Measuring and testing – Tire – tread or roadway
Reexamination Certificate
1998-04-21
2001-12-11
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Tire, tread or roadway
C073S146200
Reexamination Certificate
active
06327904
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining the tread depth of a vehicle tire while the vehicle is moving.
From German patent application 19 523 917 a method for determining the tread depth of a vehicle tire while the vehicle is moving is disclosed. Based on the measured values for the vehicle velocity and the measured values of wetness sensors, that detect the water spray caused by the tires when driving on a wet road surface, with the aid of a characteristic line field the tread depth of the vehicle tire is determined.
From German patent application 32 36 520 a method for detecting the tread depth of vehicle tires while the vehicle is driving can be taken whereby, based on the measured values of the rpm sensors at the wheels and on determined reference velocities, long term changes of the tire state (wear) and thus the actual tread depth are deduced.
From German patent application 195 14 219 a method for determining the tread depth of vehicle tires can be taken in which the momentary value of the tread depth is determined based on the initial tread depth PT
0
, a specific tire wear, which incorporates a driving behavior-proportional value SK1 determined continuously during driving by different sensors, and the driven miles.
From German Offenlegungsschrift 44 35 160 a device for determining the circumferential force of a vehicle wheel is known which functions without contacting the wheel. At least one first sensor element is provided in the sidewall of the tire which generates, when passing a sensor provided at the vehicle, a signal that is used for determining the angular position of an outer vehicle tire point relative to a hub-based coordinate system that rotates with the tire. The hub-based coordinate system is represented either by a second sensor and a second vehicle-attached sensor or by an ABS sensor of the vehicle mounted on the wheel hub.
It is therefore an object of the present invention to use the signal provided by the sensor for determining the tread depth of the vehicle tire while the vehicle is moving.
SUMMARY OF THE INVENTION
The inventive method for determining the tread depth of a vehicle tire while the vehicle is driving is primarily characterized by:
a) determining an angle of a radially outer tire location relative to a hub-based coordinate system by a sensor fastened to the vehicle, whereby the sensor circuits a corresponding signal;
b) analyzing the signal containing harmonic oscillation sent by the sensors;
c) determining based on the signal a resinate frequency corresponding to the torsional oscillation component of the tire belt relative to the wheel;
d) computing a mass moment of inertia of the tire belt about the axis of rotation based on a torsional stiffness of the tire sidewall and the determined resonant frequency;
e) calculating the actual mass and changes of the tire diameter based on the computed mass moment of inertia and based on a mass function of the vehicle tire that is a function of the tire diameter;
f) calculating a loss of tread depth based on the changes of the tire diameter.
Preferably, in step d) the torsional stiffness of the tire sidewall is determined based on the angle of the outer tire location relative to the coordinate system for a known drive moment and known circumferential force of the vehicle tire in a defined driving condition of the vehicle.
According to the present invention the determination of the tread depth is carried out with the following steps:
determining the angle of an outer tire location relative to a hub-based coordinate system by a sensor attached to the vehicle;
analyzing the signal supplied by the sensor and containing harmonic oscillation and determining the resonant frequency which corresponds to the torsional oscillation component of the tire belt relative to the wheel;
computing the mass moment of inertia of the tire belt about the axis of rotation based on the torsional stiffness of the sidewall and the determined resonant frequency;
calculating the actual mass and the changes of the tire diameter based on the determined mass moment of inertia and the mass function of the tire that is a function of its diameter;
calculating the tread loss based on the changes of the tire diameter.
In a preferred embodiment of the invention it is suggested to determine the torsional stiffness of the tire sidewall based on the angle of the outer tire location relative to the coordinate system that rotates with the wheel for a known drive moment and thus known circumferential force of the tire in a defined driving state of the vehicle. This avoids, when changing the tire, having to manually enter a value corresponding to the torsional stiffness of the sidewall into the memory of a device provided at the vehicle for performing the inventive method.
REFERENCES:
patent: Re. 28775 (1976-04-01), Tarpinian
patent: 3918816 (1975-11-01), Foster et al.
patent: 4472974 (1984-09-01), Dickson et al.
patent: 5913240 (1999-06-01), Drahne et al.
patent: 3236520 (1984-04-01), None
patent: 4435160 (1996-04-01), None
patent: 1951421 (1996-10-01), None
patent: 1952391 (1997-01-01), None
Aw-Musse Abdullahi
Becker R. W.
Continental AG
Fuller Benjamin R.
R.W.Becker & Associates
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