Patent GB-553168-A (GB)
Title: Improvements in magnetic devices for transmitting energy
IPC: H02K49/10
Filed: 1941-08-07
Abstract: 553,168. Magnets. TRIST & CO., Ltd., R., and CHAMBERS, W. A. Aug. 7, 1941, Nos. 10058 and 13817. [Class 35] [Also in Group XXXVII] An energy transmitting device such as an electric switch, comprises an actuating magnet having two poles N 2 , S 2  arranged to act on and move an actuated magnet having two poles N 1 , S 1  reversibly and with snap action between two mechanically limited positions ; each snap-action results from the passage of the magnets through a position of unstable equilibrium in which the forces resulting from the reaction of the poles do not tend to bring about relative movement; the distance between N 1  and N 2  in one position of unstable equilibrium is of the same order of magnitude as that between S 1  and S 2  in the other position (which may be coincident with the first) ; and the magnets never enter any relative position which the interaction of the magnetic fields tends to maintain. Preferably N 1 , S 1  both lie close to N 2 , S 2  so that both attractive and repulsive forces act to bring about the snap action. Preferably, both magnets move, a snap or toggle action with lost motion occurs ; if only the actuated magnet moves, it is accelerated as it departs from the unstable position. In the form shown in Figs. 2 - 4 two annular permanent magnets 1, 2 are mounted to rotate about their axes 3, 4, the motion of the actuated magnet 1 being limited by an attached arm 8 moving between stops 6, 7. In Fig. 2 magnet 1 is held against stop 6 by the repulsive forces of adjacent like poles N 1  N 2 , S 1  S 2  and the attractive force of unlike poles N 1  S 2 , the attractive force between poles N 2  S 1  being too small to counteract the others. As the actuating magnet 2 is moved clockwise it reaches the position of Fig. 3 where equilibrium is unstable and as soon as it proceeds further the moment of the forces reverses and magnet 1 snaps into the position assumed in Fig. 4. On returning, the position of unstable equilibrium is not reached until magnet 2 has gone counterclockwise from the position of Fig. 3, so that a lost motion results and hunting is avoided. The annular magnets may be placed one inside the other. Their axes may also be arranged in different planes, for example, at right-angles, as in Fig. 20, the gap in driven magnet 95 being large enough to pass the driving magnet 96 in both positions. Each magnet may be made up of segments so as to present a number of poles. In one form, two magnets on the same shaft drive two magnets which move switch contacts engaging their periphery and acting also as stops. One magnet may drive a number of magnets spaced round its circumference. In Fig. 10, driving magnets 46, 47 are fixed eccentrically to the ends of a bar 42 rotating about axis 40 about which driven magnets 43, 44 also rotate freely to close contacts 52, 53 by means of discs 50, 51. The magnets may be on opposite sides of the  bar 42 or on the same side but in different planes, or the magnets 46, 47 in the same plane may drive a single magnet 43. The bar may be replaced by a disc and the position of the driving magnets thereon may be adjustable; the driven magnets may be outside the periphery of the disc. In a modification, two actuating magnets 70, 71, Fig. 13, are fixed to the ends of a bar 72 rotating about an axis 73. Two actuated magnets 74, 75 are similarly mounted about axis 77 and their movement is limited by stops 79. Magnets may be straight as in Fig. 19 where driven magnet 100 rotates about the same axis 101 as driven magnet 102 which is thereby moved between stops 103, 104. Magnets may be mounted for rectilinear motion past one another. The annular magnets may be mounted on an eccentric axis. The switch may be operated by a floating ball indicating the level of water in a boiler.