JPH07101207A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To suppress the belt end separation and minimize the deterioration of the wear property in a pneumatic radial tire for heavy load. CONSTITUTION:A cross laminated layer is formed by a second belt layer 20 and a third belt layer 22 among four belt layers. The number of placement of steel cords per unit width in the wider belt layer among the cross laminated layers is increased than that in the narrower belt width, and at the same time, the cord strength of the steel cord 25 is reduced than that of the narrower belt layer. The generation of the belt end separation which is generated by the continuous separation at the end part of the belt cord can be delayed because the cord interval of the narrower belt layer is large where th belt end separation is likely to be generated. Increase in the number of placement of thc steel cord 25 per unit width of the wider belt layer compared with that of the narrower belt layer compensates the reduction of the rigidity of the narrower belt layer and suppresses the wear property.

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 used in heavy-duty vehicles such as large trailers.

[0002]

2. Description of the Related Art Heavy-duty pneumatic radial tires are used for vehicles with large loads such as large trailers.
Normally, this heavy-duty pneumatic radial tire is provided with a plurality of belt layers made of steel cords, and the plurality of layers cross each other so that the steel cords incline in opposite directions with the tire equatorial plane sandwiched. At least one set of cross-laminated belt layers that are laminated is provided, and these cross-laminated belt layers are set to have a higher breaking strength per unit width than other belt layers.

Usually, a belt failure is caused by peeling between the rubber and the end of one of the belt cords of one of the intersecting belt layers,
It is common that this leads to separation of the end of the adjacent belt cord and progresses to separation between belt layers.

Therefore, by increasing the strength of each cord and widening the interval between the cords, the time required from the peeling of the belt cord ends to the separation is maintained while maintaining the strength of the entire belt layer. Techniques for increasing durability have been used conventionally. In this case, the cord type used for each belt layer of the cross-lamination was the same, and the number of driving per unit width was also almost the same.

[0005]

However, in the above-mentioned conventional technique, when the belt separation is suppressed, the number of driving per unit width of the two intersecting belt layers is reduced, so that the bending rigidity and the twist of the entire belt layer are reduced. However, there is a problem in that the wear characteristics of the tire are deteriorated because the rigidity of the tire decreases and the movement of the tread surface increases.

In consideration of the above facts, the present invention is intended for heavy loads, in which it is possible to increase the durability by increasing the time from separation of the belt cord end to separation, and to minimize deterioration of tire wear characteristics. It is an object to provide a pneumatic radial tire.

[0007]

According to various investigations by the inventor, the belt end separation has a belt layer that is likely to occur and a belt layer that is not likely to occur among the belt layers, and the belt end separation of the cross-laminated belt layers. Among them, it was found that the belt layer having the smaller width is likely to cause the belt end separation.

The present invention has been made in view of the above facts, and is provided with a carcass whose end portions are locked around the bead core and extends in a toroidal shape, and a belt arranged at the crown portion of the carcass. , The belt is composed of a plurality of belt layers in which steel cords in a parallel arrangement are rubberized, and at least two layers of the belt layers intersect each other so that the steel cords incline in opposite directions with the tire equatorial plane sandwiched therebetween. In the laminated pneumatic radial tire for heavy load, among the belt layers cross-laminated, in the wider belt layer, the number of steel cords to be driven per unit width is smaller than that of the narrower belt layer. It is also characterized by making the strength of the steel cord smaller than that of the narrower belt layer.

[0009]

In the heavy-duty pneumatic radial tire of the present invention, the wider belt layer among the cross-laminated belt layers has a narrower number of steel cords per unit width. And the strength of the steel cord is made smaller than that of the narrower belt layer.

That is, of the cross-laminated belt layers, the one having a narrower width where belt end separation is likely to occur has a larger cord interval, so that peeling between the end portion of the belt cord and the rubber occurs. It is possible to gain time to be connected to the peeling of the end portion of the adjacent belt cord, and to significantly delay the occurrence of belt end separation.

On the other hand, since the number of steel cords per unit width of the steel cord of the wider belt layer is set to be larger than that of the belt layer of the narrower width, the decrease in the rigidity of the belt layer is compensated for and the running growth is increased. Can be suppressed.

That is, in the heavy-duty pneumatic radial tire of the present invention, with the above-mentioned structure, it is possible to achieve both suppression of belt end separation and suppression of running growth.

[0013]

EXAMPLE An example of a heavy duty pneumatic radial tire of the present invention will be described with reference to FIG.

As shown in FIG. 1, a carcass 12 of a heavy duty pneumatic radial tire 10 is formed of one or more carcass plies consisting of cords extending in the radial direction of the tire. Both ends of the carcass 12 are locked around a bead core (not shown) as is well known.

A belt 14 is arranged outside the crown portion of the carcass 12, and a tread 15 is arranged outside the belt 14 in the tire radial direction.

The belt 14 is composed of a plurality of belt layers, in this embodiment, the first belt layer 18, the second belt layer 20, the third belt layer 22, and the fourth belt layer 24 from the carcass 12 side.
It has a number of belt layers. These first belt layers 18,
The second belt layer 20, the third belt layer 22, and the fourth belt layer 24 are steel cords 25 arranged in parallel and coated with rubber, and the steel cords 25 intersect the tire equatorial plane CL at a predetermined angle. ing.

Here, in the belt 14, at least two layers of the plurality of belt layers are steel cords 25 of each other.
Are cross-laminated so as to be inclined in the opposite direction with respect to the tire equatorial plane CL. In this embodiment, the second belt layer 20
Of the steel cord 25 and the steel cord 25 of the third belt layer 22 are inclined in directions opposite to each other with respect to the tire equatorial plane CL, and the second belt layer 20 and the third belt layer 2
And 2 form a crossed stack.

In the present embodiment, the steel cord 25 of the first belt layer 18 is inclined upward to the right so that the angle θ1 with respect to the equatorial plane CL is 50 °, and the steel cord 25 of the second belt layer 20 is equatorial plane. The angle θ2 with respect to CL is inclined to the right and the angle θ2 with respect to the equatorial plane CL is set to 17 °. Further, the steel cord 25 of the third belt layer 22 is inclined to the left with respect to the equatorial plane CL so that the angle θ3 with respect to the equatorial plane CL is 17 °, and the steel cord 25 of the fourth belt layer 24 is The angle θ4 with respect to CL is inclined to the left and the angle θ4 with respect to the equatorial plane CL is 17 °.

The inclination angle θ1 of the steel cord 25 of the first belt layer 18 is 30 ° to 60 °, and the second belt layer 20 is 20 °.
The inclination angle θ2 of the steel cord 25 is 17 ° to 20 °,
The inclination angle 3 of the steel cord 25 of the third belt layer 22 is 1
7 ° to 20 °, steel cord 25 of the fourth belt layer 24
It is preferable that each of the inclinations θ4 is 14 ° to 17 °.

Further, regarding the width of each belt layer of the belt 14, in this embodiment, the width W1 of the first belt layer 18 is 265 mm, the width W2 of the second belt layer 20 is 285 mm, and the third belt layer 22.
Has a width W3 of 260 mm and the fourth belt layer 24 has a width W4 of 13 mm.
It is 5 mm. The width W4 of the fourth belt layer 24 is preferably set to 40 to 80% of the maximum belt width.

Here, the belt 14 is cross-laminated, in the present embodiment, the second belt layer 20 and the third belt layer 22 are other belt layers, and in the present embodiment, the first belt layer 18 and the fourth belt layer 24. The breaking strength per unit width is set larger than that.

Further, in the cross lamination of the belts 14, the number of steel cords of the wider belt layer is C ₁ , the number of steel cords of the narrower belt layer is C ₂ , and the wider one is C ₂ . When the cord strength of the steel cord of one belt layer is S ₁ and the cord strength of the steel cord of the narrower belt layer is S ₂ , C ₁ > C ₂
Moreover, it is preferable that S ₁ <S ₂ .

C ₁ is 12.5 to 15.5 lines / 25 m
It is preferable that m and C ₂ are 8.5 to 11.5 lines / 25 mm.

In the heavy duty pneumatic radial tire 10 of this embodiment, the number of steel cords 25 of each belt driven, the cord strength of the steel cord of each belt layer and the raw treat gauge when each belt layer is subjected to the molding process Is as shown in Table 1 below.

[0025]

[Table 1]

Next, the operation of the heavy duty pneumatic radial tire of this embodiment will be described. In the belt end separation, the generation start point is the end of the belt layer having the smaller width in the cross lamination, but in the pneumatic radial tire for heavy load 10 of the present embodiment, the belt having the smaller width in the cross lamination is used. Since the number of driven steel cords 25 of the third belt layer 22 which is a layer is small, that is, the interval between the steel cords 25 is large, the peeling generated at the ends of the steel cords 25 grows and the ends of the adjacent steel cords 25 grow. It is possible to delay the occurrence of the belt end separation that progresses due to the separation of the parts, and it is possible to improve the durability of the belt 14.

Further, since the cord strength of the steel cord 25 of the third belt layer 22 is increased to prevent the reduction of the belt rigidity due to the reduction of the number of cords to be driven, the bending rigidity and the torsional rigidity of the entire belt 14 can be improved. It can be maintained at a predetermined level, and deterioration of wear resistance due to the decrease in rigidity can be suppressed.

That is, in the pneumatic radial tire for heavy load of the present invention, unlike the conventional pneumatic radial tire for heavy load, one of the wider belt layer and the narrower width of the cross-laminated belt layers is used. By changing the number of steel cords per unit width and the cord strength with the belt layer of, the optimum configuration was found, so the belt end separation was delayed and at the same time abrasion resistance could not be achieved with conventional technology. Can be suppressed.

The modulus of the coating rubber of the third belt layer 22 at 300% elongation is set to be smaller than that of the coating rubber of the second belt layer 20 at 300% elongation, so that the steel cord of the third belt layer 22 is It is possible to suppress the occurrence of cracks generated at the end portions of 25, and thus it is possible to further suppress the occurrence of belt end separation.

(Test Example) A heavy-duty pneumatic radial tire to which the present invention was applied and a conventional heavy-duty pneumatic radial tire were respectively prepared (each having a tire size of 38).
5 / 65R22.5), heat resistance, belt separation resistance, running growth, wear resistance and uneven wear resistance. The test results are shown in Table 3 below.
Shown in.

The specifications of the conventional heavy duty pneumatic radial tire used in the test are shown in Table 2 below, and the other structures are the same as those of the heavy duty pneumatic radial tire to which the present invention is applied. [Test method] Heat resistance: Performed with an indoor drum tester and measured the running distance until belt end separation occurs,
It is expressed by an index with the conventional tire being 100. It should be noted that the larger the value, the better the heat generation durability.

Belt separation resistance: Performed with a drum tester in a room and intermittently applied with a slip angle of 3.5 °,
After 12 hours, the tires were dissected and the crack lengths at the belt ends were compared. Here, the reciprocal of the crack length is defined as the belt separation resistance. In addition, the conventional tire is represented by an index of 100, and the larger the value is, the more excellent the belt separation resistance is.

Amount of running growth: The test was conducted with an indoor drum tester, running for 5000 km with a load of 4250 kgf, and the diameters of the equatorial planes of the tires before and after running were compared. The smaller the numerical value, the smaller the running growth amount.

Abrasion resistance: A tire is mounted on an actual vehicle, a field test is conducted, and after running near to complete abrasion, the abrasion amount is 1 mm.
The mileage per hit was calculated. In addition, the conventional tire is 10
It is represented by an index of 0, and the larger the value, the better the abrasion resistance.

Uneven wear resistance: A tire is mounted on an actual vehicle, a field test is conducted, and after running a predetermined distance, a new tread shape passing through a tread center portion on the surface of the worn tread is hypothesized. The fall height of the shoulder part is expressed as an inverse number. The index is represented by an index with the conventional tire being 100, and the larger the value, the better the uneven wear resistance.

[0036]

[Table 2]

[0037]

[Table 3]

From the test results shown in Table 3 above, the heavy-duty pneumatic radial tire of the present embodiment is superior to the heavy-duty pneumatic radial tire of the conventional structure in heat generation durability, belt end separation resistance, and wear resistance. It was revealed that it was excellent in both sex. Further, in the heavy-duty pneumatic radial tire of this embodiment, the gauge of the cross-lamination is small (because the steel cord of the second belt layer 20 is thin), so that the running growth amount is reduced and the resistance to bias is increased due to the derived effect. Abrasion is also improved.

[0039]

The pneumatic radial tire for heavy loads according to the present invention has the above-mentioned constitution, and therefore has an excellent effect that the occurrence of belt end separation can be suppressed and the deterioration of the wear characteristics of the tire can be minimized. Have.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a heavy duty pneumatic radial tire according to an embodiment of the present invention.

[Explanation of symbols]

 10 Pneumatic radial tire for heavy load 12 Carcass 14 Belt 18 First belt layer 20 Second belt layer 22 Third belt layer 24 Fourth belt layer 25 Steel cord CL Tire equatorial plane

Claims (1)

[Claims] 1. A carcass, the end of which is locked around a bead core and extends in a toroidal shape, and a belt arranged at the crown portion of the carcass, wherein the belt is rubber-lined steel cords arranged in parallel. A pneumatic radial tire for heavy load, comprising a plurality of belt layers, wherein at least two layers of the belt layers are cross-laminated so that the steel cords of the belt layers are inclined in opposite directions with the tire equatorial plane sandwiched therebetween. In the belt layer with the wider width, the number of hammered steel cords per unit width is made larger than that of the belt layer with the narrower width, and the strength of the steel cord is narrower. A pneumatic radial tire for heavy loads, characterized in that it is made smaller than that of one belt layer.