JP2011143859A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which suppresses deterioration in adhesion property due to heat generation by suppressing the heat generation in traveling without deteriorating durability against failure due to cut input. <P>SOLUTION: The pneumatic tire includes at least one layer of carcass ply 2 formed by rubber-coating a steel cord. Flexural rigidity of the steel cord is not less than 380 kg/mm<SP>2</SP>and not more than 500 kg×mm<SP>2</SP>. Hysteresis loss is not more than 3.5 kg×mm. The embedding number of steel cords is preferably not less than 3.3 pieces/50 mm and not more than 5.5 pieces/50 mm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pneumatic tire (hereinafter, also simply referred to as “tire”), and more particularly to a heavy-duty pneumatic radial tire with an improved carcass ply reinforcement cord.

  Since heavy duty tires travel mainly on wasteland and are susceptible to cut scratches, high durability is required. However, if the tread rubber layer is thickened to ensure such durability, the tire weight increases, so that there is a problem that the heat generated by the rubber increases due to repeated strain during running.

  Also, in order to ensure such durability, if a steel cord with a large-diameter double twist structure (generally a steel cord with high tensile strength) is applied to the carcass ply, the tire weight will also increase. Due to the repeated strain at the time, the heat generation of the rubber becomes high. Further, in this case, the steel cord having a double twist structure generates a large hysteresis loss at the time of bending deformation, so that the cord itself has high heat generation.

  As an improved technique related to a heavy load tire, for example, Patent Document 1 discloses a carcass layer in a tread portion for the purpose of improving cut resistance and chip resistance while ensuring good heat resistance and durability. Four belt layers are provided on the outer peripheral side, and the reinforcement cords of the second and third belt layers located second and third from the carcass layer side are arranged so as to intersect each other with the inclination direction with respect to the tire circumferential direction reversed. A heavy-duty pneumatic radial tire is disclosed in which the No. 2 and No. 3 belt layers are each divided into three in the tire width direction, and the left and right division positions of the No. 2 belt layer and No. 3 belt layer are respectively defined as predetermined. Has been.

JP-A-10-250313 (Claims etc.)

  As described above, if the tread rubber layer is thickened or a thick steel cord is applied for the purpose of ensuring the durability of the tire, the tire weight increases, so that The fever becomes high. When heat generation during driving increases, the deterioration of rubber physical properties is promoted, so separation problems starting from the end of the steel cord and separation due to a decrease in the adhesion between the rubber and the steel cord are more likely to occur. As a result, the durability of the tire was impaired.

  Accordingly, an object of the present invention is to provide a pneumatic tire that solves the above-described problem, suppresses heat generation during running without impairing durability against failure due to cut input, and suppresses a decrease in adhesiveness due to the heat generation. It is to provide.

  As a result of intensive studies, the present inventor has found that the above problems can be solved by using a steel cord having a specific property value as a steel cord used for a carcass ply, and has completed the present invention.

That is, the pneumatic tire of the present invention is a pneumatic tire provided with at least one layer of carcass ply formed by rubber-coating a steel cord.
The steel cord has a bending rigidity of 380 kg / mm ² or more and 500 kg · mm ² or less, and a hysteresis loss of 3.5 kg · mm or less.

  In the present invention, it is preferable that the number of driven steel cords is 3.3 / 50 mm or more and 5.5 / 50 mm or less. The pneumatic tire of the present invention is particularly suitable as a heavy duty pneumatic tire.

  According to the present invention, the above configuration realizes a pneumatic tire that suppresses heat generation during traveling without impairing durability against a failure caused by a cut input and suppresses a decrease in adhesion due to the heat generation. It became possible to do.

It is a width direction one side sectional view showing a pneumatic tire of an example of the present invention. It is a schematic fragmentary sectional view which shows the driving state of the steel cord in a carcass ply. It is a graph which shows the distortion-load curve of a steel cord. It is explanatory drawing which shows the measuring method of bending rigidity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional side view in the width direction of a pneumatic tire according to an example of the present invention. The illustrated tire includes a pair of left and right bead portions 11, sidewall portions 12 extending outward in the tire radial direction, and a tread portion 13 that forms a grounding portion straddling both sidewall portions 12, A single layer of carcass ply 2 formed in a toroidal shape across the bead cores 1 embedded in the bead portions 11 and covered with a steel cord, and the crown region thereof is arranged on the outer side in the tire radial direction and arranged in parallel. Further, the belt 3 is provided with at least one layer, preferably 4 to 6 layers, and in the illustrated example, 6 layers, in which reinforcing cords are crossed between the laminated layers.

In the present invention, it is important to use a steel cord constituting the carcass ply 2 having a bending rigidity of 380 kg / mm ² or more and 500 kg · mm ² or less and a hysteresis loss of 3.5 kg · mm or less. It is. By using a steel cord that satisfies the above properties as the steel cord constituting the carcass ply 2, the heat generation caused by the carcass cord during traveling is reduced, the deterioration of the adhesion between the rubber and the cord is suppressed, and the heat generation caused It has become possible to realize a pneumatic tire with improved durability against failure. The hysteresis loss of the steel cord is defined as the shaded portion surrounded by the strain-load curve of the steel cord as shown in FIG. 3 as the energy loss when the steel cord is loaded and removed. The

When the bending rigidity of the steel cord constituting the carcass ply 2 is less than 380 kg · mm ² , that is, when the cord diameter is thin, the tensile strength becomes low, and a predetermined safety factor as a tire cannot be secured. End up. On the other hand, when the bending rigidity of such a steel cord exceeds 500 kg · mm ² , that is, when the filament diameter constituting the cord is large, the fatigue property of the steel cord itself deteriorates due to repeated input due to rolling of the tire. End up. Moreover, when the hysteresis loss of such a steel cord is higher than 3.5 kg · mm, the effect of reducing the heat generation during traveling cannot be obtained, so the effect of the present invention cannot be obtained and the adhesion of the carcass ply will not be improved. . In the present invention, the bending rigidity of the steel cord constituting the carcass ply 2 is preferably 400 kg / mm ² or more and 500 kg · mm ² or less, and the hysteresis loss is preferably 2.7 kg · mm or more and 3. 3 kg · mm or less.

  FIG. 2 is a cross-sectional view showing a state in which the steel cord 20 is driven in the carcass ply 2. In the present invention, the number of driven steel cords 20 in the carcass ply 2 is preferably 3.3 / 50 mm to 5.5 / 50 mm, more preferably 4.0 / 50 mm to 5.0 / 50 mm or less. When the number of driving is larger than 5.5 / 50 mm, the tire weight becomes heavy, so that it becomes difficult to obtain the effect of reducing heat generation. In addition, since the interval between adjacent cords is narrowed and the cracks at the cord ends are likely to progress, separation from the cord ends is likely to occur. On the other hand, when the number of driving is less than 3.3 / 50 mm, the tire weight is reduced, but the number of driving is reduced, so that it is difficult to obtain a predetermined safety factor as a tire.

  Furthermore, as a steel cord to be applied to the carcass ply 2, it is preferable to use a cord having a multiple twist structure in which a plurality of core strands and sheath strands obtained by twisting a plurality of steel filaments are twisted together. In particular, both the strands and the cords themselves are preferably twisted in the same direction. Furthermore, such a strand preferably has a three-layer twisted structure in order to ensure the fatigue resistance of the cord itself. In the present invention, the values of the bending stiffness and the hysteresis loss can be adjusted within the above ranges by appropriately selecting the diameter and number of filaments constituting the steel cord, the twist pitch (twist angle), the twist method, and the like. it can.

  In the present invention, the steel cord constituting the carcass ply 2 only needs to satisfy the above conditions, and the conditions of the rubber composition of the coating rubber covering the cord, each component of the tire other than the carcass ply, etc. Is not particularly limited.

  For example, in the illustrated example, the carcass ply 2 is folded and locked around the bead core 1 from the inside to the outside of the tire. Further, a tread pattern is appropriately formed on the surface of the tread portion 13, and an inner liner (not shown) is formed in the innermost layer. Further, in the tire of the present invention, as the gas filled in the tire, normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

  The pneumatic tire of the present invention is suitable as a heavy duty pneumatic tire, and in particular, can be suitably applied to a large tire having a TRA standard of 51 inches or more according to the US tire standard.

Hereinafter, the present invention will be described in more detail with reference to examples.
A pneumatic tire having a tire size of 4000R57 was manufactured by using a carcass ply steel cord that satisfies the conditions shown in the following table. The carcass ply has one layer. The bending rigidity and hysteresis loss of the steel cords in the table below are shown in FIG. 4 using a test sample obtained by removing the vulcanized rubber to the thickness of the cord diameter after vulcanizing the rubberized cord. It was calculated from a strain-load curve obtained when bending at three points at a distance of 10 cm and a test speed of 10 mm / min. About the obtained tire, durability was evaluated regarding tire temperature and adhesiveness according to the following.

<Tire temperature>
Each test tire is filled with air pressure described in the TRA standard, loaded with a normal load, run on the indoor drum at an average speed of 20 km / h for 15000 minutes, and then measured the temperature of the carcass ply cord at the maximum bend did. Further, this temperature is indicated by an index with the temperature of the conventional example as 100. The smaller the index value, the lower the temperature and the smaller the heat generation.

<Adhesiveness>
The carcass ply cord was taken out from each of the test tires after running the indoor drum, and the rubber coverage at the maximum bent portion was examined to evaluate the adhesion. The higher the coverage, the better the adhesiveness.

  As shown in the above table, in each example using a steel cord satisfying the conditions of the present invention for the carcass ply, the temperature increase of the carcass ply is higher than that of the conventional example and the comparative example not satisfying the conditions. It can be suppressed, and it can be seen that the adhesiveness is improved.

1 Bead core 2 Carcass ply 3 Belt 11 Bead portion 12 Side wall portion 13 Tread portion 20 Steel cord

Claims (3)

In a pneumatic tire provided with at least one layer of carcass ply formed by rubber-coating a steel cord,
A pneumatic tire, wherein the steel cord has a bending rigidity of 380 kg / mm ² or more and 500 kg · mm ² or less and a hysteresis loss of 3.5 kg · mm or less.   2. The pneumatic tire according to claim 1, wherein the number of driven steel cords is 3.3 / 50 mm or more and 5.5 / 50 mm or less.   The pneumatic tire according to claim 1 or 2, which is a heavy duty pneumatic tire.

Images