Patent GB-630938-A (GB)
Title: Power transmission mechanism for motor vehicles
IPC: F16D67/00
Filed: 1947-07-18
Abstract: 630,938. Hydromechanical variable-speed gear. GENERAL MOTORS CORPORATION. July 18, 1947, No. 19254. Convention date, April 10, 1939. [Class 80 (ii)] The second and third planetary trains on the output side of the branched hydro-mechanical variable-speed gear shown in Specification 492,084 are modified whereby lowest ratio is provided by the second train acting without the third ; and reverse by the compounded second and third trains, instead of the converse arrangement shown in Specification 492,084. For this purpose the sun 40a, Fig. 4, of the second train is fast on the fluid-driven inner shaft 5, its ring-gear 80 is fast with the outer member of the disc-clutch 23 and with the sun 84 of the third train, whilst the connected planet carriers 79, 82 are fast on the output shaft 50. The ring-gear 85 of the third train is held for compounded reverse by a radially-sliding detent 90 having two profiled teeth 95 engaging with similar teeth 88 on the periphery of the ring-gear 85, by fluid-pressure acting on an integral spring-retracted piston 90b. ' The gear shown in Fig. 1 is the unmodified gear of Specification 492,084 and provides three reduced ratios, direct-drive and at least one reverse, by three sun-ring-gear planetary trains 15, 30, 40, combined with a two-element fluid-coupling 6, 7 through which latter the whole of the drive passes in the two lowest ratios, whilst in the two highest ratios the drive is branched through two paths, one including the fluid-coupling, the other a mechanical path, the arrangement being such that the effective overall slip due to the fluid-coupling, as determined by its torque-speed loading, is greatest in the lowest ratio, providing softness and minimum drag for starting, and decreases with each upshift to a minimum in the highest ratio for increased efficiency. In the lowest ratio forward or reverse, the first reaction-sun 15 is held by a first band-brake 46 so that the first ring- gear 10, fast on the engine-shaft 1, drives the input wheel 7 of the fluid coupling at reduced speed through the first planet-carrier 12, drive then passing through the fluid-coupling 7, 6 to an inner shaft 5 having fast at its rear end a second ring-gear 34 and third sun 40, so that by applying a second band-brake 47 to hold the second reaction-sun 30, the second and third trains combine to drive the third ring-gear 43, fast on the aligned output shaft 50 at lowest ratio, whilst by releasing the second brake 47 and applying a third band-brake 49 to the connected planet-carriers 33, 36 of the second and third trains, the latter acts without the second train to provide reverse. In these ratios the whole of the drive passes through the fluid-coupling, which, due to the first train 15, is driven at reduced speed and correspondingly increased torque in relation to the engine-shaft, so that slip will be a maximum. For upshift to second ratio the first brake 46 is released and the first reaction-sun connected to the first planet-carrier 12 by a first disc-clutch 20, so that the fluid-coupling 7, 6 is driven direct at engine-speed, the second brake 47 being applied as for first ratio. The whole of the drive again passes through the fluid-coupling, but since this is now driven at engine-speed the overall slip as compared with first ratio is correspondingly reduced. Third ratio, which is branched, is by releasing the clutch 20 and applying the first brake 46 to drive the inner shaft 5, and with it the connected second ring-gear 34 and third sun 40, as for first ratio ; and engaging in addition a second disc-clutch 23, whereby the second sun 30 is clutched to an outer sleeve 11 rigid with the first planet-carrier 12, providing a mechanical reduced-drive path to the second sun 30, which combines with the fluid-driven second ring-gear 34 to impart drive to the connected planet-carriers 33, 36 of the second and third trains, in which latter the drive is again combined with the fluid-driven sun 40 to drive the third ring-gear 43 and output shaft 50 in third ratio. Although the fluid-coupling is again driven at reduced speed, as in lowest ratio, the overall slip is again reduced in comparison with second ratio due to the torque-share taken by the mechanical branch path. Fourth and highest ratio, direct-drive, is by releasing the brakes and engaging both disc-clutches together, giving a oneto-one ratio through each of two paths, one through the locked first train, fluid-coupling 7, 6, inner shaft 5, and connected second ring-gear 34 and third sun 40, the other a mechanical path through the sleeve 11, clutch 23 and second sun 30. Overall slip is still further reduced in this ratio due to the one-to-one drive of the fluid-coupling and the torque-share taken by the mechanical path. This invention modifies the second and third trains as shown in Fig. 4 described above. The disc-clutches 20, 23 are engaged by fluidpressure acting on groups of pistons 52, the brakes also being engaged by fluid-pressure acting in each case on a single piston (Fig. 2, not shown) released by a spring. The brake may also be released by the same fluid-pressure which simultaneously engages the corresponding disc-clutch, for which purpose pressure acts on the rear face of the brake-piston, pressure being also supplied to its front face during a brake-disengaging upshift, to modify the brakerelease interval so that the clutch engages before the superseded brake releases, giving gradual shift. Alternatively the control porting may release the brake first, to give a neutral dwell during shift. The control (not described) may be speed and/or torque responsive or manual, and may select any single brake or clutch individually or in pairs, as may be required. Efficiency-speed curves in each ratio (Fig. 3, not shown) are provided.