Patent GB-678544-A (GB)
Title: Variable-speed power transmission mechanism for vehicles
IPC: F16H47/08
Filed: 1950-11-07
Abstract: 678,544. Hydromechanical variable speed gear. GENERAL MOTORS CORPORATION. Nov. 7, 1950 [Nov. 19, 1949], No. 27139/50. Class 80 (ii). [Also in Groups XXIX and XXXIV] In a combined hydrodynamic and planetary variableratio gear for vehicle propulsion, the fluid transmitter has a single impeller 4 and primary and secondary turbines 5, 6, the two latter individually connected to different elements of a compound planet-gear so that initially the primary 5 transmits torque in a low-speed phase, the secondary 6 absorbing torque at a reducing rate with speed increase until it begins to supply and eventually provide the whole of the torque in a secondspeed phase in which the primary 5 is overrun by virtue of a one-way clutch 14 in its drive connection. A direct-drive lockup disc clutch 65 provides a wholly mechanical high-speed phase, in which latter direct engine-braking, supplemented volitionally by dynamic braking in the fluid transmitter, is provided, whereas, in the geared low and second speed phases there is overdrive engine braking through the fluid transmitter. The clutches and brakes of the gear are all frictional and controlled by liquid pressure. Circulatory air and liquid cooling is provided for the fluid transmitter. Fluid transmitter. The vanes 54, Fig. 3, of the impeller 4 are straight, whilst those 55 of the primary turbine 5 are backwardly curved so as initially to deliver liquid backwardly to the secondary turbine 6, which thus absorbs torque in the low-speed phase whilst still rotating forwards at an enforced lower speed due to its connection with the planet gear (described below). The secondary turbine 6 has straight vanes 56 following freely pivoted vanes 56a, which in the initial low-speed phase are moved by the liquid into the backwardly inclined position shown. With increase in speed the backward flow-component changes to forward and (at 10 m.p.h.) tilts the vanes 56a into alignment with 56 whereupon the secondary turbine 6 commences to transmit torque which increases and finally supersedes entirely that of the primary 5 which latter is then overrun. The impeller 4 has external vanes 202 for circulating cooling air, and the working liquid is supplied continuously by servo pumps P.Q. of the gear, entering at 75, 204, passing radially outwards and returning inwards outside the carrier-disc of the primary turbine 5, through passages 205, 206, 207, 208, 209, a pipe connection to a heat-exchanger, set into the base of the vehicle radiator (Fig. 5, not shown) for heat exchange with the engine-coolant, and thence back to the sump S of the gear. Planet gear. The primary turbine 5 is connected through a forward-overrun clutch 14 to an inner sleeve 11 on which are fast the two suns 12, 13 of the first and second planet-trains. The secondary turbine 6 is fast on an outer sleeve 15 carrying oppositely movable clutch-cones 16 for connecting it at will to the freely-mounted first planet-carrier 17, this clutch being disengaged only during neutral. A first ring-gear 22 is fast to a second planet-carrier 23 splined on the final output shaft 50, a free ring-gear and integral brake-cone 27 completing the second train. A splined forward extension 51 of the output shaft 50 carries, on a spring-coupling D, the clutch disc 65 for directly clutching the output shaft 50 to the input flywheel 2. For, geared reduction drive in low and second speed phases the brake 27 and clutch 16 are engaged together, drive in the initial low-speed phase being from the primary turbine 5 only, with the reduction ratio (2.79) of the second train effective alone, and the secondary turbine absorbing torque by being forced to rotate forwards by the gearing at a definite fraction (0.55) of the speed of the primary turbine 5. With increase in speed the secondary turbine 6 begins (at 17 m.p.h.) to supply drive-torque and eventually (35 m.p.h.) supplies the whole of the torque through both trains compounded to provide the second-speed phase (ratio 1.53) the primary turbine being then idly overrun at 14. Direct one-to-one mechanical drive, high-speed phase is by engaging the clutch 65 which can be done at any speed but is enforced above 65 m.p.h. The gear-clutch 16 remains engaged. Reverse is by engaging the gear-clutch 16 and also a brake 21 for the first planet-carrier 17, which holds the secondary turbine 6 so that the fluid-transmitter now acts as a simple torque-converter and the first-planet train, driven by the primary turbine 5, acts alone for reverse. In neutral all the clutches and brakes are disengaged to avoid idle noise and drag. The teeth of the second planet-train are helical to provide end-thrust used in obtaining a torque-regulated transitional shift between second and high, as described below. Engine braking. If, in the geared low or second speed phase, the vehicle should attempt to overrun the engine, the one-way clutch 14 would overrun (in low) but, due to the engagement of the gear-clutch 16 and brake 27, the secondary turbine 6 will be overdriven forwardly by the output shaft 50 and its pivoted vanes 56a will assume the inclined Fig. 3 position, so as to drive the impeller 4 at increased speed, thus providing overdrive engine-braking. If, in addition, the operator engages the direct-drive clutch 65, engine-braking will occur at mechanical one-to-one ratio and in addition the reaction brake 27 and gear clutch 16 cause the gearing to enforce differential overspeeding of the turbines 5, 6 providing supplementary dynamic braking by churning of the transmitter-liquid, the heat of which is dissipated in the engineradiator (as above-described) under closedthrottle engine conditions. Clutches. The gear-clutch 16 is engaged by supplying pressure-oil through an inlet 106 to a space between its opposed male cones 16 to expand them into engagement with the double outer female cone 17 against return-springs 45. The direct-drive lock-up clutch 65 is engaged by supplying pressure-oil to an annular piston 57 through passages 58, 61, 63 and 64. Brakes. The reverse brake comprises an integral cone and annular piston 21 engaged by pressure-oil supplied to an inlet 105. The geared forward-drive brake 27 has two alternative methods of operation, one for a shift to low from neutral or reverse, in which case pressure-oil is supplied directly through an inlet 41 to the right face of a piston 30, the. left side 40 of which is exhausted, so that the piston directly applies the brake 27 to the fixed cone 28, first through inner springs 33, later positively. The second method is used for shifts in either direction between geared and direct drive, i.e. when engagement of the geared brake 27 and directdrive clutch 65 is to be interchanged, which occurs without an interval in which both are simultaneously free, thus avoiding power interruption. For the upshift, brake disengagement simultaneously with clutch engagement is effected by supplying pressure-oil both to the direct-drive clutch 65, through the passages 58, 64; and at the same time through a passage 38 to the space 40 at the left of the brake-piston 30, whilst maintaining the pressure-supply at 41 to the right face of the piston 30. The latter is thus pressure-balanced; and springs 32 move it to the right to disengage the brake' 27. Due however in part to the leftward thrust of the helical gear teeth of the second planet-train the rate of pressure increase in the balancing space 40 is in timed relation with the reduction in torque-reaction on the ring-gear 22, so that the said pressure-increase effects graduated engagement of the direct-drive clutch 65 in proportion as the torque is released from the brake 27, giving a smooth transitional shift without interruption of power. For the corresponding downshift, pressure is exhausted from the directdrive clutch 65 and the space 40 together; so that the unbalanced pressure remaining on the right face of the piston 30 effects a similarly torque-controlled brake-engagement in timed relation with the clutch-release. Except for these shifts, the left piston-space 40 is at all other times exhausted. Fluid supply system. Input and output driven oil-pumps P.Q. fed from the sump S through a common inlet 151, supply the system, the clutches and brakes being .controlled by a selector-valve, not described, in a rear coverblock 111.