GB377696A - Improvements in alternating current motors - Google Patents

Abstract

377,696. Motors. SANGAMO ELECTRIC CO., Springfield, Illinois, U.S.A. March 20, 1931, No. 8653. Convention date, Jan. 19. [Class 35.] A synchronous motor, especially adapted for driving electric clocks, is provided with two air gaps separated by a ring of polepieces and traversed in series by the magnetic flux and an armature co-operates with each air gap. In the arrangement shown one armature consists of a permanent magnet 46 and an induction member 48. The magnet 46 co-operates with the air gap between teeth 21 on a magnetic disk 16 at one end of a coil 14 carrying an alternating current and teeth 23 on a ring 22 surrounding the disk. The poles of the magnet are preferably bifurcated, the space between the divisions being equal to the width of one of the teeth 21 and the air gaps on either side of it. The ring 22 also carries pairs of polepieces 26, 27 alternating with jaws 11, 12 on a magnetic disc 13 at the other end of the coil 14. The polepieces 11, 26 are surrounded by shading rings 32 so as to produce a rotating field with which the induction member 48 co-operates. The member 48 consists of a bell of copper or the like surrounded by a band 54 of magnetic material. Fig. 5 shows a modification consisting of a body 61 of magnetic material with teeth 64, and a bell 65 of copper or the like. The member 68 may be loose on the spindle 41 carrying the magnet 46 and be connected with the magnet by a spring arm 78 or a helical spring. In a modification the two armatures are at opposite ends of the spindle 41. The polepieces 11, 12, 26, 27 being less numerous than the teeth 21, 23, the synchronous speed of the member 48 is greater than that of the magnet 46.