JP3354328B2 - Pneumatic radial tire - Google Patents

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 capable of promoting noise reduction.

[0002]

2. Description of the Related Art In recent years, with the improvement in quietness of a vehicle, the contribution rate of noise generated by tires to the entire vehicle has been increased, and it has been required to reduce the noise. It is desired to reduce noise in both the high frequency region and the high frequency region. As a main sound source in a high frequency region, there is pumping noise due to air column resonance. A sound source generated in a lower frequency region includes noise caused by vibration of the tire itself caused by an elastic change in the tread portion during running.

[0003] In the tire tread, a plurality of circumferential grooves which are generally continuous in the circumferential direction of the tire are arranged to maintain a wet grip. Such a tire forms a kind of air column with a circumferential groove with the ground on the ground contact surface, and the air flows through the air column due to the deformation of the tire tread during rolling. The sound of the wavelength is generated. This phenomenon is called air column resonance, and is a main sound source of noise of a tire having a vertical groove. For example, the contact length of the circumferential groove is 20 cm
, A sound of about 900 Hz is generated. This sound has a substantially constant frequency irrespective of the speed of the tire, and increases the in-vehicle sound and the outside sound.

On the other hand, when the tread rubber is blocked, the tread portion and the sidewall portion are vibrated during running due to the change in rigidity, and the vibration becomes air noise.

[0005]

As means for preventing the air column resonance, 0.3 to 0.4 of the ground contact length of the circumferential groove is used.
A technique has been proposed to provide a shield in the circumferential groove at a circumferential pitch equivalent to twice to prevent air column resonance, but the shield in such a circumferential groove prevents air column resonance. House,
There is a problem that the water flow is hindered and the wet grip performance, which is the original purpose of the circumferential groove, is reduced.

As means for suppressing the vibration of the tire itself, there are conceivable methods of increasing the sectional thickness of the tread portion and the sidewall portion or increasing the rubber hardness of the tread rubber and the sidewall portion. Such an increase in the rigidity of the tire base causes a reduction in ride comfort and running performance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire capable of lowering the sound pressure of noise in a low frequency range and a high frequency range and reducing tire noise while maintaining running performance and wet grip performance. I do.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a carcass comprising a carcass cord in a radial arrangement while turning around a bead core of a bead portion from a tread portion through a sidewall portion, and a carcass made of a radially arranged carcass cord. A pneumatic radial having a belt layer disposed outside and a tread rubber layer disposed outside the belt layer in a radial direction and forming a tread surface, and further provided with a plurality of circumferential grooves extending circumferentially on the tread surface. A tire, wherein the belt layer is formed by a belt ply using a belt cord made of wholly aromatic polyester fibers,
The tread rubber layer is characterized in that foam rubber having an expansion ratio of 20% or more and 100% or less is provided while being exposed only inward in the tire radial direction of each of the circumferential grooves and on the groove bottom surface of the circumferential groove. Pneumatic radial tire.

[0009]

According to the present invention, by forming a circumferential groove extending continuously in the tire circumferential direction on the outer peripheral surface of the tread rubber layer, a continuous drainage channel can be secured when the tire is in contact with the ground, and the wet grip is provided. Can be maintained.

A wholly aromatic polyester fiber is a rigid, high-performance organic compound having a molecular structure represented by, for example, the following chemical formula 1 in which an aromatic compound having a benzene ring and a ring in which a plurality of benzene rings are condensed is ester-bonded (-O-CO) It is a fiber and is known as a so-called polyarylate fiber.

[0011]

Embedded image

[0012]

[Table 1]

[0013]

[Table 2]

As shown in Table 1, the high tensile strength, the tensile modulus and the low fracture of the aromatic polyamide fiber, which is known as other high-performance organic fiber, are almost the same as those of the so-called para-type aramid fiber (PPAT). Elongation, so that sufficient belt layer strength can be maintained without increasing the number of belt plies. The flexural fatigue resistance, that is, the strength retention of a short fiber of 1500 d / 1 and 80 t / m when subjected to a bending test at a bending angle of 130 ° and 10,000 times of bending, for example, as shown in Table 2. The total aromatic polyamide fiber is 51%, while the total aromatic polyester fiber is 9%.
It is as large as 7%. Therefore, when the tire is repeatedly deformed, the vibration of the tread portion can be reduced over substantially the entire noise range, and the tire noise can be reduced.

The tread rubber layer is exposed only at least at the bottom of each circumferential groove and has a foaming ratio of 20.
% Or more and 100% or less of foamed rubber.

Such a foamed rubber can absorb air passing through the circumferential groove into the foamed rubber through the foamed bubbles, thereby reducing air column resonance.

Further, the foamed rubber can absorb the vibration of the tread rubber during running of the tire, suppress the resonance of the side wall portion in cooperation with the belt layer having the above-described configuration, and suppress the noise due to the tire vibration.

If the expansion ratio is less than 20%, the foamed rubber cannot absorb air column resonance due to the flow of air passing through the circumferential groove, resulting in poor noise reduction. If the expansion ratio exceeds 100%, the vicinity of the circumferential groove in the tread portion is reduced. As a result, the steering stability of the vehicle decreases. The expansion ratio is 25% or more and 80%
More preferably, it is in the following range.

Although it is not easy in terms of production to provide foamed rubber on the side wall surface of the circumferential groove, it is relatively easy to arrange it at the bottom of the groove, as described later.
Further, when the foamed rubber is extended to the side wall surface, the cross-sectional shape of the circumferential groove fluctuates during running of the tire, and the running stability is reduced.

As described above, according to the present invention, noise can be reduced over substantially the entire sound range by combining the above-mentioned components organically and integrally.

[0021]

An embodiment of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, a pneumatic radial tire 1 includes:
A pair of sidewall portions 3 extending inward in the tire radial direction from the tread portion 2 and both sides thereof;
And a bead portion 4 extending inward.

In the pneumatic radial tire 1, a folded portion is formed by turning a bead core 5 around the bead core 5 from the inside to the outside in the tire axial direction to a main body 6a extending from the tread portion 2 to the sidewall portion 3 to the bead portion 4. 6b, a belt layer 7 disposed outside the carcass 6 and inside the tread portion, and a tread rubber disposed radially outside the belt layer 7 and forming a tread surface 2A. In this embodiment, a bead apex 8 made of hard rubber and having a triangular cross section is provided between the main body portion 6a and the folded portion 6b of the carcass 6.

In the present embodiment, the carcass 6 is composed of one carcass ply, and each carcass ply is made of nylon,
Carcass cord made of organic fiber such as polyester, rayon, aromatic polyamide, etc.
It is formed as a radial or semi-radial array inclined at an angle of 5 to 90 [deg.], And the carcass cords are arranged so as to cross each other between the carcass plies.

In the present embodiment, the belt layer 7 is made of a carcass 6.
And an outer belt ply 7B disposed radially outward of and adjacent to the carcass 6, and an outer belt ply 7B disposed outside of the inner belt ply. The fibers made of wholly aromatic polyester are inclined at an angle of 16 to 24 ° with respect to the circumferential direction of the tire and are arranged opposite to each other. The belt plies 7A, 7B
Consists of a cut ply in which the arranged belt cords are covered with topping rubber.

The belt cord has a high tenacity retention rate by using a wholly aromatic polyester fiber as described above, and has a denier of 1200d / 2 to 1800d when used for a belt ply for passenger cars and light trucks. / 2,
The number of shots is preferably in the range of 25 to 50 per 5 cm.

The tread rubber layer 9 has a JISA hardness of 55
The tread surface 2A is formed of a rubber of about 70 degrees, and a groove portion including a plurality of four circumferential grooves 10 in this example is provided in the tread surface 2A.

The tread rubber layer 9 has the circumferential grooves 10
The rubber foam 11 which is located inward in the radial direction and is exposed on the groove bottom surface 10A and circulates is embedded. The foamed rubber 11 is formed of, for example, rubber compositions A to D shown in Table 3.

The foamed rubber 11 has closed cells, and the expansion ratio is 20 to 100%, preferably 25 to 8%.
0%. If the foaming ratio is too small, the sound absorbing effect is inferior. On the other hand, if it is too large, the steering stability tends to deteriorate.

The rubber thickness T of this foamed rubber in the radial direction is:
The tread rubber layer 9 is interposed between the belt layer 7 and 0.1 times or more and 0.5 times or less the groove depth GH of the circumferential groove 10 in which it is arranged. Rubber thickness T is groove depth GH
If it is less than 0.1 times, the sound absorbing effect is inferior, and if it exceeds 0.5 times, there is a risk of impairing the steering stability.

The width of the foamed rubber 11 in the tire axial direction is preferably substantially equal to the width of the groove bottom 10A, but may be slightly larger than the width of the circumferential groove 10.

In order to dispose the foamed rubber in the tread rubber layer, when extruding the unvulcanized tread rubber, a space in which the foamed rubber is fitted is provided in advance and the unvulcanized tread is provided. It is obtained by forming a rubber, fitting a foamed rubber in the space, and integrating them by vulcanization.

[0032]

[Specific example] The tire size is 180 / 70R14 and a prototype is manufactured according to the specifications shown in Table 4 (Example).
The performance was tested. Note that a tire having a conventional configuration (conventional example) and a tire not having the configuration of the present application (Comparative Examples 1 and 2)
Was also tested and the performance was compared. The test method is as follows.

A) Road noise The overall noise on a rough asphalt road at a speed of 50 km / h was measured by placing a microphone in the middle of the driver's seat at the center of the ear.

The test results are shown in Table 4, and the results of frequency analysis of the noise are shown in FIG.

[0035]

[Table 4]

As a result of the test, it can be confirmed that the load of the embodiment is reduced in road noise as compared with those of the conventional example and the comparative example, and the reduction extends to both the low frequency range and the high frequency range. Was.

[0037]

As described above, the tire of the present invention, having the above-described structure, can reduce noise generated at the time of traveling while maintaining steering stability, wet grip performance, and riding comfort. It can be reduced over substantially the entire area.

[Brief description of the drawings]

FIG. 1 is a right half sectional view showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a main part thereof.

FIG. 3 is a graph showing a frequency analysis of noise.

[Explanation of symbols]

 2 Tread portion 2A Tread surface 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer 9 Tread rubber layer 10 Circumferential groove 10A Groove bottom 11 Foam rubber

[Table 3]

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B60C 11 / 00,11 / 04 B60C 11 / 13,1 / 00 B60C 9/18-9/20 D02G 3 / 48

Claims (1)

(57) [Claims] 1. A carcass comprising a radially arranged carcass cord while turning around a bead core of a bead portion from a tread portion through a sidewall portion, and a belt layer disposed inside the tread portion and radially outside the carcass. A pneumatic radial tire having a tread rubber layer disposed radially outward of the belt layer and forming a tread surface, and further provided with a plurality of circumferential grooves extending in a circumferential direction on the tread surface. Is formed by a belt ply using a belt cord made of wholly aromatic polyester fibers, and the tread rubber layer is exposed only in the tire radial direction inside of each of the circumferential grooves and on the groove bottom of the circumferential groove. A pneumatic radial tire provided with foamed rubber having an expansion ratio of 20% or more and 100% or less.