Patent GB-1452721-A (GB)
Title: Transmissions
IPC: F16H63/44
Filed: 1975-02-27
Abstract: 1452721 Change-speed gear; friction clutches; clutch control GENERAL MOTORS CORP 27 Feb 1975 [7 March 1974] 8218/75 Headings F2C, F2D and F2L In a vehicle transmission, for use with an engine having a high no-load idle speed such as a two-spool gas turbine 10 with power transfer clutch between the compressor and load turbines 13, 22, for providing a controlled progression from idle to maximum torque capacity drive, and wherein a fluid coupling 72 and slippable friction starting clutch 84, the torquecapacity of which latter is varied during a starting phase, are arranged in parallel between an engine-driven input shaft 56 and an intermediate shaft 78 which drives a final output shaft 211 through, e.g. a four speed and reverse planet gear, providing a definite neutral and selectively operable to establish a starting drive, with the load initially stationary and the fluid coupling stalled at maximum torque, the capacity of the fluid coupling is substantially equal only to the idle torque of the engine under this condition, (approximately 10 percent of the maximum engine torque) and the torque capacity of the friction clutch is controllable from zero to a maximum for starting and driving the vehicle. Thus, with the transmission in neutral the engine establishes a high idle speed, e.g. 1600 r.p.m., unsuitable for starting, and determined only by the load of the engine and vehicle accessories 47, 55, such as altenator, pumps and air conditioning, the fluid coupling being unloaded, whereas on entering a forward or reverse drive in the following transmission, the stationary output causes the fluid coupling to stall and thereby reduce engine idle speed to a lower idle speed value (800 r.p.m.) suitable for initiating vehicle drive through the friction clutch 84. The fluid coupling automatically regulates this constant lower idle speed since coupling stall torque increases, whilst engine torque decreases with increase in engine speed. The slippable starting clutch 84 is engaged by differential fluid pressure on opposite sides of a piston 92, engaging pressure 93 (maximum 150 p.s.i.) being supplied to the right side through a restrictor 99 through a clutch pressure regulator valve 316, loaded as described below, whilst disengaging pressure 103 (maximum 90 p.s.i.) is constantly supplied to the left  side through a coupling pressure regulator valve 286, having constant springload, this pressure also feeding the feed coupling 72 through apertures 108, 109 in the clutch parts, in a circuit which cools and lubricates the waffle-grooved plates of the friction clutch 84, and returns through a restricted path 119, 118 to a cooler 303.  Fluid pressure supply and regulation. Pressure supplied by a single pump 228, driven, along with other engine-driven accessories 47 such as a fuel pump 32, is regulated to a main line 229 by a differentially landed main pressure regulator 266, loaded in the upward, pressure increase, direction by a spring 273, and downwards, for pressure decrease, by line pressure 229 reaching its upper chamber 272 through a bore in the valve spool, and by pressure in a line 282, which is exhausted in R setting of a manual DNR selector valve 306 to provide pressure augmentation in reverse. A first overspill feeds the fluid coupling supply line 103 through the fluid coupling pressure regulating valve 286 which has no exhaust, since the exit line 118 from the coupling is restricted. Control pressures. The starting clutch engage pressure 93 and the transmission shift control 373 (not described) are controlled by governor pressure 367, produced by an output driven governor (not described), and modulator pressure 232, produced by a modulator valve 231, which is loaded in the pressure decrease, downward, direction by compressor discharge pressure 37, acting at 258 on a regulator valve spool through a piston 257 sealed by a rolling diaphragm 251. Compressor discharge pressure is a measure of engine torque demand or setting of the engine fuel control 33, so that modulator pressure 232 is the inverse of engine torque demand (I.T.V. pressure). Clutch pressure regulator valve 316, regulates line pressure 229 to the engage line 93 of the starting clutch 84, under the influence of pressure decrease, upward, loading at 322 from delivery 93; ITV pressure 232 acting on a differential land c, and pressure increase ,downward, loading by line pressure supplied at 334 through a line 338 which is exhausted in Neutral, but pressurized on entering Drive or Reverse, through lines 309, or 311 respectively, pressurised by the manual FNR valve 306 and communicating with the line 338 through a shuttle valve 336. This last downward load 338 acts in the valve spool 317 through a spring- loaded timing piston 323, an internal spring 348 and floating piston 342 and is subject to a time delay through a restrictor 339, which is bypassed by a one-way valve 341 for rapid pressure release on re-entering Neutral. The arrangement is such that, in neutral, with both lines 309, 311 exhausted, and the engine throttle closed, making ITV pressure 232 a maximum, the clutch pressure regulating valve 316 establishes a clutch engaging pressure 93 equal to coupling feed (clutch release) pressure 103, any difference being zeroised by a bleed 101 in the clutch piston 92. The fluid coupling 72 is unloaded and the engine operates at the high idle speed (1600 r.p.m.), being loaded only by the accessories. On entering D or R, with closed throttle, and hence ITV pressure 232 still at a maximum, the regulator valve 316 establishes a differential clutch-engaging pressure of a nominal minimum value (2 p.s.i.), sufficient only to load the clutch plates into no-torque slipping engagement at the dynamic friction coefficient, the rate of this increase being determined by the restrictor 339 and timing piston 323. At this time, the stationary output stalls the fluid coupling 72 at maximum torque, thereby loading the engine to reduce its idling speed to the constant low idle value (800 r.p.m.) suitable for starting the vehicle. On depression of the engine fuel pedal 33, ITV pressure 232 is progressively reduced towards a minimum at full throttle, thus reducing the upward load on the regulator valve 316, to cause corresponding increase of clutch engaging pressure 93 to a non-slip maximum, the actual effective engaging pressure, i.e. the differential pressure being then 150 - 90 = 60 p.s.i. During the initial stage at low throttle, increase in engine speed increases the stall torque of the fluid coupling which contributes to the output torque. This control of clutch engaging pressure is exerted during the starting phase only, and is terminated when, at a vehicle speed of 6 m.p.h. governor pressure 367 depresses an override valve 356, which supplies line pressure 229 through a line 349 to depress the spool 317 of the clutch pressure regulator valve 316 fully downwards, thereby terminating its regulating function and supplying full line pressure 229 to the clutch engage line 93. The specification includes plots of engine speed, torque and horsepower, gasifier speed and pressure, modulator (ITV) pressure, throttle setting and timing of pressure increase on the starting clutch. Change-speed gear. The parallel fluid coupling 72 and start clutch 84 drive the input shaft 78 of three compounded simple sun-ring-planet trains 131, 132, 133, of which the first ring 189, and second and third carriers 192, 193 are secured to a final output shaft 211. A forward clutch 136, engaged in all forward ratios, drives an inner shaft 183 on which are fast the third sun 107 and second carrier 206. First and second suns 184, 186 are fast on a sleeve 182 driven by a direct-reverse clutch 137. Three reduced ratios are provided respectively by a lowreverse brake 212 for the first ring 133; second brake 176 for the first carrier 188; and third brake 163 for the first two suns 184, 186; direct drive by the two clutches 136, 137; and reverse by the clutch 137 and brake 212. The clutch plates and pistons of all three clutches 84, 136, 137 are common, but the starting clutch 84 has more plates than the other two since it is engaged by a differential pressure which is less than the pressure applied to the other two clutches. The starting clutch 84 has thus more heat rejection capacity.