Patent GB-788367-A (GB)
Title: Improvements in or relating to electro-centrifugal clutches
IPC: F16D47/00
Filed: 1955-05-19
Abstract: 788,367. Friction clutches. SOC. ANON. FRANCAISE DU FERODO. May 19, 1955 [May 20, 1954], No. 14505/55. Class 80 (2). A clutch, for use between an engine shaft 10 and a change-speed gear input shaft 11 on a motor vehicle, comprises in series an expanding- shoe centrifugal friction clutch 21, which alone takes all the starting slip, and an electromagnetic friction disc clutch 33, released during gear-shift by pressure on a yielding gear-shift lever (not described). The friction shoes 21 comprise centrifugal masses faced with " Ferodo " (Registered Trade Mark) and may, as shown, be carried on leading pivots 22 on the engine flywheel 13 to be self-tightening in the over-run direction only. The masses may have dissimilar characteristics and are retracted by compression, torsion or tension springs 24. Negative torque at near zero speed, for a towed engine start, may be provided by using springs to press the shoes into engagement or by auxiliary pivoted shoes pressed into engagement and retracted at idle speeds by centrifugallyweighted tails (Fig. 8, not shown). In these cases idle forward drag and intermediate member kinetic energy are overcome by an automatic clutch-stop described below, and by speedresponsive de-energization of the magnetic clutch. In Fig. 9, the ends of centrifugal shoes 46 are guided between surfaces 47, 48 on blocks attached to the engine flywheel 13, and differentially inclined, or one radial to increase, decrease or leave unaffected engaging pressure in the forward or over-run direction as required. Inclined slots in the shoes engaging the pivots 21 in Fig. 1 may be provided for a similar purpose. A strip 51 of inclined corrugations is attached to the driven drum 18 to pump cooling air. The friction surfaces may be coned to a semi-apex angle of 0 to 45 degrees. The electromagnetic clutch comprises an input magnet yoke 16, journalled at 17 on the engine flywheel 13, and attached by screws 29 to the output drums 18 of the centrifugal clutch 21 and to a back-plate 30. A co-operating armature 36 is attached to a presser plate 31, which clamps a final driven disc 33 against the back-plate 30. The driven disc 33 has facings 32 of slowly wearing " Ferodo " (Registered Trade Mark) to permit use of a short air-gap. Live and grounded collector rings 42, 43 feed the energizing winding from the battery or usual speed-responsive generator, through an accelerator-shorted resistor; speedresponsive energization being such as to cause automatic disengagement below fast-idle speed, to reduce drag of the centrifugal clutch. The friction surfaces may be coned to a semi-apex angle of 45 to 90 degrees. The clutch-stop, above referred to, for overcoming the kinetic energy of the intermediate member, comprises, in Figs. 11 and 12, not shown, a spring-centralized band, contracted on to a smooth external surface of the driven drum 18 of the centrifugal clutch by a solenoid energized automatically at engine idle speeds only. Fig. 13, not shown, replaces the band by a single leveroperated pivoted shoe. In Figs. 14 to 16, not shown, a friction shoe, pivoted on the rotating drum 18, is spring-pressed outwardly into engagement with the inner surface of a fixed brake-drum, and released therefrom at speeds above idle by a centrifugally-loaded tail on the shoe. The following performance data are specified. For the centrifugal clutch :-Forward drive torque capacity is less than that of the electromagnetic clutch until engine speed at full throttle reaches a speed corresponding to a minimum of 60 per cent and preferably 75 per cent of maximum torque, up to which point slip occurs in the centrifugal clutch only. Torque capacity is approximately zero at fast idle and becomes equal to engine torque at a speed corresponding to full throttle at an engine torque between maximum and two-thirds thereof. Over-run torque-capacity is 150 per cent of forward. The electromagnetic clutch has a high time-constant, increasing for engines with greater maximum torque (0.2 second to 90 per cent maximum intensity for a maximum torque of 3 kg. metres; 0.6 for 15 ; inductances 0.1 and 0.6 henry respectively). Limiting torque capacity is 1.2 to 2 times maximum engine torque to act as a safety device. Maximum over-run engine-brake torque, with released accelerator, is limited to 0.15 to 0.5 of maximum forward engine-drive torque.