Optics: measuring and testing – Angle measuring or angular axial alignment – Wheel alignment with photodetection
Reexamination Certificate
1998-07-31
2002-01-22
Black, Thomas (Department: 2171)
Optics: measuring and testing
Angle measuring or angular axial alignment
Wheel alignment with photodetection
C356S055000, C033S203180, C382S104000, C382S203000, C701S082000, C702S095000, C702S150000, C702S151000
Reexamination Certificate
active
06341013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This patent relates to a method for measuring the characteristic angles of the attitude of a vehicle for the purpose of its regulation, and the device for implementing the method.
2. Description of Background Art
Periodically checking the attitude setting of a vehicle is important in ensuring the best road holding and best driving comfort.
Road holding is directly proportional to the vehicle road adherence, which is itself a function mainly of two factors, namely the area of contact of the tires with the ground, and the wheel drift, these both depending on the geometry of the vehicle frame and of the suspensions.
The geometry of a vehicle frame provided with wheels and suspensions defines the characteristic wheel angles, ie the angles between each wheel and the others, between each wheel and the longitudinal and transverse frame axes, between each wheel and the vehicle running axis and between each wheel and the vertical to the ground, and the steering angles. The correct values of these angles are dictated by the vehicle manufacturer.
These angles must therefore be able to be measured in order to set them to the appropriate values.
The characteristic angles are:
left, right and total front convergence
left, right and total rear convergence
right and left front camber
right and left rear camber
right and left incidence
right and left kingpin
front and rear set-back
thrust angle
track difference
The text will be better understood from the following definitions of the characteristic angles:
the convergence is the angle formed between the plane perpendicular to the axis oil each wheel and the longitudinal axis of symmetry of the vehicle;
the total convergence is the sum of the angles of convergence of the wheels pertaining to one and the same axle;
the track angle is the angle formed between the plane perpendicular to the axis of each wheel and the vertical plane;
the angle of incidence is the angle between the projection of the steering axis onto the vehicle longitudinal plane and the vertical;
the kingpin angle is the angle formed between the projection of the steering axis onto the vehicle transverse plane and the vertical;
the set-back is the misalignment of the wheels of one and the same axle to the vehicle axis of symmetry;
the thrust axis is the axis defined by the bisector of the total rear convergence angle;
the track difference is the angle between the line joining the wheels positioned on one and the same side, but pertaining to two different axles, and the vehicle axis of symmetry.
The most recent known devices used for regulating the attitude of vehicle wheels are based on opto-electronic measuring and sensing instruments.
These devices comprise angle measuring instruments which are generally applied to the vehicle wheels and mutually interact mechanically or optically, or are fixed to the ground to obtain the image of reference markers positioned on the wheels. These reference markers can be either solid locators fixed to the wheels, or images projected onto the wheels.
The data obtained by said devices are fed to a processor which processes them using known geometrical formulas which give as their result the values of the characteristic angles of the frame attitude.
Known devices however suffer from a series of problems which substantially limit both their use and their accuracy.
A first important drawback is the time required for taking the measurements and making the relative adjustment. In this respect, in known devices, more than twenty operations are required for preparing the vehicle and taking a measurement, and it has been found that the preliminary operations involve on an average more than 70% of the time required for carrying out a normal measurement cycle.
A further drawback is determined by the systematic errors introduced by the compensation operation.
The compensation operation reduces the measurement errors deriving from the geometrical deformation of the wheel rim and from the sensor-wheel coupling.
This is achieved by introducing into the measurement a correction factor calculated using data obtained during one turn of the vehicle wheel.
However to achieve a wheel turn without involving considerable space the wheel has to be raised from the ground, so releasing the vehicle weight from the suspension-shock absorber unit.
However this introduces errors due to the fact that during their working stroke the suspensions induce variations in the characteristic angles of the vehicle, hence raising the wheel from the ground leads to the drawback of finding the wheels positioned in a different manner from that when in the running state, which is achieved only after the suspensions have settled.
A further limit of current aligners is the maximum range of angular measurement of the transducers. In particular, this limit is apparent in measurements on the steering geometry.
Motor vehicle manufacturers have generally used a linkage scheme for the steering members known as a “Jeantaud triangle”. This configuration ensures concentricity of the circumferences travelled by the wheel through large-radius bends, however for steering through a smaller radius of curvature the Jeantaud triangle creates a condition which progressively deviates from the ideal.
It is therefore apparent how important it is to make accurate measurements on the steering geometry in order to guarantee the safety and road holding of the vehicle.
For effecting these measurements, currently available opto-electronic aligners use rotating plates positioned below the steered wheels and provided with electronic devices. The steering angle is measured by graduated pointers or by electronic transducers which measure the plate rotation.
These systems partly overcome the limited measurement range of transducers, but make indirect measurements which are subject to errors due to the roto-translational movement of the plate. In this respect, during steering, the wheel movement can be resolved into a translation component and a rotation component, this phenomenon being due to the steering axis not passing through the wheel center.
It is apparent that an indirect measurement, such as that made by known devices, is subject to errors due to the double nature of the phenomenon to be measured.
The attitude can be measured and then regulated either by apparatus which take the measurements using devices connected to the wheel rim or by apparatus which do not use any device fixed to the wheel rim.
Apparatus are known for measuring the characteristic attitude angles by mounting measuring devices on all the vehicle wheel rims.
These devices are in the form of goniometers or angle transducers interacting with identical instruments fixed to the wheel rims of two adjacent wheels, in the transverse and longitudinal directions.
This interaction between said instruments can be achieved either mechanically by means of wires or springs, or by electrical and/or optical devices.
When the measurements have been taken, a processor processes the measured data by mathematical algorithms of known type.
Devices are also known which use measuring systems in which no reference material is positioned on the wheel rim.
U.S. Pat. No. 4,899,218 in the name of WALDECKER illustrates a measurement process based on projecting an oscillating structured light beam onto the wheel in such a manner as to produce at least two reference images on it.
Said images are read by video cameras positioned at a certain angle to the optical plane defined by the plane of oscillation of said beam.
The spatial position of the outlines and hence of the wheel is calculated by a computer using a known triangulation system.
Having defined the spatial wheel position in this manner, a processor calculates the characteristic attitude angles relative to a suitable reference system.
The devices utilized in the stated patent are very complicated to use, especially with regard to the procedure for calibrating the apparatus.
Published patent application DE 2948573 in the name of SIEMENS describes an apparatus in which
Battiti Roberto
Corghi Remo
Birch & Stewart Kolasch & Birch, LLP
Black Thomas
Corghi S.p.A.
Veillard Jacques
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