860,846. Change-speed gear. FORD MOTOR CO. Ltd. May 23, 1957 [May 23, 1956], No. 16363/57. Class 80 (2). [Also in Group XXXIV] A fluid-pressure servo 196, particularly for engaging a friction brake 176, Fig. 3, or clutch in a change-speed gear on a motor vehicle, comprises a pair of concentric pistons, the inner, 294, of which applies the brake through a stem 280 and lever 270, and can move relatively in the outer piston 284 between stops 296, 298, in opposition to springs 300, 302, one 302 of which yieldingly transmits apply pressure 290 from the outer to the inner piston to cause a gradual rise of apply pressure at a constant rate independent of servo-pressure level, after rapid initial engagement. In the absence of fluid pressure the springs 300, 302 hold the inner piston in an intermediate position, but release fluid pressure, supplied constantly during operation, passes through ports 310 to an accumulator space 304 between the pistons to move the inner piston 294 relatively left against the stop 296, and also acts rightwards on a differential area of the outer piston 284 to move the piston assembly right, against the end 286 of the stepped cylinder 274. When apply fluid pressure is supplied to the space 290, the piston assembly moves rapidly left for initial brake application, whereafter further pressure increase causes the spring 302 to yield and the outer piston 284 moves over the inner 294 for gradual pressure increase, until the stop 298 contacts the inner piston 294, after which the pistons move solidly together to transmit pressure directly. Function summary.-The gear provides reduced, direct and overdrive, and one reduced reverse, with a hydrodynamic torque-converter always transmitting all the drive torque. Fluid pressure operation of ratio clutches and brakes is controlled automatically by two shift valves LDSV and ODSV subject to opposing fluid pressures responsive respectively to an output-driven governor valve 192 and an accelerator-loaded valve TV, which includes a kick-down section for forced downshift from overdrive to direct only. A separate manual valve DV provides a direct-low forced downshift. A manual selector valve MSV, in addition to reverse, neutral and low (RNL) settings, has two drive settings, one, DR2, providing automatic use of all ratios, the other, DR1, cutting out overdrive. Gear arrangement.-A rear train having intermeshed planets carried by a final output shaft 94, provides reduced drive, reverse and direct drive respectively by brakes 142, 144 and a clutch 130, an input sun 98 of the train being driven through the torque converter, the impeller 50 of which is driven by an input shaft 20 through a direct-overdrive simple planet train 40, the direct drive of which includes an overrun clutch 54 which takes forward drive torque and a friction clutch 150, engaged in all but overdrive, which takes overrun torque to prevent free-wheeling. The overdrive train comprises a planet carrier 42, directly connected to input 20 through a shell 30, spring coupling 34 and drum 38; an output ring gear 40 directly connected to the impeller 50 of the torque converter; and a reaction sun 156 which can be held by the brake 176 for overdrive, or clutched at 150 to the carrier for direct drive. In the rear train planets 100 mesh the input sun 98, directly connected to the converter turbine 62 through an inner shaft 66, and planets 104 which mesh also a reaction sun 116, held by the brake 142 for reduced forward drive, and a reaction ring 106 held by the brake 144 for reduced reverse. The clutch 130 connects the two suns 98, 116 for direct drive. Reverse, first and second ratios are given respectively in the rear train by the brakes 144, 142 and the clutch 130, the overdrive train driving, direct through the one-way clutch 54, locked'against overrun by the clutch 150. For overdrive third ratio the overdrive clutch 150 is released, and the brake 176 applied. The rear train remains in direct-drive only. Servo-pressure supply and regulation.-Input and output driven pumps 164, 178 supply a system main 198 through check valves 200, 238, the input pump 164 being driven by the reaction sun 156 of the overdrive train which is held stationary in overdrive, the pump then being idle. A main regulator valve MRV, governed by a TV-loaded pilot regulator valve PRV acts as follows. Line pressure 198 passes through an orifice 204 in the main regulator valve MRV into a chamber 202, where it acts downwards on the pilot regulator valve PRV in opposition to upwardly-acting spring and TV pressure 242, the latter supplied through a TV pressure limit valve PLV. The pilot regulator valve PRV is thereby moved downwards to open an exhaust communication 208, and the consequent flow through the orifice 204 creates a pressure differential, the higher pressure acting downwards on the top of the main regulator valve MRV through a passage 210, causing the main regulator valve to move downwards to feed the torque converter through a line 212 and to control a by-pass 220 to pump suction, thereby regulating system pressure, which is torqueresponsive in view of the upward TV pressure 242 loading the pilot regulator PRV. The efflux 214 from the torque converter passes through a heat-exchanger 216 to a lubrication line 218. Control.-Line pressure 198 always passes directly to the release chamber 304 of the overdrive brake servo 196. In N setting of the manual selector valve MSV, all other servos are exhausted. In DR2 setting the manual selector valve MSV supplies line pressure 198 through a line 222 to apply the low-speed brake 142, and, through a line 224, the overdrive clutch 150, for a start in low. Vehicle motion causes the output-driven governor 192 to meter speed-responsive pressure 226 from the main 198 to act upwards on low-direct and overdrive shift valves LDSV and ODSV, in opposition to TV pressure 240, 246 from the accelerator-loaded valve TV. When speed prevails the low-direct shift valve LDSV rises, and line pressure 228 passes through a line 230 to engage the direct drive clutch 130, and through a branch line 232 to release the low brake 142 to introduce direct drive. At a higher speed the overdrive shift valve ODSV lifts to supply pressure from a manual valve line 234 through a line 236 to apply the overdrive brake 176 (as above described) and to shift right an overdrive transition valve ODTV which exhausts the overdrive clutch line 224, completing the direct-overdrive shift. In DR1 setting (shown) the manual selector valve MSV exhausts the line 234 and the shift to overdrive cannot occur. Forced downshifts.-If, when operating in overdrive, the accelerator pedal is fully depressed, the kick-down section of the TV valve TV feeds line pressure 198 through a line 252 to act downwards on a land of the overdrive shift valve ODSV, causing downshift to direct. Rightward movement of the direct-low downshift valve DV supplies TV pressure 242 through a line 254 to act downwards on the low-direct shift valve causing forced downshift if TV pressure is near its maximum value.