Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1997-07-23
2001-07-03
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S531000, C152S533000, C152S541000, C152S543000, C152S546000, C152S554000
Reexamination Certificate
active
06253816
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic radial tire in which excellent stability and controllability are provided and a large amount of road noise can be reduced
2. Description of the Related Art
In recent years, since requirements for the sophistication of vehicles have been increasing, especially passenger cars, improvements of riding qualities have been proceeding. Therefore, as requirements for a tire, reduction of noise caused by a tire and higher riding qualities through a tire are needed.
It is especially desired that a large amount of noise which is caused at the interior of a vehicle can be reduced. In this case, improvement requirements for so-called “road noise” that is one of the above-described noises have been extremely increasing. Namely, road noise is caused by the tire during travel of a vehicle picking up irregularities on a road surface. The resultant vibration is conveyed to the interior of a vehicle, thereby causing the air to vibrate in the interior of the vehicle.
Further, simultaneously with the sophistication of vehicles, speed-up and/or power-up of vehicles also occurs. Accordingly, a tire for which only problems in riding qualities and road noises have been solved in the same manner as a conventional tire cannot comply with the aforementioned requirements. As a result, it is necessary to maintain a tire to a high level of speed resistance, uniformity performance, stability and controllability, and rolling resistance.
In a conventionally known method of reducing road noise, a method can be provided in which the entire portion or the widthwise direction end portions of a crossing belt layer is/are held by a reinforcing layer which is made of rubber-coated cords such as nylon cords which are disposed in the circumferential direction of a tire so that the rigidity of the aforementioned belt layer in the circumferential direction thereof can be reinforced.
In accordance with this method, a ribbon-shaped strip is formed by rubber-coating a nylon cord or a plurality of nylon cords which are disposed in parallel to each other, and is wound around a tire substantially in the circumferential direction thereof. A green tire to which a tread member unvulcanized is attached is vulcanized on the above resulting tire so that a tire as a product is manufactured.
However, a problem arises in that, because nylon cords generally show Young's modulus which is relatively low at the range of temperature depending upon the use conditions of a fire (a large elongation 4.2% was resulted under load of 1.4 g/d at the temperature of 50±5° C.), it is impossible to improve road noise to the desired level. Moreover, since nylon cords tend to generate a flat spot on a fire, especially in winter, when a vehicle runs after having been parked for a long time, abnormal vibration may be caused.
On the other hand, in the case of aromatic series polyamide fiber (alamide fiber from Dupont Co., Ltd.), since Young's modulus is high even at the vulcanized temperature of 170±5° C. (a small elongation 0.8% was resulted under load of 0.7 g/d at the temperature of 170±5° C.), when cords are disposed in parallel to each other in the circumferential direction of a tire, they are not elongated during the inflation and vulcanization of a tire. Accordingly, the angle formed between the cords and a crossing belt layer (especially, a belt layer which is made of steel cords) which is positioned inwardly in the radial direction of a tire, i.e., the angle formed at the time when a green tire is inflated due to an internal vulcanization pressure, can be prevented from being changed so that desirable angle changes cannot be provided. Further, it is difficult to provide an essential amount of gauge for the rubber between a belt reinforcing layer and a belt layer so that the upper and lower cords are kept in close contact with each other, thereby causing a separation failure to the tire. In an excessive case, the belt reinforcing layer and the belt layer are displaced from each other, thereby affecting the uniformity of a tire adversely. This causes problems in noise and stability and controllability of a tire.
SUMMARY OF THE INVENTION
In view of the aforementioned facts, it is an object of the present invention to provide a pneumatic radial tire in which excellent stability and controllability can be provided and a larger amount of road noise is reduced.
In accordance with the present invention, there is provided a pneumatic radial tire, comprising a pair of bead portions, a carcass having a toroid-shaped configuration and extending over the bead portions, a tread portion which is positioned at the crown portion of the carcass, and a pair of side wall portions, in which at least two belt layers are disposed inwardly from the tread portion, at least one belt reinforcing layer is disposed outwardly from the belt layer in the radial direction thereof at positions corresponding to the whole portion and/or the end portions of the tread portion, the belt reinforcing layer is formed by spirally winding a rubber-coated and narrow strip made of a single fiber cord or a plurality of fiber cords around a tire such that the fiber cord/cords are provided substantially in parallel to the circumferential direction of the tire, and a pair of bead fillers are disposed directly above bead cores of a pair of the bead portions, respectively, wherein the belt reinforcing layer is made of organic fiber cords, the fiber cord has a 2.7% or less elongation under load of 1.4 g/d at the temperature of 50±5° C., and has a 1.5 to 6.0% elongation under load of 0.7 g/d at the temperature of 170±5° C., the height of each of the bead fillers corresponds to 20 to 60% of the cross sectional height of a tire.
In accordance with the present invention, the fiber cords forming the belt reinforcing layer need to have a 1.5 to 6.0% elongation under load of 0.7 g/d at the temperature received by the fiber cord at the time of vulcanizing forming of a tire, i.e., 170±5° C. During forming of a tire, when a vulcanization forming die is inserted into a green tire, an internal pressure is filled in the green tire, and the green tire is pressed onto the internal surface of a forming die, it is important to keep respective portions of a tread, whose elongation is unfixed, in close contact with the forming die so that the tread elongates sufficiently. Therefore, the cords used to form the belt reinforcing layer made which is spirally wound around a tire should have an elongation 1.5 to 6.0% or the like which make a tread conform or applicable to a vulcanization forming die, thereby resulting in excellent vulcanization forming performance of a tire, uniform quality and status of a belt reinforcing layer, and uniform road holding. As a result, excellent reduction of road noise of a tire, higher stability and controllability, higher uniformity performance, and higher biased-abrasion resistance can be accomplished. Further, angle changes of the cords intersecting on a belt layer can be prevented so that the rubber gauge can be secured sufficiently between a belt reinforcing layer and the belt layer, and a separation failure is not thereby caused. The reason why an elongation under load of 0.7 g/d is employed for the belt reinforcing layer is because the average tensional force which is applied to a fiber cord of the belt reinforcing layer which is spirally wound around at the inside of the vulcanization mold is generally about 0.7 g/d. Assuming that the elongation is less than 1.5% as in the case of aromatic series polyamide fiber, such drawbacks arise in that a tread cannot elongate sufficiently within a vulcanization forming die, a successful vulcanization mold cannot be accomplished, road holding is not uniformed, road noise cannot be reduced effectively, thereby adversely effecting the stability and controllability of a tire. Further, in the case where the elongation is over 6.0%, after a tire has been removed from a vulcanization forming die, when
Bridgestone Corporation
Johnstone Adrienne C.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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