Apparatus and method for measuring uniformity and/or dynamic...

Measuring and testing – Rotor unbalance – Dynamic

Reexamination Certificate

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C073S462000

Reexamination Certificate

active

06658936

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to method and apparatus of measuring a tire uniformity and/or dynamic balance.
There have been known method and apparatus of measuring a tire uniformity and dynamic balance in order to evaluate whether a tire may cause the vibration and acoustic noise of a motor vehicle on which the tire is mounted. When a uniformity measurement is performed, a tire to be tested is rotated with a rotary drum being press-contacted the circumferential surface thereof when it is rotated, and radial and/or thrust force variations are detected. When a dynamic balance measurement is performed, based on a centrifugal force when the tire is rotated, the eccentricity of the tested tire is detected.
An example of the tire uniformity and dynamic balance measuring apparatus is disclosed in Japanese patent Application Provisional Publication No. HEI 11-183298. In the above-described publication, a tire is mounted on a rotary spindle, which is rotatably supported within a spindle housing using ball bearings, and is rotated at a predetermined rotation speed.
Specifically, when the uniformity measurement is performed, the rotary drum is press-contacted with the circumferential surface tested tire at several hundreds Kgf or more, and the tire is rotated together with the spindle. The force variation can be detected by load cells fixed to the rotary drum. Since the load cells detect force based on the deformation thereof, for detecting the force variation at high accuracy, the rotation axis of the tested tire must be prevented from vibrating during the uniformity measurement.
On the other hand, when the dynamic balance measurement is performed, the tire is rotated without the rotary drum. Then, the centrifugal force generated in the tested tire due to unbalance of the tire is detected using the load cells provided between the spindle housing and a base of the apparatus. It should be noted that, during the dynamic balance measurement, the spindle housing should be allowed to vibrate freely.
Accordingly, the conventional tire uniformity and dynamic balance measuring apparatus must include a lock/unlock mechanism for preventing the vibration of the tested tire during the uniformity measurement and allowing the vibration of the tested tire during the dynamic balance measurement, which requires a relatively complicated system.
Furthermore, in order to perform the measurements for wheeled tires, by the conventional apparatus, hub holes of the wheel should be fixed to cylindrically-shaped protruded potions of the spindle unit. The axis of the protruded portions coincides with the rotational axis of the spindle at high accuracy in order to position the wheeled tire.
However, the system limit of the diameter of the hub hole is typically around 0.2 mm, so the system limit of coaxiality between the rotational axis of the tested tire and the rotational axis of the spindle can be up to 0.1 mm. That is, the rotational axis of the tire can be divided from the rotational axis up to 0.1 mm. It is therefore difficult to the dynamic balance and/or uniformity at high accuracy.
The uniformity measurement is defined by JASO C607 standard. In the standard, the rotational speeds of a tested tire is defined to 60 r.p.m., which corresponds to a vehicles speed of approximately 7 kilometers/hour, which might be insufficient to evaluate the tires. It is desirable to measure a high-speed uniformity of tires for evaluating the behavior thereof when a motor vehicle runs at a higher speed.
In particular, the tractive force variation affects the vibration and acoustic noise of a motor vehicle which is driving at a relatively high speed. It is therefore desirable to detect the tractive force variation in the high-speed uniformity measurement.
Moreover, the above-mentioned conventional measuring apparatus rotates the spindle using a belt driving mechanism which employs an endless belt for the dynamic balance measurement. In order to rotate the spindle at the desired revolution speed at high accuracy, inelastic belt, such as a canvas belt, is preferably used as the endless belt. Such an inelastic belt can, however, transmit most of vibrations, caused by friction between the belt and pulleys to which the belt is wound. The vibration is transmitted to the spindle, which makes it impossible to measure the dynamic balance at high accuracy.
SUMMARY OF THE INVENTION
In view of the above, an advantage achieved by the present invention is to provide a simple-structured apparatus and method of measuring the uniformity and/or the dynamic balance of a tested tire.
A further advantage of the present invention is to provide an apparatus and/or a method capable of positioning the wheeled tire for the spindle of the apparatus with high accuracy.
A furthermore advantage of the present invention is to provide an improved apparatus and method capable of measuring the uniformity suitable for measuring the high-speed uniformity.
In one aspect of the present invention, there is provided an apparatus for measuring uniformity and dynamic balance of a tire, comprising:
a spindle rotatably supported in a rigidly-supported spindle housing, said tire being fixedly mounted on said spindle, said spindle being rotated when measurement is performed; and
at least one piezoelectric force sensor mounted on a surface of said spindle housing, said at least one piezoelectric force sensor detecting a force generated by rotation of the tire as said spindle is rotated.
The piezoelectric force sensor can detect the force while deforming little. It is therefore capable of detecting the force generated during the dynamic balance measurement although the spindle housing is rigidly supported.
In the preferable embodiment of present invention, there is provided an apparatus for measuring uniformity and/or dynamic balance of a tire, comprising:
a spindle rotatably mounted in a spindle housing via at least one bearing, the tire being fixedly mounted on said spindle; and
at least one radial cylindrical bearing that rotatably supports said spindle in said spindle housing, said radial cylindrical bearing including at least a radial double-row cylindrical bearing.
The radial cylindrical bearing is capable of supporting higher load although the strain of the bearing is lower than a ball bearing. The vibration of the spindle against the spindle housing can be prevented, therefore the force generated in the spindle can be transmitted to the spindle housing with high accuracy.
Preferably, a part of a circumferential surface of said spindle on which said radial cylindrical bearing is to be attached is tapered, an inner surface of said radial cylindrical bearing is tapered such that a cone angle of said inner surface is the same as a cone angle of the tapered part of the circumferential surface of said spindle, and said radial cylindrical bearing is attached to said spindle so that the inner surface of said radial cylindrical bearing tightly fits on said tapered part of the circumferential surface of said spindle.
The inner ring of said radial cylindrical bearing tightly fits to said tapered part of the circumferential surface of said spindle, therefore the vibration of the spindle against the spindle housing can be further prevented.
In the preferable embodiment of present invention, there is provided an apparatus for measuring uniformity and/or dynamic balance of a tire, comprising:
a spindle rotatably mounted in a spindle housing via at least one bearing, the tire being fixedly mounted on said spindle,
wherein said spindle holds the tire between a lower rim attached to said spindle and an upper rim which is arranged oppositely with respect to the lower rim, said upper rim is movable upward and downward with respect to said spindle, said upper rim including a lock shaft downwardly extending from a rotation center of said upper rim, said lock shaft being capable of fitting to a fitting portion formed in said spindle.
Preferably, said spindle is rotatably supported in said spindle housing via a plurality of bearings, and wherein the fitting porti

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