Arrangement for determining the travel of a piston

Abstract

An arrangement for determining and measuring the position or travel of a piston in a cylinder, e.g., suspension component such as a vibration damper, gas-spring or hydropneumatic suspension, uses a structure having no moving electrical contacts, nor any movable electrical leads. The arrangement measures a variable impedance, e.g., a capacitance which is created by first and second electrodes formed within the suspension component and is distinguished in that the electrodes are fixed and are immovable with respect to each other. Capacitance variation is achieved, for example, by allowing a dielectric medium, such as a ceramic or epoxy resin cylinder to enter between two electrodes, the extent of the entry of the dielectric medium being made to be proportional to the relative travel of the piston in the cylinder. In a variation, an additional electrode forming a fixed reference capacitance with the first electrode is provided. The fixed reference capacitance is used together with the measured variable capacitance in a measuring bridge, e.g., Wheatstone bridge, so that undesirable effects of varying temperature and pressure on the capacitances inside the suspension component are compensated during measurement. By virtue of the fact that all the electrodes are fixed relative to one another, the conductive leads from the fixed electrodes can be made immovable relative to each other, whereby measurement problems owing to improper leads and connections are eliminated.