Electricity: measuring and testing – Magnetic – Displacement
Patent
1995-08-16
1997-03-11
Arana, Louis M.
Electricity: measuring and testing
Magnetic
Displacement
324236, G01B 714, G01N 2772
Patent
active
056105142
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an electric circuit for measuring the length of a shock absorber unit of a vehicle, comprising: a coil with windings which are fitted around the shock absorber unit, of which a casing of electrically conducting material connected to a part of the wheel suspension of the vehicle is axially movable relative to the coil when there is a change of length of the shock absorber unit as a result of a change in the force absorbed by the wheel suspension; an oscillator connected to the coil, for exciting the coil with an excitation signal of a predetermined frequency; and processing means which are connected to the coil and are designed for determining the value of a relation between the voltage across the coil and the current through the coil, which value is a measure of the length of the shock absorber unit. In this connection, the length of a shock absorber unit should be understood as the distance between two fixing points thereof in the wheel suspension, while the wheel suspension of the vehicle should be understood as the damped spring construction which couples a wheel in a supporting manner to the body. In this case, the casing of the shock absorber unit can be connected to the body and the coil to the wheel, or the casing can be connected to the wheel and the coil to the body. The term vehicle below should be understood not only as a road vehicle such as a lorry or private car, but also as a rail vehicle or an aircraft on the ground.
BACKGROUND
Shock absorber units which are provided with means for an inductive length measurement thereof are generally known, in particular from U.S. Pat. No. 4,502,006, which discloses how a cylindrical electric coil is disposed coaxially around a shock absorber housing, which housing is axially movable in the coil when there is a change of length of the shock absorber unit. When there is a change in the position of the housing relative to the coil, the electrical properties of the coil change. The phase difference between the alternating current through and the alternating voltage over an excited coil is a measure of the length of the shock absorber unit at the frequency used.
A drawback of the conventional measuring circuits is the sensitivity of the measurement to the temperature of the coil, since the electrical resistance of the coil is dependent on temperature. It is therefore necessary to take an additional measure for temperature compensation, which measure according to EP-A-0 466 604 consists of incorporating a reference resistor in the length measuring circuit. However, this gives only local information on the temperature, which information is therefore not a reliable reflection of the current temperature at the position of a measuring coil.
The accuracy of the length measurement is also adversely affected by the temperature dependence of the electric and magnetic properties of the casing of the shock absorber unit movable inside the coil.
The object of a measurement of the length of a shock absorber unit is generally to gain an idea of the load situation (or, of course, the relative position of components) of the wheel suspension of which the shock absorber unit forms part, or to put it in more general terms: the length of the shock absorber unit is a measure of the force absorbed by the corresponding wheel suspension.
A disadvantage of the shock absorber unit length measuring circuit according to the prior art is the limited band width as a result of the measuring principle used. A narrow-band measurement of the length of the shock absorber unit rules out certain important applications of such a measurement, in particular use of the measurement of the wheel suspension load condition by means of the shock absorber unit length measurement for controlling functions improving ride or riding safety, for example quick-acting active spring systems, anti-lock braking systems etc. Such applications require measurement of the speed or the acceleration of a length change of a shock absorber unit, and therefore require a gre
REFERENCES:
patent: 4502006 (1985-02-01), Goodwin et al.
patent: 4674768 (1987-06-01), Morra
patent: 4898027 (1990-02-01), Morra
patent: 5210490 (1993-05-01), Munch et al.
Arana Louis M.
Bednarek Michael D.
Phillips Roger
V.O.F. Hedon Electronic Developments
LandOfFree
Inductive system for measuring the length of a shock absorber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inductive system for measuring the length of a shock absorber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inductive system for measuring the length of a shock absorber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-446074