Patent GB-939974-A (GB)
Title: Improvements in or relating to automatic gear control systems
IPC: F16H61/02
Filed: 1958-11-05
Abstract: 939,974. Transistor switching circuits. SIMMS MOTOR UNITS Ltd., R. H. SHIMWELL, and E. L. ROBINSON. Nov. 4, 1959 [Nov. 5, 1958,] No. 35586/58. Class 40 (6). [Also in Group XXIV] A transistor circuit, for operating a gear change mechanism, comprises a number of solenoids which are operated in succession or in combination under the control of a voltage which increases as the engine speed increases. In Fig. 1 the gears are engaged by energizing respective operating coils 1, 2, 3 and 4. When the engine is idling the accelerator contact Q1 is made so that a negative supply is provided through R16 to the bases of transistors T4, T4<SP>1</SP> and T11 to render them conducting. Transistor T4 prevents transistor T2 from conducting so interrupting the energizing path for coils 1 and 2 while transistors T4<SP>1</SP> and T11 apply potentials through diode D8, D9, D10 and D11 to transistors T3, T7 and T8 to render them non-conducting so that the energizing path for coils 3 and 4 are also interrupted. Movement of the accelerator pedal to engage contact Q2 removes the bias from transistor T4 so that transistor T2 is conditioned to conduction and also removes the bias from transistors T4<SP>1</SP> and T11 permitting these also to conduct. Negative voltage is applied through accelerator contact Q2 to the base of transistor T1 to render this transistor conducting and also through rectifiers D1 and D2 to the bases of transistors T5 and T2 to render the transistors conducting so that a path is established through transistors T1, T2 and T5 to energize coil 1 and engage first gear. An alternator SG is coupled to the engine shaft and to a rectifier so that as the engine speed increases an increasing D.C. voltage is applied to the upper terminal of a resistor R1. This voltage is applied through a rectifier D3 to maintain the transistor T1 conducting and also to a Zener diode Z1 so that when the engine speed reaches a predetermined value the output voltage from the generator is sufficient to cause the diode to conduct. This applies a voltage through diodes D6 and D7 to transistors T2 and T6 to cause them to conduct and provide a current path for coil 2. Simultaneously, a voltage is applied through resistor R6 to transistor T9 to render it conducting so that a voltage is applied through a rectifier D4 to transistor T5 to render it non-conductive and de-energize coil 1. A further increase in speed of the engine causes an increase in generator output voltage such that a Zener diode Z2 conducts. This applies a voltage through rectifiers D8 and D9 to transistors T2 and T7 to render them conducting and so provide a path to energize coil 3 and at the same time a voltage is applied through a resistor R8 to render transistor T10 conducting so that voltages are supplied through diodes D5 and D7 to transistors T6 and T2 to render them non-conducting and so de-energize coil 2. A still further increase in engine speed causes a Zener diode Z3 to conduct and so apply a voltage through diodes D10 and D11 to transistors T8 and T3 to render them conducting and energize coil 4. At the same time the voltage is applied through resistor R10 to the base of transistor T11 causing it to conduct so that the voltage is applied through a diode D8 to transistor T7 to render it non- conducting so as to de-energize coil 3. Transistors T5 and T6 are cross-coupled to form a bistable circuit so that only one transistor can conduct at any time. Similarly transistors T7 and T8 and transistors T2 and T3 are cross- T7 and T8 and transistors T2 and T3 are crosscoupled. Depression of the accelerator pedal to engage contacts Q3 to Q8 progressively increases the bias on a transistor T12 so as progressively to increase its collector current. This has the effect of decreasing the voltage at the lower end of resistor R1 so reducing the effective output voltage of the generator and delaying the change in gear. If the accelerator pedal is released while the engine is running at a speed greater than its idling speed the circuits through R2 and diode D3 from the generator prevents the de-energization of the coils and thus the return to neutral gear. In addition, if the vehicle is in third or fourth gear and its accelerator pedal is released contact Q1 applies potential to transistors T4 and T4<SP>1</SP> to inhibit a change into second and first gear and so maintains cruising gear to a near standstill. The operation of transistor T1 at a more definite speed may be ensured by replacing the transistor by a cross-coupled trigger circuit (Fig. 2, not shown). In addition it is stated that to facilitate choice of speed at which gear change occurs the several selector circuits may be fed from separate windings of the alternator or from transformer taps so that the gear change speed is not dependent only on the Zener diodes Z1, Z2 and Z3. Fig. 3 shows an alternative circuit in which three gears are engaged respectively by energizing coil A, coil B and coil A and B together by means of series of transistors TA and TB. When the engine is idling, transistors TC1, TC2 and TC3 are conducting so that the currents through resistors R21, R31 and R49 are sufficient to bias the transistors TA and TB to cut-off. Increase in engine speed resulting from depression of the accelerator pedal P causes the output from the alternator rectifier system coupled to the engine to increase so as to increase the bias on a transistor TR and accordingly the output from its emitter electrode. At a predetermined engine speed the output voltage applied from the emitter through resistor R25 is sufficient to cause transistor TD1 to conduct. This renders transistor TC1 non- conducting so that the voltage at the lower end of resistor R31 will rise to a value sufficient to cause a "Zener" " diode D11 to conduct so rendering transistor TA conducting and causing first gear to engage. A further increase of engine speed eventually produces a sufficient voltage at the emitter of transistor TR to render a transistor TD2 conducting so as to cut off transistor T62. This causes the voltage at the lower end of R49 to become sufficiently negative to cause transistor TB to conduct and so energize coil B. Simultaneously, the voltage applied through R49 to the case of transistor T1 causes this transistor to conduct so that the voltage at the lower end of resistor R31 drops to a value such that transistor TA is rendered non-conducting. Second gear is now engaged. A further rise in engine speed will cause further rise of the voltage at the emitter of transistor TR which will eventually reach a value at which transistor TD3 is rendered conducting. This causes the voltage at the lower end of R32 to become sufficiently negative to cause a "Zener" diode D13 to conduct and so render TA conducting so that third gear is now engaged. Release of the accelerator pedal when the car is cruising will cause contact Q to be made so that transistors H1, H2 and H3 are maintained in a conductive condition and top gear will be held. When transistor TD1 is rendered conducting by the increase in voltage from the engine to the generator S6, transistors TC1 and H1 are rendered conducting and non-conducting respectively. This change is assisted by cross-coupling between transistors TC1 and TD1 and between TC1 and H1. Similar cross-coupling is provided between transistors TC2 and TD2 and H2 and also between TC3 and TD3 and H3.