Patent GB-835327-A (GB)
Title: Improvements in or relating to variable speed transmissions
IPC: F16H47/08
Filed: 1957-08-28
Abstract: 835,327. Change-speed gear. FORD MOTOR CO. Ltd. Aug. 28, 1957 [Aug. 29, 1956], No. 27136/57. Class 80 (2). In a three-speed and reverse gear on a vehicle, comprising front and rear planet trains in series, controlled automatically by clutches and brakes engaged by fluid pressure supplied by input- and output-driven gear pumps 134, 202, the input pump 134 is driven by a reaction sun 106 of the front train, which sun is stationed in the highest ratio (overdrive), thus saving power. Function summary.-A manual selector valve 243 provides, in addition to neutral N, reverse R and a fixed low L, two drive ranges, one D-1 giving automatic shift, in response to opposing vehicle speed and accelerator pedal setting, between all three forward ratios, the other D-2 automatic shift between the first two ratios only. 3-2 and 2-1 accelerator kick-down shifts are provided, the latter subject to a speed-sensitive timer valve 305 which permits the engine more free time to accelerate when 2-1 down shifting at higher vehicle speeds. Closed throttle automatic 2-1 downshifts are similarly timed by a throttle-sensitive timer valve 287 which permits more free engine time at low throttle openings. An accumulator 297 causes gradual application and release of a low brake 216 during shift. Servo pressure increases with torque demand and is augmented in reverse, Line pressure operates at 314 a park-pawl inhibitor (not shown). Gear arrangement.-The two series planetary trains provide over-, direct-, reduced-drive and one reduced reverse. An hydrodynamic torque converter transmits the whole of the torque between the trains and is always effective. The front train, having a planet carrier 96 directly connected to a shell 12 fast on an engine crankshaft 14, overdrives the impeller 49 of the torque converter through its ring-gear when a front band brake 214 is applied to its reaction sun 106. Direct drive to the impeller 49 is through a one-way clutch 86 which overruns during overdrive but which, in direct drive in the front train, is prevented from overrunning by locking up the front train by engaging a front clutch 122 connecting the reaction sun 106 and the planet carrier 96. Drive to the rear train passes from the turbine 56 of the torque converter through a central shaft to a sun 178. The rear train comprises intermeshed planets carried by the final output shaft 16, and provides reduced ratio when a centre band brake 216 is applied to a reaction sun 170; direct drive when a rear clutch 150 is engaged to connect the two suns 170, 178; and reverse when a rear band brake 218 is applied to a ring gear 180. Overall ratios are: first, direct-reduced, clutch 122 and brake 216; second, direct-direct, clutches 122, 150; third, overdrive-direct, brake 214 and clutch 150; reverse, direct-reduced reverse, clutch 122 and brake 218. Fluid pressure supply.-All the brakes and clutches are engaged by fluid pressure supplied by the two crescent-type gear pumps, one, 203, mounted on and driven by the final output shaft 16, the other, 134, connected to the reaction sun 106 of the front train so that this pump (134) is stationary (for power saving) when the sun 106 is braked for overdrive, but is input driven at all other times. The pumps supply a common pressure main 242 through check valves 224, 308. Pressure regulation.-A main regulator valve 223 meters a pressure-inlet chamber 222, first to the torque-converter feed 236, later to exhaust 240. The regulator 223 is loaded upwards by a spring 228 and downwards by the differential pressure created across an orifice 226 in the valve member itself, by flow from the inlet chamber 222 through the orifice 226 to an exhaust X metered by a pilot regulator valve 229, subject to downward loading by pressure on the downstream side of the orifice 226, and upward loading by a spring 232. Further upward loading is provided by a line 284 in which is fluid pressure varying with accelerator depression, to increase regulated pressure with increased torque demand, and in a branch from a line 294 feeding the reverse brake 218 to augment system pressure in reverse. Fluid system components.-In addition to parts already referred to above, the system includes an output-driven governor valve 210 supplying speed-responsive governor pressure 264; a valve 269 which supplies throttlevariable (" TV ") pressure 282 under loading through a spring by a valve 270 linked to the usual accelerator pedal and itself providing 3-2 kick-down shift; a further accelerator-operated valve 300 opened only at full throttle for 2-1 kick-down shift; 1-2 and 2-3 automatic up and down shift valves 265, 255 loaded by opposing governor and TV pressures; an overdrive transition valve 293 governing pressure supply to the front clutch 122. Operation. Neutral.-In N setting the manual valve 243 supplies main pressure 242 to the front clutch 122 only, through lines 260, 246. D-1.-In D-1 setting the manual valve 243 supplies pressure 242 additionally to links 250, 252, the latter, 252, directly applying the centre brake 216 and also feeding the 1-2 shift valve 265; the former, 250, feeding the 2-3 shift valve 255. First speed, direct-reduced, is thus established. When, on increasing speed, governor pressure 264 overcomes TV pressure 282, 284 in the 1-2 shift valve 265, the latter rises to direct pressure 252 through a line 292 to engage the rear clutch 150, and through a branch line 292<SP>11</SP> to the release side of the servo of the centre brake 216, releasing the latter, thus upshifting the rear train for second speed, direct-drive. With further speed increase governor pressure 264 overcomes TV pressure 282, 284 in the 2-3 shift-valve 255, raising the latter to direct pressure 250 through a line 258 to apply the overdrive front brake 214 and to shift right the overdrive transition valve 293 which then cuts off pressure 246 from, and exhausts the front clutch 122, thus upshifting the front train for third speed, overdrive-direct. D-2 and L.-In D-2 setting the manual valve exhausts the feed line 250 of the 2-3 shift valve 255, thus preventing shift to third speed, whilst in L setting the feed 252 to the 1-2 shift valve 265 is similarly exhausted to prevent upshift to second speed. R.-In reverse setting R the manual valve 243 pressurizes apply lines 294 of the reverse brake 218 and 246 of the front clutch 122, as well as a branch line 296 holding the 1-2 shift valve 265 in the depressed downshift position, and a branch line feeding pressure to below the pilot regulator valve 229 to augment system pressure. Kick-down shifts.-A first kick-down is provided at a particular throttle opening by the valve 270 supplying line pressure 242 through a line 299 to depress the 2-3 shift valve 255 producing a 3-2 downshift. At full throttle the second kick-down valve 300 is opened to direct TV pressure 284 through a line 304 to depress the 1-2 shift valve 265 for 2-1 downshift, and to maintain depression of the 2-3 shift valve 255. Timer valve action.-During an automatic 2-1 downshift, which involves application of the centre brake by exhausting its release pressure line 292<SP>11</SP>, such exhaust passes through a coast downshift timer valve 287, which, at low throttle openings, is held right by a spring to insert a restrictor in the line, thus delaying brake application to permit time for engine acceleration. At the same time line pressure 306 from the manual valve 243 passes through the coast downshift timer valve 287 and a line 306<SP>1</SP> to reinforce the leftward bias maintaining the overdrive transition valve 293 in its left setting for supply to the front clutch 122. At higher throttle openings TV pressure 282, 284 shifts the coast downshift timer valve 287 left, providing unrestricted exhaust from the release line of the centre brake. During 2-1 kick-down shift at moderate speeds the forced down shift timer valve 305 is held right by a spring, and does not restrict exhaust of the centre brake release line 292<SP>11</SP>, but at higher vehicle speeds governor pressure 264 shifts the forced downshift timer valve 305 left to insert a restrictor in the exhaust line, delaying application of the centre brake to provide increased time for engine acceleration. Accumulator.-The accumulator 297, having opposed chambers connected to the apply and release lines 252, 292<SP>11</SP> of the centre brake 216, cushions brake application and release during shift to and from first ratio. Overdrive brake servo.-This is cushioned by the constant supply of line pressure 242 to a chamber 312 where it acts constantly on an inner piston which is not large enough to operate the servo.