Patent GB-851424-A (GB)
Title: Improved control system for a variable-ratio power transmission mechanism
IPC: F16D48/02
Filed: 1958-05-06
Abstract: 851,424. Change-speed gear; friction clutches. GENERAL MOTORS CORPORATION. May 6, 1958 [May 6, 1957], No. 14415/58. Class 80 (2). [Also in Group XXXIV] A fluid pressure control system particularly for actuating ratio-establishing clutches and brakes in a vehicle change speed gear under control of a manual selector-valve 291, has a pressure regulator valve 221 subject to fluid pressure loading 311 controlled by the manual selector valve 291 to augment regulated pressure 234 in low, neutral and reverse settings; and subject to opposing loading by output-speedresponsive governor pressure 242 which reduces regulated pressure 234 with increase in vehicle speed; further control being exerted by a flow valve 276, which, in response to system flow during a ratio shift, temporarily disables governor pressure 242 to permit regulated pressure 234 to increase to a maximum value. Function summary.-Four forward ratios, neutral and two reverse are controlled solely by the seven-position manual selector valve 291. A lock-up disc clutch 11, by-passing a hydrodynamic torque converter 10, through which the gear is driven, is engaged automatically at a predetermined turbine speed in fourth, third, and second forward ratios only and, if engaged, is automatically released momentarily during ratio shift and re-engages at a controlled rate only after completion of shift. Servo system pressure is augmented in low, neutral and both reverse ratios, is decreased with increasing turbine speed, and is increased to its maximum during any gear shift by cancelling the speed factor. A hydrodynamic brake 76 on the turbine shaft is controlled by an independent manual valve 356, which also limits pressure in the brake and hence its torque capacity. Gear arrangement.-The gear comprises a series arrangement of the torque-converter 10, with lock-up clutch 11; a direct-overdrive sunring planet train 13 forming a front unit; and three sun-ring planet trains 14, forming a rear unit providing two reduced speeds, direct drive and one reverse. Six forward and two reverse ratios are therefore possible, but the control described uses only four forward ratios and two reverse. The torque converter 10 has two overrun reactors, an impeller 10 connected to the engineshaft 18 through a resilient disc 19, and a turbine 36, fast to the gear input shaft 41 and carrying the driven disc of the lock-up clutch 11, which is clamped against a back-plate by a piston 63 energised by pressure fluid supplied through a line 271, and retracted by an undulating spring 64. The front gear unit 13 comprises a planet carrier 86 splined on the input shaft 41, a ring gear 89 splined on an intermediate output shaft 92, and a reaction sun 88, which, for overdrive, is held by a brake 99 and, for direct drive, is clutched to input 41 by a clutch 101. The three-train rear unit 14 comprises a first sun 137 (middle) and second sun 138 (front), fast with the intermediate shaft 92, now the input; a final output shaft 172 fast with the first and third (rear) planet-carriers 171, 191 ; a first ring-gear 174, fast with the second planetcarrier 141 and third sun 193; and unattached second and third ring gears 143, 194. A brake 181 on the first ring 174 provides first reduced ratio, using the first (middle) train alone. A brake 144 on the second ring 143 provides a higher reduced ratio, using first and second trains compounded. A clutch 146 between input 92 and the second ring 143 gives direct drive, whilst a brake 197 on the third ring 194 gives reduced reverse compounded in the first and third trains. Clutches and brakes-are all of the multidisc friction type engaged by fluid pressure. The clutches 101, 146 are each engaged by a piston e.g. 117, splined to the input cylinder in which fluid pressure acts only in an annular zone lying radially inside the clutch. Fluid pressure, when cut off, drains from the cylinder through a centrifugally unseated ball valve 120. Diaphragm retraction springs 121 are provided. In the brakes the apply piston, e.g. 106, bears directly against the end disc which is non-rotary, thus avoiding the necessity for rotation-preventing pins on the piston. Lubrication is supplied by a line 251 fed through a restrictor 250 by a torque-converter feed line 244. Fluid-pressure supply and regulation.-Input and output driven pumps 216, 208, the former driven by a gear-wheel 71, supply a chamber 218 of the regulator valve 221 in which pressure passes through a filter 222, with by-pass relief 226, and through a non-return valve 237, to act leftwards on a plunger 227 metering to a servo main 234, in opposition to rightward loading by a spring 229 and fluid pressure acting on a piston 231 and derived from a line 261 which is pressurised through the manual selector valve 291 in first ratio, neutral and two reverse settings only, to provide pressure augmentation in those settings. Governor pressure 242, proportional to the speed of the converter turbine, acts leftwards on the regulator plunger 227 to reduce regulated pressure with increasing speed up to a speed limit at which governor pressure 242 equals regulated servo pressure 234, whereupon further increase in governor pressure is prevented by opening of a valve 289 feeding excess governor pressure 242 to the servo main 234, the regulated pressure in which latter thereafter remains constant and independent of speed. During gear shift, governor pressure 242 is momentarily exhausted by the flow-valve 276, permitting the regulator valve 221 to increase regulated pressure to a maximum value. The torque converter is fed from a regulatorvalve port through a line 244 having a pressure relief valve 254. Fluid leaving the converter through a line 346 passes to exhaust through a low-pressure check valve 347, a cooler 348 and a relief valve 377, which, in addition to controlling brake pressure as described below, limits converter outlet pressure. The manual selector valve 291 receives pressure from the servo main 234 through a flow valve 276 (see below) and a line 283. Fluid-system components.-In addition to those referred to above, these include the following. A lock-up shift valve 266 controls the lockup clutch 11. The flow valve 276 is actuated in response to the temporary decrease shift pressure at the beginning of a shift to release the lock-up clutch 11 and after shift, to cause its gradual re-engagement. Flow valve action also exhausts governor pressure to increase regulated servo pressure. A relay valve 301 produces upshift in the front gear unit when the manual valve 291 selects the higher reverse ratio. A trimmer valve 326 causes gradual engagement of the intermediate brake 144 of the rear gear unit, and additional trimmer valves may be provided for the other brakes and clutches. Governor pressure 242 responsive to turbine speed is provided by a pitot head 127 facing tangentially in a channel 129 secured to the converter-output and gear-input shaft 41, and kept filled with liquid by spray from a line 253 fed through restrictors 250, 252 from the torque-converter feed-line 244. Operation.-In its fourth ratio setting, shown, the manual valve 291 feeds pressure from its supply line 283, through its hollow stem to lines 312, 314 applying the overdrive brake 99 of the front unit, and a line 311 engaging the directdrive clutch 146 of the rear unit. When governor pressure 242 exceeds a predetermined value it shifts the lock-up shift-valve 266 left to supply servo pressure 234 to the engaging line 271 of the lock-up clutch 11. 4-3 downshift, produced by moving the manual valve 291 to setting 3, involves shift from overdrive to direct in the front unit only. The manual valve 291 switches pressure from the overdrive brake lines 312, 311 to the direct-drive clutch lines 318, 316. During shift the temporary reduction in pressure in the manual valve feed line 283 due to shift unbalances the flow valve 276 causing servo pressure 234 to move it left, which exhausts governor pressure 242, permitting a spring to move the lock-up shift valve 266 right (position shown), exhausting the engaging line 271 of the lock-up clutch 11 which then disengages. Servo pressure 234 now passes at a controlled rate into the manual-valve feed line 283 through a restrictor 282 to engage the gear clutches and also, through a one-way restrictor 285 to act rightwards on a differential land of the flow valve 276, shifting it right (position shown), in opposition to equalised servo pressure 234, to cut off the governor line exhaust, restoring governor pressure 242. The latter re-opens the lock-up shift valve 266 which pressurises the apply line 271 of the lock-up clutch 11, which re-engages after an interval determined by the one-way restrictor 285 and only after completion of the gear-shift. This lock-up release takes place in all shifts up or down between second and fourth ratios if the lock-up clutch is engaged at the time. Since governor pressure 242 is exhausted during any shift, regulated servo pressure 234 rises to its maximum, to provide a higher clutch and brake engaging pressures whilst the dynamic friction coefficient is effective, the restoration of governor pressure after shift again regulating pressure to a lower value. For shifts into second ratio, the manual valve 291, through a stem port 296, pressurises an apply line 322 of the intermediate brake 144 of the rear train, as well as that 316 of the front clutch. Initial pressure in the line 322 causes it to exhaust at 336 by moving left the trimmer valve 326, closure bias on which is provided by a spring and pressure in the line 322 itself, acting rightwards on the trimmer valve 326 through a one-way restrictor 339, which latter determines the rate at which the trimmer exhaust is subsequently closed by the rightward pressure and hence the rate of increase of brake pressure in the apply line 322. The high reverse ratio R 2 , requires upshift to overdrive in the fron