cm2 rim 8.25 x 24.5, measure the diameter (average value in the circumferential direction and width direction of the tire) of the non-contact area of the tread surface created by the cylindrical protrusion, and calculate this value as the tread diameter. It was evaluated as a static envelope characteristic, which is a surrogate characteristic for measuring the stress concentration in the area. The larger the value, the better the envelope characteristics due to stress relaxation.

In addition, both tests are also shown as an index with Comparative Example 1 set as 100.

As shown in Table 1, compared to the tire of Comparative Example 1, in which the No. 1 belt layer is arranged over almost the entire tread area, the tire of the example has improved envelope characteristics, and has flexibility in the center of the tread area. It has been found that this material has the effect of imparting flexibility, improving the ability to follow unevenness such as protrusions on the road surface, and alleviating local stress concentration. At the same time, the outer diameter growth is significantly less than that of the tire of Comparative Example 2, in which the first belt layer has a split structure, and the durability and belt rigidity are maintained at a level almost similar to that of the tire of Comparative Example 1. is recognized.

[Effects of the Invention] As explained above, in the heavy-duty pneumatic radial tire according to the present invention, the first belt layer counted from the carcass sprue I in the tread direction is arranged over almost the entire tread area, and the first belt layer The cord angle with respect to the circumferential direction of the layer is made larger than the cord angle with respect to the circumferential direction of two or more layers of steel belts laminated on the upper surface, and the second belt layer and the third belt are counted from the carcass ply to the tread direction. A structure in which the cords of the layers cross each other in the tire circumferential direction, and an intermediate rubber layer is interposed between the outermost belt layer closest to the tread and the other belt layers, so that the outermost belt layer is free. Therefore, the durability of the tread portion on rough roads can be improved without reducing the belt rigidity, and the durability of the tire can be maintained at a good level.

[Brief explanation of the drawing]

FIG. 1 is a half-sectional view of a heavy-duty pneumatic radial tire according to an embodiment of the present invention, FIG. 2 is a conceptual diagram showing the developed state of the belt structure of the same tire, and FIGS. 3 and 4 are conventional examples. FIG.

Claims (2)

[Claims] (1) Pass through the tread and sidewall of the tire,
A heavy-duty pneumatic radial tire having a carcass ply of at least one layer arranged in the radial direction, the ends of which are rolled up and locked around a bead portion, and a steel belt layer consisting of at least three or more layers that tighten the carcass ply. In the steel belt layer, the first belt layer counted in the tread direction from the carcass ply is arranged over almost the entire tread area, and the cord angle with respect to the circumferential direction of the first belt layer is determined by the two or more layers laminated on the top surface. The cord angle is made larger than the cord angle with respect to the circumferential direction of the steel belt, and the cords of the second belt layer and the third belt layer, counting from the carcass ply to the tread direction, are crossed with each other in the tire circumferential direction, and the carcass ply layer A heavy-duty pneumatic pump characterized in that an intermediate rubber layer is interposed between the outermost belt layer disposed on the outermost side and the other belt layers to separate the outermost belt layer from the other belt layers. radial tire. (2) The pneumatic radial tire for heavy loads according to claim 1, wherein the thickness T of the intermediate rubber layer is in the range of 3 to 20% of the total thickness H of the tread portion in the tire equatorial plane.