GB1457887A - Automatic gearboxes - Google Patents

Abstract

1457887 Change-speed control AUTOMOTIVE PRODUCTS Ltd 12 Nov 1974 [21 Nov 1973] 54112/73 Heading F2D In an automatic transmission on a motor vehicle, wherein ratio establishing clutches and brakes of a planetary gear are engaged by fluid pressure supplied through solenoid valves energized by an electronic circuit responding to signals 110, 156 representing respectively vehicle speed and engine throttle setting, and to a manual switch 301 ... 303 which holds selected ratios, e.g. 3, 2 or 1, upshifts to ratios above that selected manually occur automatically at speeds at which upshifts would occur during full throttle operation. Automatic shifts to ratios below the manually selected ratio occur at normal speeds. General.-Each ratio has its own speedthrottle signal generator; Miller integrators delay release of an off-going ratio and provide undelayed engagement of an on-going ratio for torque-overlapped shift; up-down hysteresis is provided. Servo pressure is increased in one step only at throttle openings above 25% at speeds below 35 m.p.h. Ratio clutches and brakes.-A forward clutch is engaged in all forward ratios by completing the energizing circuit of its solenoid valve at a terminal 308. A direct-reverse clutch for fourth ratio and reverse, a reverse brake, and second and third ratio brakes are similarly engaged by switching on output transistors 243, 205, 212 and 229 respectively. First ratio in automatic is by a one-way sprag brake. Circuit.-A signal at a frequency proportional to output speed is supplied by an inductive pick up to a terminal 110, is square shaped at 113, 114, amplified and limited at 116, 117, and applied to individual transistor pump circuits 120 ... 123, the first three of which control the respective ratio shifts, whilst the fourth, 123, controls a pressure modulator valve. The outputs of the first three pumps 120 ... 122 are applied to voltage dividers 138 ... 146, connected to emitter-follower transistors 150 ... 152, the bases of which receive an engine throttle signal from a terminal 156 connected to a throttle-operated potentiometer which produces a throttle signal which is at a minimum voltage at full throttle and maximum at closed throttle. Diodes 157 ... 159 limit the signal maximum to avoid undesired low-throttle shifts. Speed-throttle signals thus appearing on lines 165, 166, 167 are applied to amplifier triggers 170, 171, 172 which all trigger at the same voltage but in response to different speedthrottle values determined by the constants of the preceding pump circuits 120 ... 122, the circuits 170 ... 172 triggering respectively 1-2, 2-3 and 3-4 ratio shifts. Each trigger 170 ... 172 triggers at a first value effective during speed increase for upshift which is greater than a second value effective for speed decrease downshift, thereby producing hysteresis. Between the triggers 170 ... 172 and twostage amplifier output circuits 199, 211, 231 and 242 completing energizing circuits to the ratio valve solenoids are the following. A transistor 203 stabilizes the voltage supply to the output stages. Connected to the respective collectors of the two transistors 173, 174 of the first trigger 170 are inverter amplifier transistors 196, 198, which are respectively non-conductive and conductive below the upshift point of the trigger, at which time the output transistor 205 of the reverse brake output stage 199 is conductive. This would normally energize the reverse brake solenoid, but in Drive this is prevented by a bias applied by the manual selector switch 301 to the transistor 205 to maintain it non-conductive. When the 1-2 upshift point is reached the transistors 196, 198 become conductive and non-conductive respectively, maintaining the reverse output transistor 205 non-conductive and also causing the potential at a junction 210 to fall, whereupon the output transistor 212 of the stage 211 conducts and completes an energizing circuit to the solenoid of the second ratio brake. The 2-3 shift requires torque overlap, for which purpose Miller integrators 216, 221 are arranged between the trigger 171 and the output stages 211, 231. At the upshift point the integrator transistor 223 becomes non-conductive and 218 conductive, causing voltage to be applied to a function 230, whereby the transistor 229 conducts to produce undelayed energization of the third ratio brake solenoid, whilst de-energization of the off-going second brake solenoid is delayed as the potential at the junction 210 rises at a rate determined by the discharge of a capacitor 219 through a resistor 214 of the Miller integrator 216. Further Miller integrators 232, 233 similarly control overlap of the 3-4 shift by the trigger 172 and output stage 242. Manual shift.-The manual selector is a three-bank wafer switch 301, 302, 303, the first, 301, of which disables the speed signal 110 in P, R and N, whilst in manual 3, 2 and 1 it zeroizes the throttle signal applied by the respective transistor 152, 151 or 150 to the corresponding voltage divider whereby the speed-throttle signal for the particular ratio, and for higher ratios than that selected, is equivalent to that at full throttle, whilst the signals for the remaining lower ratios remain at the normal automatic level. The second wafer bank 302 provides a bias in all settings except manual 1 and R to maintain the inverter transistor 196 conductive and hence the reverse brake output transistor 205 non-conductive, and also renders conductive the direct-reverse transistor 243 in reverse and manual 1. The third wafer bank 303 completes the energizing circuit 307 to the forward clutch terminal 308 in all forward ratios, completes a circuit in P and N to an engine start terminal 305 and in R to a reverse signal lamp terminal 306. Servo pressure control.-The circuit of a servo pressure modulator valve is energized, to reduce servo pressure, by rendering conductive a transistor 257, which occurs when the throttle signal, 156, applied through a resistor 255, and decreasing with throttle opening, falls below a value corresponding to 25% full throttle, this operation being overriden by a switching circuit 250, controlled by the fourth pump circuit 123, at speeds above 35 m.p.h., by which time torque multiplication in the usual torque converter has ceased, so that increased servo pressure is unnecessary even at throttle openings above the 25%.