753,110. Change-speed gear. GENERAL MOTORS CORPORATION. Sept. 13, 1954 [Nov. 23, 1953], No. 26420/54. Class 80(2) A variable speed gear for a motor vehicle includes a three-element train (16 17. 19). one element (17) of which, for reduced ratio, reacts on a one-way detent 25 which is overrun when direct drive is introduced by filling a fluid coupling B connecting two elements (16, 17), such filling and also emptying being through an automatic shift-valve responsive to speed and an accelerator or like engine control. Gear arrangement. Front and rear sunring direct-reduced planet trains in series provide three reduced and direct drives. a third sun-ring train 40 acting in compound with the rear train for reverse. Third speed is torque split by a main fluidcoupling A and although second and fourth are also dependent on the secondary fluid coupling B, this is frictionally locked in direct drive. In first speed, reducedreduced the secondary fluid-coupling B is empty and a brake 45 is applied to the ring-gear 35 of the rear train whilst a one-way reduced drive is transmitted to its sun 34 through the front train from an input 12 through vibration-damper 14, outer shaft 15 front ring-gear 16, front planet-carrier 19, with the front sun 17 reacting on a one-way detent 25, intermediate shaft 28, main fluid-coupling A (always filled), inner shaft 31 and rear sun 34. The rear planet-carrier 37 thus drives the final output shaft 38 in reducedreduced. In second speed, direct-reduced, the front train 16 is fluid-locked by filling the secondary fluid-coupling B to connect together the sun 17 and ring 16. The rear sun 34 is thus driven at input speed through the locked front train and main fluid-coupling A whilst the rear train reduces as before. For third speed, reduceddirect, the secondary fluid-coupling B is emptied so that the front train passes a one-way reduced drive through the main fluid-coupling A to the rear sun 34 as in first speed; the rear brake 45 is released and a disc clutch 50 engaged to connect the second ring 35 mechanically to the front planet-carrier 19. With the rear sun 34 and ring 35 thus driven at the same reduced speed respectively through the main fluid-coupling A and mechanically, a split torque, reduced-direct, one-way drive issues from the rear train. For fourth speed, direct-direct, the secondary fluid coupling B is filled to lock up the front train. The rear ring 35 and sun 34 are thus both driven at input speed from the carrier 19 of the fluid-locked front train. the former, 35, through the friction clutch 50, the latter, 34, through the main fluid-coupling A. For reverse, a rearmost brake 60 is applied alone to a third ring-gear 41 and the secondary fluidcoupling B is emptied so that the front train passes a one-way reduced. drive through the main fluid-coupling A to the rear sun 34. The rear ring 35 is fast to the third sun 40, so that the rear and third trains compound to pass a reduced reverse to the final output shaft 38 through the rear and third carriers 37, 39 fast thereon. To avoid slip in the secondary fluid-coupling B in fourth ratio (direct drive) a disc clutch 70 is engaged after a time-delay to connect the front ring 16 and sun 17. To obtain two-way drive in the one-way ratios (first and third) a cone brake 80 is applied to the front sun 17 when a three or two-speed range is manually selected as described below. Function summary. A manual valve 101, Figs. 2 and 3, controlled from the vehicle steering-column, has settings N (neutral); DR4 (drive-range 4); DR3 (drive range 3); LO (low range) and R (reverse). Settings DR4, DR3 and LO give automatic shifts between respectively all four ratios, the first three ratios, and the first two ratios, DR3 and LO being also subject to a safety upshift in the event of excessive engine speed. In DR4 first and third ratios are one-way (due to the reaction detent 25), but in DR3 and LO the detent 25 is bridged by the front friction brake 80 for two-way drive. Accelerator kickdown shift is provided below predetermined vehicle speeds from all ratios above first. Output speed and accelerator pedal position govern opposing fluid pressures acting on shiftvalves for the automatic shifts. Servo pressure varies with the load by enginethrottle-variable pressure loading a main regulator valve, which is further loaded for pressure-augmentation in reverse, engagement of which latter is inhibited at 272, Fig. 2, above 8 m.p.h. forward speed. A positive park-lock pawl 217 is prevented at 216 from engaging external teeth on the reverse ring-gear 41 whilst pressure exists in the system. Both the park-lock and reverse obstruction are the same as those in Specification 728,461. Friction clutch and brake servos. With the exception of the rear unit reduction band-brake 45 all the brakes and clutches are engaged by line pressure and disengaged by simple exhausting. The bandbrake 45 is disengaged by line pressure and engaged by springs assisted by a, throttle-variable compensating pressure. Fluid system. In respect of the following items the system is practically the same as that described in Specification 728,461. The manual range selector valve 101; automatic shift-valves 120, 124, 128, Figs. 2 and 4, controlling respectively shifts between first and second; second and third; and third and fourth speeds; a valve 110, Figs. 2 and 3 actuated by the accelerator pedal or engine-throttle control to provide a throttle-variable pressure, referred to later as "TV" pressure; a TV regulator valve 132, Figs. 2 and 4, which further meters TV pressure before supplying it for rightward loading of the automatic shift valves; an output-driven governor valve 218, Fig. 2, providing two distinct stages G1 and G2 of speed-responsive pressure to act leftwards on the automatic shift-valves in opposition to regulated TV pressure for producing automatic shifts; a compensator valve 116, Figs. 2 and 3, loaded by TV pressure, to supply metered line pressure for torqueresponsive loading of the rear unit servo brake band 45; a double-transition or "DT" valve 115, Figs. 2 and 3, which ensures that in shifts between second and third ratios, which involve changes in both front and rear trains, the rear unit change takes precedence; a "timer" valve 227, Fig. 2, controlling the rate of change of servo pressure in certain servos during kickdown shift; a system exhaust valve 181 for rapidly draining the system to permit engagement of the park-lock pawl 217 after pump-pressure ceases; a check-valve 176 between input-and output-driven pressure supply pumps 170, 290. The main pressure regulator is also similar to that in Specification 728,461 with the exception that, instead of being loaded only by TV pressure through a conduit 251, it is now loaded also by reverse-brake apply pressure 470 to provide servo pressure augmentation in reverse. The following items, all used in the control of the front train, do not appear in Specification 728,461. A limit valve 141. Fig. 2, which closes under calibrated spring pressure to prevent further supply of liquid to the secondary fluid coupling B during an upshift in the front train when the volumedemand of the fluid coupling is so great as to reduce the remaining servo pressure below a predetermined minimum. A coupling-valve 145, Fig. 2, actuated by the shift-valve block to control supply to or exhaust from the secondary fluid coupling B. A clutch valve 155, Fig. 2, for engaging the front clutch 70 to lock-up the front train a predetermined time interval after filling the secondary fluid coupling B in fourth ratio. A brake-valve 165, Fig. 2, for applying the front brake 80 for two-way drive in manual DR3 and LO ranges. Shift control pressures. The automatic shift valves 120, 124, 128, Fig. 4, are selectively positioned in response to leftward upshift pressure provided by the two governor pressure stages G1, acting at 270 and G2 at 280, the upper pressure stage G2 being used in the 2-3 and 3-4 shift valves 124, 128, but not in the 1-2 valve 120. Opposing rightward regulated TV pressure is provided initially in the TV valve 110, Fig. 3, which takes in line pressure 182 through a manual valve port 245, exhausted in N setting of the manual valve 101, and meters it to a TV pressure line 251 acting rightwards on a differential-landed metering member 246 in opposition to leftward compression of a spring 112 by the accelerator pedal acting on the stem 110. For shift valve loading, TV pressure 251 is further regulated by a spring loaded TV regulator valve 132, Fig. 4, which it enters at 258 and leaves as regulated TV pressure at 259, 262, such pressure reaching shiftvalve loading chambers 265, 266, 267. Supplementary kickdown pressure acts rightwards on the shift-valves for kickdown shift as described below. Operation. Neutral, N. Initially all the automatic shift valves 120, 124, 128 are spring-loaded to rightward downshift positions shown. With the input pump 170 operating and the manual valve 101 selecting N, all lines exhaust except the supply main 182 and a communication therefrom through the manual valve 110 to a line 185 supplying release pressure to the rear brake servo where it acts rightwards on two connected pistons 91, 92 in opposition to engaging springs. All brakes and clutches are disengaged. Starting. The vehicle always starts in first irrespective as to which forward range is selected. Assuming selection of DR4, permitting use of all four ratios, the rear clutch apply, rear brake release passages 200, 185 are exhausted at passages 228, 229 of the 2-3 shift-valve 124, Fig. 4. Springs acting on the pistons 91, 92, Fig. 2, apply the rear brake 45 for reduction in the rear unit. Acceleration of the engine starts the vehicle through the fluid coupling A, with the front unit reacting on its one-way detent 25, giving first speed (low-low), and also loading the TV valve 110, Fig. 3, to supply TV pressure 251 at 25