Patent GB-970535-A (GB)
Title: Improvements in or relating to control means for automatic gear-change mechanisms
Inventor: HARPER PATRICK DUNDAS
IPC: F16H63/02
Filed: 1959-10-08
Abstract: 970,535. Change speed control. S. SMITH & SONS (ENGLAND) Ltd. Jan. 9, 1961 [Oct. 8, 1959], No. 34204/59. Heading F2D. A change-speed control for a motor vehicle comprises an output speed responsive alternator 11 and means responsive to one other variable (e.g. engine condition) which generate a signal that is applied to a trigger circuit 15 or 16 which when the signal reaches a predetermined value energizes a gear change relay 17 or 17a. As shown, the alternator 11 is connected through a rectifier 14 to a sliding contact 24 of a resistor R2 in series with resistors R1 and R3 and the three resistors are in parallel with a Zener diode 12 which maintains a constant potential difference across them. The sliding contact 24 is positioned by the accelerator pedal 10 or by engine manifold depression. Series resistors R15 ... R17 and R18 ... R20 are connected in parallel with the rectifier 14 and with each other. Sliding contacts 19, on the resistor R16, and 22, on the resistor R19, are connected through variable resistors R21, R22 to the bases of transistors T1, T3 in the trigger circuits 16, 15, respectively. Thus the potential difference between the points A and B or A and C is a function of vehicle speed and accelerator pedal position. When the potential difference between the points A and B is below a predetermined value the transistor T1, which is in series with a resistor R5 across a 12-volt D.C. supply, is conductive and a transistor T2, which is in series with the gear change relay 17 across the 12-volt D.C. supply and has its base connected through a resistor R8 to the output side of the transistor T1, is non-conductive and the relay 17 de-energized. When the potential difference between the points A and B reaches the predetermined value the transistor T1 becomes non-conductive and the transistor T2 conductive to energize relay 17 which effects a 2-3 upshift. The current to the relay 17 is maintained for a minimum of one second, by a series capacitor C4 and resistor R23 in parallel across a resistor R7, to prevent hunting. The trigger circuit 15 which effects a 1-2 ratio shift is identical with the trigger circuit 16 above described with the exception that no provision is made to maintain a current through the relay 17a for a minimum time. The position of the sliders 19, 22 adjust the points at which ratio shift oocurs and the variable resistors R21, R22 adjust the hysteresis to ensure that upshift occurs at a higher vehicle speed than downshift., In Fig. 2 (not shown) the trigger circuits are identical with those of Fig. 1 but the alternator is connected through a variable impedance, rectifier and resistor to the point A and the points B and C are connected to sliders on resistors in parallel with the alternator, impedance and rectifier. The impedance may be inductive, capacitive, or resistive and is varied in accordance with throttle pedal position. The PNP junction type transistors may be replaced by NPN type transistors with the appropriate modification of the connections.