Patent GB-790617-A (GB)
Title: Improved control system for variable speed power transmission mechanisms
IPC: F16D67/00
Filed: 1955-12-08
Abstract: 790,617. Change-speed gear. GENERAL MOTORS CORPORATION. Dec. 8,1955 [Dec. 27, 1954; Dec. 27, 1954; Dec. 27, 1954], No. 35271/55. Class 80 (2). [Also in Groups XXIX and XXXIV] In a planet gear-train B on a vehicle, a sun 19 reacts on a one-way detent 55 for reduced drive, and a fluid coupling D, between the sun 19 and an input ring 16, is filled for direct-drive in the train B and emptied for reduced drive, under control of a coupling-valve 280, actuated by opposed fluid-pressures responsive respectively to accelerator-pedal position and output speed. Function summary.-The gear provides three reduced ratios, direct-drive and reduced reverse, under control of the manual selector valve 170 which has settings P, N, D, I, L, R, as follows. In P, park, and N, neutral, the main fluid coupling A is filled (if the engine is running) and all gears released. D, drive, provides automatic shift between all four forward ratios, starting in first, under control of three shiftvalves subject to opposing fluid pressures responsive respectively to output speed and accelerator-pedal position, the latter factor being cancelled on upshift so that return downshift is at a lower speed and is responsive to speed only. Direct and reduced drive in the front gear train B are respectively by filling and emptying the ratio fluid-coupling D. In D setting of the manual valve 170 all three indirect ratios are one-way only. In I, intermediate, shift to fourth ratio is prevented except above excessive engine speed, and third ratio is two-way. L setting limits operation to the first two ratios only except for automatic shift to third above excessive engine speed, and second ratio is two-way. In D, 4-3 and 3-2 accelerator kickdown shifts can be made in succession below predetermined safe-engine speeds, or occur successively at appropriate speeds if kickdown position is maintained. In I, one 3-2 kickdown can be made. Manual downshift to L, although still subject to safe engine speed limit, permits downshift at higher speed than for kickdown in either D or I. Servo system pressure is reduced in fourth ratio, increased in reverse and regulated to constant values in these and other running conditions. The rate of loading of a ratio clutch during a shift is controlled by restrictors, an accumulator and by accelerator pedal position. Three stages of speed-responsive pressure are used, two provided by a governor 230 having two centrifugal regulator valves and the third by a governor-amplifier valve 261. Engine starting is possible only in neutral and park positions. Gear arrangement.-Four forward ratios are provided by two direct-reduced sun-ring trains B, FJ in series, reverse being by compounding a third sun-ring train J with the rear train F. A main fluid-coupling A is arranged between the trains B, FJ and is torque-split in third and fourth speeds. In first speed, reduced-reduced, a sun 19 of the front train reacts on a one-way detent 55 so that its planet-carrier, driven by an input ring 16, drives at reduced speed the impeller 14 of the main fluid-coupling A, the turbine 15 of which drives, through an innermost shaft 74, a sun 75 of the rear train F. The ring-gear 78 of the latter reacts on the casing through a drum 79, one-way detent 94 and controllable disc brake G, so that a further reduced drive passes to the planet-carrier and integral output shaft 100. For second-speed, directreduced, the sun and ring of the front train B are bridged by filling the ratio fluid-coupling D, the detent 55 over-running. In third-speed, torque-split reduced-direct, the fluid-coupling D is emptied so that the front train B reverts to reduced drive, and a rear disc clutch L is engaged, to provide a mechanical drive from the impeller 14 of the main fluid-coupling A, through a sleeve-shaft 70 and clutch L to the rear-train ring. The rear-train sun 75 receives a fluid drive at substantially the same reduced speed from the turbine 15 of the main fluid coupling A, whereby the rear train drives direct and re-combines the split-torque. In fourth speed, split-torque, direct-direct, the second fluid-coupling D is filled, to bring the main fluid coupling A to input speed as in second speed, and the rear train drives direct as in third speed. For reverse, the double-cone brake K is applied to a ring-gear 104 of the reverse train J, which has planets carried by the output shaft 100 and a sun fast to the ring of the rear train F. The detent brake G is released to permit reverse rotation of the ring 78. The front train drives in reduced, as in first speed, the compounded rear trains giving reverse, further reduced. Brakes.-In addition to the reverse brake K and anchor-brake G of the one-way detent 94, there are a disc brake E in parallel with the front one-way detent 55 and engaged for twoway drive in the front train B, and a band-brake H, in parallel with the rear one-way detent 94 and brake C, for two-way drive in the rear train F. The band-brake H is engaged by applying fluid-pressure 650 to a piston 652 having a lostmotion connection with an actuating stem 656, absorbed by a spring 655, for gradual engagement. The reverse brake K comprises a double cone 105 applied against a fixed cone 111 by an internally-coned non-rotating piston 114 energized by fluid pressure 412. A diaphragm spring 116 releases the brake cone. In park position P, of the selector valve 170, a pawl engages teeth 103 to lock the output shaft 100 positively. Fluid supply system.-Input and output driven pumps 60, 120 provide pressure for servos, couplings and lubrication. The delivery 125 of the output pump 120 supplies the system main 65 through a one-way valve 124 when its pressure exceeds that 122 of the input pump 60. The input pump has the main supply duty, output pump delivery 125 being short-circuited to pump suction 121 to save power above a predetermined output speed by a speed-responsive pressure-line 496, 241, acting on an output pump by-pass valve 126. The input pump 60 is of the kind having rotating vanes 63<SP>1</SP> in a casing 61, guided for radial eccentric movement under control of opposing fluid pressures 68, 69, one 69, assisted by a spring 62, tending to increase eccentricity and hence delivery, the pressures 68, 69 being supplied from pump delivery 66 through drillings 137, 138 in the piston of a pressure regulator valve 130, which supplies either line 68, 69 as required to develop the required pressure with minimum delivery. The regulator valve 130 is loaded downwards by delivery pressure 66 and upwards by a spring 133 to maintain a normal system pressure of 95 p.s.i. In fourth ratio this is reduced to 65 p.s.i. by main pressure applied through the manual selector valve 170, a shift-valve 320 and line 495 to act downwards on a differential land of the regulator valve 130. In reverse, pressure is raised to 195 p.s.i. by reverse brake pressure acting upwards at 412. Initially the spring 62 loads the pump-slide 61 to maximum eccentricity, in which position the slide shuts off a valve 141 in a line 65, 66, 148, feeding, through a cooler and line 149, the main fluid-coupling A, the cooler having a spring-loaded by-pass valve 150. As the pump 60 develops pressure, the line 68 loads its slide to lesser eccentricity, whereupon the valve 141 is permitted to open and feed the main fluid coupling A, a relief valve 155 in the turbine hub of which feeds a lubrication line 156. Fluid system components.-These include, in addition to those referred to above, automatic 2-3 and 3-4 shift valves 305, 320, and the coupling-valve 280 controlling filling and emptying of the ratio fluid-coupling D, including filling for the 1-2 and 3-4 shift. An output-rotated governor valve 230 has two radially arranged centrifugal valves G1, G2, of differing mass which regulate main pressure 65, 240 into two lines 241, 249 providing respectively G1 and G2 governor pressures in different ranges. The valve G1 has a centrifugal assisting spring 236 to provide an initial G1 pressure of 5 p.s.i. with the output shaft stationary. G1 and G2 governor pressures load the 2-3 and 3-4 shift valves 305, 320 in the rightward upshift direction, but governor pressure for similarly loading the coupling valve 280 is increased in the ratio five to one from G1 pressure 241 to G5 governor pressure 267, in a differentially - landed amplifier valve 261. Throttle-variable, i.e. " TV " pressure 192 for opposing governor loading of the shift and coupling valves is provided by a TV valve 181, fed with main pressure 65, 180, the loading- spring 190 of which valve is variably compressed through a plunger 182 by the usual accelerator-pedal (not shown), TV pressure 192 also reacting at 200 on the outer land of the plunger to relieve the operator of loading force. A separate kickdown valve 205, when operated by accelerator overtravel, supplies maximum TV pressure 192, 200, 201 to kickdown lines 500, 550. Front and rear brake valves 340, 220 control respectively the front detent bridging brake E and the rear detent anchoring brake G. A spring-loaded accumulator 382 regulates rate of increase of engaging pressure 390, 381 of the rear clutch, and its spring load is opposed by TV pressure 192, 461, whereby clutch engagement is more rapid at wider throttle openings. A limit valve 290 maintains a minimum pressure in the servo main 65 during filling of the ratio fluid-coupling D during shift, and also serves as an excess pressure relief. Four centrifugally and spring-loaded coupling exhaust valves 40 (see also Fig. 10) are moved radially inwards by fluid pressure 435, 436, 437, to close exhaust ports 46 when the ratio coupling D is filled by a pressure line 425, 426, 429,430. The skirts of the exhaust valves 40 have chamfered clearances for permitting leakage for flushing the valve seats. A double-transition valve 270 controls shifts requiring simultaneous change in both gear units. A reverse-block piston 364;