Patent GB-627008-A (GB)
Title: Electrically operated clutch
IPC: F16D21/02
Filed: 1945-07-26
Abstract: 627,008. Electric jack-type actuators. MILES AIRCRAFT, Ltd., and HUNT, C. L. July 26, 1945, No. 19128. [Class 78 (iii)] [Also in Group XXIV] An electric actuator comprising an electric motor driving an output member through reduction gearing is characterized by the inclusion in the power train of an electromagnetically-operated clutch one member of which carries ball-ended clutching elements outwardly movable to engage between circumferentiallyspaced rollers on the co-acting member. As shown, a reversible electric motor 21, Fig. 3, epicyclic or other reduction gearing 23, the clutch 24 and an output screw jack 27, 29 are co-axially arranged in a casing 30. The clutch 24 comprises a driving member 1 carrying rollers 3, and a hollow driven hub 4 carrying, in bores whose inner ends may be substantially tangential to the interior surface of the hub, coupling elements each consisting of two balls 10, 11 spaced apart by a distance piece 12. The armature 14 of a solenoid 16 fixed to the member 1 carries a hard steel plunger 13 having a tapered surface co-acting with the balls 10 to force them outwards when the solenoid is energised and cause the balls 11 to engage between the rollers 3. A clutch disengaging spring 20 is provided, slight lost motion between the plunger and armature and a slight taper of the thickened end of the plunger assisting its action. The solenoid is supplied with current through slip rings 34, and limit switches 31a, 31b control the maximum travel of the output member 29. The motor armature may be provided with an electromagnetically-operated brake which is automatically applied and released when the motor is switched off and on respectively. A disc 36, Fig. 4, rigid with the armature spindle 25, co-acts with a non-rotary but axially slidable disc 37 spring-urged to engage the disc 36 and forming the armature of a solenoid having windings 33a, 33b, one of which may be omitted, in parallel and series respectively with the motor armature windings 21c. The motor has forward and reverse drive windings 21a, 21b which may be alternatively energised by a switch 32, Fig. 6, and are in series with the limit switches 31a, 31b. The clutch solenoid 16 may also be in circuit with the motor windings so that the clutch is engaged and disengaged simultaneously with the release and application of the brake, but is preferably independently energised as shown in Fig. 6 so that the clutch normally remains permanently engaged and is only disengaged upon a failure in the electric supply, when the jack 27, 29, which is reversible, may be expanded or collapsed by external means. Such an arrangement may be applied to the control of a two-speed supercharger wherein the actuator is brought into operation by an altitude switch to change from low to high gear, and allows the supercharger to return to low gear under spring action upon current failure at high altitudes. In Fig. 7, an actuator having a modified form of clutch combined with a friction clutch is shown. The solenoid 161, supplied through slip rings 34<SP>1</SP>, is here secured to the hub 41 which is rigid with the output member 221 of the actuator. Single engaging balls 101 co-act with rollers 31 mounted on pins 21 connecting two discs 1', one of which carries friction facings 4<SP>1</SP> and forms one plate of a friction clutch the other plate 23<SP>1</SP>a of which is connected to the actuator reduction gearing. The friction clutch is engaged by a spring 42 and slips on overload. Specification 627,004 is referred to.