GB561023A - Improvements in magnetic and electro-magnetic clutches, brakes and the like - Google Patents

Abstract

561,023. Dynamo electric machines. BRAHAM, G. W. Oct. 13, 1942, No. 14365. [Class 35] [Also in Groups XXIV and XXXIV] Driving and driven shafts g, f are coupled by clutch members e, d, attached to the shafts and having adjacent end faces t, s, which are moved into contact to transmit torque by a stationary electromagnet surrounding the members and comprising a. yoke a and polepieces b, b<SP>1</SP>, enclosing an energizing coil r. The magnet is supported from the shafts by brackets k, h. The member d is splined to the shaft f to allow that member to move axially into contact with the member e when the coil r is energized. A spring p, which may be enclosed by a cap n enclosing lubricant for the splined connection, maintains the clutch members out of contact when the coil r is de-energized. The clutch member d rotates as a unit with the member e when the coil is energized and the torque resisting rotation of the shaft f is not greater than can be transmitted by.the magnetic forces causing the two members to adhere, but when the torque exceeds that value, slipping occurs and current circulates from one end face to the other due to the difference in speeds of the two members in the magnetic flux. This current produces on the member d an additional torque assisting rotation of the shaft f due to a motoring action. Good conducting material such as. copper may be applied to the end faces of the clutch members to increase the current which flows during slipping, and graphite or other lubricant may be contained in pockets in the end faces to prevent abrasion of these faces during slipping. The torque necessary to cause the clutch members to slip may be varied by providing variable excitation of the coil r, and in cases where constant torque is to be transmitted, a permanent magnet may be utilized instead of the electromagnet. The device may be used as a brake by the provision of means for temporarily constraining one member against rotation so that the second member is restrained by the action of the adhesive and electromagnetic forces. In a modified construction, the clutch surfaces are formed between the polepiece b<SP>1</SP> and yoke a of the electromagnet and the driving and driven shafts are arranged coaxially, the driven shaft carrying a support w, for the unitary parts a, b of the magnet which rotate with the shaft. The coil r is stationary and surrounds a central stationary iron core through which the shaft g passes. The bracket k supporting the polepiece b<SP>1</SP> is rigidly secured to the shaft g.