Measuring and testing – Tire – tread or roadway
Reexamination Certificate
1999-04-28
2002-02-19
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Tire, tread or roadway
Reexamination Certificate
active
06347547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of modifying uniformity of tire, in details, to a method of reducing the second harmonic of TFV (tangential force variation) which is one of factors for causing vehicular vibration in high speed running of an automobile.
2. Description of the Related Art
Vehicular vibration such as vibration of a steering wheel caused in high speed running of an automobile, is caused by being inputted with force variation of tire owing to unevenness referred to as tire nonuniformity or force variation in centrifugal force caused by rotation of tire based on unevenness of mass of tire in its circumferential direction referred to as unbalance in correspondence with a vibration characteristic of suspension or the like of a vehicle. Among them, in respect of vibration of the first harmonic of tire rotation, there have been proposed a method concerning its mechanism and improvement.
For example, in respect of force variation caused by mass unbalance in the circumferential direction of tire, the variation is reduced by attaching a balance weight to a road wheel. Further, in respect of the first harmonic of TFV or radial force variation (RFV) caused by a variation in the diameter of tire, the variation is reduced by reducing force variation or diameter variation in the circumferential direction of tire.
Meanwhile, in respect of the second harmonic or higher harmonics, although they are normally small and not problematic, their levels are increased by an increase in the running speed of an automobile, further, they are considerably increased when the frequencies of the harmonics coincide with the resonance frequency of tire in high speed running.
Particularly, in respect of the second harmonic of TFV, a resonance frequency of a longitudinal torsional vibration of tire is at a vicinity of 25 through 40 Hz and accordingly, a frequency of the second harmonic of tire rotation and the longitudinal torsional resonance frequency coincide with each other at a vicinity of normal running speed of 100 km/h at high speed running, hence, the second harmonic of TFV increases significantly to thereby constitute a factor of generating vehicular vibration.
However, in respect of the second harmonic of TFV, its mechanism of occurrence and method of improvement thereof have not been clarified and even when a balance weight is attached to a road wheel similarly to reducing the force variation by unbalance, the second harmonic of TFV is not reduced.
Therefore, conventionally, a position of a seam of material is changed in producing tire or promoting accuracy of production steps, as a result, the second harmonic of TFV is reduced.
In view of such an actual situation, it is an object of the invention to reduce the second harmonic of TFV constituting one factor of vibration in high speed running of a vehicle.
SUMMARY OF THE INVENTION
As a result of an intensive study by ascribing the second harmonic of TFV to mass unbalance in the circumferential direction of tire and diameter variation in the circumferential direction, the inventors have found that the second harmonic of TFV is reduced by providing or eliminating masses at pertinent two locations opposed to each other in the diameter direction of tire and completed the invention.
That is, according to a first aspect of the invention, there is provided a method of modifying uniformity of tire wherein a tire is rotated at a vibration generating speed based on the second harmonic of TFV and a phase and an amplitude of the second harmonic are measured, and wherein the second harmonic of TFV is reduced by providing mass members specified based on the amplitude at two locations opposed to each other in a diameter direction of the tire specified based on the phase such that the measured second harmonic of TFV is canceled by the second harmonic of TFV caused by providing the masses.
More specifically, the measured phase of the second harmonic of TFV is converted into the first harmonic phase of the tire and the mass members are provided within a range of 32.0 through 61.0 deg in a rotational direction in measuring the second harmonic from tire positions minimizing the second harmonic by which the second harmonic of TFV can be reduced.
According to a second aspect of the invention, there is provided a method of modifying uniformity of tire wherein a tire is rotated at a vibration generating speed based on the second harmonic of TFV and a phase and an amplitude of the second harmonic are measured, and wherein the second harmonic of TFV is reduced by eliminating masses specified based on the amplitude at two locations opposed to each other in a diameter direction of the tire specified based on the phase such that the measured second harmonic of TFV is canceled by the second harmonic of TFV caused by eliminating the masses.
More specifically, the measured phase of the second harmonic of TFV is converted into the first harmonic phase of the tire and the specified masses are eliminated within a range of 32.0 through 61.0 deg in the rotational direction in measuring the second harmonic from tire positions maximizing the second harmonic by which the second harmonic of TFV can be reduced.
Next, a detailed description will be given of the operation of the invention.
In the case in which there causes mass unbalance in the circumferential direction of tire, as shown by
FIG. 3
, when the tire is rotated, unbalance force based on unbalanced mass m is caused by centrifugal force and TFV is caused by a component thereof TF in the longitudinal direction.
The longitudinal direction component TF of the centrifugal force of the unbalanced mass m is given as follows by acceleration &agr;
Z
in the diameter direction and acceleration &agr;
X
in the circumferential direction.
TF=m
(&agr;
X
cos &thgr;+&agr;
Z
sin &thgr;) (1)
In this case, the accelerations &agr;
X
and &agr;
Z
are measured by an inner face acceleration meter, changed in accordance with a position &thgr; of the unbalanced mass m and is increased before and after grounding as shown by FIG.
4
. This is because the substantial radius is changed when the unbalanced mass m is grounded. Owing to such a change of the accelerations &agr;
X
and &agr;
Z
, even when there causes mass unbalance of the second harmonic at two locations (a state in which unbalanced masses are present at two locations opposed to each other in the diameter direction of tire), these are not canceled by each other.
Hence, as shown by
FIG. 5
, assume that unbalanced masses m are present at two locations opposed to each other in the diameter direction (phase=0 deg, 180 deg) on the circumference of the tire, TFV is calculated by calculating the longitudinal direction component TF of the centrifugal force of the unbalanced masses m by Equation (1) mentioned above and the result of calculation is subjected to Fourier analysis to thereby calculate the amplitude and the phase of the second harmonic of TFV. In that case, in respect of the magnitude of TF, magnitudes of respective frequency components are corrected in consideration of the transmissibility in the longitudinal direction of the tire.
The result is shown by FIG.
5
and in
FIG. 5
, the phase of the second harmonic of TFV is shown to be converted into the first harmonic phase of the tire. As shown by
FIG. 5
, according to the second harmonic of TFV, peak positions (positions having maximum values) P thereof are disposed at two locations opposed to each other in the diameter direction of 46.5 deg and 226.5 deg as tire positions and bottom positions (positions having minimum values) B are present at positions (136.5 deg and 316.5 deg) of a phase difference of 90 deg as tire positions from the peak positions P.
It is known thereby that according to the second harmonic of TFV caused by mass unbalance, the peak position P is provided with shift of phase of −93 deg from the position of the unbalanced mass m or rearward therefrom by 46.5 deg in a rotational direction in measuring the seco
Ishitsuka Toru
Moriguchi Kinya
Aw-Musse Abdullahi
Fuller Benjamin R.
Jordan and Hamburg LLP
Toyo Tire & Rubber Co., Ltd.
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