GB676637A - Device for regulating the speed of fractional horsepower electric motors - Google Patents

Abstract

676,637. Centrifugal switches ; magnetic switches. MULLER, A., and BRUTSCH, L., (trading as BRUTSCH & CO.). June 17, 1949. [April 22, 1949] No. 16216/49. Class 38 (v). A speed responsive switch, for electric motor speed control, is opened against adjustable spring loading at a predetermined speed by a torque/ speed responsive coupling to the motor shaft. The coupling may be eddy - current induction, centrifugal clutch or pneumatic type. The contacts are held permanently open and permanently closed at positions of the loading spring adjustment. Coupling. As shown Fig. 1 the eddy-current coupling comprises a permanent magnet rotor 3 carried by the motor shaft 2 to exert a drag on a concentrically pivoted cup member 4 having an iron rim 5 surrounding the magnet and a pin 6 projecting through a slot in the housing to engage the moving contact arm 14. The coupling may alternatively be (i) a centrifugal type comprising three weights slidable on the arms of the rotor Figs. 3, 4, (not shown) or number of balls in a slotted rotor Figs. 5, 6, adapted to engage and exert a drag on the cup member or (ii) a pneumatic type comprising for example a radial impeller on the shaft blowing air into chambers in the cup member Figs. 7 and 8 (not shown). Contact adjustment. The speed of adjustment (contact loading) is provided by a compression spring 23 between the movable contact arm 14 and a "bell crank" lever 18, 19 pivoted at 13 and biassed by a spring 20 against an adjustable back-stop 25, which may be a set screw or a sliding (e.g. foot operated) plunger. Actuation by the coupling is suspended in the full in plunger-position by a cam 28 on arm 18 which holds the contact arm closed, and in the full out position by a lug on the arm 19 which engages the contact arm to hold it open.