Patent GB-1460578-A (GB)
Title: Epicyclic gear ''semblies
IPC: F16H37/04
Filed: 1974-04-24
Abstract: 1460578 Change-speed gear GKN TRANSMISSIONS Ltd 18 Oct 1974 [8 Nov 1973 24 April 1974] 51782/73 and 17844/74 Heading F2D Relates to a planetary change-speed gear, particularly an over- or under-drive auxiliary gear in a motor vehicle, having, for the planetary ratio, a brake 35 and, for direct drive, a friction clutch 27, with or without a forward drive oneway clutch 50, and in which the gear teeth are helical to generate a rightward axial thrust which reinforces direct-drive clutch pressure when reverse is selected in a preceding main transmission, or on overrun. With such an arrangement there is a risk that, if the vehicle is brought to rest in the planetary ratio, and is subsequently restarted in reverse, the directdrive clutch may slip, since in the initially stationary condition there would be no relative rotation to remove oil from the friction surfaces of the clutch. To avoid this the rightward axial thrust is caused to engage synchronously directdrive positive clutch teeth 14, 22, which are otherwise biased out of engagement by springs 16. During forward drive the tooth thrust is in the opposite direction (leftwards), which reinforces brake pressure in the planetary ratio, but slightly reduces clutch pressure in direct-drive, the latter being immaterial particularly where the one-way clutch is provided. In the commercial vehicle overdrive gear, Figs. 1 and 2, a planet carrier 18 is fast on an input shaft 10, a ring gear 25 fast with output, and a sun 13 is splined for limited axial movement on a freely mounted sleeve 11 on which is fast a clutch-brake member 28, which is shifted left by compressed air applied at 45 to a piston 44 to engage an overdrive brake 35 and right by compressed air applied at 49 to a non-rotary piston 46 to release the brake and engage directdrive friction coned clutch surfaces 27. Forward drive torque on the helical gears generates a leftward axial thrust on the sun 13, which increases brake engaging pressure and slightly reduces clutch engaging pressure. The latter reduction is immaterial due to the preferable provision of a direct-drive one-way clutch 50. In reverse, and also in forward overrun, tooth gear thrust on the sun 13 is rightward and serves to move the sun axially from a normal position, Fig. 2, in opposition to bias leaf springs 16 in recesses 15, to engage the sun gear teeth positively with clutch teeth 22 on the planet carrier, such engagement taking place synchronously as the clutch slips. As shown the disengagement of the positive clutch teeth is produced by the leftward movement of the sleeve 11 acting on the sun through a snap ring 33. In Fig. 3, not shown, the directdrive clutch (133) is engaged by a diaphragm spring (146) opposing an hydraulic piston (151) engaging the overdrive cone brake (148), and because the spring has necessarily a shorter travel (<SP>1</SP>/ 16  inch) than the piston 46 of Fig. 1, the positive clutch (112, 173) is arranged to disengage before disengagement of the friction clutch begins. For this purpose the sun (113) is fast to its mounting sleeve (111), and the clutch-brake member (134) is splined for relative axial movement thereon, and is moved axially by an abutment ring (137) on the sleeve (111) to compress the diaphragm spring (146) for clutch release, only after the sleeve (111) itself has been moved by the piston (151) sufficiently to release the positive clutch (112, 173). This reduces the axial travel necessary for spring compression. Radial spring ball detents (166) oppose the engaging movement of the positive clutch. The shaft has lubrication passages (117, 176) and the hollow planet spindles are fed with lubricant guided to a collector ring (125) by a shield (178).