JPH09150603A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire having good resistance to partial wear and good handling stability by making the roadholding shape of the tire a proper shape projecting at the center of the crown in a circumferential direction. SOLUTION: A distance A between the right and the left folded back ends of the carcass ply 2 of a tire is about 25 to 85 % of the cross sectional width of a belt. A rubber sheet 5 having the thickness substantially equal to the thickness of the carcass ply 2 is disposed at the crown part such that it abuts on both folded ends of the carcass ply across the center part of the crown and the complex modulus (E') of the rubber sheet is 50 to 100 kg/cm<2> and the loss tangent (tanδ) is 0.05 to 0.25.

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 for passenger cars, and in particular, to a bead core provided on a pair of left and right bead portions, and to both bead portions from a crown portion through both side portions. A carcass ply made of a radial cord layer that extends and folds the bead core from the inside to the outside and extends to the crown part through both side parts; and a layer arranged outside the crown part radial direction of the carcass ply. A belt comprising the above cord layers and a tread arranged radially outward of the belt are provided, and the distance between the left and right folded edges of the carcass ply is about 25 to 85% of the sectional width of the belt. It concerns a pneumatic radial tire for a passenger car.

[0002]

2. Description of the Related Art Conventionally, a pneumatic radial tire for a passenger vehicle extends from a crown portion through both side portions to both bead portions, and the bead core is folded back from the inside to the bead portions. Tires with carcass plies arranged in radial cord layers are common. However, from the viewpoint of reducing the weight of the tire and improving the productivity, a so-called envelope structure in which the folded edge of the carcass ply is extended to the crown portion via both side portions without being stopped at both bead portions is preferable.
In that case, the distance between the left and right folded end edges of the carcass ply is set to about 25 to 85% of the sectional width of the belt. If it is less than 25%, the tire manufacturing becomes difficult, and if it is more than 85%, the belt end, the carcass ply end and the side tread end overlap, which may cause a trouble. Because.

[0003]

However, the pneumatic radial tire for passenger cars having the carcass ply of the so-called envelope structure as described above has a ground contact shape in the center of the crown, which is circumferentially recessed at both ends of the crown. There is a disadvantage that the tire has an abnormal ground contact shape that is convex in the circumferential direction at the portion (see FIG. 3), and as a result, the uneven wear resistance characteristics and steering stability performance of the tire deteriorate.

An object of the present invention is to solve the problems of the prior art as described above, and to make the ground contact shape of a pneumatic radial tire for passenger cars having an envelop structure carcass ply as described above into a crown central portion. By providing a normal convex shape in the circumferential direction (see FIG. 2), it is possible to provide a tire having excellent uneven wear resistance and steering stability.

[0005]

In order to achieve the above object, a pneumatic tire of the present invention comprises a bead core provided on a pair of left and right bead portions, and both bead portions from a crown portion through both side portions. A carcass ply consisting of a radial cord layer, which extends to the crown portion via both side portions by folding back the bead core from the inside to the outside,
The carcass ply includes a belt formed of one or more cord layers arranged radially outside the crown portion, and a tread arranged radially outside the belt, and the left and right folded edges of the carcass ply are provided. In a pneumatic tire in which the distance between them is about 25 to 85% of the sectional width of the belt, (1) one of the carcass plies has a rubber sheet having a thickness substantially equal to the thickness of the carcass plies. Of the carcass ply so as to be adjacent to the folded edge of the carcass ply and to be adjacent to the other folded edge of the carcass ply. (2) The complex elastic modulus (E ′) of the rubber sheet is 50 to A pneumatic radial tire having a loss tangent (tan δ) of 0.05 to 0.25 at 100 kg / cm ² . In order to achieve the above object, in the pneumatic radial tire of the present invention, the thickness of the rubber sheet is preferably 0.5 to 2.0 mm.

In the pneumatic tire of the present invention, as described above, the rubber sheet having a thickness substantially equal to the thickness of the carcass ply is adjacent to one of the folded end edges of the carcass ply and has a crown central portion. Since the carcass ply is arranged in the crown portion so as to be adjacent to the other folded back edge of the carcass ply, there is no step in the thickness between the left and right folded edges of the carcass ply, and the ground contact shape of the tire has The part has a normal shape that is convex in the circumferential direction, and thus a tire having excellent uneven wear resistance and steering stability can be obtained. The thickness of the rubber sheet is preferably 0.5 to 2.0 mm, and outside this range, the difference in thickness from the carcass ply becomes large and the ground contact shape of the tire deteriorates.

In the pneumatic tire of the present invention, the complex elastic modulus (E ') of the rubber sheet is 50 to 100 k as described above.
The loss tangent (tan δ) is 0.05 to 0.25 at g / cm ² . The complex elastic modulus (E ') of the rubber sheet is 5
When it is less than 0 kg / cm ² , workability during tire production is deteriorated, and there arises a problem that steering stability performance and uneven wear resistance of the product tire are deteriorated. When it is more than 100 kg / cm ² , work during tire production is performed. Performance deteriorates, and the riding comfort performance and uneven wear resistance performance of the product tire deteriorate. Also, the loss tangent (tan) of the rubber sheet
When δ) is less than 0.05, the rubber itself cannot be sufficiently reinforced and the durability of the tire is deteriorated. On the other hand, when it is more than 0.25, the heat resistance is deteriorated and the durability of the tire is deteriorated. It causes a problem that the value decreases.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention and conventional examples will be described below with reference to the drawings. Both have tire sizes of 185R14. A tire according to an embodiment of the present invention shown in FIG. 1 includes a bead core 1 provided at a pair of left and right bead portions, and a bead core 1 extending from a crown portion to both bead portions via both side portions from inside to outside. Fold back to extend through both sides to the crown,
A carcass ply 2 made of a radial cord layer, a belt 3 made of two layers of cords arranged radially outside the crown portion of the carcass ply 2, and a tread 4 arranged radially outside the belt 3. Is equipped with. The distance A between the left and right folded edges of the carcass ply 2 is 96 mm, and the belt sectional width B is 136 mm, so A / B is 71%. Carcass ply 2
Of the carcass ply 2 is adjacent to one of the folded end edges of the carcass ply 2 through the center of the crown and is adjacent to the other folded end edge of the carcass ply. It is located in. The complex elastic modulus (E ′) of this rubber sheet 5 is 72.4 kg / cm ^2.
Therefore, the loss tangent (tan δ) is 0.199.

The pneumatic tire of the conventional example is substantially the same as the pneumatic tire of the above-described example except that the rubber sheet 5 is not provided.

The pneumatic tire of the example according to the present invention and the pneumatic tire of the conventional example were subjected to a comparative test of ground contact shape, uneven wear resistance and steering stability.
As a comparative test condition of the ground contact shape, a test tire mounted on a regular rim 5-1 / 2JJ and filled with a regular internal pressure of 4.5 kg / cm ² was statically loaded with a regular load of 840 kg, and a rectangular ratio was measured. As shown in FIG. 2, the rectangular ratio is obtained by measuring the circumferential length E of the central portion of the ground contact surface of the tire and the circumferential lengths F and G at a position of 80% to the left and right from the central portion. F + G)
It is a value calculated by / 2E. The test for uneven wear resistance is
This is based on a general road test. The steering stability test was carried out by mounting the tires on the regular rim 5-1 / 2JJ and the test tires filled with the regular internal pressure of 4.5 kg / cm ² on the vehicle and traveling on the test course at a speed of 40 to 120 km / h. did.

The rectangular ratio was 85% for the pneumatic tires of the above examples according to the present invention, but 98% for the pneumatic tires of the above conventional examples. The test results of uneven wear resistance are
The pneumatic tire of the above-mentioned conventional example had uneven wear due to dragging in the center portion, whereas the pneumatic tires of the above-mentioned examples according to the present invention were in a substantially uniform worn state. When compared with the pneumatic tires of the above-described examples, the pneumatic tires of the above-described examples according to the present invention obtained far superior results in a feeling evaluation by a steering stability test driver.

[0012]

From the above evaluation results, the pneumatic tires of the examples according to the present invention have a ground contact shape of a normal shape which is convex in the circumferential direction at the center of the crown as compared with the conventional pneumatic tire. By doing so, it is understood that the uneven wear resistance property and the steering stability performance are improved.

[Brief description of the drawings]

FIG. 1 is a meridional section schematic view of a pneumatic tire according to the present invention.

FIG. 2 is a schematic view of a normal ground shape.

FIG. 3 is a schematic diagram of an abnormal ground shape.

[Explanation of symbols]

 1 bead core 2 carcass ply 3 belt 4 tread 5 rubber sheet

Claims (2)

[Claims] 1. A bead core provided on a pair of left and right bead portions, and a crown portion extending to both bead portions through both side portions, and the bead core is folded back from the inner side to the outer side and crowned through both side portions. A carcass ply made of a radial cord layer extending to a part, a belt made of one or more cord layers arranged radially outside the crown part of the carcass ply, and a belt radially arranged outside the belt. A pneumatic tire having a tread, wherein the distance between the left and right folded end edges of the carcass ply is about 25 to 85% of the sectional width of the belt,
(1) A rubber sheet having a thickness substantially equal to the thickness of the carcass ply is adjacent to one of the folded end edges of the carcass ply and passes through the center of the crown to the other folded end edge of the carcass ply. (2) the complex elastic modulus (E ′) of the rubber sheet is 5
A pneumatic radial tire having a loss tangent (tan δ) of 0.05 to 0.25 at 0 to 100 kg / cm ² . 2. The rubber sheet has a thickness of 0.5 to 2.0.
The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire has a diameter of mm.