Patent GB-1420307-A (GB)
Title: Electronic control system for power transmission systems  providing automatic changes of gear ratio
IPC: F16H61/02
Filed: 1971-12-15
Abstract: 1420307 Change-speed control AUTOMOTIVE PRODUCTS Ltd 15 Dec 1972 [15 Dec 1971] 58282/71 Heading F2D An electronic control for energizing solenoids 40 . . . 43, 57 of valves controlling fluid-pressure-engaged ratio-selecting friction clutches and brakes in an automatic transmission on a motor vehicle, comprises a number of bi-stable circuits 26 ... 28, controlling, through further circuits, shift-valve energization, and changed in state by signals responding to vehicle speed, the further circuits including timing circuits 52 &c., which delay de-energization of an offgoing solenoid, whilst allowing undelayed energization of an on-going one, to produce a torque-overlapped shift. The speed signal is modulated by the engine throttle control and the latter also electronically reduces servo pressure below 25% throttle opening. In Figs. 3 to 8 the bi-stable circuits are Schmidt triggers 26 ... 28, whilst in Figs. 9 and 10, not shown, they are level detectors formed by differential amplifiers associated with switching transistors. Gear arrangement.-The gear, Fig. 1, not shown, provides three reduced ratios, direct drive and one reverse, by a stepped planet bevel train (3 ... 8) driven by a torque-converter-driven parallel input wheel, and controlled by two output clutches, one (10) engaged for all forward ratios, the other (13) for direct drive and reverse; and by three band brakes (14, 15, 16), the first, (14) in parallel with a one-way brake. Block diagram.-In Fig. 3 a speed-responsive frequency, picked up at 20, is converted to a voltage analogue at 21 and supplied as one input signal to each of three summing circuits 22 ... 24, the other input signal to which is taken from the wiper 25 of a potentiometer actuated by the engine throttle control to give a signal which decreases with throttle opening. The output of the summers is fed to the Schmidt triggers 26 . . . 28, feeding differential amplifiers 29 . . . 31, each having two outputs which are changed over by the triggers and form the inputs of summing circuits 32 . . . 35 controlling switching circuits 36 . . . 39, the enablement of which energizes selectively the shift-valve solenoids 40 . . . 43. Additional switching circuits 56, 58 control respectively the valve-solenoid 57 of the forward clutch (10), engaged in all forward ratios, and a pressure modulator which reduces line pressure at below quarter throttle. The switching circuits 36 . . . 56 have additional inputs from delay and inhibitor circuits 52 ... 55 as described below. A manual switch SW has settings reverse, neutral, automatic all four ratios, and third, second and first hold, in positions 44 to 49 respectively, these taking effect as follows. In reverse setting 44 the switch SW connects negative supply 50 to the speed analogue circuit 21, thereby inhibiting the latter from issuing an upshift signal, so that the first-reverse brake solenoid 40 remains effective; and also connects positive supply 51 through the delay circuit 52 to cause the switching circuit 39 to energize the valve solenoid 43 of the directreverse clutch, the circuit 52 producing delay for disengagement and instantaneous engagement when changed. In neutral setting 45, shown, the manual switch SW again inhbits the speed analogue circuit 21 and also connects the positive supply 51 through a delay circuit 54 to the switching circuit 38 for energizing the valve solenoid 42 of the third ratio brake, and through an inhibit circuit 53 prevents the switching circuit 36 from energizing the solenoid valve 40 of the first-reverse brake (14). The fluid ratio brake (15) thus remains engaged alone in neutral, so that when the appropriate clutch and brake for forward or reverse are subsequently selected, the gear is brought to a standstill during the delay period required for disengagement of the third ratio brake after leaving neutral, which avoids jerky establishment of forward or reverse. In all forward settings 46 . . . 49 the manual switch SW directs positive supply 51 through the delay circuit 55 to the switching circuit 56 of the valve solenoid 57 of the forward clutch (10) thus causing engagement of the latter; breaks the inhibit connection between negative supply 50 and the speed analogue circuit 21 thus permitting energization of the valve solenoid 40 of the first-reverse brake (14). In setting 46 the manual switch SW connects negative supply 50 to the throttle-controlled potentiometer 25 and all four ratios are rendered available under automatic speed-throttle shift control, together with throttle responsive control of line pressure through the pressure modulator circuit 58. Upshifts are effected by successive triggering of the Schmidt triggers 26 . . . 28 from non-conductive to conductive state, e.g. when 26 becomes conductive the potentials at the output of the differential amplifier 29 change, thereby de-energizing the first solenoid 40 and energizing the second for 1-2 upshift. Successive downshifts, on speed decrease, occur at lower speeds than those of corresponding upshift, the hysteresis being provided in the trigger circuits. In setting 47 the manual switch SW disconnects negative supply 50 from the throttle potentiometer 25 and connects it through a resistor 59 to a second input of the trigger 27, preventing it from changing state to de-energize the third solenoid 42, thereby holding third ratio, whilst in setting 48 a negative connection to the trigger 26 similarly holds the second ratio solenoid 41 energized. In setting 49 the forward clutch solenoid 57 remains energized, the negative supply 50 is cut off so that initially the solenoid 40 of the first-reverse brake (14) is energized giving first ratio. In all the hold settings the speed analogue 21, unopposed by throttle voltage, is effective for preventing downshift above maximum engine speeds. Shift pattern (Fig. 2, not shown).-The throttle control signal derived from the potentiometer is such that for shifts between the first three ratios, the shift speeds are raised by throttle opening, for openings only over half throttle, and between third and fourth only over a quarter throttle. For this purpose the potentiometer slide 25 feeds a circuit, Fig. 4, not shown, consisting of an emitter-follower input transistor (137) and two similar output transistors (138, 139), the first (138) connected to the one to three summing circuits 22, 23, the second (139) to the three to four 24. Resistors (140 ... 146) and diodes (142, 145) limit the signal at the bases of the first and second transistors (138, 139) respectively to half and threequarters of the supply voltage. Circuit details.-The three Schmidt triggers 26 . . . 28, Fig. 3, comprise pairs of transistors (148, 169; 156, 157 and 160, 161, Fig. 4, not shown), the threshold voltages of which are compensated for variation in supply voltage by supplying a constant current, controlled by a Zener diode (166) and resistors (163 . . . 165) to the bases of the trigger transistors (148, 156, 160) which compensates for the approximately constant voltage drop of their emitters, whereby the trigger threshold voltage is proportional to supply voltage. Thus any variation in the speed signal voltage input (250) due to supply voltage variation is compensated by a corresponding variation in trigger threshold voltage. The designed hysteresis in the trigger circuits is constant and independent of both speed and throttle. The differential amplifiers 29 . . . 31, Fig. 3, each comprise pairs of transistors 172, 173; 175, 176; 178, 179, Fig. 5, the bases of the first of each pair 172 &c. receiving the signals 154, 158, 162 of the respective Schmidt triggers 26 . . . 28, whilst the collectors of the second 173 &c. are connected through resistors 189 &c. to resistor junctions 191, 195, 200, 205, Fig. 7, forming the summing circuits 32 . . . 35, Fig. 3, connected to the respective shift solenoid switching circuits 36 ... 39. Junctions 191 and 205 are also earthed through resistors, whilst 195 and 200 are each connected to two collectors of transistors 172, 176 and 175, 179 respectively of the differential amplifiers. Each amplifier 29 . . . 31 receives a potential of - V and earth, E, and the arrangement is such that initially, with no trigger output signal, the junctions 195, 200 and 205 are all at - V/2, whilst 191 is at earth, as shown in Fig. 7, causing the switching circuit 36 to energize the first brake solenoid 40. When the speed-throttle signal changes the state of the first Schmidt trigger 26, the outputs of the differential amplifier 29 reverse potential, the upper becoming - V, the lower E, the others remaining unchanged, so that junction 191 becomes - V/2, de-energizing the first brake solenoid 40, and 195 becomes E, causing the switching circuit 37 to energize the second ratio brake solenoid 41, producing 1-2 upshift. Similarly functions 200, 205 successively assume E as the potentials of the amplifiers 30 and 31 are successively reversed by the shift signals from the triggers 27, 28, producing 2-3 and 3-4 upshift. The delay circuits are introduced in the collector circuits of the differential amplifier transistors 175, 176, 178, 179 and comprise capacitors 206 . . . 209 which charge rapidly through diodes 210 . . . 213 for energizing an on-going shift-valve solenoid, and discharge slowly through resistors for delayed de-energization of an off-going solenoid. These control shift sequence. In addition energization of the direct-reverse clutch solenoid 43, when produced by moving the manual switch SW to reverse 44, is delayed by a capacitor 234 and variable reresistor 233 (circuit 52, Fig. 3) in the base circuit of a switching transistor 217 and similar delay is provided for energizing the forward clutch solenoid 57 by a capacitor 220 and variable resistor 219 (delay circuit 55). A double-controlled capacitor 224 (delay circuit 54) provides for rapid energization of the third ratio b