Improvements relating to Electric Motors

1,157,272. Electromagnetic brakes. ENGLISH ELECTRIC CO. Ltd. 13 Sept., 1966 [17 Sept., 1965], No. 39780/65. Heading F2E. [Also in Division H2] In an induction motor having a laminated rotor core 13 carrying a squirrel cage rotor winding with end rings and, axially movable relatively thereto, a friction brake mechanism 20 which is resiliently biased towards the braking position, initial movement from the engaged position is effected by magnetic forces established by current flowing in the winding and one end ring 37 when the motor is initially energized, whereafter the mechanism is moved fully to and held in its disengaged position by magnetic forces established within the rotor core as it accelerates to and reaches its full speed such forces acting upon a magnetizable portion of the mechanism which extends into the core. Thus the mechanism comprises a magnetizable sleeve 23 having an annular member 30 carrying a friction element 31, flange portions 33, 35 defining the initial flux path (P), Fig. 2, and a cylindrical flange portion 34 which is grooved similarly to a magnetic sleeve 51 in the rotor core and forms the second flux path when in alignment. The resilient bias is created by a helical spring 42 or, in modifications, a plurality of compression springs, tension springs provided in the region of the shaft bearing 16, elastomeric material, or Belleville washers. The braking force is transmitted to the shaft 15, and the sleeve movement is limited, by a pin 26 in an elongated aperture 27 and engaged by a screw 28 which adjustably sets the brake position but may be adjusted to render the brake inoperative. Air cooling of the brake is by a fan 21 and ribs 18, and of the motor end turns 12 by webs 39.