Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-12-14
2003-04-22
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209160, C152S517000, C152S555000
Reexamination Certificate
active
06550509
ABSTRACT:
TECHNICAL FIELD
The present invention relates to pneumatic radial ply runflat passenger tires and to management of tread lift and vehicle handling during runflat operation.
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 in such a way that the tire structure alone has sufficient rigidity and strength to support the vehicle load when the tire is operated in the uninflated condition. 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 other devices to prevent the tire from collapsing.
An 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.
Numerous methods have been used to achieve workable runflat tire designs. Generally, such tires incorporate sidewall designs 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 methods used in sidewall stiffening include the incorporation of circumferentially disposed 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, the sidewalls are thickened in a way that each is approximately uniformly thick in the sidewall 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. However, the outer portions of the reinforced sidewalls are in tension due to bending forces which deflect the sidewalls outward or apart from one another in the regions of the sidewall that are adjacent to the ground-contacting portion of the tread. The inner portions of such reinforced sidewalls, in the region near where the tread contacts the ground, tend to be in compression during runflat operation.
A Goodyear U.S. Pat. No. 5,368,082 ('082) disclosed 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 lb 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 was even more problematic when the tire designers attempted to build high-aspect-ratio tires for large luxury touring sedans. These taller sidewalled tires, having aspect ratios in the 55% to 65% range or greater, produces correspondingly greater sidewall bending stresses than were encountered in the earlier low-aspect-ratio runflat tires disclosed in the '082 patent. Thus the sidewalls of high profile tires had to be stiffened to the point of compromising ride characteristics. Luxury vehicle owners generally do not wish to sacrifice ride quality for runflat capability. The design requirements for runflat tire design require that there be no loss in ride quality or handling performance. In the very stiff suspension performance type vehicle, such as sport cars and various sport/utility vehicles, the ability to provide such runflat tires is relatively straightforward compared to providing similar runflat tires for luxury sedans which require softer ride characteristics. Light trucks and sport utility vehicles, although not as sensitive to ride performance, provide a runflat tire market that ranges from accepting a stiffer ride to demanding the softer luxury type ride.
In general, runflat tire design is based on the installation of one or more inserts inside each sidewall flex area. The inserts in each sidewall, in combination with the plies, add rigidity to the sidewalls in the reduction or absence of air pressure during runflat operation. While the high resistance to compression deflection of the inserts provides the necessary resistance to the collapse of the uninflated loaded tire, this method has several drawbacks which include the above mentioned increase in tire weight as well as, during runflat operation, changes in the tread-to-road contact, which adversely affect vehicle handling, especially during high-speed runflat operation.
The changes in the tread-to-road contact during runflat operation derive from the tendency of the thick reinforced sidewalls to transmit bending forces to the portion of the tread that contacts the ground. The result is that the central portion of the tread tends to buckle upwards from the ground. The upward buckle reduces the ground contact in the tread's central region, resulting in compromised vehicle handling as well as reduced runflat tread life due to severe cyclical flexure, and corresponding heat buildup, of the central portions of the tread, especially during sustained high-speed operation.
Clearly, the goal in runflat tire design is to provide a tire which gives good runflat vehicle handling as well as good service life of the tire during runflat operation. Since the handling deficit associated with runflat operation derives at least partially upward buckling of the central portion of the tire tread, various methods have been introduced to minimize such buckling or “tread lift,” as it is sometimes called. Such methods include means by which to increase the lateral stiffness of the tread by the employment of additional structures, such compressive-stress-bearing breaker reinforcements, tensile-stress-bearing ply reinforcements, and wedge inserts located between the breakers and plies. (The latter wedge inserts give mechanical advantage to the respective tension-bearing and compression-bearing structures). The main disadvantage of such tread-stiffening structural additions is greater tire weight, in addition to the increased weight of the reinforced sidewalls.
Another aspect of the tire design that effects runflat operation relates to the tread contour. Treads designed specifically for the passenger vehicles traditionally have been designed such that the cross-sectional, or translateral, contour of the tread has been defined according to multiple radii of curvature which are joined in such a way that adjacent circular curves meet one another tangentially, i.e., without discontinuity in the curvature of the tread across its lateral dimension. Furthermore, the radius of curvature defining the cross-sectional contour of the central portions of the tread tends to be much longer than the radii of curvature that define the cross-sectional c
Close Roland
Nguyen Gia Van
Thielen Georges Marcel Victor
Verbeke-Ensch Agnes Nathalie Iwana
Cohn Howard M.
Maki Steven D.
The Goodyear Rubber & Tire Company
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