Patent GB-784295-A (GB)
Title: Improvements in or relating to friction gear transmission
IPC: F16H15/38
Filed: 1954-04-05
Abstract: 784,295. Variable-speed gearing; friction gearing; screw-and-nut gearing. WEISEL, Z. V. April 5, 1954 [June 23, 1953], No. 9886/54. Classes 80 (1), 80 (2) and 80 (3). Variable-speed friction gearing, particularly for driving an alternator in an aeroplane at a constant speed, comprises driving and driven discs with concave friction faces engaged by convexly faced idlers, universely mounted on tilting members so that they precess when changing ratio. In one form, driving and driven. toric discs 32, 60, Fig. 1, are connected by tiltable, non-planetating idler rollers 64, spiral grooves 46 &c. formed circumferentially around the engaging surfaces of the discs and idlers allowing lubricant trapped between them to escape. Lubricant is conveyed from the bottom of the surrounding casing 54 by wicks 246, 248, 250 to the bearings supporting the gear shaft and to the friction surfaces of the discs. The radius of curvature of the friction faces of the rollers 64 is less than the radius of curvature of the friction faces 46, 62 of the discs 32, 60. A driving shaft 22 is connected through cam and inclined slot means 28 to the driving toric disc 32 which is moved axially thereby, with increasing torque, to increase the frictional engaging pressure between the parts. Under full, or near-full, load, the surfaces of the rollers 64. deform to approximately the curvatures of the disc surfaces 46, 62: A Belleville washer 71 causes initial engagement. Each roller 64 is mounted through ball bearings 721 on a cup 74 containing a large ball 76, between which and a stem 80 are a number of balls 78. This stem 80 is secured to a trunnion shaft 82, Fig. 2, pivoting in the surrourding casing 54. The trunnion shaft can be centred with respect to the driving and driven shafts by screw and nut means. Control arms 94 on the cups 74 have ball connections 96 with a control ring 100 coaxial with the driving and driven discs. Teeth on the control ring 100 mesh a gear 104 driven from the shaft 106 of a servomotor 108. The servomotor is controlled by rotation of a shaft 110 carrying a disc 112 continuously rotated by the driven disc 60 of the gearing, which it engages. If the speed of the driven disc varies, the servomotor rotates the control ring 100 to tilt the rollers 66 which then precess to a position inclined to that shown in Fig. 1, to change the velocity ratio. The discs 32, 60 are formed with radially directed passages 134, 136 to act as centrifugal pumps and draw air therethrough, so as to cool the friction surfaces. The air enters through passages 120, 122 to the discs from passages 116, Fig. 2, in a case surrounding the gear-case 54, and leaves through passages 138, 140. In a modification, the friction surfaces are cooled by oil introduced from an inlet 150, Fig. 7, to conduits 152, 154 whence it flows through passages 158, 160 in the discs 32, 60. Some of the oil leaving the conduits 154 flows through gaps 162 to lubricate the torque-responsive ball means 28, frictionally engaging the discs and rollers, and the bearing supporting the driving disc 32. Passages 188 are provided in the driven disc 60 through which oil passes to lubricate the bearings supporting this disc. Oil is also sprayed over the servomotor 108 from outlets 192 to cool it. The cooling and lubricating oil drains back to a sump (not shown) through passages 170 &c. In this form, the servomotor 108 is controlled by a disc 196 engaging the edge of the driven toric disc 60. In a modified form of support for the tilting rollers 64, Fig. 8 (not shown), the tilting bearings 72<SP>1</SP> are carried by a convexlyshaped member co-operating through a number of small balls with a concavely-shaped member mounted in the trunion shaft 82. In a further modification, driving and driven discs 254, 258, Fig. 9, have smooth surfaces and are engaged by tilting rollers 260 provided with spiral grooves 262. The rollers are each mounted on two thrust bearings on a stem 288 and trunnion shaft 270. Oil under pressure is passed through a line 334 and cavities 318, Fig. 11, in the trunnion shafts to cavities 316 in the stems 288, whence it flows through spiral grooves 313 past the inner races of bearings 310 to cool them and thence through passages 330, Fig. 10 (not shown), in the tilting arms 272 to empty into the main housing away from the rolling path. The rollers are tilted, to change the velocity ratio and keep the speed of the driven shaft constant, by rotation of a control ring 100 which tilts the stems 288 &c. and causes the rollers to precess substantially as described above. The control ring is rotated either by a servomotor (not shown) or by other speed-responsive means (not further described). A tachometer 340 is driven from the driven disc 258. A modified arrangement is shown for producing a frictional engaging force between the discs and rollers. The driving shaft 252 of the gear drives a surrounding sleeve 360 through freewheel sprags 364. The end of the sleeve 360 is formed with a helical groove 368. The driving disc 254 is formed with a correspond helical groove 370, Fig. 14, the two grooves forming a channel for balls 374 (Fig. 9). The groove 370 is provided with a notch 376 of slightly increased depth, Fig. 16 (not shown) by which the end of the groove is connected to its beginning. The balls 374 are thus able to recirculate from the end of the groove back to the beginning. The sides of the notch 376 are formed by curved rods 378. A disced spring 385 provides initial engagement of the discs and rollers, the screwing action of the sleeve 360 and disc 254 through the balls 374 &c., providing additional friction engaging pressure proportional to the torque. In a further modified form of torque responsive frictional pressure producing means, Figs. 18, 19 (not shown), the driving shaft carries and drives a sleeve through freewheel sprags, the sleeve having a cone-shape and engaging balls in a cage, the balls also engaging inclined grooves in the driving disc 254. Specifications 784,296 and 784,297 are referred to.