JP2003276407A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire having greatly reduced rolling resistance while maintaining good ride comfort performance and control stability. <P>SOLUTION: The pneumatic radial tire comprises a carcass layer 4 mounted between bead portions 3, 3, a belt layer 7 arranged on a tread portion 1, and sectionally triangular bead fillers 6 arranged on outer end portions of circular bead cores 6. A rubber composition constituting the bead filler 6 has a JIS-A hardness of 80 or more. The bead filler 6 has a height of 35 mm or lower and a cross section area X satisfied with a relationship, 1.1×H×W/2<X <1.6×H×W/2, where W is the width of the bottom of the bead filler 6, H is the height from the bottom up to a peak and X is the cross section area. A rubber composition constituting a sidewall rubber layer 2a outside at least the carcass layer 4, out of a rubber member existing in a buttress region B ranging from an edge 7e of the belt layer 7 to a tire maximum width position m has a JIS-A hardness of 50 or less. <P>COPYRIGHT: (C)2003,JPO

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 in which rigidity distribution is optimized according to tire parts, and more specifically, pneumatic tires in which ride comfort performance, steering stability, and rolling resistance are improved in a well-balanced manner. Concerned radial tires.

[0002]

2. Description of the Related Art In pneumatic radial tires, it is desired to simultaneously improve a plurality of tire performances such as riding comfort performance, steering stability and rolling resistance. Among them, the rolling resistance not only affects the fuel efficiency of the vehicle but also causes the deterioration of the global environment due to the large consumption of fuel, and thus it is desired to be reduced as much as possible. Demand for tires that meet these requirements is on the rise in the future.

As a technique for simultaneously improving the performance of a plurality of tires, for example, Japanese Patent Laid-Open Nos. 11-28916, 9-193636, and 8-132830 have been proposed.

Japanese Laid-Open Patent Publication No. 11-28916 aims at improving steering stability and riding comfort damping of a tire without deteriorating road noise and rolling resistance of the tire as much as possible. Therefore, a carcass that extends in a toroidal shape across a pair of bead cores, and a pneumatic radial tire that includes a bead filler that extends along the carcass while adjoining the bead cores and that extends beyond the maximum tire width position, a bead filler The upper part of the bead filler is formed by a narrow width part in cross section, and the lower part of the bead filler is formed by a wide width part in cross section. However, when the upper portion of the bead filler made of hard rubber is extended to the outer side in the tire radial direction from the tire maximum width position, deterioration of rolling resistance cannot be avoided.

JP-A-9-193636 aims at reducing rolling resistance and improving curb cutting resistance. Therefore, in a pneumatic tire having a pair of bead portions, a sidewall portion connected to these bead portions, and a tread portion that straddles both sidewall portions, and in which a carcass layer is mounted between the pair of bead portions. In each bead part, a bead filler is arranged so that the gauge in the vicinity of the tip of the rim flange is extremely thick and becomes thinner toward the tread part, and the winding part of the carcass layer is arranged along the bead filler and at the outside thereof. A reinforcement layer is arranged. When the bead filler has a special shape in this manner, it is possible to reduce energy loss due to compression bending deformation of the bead filler and reduce rolling resistance. However, if you try to achieve both rolling resistance and other tire performance such as riding comfort and steering stability,
There is no choice but to increase the bead filler by increasing the amount of filler rubber used, and as a result, it becomes difficult to reduce the rolling resistance.

JP-A-8-132830 aims at improving steering stability while suppressing deterioration of riding comfort performance. Therefore, the bead filler has a constricted portion on the tire radial direction inner side than the tire maximum width position, and a portion on the tire radial direction outer side of the constricted portion forms the tire maximum width position while forming a substantially crescent-shaped cross-sectional shape. It extends beyond. Also in this case, since the upper part of the bead filler made of hard rubber is extended to the tire radial direction outer side from the tire maximum width position, deterioration of rolling resistance cannot be avoided.

That is, it is not possible to improve the ride comfort performance, steering stability and rolling resistance in a well-balanced manner simply by devising the cross-sectional shape of the bead filler as described above.
In particular, it is difficult to reduce rolling resistance.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire capable of significantly reducing rolling resistance while maintaining good riding comfort performance and steering stability.

[0009]

In the pneumatic radial tire of the present invention for achieving the above object, a carcass layer is mounted between a pair of left and right bead portions, and a belt layer is provided on an outer peripheral side of the carcass layer in a tread portion. A pneumatic radial tire in which a bead filler having a triangular cross-section is disposed on the outer end portion of the annular bead core embedded in each bead portion, JIS-A of the rubber composition constituting the bead filler.
When the hardness is 80 or more, the width of the bottom of the bead filler is W, the height from the bottom to the apex of the bead filler is H, and the cross-sectional area of the bead filler is X, the height H Is 35 mm or less, the cross-sectional area X satisfies the relationship of 1.1 × H × W / 2 <X <1.6 × H × W / 2, and from the edge of the belt layer to the tire maximum width position. Among the rubber members existing in the region (1), at least the rubber composition constituting the sidewall rubber layer outside the carcass layer has a JIS-A hardness of 50 or less.

The rolling resistance of a tire is the energy consumed by the repeated deformation associated with the rolling of the tire, and the amount of this energy is compared with that of each portion such as the tread portion and the sidewall portion constituting the tire. It is known that the tread area is the largest. Therefore, it is possible to reduce the rolling resistance by making the rubber gauge of the tread portion thin, but in this case, the deterioration of the durability of the tire cannot be avoided.

On the other hand, when the energy loss during rolling was investigated in detail with respect to the portion excluding the tread portion, the portion with large energy loss was a region from the edge of the belt layer to the tire maximum width position (buttless region), It was found to be the top of the bead filler. A large energy loss is generated in the buttress region mainly because a large compressive stress is generated in the portion at the time of grounding. Also,
The bead filler undergoes compressive deformation in the upper part as it collapses, but the dissipation of the stress is greatly affected by the height of the bead filler.

According to the present invention, based on the above findings, the rigidity of the buttress region is lowered, the height of the bead filler having high rigidity is lowered, and the tire rigidity is optimized to reduce energy loss, Rolling resistance is reduced. In addition, since the spring constant in the lateral direction of the tire is increased by specifying the hardness and cross-sectional area of the bead filler, even if the rolling resistance is reduced, riding comfort performance and steering stability are maintained well. It is possible to

In the present invention, in addition to the JIS-A hardness of the rubber composition constituting the sidewall rubber layer in the buttress region being 50 or less, JIS-A of the rubber composition coating the carcass cord of the carcass layer. If the hardness is 50 or less, the rolling resistance can be further reduced. Also,
If at least one belt reinforcing layer having a cord angle with respect to the tire circumferential direction of 0 ° to 5 ° is arranged at a position corresponding to the edge of the belt layer, and the rigidity in the tire circumferential direction is supplemented, riding comfort performance and The steering stability can be further improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a pneumatic radial tire according to an embodiment of the present invention, in which 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the pair of left and right bead portions 3, 3, and an end portion of the carcass layer 4 is folded back around the annular bead core 5 from the tire inner side to the outer side. A bead filler 6 having a triangular cross section is arranged on the outer end of the bead core 5.

On the other hand, the carcass layer 4 in the tread portion 1
A plurality of belt layers 7 are embedded on the outer peripheral side of the. The belt layers 7 are arranged such that the cords are inclined with respect to the tire circumferential direction and the cords intersect each other between the layers. A belt reinforcing layer 8 having a cord angle of 0 ° to 5 ° with respect to the tire circumferential direction is arranged at a position corresponding to the edge 7e of the belt layer 7.

In the pneumatic radial tire, the height of the bead filler 6 is made lower than usual, its cross-sectional area is made larger, and the rigidity of the rubber member arranged in the buttress region B is made lower, so that the riding comfort performance is improved. It is possible to reduce rolling resistance while maintaining good steering stability.

Of the rubber composition constituting the bead filler 6
JIS-A hardness is 80 or more, more preferably 80 to 100
To If this hardness is less than 80, steering stability becomes insufficient. When the width of the bottom of the bead filler 6 is W, the height measured from the bottom of the bead filler 6 to the apex in the tire radial direction is H, and the cross-sectional area of the bead filler 6 is X, the height H is 35 mm. Or less, more preferably 20
The cross-sectional area X is 1.1 × H × W / 2 <X <
The relationship is 1.6 × H × W / 2. That is, the bead filler 6 is lower than usual and thicker than the triangular shape in which both corners and apex of the bottom are connected by a straight line. This height H is 35
If it is more than mm, the effect of reducing rolling resistance cannot be obtained. Further, if X ≦ 1.1 × H × W / 2, the lateral spring constant of the tire is insufficiently increased, resulting in insufficient steering stability. Conversely, X ≧ 1.6 × H × W / When it is 2, the riding comfort performance is insufficient.

Among the rubber members existing in the buttress region B, the rubber composition constituting at least the sidewall rubber layer 2a outside the carcass layer 4 has a JIS-A hardness of 50 or less, more preferably 45 to 50. This hardness is 50
If it is too high, the riding comfort performance will be insufficient. In the tire meridian cross section, the buttress region B is a straight line L1 orthogonal to the carcass layer 4 passing through the outermost edge 7e of the belt layer 7 in the tire width direction, and a straight line L1 passing through the tire maximum width position m and parallel to the tire axial direction. It is defined by the straight line L2. Of course, the above hardness can also be applied to the rubber member such as the inner liner layer existing in the buttress region B.

The JIS-A hardness of the rubber composition (coat rubber) covering the carcass cord of the carcass layer 4 is 50 or less,
More preferably, it should be 45 to 50. This hardness is 5
By setting it to 0 or less, the rolling resistance can be further reduced.

The cord angle with respect to the tire circumferential direction is substantially 0 at a position corresponding to the edge 7e of the belt layer 7.
It is preferable to arrange the belt reinforcing layer 8 having an angle of °. That is, when the hardness of the rubber member existing in the buttress region B is reduced to lower the rigidity in the tire circumferential direction, the riding comfort performance and the steering stability are degraded.
To make up for it. As the cord of the belt reinforcing layer 8, it is preferable to use an organic fiber cord represented by an aramid fiber cord having low heat generation and high elasticity.

[0022]

EXAMPLES In a pneumatic radial tire having a tire size of 205 / 65R15 94H, the height H of the bead filler, the width W of the bottom of the bead filler, the cross-sectional area X of the bead filler, and the cross-sectional area ratio X / (H × W / 2 ), JIS-A hardness of sidewall rubber, JIS-A hardness of bead filler rubber, JIS-A hardness of carcass coat rubber, comparative tires 1 to 5 and tires 1 to 1 of the present invention in which the presence or absence of a belt reinforcing layer is variously changed. I made 3 respectively. The belt reinforcing layer is composed of aramid fiber cords (1100 dtex / 2) arranged substantially at 0 ° with respect to the tire circumferential direction.

With respect to these test tires, rolling resistance, steering stability, and riding comfort performance were evaluated by the following methods,
The results are shown in Table 1.

Rolling resistance: Test tire with rim size 15
Assembled on a 6.5JJ wheel, drum diameter 1707m
m drum tester, air pressure 200 kPa, load 4
The resistance was measured under the conditions of kN and speed of 50 km / h, and this was defined as rolling resistance. The evaluation results are shown by an index with the comparative tire 1 (conventional tire) being 100, using the reciprocal of the measured value. A larger index value means less rolling resistance.

Steering stability: Test tire with rim size 15
Installed on a 6.5 JJ wheel, mounted on a domestic 2.5-liter class test vehicle, and a test course consisting of a flat peripheral circuit under air pressure of 200 kPa for 60 to 120
The vehicle was driven at a speed of km / h, and the steering characteristics when changing lanes and cornering and the stability when going straight were evaluated by three specialized panelists. The evaluation results are shown by an index with the comparative tire 1 (conventional tire) being 100. The larger the index value, the better the steering stability.

Riding comfort: Test tire with rim size 15
Attached to a 6.5 JJ wheel, mounted on a domestic 2.5 liter class test vehicle, and run a straight test course with unevenness at 50 km / h under the condition of air pressure of 200 kPa, and the reaction by 3 specialized panelists An evaluation was made. The evaluation result is 100 for the comparative tire 1 (conventional tire).
It was shown by the index. The larger the index value, the better the riding comfort performance.

[0027]

[Table 1]

As is clear from Table 1, the tires 1 to 3 of the present invention have improved rolling resistance, steering stability and riding comfort as compared with the comparative tire 1. Comparative tire 2 has a lower bead filler than comparative tire 1, and as a result, steering stability and riding comfort performance have deteriorated. In Comparative Tire 3, the bead filler rubber was too soft and the steering stability was reduced. In Comparative Tire 4, the riding comfort performance was deteriorated because the bead filler was too thick. In Comparative Tire 5, the riding comfort performance was deteriorated because the sidewall rubber was too hard.

[0029]

As described above, according to the present invention, the carcass layer is mounted between the pair of left and right bead portions, the belt layer is arranged on the outer peripheral side of the carcass layer in the tread portion, and the carcass layer is embedded in each bead portion. In a pneumatic radial tire in which a bead filler having a triangular cross-section is arranged on the outer end of an annular bead core, JIS-A hardness of the rubber composition constituting the bead filler is 80 or more, and the bottom of the bead filler is Is W, the height from the bottom to the apex of the bead filler is H, and the cross-sectional area of the bead filler is X, the height H is 35 mm or less and the cross-sectional area X is 1.1 ×.
Of the rubber members existing in the region from the edge of the belt layer to the maximum width position of the tire in the relationship of H × W / 2 <X <1.6 × H × W / 2, at least the sidewall rubber outside the carcass layer. By adjusting the JIS-A hardness of the rubber composition that constitutes the layer to 50 or less, the distribution of tire rigidity was optimized, so rolling resistance was greatly reduced while maintaining good ride comfort and steering stability. can do.

[Brief description of drawings]

FIG. 1 is a half sectional view showing a pneumatic radial tire according to an embodiment of the present invention.

[Explanation of symbols]

1 tread section 2 Side wall part 2a Side wall rubber layer 3 bead part 4 carcass layers 5 bead core 6 bead filler 7 Belt layer 7e edge 8 Belt reinforcement layer m tire maximum width position H Bead filler height W bead filler bottom width

Claims (3)

[Claims] 1. A carcass layer is mounted between a pair of left and right bead portions, a belt layer is arranged on an outer peripheral side of the carcass layer in a tread portion, and an outer bead portion of an annular bead core embedded in each bead portion is disposed. In a pneumatic radial tire in which a bead filler having a triangular cross section is arranged, JIS-A hardness of the rubber composition constituting the bead filler is 80 or more, and the width of the bottom portion of the bead filler is W, and the bead filler is Where H is the height from the bottom to the apex, and X is the cross-sectional area of the bead filler, the height H is 35 mm or less, and the cross-sectional area X is 1.1 × H × W /
2 <X <1.6 × H × W / 2, and at least the sidewall rubber layer outside the carcass layer among the rubber members existing in the region from the edge of the belt layer to the tire maximum width position. A pneumatic radial tire having a JIS-A hardness of 50 or less for the rubber composition constituting the. 2. The JIS-A hardness of the rubber composition coating the carcass cord of the carcass layer is 50 or less.
Pneumatic radial tire as described in. 3. The air according to claim 1, wherein at least one belt reinforcing layer having a cord angle with respect to a tire circumferential direction of 0 ° to 5 ° is arranged at a position corresponding to an edge of the belt layer. Radial tires with.