GB1427113A - Transmission controls - Google Patents

Abstract

1427113 Change-speed gear GENERAL MOTOR CORP 13 June 1974 [30 July 1973] 26247/74 Heading F2D A control for a motor vehicle transmission driven by a two-spool gas turbine and comprising fluid-pressure-engaged ratio-establishing friction drive-engaging means, such as clutches 24, 26 and brakes 56, 60, one of which, brake 56, is engaged for reaction in both low and reverse under control of a manual ranging valve 88, engagement of the said one brake 56 is subject to a disconnect (i.e. a declutch) valve 254 loaded by throttle pressure 148, representing (inversely) engine power, which prevents engagement of the reaction brake 56 in any forward setting of the manual valve 88 when engine power is below a predetermined value, and also prevents its engagement in reverse setting when engine power is above a predetermined value. Gear arrangement.-A two-train Simpson planetary gear set provides two reduced ratios, direct drive and one reverse, established by the usual forward clutch 24, direct-reverse clutch 26, low-reverse brake 56 and intermediate brake 60. A fluid coupling 22 permanently connects an engine-driven gear-input shaft 18 to the forward input ring gear 34 and is used for starting, after which it becomes locked up by speed-responsive engagement of the forward clutch 24, although the fluid coupling may additionally be used for torque splitting in direct drive, depending on the engagement condition of the forward clutch 24. Reverse is always all mechanical through the clutch 26, and although the fluid coupling preferably remains filled, it may be emptied in reverse. Function summary.-Fluid pressures responsive to output speed and compressor discharge pressure actuate 1-2 and 2-3 shift signal valves 94, 96, controlling corresponding relay valves 212, 236, which establish shifts between all three forward ratios in DR3 setting of the manual valve, with third, and third-second suppressed in DR2 and DR1, unless excessive engine speed results. Regulated pressure is augmented in reverse, and establishment of reverse is inhibited during forward movement. The rate of pressure increase during shift is controlled by individual trimmer valves 320, 324, 326 of known type. Fluid pressure supply and regulation.- Pressure in a main 84, fed by a single pump 78 driven by the transmission input shaft 18, is regulated by a regulator valve 86, loaded in the upward, pressure-increase, direction by a spring 106, and downwards by pressure on differential areas from line 84, also reaching the upper chamber of the valve through a spoolbore and port 108, and from a "forwardneutral knockdown " line 116 from the manual valve 88 which exhausts that line 116 in reverse only, for pressure augmentation. A first spill line 112 feeds the fluid coupling. Shift pressures.-A flyweight governor valve 92, output-driven through a gear 164, is supplied with line pressure 84 through an individual filter 100, and supplies governor pressure to a line 162, which feeds the disconnect valve 254 directly, and also to a shift-valve loading line 186 through a one-way restrictor 184, which allows unimpeded pressure rise in the shift line 186, but retards pressure reduction therein to avoid unwanted downshift on sudden deceleration. Pressure inversely proportional to engine power is regulated to a throttle pressure line 148 by a regulator valve 90, loaded by compressor discharge pressure acting on a diaphragm 158. Shift valves.-The 1-2 signal valve 94 comprises two butting differentially loaded spools 190, 194, loaded from a downshifted lower position shown, by the upward load of governor pressure 186 and inverse throttle pressure 148, which together upshift both valve spools against a spring 198 to supply line pressure 84 to a previously exhausted shift signal line 206, which then upshifts the 1-2 relay valve 212 by moving its spool downwards. Upshift of the 1-2 signal valve 94 in DR1 setting is prevented by hold pressure 132 from the manual valve 88 acting between the valve spools 190, 194, to maintain the latter, 194, in the downshifted position except when overruled at excessive speed by governor pressure 186. The 1-2 relay valve 212 in its downshifted, top, position shown, supplies line pressure to the low-reverse brake line 74 from a line 126, pressurized with line pressure 84 from the manual valve 88 in all settings except neutral, a line 246, and the disconnect valve 254 when positioned as shown. In its upshifted bottom position the relay valve 212 exhausts the line 246 and pressurizes a line 244, leading, through the 2-3 relay valve 236 to the intermediate brake line 60. The 2-3 shift signal valve 96 and 2-3 relay valve 236 are similar to the 1-2 valves, 2-3 shift signal pressure being produced in a line 230. Forward clutch 24 has its line 70 pressurized from line 84 through a forward clutch valve 98 when that valve is moved downwards by governor pressure supplied through the line 186, restrictor 286 and line 280, and assisted by inverse throttle pressure 148 acting downwards on a differential land c. Thus, after starting on the fluid coupling, the latter is bridged by the forward clutch 24 at a powerrelated speed. In reverse, the clutch-valve governor line 280 is exhausted through a oneway valve 288, the " forward-neutral-knockdown " line 116, a bore 122 of the manual valve 88 and exhaust 124, causing release of the forward clutch. Disconnect valve 254 forms the main feature of the invention. In its rightward position shown, to which it is biased by governor pressure 180 and a spring, the valve provides free communication from the line 246, pressurized by downshifted 1-2 relay valve 212, to the low-reverse brake line 74. The rightward bias is opposed by inverse throttle pressure 148, acting between the valve spool 290 and an end plug 294. This in forward drive settings, if the engine power is below a predetermined limit, e.g. at engine idle, the consequent increase in inverse throttle pressure 148 shifts the spool 290 left, exhausting the low-reverse brake line 74 through a line 134 and exhaust 124 of the manual valve 88, preventing engagement of the low reverse brake, which may then be engaged by the operator progressively opening the engine throttle to reduce inverse throttle pressure 148. In reverse setting the manual valve 88 pressurizes the line 134, to engage the directreverse clutch 26 through the downshifted 2-3 signal valve 236 and line 72. In this case when, on decrease in engine power, the increase in inverse throttle pressure 148 causes leftward movement of the disconnect valve spool 290, the low-reverse brake line 74 is maintained pressurized from the line 134, and this pressure also passes through lines 304, 306 to act leftwards on the end plug 294, to ensure completion of the leftward movement and the application of full line pressure 134 to the low-reverse brake line 74. Increase in engine power above a predetermined value in reverse reduces inverse throttle pressure 148 and the disconnect valve 254 shifts rightwards to prevent engagement of the low-reverse brake. During forward movement, governor pressure 180 maintains the disconnect valve 254 in its rightward position and the valve cannot be shifted left to establish reverse until the vehicle is stationary and the throttle idled. Hold pressure regulator.-The 2-3 and 1-2 shift valves 96, 94 are held in their respective downshifted positions (shown) in the DR2 and DR1 hold settings of the manual valve 88 by pressure supplied to respective lines 130, 132 through a hold pressure regulator valve 308, which receives line pressure at 128 in the hold and reverse settings and regulates it to a lower constant value into the hold lines 130, 132. Trimmer valves 320, 324, 326 communicate with the respective engaging lines 70, 74, 76 of the forward clutch 24, low-reverse brake 56 and intermediate brake 60. Each comprises a plug 336 spring-loaded against a hollow piston 328, having a restrictor 344 through which clutch or brake engaging pressure 70 passes to shift the plug 336 slowly downwards until arrested by a stop 346 whereafter the engaging pressure rapidly assumes its full line value.