Hydraulic cylinder comprising at least one electric position indicator

Abstract

A hydraulic cylinder (1) with a piston (5) made completely or partially of electrically conductive material comprises at least one opening (19, 20) for the mounting of an electric position indicator (21, 22). The openings (19, 20) are closed in a liquid and pressure-proof manner towards the interior of the cylinder (1) by means of circular plate-shaped bodies (17, 18) glued to the inner surface of the cylinder (1). As the plate-shaped bodies (17, 18) are made of a ceramic material, preferably steatite, they may allow passage of the magnetic field transmitted from the electric position indicators (21, 22). The openings (19, 20) are adapted in the end covers (2, 3) of the cylinder (1) for the determination of the end positions of the piston (5). Furthermore the cylinder may be provided with piston-braking means in the form of seal rings (12, 13). As the piston (5) penetrates the magnetic field, an altered signal indicating the position of the piston (5) will be transmitted from the electric position indicator, which is preferably an inductive sensor. Very narrow inductive sensors being used it is now possible to built these into even very small hydraulic cylinders, so that these inductive sensors can be built into hydraulic cylinders of all sizes without being influenced by the high pressure of the cylinders. The hydraulic cylinder (1) according to the invention may even be manufactured in a very inexpensive and simple manner, and by building in the inductive sensors a previously unknown exact and reliable determination of the positions of the piston may furthermore be obtained.

Dependencies are inferred from the claim text.