JP2980353B2 - Pneumatic radial tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a belt structure of a pneumatic radial tire, and particularly to a large construction vehicle, such as a heavy construction vehicle, which is used for traveling on unpaved rough roads under heavy load conditions. Or truck
For pneumatic radial tires used for heavy loads for buses,
A belt structure with improved durability is proposed.

[Prior art] Pneumatic radial tires traveling on uneven terrain or unpaved roads are scattered with stumps after cutting, rocks and crushed lumps,
This not only causes a decrease in durability life due to tire tread cut damage, but also when such cut damage penetrates the belt as a reinforcing element of the tread rubber layer, a gap between the tread and the belt caused by this damage. Separation may occur.

In such a case, the loss time of tire replacement is enormous, so that the operability of a vehicle for traveling on uneven terrain such as an expensive large construction vehicle or a large vehicle for traveling on a bad road is reduced.

Therefore, effective prevention of belt separation, particularly separation between treads and belts, due to tire trend trauma during running on uneven terrain or unpaved roads is desired.

To cope with this problem, Japanese Patent Application Laid-Open No. 59-199304 discloses a technique in which the outermost layer of the belt is arranged with cords having lower bending stiffness than the remaining layers and having a higher driving density.

Also, in Japanese Patent Application Laid-Open No. 63-38007, a reinforcing portion for reinforcing the outside of the large-diameter cord with a smaller-diameter cord is provided for the large-diameter cord constituting the belt portion, and the reinforcing portion is generated at the belt end. There is a method in which the same strain as the shear strain is generated at the end of the reinforcing portion to reduce the strain stress at the end of the belt, thereby improving the durability of the belt.

However, no consideration has been given to properly arranging coating rubbers having different hardnesses, so that the occurrence of such separation cannot be sufficiently prevented.

[Problems to be Solved by the Invention] A more advantageous belt reinforcing structure without the drawbacks associated with the measures taken to enhance the cut resistance of the conventional belt described above does not cause any particular disadvantage in terms of tire cost. It is, therefore, an object of the present invention to propose a pneumatic radial tire for traveling on rough terrain, which is, of course, free from the occurrence of heat generation.

[Means for solving the problems] This invention comprises a radial carcass, a pneumatic radial tire having a belt retainer band tightening the crown portion, the outermost layer of the trunk layer of the belt cord diameter phi _A (Mm)
Metal cords are arranged obliquely with respect to the tire equatorial plane.
The outermost layer of the protective layer, which is embedded in the covering rubber A having a spring-type hardness (A type) of _HA and is disposed radially outward of the main trunk layer, has a cord diameter φ _B smaller than the cord. the metal cords of (mm) inclined arrangement with respect to the tire equatorial plane, will be JIS spring hardness (a type) is embedded in coating rubber B is H _B, cord diameter phi _a, phi _B and coating rubber _A pneumatic radial tire characterized in that hardness H _A H _B satisfies the following equation: 1.0 <H _A / H _B <(φ _A / φ _B ) ^1/2 , wherein a main trunk layer constituting a belt and Among the protective layers, the main trunk layer is usually composed of a plurality of layers arranged so as to cross each other with the tire equatorial plane interposed therebetween, and plays a main role of reinforcing the belt.

On the other hand, the protective layer is disposed outside the main trunk layer in the tire radial direction, and plays a role of protecting the main trunk layer.

In the case of radial tires for large construction vehicles, a plurality of protective layers are usually provided.However, in the case of radial tires for relatively small construction vehicles and radial tires for trucks and buses on rough roads, the protective layer is usually a single layer. There are many.

It is preferable JIS spring type hardness H _A of the coating rubber A in order to satisfy the belt reinforcing of such trunk layer is 60 to 80.

(Operation) In the case of a pneumatic radial tire for heavy loads on rough terrain or rough roads, it is common to use a large-diameter cord for the belt in order to suppress heavy loads and high internal pressure. In this case, the strain stress of the belt can be reduced, but heat generation occurs due to an increase in the volume of the entire crown portion in order to obtain belt rigidity, and sufficient durability cannot be obtained.

Also, if the hardness of the covering rubber is low, the belt rigidity is reduced, and the belt durability is impaired.

On the other hand, in the case of a heavy-duty pneumatic radial tire for rough terrain or rough roads, the factor that affects the cut resistance of the belt is the cut input (the tread is dent-shaped when riding on a convex part such as rocks). ) Is a large deformation, and considering that it is a constant-strain input (the tread is recessed by the height of the rock), the bending rigidity of the belt and the breaking strength (strength) of the steel cord used for the belt And the like.

First, the bending stiffness of the belt affects the so-called envelope property, which means that the tread of the tire rides on a convex part such as rocks scattered on the surface of the ground, meaning that it wraps around it. The smaller the value, the more advantageous. Therefore, the smaller the number of laminated layers of the belt, the smaller the steel cord of the belt, and the lower the hardness of the coated rubber, the more advantageous.

About the breaking strength of the cord, it means whether or not the steel cord breaks when the sharp ridge of the rock fragment enters the rubber layer from the cut flaw generated in the tread,
A large diameter cord having a large breaking strength is advantageous.

By the way, in order to prevent the cut penetrating the tire belt from progressing to the separation at the boundary between the tread and the belt, the rubber covered with the steel cord plays a major role, and according to experiments and studies by the inventor, It has been found that the lower the hardness of the coated rubber, the better.

Therefore, if the belt is functionally separated into a main layer and a protective layer, a large-diameter cord and a high-hardness coated rubber are arranged in the main layer, and a small-diameter cord and a low-hardness coated rubber are appropriately arranged in the protective layer, the belt rigidity can be improved. , While improving the cut resistance.

When the relationship between rubber hardness and cord diameter is H _A / H _B > (φ _A / φ _B ) ^1/2 , there is a large difference in rigidity at the interface between the outermost layer of the main trunk layer and the protective layer formed by the small diameter cord. It is not preferable because of excessive distortion and distortion.

In addition, the coating rubber A of the main trunk layer preferably has a JIS spring-type hardness (A type) of 60 to 80 from the viewpoint of the durability of the main trunk layer and the protective layer.

In addition, in the cord for reinforcing the main trunk layer and the protective layer, organic fibers such as polyester fibers, aliphatic polyamide fibers, and aromatic polyamide fibers can be used.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a heavy-duty pneumatic radial tire used for large construction vehicles and the like.
Has a carcass 2 reinforced by cords arranged in a radial direction, and a main trunk layer 4 of a belt for tightening and strengthening a crown portion 3 of the carcass.

The main trunk layer 4 is composed of at least one belt layer A, preferably a plurality of layers in which cords 6 for reinforcing the belt layer A intersect with each other across the equatorial plane. In this example, the main trunk layer 4 has three layers.

Further, a protective layer 5 that protects the main trunk layer 4 is provided outside the tire of the main trunk layer 4 in the radial direction. This protective layer 5
The cords 7 for reinforcing the single layer or the belt layer B are constituted by a plurality of layers intersecting with each other with the equatorial plane interposed therebetween. In this example, the cords 7 are constituted by a single layer.

Cord diameter phi _A code 6 for reinforcing the belt layer A is larger than the cord diameter phi _B of the cord 7 for reinforcing the belt layer B, trunk layer 4, the so-called hoop clamping a circumferential main tension member of the crown part 3 Has an action.

The protective layer 5 functions not only as an auxiliary tension member for reinforcing the main trunk layer 4 but also as a protective layer for protecting the main trunk layer from external damage.

The code 6 of the belt layer A is JI specified by JIS K6301.
S spring hardness (A type) is embedded in the coating rubber 8 H _A, code 7 is also JIS spring hardness of the reinforcing layer B (A type) is embedded in the coating rubber 9 H _B.

By making the hardness H _A of the covering rubber 8 harder than the hardness H _B of the covering rubber 9, the movement of the cord 6 of the highly rigid belt layer A is suppressed as much as possible, while using a soft rubber for the covering rubber 9. In addition, it enhances envelope properties and suppresses the progress of separation due to trauma.

The coating rubbers H _A and H _{B of} the belt layers A and _B and the cord diameters φ _A and φ _B are H _A / H _B <(φ _A / φ _B ) ^1/2 and (φ _A / phi _B) by reducing the H _a / H _B than ^1/2, it is possible to avoid stress concentration on the rubber interface 12 by extreme hardness difference of the coating rubber 8 and 9.

Tire Test: Next, test examples will be described. The tires used for testing were pneumatic radial tires for heavy loads on rough roads, size 1
8.00R33, and its sectional view is shown in FIG.

The three belt layers constituting the main trunk layer 4 have a cord diameter of 1.89.
The 7x7 + 1 mm metal cord is 69 degrees to the upper right, 69 degrees to the left, and 69 degrees to the upper right from the radial inside of the tire with respect to the equatorial plane.
They are crossed in degrees.

The belt layer B serving as the protective layer 5 has a cord diameter of 1.06 mm and 1 ×
5 × 0.38mm single twist metal cord goes up to the equatorial plane
It is crossed at 69 degrees with the main layer and the outermost layer.

Covered rubber with the above configuration in common, as shown in the attached table
Tires having JIS spring type (A type) hardness were subjected to the test.

Note that (φ _A / φ _B ) ^1/2 is 1.34.

The diameter of the metal cord is the average value of all cord diameters measured at four cross sections on the tire circumference.

As shown in the attached table, for each of the five prototype tires, a cut was made to reach the protective layer 5 of the belt from the surface of the tread, and after pouring the same amount of water from the wound, a drum tester with an outer diameter of 5 m was applied. Again, tire internal pressure 7kg / cm ² , load 10900kg
During running at a speed of 30 km / h under the conditions described above, the time required for cut separation to occur was compared in an index notation with the result of the control (Comparative Example) being 100.
The larger the index, the better.

 The results are shown in the lower column of the separate table.

From this result, it can be seen that in Examples 1 to 3 based on the present invention, the belt durability was significantly improved.

[Effects of the Invention] As described above, according to the present invention, a main trunk layer composed of a large diameter cord and a protection layer composed of a small diameter cord are provided. In a pneumatic radial tire provided with a layer, cut resistance and cut separation resistance can be simultaneously improved, and the tire can be used for various tires.

[Brief description of the drawings]

FIG. 1 is a meridian sectional view of a tire showing one embodiment of the present invention, and FIG. 2 is an explanatory view of a main part of an outermost layer of a main trunk layer and a protective layer. 4 ... Main layer 5 ... Protective layer 6 ... Main layer outermost layer code 7 ... Protective layer reinforcing cord 8 ... Main layer outermost layer covering rubber 9 ... Protective layer covering rubber A ... Outer layer of main layer B ... … Protective layer

Claims (3)

(57) [Claims] 1. A pneumatic radial tire having a radial carcass and a belt for fastening a crown portion thereof, wherein the outermost layer of a main trunk layer of the belt has a cord diameter φ _A (mm).
Metal cords are arranged obliquely with respect to the tire equatorial plane.
The outermost layer of the protective layer, which is embedded in the covering rubber A having a spring-type hardness (A type) of _HA and is disposed radially outward of the main trunk layer, has a cord diameter φ _B smaller than the cord. the metal cords of (mm) inclined arrangement with respect to the tire equatorial plane, will be JIS spring hardness (a type) is embedded in coating rubber B is H _B, cord diameter phi _a, phi _B and coating rubber _A pneumatic radial tire characterized in that hardness H _A H _B satisfies the following expression: 1.0 <H _A / H _B <(φ _A / φ _B ) ^1/2 . 2. The coated rubber A has a JIS spring hardness H _A of 60.
2. The pneumatic radial tire according to claim 1, wherein the number is from 80 to 80. 3. The pneumatic radial tire according to claim 1, wherein the main trunk layer of the belt portion is constituted by a plurality of layers arranged so as to cross each other with an equatorial plane interposed therebetween.