Arrangement for determining the travel of a piston

Abstract

A contactlessly, measuring arrangement for determining the position of a piston in a suspension component such as a vibration damper, gas spring or hydro-pneumatic suspension. In one embodiment, the piston and/or the piston rod of the suspension component and a further electrode are mounted inside the cylinder of the suspension component to form a variable capacitor which, with the aid of other circuitry, measures the position of the piston. The further electrode preferably is in the form of a tube extending from the base of the cylinder into a hollow cylinder formed within the piston rod which receives the tube. In the capacitive embodiment, additionally, there may be provided a further tube within the first tube to form a reference, second capacitor which is sensitive to pressure and temperature in the same manner as the first capacitor. The first capacitor serves as the variable capacitor for making a position measurement of the piston and the two tubes fixed relative to one another are employed to form the reference capacitor. In an alternative embodiment, the outer surface of the cylinder has an inductive coil wound therearound for producing a magnetic field which is variable dependent upon the position of the piston within the cylinder. Both measuring arrangements when connected in a Wheatstone Bridge circuit produce an electrical signal indicative of the position of the piston.