GB1360596A - Control means for change-speed mechanism - Google Patents

Abstract

1360596 Change-speed control WILSON MILLER & CO Ltd 4 Aug 1971 [5 May 1970] 21690/70 Addition to 1201612 Heading F2D An electronic circuit, for initiating up and downshift of a change-speed, e.g. overdrive gear, on a motor vehicle driven by a spark-ignition I.C. engine comprises first and second circuits C1, R1 and C2 R2, producing voltage signals representing engine speed and torque respectively from pulses in the engine ignition circuit, applied at 4, which signals are applied in opposition to the base of a transistor TR1 forming one of a bi-stable pair TR1, TR2; controlling energization of a shift solenoid or electromagnetic valve 7, through a two-stage amplifier circuit TR3, TR4. A long time-constant provided by R1 C1 in the first circuit uses the square-wave make and break pulse of the ignition contact breaker to supply charging current related to engine speed to a capacitor C3, which, with the aid of pumping diodes D3, D4, and a leakage resistor R3, is charged to a voltage proportional to engine speed, the negative side of which is applied to the base of the transistor TR1, the emitter of which is biased negatively with respect to battery positive terminal 1 by a voltage divider R14, R16, R17, R18, across the battery terminals 1, 6, so that when the engine-speed negative signal exceeds emitter potential, TR1 conducts, causing conduction of TR2, TR3, TR4 to produce upshift. The much shorter time-constant of R2, C2 in the second circuit similarly charges a capacitor C4 from the high frequency transient at the ignition contact breaker, this charging voltage representing engine torque. The negative voltage of the capacitor C4 is applied to the emitter of TR1, whilst its positive voltage is applied through resistors R6, R7 to its base, this torque voltage being thus in opposition to the speed voltage from C3. A bias resistor R10 biases the torque signal on the emitter in accordance wth the direction of current flow in that resistor, bias being towards positive at low speeds and negative at high, so that greater torque increments are required to produce downshift at higher speeds, adjustment of a resistor R9 determining the current reversal point. In the TR1, TR2 circuit a resistor R11 renders the circuit bi-stable and also prevents hunting. Temperature compensation is provided by negative temperature characteristic resistors NTC1 and NTC2 arranged respectively near the ignition coil or engine, and in the circuit. Closure of a kickdown switch across terminals 2, 3 applies more positive potential to the base of TR1 through a resistor R5, producing downshift up to any desired speed. Connection of the terminal 2 to the capacitor-side of the resistor R4 would provide a delay in kickdown in accordance with the time required to reduce the charge in C3. An inhibitor switch, not shown, disables the automatic control in lower ratios of the main gear. The Specification also includes the kickdown switch forming the subject-matter of Specification 8484/74.