633,781. Fluid-pressure servomotor control systems; hydraulic transmission of power. GENERAL MOTORS CORPORATION. July 18, 1947, No. 19256. Convention date, Oct. 16, 1939. [Classes 69 (ii) and 135] [Also in Group XXIV] Relates to a selector-control for a variablespeed gear, shown as being of the Lysholm- Smith type, wherein a pair of nested main discclutches C, D drive selectively from an input shaft 1 to a concentric driven sleeve 9, bevelgeared to a vehicle propeller-shaft 60, either through a central shaft 2 and a hydrokinetic torque-converter T (through clutch C), or by a direct mechanical connection (through clutch D), the converter-path including a forwardneutral-reverse countershaft gear R, operated by a sliding clutch-pinion 26, and a one-way clutch F effective in forward drive only. In such a gear the ratio-selecting clutches C, D are operated by a servo cylinder 105, shown as electro-pneumatic, under control of a centrifugal governor G, driven by an output-shaft bevel 60a, and an accelerator kick-down switch S<SP>3</SP>, and, to relieve converter drag, a hand-lever 245, which operates the forward-neutral-reverse pinion 26 through positive linkage, has a compulsory initial movement, as by rocking it laterally out of its operative notches F, N, R, as shown in Fig. 16, or by depressing a button on a shaft sliding in the lever (Fig. 10, not shown), which operates a switch S<SP>4</SP> in the servo-system to bring about a locked disengagement of both friction clutches C, D before the lever 245 can make a forwardreverse selector movement, which can thus occur without coupling-drag. The ratio-selecting clutches C, D are selectively clamped to the driving fly-wheel by opposite movements of a common intermediate presser-plate 61, effected through a lever 81 by a thrust-collar 72, which acts in the appropriate direction on the radially slotted inner periphery of a single common clutch-loading diaphragm-spring 70 carried by the presserplate 61 and fulcrumed at 62 on the fly-wheel back-plate. Positioned as in Fig. 17 a spring 102, in the servo-cylinder 105, holds the clutchlever 81 at the left for converter drive (clutch C), the lever 81 being moved to the right for direct mechanical drive (clutch D) when a solenoid shift-valve 135 is energized to direct air-pressure from a supply-pipe 120 to the left end of the servo-cylinder 105, pressure at the same time passing to a smaller engineidling cylinder 92 which temporarily closes down the fuel-injection rack 257, Fig. 17, or throttle 35, Fig. 15, of the driving engine during upshift, a telescopic spring connection 32 permitting this movement without movement of the linked accelerator-pedal 8. Ratio-shift circuit. Fig. 15 shows the ratioshift circuit, the shift-servo (105, Fig. 17) not shown in this Figure, being fed by the delivery 124 of the solenoid-valve 135; whilst Fig. 17 shows the separate neutralizing circuit, part of the Fig. 15 parallel shift-circuit being shown dotted. In the shift-circuit, Fig. 15, the valve-solenoid 135 is energized to supply airpressure through the duct 124 to the throttleclose cylinder 92, and to the clutch-shift cylinder 105, Fig. 17, for upshift to the directdrive clutch D, when, above a predetermined vehicle-speed (20 m.p.h.) the centrifugalgovernor G closes a switch in a series circuit including (1) a normal closed switch S<SP>3</SP> which is opened by overtravel of the acceleratorpedal 8 to close the solenoid-valve 135, venting the shift servo 105 to allow its spring 102 to produce a downshift to converter-drive; and (2) a normally closed manual switch S<SP>1</SP> which can be opened at any time to enforce a permanent converter-drive. Anti-drag circuit. In the separate, but paralleled neutralizing circuit, Figs. 16 and 17, lateral movement of the forward-reverse lever 245, which must be made to bring the lever out of any of its operative notches F, N, R into the connecting slot 249 for shifting the reverse clutch-pinion 26, closes a switch S<SP>4</SP> to energize the shift-solenoid-valve 135 as if to produce an upshift from converter to direct-drive, but at the same time the circuit energizes a series lock-solenoid 160 which advances a spring- loaded fork 162, Fig. 12, into the path of a shoulder 163 on the piston rod of the clutchshift servo 105, which is thus arrested in a mid-position with both main-clutches C, D disengaged, thereby relieving the gearing of any drag from the previously engaged converterdrive, and facilitating shift of the reverse pinion 26. Similarly, during operation in converter-drive, the reverse-lever 245 may be moved to the left of its operative slot to relieve drag to prevent creep of the vehicle in traffic. To cushion the air-actuated movement to direct-drive the piston of the shift-servo cylinder 105 uncovers at mid-stroke a port 109, Fig. 6, communicating with a surrounding expansion-chamber 110, so as to produce a dwell, effective for upshift only. A pipe 98 may also communicate the upper end of the engine-idling cylinder 92 with a port in the side of the shaft-servo cylinder 105 which is uncovered when the piston of the latter completes a stroke to the direct drive position, thus supplying equalized pressure to both sides of the engine-idling cylinder 92 to permit its spring to effect return to the inoperative position. Reverse-gear. In the reverse-gear the output shaft 15 of the converter T carries a fast pinion 16 driving a countershaft 29 through an idler, and also carries the fast inner member of the one-way clutch F, the outer member of which can be clutched directly to the final driven shaft 9 (position shown) by the sliding clutchpinion 26, splined on the driven shaft 9, for oneway forward drive, or the pinion 26 can be slid to the left to release the outer one-way clutch member, and to mesh with a wheel 28 on the countershaft for bi-directional reverse. Specification 532,496, [Group XXIV], is referred to.