Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2002-08-09
2004-04-13
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S209160, C152S517000, C152S523000
Reexamination Certificate
active
06719029
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the design of pneumatic, radial ply, runflat passenger tires.
BACKGROUND OF THE INVENTION
Various methods have been devised for enabling the safe continued operation of unpressurized or underpressurized vehicle tires with the intent of minimizing further damage to the uninflated tire and without simultaneously compromising vehicle handling over a distance from the place where the tire has lost its pressure to a place desired by the driver, such as a service station where the tire can be changed. Loss of tire pressure can result from a variety of causes, including puncture by a foreign object such as a nail or other sharp object piercing the pneumatic tire installed on a vehicle.
Pneumatic tires designed for sustained operation under conditions of unpressurization or underpressurization are also called runflat tires, as they are capable of being driven in the uninflated, or what would generally be called “flat,” condition. The conventional pneumatic tire collapses upon itself when it is uninflated and is carrying the weight of a vehicle. The tire's sidewalls buckle outward in the circumferential portion of the tire where the tread contacts the ground, making the tire “flat.”
The term “runflat” is generally used to describe a tire that is designed such that the tire structure alone, in particular the structure of the sidewalls, has sufficient rigidity and strength to support the vehicle load when the tire is operated without being inflated. The sidewalls and internal surfaces of the tire do not collapse or buckle onto themselves, and the tire does not otherwise contain or use other supporting structures or devices to prevent the tire from collapsing.
An early example of a runflat tire design is described in U.S. Pat. No. 4,111,249, entitled the “Banded Tire,” in which a hoop or annular band approximately as wide as the tread is circumferentially deployed beneath the tread. The hoop in combination with the rest of the tire structure could support the vehicle weight in the uninflated condition.
Another approach taken has been simply to strengthen the sidewalls by increasing their cross-sectional thickness. However, due to the large amounts of rubber required to stiffen the sidewall members, flexure heating becomes a major factor in tire failure during runflat operation. This is especially so when the tire is operated for high speeds in the uninflated condition. Pirelli discloses such a runflat tire design in European Patent Publication No. 0-475-258A1.
In general, runflat tires incorporate sidewalls that are thicker and/or stiffer so that the tire's load can be carried by an uninflated tire with minimum adverse effects upon the tire itself and upon vehicle handling until such reasonable time as the tire can be repaired or replaced. The typical methods used in sidewall thickening and stiffening include the incorporation of circumferentially disposed wedge inserts in the inner peripheral surface of the sidewall portion of the carcass, which is the region in the tire usually having the lowest resistance to deformation under vertical loading. In such runflat tire designs, each sidewall is thickened in such a way that its overall thickness (gauge) is increased in the region between the bead and the tread shoulder.
The reinforced sidewalls of such tires, when operated in the uninflated condition, experience a net compressive load in the region of the sidewall that is closest to the road-contacting portion of the tire. Also, the bending stresses on the sidewalls are such that the outer portions of the reinforced sidewalls experience tensile forces while the inner portions experience compression stresses during runflat operation.
A Goodyear patent U.S. Pat. No. 5,368,082, by Oare et al, ('082), which has a common assignee and is incorporated in its entirety by reference herein, discloses a low aspect ratio runflat pneumatic radial ply tire which employs special sidewall inserts to improve stiffness. Approximately six additional pounds of weight per tire was required to support an 800 pound load in this uninflated tire. This earlier invention, although superior to prior attempts at runflat tire design, still imposed a weight penalty that could be offset by the elimination of a spare tire and the tire jack. However, this weight penalty becomes even more problematic in the design of tires having higher aspect ratios.
U.S. Pat. Nos. 5,427,166 and 5,511,599 of Walter L. Willard, Jr., disclose the addition of a third ply and the addition of a third insert in the sidewall of a tire to further increase the runflat performance of the tire over that of the U.S. Pat. No. 5,368,082 Oare et al. These two latter patents discuss some of the load relations that occur in the uninflated condition of the tire and they demonstrate that the Oare et al. concept can be applied to additional numbers of plies and inserts.
In general, runflat tire design is predicated upon the installation of reinforcing inserts inside each sidewall flex area. The inserts in each sidewall, in combination with the plies, add rigidity to the sidewalls in the absence of air pressure during runflat operation. The '082 Patent teaches a sidewall construction for runflat tires in which the tire is constructed with two plies, an inner liner and two reinforcing wedge inserts in each sidewall. The two inserts in each sidewall are disposed such that one insert is located between the two plies while the other insert is located between the inner liner and the first or innermost ply.
While the high resistance to compression deflection of the inserts provides the necessary resistance to the collapse of the uninflated loaded tire, the use of multiple plies and, in each sidewall, more than one reinforcing wedge insert, has drawbacks which include the above mentioned increase in tire weight and flexure-induced heat build up. Such designs also increase the tire's complexity in ways that adversely affect manufacturing and quality control.
U.S. Pat. No. 3,464,477 of Henri Verdier, and assigned to Michelin Corporation, discloses a pneumatic tire particularly for off-highway (OTR) use wherein the inflated tire is to be protected against damage such as cuts and abrasion to the sidewalls when the tire is used on rocky or rough ground. Although this is not a runflat design, there are useful teachings presented since the inventor has determined that sidewall damage from such OTR operation can be ameliorated by reinforcing the tire sidewalls: “surprisingly . . . the sidewalls should be reinforced inwardly of the carcass plies.” The disclosed reinforcement of each sidewall is a single reinforcing wedge insert (“elastomeric reinforcement”) which has a maximum thickness at the mid height of the sidewall of the tire between about 1% and 3% of the overall maximum width of the tire, the reinforcement tapering toward its edges, that is toward the tread and toward the corresponding head of the sidewall and extending about half of the height of the tire.
While a high resistance to compressive deflection of the inserts provides the necessary resistance to collapse of the uninflated loaded tire, the use of multiple plies and more than one reinforcing wedge insert in each sidewall has drawbacks which include the increase in tire weight and cyclical-flexure-induced heating.
In the interests of operating efficiency and performance when operating with the tire normally inflated, the modifications to the sidewall and other areas of the tire for providing runflat operation should not adversely interact with the normal inflated operation of the tire. However, as the structure of the sidewall is stiffened with inserts and additional plies to provide runflat operation, some of the desirable operational characteristics of the tire in its inflated state are compromised.
The weight of additional sidewall plies and inserts resists the ability of the automobile suspension to allow the wheel to move in response to variations in the road surface. The increase in stiffness of the sidewall reduce
Cohn Howard M.
Johnstone Adrienne C.
The Goodyear Tire & Rubber Company
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