Patent GB-824892-A (GB)
Title: Improved brake mechanism in the transmission between an aircraft engine and a propeller
IPC: F16D55/30
Filed: 1957-10-09
Abstract: 824,892. Disc brakes. GENERAL MOTORS CORPORATION. Oct. 9, 1957 [Nov. 5, 1956], No. 31547/57. Class 103 (1). A brake mechanism in the transmission between an aircraft engine and a propeller includes a brake element on a disc normally spring-urged to the brake applied position and released by centrifugal balls between a flange fixed to a shaft and the brake element, helical splines securing the disc to the shaft are so handed as to release the brake when the engine is driven by a starter. A starter shaft 21 is splined at 22 to a sleeve 20 having left-handed helical splines 26 engaging complementary splines on an accessory gear 9, connected to gear 7 by splines 8, the gear 7 driving a gear 6 to rotate an engine 1, Fig. 1. The sleeve 20 is rotatably mounted in a case 3 on ball bearings 18, 19 and is prevented from axial displacement by ring 23 and a washer 24 abutting ball-bearing 19 and by flange 60 abutting bearing 18 abutting on flange 25 on a member 16 bolted to the casing 3. An annular flange 12 of gear 7 carries a friction member 13 for engagement with an element 14 having helical splines 15 engaging complementary splines on member 16. A spring washer 29 abutting ring 30 on member 16 and the element 14 biases this element to the right whilst a spring washer 27 abutting ring 28 on flange 12 and a flange 61 of sleeve 20 biases the flange 12, gears 7 and gear 9 which is bolted to gear 7 to the right to the brake applying position. A ball carrier 32 fastened by nut 11 to gear 7 carries a plurality of balls 33 in peripheral slots 34, the balls coacting with the internal wall of gear 7 and the cam face 35 of flange 61 so that on rotation of the gear 7 the balls due to centrifugal force react on the cam 35 to move gear 7 and its flange 12 to the left to the brake release position. A pump 39, Fig. 1, driven by the gear train supplies fluid at a pressure proportional to the propeller and engine speed through a rotatable slip-tube 37, a bore 41 in a plug 36 fixed to sleeve 20, an annular groove 42 in plug 36 and the bore 43 into chamber 44 between gears 7 and flanges 61 and 12. When the assembly is in brake applied position some fluid passes from chamber 44 through bores 46 in gears 7, 9, annular groove 63 in gear 9, bore 47 and sleeve 20, annular groove 48, a bore (not shown) and a groove 50 in plug 36, bore 51 in sleeve 20 to a chamber 64 for lubricating bearing 18 and for cooling by passing through grooves, not shown, in friction member 13. In operation.-Normally the brake is lightly applied by springs 27 to prevent wind-milling of the propeller. Operation of the starter 65 rotates shaft 21, sleeve 20 and through splines 26 the gears 9, 7, gear 7 transmitting rotation to the engine 1 and propeller 5, the torque transmitted by the helical splines 26 causing the gear 7 and flange 12 to move to the left and disengage the brake. At the same time pump 39 supplies fluid to the chamber 44 and as the engine picks up the pressure builds up to maintain the brake release, also due to the rotation of the gears 7 and ball mechanism 32, 34 a centrifugal oil pressure is built up as well as centrifugal force by the balls 33 on cam 35 to help hold the brake released, should fluid supply be cut off then the centrifugal force is alone maintaining the brake released. If during flight the propeller is feathered and then tends to move past the fullfeathered position, the spring 27 applies the brake with sufficient force to drag element 14 around in the reverse direction, the splines 15 moving element 14 to the left for stronger brake engagement to prevent backward rotation. On engine shut down the oil pressure is decreased and the brake is maintained released until spring 27 overcomes the centrifugal forces of the fluid and balls, the brake being gradually engaged as the engine slows down.