JPH06106922A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire wherein weight can be lightened without worsening fatigue resistance in a side wall part. CONSTITUTION:A rubber layer of side wall parts 2, 2' is constituted of inner side rubber layers 2d, 2'd and outer side rubber layers 2u, 2'u different from each other in a tire radial direction, the inner side rubber layers 2d, 2'd are constituted of foaming rubber having a closed cell, and the outer side rubber layers 2u, 2'u are constituted of nonfoaming rubber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire which enables weight reduction without deteriorating fatigue resistance of sidewall portions.

[0002]

2. Description of the Related Art As a global environmental protection measure against recent acid rain, global warming, etc., further reduction of fuel consumption of automobiles is required, and as a part thereof, weight reduction of pneumatic tires is strongly demanded. There are various possible measures for reducing the weight of this pneumatic tire, but as in the invention disclosed in Japanese Patent Laid-Open No. 62-199506 proposed for the purpose of improving weather resistance, the sidewall portion is made of foamed rubber. That is one effective means.

However, since the foamed rubber has low fatigue resistance and cut resistance, if it is used as it is as the rubber layer of the sidewall portion, it is possible to sufficiently secure the durability which is the originally required characteristic of the sidewall portion. There was a problem that I could not do it.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire which can be reduced in weight without deteriorating the fatigue resistance of the sidewall portion.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to form a rubber layer of a sidewall portion with an inner rubber layer and an outer rubber layer which are different from each other in a tire radial direction, and the inner rubber layer is a closed cell. It is possible to achieve this by forming the outer rubber layer from a non-foamed rubber.

As described above, the non-foamed rubber having excellent fatigue resistance and cut resistance is arranged in the rubber layer corresponding to the flex zone on the outer side of the tire in the radial direction of the sidewall portion where severe bending strain is applied, and the high hardness bead filler is used. By arranging foamed rubber in the rubber layer on the inner side in the radial direction of the tire reinforced by, for example, it is possible to reduce the weight of the pneumatic tire while ensuring the fatigue resistance which is the originally required characteristic of the sidewall portion.

In the present invention, the sidewall portion is
It refers to "the part between the tread and the bead" specified in the JATMA automobile tire safety standard edition, and does not include the rim cushion part. Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is a pneumatic radial tire. In the figure, 1 is a tread portion, 2 and 2'are sidewall portions, 3 and 3'are rim cushion portions, 4 is a carcass layer, and 5 and 5'are bead cores.

Both ends of the carcass layer 4 are respectively folded back from the inside of the tire to the outside of the bead cores 5 and 5'so as to wrap the bead fillers 6 and 6 '. On the outer peripheral side of the carcass layer 4 corresponding to the tread portion 1, two belt layers 7 and 7'are arranged so as to intersect each other at a cord angle of 10 to 35 ° with respect to the tire circumferential direction. The sidewall portions 2 and 2'are divided into two in the vicinity of the maximum tire width, and each of the sidewall portions 2 and 2'includes an inner rubber layer 2d, 2'd and an outer rubber layer 2u, 2'u which are different from each other in the tire radial direction. The upper end portions of the outer rubber layers 2u and 2'u are joined to the shoulder portions of the tread portion 1, and the inner rubber layers 2d and 2'd
The lower end portion of the rim cushion portion and the upper end portion of the rim cushion portions 3, 3 ′ overlap. The inner rubber layers 2d and 2'd are made of foamed rubber, while the outer rubber layers 2u and 2'u are made of non-foamed rubber.

In the above structure, the rubber layers 2u and 2u 'on the tire radial outside of the sidewall portions 2 and 2'correspond to the flex zone to which the largest bending strain is applied when the pneumatic tire rotates on the ground. In contrast,
The rubber layers 2d and 2d ′ on the inner side in the tire radial direction are composed of bead fillers 6 and 6 ′ made of high hardness rubber, rim flanges R and
It is a region reinforced by R '.

As described above, the outer rubber layers 2u and 2u 'of non-foamed rubber having excellent fatigue resistance and cut resistance are arranged in the flex zone on the outer side in the tire radial direction, and the inner side in the tire radial direction where fatigue resistance is not so required. Since the inner rubber layers 2d and 2d 'of the foamed rubber are arranged in the above, it is possible to reduce the weight while suppressing the deterioration of the fatigue resistance. In the present invention, in order to further improve the above-described function and effect, the rubber thickness center of the connection interface between the outer rubber layers 2u and 2'u and the inner rubber layers 2d and 2'd (position of 1/2 of the rubber thickness) It is desirable that the height h from the rim base in 4) is in the range of 40 to 50% of the tire cross-section height H. By setting the height h of the center of the connection interface from the rim base to be 40% or more of the tire cross-section height H, the weight saving effect can be made more reliable. Further, when it is 50% or less, the effect of suppressing the deterioration of the fatigue resistance of the sidewall portion can be made more reliable.

In the present invention, the method of joining the outer rubber layer and the inner rubber layer in the tire radial direction is not particularly limited, but preferably, as shown in the figure, both ends of the outer rubber layer and the inner rubber layer are diagonally overlapped. Is good. In the present invention, the foamed rubber of the rubber layer on the inner side in the radial direction of the tire has an average bubble area of 80 to 8,000 μm ² per bubble when measured in an arbitrary cross section, It is desirable that the bubble occupying area ratio is 5 to 40%. The weight saving effect can be further enhanced by increasing the average bubble area to 80 μm ² or more and the bubble occupying area ratio to 5% or more to increase the proportion of closed cells. Further, by setting the average bubble area to be 8,000 μm ² or less and the bubble occupying area ratio to be 40% or less, the strength of the foamed rubber can be made sufficient.

Here, the average cell area is determined by cutting out a test piece from an arbitrary unit cross section of the rubber layer (foamed rubber) on the inner side in the tire radial direction, making it a flat surface, and then enlarging it 165 times to expand the air bubbles in the foamed rubber. This is a value calculated by calculating the area of 10 bubbles and averaging them [(sum of areas of 10 bubbles) / 1
0]. Further, the bubble occupied area ratio is a percentage (%) of the area occupied by the total number of bubbles in an arbitrary unit cross section of the rubber layer (foamed rubber) on the tire radial direction inner side.

As a rubber composition forming such a foamed rubber, a rubber composition containing various known foaming agents can be used and is not particularly limited. It is preferable that a urea auxiliary agent is blended in less than the same amount as the blending amount of the foaming agent. Such a rubber composition is applied as a rubber layer on the tire radial direction inner side of the sidewall portion, and the foaming agent is thermally decomposed at its vulcanization temperature (usually about 150 to 175 ° C.) to obtain the above-mentioned average cell area. It becomes possible to form a foamed rubber having a bubble occupying area ratio.

[0014]

EXAMPLES The tire size was made 185 / 70SR13 in common, and two types of rubber compositions a and b shown in Table 2 were used, and the structures of the sidewall portions were made different as shown in Table 1. The tire of the present invention, the conventional tire, and the comparative tires 1 and 2 were manufactured. Further, the height h from the rim flange at the center of the connecting interface between the outer rubber layer and the inner rubber layer of the sidewall portion of the tire of the present invention and the comparative tire 2 is 50% of the tire cross-section height H. did.

Regarding these four types of pneumatic tires,
Fatigue resistance and weight reduction were evaluated by the following methods. The results are shown in Table 1. Fatigue resistance : The tire was assembled on a rim of 13 × 5J, filled with air pressure of 1.8 kg / cm ² , and the height from the rim flange was 25% and 75% of the tire cross-section height. After inserting a 5 mm long and 0.8 mm deep female cut into each position, attach it to a drum with a diameter of 1707 mm, apply a load of 360 kg, and run at a speed of 81 km / hr for 5,000 km, and then perform the female cut. The length after growth was measured and evaluated from the sum of the measured values at two locations.

The evaluation result is based on the value of the conventional tire (10
It is indicated by an index of 0). The larger this index is, the poorer the fatigue resistance is. Weight reduction property : The weight of each test tire was measured and indicated by an index based on the weight of the conventional tire (100). The larger this value is, the larger the tire weight is.

[0017]

[0018] Note: ¹⁾ "Cellular" D (dinitrosopentamethylenetetramine ²⁾ manufactured by Eiwa Chemical Industry Co., Ltd. "Cell paste" K5 (urea compound) manufactured by Eiwa Chemical Industry Co., Ltd. From Table 1, the tire of the present invention is lighter than the conventional tire. And has almost the same fatigue resistance.
On the other hand, although the comparative tires 1 and 2 are lighter than the conventional tires, the fatigue resistance is significantly reduced.

[0019]

According to the present invention, the rubber layer of the sidewall portion of the pneumatic tire is divided into an inner rubber layer and an outer rubber layer which are different from each other in the tire radial direction, and the inner rubber layer is made of foamed rubber. However, since the outer rubber layer is made of non-foamed rubber, it is possible to reduce the weight while ensuring the original fatigue resistance of the sidewall portion most efficiently.

[Brief description of drawings]

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

[Explanation of symbols]

2, 2'side wall part 2d, 2'd inner rubber layer 2u, 2'u outer rubber layer

Claims (1)

[Claims] 1. A rubber layer of a sidewall portion is composed of an inner rubber layer and an outer rubber layer which are different from each other in a tire radial direction, the inner rubber layer is composed of foamed rubber having closed cells, and the outer rubber layer is A pneumatic tire made of non-foamed rubber.