Patent GB-617406-A (GB)
Title: Improvements in electro-magnetically actuated friction clutches
IPC: F16D27/08
Filed: 1946-09-30
Abstract: 617,406. Electromagnetically-operated friction clutches. SAMPIETRO, A. C., and ROBERTSON, D. R. Sept. 30, 1946, No. 29170. [Class 80 (ii)] In an electromagnetically-operated friction clutch having coacting screw-threaded members relatively rotatable to adjust the polar air-gap, locking means normally preventing such relative rotation are disengaged by the application of an adjusting spanner which maintains the disengagement throughout the subsequent relative rotation of the members. As shown, applied to the main clutch of a light motor vehicle, the engine fly-wheel 10, Fig. 1, forms the armature of an electromagnet 13 slidably mounted on pins 18 on the fly-wheel and coacting therewith through air-gaps 15, 16 shaped as described in Specification 607,820 so that the attraction between the coacting parts remains approximately constant over a wide range of mutual movement. A conventional driven clutch disc 34 faced on both sides with moulded friction composition coacts with driving clutch discs 19, 25, the first of which is bolted to the fly-wheel 10 and the second of which is constrained by splines 27 to rotate with a cover-plate 23 bolted to the periphery of the electromagnet 13, shims 37 being provided for initial clutch adjustment. The disc 25 abuts a bush 28 which screws into the coverplate 23 and is normally located relative to the plate by an outwardly spring-pressed plunger 31 engaging a notch 33 therein. The fly-wheel 10 has a bore 36 to accommodate a depth gauge 38 coacting with the electromagnet 13 and marked to show the permissible air-gap variation, which equals the pitch of the bush thread. Adjustment may, therefore, be effected by engaging a hexagonal surface 29, Fig. 2, on the bush with a spanner 30 which depresses and frees the plunger 31, and cranking the engine through one revolution whilst holding the spanner stationary. According to the Provisional Specification, the electromagnet may be connected to the fly-wheel by an annular flexible diaphragm or by tangentially disposed blade springs instead of by drive pins. In a heavy-duty version, the engine fly-wheel incorporates the electromagnet 39, Fig. 4, whose armature 44 is slidably mounted on the first driving clutch disc 42 and is adjustably threaded into a ring 49 bolted to the cover-plate 45 which is slidably splined on the disc 19 and itself acts as the second driving clutch disc. The armature 44 is normally located relative to the ring 49 by an outwardly spring-pressed key 53 in the former engaging a notch 55 in the latter. To distribute the locking stress uniformly around the clutch axis, similar circumferentially-spaced auxiliary keys 53A, Fig. 5, are provided. A blocking ring 58, having slots 60 to allow limited rotary movement relative to pins 59 on the ring 49, has a rectangular slot 61 coacting with the key 53 and chamfered slots 62 coacting with the keys 53A to depress them on relative rotary movement after the key 53 has been independently depressed by engaging a twopronged spanner 68, Fig. 6, with notches 70 in the armature 44. The ring 58 may conveniently be rotated by a pinion sector 71 on the spanner which engages teeth 72 on the ring. A gauging bore 67 in the fly-wheel is provided and adjustment of the air-gap is effected by engine cranking as before.