JPH08156526A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE: To reduce noise while holding steering stability, wet grip property, and comfortableness. CONSTITUTION: A belt layer 7 arranged in the inner part of a tread part 2 and on the radial outside of a carcass 6 is formed of a belt ply using a belt cord consisting of full aromatic polyester fiber, and a tread rubber layer 9 has a foamed rubber 11 exposed to the groove bottom surface 10A of a circumferential groove 10, and having a foaming magnification of 20-100%.

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, the contribution of noise generated by tires to the entire vehicle has increased with the improvement of the quietness of the vehicle, and it has been required to reduce it. In particular, the low frequency range of 160 Hz, 250 Hz and 800 Hz or more are required. It is desired to reduce noise in both high frequency region and high frequency region. Pumping noise due to air column resonance is a main sound source in the high frequency region. The sound source generated in the lower frequency region includes noise due to vibration of the tire itself caused by elasticity change of the tread portion during traveling.

In order to maintain a wet grip, the tire tread is generally provided with a plurality of circumferential grooves which are continuous in the tire circumferential direction. Such a tire forms a kind of air column with the circumferential groove with the ground at the ground contact surface, and the deformation of the tire tread during rolling causes air to flow into the air column, thereby identifying the air column. Sound of wavelength is generated. This phenomenon is called air column resonance and is the main source of noise in tires having vertical grooves. For example, the contact length of the circumferential groove is 20 cm
, A sound of about 900 Hz is generated. This sound becomes a sound having a substantially constant frequency regardless of the speed of the tire, and increases the sound inside the vehicle and the sound outside the vehicle.

On the other hand, in the case where the tread rubber is blocked, the tread portion and the sidewall portion are vibrated during traveling due to the change in rigidity, and the vibrations cause air noise.

[0005]

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

As means for suppressing the vibration of the tire itself, a method of increasing the sectional thickness of the tread portion or the sidewall portion, or increasing the rubber hardness of the tread rubber or the sidewall portion can be considered. Such an increase in the rigidity of the tire base body causes a decrease in riding comfort and running performance.

An object of the present invention is to provide a pneumatic radial tire capable of reducing tire sound pressure and lowering tire noise generally in a low frequency region and a high frequency region while maintaining running performance and wet grip performance. To do.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a carcass formed of a carcass cord having a radial arrangement and folding back around a bead core of a bead part through a tread part, a sidewall part, and a carcass inside the tread part and in a radial direction of the carcass. A pneumatic radial provided with a belt layer arranged on the outer side and a tread rubber layer arranged on the outer side in the radial direction of the belt layer and forming a tread surface, and further having a plurality of circumferential grooves extending in the circumferential direction 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 fiber,
The tread rubber layer is provided with a foamed rubber having a foaming ratio of 20% or more and 100% or less, which is exposed only inward in the tire radial direction of each circumferential groove and only on a groove bottom surface of the circumferential groove. It is a pneumatic radial tire that does.

[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 a wet grip is provided. Can be maintained.

The wholly aromatic polyester fiber is a rigid, high-performance organic compound having a molecular structure shown in Chemical formula 1, for example, 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). Fibers are known as so-called polyarylate fibers.

[0011]

Embedded image

[0012]

[Table 1]

[0013]

[Table 2]

As shown in Table 1, this fiber has a high tensile strength, a tensile elastic modulus and a low breaking strength which are almost the same as those of aromatic polyamide fiber known as another high performance organic fiber, so-called para-aramid fiber (PPAT). Elongation, and therefore, sufficient belt layer strength can be maintained without increasing the number of belt plies. Further, this product has flexural fatigue resistance, that is, the tenacity retention ratio when a flexing test of 1500 d / 1, 80 t / m of a short fiber was carried out at a flexing angle of 130 degrees and a flexing number of 10,000 times, as shown in Table 2. The wholly aromatic polyamide fiber is 51%, while the wholly aromatic polyester fiber is 9%.
It is extremely large at 7%. Therefore, when the tire is repeatedly deformed, the vibration of the tread portion can be reduced over almost the entire noise range, and the tire noise can be reduced.

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

Such foamed rubber can absorb air passing through the circumferential groove into the foamed rubber through the foamed bubbles, and can reduce air column resonance noise.

Further, the foamed rubber can absorb the vibration of the tread rubber when the tire is running, and can suppress the resonance of the sidewall portion in cooperation with the belt layer having the above-mentioned structure and 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 through the circumferential groove, resulting in poor noise reduction. If it exceeds 100%, the tread portion near the circumferential groove. The reduction in the rigidity of the vehicle causes a decrease in steering stability. The expansion ratio is 25% or more and 80%
The following range is more preferable.

Providing the foamed rubber on the side wall surface of the circumferential groove is not easy in production, but arranging it only at the groove bottom can be performed relatively easily as described later.
Further, when the foamed rubber is extended to the side wall surface, the cross-sectional shape of the circumferential groove changes when the tire is running, the running stability is reduced, and there is a risk that the circumferential groove is damaged when stone is caught.

As described above, the present invention can reduce the noise over substantially the entire sound range by organically and integrally combining the above constituent elements.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2, the pneumatic radial tire 1 is
The tread portion 2 and a pair of sidewall portions 3 extending inward in the tire radial direction from both sides thereof, and the sidewall portion 3
And a bead portion 4 extending inward.

Further, in the pneumatic radial tire 1, a folded-back portion is formed by folding the bead core 5 around the body portion 6a from the tread portion 2 through the sidewall portion 3 to the bead portion 4 from the inner side to the outer side in the tire axial direction. A carcass 6 integrally provided with 6b, a belt layer 7 arranged outside the carcass 6 and inside the tread portion, and a tread rubber arranged radially outside the belt layer 7 and forming a tread surface 2A. In this example, a bead apex 8 having a triangular cross section and made of hard rubber is provided between the main body portion 6a of the carcass 6 and the folded portion 6b.

In the present example, the carcass 6 is composed of one carcass ply, and each carcass ply is made of nylon,
Carcass cords made of organic fibers such as polyester, rayon, and aromatic polyamide are attached to the tire equator C at 7
The carcass cords are formed in a radial or semi-radial arrangement inclined at an angle of 5 to 90 °, and the carcass cords are arranged so as to intersect each other between the carcass plies.

The belt layer 7 is, in this embodiment, the carcass 6
Of the inner belt ply 7A arranged radially outside of and adjacent to the carcass 6 and an outer belt ply 7B arranged outside the inner belt ply, and each belt ply 7A, 7B is Fibers made of wholly aromatic polyester are inclined at an angle of 16 to 24 with respect to the tire circumferential direction and arranged in reverse. Belt ply 7A, 7B
Is a cut ply obtained by coating the arranged belt cords with a topping rubber.

The belt cord has a high tenacity holding ratio by using the wholly aromatic polyester fiber as described above, and when it is used for a belt ply for passenger cars and light trucks, the denier is 1200d / 2 to 1800d. / 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 made of rubber having a hardness of about 70 degrees, and the tread surface 2A is provided with a plurality of groove portions including four circumferential grooves 10 in this example.

In the tread rubber layer 9, the circumferential groove 10 is formed.
The foamed rubber 11 which is located radially inward and is exposed at the groove bottom surface 10A and circulates is embedded. The foamed rubber 11 is formed of, for example, the rubber compositions A to D shown in Table 3.

The foamed rubber 11 has independent cells, and the expansion ratio is 20 to 100%, preferably 25 to 8%.
It is 0%. This is because if the expansion ratio is too small, the sound absorbing effect is poor, while if it is too large, the steering stability tends to be worsened.

The rubber thickness T in the radial direction of this foamed rubber is
The tread rubber layer 9 is provided 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 steering stability.

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

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

[0032]

SPECIFIC EXAMPLE A tire size is 180 / 70R14 and a prototype is produced according to the specifications shown in Table 4 (Example),
The performance was tested. In addition, tires having conventional configurations (conventional examples) and tires having configurations other than the configurations of the present application (comparative examples 1 and 2)
Also, a test was conducted to compare the performance. 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 near the center ear of the driver's seat.

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 was confirmed that the road noise of the example was lower than that of the conventional example and the comparative example, and that the reduction was in the low frequency region and the high frequency region. It was

[0037]

As described above, the tire of the present invention is provided with the above-mentioned constitution, so that the noise generated from the tire at the time of running can be suppressed while keeping the steering stability, the wet grip property, and the riding comfort. It can be reduced over almost the entire area.

[Brief description of drawings]

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

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

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

[Explanation of symbols] 2 tread portion 2A tread surface 3 sidewall portion 4 bead portion 5 bead core 6 carcass 7 belt layer 9 tread rubber layer 10 circumferential groove 10A groove bottom surface 11 foam rubber

[Table 3]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location D02G 3/48

Claims (1)

[Claims] 1. A carcass comprising a carcass cord of radial arrangement and folding around a bead core of a bead part through a sidewall part from a tread part, and a belt layer arranged inside the tread part and radially outside the carcass. A pneumatic radial tire having a tread rubber layer disposed on the outer side in the radial direction of the belt layer and forming a tread surface, and further having a plurality of circumferential grooves extending in the circumferential direction on the tread surface, wherein the belt layer Is formed by a belt ply using a belt cord made of wholly aromatic polyester fiber, and the tread rubber layer is exposed only inward in the tire radial direction of each circumferential groove and on the groove bottom surface of the circumferential groove. A pneumatic radial tire provided with a foamed rubber having a foaming ratio of 20% or more and 100% or less.