Patent GB-1394904-A (GB)
Title: Magnetic means for directing and conducting magnetic flux
IPC: H02K23/02
Filed: 1972-05-19
Abstract: 1394904 Permanent magnets KOLLMORGEN CORP 19 May 1972 [28 May 1971] 23605/72 Heading H1P [Also in Division H2] [28May 1971] A magnetic circuit for directing and containing magnetic flux comprises plural at least 3 sources of MMF and a first body of magnetically permeable material with surfacel, of which a portion defines working gap surfaces crossed by magnetic flux and a further portion in contact with the sources of MMF; the further portion having an area >1À5 times the area of the working gap surfaces and the sources of MMF having polar axes extending in different directions; more than one such polar axes having flux components normal to the average direction of the magnetic flux at the working airgap surfaces so as to oppose undesired flux emissions from surfaces of the magnetically permeable material other than the working air gap surfaces, and further comprising a second body of magnetically permeable material as a flux return path; the reluctance of the magnetomotive sources approximating the reluctance of the magnetic load including the airgap excited thereby. A D.C. electric motor (Fig. 1) has a 2 pole armature 20 on shaft 21 in enclosing housing 10 having ferromagnetic vertical flux return plates 12, 14, horizontal flux return plates 15, 16, and end bells (not shown); the armature rotating between high saturation ferromagnetic salient poles 22, 24 whose opposite radially inwardly converging sides have flat peripheral surfaces 27, 28 and pole faces 29, 30 defining a working airgap with the armature. Permanent field magnets 32, 34 contact the flat peripheral surfaces 27, 28 linking the field of fluxpath 35. Magnetic flux is concentrated in pole faces 29, 30 and leakage reduced by providing components of flux in quadrature with the major flux direction from auxiliary crossfield permanent magnets 36, 37, 38, 39 adjacent the sides 25, 26 of the polepieces; with polar axes intersecting these of the field magnets 32, 34 internally of the polepieces to develop axial flux components perpendicular to the radial flux in the airgaps; whereby leakage flux from the primary magnets 32, 34 is counteracted and the polepiece flux is increased. Segmented soft iron blocks 40, 41 link magnetically the auxiliary magnets 36 to 39 to complete the magnetic paths 43 through the polepieces. Auxiliary magnets may also be applied to the ends of the polepieces. As shown in Fig. 3, the polar axes 42, 44 of the cross field magnets 36, 37 intersect the polar axis 46 within the main polepieces, and the crossfield magnets comprise plural segments 36a, 36b; 37a, 37b of which the segments adjacent the flux emergent surface 29 have the higher field strength to more effectively discourage leakage by flux in path 45. The reluctances of the several magnetic circuits are matched, and an equivalent magnetic circuit is derived (Fig. 6, not shown). In a modification (Figs. 2, 4, 5, not shown) the polepieces are of arcuate periphery and magnetic sources provide angularly related magnetic domains defining magnetic axes intersecting within the polepieces; the latter having circular or elliptical outer peripheries surrounded by magnetic sources comprising numerous adjacent magnetic segments with axes normal to the polepiece peripheries; the individual segments counteracting any emergent leakage flux. The segments are completely surrounded by a laminated or sectioned ferromagnetic housing, and the system establishes a closed magnetic path intersecting the polefaces and the rotor. The magnetic sources may be cylindrical and moulded, comprising a large number of indefinitely small segments. In a further modification (Fig. 8, not shown) generally similar to the arrangement of Fig. 1 the two polepieces are pentagonal with magnetic sources applied to each outer face and received within an external unitary casting. In a further modification (Figs. 9, 10) a disc motor comprises a printed circuit armature 80 rotatable on shaft 81 between opposed poles 82, 84 whose flux is normal to the plane of the disc; the pyramidally convergent polepieces 85, 87 being excited by main magnets 92, 94 and crossfield magnets 96, 97. Outer flux return rings 99, 100 and 101, 102 are mounted on the housing plates on each side of the disc to provide an iron sheath for the poles, and crossfield magnets 106, 107 are provided at the side surfaces of the polepieces; with rings 99, 100 in magnetic circuits 103, 105 comprising magnets 96, 97 the polepieces, and flux return plates 108, 109. Adjacent poles and adjacent magnetic sources are of alternative polarities. In a further modification (Figs. 11, 12) a 4 pole motor comprises 4 polepieces 110 interacting with rotor 111 in which a major part of the flux is provided by interpole magnets 113 of axes normal to the adjacent side faces of the polepieces and a minor part is supplied by angularly disposed magnets 115, 116 on the sides of the polepieces opposed to the airgap 117. The enclosing housing 122 has internal surfaces conforming to the stator assembly and provides a return flux path, while brushes and holders 120, 119 are inserted in the inerpolar spaces. A mathematical analysis is derived, and the characteristics of suitable magnetic materials are indicated graphically (Fig. 7, not shown). The invention is applicable to other magnetic apparatus.