Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
2000-01-27
2003-07-01
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S345000, C264S348000
Reexamination Certificate
active
06585918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the modification of uniformity in tires, particularly pneumatic radial tires having a carcass ply of organic fiber cords, especially small-size tires such as passenger car radial tires, which effectively and advantageously modifies a radial force variation (hereinafter abbreviated as RFV) and a conicity force (hereinafter abbreviated as COF) of the tire as well as tires applying the above process.
2. Description of Related Art
It is well-known that the uniformity of the tire, particularly the radial tire is an important property depending upon the quality of tire performances. Among uniformity properties, RFV has an influence on performances of almost all radial tires, and COF has particularly a remarkable influence on a straight running performance of the passenger car radial tire. Firstly, RFV will be described below.
When the tire is placed on a uniformity testing machine and run thereon under loading at a state of fixing a loaded radius, the load always varies regardless of a large or small variation during one revolution of the tire, and the quantity of such a variation (all amplitude) is called as RFV. In general, the variation of the load measured by the testing machine can be taken out as a waveform that a primary component forms substantially a sine wave and secondary or more components are superposed thereon when the load applied to the tire is represented on the longitudinal axis and the distance during one revolution of the tire is represented on the horizontal axis. An example of RFV is shown in FIG.
15
.
In the tire mounted onto a vehicle, RFV is a variation quantity of reactive force in a radial direction from a road surface per one revolution of the tire running under loading. Therefore, RFV of the tire renders a force for adding vibration to the vehicle, so that the tire having a large value of RFV has problems that the ride comfort of the vehicle against vibrations is degraded and in some cases, an uneven wear is created in the tread rubber to considerably damage the steering stability of the vehicle during the high-speed running.
Therefore, it is necessary to control RFV of the tire within a range not creating the above problems. For this end, all of the tires attaching importance to the uniformity property, particularly the radial tires for passenger cars after the building through vulcanization are subjected to an inspection for sorting acceptance or rejection of uniformity by mounting each of the tires onto a given rim and applying a given internal pressure thereto. As a result, the tires showing a RFV value of more than a given rated value are removed from a forward line as a rejected product. These rejected tires are scrapped or subjected to modification for adjusting the RFV value to a range of the rated value.
And also, the uniformity of the tire includes a longitudinal deflection and a lateral deflection based on the dimensional change in addition to the above force variation. Among these deflections, the longitudinal deflection in the radial direction of the tire particularly affects the tire properties. The absolute value (maximum value) of the deflection in the radial direction is called as radial runout (hereinafter abbreviated as RR) and RR is said to have a close relation to RFV.
After RR is measured together with RFV by the inspection for sorting the acceptance or rejection of uniformity, tires having rejected RFV values are marked at a position showing a maximum value of RR without scrapping as far as possible and removed from the inspection line and subjected to RFV modification. The modification process is a process wherein the RFV-rejected tire is mounted onto a given rim and inflated under a given internal pressure and thereafter the marked surface of the tread rubber is subjected to buffing through a grinder to grind out only a partial area of the tread rubber by a gauge corresponding to RFV value to thereby decrease the RFV value.
Since the waveform of RR does not always correspond to the waveform of RFV as regards peak positions of both waveforms, a process for directly conducting RFV modification through the buffing is carried out in such a partial area along the circumference of the tread portion that centers a position showing a maximum value of RFV in a primary component taken out from the waveform of RFV.
However, even if the RFV value is modified to a proper range by the buffing to relieve the rejected tire according to anyone of the above processes, it is hardly impossible to perfectly repair the appearance of the tread portion subjected to the buffing, so that it is undeniable to lower the worth in the appearance of the tire. Furthermore, it should pay attention to a problem that the powder dust of the rubber caused by the buffing of the tread rubber worsens the working environment.
In JP-T-6-507858 (U.S. Pat. No. 5,616,859) is disclosed a process of modifying the uniformity, wherein RR comes up as a property of the modifying target of the uniformity and a part of a cord in at least one ply at a sidewall portion is subjected to a permanent deformation so as to render RR below an acceptable value and such a permanent deformation restrains a part of the tire other than a position to be modified under an inflation of a previously set pressure to restrict the stretching of the cord in the restrained part.
According to the process disclosed in the above publication, it is certainly possible to conduct the modification of RR within at least an acceptable range without damaging the appearance of the tire. However, the positions showing the maximum value and the minimum value do not always agree between RR and RFV as previously mentioned, and there is frequently caused a case that their positions widely shift each other.
And also, the correlation coefficient between RR and RFV is not so high even in the maximum value and minimum value. Because, RR is a phenomenon based on the unevenness at the cross-sectional shape of the tire, while RFV is a phenomenon based on the change of the rigidity along the circumference of the tire. The unevenness at the cross-sectional shape of the tire is caused by ununiform gauge of the tread portion along the circumference of the tire and the disorder in the arrangement of the constituting members arranged in the tread portion, especially the disorder in the cord arrangement of the cord layer constituting the belt. From this point, it is clear that RFV based on the change of the rigidity along the circumference of the tire is not always coincident with RR.
Moreover, in order to permanently deform a part of the ply cord of the carcass, it is required to apply a very high tension to the ply cord. For this purpose, the internal pressure of the tire should be a very high pressure, so that there is a fear of braking the tire during the permanent deformation of the cord.
Next, COF is a lateral force produced toward the rotating axial direction of the tire by running the tire under loading. A significant point of COF lies in a force generated in a constant direction irrespectively of the rotating direction of the tire. COF is a force mainly generated when the tread portion and the belt arranged therein form a surface of cone frustum shape and corresponds to so-called camber thrust.
COF is measured by using a uniformity testing machine in the same manner as in the measurement of RFV. In the measurement, the lateral force generated from the tire is taken out at a state of dividing into forward rotation and backward rotation of the tire. The lateral force measured is shown in
FIG. 16
as a diagram. As shown in
FIG. 16
, the lateral forces LF
P
and LF
N
vary in the rotation of the tire, respectively, and also the direction of generating the lateral force differs between the forward rotation and the backward rotation. In
FIG. 16
, the lateral force LF
P
in the forward rotation of the tire is shown at plus side (+) and the lateral force LF
N
in the backward rotation of the tire is shown at minus side (−).
C
Kata Takehiro
Kumagai Moriyasu
Bridgestone Corporation
Sughrue & Mion, PLLC
Vargot Mathieu D.
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