Patent GB-647771-A (GB)
Title: Improvements in control means for variable speed power transmissions for motor vehicles
IPC: F16H61/02
Filed: 1947-02-28
Abstract: 647,771. Hydromechanical change-speed control. PACKARD MOTOR CAR CO. Feb. 28, 1947, No. 5874. Convention date, March 16, 1946. [Class 80(ii)] [Also in Group XXIX] In a hydromechanical planetary change-speed gear on a motor vehicle, a reaction-brake 27. for holding a planet-carrier 26 to produce a two-ratio reduced drive, is applied by fluid-pressure, provided e.g. by an oil-pump 58, Figs. 3, 4, under control of a valve 73 operated by depression in the enginemanifold 95, which communicates with a diaphragm 81 of the brakevalve 73 through a conduit 96<SP>1</SP> including a normallyclosed valve 106, which is opened automatically, to apply the reaction-brake, by a cam 114 on the engine-throttle spindle when the driver depresses the accelerator-pedal 108 beyond idling position. Drive in geared ratios is thus automatically disconnected by accelerator release. Automatic shift to and from direct-drive, with accelerator kickdown shift; and an anti-idle-drag brake for facilitating operation of a planetary reverse-gear 49, are also provided. In the stepped-planet gear, an output sun 22 is fast on the tail-shaft 19 and two input suns 20, 21 are driven respectively by primary and secondary runners 15, 16 of a threeelement fluid-coupling, the input impeller 13 of which is also connected directly to the planet-carrier 26 through a resilient coupling 44 and a multi-disc friction-clutch 35, which is applied automatically to produce a two-path hydromechanical direct-drive when pressure-fluid from the pump-fed line 62 is supplied to clutch-engaging pistons 38 through a valve 84, the element 87 of which is moved downwards to an open position in opposition to a closing spring 92 by the combined effort of a vehicle-driven centrifugal governor 97 and engine-manifold depression acting directly through a conduit 96 on a diaphragm 93 attached to the piston valve-element 87. The latter has differential pistons 88, 89, which, when the valve is open, cause outlet-pressure to supplement the effort of the governor and engine-suction in maintaining the valve open, whereby closure occurs at a lower speed than  opening and hunting is prevented. With the valve-element 87 in its upper closed position the clutch-line is exhausted at 88a. In operation, on starting, depression of the accelerator-pedal 108 applies the carrier-brake 27 whereby two geared driveratios are applied successively to the tailshaft 19 through the primary and second- _ ary runners 15, 16 of the fluid-coupling, which are connected by a one-way coilclutch 33. to allow the secondary to overrun the primary when it takes over as the speed increases. At approximately 12 m.p.h. the governor 97 and engine-suction together open the valve 84 to apply the direct-drive clutch 35, the carrier-brake 27 remaining in engagement due to the provision of an overrunning clutch 31 between the brake and carrier. Downshift to geared drive occurs automatically at a predetermined lower speed but can be enforced at any time by accelerator kickdown to close a switch 124, energizing a solenoid 120, which closes the direct-drive clutch-valve 84 in opposition to the governor 97 and enginesuction, this energizing circuit being disabled when not required by opening a manual switch 131. The tail-shaft 19 drives the vehicle propeller-shaft through the input sun 47 of a planetary reverse-gear, operated by sliding the planet-carrier 49 with the sun 47 to dog-clutch teeth 53 on the output-shaft 45, carrying the ring-gear 46, for solid forward drive, or to engage fixed detent-teeth 51 for reverse. The forward - neutral - reverse shift-rail 68 is operated by a Bowden-controlled lever 65, and its end 71 acts as a valve to shut off the pressure supply to the clutch-brake line 62 in neutral. In addition the shift-rail 68 slidably carries a sleeve-valve 138 which, in neutral, directs pressure from the pump-line 61 to an antidrag disc-brake 54 on the tail-shaft 19. The shift-lever 65 operates the sleeve-valve 138 before the forward-reverse shift-rail 68, the latter subsequently following under the influence of one or other of two springs 140, 141, when the brake 54 has reduced the drag on the tail-shaft 19 sufficiently to permit the forward or reverse dogs to mesh.