Measuring and testing – Tire – tread or roadway
Reexamination Certificate
2001-07-09
2004-01-06
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Tire, tread or roadway
C073S118040
Reexamination Certificate
active
06672148
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application relates to applications entitled METHOD OF IMPROVING STEERING PERFORMANCE ROBUSTNESS UTILIZING DIMENSIONAL NON-UNIFORMITY IN TIRE/WHEEL, and METHOD OF IMPROVING STEERING PERFORMANCE ROBUSTNESS UTILIZING STIFFNESS NON-UNIFORMITY IN TIRE/WHEEL, both having a filing date concurrent with that of the present application.
TECHNICAL FIELD OF THE INVENTION
This invention relates to methods of improving the steering performance of vehicles, particularly passenger vehicles having pneumatic tires.
BACKGROUND OF THE INVENTION
The term “steering performance” (or simply “steering”) refers to a vehicle driver's feeling that a vehicle's steering (and/or “handling”) is responsive to movement of the steering wheel. The better the steering performance, the better the driver's “feeling” of having control over the vehicle's steering. Because it relates to a “feeling” on the part of a driver, steering performance is essentially a subjective evaluation of a vehicle's steering. Steering performance can change over time, mainly deteriorating as components in the vehicle steering system wear, age, or suffer damage. Steering system components include the steering wheel, the tires and wheels, and everything in between such as the steering box, any power assist components, and linkages and joints. Steering performance can also vary with operating conditions, including, for example, road texture, vehicle speed, steering wheel settings, minor tire inflation pressure changes, and tire/wheel uniformity changes (e.g., balance).
Worsening steering performance is generically referred to as “steering performance loss” (SP-Loss), or “give-up”. A steering system or component which is resistant to steering performance loss is “robust” or can be said to possess “steering performance robustness”. Similarly, any component change which appears to delay or prevent SP-Loss in a vehicle steering system can be said to improve steering performance robustness. Also, it has to be mentioned that SP-Loss is more noticeable on vehicles which have, in general, a very good and crisp steering. Finally, it has been noted that steering component changes which improve steering performance robustness usually also enhance the driver's perception of steering performance. The inverse may not be true, i.e., a component change which enhances steering performance initially may not be robust and therefore quickly deteriorates to yield a net steering performance loss.
Steering performance loss is mostly a concern in passenger vehicles with pneumatic tires and power assisted steering (power steering), although the phenomenon has also been observed in passenger vehicles without power steering. Although a trained driver can determine steering performance at virtually any vehicle speed, the steering performance (and therefore a change in performance, e.g., SP-Loss) is most noticeable above a certain vehicle speed threshold. Even though SP-Loss is generally a change over time, it can be practically instantaneous.
Certain vehicles appear to be more susceptible to SP-Loss, and it has been noted (especially on these vehicles) that steering performance is affected by differences in tire construction, or even by changes from one tire to another of the same tire construction. (The common industry term “tire construction” includes all elements of a tire's design—including, for example, tire/carcass shape, tread pattern, number and type of plies, materials and manufacturing methods used, etc.) It is well known that tire uniformity (e.g., balance) varies from tire to tire, and that an unbalanced tire causes vibrations which are felt in the steering, therefore tire uniformity is almost universally controlled in tire and wheel design, during tire and wheel manufacturing, and after forming a tire/wheel assembly. It is generally assumed that improved tire/wheel uniformity will improve steering performance and hopefully will also help with steering performance robustness. As noted above, this is not always the case, and thus a great deal of research has been directed toward additional solutions to SP-Loss, such as various tire design changes.
Regardless of tire construction/design, the tire and vehicle industry generally strives for the best possible tire uniformity and, by extension, uniformity of the tire/wheel assembly whenever a tire is mounted on a wheel for use on a vehicle. This is a multi-part optimization process whereby the tire manufacturer strives for optimum tire uniformity, the wheel manufacturer strives for optimum wheel uniformity, and then the vehicle operator has the tire/wheel assembly tested and corrected for “balance”.
Tire uniformity and tire/wheel balance are well known topics in the tire industry. A brief description of certain relevant portions of these topics will now be presented.
Uniformity and Balance
Tire manufacturers generally perform quality checks on tires at various points during the manufacturing process. Tire uniformity is an important, performance-related check typically performed on a tire uniformity machine (TUM) which is well-known in the art and will not be described in detail herein. Tire uniformity machines most commonly rotate a tire mounted on a known-to-be-uniform or “true running” wheel, and measure variations in forces on the wheel axis (or on a load wheel) and/or measure variations in tire outer surface positions. Typical force variation measurements include radial force variation (RFV) which is indicative, for example, of static imbalance or radial runout; and lateral force variation (LFV) which is indicative, for example, of couple imbalance, lateral runout, or tire radial runout skewness. Tire surface measurements are directly indicative of runout conditions and conicity. Another measurement, generally done on a sampling basis on special laboratory grade, high speed TUMs, is tangential force variation (TFV), or fore-aft force variation which is experienced at the surface of contact between a tire and a road surface in a direction both tangential to the tire tread and perpendicular to the tire axis of rotation.
In terms of effect on a vehicle and its tires, all of the types of force variations can cause vibrations dependent upon the magnitude of the force variation (modified by vehicle characteristics such as wheel suspension mass/stiffness/damping conditions). The lateral force variation (and/or couple imbalance) primarily cause vibrations due to a wobbling motion of the tire, with the axis of rotation for the oscillation being vertical or horizontal, parallel to the tire's circumferential plane, and approximately centered within the tire/wheel volume. In contrast, radial and tangential force variation and/or static imbalance mainly cause vibrations due to movement in vertical and fore-aft directions (although some lateral movements exist, they are distributed symmetrically about the equatorial plane and involve only a small percentage of the total tire/wheel assembly mass).
Static and Couple Imbalances
Generally speaking, when a tire/wheel assembly is “balanced”, the modern practice is to test, and correct if necessary, both the static and the couple balance of the assembly. This balancing is generally performed using special-purpose equipment. For couple balancing, the equipment generally rotates the tire/wheel assembly at a relatively high speed, and the tire is not in contact with any surface (compare to the road-wheel used in TUM testing).
Static imbalance arises in a rotational system such as a tire and wheel assembly when the mass of the rotating tire/wheel assembly is non-uniformly distributed about the axis of rotation in such a way that the sum of the centrifugal force vectors arising from each moving part of the rotating system is non-zero. The term “static,” when used in reference to rotational balance, refers to the fact that rotational motion is not needed to identify, locate and correct the rotational imbalance. That is, a wheel that has a static imbalance will, at certain stationary angular orientat
Croissant Bernard
Koeune Thierry
Kunsch Romain
Michel Edouard
Cohn Howard M.
Lefkowitz Edward
Stevens Maurice
The Goodyear Tire & Rubber Company
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