GB1173123A - Variable Speed Induction Motor - Google Patents

Abstract

1,173,123. Variable speed induction motors. A. MœLLER. 11 March, 1968 [11 March, 1967], No. 11662/68. Heading H2A. [Also in Division G3] In a variable speed induction motor having an air gap receiving an axially shiftable bell member 8 which is rotatable with the motor output shaft 13 whose speed and torque depend upon the depth of penetration of the bell member into the air gap, such axial shifting is controlled by an electrical signal, corresponding to the shaft speed, produced by a measured value transmitter 23, e.g. a tacho-dynamo. The latter is driven by the shaft 13 and, in the embodiment shown, controls a servomotor 21 whose threaded rod 20 when rotated effects the axial shifting via a threaded nut 19, lever 14, a cylinder 16, and a quill 10 slidably keyed at 12 to the shaft 13. A squirrel-cage rotor 7 on a hollow shaft 22 drives a fan 24 at a speed irrespective of that of the output shaft 13, and the motor may also be pipe ventilated by a blower, or liquid-cooled. Also on the shaft 13 is a brake disc 26 associated with a ferromagnetic ring 28 acted upon by adjustable springs 27 and an electromagnet 29. In other embodiments the shifting is effected electromagnetically or, Fig. 4, by a further, coaxial, induction servomotor (43). The bell member may have oblique slots, open or filled with ferromagnetic material, and control of its servomotor to provide an adjustably constant speed with varying load is by relays or a transistor circuit Fig. 3.