GB999754A - Improvements relating to electric motors - Google Patents

Abstract

999,754. Motor driving arrangements. LIMIT ENGINEERING GROUP Ltd. Sept. 22, 1961 [Sept. 22, 1960], No. 32566/60. Heading H2A. In a motor driving arrangement the axially moving rotor of the motor is prevented from movement due to the magnetic pull between the rotor and stator by spring means until the motor has gathered speed so that the engagement of clutch plates connected to the load and carried by the rotor is delayed. As shown the shaft 4 of a motor carries a member 12 provided with a flange 5, having a facing of friction material 6, keyed to the shaft 4 so that it is slidable along the shaft but rotatable with it. The member 12 and associated flange 5 are held against the end of the shaft by spring 7 compressed between washer 8, held in position by bolt 9, and a shoulder 10 on the member spaced from the end of the shaft by spacer 11. When the motor is energized the rotor does not move axially to the right until the magnetic pull between the rotor and stator is sufficient to overcome the bias of a spring (not shown) biasing the rotor and motor shaft to the left. However, on reaching a sufficiently fast motor speed the motor connections may be switched from star to delta connections to increase the flux density and hence the magnetic pull between the rotor and stator sufficient to overcome the spring bias and move the rotor to the left, when the flange 5 moves into engagement with a pulley 3 mounted on ball-bearings 2 on the motor frame 1 and is held in contact with the pulley 3 by spring 7. In a single-phase motor an appropriate change in magnetic flux and pull may be effected by the use of a tapped winding and an appropriate switch or by changing the magnitude of the supply voltage to the motor. Alternatively the flux may be changed automatically by a centrifugal switch which operates to apply full voltage to the motor when it has run up to the required speed.