Patent GB-1344736-A (GB)
Title: Reciprocating linear induction motors
IPC: H02K41/025
Filed: 1971-04-26
Abstract: 1344736 Linear induction motors JEUMONT-SCHNEIDER 26 April 1971 [28 April 1970] 11466/71 Heading H2A [Also in Division F2] A reciprocating linear induction motor actuator excited with polyphase A.C. comprises (Fig. 1) a field structure including coils 1 separated by sheet metal discs 2 of equal diameter clamped between cheeks 3 centrally of a ferromagnetic tube 4 so that the field extends longitudinally of the discs. The tube is closed sealedly by end plates with central apertures and glands accommodating a shaft 9, comprising an enlarged central portion 9a response to the magnetic field and end extensions of less diameter traversing the glands. An axial passage 10 and radial passages 11 interconnect chambers A, B filled with insulant liquid, e.g. oil which on displacement of the shaft flows between the chambers for cooling and limitation of speed of movement; braking at the ends of travel, beingimposed by opposition of passages 11 to cheeks 3. Volumetric expansion of the liquid with temperature is compensated by coaxial pistons 100, 101 of equal areas balanced by spring 102. In a modification (Fig. 2, not shown) the armature is supported by a piston at each end, with a reduced diameter shaft extending from one end only, and cooling fins on the exterior of the tube. In a further modification (Fig. 3, not shown) the field structure is situated at one end of the tube adjacent a gland through which the armature passes; the other end of which carries a piston and a shaft of reduced diameter sliding in a further corresponding closed axial tube; the piston dividing the larger tube into the chambers connected externally through an adjustable construction and an electromagnetic valve energized and de-energized with the field to close and lock the movement on deenergization. The piston in its end positions closes the appropriate connecting orifice, and electromagnetic force may operate in one sense only with free fall or spring return. The devices of Figs. 1, 2, may alternatively have similar external interconnection, or an internal valve of the axial passages may be operated electromagnetically to open against spring bias and permit flow. In a further modification (Fig. 4) the central portion comprises ferromagnetic tube 25 sliding in field structure 12 and glands 22b in ring 3a with shafts 9d of smaller diameter sliding through glands 22b of the tube end plates. Radial passages 26 are formed in the tube which contains a hollow valve of magnetic material 27 also with radial passages 26a slidable against spring loading in the bore of tube 25. On field de-energization, valve 27 is central so that the passages 26, 26a are offset to close the connection between chambers A, B but on energization the valve is shifted in the appropriate sense so that the passages register and allow fluid flow and armature movement until closure on de-energization. A mechanical lock may be used as an alternative, safety valves and limit switches may be employed, or the construction may be replaced by a device giving pressure limitation or differential speeds in opposed directions.