Patent GB-747979-A (GB)
Title: Improvements in or relating to centrifugal clutches
IPC: F16D43/10
Filed: 1953-12-23
Abstract: 747,979. Friction clutches. SOC. ANON. FRANCAISE DU FERODO. Dec. 23, 1953 [Dec. 23, 1952; July 11, 1953], No. 35824/53. Class 80(2) In an electro-magnetically controllable contrifugal friction clutch of the Gravina type (Specification 586,910), wherein a driven disc 13 is clamped against a driving flywheel 18 by thrust applied to a presserplate 20, through a thrust-bearing 66 by centrifugal masses 30, acting on a, camplate 27 and pivoted on a carrier 32, which can be clutched to the driving member to drive the masses for centrifugal engagement of the main clutch, or held stationary by an electromagnetic brake 42 for clutchrelease, the centrifugal mechanism 30 &c. is housed in a closed casing 38 separate from that of the friction section 13. This renders possible the uncontaminated lubrication of the centrifugal mechanism; its removal as a unit for independent preadjustment; and the roller-bearing mounting of the masses 30 and rollers 28 through which they apply axial pressure to the camplate 27. A negative-torque one-way clutch 73, automatically disabled at normal running speeds, is provided for a towed engine start on a vehicle, and one form, Fig. 7, has also a series friction coupling which has a slip-limited overrun torque-capacity. The mass-carrier 32 is journalled axially fixed in the flywheel-mounted housing 38 on a ball-bearing 37, and is splined on a sleeve 33 loaded leftwards by springs 36, which clutch the sleeve to the driving housing 38 through a clutch-brake disc 40 for centrifugally controlled engagement of the main clutch 13 when the brake-magnet 42 is de-energized and, through the same disc 40, hold the mass-carrier 32 stationary to collapse the masses and so release the main clutch when the winding 42 is energized. The outward clutch-engaging movement of the masses 30 about their pivots 31 acts leftwards on the main pressureplate 20 through the cam plate 27, thrustbearing 66, an intermediate plate 24 and springs 22. An oil seal 70 or baffle on the plate 24, together with shields for the ballbearings 37, 66, separate the housings of the clutch 13 and its centrifugal mechanism. The intermediate plate 24 has radial slots 25, drivingly engaging lugs 26 on the presser plate 20, which latter is tied to and centred on the casing 38 by tangential flexible strips 47. Axial coil springs (Fig. 3, not shown) tend to separate the flywheel 18 and presser plate 20. After removing the bolts 44 which secure the casing 38 to the flywheel 18, the entire centrifugal assembly up to and including the presserplate 20 can be removed as a unit for independent adjustment. Cooling air is circulated continuously by a vane formation of the main clutch disc 13, the friction facings of which are formed as well-spaced segments, (see Fig. 7), on radial vanes which draw in air at 83 and expel it at 46. Fig. 9 (not shown) differs constructionally in that the clutch springs 22, Fig. 1, are arranged outside the casing 38, with their enclosed barrels passing freely through holes in the casing 38 which is radial at this region. Both the presser- and intermediate-plates 20, 24 now have peripheral toothed engagement with flywheel lugs, the flexible strips 47 being omitted. A clamped angle-seal replaces the ring-seal 70 of Fig. 1. The negative-torque clutch, providing for towed start, comprises pawls 73, pivoted at 74 on the presser-plate 20 and spring- pressed radially inwards on to ratchet teeth 72 on a hub 15 splined on the output shaft 11 and carrying the clutch disc 13 on the usual circumferential spring mounting 14. The pawls engage to transmit overrun torque for engine starting at near-zero speeds, but, to prevent damage due to possible re-engagement with a stalled engine at normal running speeds, the device is disabled by centrifugal force on the pawls 73 lifting them out of engagement, and by a mask 79, which is moved axially over the ratchet teeth by centrifugal balls 80 opposed by return springs 82. In Fig. 7 the circumferential spring coupling 14 of Fig. 1 is replaced by a series friction coupling which limits overrun torque by slipping. Riveted to the friction disc is a cam member 90, ramps on which engage free friction wedges 87, which, in the forward direction of drive, they expand, with the assistance of spring 89, into wedging engagement with a surrounding drum 85 formed on the driven hub 16, which is journalled freely in the friction disc 13. Forward drive is thus without slip, but on overrun the wedge-expanding springs 89 act alone and the wedges can therefore transmit only a limited torque before slipping. Centrifugally loaded negative torque pawls are provided on the pressure-plate as at 73 in Fig. 1, but the ratchet teeth 93 on the limb now have base-plates 94, which, at normal running speeds, pivot centrifugally outwards to blank off the ratchet teeth 93. Reference has been directed by the Comptroller to Specification 586,910.