JPH06297910A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire with desirable high speed durability by dividing a tread part into a center area and both side areas in the width direction, and setting the circumferential tension of a hoop reinforced layer, corresponding to these areas, larger in each side area than in the center area. CONSTITUTION:A tire is provided with a tread part 8 reinforced by a belt 4 and a hoop reinforced layer 7. In the tread part 8, the 75% area of the tread width W with the tread center circumference as the center is made a center area 9, and each width direction outside of the center area 9 is made a side area 10. The circumferential tension of the hoop reinforced layer 7 corresponding to these areas 9, 10 is to be 2.5% in the center area 9 and 4% in the side area 10, in the coefficient of extension after curing to the time of being attached to a BT drum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire having excellent high-speed durability while suppressing increase in tire mass and cost as much as possible.

[0002]

2. Description of the Related Art Pneumatic radial tires cause radial expansion due to centrifugal force generated during high-speed running, and this radial expansion tends to cause belt separation and deteriorate high-speed durability. Therefore, a hoop formed by spirally winding a strip-shaped strip made of a rubberized layer of a plurality of heat-shrinkable cords such as nylon 6 and nylon 66 so as to substantially wrap the entire outer periphery of the belt on the outside in the radial direction of the belt. A technique is known in which a reinforcement layer is provided to suppress expansion in the tire radial direction and ensure high-speed durability. Further, in the conventional manufacturing method, generally, the circumferential tension in the lateral region of the tread portion is smaller than the circumferential tension in the central region, so that the tire radial expansion easily occurs in the lateral region, which is prevented. In order to do so, it was necessary to provide a narrow hoop reinforcing layer in the lateral region as well as the hoop reinforcing layer.
Therefore, in the conventional pneumatic radial tire, high-speed durability is ensured by appropriately disposing the hoop reinforcing layer in a portion where expansion in the tire radial direction occurs.

[0003]

However, in the above-mentioned tire, it is essential to add a hoop reinforcing layer as a condition for suppressing the expansion in the radial direction, but this is accompanied by an increase in the tire mass, so that the rolling resistance is increased. Has a drawback that the fuel efficiency is deteriorated, and the belt structure is complicated because it is appropriately arranged at the portion where expansion in the tire radial direction occurs, which is also disadvantageous in terms of productivity and cost. It was Further, since the rigidity in the tire width direction is unbalanced, steering stability may be adversely affected.

It is therefore an object of the present invention to develop a pneumatic radial tire having good high speed durability without the addition of a hoop reinforcing layer which causes an increase in tire mass and cost.

[0005]

SUMMARY OF THE INVENTION The present invention provides a toroidal carcass of at least one ply which is substantially orthogonal to a plane containing the tread circumference on an outer periphery of a relatively small angle to the plane. A belt composed of at least two layers of high elastic modulus rubberized layers arranged in a crossed arrangement,
On the outer periphery of the belt, a hoop reinforcing layer made of a rubberized layer of at least one heat-shrinkable cord that is arranged substantially parallel to the plane is provided, and a belt and a tread portion reinforced by the hoop reinforcing layer are provided. In a radial tire, the tread portion is divided into a central region and both side regions in the width direction, and the circumferential tension in each side region of the hoop reinforcing layer corresponding to these regions is greater than the circumferential tension in the central region. It is a pneumatic radial tire characterized by being large.

FIG. 1 shows a cross section in the width direction of a typical pneumatic radial tire according to the present invention. In the figure, 1 is a pneumatic radial tire, 2 is a carcass, 3 is a rubberized layer, 4 is a belt, and 5 is a cap. A layer, 6 is a layer layer, 7 is a hoop reinforcing layer, 8 is a tread portion, 9 is a central region, and 10 is a lateral region. A pneumatic radial tire 1 shown in FIG. 1 has a toroidal carcass 2 consisting of one ply, which is arranged substantially orthogonal to a plane including a tread circumference, on a periphery of the toroidal carcass 2. A belt 4 composed of two layers of rubberized layer 3 having a high elastic modulus cord, and a cap layer which substantially envelops the entire outer periphery of the belt 4 and which is a substantially parallel arrangement of heat-shrinkable cords with respect to the plane. 5
And a hoop reinforcing layer 7 that covers both ends of the cap layer 5 and that is composed of a pair of narrow layer layers 6 having a substantially parallel arrangement of heat-shrinkable cords with respect to the plane, and the belt 4 and the hoop reinforcing layer 7 A reinforced tread portion 8 is provided, and the tread portion 8 is divided into a central region 9 and side regions 10 in the width direction, and the hoop reinforcing layer 7 corresponding to these regions 9 and 10 is provided in each side region 10. The circumferential tension is characterized by being larger than the circumferential tension in the central region 9. The central area 9 and the lateral areas 10 are 20% to 85% of the tread width W centered on the central circumference of the tread.
And the lateral areas are areas that extend outward in the width direction from the central area.

In the manufacture of tires, usually, a belt, a hoop reinforcing layer, and a tread rubber are stuck on a flat BT drum to form a ring member, and the ring member is fitted to the outer circumference of the green case, and then the diameter of the green case is reduced. In this case, the flat tire is replaced by the flat BT drum instead of the flat BT drum in the case of the inventive tire shown in FIG. 1a. A drum 11 (FIG. 1b) having a curved shape is used, and a belt member, a hoop reinforcing layer 7, and a tread rubber are laminated on the drum 11 to form a ring member, which is manufactured by the same manufacturing process as described above. is doing. The drum 11 at this time
It is preferable that at least the curvature of the position corresponding to the lateral region 10 of the tread portion 8 is smaller than the curvature of the cavity surface of the corresponding vulcanization mold 12, and the tread portion 8
The shape of the drum 11 corresponding to the central area 9 of the
It may be flat or have some curvature as long as the circumferential tension at 0 is greater than the circumferential tension at the central region 9. Further, as a method for making the circumferential tension in each side area 10 larger than the circumferential tension in the central area 9, in addition to the above-described method, stretching when sticking the hoop reinforcing layer 7 onto the drum is performed by stretching the width of the drum. However, the method is not limited thereto. The number of hoop reinforcing layers 7 is preferably one from the viewpoint of mass and cost, but it can be slightly increased if necessary in consideration of high-speed durability. Cord rubberized layer 3 of belt 4
Arranges the high elastic modulus cords intersecting the tire equatorial plane at relatively small angles, preferably at 24 to 34 °.

[0008]

In the conventional pneumatic radial tire 1, the inner liner and the carcass ply are laminated on the drum, the bead cores are set at the ends of these, and the bead cores are folded back around them to form a green case into a shape close to the crown of the product tire. Then, a ring member formed by laminating a belt, a hoop reinforcing layer and a tread rubber on a flat BT drum 13 (FIG. 2) different from the drum is fitted to the outer circumference of the green case, and then the green case is radiated. The green case and the ring member are integrated by performing expansion molding, and the integrated green tire is vulcanized and cured. In this manufacturing method, the inner diameter of the ring member when bonded to the flat BT drum is substantially the same in the width direction, and the tension when bonding is generally constant in the width direction. On the other hand, the green case is molded so that its outer shape is close to the crown of the product tire. Therefore, when the ring member is fitted into this green case and vulcanized and cured, a force is applied to the ring member in an attempt to expand it in the radial direction of the tire, and the ring member is finally molded into the crown shape of the product tire. It However, the rate at which the ring member is expanded in the radial direction by this molding is different in the width direction of the ring member, that is, the rate is large in the central region of the tread portion and small in the lateral region. The circumferential tension applied to the member also increases in the central region and decreases in the lateral regions. For this reason, the circumferential tension required in the lateral region of the tread portion, which tends to expand in the tire radial direction due to centrifugal force during high-speed running, tends to be insufficient. Therefore, in the case of the tire manufactured by the above manufacturing method, a hoop reinforcing layer had to be additionally provided at a position corresponding to the lateral region of the tread portion in order to secure high-speed durability.

On the other hand, according to the present invention, at least one hoop reinforcing layer 7 is provided on the outer circumference of the belt 4, and the circumferential tension of the hoop reinforcing layer 7 is properly adjusted in the width direction of the belt 4. That is, by setting the circumferential tension in the lateral region 10 to be larger than that in the central region 9, when a large centrifugal force is generated in the tire during high speed running, the lateral region 10 of the tread portion 8 The radial expansion of the tire is suppressed. Further, unlike the conventional case, it is not necessary to newly provide a narrow layer layer or the like for reinforcing the lateral region, so that the belt structure is not complicated.

[0010]

EXAMPLES Specific examples of the pneumatic tire according to the present invention will be described with reference to the drawings. -Example 1 The tire used in Example 1 is the invention tire shown in FIG. 1a, and the tire size is 255 / 40ZR17. This tire is a belt in which two steel cord rubberized layers 3 are cross-laminated on the outer circumference of a toroidal carcass 2 consisting of two plies of rubberized layers in which rayon cords are arranged at 90 ° to the tire equatorial plane. 4 and one cap layer 5 that substantially envelops the entire outer periphery of the belt 4 to form a parallel arrangement of nylon cords with respect to the plane, and covers both ends of the cap layer 5, and a parallel arrangement of nylon cords with respect to the plane. The hoop reinforcing layer 7 is formed of a pair of narrow layer layers 6 and the tread portion 8 reinforced by the belt 4 and the hoop reinforcing layer 7. In the tread portion 8, 75% of the tread width W centering on the tread center circumference is defined as a central area 9, and the widthwise outside of the central area 9 is defined as a lateral area 10. The circumferential tension of the corresponding hoop reinforcing layer 7 is set to the expansion ratio after vulcanization which is different when the hoop reinforcing layer 7 is attached to the BT drum, and the central region 9
Was 2.5% and lateral area 10 was 4%. This tire was manufactured by a method of forming a ring member with a BT drum having the above-mentioned curvature.

Example 2 The tire used in Example 2 is substantially the same as the tire used in Example 1 except that the layer layer 6 is not provided. -Conventional example The tire used in Example 1 is almost the same as that of the tire used in Example 1 except that the hoop reinforcing layer is attached to the flat BT drum with a uniform tension in the width direction of the drum together with the belt and the tread rubber.

Test method The test was conducted for high speed durability, and also for tire mass and cost. The high-speed durability is as follows: Under the conditions of a tire internal pressure of 250 kPa and a load mass of 50 kg, the above-mentioned test tire is load-rolled on a drum, and the rotational speed of the drum is increased by 10 km / h every 20 minutes. It was evaluated by measuring the rotation speed and time of the drum when the failure occurred. Table 1 shows these results. The numerical values in the table are all represented by an index ratio with the conventional example being 100, and the higher the high-speed durability is, the better the tire mass and the lower the cost are.

[0013]

[Table 1]

From the above results, Example 1 and Example 2
Is superior to the conventional example in high-speed durability. In particular, Example 2 is superior to the conventional example in high-speed durability, and has a reduction in tire mass and cost, despite having no layer layer.

[0015]

According to the present invention, at least one hoop reinforcing layer 7 is provided on the outer circumference of the belt 4, and the circumferential tension of the hoop reinforcing layer 7 is properly adjusted in the width direction of the belt 4. Specifically, the circumferential tension is set to be larger in the lateral region 10 than in the central region 9, so that when a large centrifugal force is generated in the tire during high-speed traveling, the lateral region 10 of the tread portion 6 is generated.
Since expansion of the tire in the radial direction can be suppressed, belt separation can be prevented, and as a result, sufficient high-speed durability can be obtained. Also, since it is not necessary to provide a hoop reinforcing layer that has been newly added to conventional tires,
It is also advantageous in terms of tire mass and cost.

[Brief description of drawings]

FIG. 1A is a cross-sectional view of essential parts in the width direction of an inventive tire used in Example 1, and FIG. 1B is a cross-sectional view of a BT drum used to form a ring member of the inventive tire in Example 1 in the width direction. It is a principal part sectional view when it cut | disconnects, c is a width direction principal part sectional view at the time of charging a green tire in a vulcanization metal mold.

FIG. 2 is a cross-sectional view of essential parts when a normal flat BT drum used to form a ring member of a conventional tire used in a conventional example is cut in the width direction.

[Explanation of symbols]

 1 Pneumatic radial tire 2 Carcass 3 Rubberized layer 4 Belt 5 Cap layer 6 Layer layer 7 Hoop reinforcement layer 8 Tread portion 9 Central area 10 Side area 11 BT drum 12 Vulcanizing mold 13 Flat BT drum W Tread width

Claims (1)

[Claims] 1. A toroidal carcass consisting of at least one ply that is arranged substantially orthogonal to a plane including the tread circumference, and at least two layers of a toroidal carcass which are arranged in an intersecting arrangement at a relatively small angle with respect to the plane. A belt made of a rubberized layer of a high elastic modulus cord, and a hoop reinforcing layer made of a rubberized layer of at least one heat-shrinkable cord which is arranged substantially parallel to the plane on the outer periphery of the belt, and a belt. In a pneumatic radial tire having a tread portion reinforced with a hoop reinforcement layer, the tread portion is divided into a central region and both side regions in the width direction, and each side region of the hoop reinforcement layer corresponding to these regions. The radial radial tire is characterized in that the circumferential tension in is larger than the circumferential tension in the central region.