Patent GB-820395-A (GB)
Title: Improved control systems for variable-speed power transmission mechanisms for motor vehicles
IPC: F16H61/02
Filed: 1957-10-02
Abstract: 820,395. Change-speed control. GENERAL MOTORS CORPORATION. Oct. 2, 1957 [Oct. 8, 1956; Oct. 16, 1956], No. 30824/57. Class 80 (2). [Also in Group XXXVIII] The rate of engagement of a ratio-establishing fluid-pressure engaged friction clutch 24 or brake in a change-speed gear on a motor vehicle is varied by a pressure regulator valve 102, Fig. 1, or 320, Fig. 2, responsive to the rate of change of speed of the input member. Thus if, as shown, the friction clutch produces upshift, any excessive reduction in engine speed which may be caused by too abrupt clutch engagement is prevented by a corresponding reduction in clutch-engaging pressure, whilst too slow a reduction in engine speed is prevented by a corresponding increase in clutch pressure. If the friction device were to produce downshift, this pressure - change function would be reversed. Function summary.-The gear shown provides reduced and direct drive, engagement of which latter is produced by fluid pressurecontrolled automatically by a shift valve actuated by opposing fluid pressures responsive to output speed and accelerator-pedal position in Fig. 1; or to output speed only in Fig. 2. In Fig. 1 the regulator valve 102 controlling rate of engagement of the direct-drive clutch 24 is actuated wholly hydraulically in response to a pressure responsive to engine speed and a timed release of a pressure responsive to accelerator pedal position. In Fig. 2 the regulator valve 320 is actuated electronically in response to engine speed and rate of change of engine speed. The same pressure regulation of the direct drive clutch is also effective during continuous running. Gear arrangement.-A simple three-element train has planets, carried by an output shaft 19, meshing a sun 14 driven by the engine 20 and a reaction ring 16, held by a brake 22 for reduced drive and clutched by the clutch 24 to output 19 for direct. Fluid-pressure supply.-Fluid pressure for engaging the direct-drive clutch 24, Fig. 1; 224, Fig. 2, is supplied by a single pump 30, Fig. 1, of unspecified drive; or 236, Fig. 2, driven by either the input or output shaft. Shift control.-In Fig. 1, supply of directdrive clutch pressure through lines 132, 128, is controlled by a shift-valve 118 loaded rightwards for upshift by output-speed-responsive pressure 114 supplied by an output-driven governor valve 46 (not described), in opposition to leftward (downshift) loading by a spring 110 and engine-throttle-variable (" TV ") pressure 70 supplied by a metering valve 52 loaded by the usual accelerator pedal 54. When governor pressure 114 predominates, the shift-valve 118 moves right to pressurize the clutch line 128 from a pump-fed line 48, whilst in the leftward, TV-dominant, position the line 128 is exhausted at 130. In Fig. 2, TV pressure is absent, and a simple shift-valve 252 supplies pump-pressure 250 to the direct-drive clutchline 264 when pressure 256, supplied by an output-driven governor 254, overcomes an opposing spring 262. Pressure regulation.-Both embodiments have a general pressure regulator PR (not described) in addition to the regulator controlling clutch engagement. In the wholly hydraulic form, Fig. 1, the regulator 102 controls communication of the direct-drive clutch-line 132 with either the pressure feed line 128 or exhaust 148 in accordance with opposing fluid pressures, one, 142, input speed responsive and supplied by an engine-driven governor 42; the other, 104, fed with TV pressure 70 through the shift valve 118, line 77, a one-way restrictor 78 and an accumulator 80, acting as follows. In the downshift position, shown, the accumulator 80 is fully charged through the shift valve 118 by TV pressure 70, the restrictor 78. having an orificed spring disc which opens freely in the charge direction. Rightward upshift movement of the shift valve 118 also exhausts the accumulator line 77 but the orifice in the restrictor 78 is now effective to regulate decrease of accumulator pressure to a constant rate. If clutch engagement causes engine speed to decrease at a rate exceeding the constant rate of decrease of accumulator pressure 104, clutch engagement is too abrupt, and the consequent decrease in input-governor pressure 142 permits accumulator pressure 104 to move the regulator valve 102 left, to reduce clutch-engaging pressure, and conversely if engine speed decreases too slowly, input governor pressure 142 predominates and moves the regulator valve right, to increase clutch pressure, a constant setting and clutch engagement rate being obtained when the governor and accumulator pressure decrease rates are equal. If the engagement of the friction clutch or brake is such as to produce increased engine speed (e.g. downshift), the pressure 104 opposing input governor pressure is arranged to rise instead of fall. Fig. 2 provides electronic pressure control by a regulator valve 320, controlling communication between a direct-drive clutch-line 342 and either a shift-valve-fed line 264 or exhaust 344, the position of the regulator valve 320 being determined by fluid pressures supplied to opposite ends of the valve 320 from a pump-fed line 246 through restrictors 326, 328, the valves of the opposing fluid pressures being controlled by selectively exhausting them through a pivoted valve 310 actuated by a pair of opposed electromagnets 276, 278 energized as follows. The magnet windings 276, 278 lead to collector electrodes 286 of two pushpull transistors 280, 282 of the p-n-p junction type (or equivalent valves), the emitters 288 of which are fed by a battery 290, whilst their control bases 284 are connected to opposite ends of a resistor 302 fed by an engine-driven D.C. generator 270 producing speed-responsive voltage. The resistor 302 has an earthed tapping 303 which is adjusted to unbalance the magnet currents in a direction tending to retard clutch engagement. A differential circuit, introducing a time constant, is provided by a capacitor 298 and shunt resistor 300. During direct-drive clutch engagement the differential circuit causes alternate variations in the relative energization of the magnets 276, 278, to shift the regulator valve 320 left or right as the rate of change in engine speed falls or rises above a predetermined value determined by the circuit constants.