GB473648A - Magnetic circuit and construction thereof - Google Patents

Abstract

473,648. Magnets. CONTINENTAL MOTORS CORPORATION. April 14, 1936, No. 10741. Convention date, April 13, 1935. [Class 35] [Also in Group XXXIX] In a permanent magnet assembly in which a composite centre polepiece comprising a permanent magnet portion and a polepiece portion has one end associated with a portion of magnetic material and the other end associated with an opening in a parallel portion of magnetic-material to provide an annular gap, the permanent magnet portion has a diameter greater than its length and the polepiece portion associated with the gap is of substantially homogeneous structure throughout its length; is of varying cross-section and has a plane under-surface, contacting with the magnet and of cross-sectional area equal to that of the magnet at the plane of contact. As shown in Fig. 1, the polepiece portion 7 is secured to the magnet portion 6 by a bolt 8 passing through a yoke member 3 of soft iron to which is secured a pole-plate 2. A circular opening in the pole-plate in conjunction with the smaller end of the polepiece 7 forms a gap for a moving coil 9<1>. The centre polepiece 6, 7 is centred by a brass ring 21 secured to the outer pole-plate 2. In a modified construction, Fig. 3, which forms the subject-matter of Specification 473,672, the permanent magnet portion 31 has a curved outer surface and the pole-plate 2 is secured to the yoke 3 by clamps 40. In a further modification, Fig. 4, the permanent magnet is formed by a central cylindrical magnet 34 and concentric magnet rings 33, 33<1>. The polepiece is secured to the permanent magnet by a sleeve 35 secured to the yoke 3 by rivets. In further modifications, Figs. 5, 6 (not shown), the permanent magnet is formed with concentric recesses parallel to its axis and the yoke and pole-plate are formed as a single U-shaped member respectively. The Specification as open to inspection under Sect. 91 includes a construction, Fig. 3 (Cancelled, not shown), in which the positions of the magnet and polepiece are reversed, i.e. the permanent magnet projects into the gap, and a further construction, Fig. 5 (Cancelled, not shown), in which the centre polepiece is constituted solely by a magnet member. In a further construction, Fig. 7 (Cancelled), the polepiece portion 7 and permanent magnet portion 36 are separately mounted between parallel plates 2, 3 of magnetic material, the polepiece member being centred relative to the gap by a ring 21 of non-magnetic material. This subject-matter does not appear in the Specification as accepted.