Patent GB-1201612-A (GB)
Title: Improvements in methods of controlling change-speed transmissions
Inventor: MILLER ALBERT ARTHUR
IPC: F16H63/02
Filed: 1966-07-19
Abstract: 1,201,612. Change-speed control. WILSON MILLER & CO. Ltd. 19 Oct., 1967 [19 July, 1966], No. 32351/66. Heading F2D. In a control system for an auxiliary two-speed transmission, e.g. a vehicle overdrive, in which automatic control is effected by a first signal derived from the ignition circuit of an I.C. engine and proportional to the speed of the engine, a second signal responsive to the transient current flowing in the ignition circuit and hence related to the torque of the engine, is used to modify the automatic control so that a change to a higher ratio is inhibited at all speeds on full throttle and a change to the lower ratio occurs at any speed on fully opening the throttle. As shown, the cyclic changes in potential at the point 11 between the contact breaker 7 and primary winding 4 of the ignition coil 3 due to the opening and closing of the contacts 6 produce an alternating current in condenser 13 and resistor 14 which acts on the base of a transistor 19 to cause pulses to flow from a capacitor 20 thus raising point A to a potential proportional to the number of pulses flowing and hence proportional to the engine speed. The potential at A is conveyed via resistor 28 and the collector and emitter of a transistor 30 to the base of a transistor 31 and when said potential rises to a value corresponding to a suitable engine speed, current flows through transistor 31 to the operating coil of a primary relay 34 whose contacts 34a then complete the circuit of a secondary relay 36 which actuates an overdrive to the higher ratio. Contacts 34a also connect in circuit a resistor 37 which raises the potential at the base of transistor 31 to compensate for the reduction in potential at point A consequent upon the reduction in engine speed due to the change to the higher gear ratio. At a significantly lower engine speed, the potential at the base of transistor 31 falls low enough to interrupt the current flow to relay 34 and the overdrive reverts to the lower ratio. Also connected to point 11 are a condensor 38 and resistor 39, the values of which are chosen so that they are responsive to the transient currents flowing in the ignition circuit. The cyclic changes in potential at point 11 produce an alternating current in condenser 38 which is reinforced by the transient currents, the resultant current increasing as the engine throttle is opened. This current passes through diode 41 to a capacitor 42 from which pulses are caused to flow to point B the arrangement being such that the potential at this point exceeds that at A at all engine speeds when the throttle is fully opened. Point B is connected to the base of a transistor 47, the emitter of which is connected to point A. Thus, when the potential at B exceeds that at A, current flows through transistor 47 to the base of a transistor 49 which then allows current to flow to the base of transistor 30. The latter is then biased so that current from A is cut off from the base of transistor 31. Relay 34 is then de-energized or prevented from being energized. To prevent hunting between the higher and lower ratios as a result of changes in engine torque or throttle position, auxiliary contacts 34b on relay 34 are arranged to break or complete a circuit from point 27, which is at potential A, to the base of transistor 47. When complete, this circuit reduces the effect of potential B on transistor 47 so that a substantial increase in torque or throttle opening is required to effect a change down. An isolating switch 23 operated by the main gear-box selector breaks the control circuit when lower main gear ratios are selected thus rendering the overdrive inoperative. On reclosure of switch 23 the time taken for capacitor 20 to charge permits the change to the high ratio in the main gear-box to become established before the overdrive can be actuated. Also in the control circuit is a master switch 22 for manual operation by the driver. In the position shown, the system operates automatically and in a second position the system is rendered inoperative. A third position establishes a direct connection to relay 34 so that provided switch 23 is closed, the high overdrive ratio is held operative.