Patent GB-728461-A (GB)
Title: Improved control system for variable-speed power transmission mechanism
IPC: F16H61/02
Filed: 1952-06-20
Abstract: 728,461. Change-speed gear. GENERAL MOTORS CORPORATION June 20, 1952 [July 5, 1951], No 15545/52. Class 80 (2). [Also in Group XXXIV] A change-speed gear for a motor vehicle comprising two direct-reduced planetary trains in series, together with a fluid coupling and controlled by fluid - servo - operated friction clutches and brakes under conjoint automatic control of output-speed and accelerator-pedal responsive means, has also a manual selector valve 160 movable to select at least three ranges of ratios in each of which a different number of ratios is automatically selectable. Thus " drive " position provides automatic shifts between all four ratios ; " intermediate," between the first three ; and " low " between the first two. Accelerator kickdown shift is provided in all ranges. Gear arrangement.-The gear, Fig. 1, provides three reduced ratios, direct-drive high and one reverse by means of two direct-reduced planet trains in series, together with a final train 52 which acts compounded with the adjacent preceding train for reverse. In the connecting power-path between the two forward trains is a fluid-coupling which transmits the whole of the torque in reverse, first and second ratios, whilst branching with a mechanical path for a split-torque third and high. An input shaft 1 drives directly through a coupling- casing 3, spring-coupling 4 and outermost sleeve 6, the ring-gear 9 of the front train which comprises also a reaction sun 11 held, for reduced drive, by a band-brake 16 or clutched at 22 for direct drive to the output planetcarrier 20 which latter is fast on an intermediate sleeve 21 on which is fast at the forward end the impeller 25 of the fluid coupling and at its rear end the inner member of a disc clutch 39 connecting it to the ring gear 36 of the rear train, which ring gear 36 can be held by a band brake 45 for reduced drive. The rear train is completed by a planet-carrier 35 integral with a final output shaft 50, and a sun 32 integral with an inner shaft 30 on the forward end of which is fast the fluid-coupling turbine 26. Also fast on the final output shaft is the planetcarrier 52 of the compounding reverse train which is completed by a freely-mounted sun 48 rotationally fast with the ring 36 of the rear train, and a ring-gear 57, held fast for reverse by a cone brake 61 and also carrying teeth 60 for a positive park-lock, as described in Specification 716,134. Reverse train teeth are helical to provide end thrust assisting brakepressure in the reverse driving direction. The ratios provided are as follows. First, by applying both band-brakes 16, 45 for all-fluid low-low, with the fluid-coupling driven at the reduction ratio of the front train ; second by applying the front clutch 22 and rear band-brake 45, foi allfluid direct-low, with the fluid coupling driven at engine speed ; third by applying the front band-brake 16 and rear clutch 39 for split-torque low-direct, with the fluid coupling driving, at the reduction ratio of the front train, the sun 32 of the rear, and a mechanical drive at the same ratio to the ring-gear 36 of the rear train, which then combines the torques ; fourth with both clutches 22, 39 engaged and a one-to-one drive, fluid to the rear sun 32, mechanical to the rear ring 36, giving direct-direct ; and reverse by applying the front band-brake 16 and reverse cone-brake 61 for all-fluid low plus compounded reverse. Clutches and brakes. The front and rear train clutches 22, 39 are both multi-disc friction clutches engaged by oil pressure applied through valving (described below) and passages 368, 357 respectively, to annular pistons 18, 43. The front and rear train brakes are single-wrap contracting bands 16, 45 respectively, the front 16, being applied and released by oil pressure, whilst the rear, 45, is applied by springs together with augmenting oil pressure under certain conditions (see below), and released by oil pressure. The servo-unit for the front brake 16 comprises an actuating stem 112, Fig. 3, carrying at its lower end a piston 113 to the underface of which oil-pressure is supplied through a duct 360 to apply the brake. A fixed partition 115 divides the cylinder into two compartments in the upper of which is a piston 121 secured to the stem 112 and, during brakeon periods supplied with oil-pressure on its underface through a duct 366a to augment the line-pressure acting on the main piston 113, such augmenting pressure being supplied through a valve 415, Fig. 5, from two alternative sources: (1) a compensating valve 210 (see below), which modulates pressure to torque-demand by accelerator-depression as described below, and (2) full line pressure introduced above a predetermined output speed as described later. Slidable on the upper part of the stem 112 is a larger piston 126, between which and the small piston 121 are two springs 119, 127 separated by a cap 128. Disengagement is effected by supplying line pressure at 368 to act downwards on the lower piston 113 and pass through the hollow stem at 122, 123 to act downwards on the large upper piston 126, which, in the brakeapplying position is in contact with the smaller piston 121. Downward pressure thus overcomes upward and disengages the brake. The rear train brake band 45 is applied by a stem 133, Fig. 4, to which are secured two pistons 134, 140, loaded leftwards to apply the brake by springs 141, 143 assisted by acceleratormodulated compensating pressure supplied through a duct 366 to act leftwards on both pistons, pressure reaching the piston 140 through a slot 147 and boring 144 in the stem. Disengagement is effected by supplying linepressure through ducts 359a, 359b to act rightwards on the pistons, pressure reaching the piston 140 through an apertured check valve 137. Secured to the piston 134 is a spring 146 which, at a predetermined point in the stroke, contacts a fixed dividing wall 135 of the cylinder to provide additional resistance to the disengaging movement. During a shift involving application of the rear brake, the check-valve 137 checks exhaust from the front chamber 139 of the rear piston 140 unless the accelerator pedal is depressed to supply compensating pressure through the line 366, which acts through a plunger 138 to open the check valve 137 for rapid exhaust of the chamber 139. The reverse brake cone 61, Fig. 2, is gripped internally and externally by supplying oil pressure to the right face of a cone-piston 62 retracted by springs 66. Fluid system. The main pressure-line 351, Fig. 5, is fed through an exhausting-valve 435, Fig. 16 (not shown), which automatically opens the feed line 351 to exhaust 439 in the absence of supply pressure, provided by input- and output-driven pumps P, Q (see also Figs. 1 and 2), the latter Q feeding through a non-return valve 347, whilst the former has a pressureregulating valve 451 having line-pressure loading supplementing spring loading in reverse to provide increased pressure. The following valves, described in detail later, control the system : A manual selector valve 160 (see also Fig. 6) linked to a steering-column-mounted shift lever, Fig. 13 (not shown), and having positive park-lock, neutral, drive-range (auto shift between all four ratios), intermediaterange (auto shift between first three ratios), and low range (auto shift between first two ratios) ; a regulator-valve, hereafter termed " T-V " valve 182, variably loaded by a cam 475 linked to the engine accelerator pedal to provide " T-V " pressure at 365 responsive to engine throttle opening and hence torquedemand, and providing also accelerator kickdown shift in each range. A double governorvalve 388, Fig. 5, on a shaft 55 driven by the final output planet-carrier 52, Fig. 2, and providing two different speed-responsive pressures GI and G2 in ducts 380, 381 respectively ; firstsecond (1-2), second-third (2-3) and thirdfourth (3-4) shift-valves 240, 270, 310 (see also Fig. 7), controlling shift-circuits and subject to opposing pressures provided by the governor and by T-V pressure, the latter modified by a T-V regulator valve 330 which exhausts all T-V pressure from the shift-valves below 15 p.s.i. to permit upshift at low speeds with light throttle-openings; a timing valve 400, Fig. 5, which prevents full release of the rear clutch and application of the rear brake (rear train downshift) until the front clutch is fully applied (front train upshift) for 3-2 kickdown shift; a compensator valve 210 (see also Fig. 6), the output 366 of which is metered from line pressure 352 by T-V pressure at 365, such compensating pressure variably augmenting the front and rear brake-applying pressures to prevent slip at high torque, and being exhausted to zero in reverse ; a " double-transition valve " 230 which is actuated during shifts between second and third ratios (i.e. shifts in both trains together) to control the shift sequence ; a front-brake valve 415, Fig. 5, controlled by G1 governor pressure 380 such that below a predetermined vehicle speed the augmenting pressure supplied to the front-brake servopiston 121, at 366a is compensating pressure 366, whilst above that speed full line pressure 360 is supplied. In addition to these valves there are a reverse-block piston 446 preventing shift into reverse above 5 m.p.h. and a parklock block piston 445 preventing engagement of the park-lock whilst pressure exists in the supply system. Operation-neutral. Figs. 5 and 6. With either pump operating, the main pressure line 351 feeds the manual selector-valve 160 through which it passes out at 358 to a branch duct 359 releasing the rear brake 45, and also moving the double-transition valve 230 to the left. The rear clutch-line 357 is exhausted at 161 ; the front-brake apply line 360 at 171, and the front clutch line 368 through the double-transition valve 230, line 367, 3-4 valve 310, Fig. 7, and exhaust port 324. Drive range. Four ratios, all automatic