Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1998-10-30
2002-08-13
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S902000
Reexamination Certificate
active
06431234
ABSTRACT:
BACKGROUND OF THE INVENTION
Each year, vehicle vibration is among the most common source of new vehicle dissatisfaction. Any rotating component of a vehicle is potential excitation source for vibration, from brake rotors, the engine, driveline, wheels, tires, or even the highway surface itself. Generally, this invention relates to the use of a low speed tire uniformity machine to correct for the variation of the directional forces exerted by tires rotating against a wheel with constant deflection. This invention specifically relates to an improved method for optimizing tire uniformity, wherein a process for correcting radial force variation simultaneously reduces the directionally dependent tangential force variation caused by the uniformly sloped tread-blocks or “heel-to-toe” effect of conventional force correction techniques, thereby reducing the tangential force variation and improving the ride comfort of the tire.
FIG. 8
displays the tire uniformity coordinate system typically used in the tire industry for low and highway speed uniformity machines. The system illustrates the forces and moments generated by the tire as it rotates through the tire footprint or tread surface. Force variation produced by a tire rotating at constant deflection is broken down into three orthogonal forces referred to in industry literature as radial (Fz), lateral (Fy), and tangential (Fx). Radial force is the vertical force between the tire and the road surface, most typically the road across which the tire travels. Radial force is applied on an axis that is perpendicular to the road, and is in effect the “up and down” force acting upon a wheel's axle. Tangential or fore/aft force is the horizontal force between the tire and the road. The tangential axis is parallel to the road, in the direction of travel. It is on this axis that the tangential or driving force is applied. Tangential force is effectively the front-to-back force that acts upon the axle. Lateral force is the side-to-side force along the rotational axis between the tire and the road. The lateral axis is where side-to-side forces are applied by the tire, and this axis is parallel to the road surface, perpendicular to the direction of travel. That these three forces will be generated by a tire rotating against a load is a law of physics—they will always be present.
A goal of tire manufacturing is to eliminate or reduce any adverse effects that these forces may have on the ride of a tire, such as wheel hop or vibration. The mere existence of such forces does not create ride disturbance per se. For example, when the forces remain constant throughout the entire revolution of a tire, the tire's ride will be undisturbed. It is only when the forces vary throughout the course of a tire's revolution that ride disturbance is observed.
To illustrate this point, consider the force of gravity. Practically speaking, the earth's gravitational force is perpetual and constant in its magnitude. So while it is always acting upon every object on or near the earth's surface, it acts upon those objects in the same way at all times. In that sense, the force of gravity does not disturb the regular course of activity on earth. However, if the force of gravity were to change throughout the course of a day, activity on earth would be greatly disturbed. If the earth's gravity were to change, the weight of everything on earth would change as well. It is neither desirable nor possible to eliminate the force of gravity, but it is desirable that it remain constant. And so it is with the forces generated by tires. It is not the forces themselves that noticeably affect the ride of a tire, but the variation in force that is responsible for ride disturbance.
Force variation is generated by the rotation of a tire that is not uniform. Two primary tire deformities result in radial force variation: being “out of round” or slightly misshapen, and a variation in the tire's carcass stiffness. Carcass stiffness is the measure of a tire's resistance to flexing while revolving against a load. Resistance to flexing is simply another way of describing how much force the tire carcass is exerting against the road. Both of these deformities generate a vertical force component that disturbs the equilibrium of the wheel's axle and causes it to undergo an up and down movement during each revolution of the tire. This occurs on a tire that is out of round because some portions of the tread surface are simply farther away from the axle than others, therefore making the vertical distance between the axle and the road dependent upon which portion of the tread surface is making contact with the road. Similarly, a tire with a variable carcass stiffness will cause the axle to move up and down during the course of a rotation because some portion of the carcass will push less hard against the road than the remaining portion. If the variation in stiffness is great enough, the axle will be pushed farthest from the road when the stiffest portion of the carcass rotates across the road, and it will fall closer to the road when the most flexible portion of the carcass comes in contact with the road.
Generally, many of the deformities that cause radial force variation also cause tangential force variation. Tangential force variation is generated when the angular velocity of the tire changes throughout the course of its revolution. A change in angular velocity means that for a tire driven at constant rotational speed, some points on the tread surface of the tire are traveling at a faster linear speed than are others. This is easy to conceptualize for a tire that is out of round. In order to be out of round, some points on the tread surface must be farther away from the axle than are the others. That means that during the course of one rotation, the point farthest from the axle will travel a greater linear distance to complete its rotation than all of the other points, yet it will have done so in the same amount of time. Because speed equals distance traveled divided by time, the linear speed of the tire at the point farthest from the axle must be traveling faster than all of the other points. When that point makes contact with the road, the tire in effect pulls or accelerates the axle forward. However, as soon as that point passes the road, a slower point comes into contact with the road and acts to decelerate the axle or push it back. This pushing and pulling motion will occur once every rotation, resulting in ride disturbance. Variation in carcass stiffness will also cause this pushing and pulling effect because the least rigid portion of the tire will travel more slowly across the road than the rest of the tire.
Because many tire deformities are generally responsible for both radial and tangential force variation, it is logical that detecting and correcting the deformity would correct for both types of variation. Grinding is an effective technique for correcting tires that are either out of round or have variable carcass stiffness. A tire that is out of round can be ground so that it is uniform. Grinding can also make carcass stiffness more uniform. If carcass stiffness is thought of as the spring force of the tire, then the goal is to make the force a constant. A spring's force or potential is the product of its length and its spring coefficient, which is a constant unique to that spring. If each point on a tire's tread surface is thought of as a spring from that point to the axle, then the spring force would be the product of the length of that spring and its coefficient. If the spring lengths are not uniform, the tire is obviously out of round, and grinding can remedy this. If the tire is uniformly circular, but of variable carcass stiffness, then the variance is in the spring coefficients. Because a spring's coefficient is constant, and the goal is to make the spring's force constant, the only factor than can be corrected for is spring length. Grinding minute amounts of rubber at those points of greatest spring force will reduce th
Edwards, II Henry Buel
Gast, Jr. George E.
Gormish Kenneth J.
Zolton Gary Paul
Continental Tire North America, Inc.
Maki Steven D.
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