Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1994-10-11
2001-04-17
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S532000
Reexamination Certificate
active
06216757
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to tires for use in general vehicles, particularly trucks, buses and modern urban traffic vehicles such as monorail cars, subway trains using rubber tires and the like. More particularly, the invention relates to a low noise level tire which lowers both passing noises and acceleration noises generated from the tire to reduce vehicle-outside noise including the noises of these types, and simultaneously maintains its wear-resistance as an essential performance at a high level as desired.
(2) Related Art Statement
Recently, great interest has risen in the noise dispersed from vehicles among various factors of tires affecting the social environment, and demand for the reduction of the noise generated from the tires themselves has been increasing, in addition to the economical improvement of tires, which is a fundamental requirement. Such demand for the reduction of noise has risen with respect to not only tires for cars running on general roads but also tires for monorail cars, subway trains and other modern urban traffic vehicles.
In the past, noise generated from the tire to the outside of a test vehicle (vehicle-outside noise) was usually measured in a state where the vehicle was drifted after a clutch in the vehicle had been disengaged. A microphone was fixedly arranged at a position spaced 7.5 m from a running way of the tire to be tested, and the noise was measured when the vehicle passed by the position. The magnitude of the passing noise was judged by the measured results. However, since it is considered that the passing noise is not sufficient to represent the actual vehicle noise, a conclusion has been reached that a combination of the acceleration noise and the passing noise must be considered with the same importance for estimating the actual vehicle noise.
In order to lower the passing noise in the reduction of the tire noise, it has been proposed to modify grooves formed in treads or to change the configuration of treads.
Moreover, for example, Japanese Patent Application Laid-open No. 2-225106 disclosed a tire whose tread is composed of a usual cap rubber layer and a base layer made of a foam rubber having a low elastic modulus and a high loss tangent in order to maintain wear-resistance and improve the riding comfortability against vibration, although it does not aim to directly reduce the vehicle-outside noise.
Furthermore, Japanese Patent Application Laid-open No. 2-60803 disclosed a tire adapted to reduce the noise in a vehicle caused by vibration when running on a bad road without lowering the cornering performance, although it does not aim to directly reduce the vehicle-outside noise, either. The disclosed tire has a tread including a cap layer and an inner layer. The cap layer is made of a usual rubber having a high hardness and a high elastic modulus, and the inner layer is made of the same rubber as that of the cap layer but mixed with 3% to 10% by volume of a vulcanized rubber particles having a low hardness to have a low elastic modulus and a low loss tangent.
Among the proposals described above, with the modified grooves in the treads or the modified treads themselves, the wear-resistance is unavoidably lowered and further reduction in acceleration noise is scarcely possible because no attention is paid to the reduction in the acceleration noise, although the passing noise can be reduced.
The techniques disclosed in Japanese Patent Application Laid-open Nos. 2-225106 and 2-60803 have suggested the reduction in the vehicle-outside noise. However, with the tire disclosed in the Japanese Patent Application Laid-open No. 2-225106, the acceleration noise is rather increased according to results of experiments carried out by the present inventors, although both wear-resistance and the riding comfortability against vibration can be simultaneously improved and the passing noise can be lowered, the acceleration noise inversely becomes greater.
Moreover, with the tire disclosed in Japanese Patent Application Laid-open No. 2-60803, the passing noise greatly increases with respect to the vehicle-outside noise, although the acceleration noise can be reduced.
By way of experiment, tires were produced whose cap layer of the tread was made of a rubber having a low elastic modulus and a high loss tangent within a range guessed at from the disclosures of the above two Japanese Applications, and these tires were tested. As a result, the passing and acceleration noises were reduced, but the wear-resistance was lowered to an extent that the tires could not be practically used.
In measuring the passing and acceleration noise in the present invention, a microphone is arranged adjacent a tire so as to measure only the noise generated from the tire in order to exclude the influence of background noise as much as possible. This is different from the conventional measurement made by arranging a microphone at a position remote from the vehicle as described above.
From the above explanation, it is concluded that there is no prior art technique which can reduce the passing and acceleration noise simultaneously without lowering the wear-resistance of a tire.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a low noise level tire capable of maintaining grooves and the shape of a tread in best configurations without modification of them, which tread grooves and shape greatly affect performance of the tire, such as wear-resistance, simultaneously reducing both the passing and acceleration noises which have been incompatible with each other as in the prior art described above because one of them is decreased to in turn increase the other, and further preventing the great reduction in wear-resistance which tends to occur when both the passing and acceleration noise are simultaneously reduced.
In other words, the object of the invention is to provide a low noise level tire which can maintain or improve wear-resistance which is fundamentally essential for the tire, and can simultaneously reduce both the passing and acceleration noises dB (A) which have been increasingly demanded to be lowered recently. Namely, the object of the invention is to provide a tire having the above effects without modifying the skeleton and the construction of the tire.
In order to accomplish the object, the present invention is to provide a low noise level tire including a carcass of at least one ply toroidally extending between a pair of bead cores, and a tread arranged radially outwardly of the carcass and composed of an outer cap rubber layer and an inner base rubber layer, wherein the cap layer is made of a rubber having a dynamic storage modulus of not less than 1.0×10
8
dyn/cm
2
and not more than 2.0×10
8
dyn/cm
2
and a loss tangent of not less than 0.15 and not more than 0.35, and the base layer is made of a rubber having a dynamic storage modulus of not less than 1.2×10
8
dyn/cm
2
and not more than 2.2×10
8
dyn/cm
2
and a rate of foaming more than 5% and less than 50%.
In the present invention, the maximum width of the base layer in its axial width direction is preferably at least equal to the entire width of the tread of the tire.
The low noise level tire having the above features according to the invention can improve or maintain the wear-resistance at high level, which is essential for any tire, and can simultaneously lower both the passing and acceleration noise to desired levels, which could not be achieved in the prior art.
In order that the invention may be more clearly understood, preferred embodiments will be described, by way of example, with reference to the accompanying drawings.
REFERENCES:
patent: 4349061 (1982-09-01), Hirakawa et al.
patent: 4381810 (1983-05-01), Cody et al.
patent: 5046542 (1991-09-01), Ohta et al.
patent: 5109902 (1992-05-01), Kobayashi
patent: 0161793 (1985-11-01), None
patent: 0301138 (1989-02-01), None
patent: 0370724 (1990-05-01), None
patent: 2150509 (1985-07-01), None
patent: 0116506 (1985-06-01), None
patent: 0283001 (1987-12-01
Ohara Masashi
Takiguchi Eiji
Bridgestone Corporation
Maki Steven D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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