Patent GB-755004-A (GB)
Title: Improvements relating to variable-speed power transmission mechanisms for motor vehicles and control systems therefor
IPC: F16D67/00
Filed: 1954-11-24
Abstract: 755,004. Change-speed gear. GENERAL MOTORS CORPORATION. Nov. 24 1954 [Dec. 23, 1953], No. 34071/54. Class 80(2) [Also in Group XXIX] In a motor-vehicle change-speed control wherein ratio-establishing clutches and brakes are fluid-pressure operated under control of a manuel selector-valve 200 and automatic shift valves 214, 215, 216 responsive to opposing fluid-pressures varying with output speed and engine-throttle setting, the manual valve 200 is movable to a setting F-2 in which it operates a lock-valve 404, Fig. 8, which cuts off the throttlevariable pressure from the shift-valve control and substitutes therefor a higher (full line) pressure, whereby the automatic shift speeds are all raised to a higher value, e.g. 200-300 R.P.M. higher than maximum fuel-fed governed speed of the engine. This facilitates steep ascents and preserves engine braking on steep descents. One, two or more complete change-speed gear units may be used in parallel, the shifts occuring alternatively in the different gears. An auxiliary output direct-reduced gear, with manual fluid-pressure control, doubles the available ratios. Function summary. Excluding the auxiliary gear all shifts are wholly automatic only, except that into neutral or reverse, the manual valve 200 having in addition to neutral and reverse settings N, R, only two forward drive positions one, F1, providing for speed-and throttle-responsive shift, the other, F2, cutting out the throttle response and raising the shift speeds. Movement of the manual selector into reverse as well as movement of the separate manual selector valve 121, Fig. 11a of the auxiliary two-speed gear, are automatically prevented above a predetermined output speed. Servo-pressure is doubled when applying the reverse brake, the same pressure being halved by a limiter valve 208, Fig. 8, before passing to a brake of the preceding gear unit which also operates during reverse. Gear arrangement. Two complete automatic four-speed and reverse gears are arranged in parallel, their input shafts 26, 26<SP>1</SP> being driven by a single engine flywheel 20 through a common fluid-coupling 21 and torque-dividing planet gear the input planet-carrier 24 of which is connected to the turbine 22, the sun 25 direct to the input shaft 26 of the upper gear and the ring 28 to the input shaft of the lower gear through gear 30, idler 31 and gear 32. The output shafts 65, 65<SP>1</SP> of the two gears are geared together at 80, 80<SP>1</SP> through an idler 81, the gear ratio being such that the upper output shaft 65 rotates at 1.25 times the speed of the lower 65<SP>1</SP>, which with the gear-step chosen, results in the two gears being shifted alternately to provide seven equally spaced ratios. A directreduced planet gear 85 arranged between the gear output shaft 65<SP>1</SP> and the final output shaft 87 doubles all the ratios. Each gear comprises identical front, rear and reverse sun-ring trains 37, 50, 68, the front and rear trains, which are in series, each providing solid and reduced drives by a disc clutch and band brake. In the front train the input shaft 26 drives the ring 27. the planet-carrier 35 being secured to an intermediate shaft 36 carrying the input sun 50 of the rear train, whilst the freely mounted sun 37 is braked at 42 or clutched to the output planet carrier 35 at 41. In the rear train the ring 67 is braked at 57 or clutched at 56 to the sun 50 which is now the input. For reverse, the rear train compounds with the reverse train when a freely mounted ring 70 of the latter is held by a double-cone brake 71. The planets of the reverse train are carried by the output shaft 65, and its sun 68 is connected to the ring 67 of the preceding rear train. In the final output gear, reduced drive is by holding a ring- gear 88 by a double-cone brake 96. The planets are carried by the final output shaft 87 which is directly driven when an input sun 85 is disc-clutched at 91 to the ring 88. All the clutches and brakes are fluid-pressure operated. The torquedividing input planet gear 26 may be of the bevel type (Fig. 12, not shown), and the fluid coupling may be omitted as may also the auxiliary gear (Fig. 13, not shown). The gear units may be of the torque converter with gear type. Brake-band servos. The rear brake-band 57 is engaged in part by springs 159, 164, 165, Fig. 6, acting on two pistons 158, 162, connected by a strut 161 which is hollow to permit compensator pressure (described below), supplied at 168 to act on both pistons to assist the engaging springs. Disengaging pressure 304 acts rightwards on both pistons. A spring 160, fixed at one end to the piston 158 has its free end spaced from the adjacent fixed end-wall which it contacts after a predetermined rightward travel to provide additional resistance to disengagement. The front band-brake 42 is disengaged with the assistance of an inner spring 178, Fig. 7, acting upwards on a piston 175 secured to an actuating stem 171, by fluid-pressure 181 acting upwards on an upper piston 172 fixed to the stem 171, and on a lower piston 174 freely slidable thereon and pressed downwards by an outer spring 177 which supports an abutment cup for the inner spring 178. Engagement is by supplying fluid-pressure at 312, to the upper face of the upper piston 172, assisted by compensator pressure 180 in a chamber below a fixed partition 176, to act on the piston 175. Fluid coupling. The impeller 21 carries a number of plungers 102 which, at normal speeds are centrifugally moved outwards out of the fluid-circuit but which, at idle speeds, are spring-pressed inwards, as shown, to impede fluid circulation in the coupling and thus reduce idle drag - Fluid system. Each gear has its own complete fluid control system with the exception of the following parts which are common to both gears. Input and output driven pumps 33, 278, Fig. 11, the former of variable capacity, scavenge pump 275 for the auxiliary gear case, and an accumulator 146. The auxiliary gear has its own manual selector valve 121, blocker 268 for preventing its operation above a predetermined speed, and a pressure regulator 131. The control system of each automatic gear includes the following parts, those of the lower gear being denoted by the same reference numerals as those of the upper but with a suffix. The manual valve 200; a "TV'' valve 201, loaded through a spring and cam 205 connected to the engine throttle control to provide at 221 throttle-variable pressure hereafter referred to as "TV" pressure: a compensator valve 206 for further metering TV pressure to provide at 271 compensator pressure for assisting the brakeapplying servos of both front and rear gear units to increase their pressure with increased throttle openings; the limitervalve 208 above referred to; a doubletransition valve 207 governing sequence of shifts between second and third speeds which involve shifts of both front and rear units of a gear; an output-driven governor-valve 226 comprising two separate radial valve units in a rotating body and loaded by unequal masses 226, 228 to regulate pump-pressure 229 to upper and lower speed-responsive ranges hereafter referred to as G1, at 235, and G2 at 238; 1-2, 2-3 and 3-4 automatic shift valves 214, 215, 216, Fig. 9, responsive to opposing governor and regulated TV pressures: the lock-valve 404 which substitutes full line pressure for TV in the F-2 drive-setting, and also, in F-1 setting, regulates TV pressure to a lower value before passing it to the shift-valves; a G1 governor pressure responsive reverse blocker 262; the front and rear brake and clutch servos, and reverse brake servo; and a restrictor valve 186, Fig. 7, in the front brake servo for retarding the supply of engaging pressure thereto at high G1 governor pressures, thus delaying application of the front brake during a 4-3 downshift. The manual valves 200, 200' of upper and lower gears always move together. Operation. In the following description action in the upper and lower gear assemblies is identical unless otherwise stated, hence action in the upper assembly only is described. Neutral. With the engine running and the manual valve 200 in neutral setting, the front pump 33, Fig. 11, charges the accumulator 146 through a non-return valve 144. Pressure 301 is directed to the rear brake release line 304, and through a connected line 305 to move the doubletransition valve 207, Fig. 8, left exhausting the connected front clutch apply, front brake release lines 314, 315 through a line 340 and the 3-4 shift valve 216, Fig. 9. F-1 setting. In this position the manual valve 200, Fig. 8, completes a pump pressure passage 310, 311, past the not-fully open land 371 of the limiter valve 208, which effects a slight throttling, through a line 312 and fully open restrictor valve 186, Fig. 7, to act downwards on the piston 172 and apply the front brake. The rear clutch-apply rear brake-release passages 308, 304 are now connected through the manual valve 200 and exhausted through a line 309 and the 2-3 shift valve 215, Fig. 9. The line 305, connected to 304, also exhausts, permitting the double transition valve 207. Fig. 8, to spring- return to the right, but the front brakerelease, front clutch-apply lines 314 315 are still exhausted through that valve 207 at 316 and the 3-4 valve 216, Fig. 9. With the front and rear brakes thus applied (the latter by its springs), depression of the accelerator pedal starts the vehicle through the fluid-coupling in first speed low-low in both gears. Accelerator depression also acts leftwards through the cam 205, Fig. 8, in opposition to outlet pressure 221 acting on a centre land of the TV valve 201 to cause the said land to meter line pressure 301, 320 (regulated at the input pump 33 to 100 p.s.i.). to a TV delivery passage 221 (regulated to 67.5 p.s.i. at full throttle). A line-pressure loaded detent plug 203 a