Patent GB-983245-A (GB)
Title: Automatic transmission mechanism for road vehicles
Inventor: REVAL HARDER
IPC: F16H61/02
Filed: 1961-11-15
Abstract: 983,245. Change-speed control. C.A.V. Ltd. Nov. 23, 1962 [Nov. 15, 1961], No. 40832/61. Heading F2D. The three electromagnets which control the engagement of the three respective gears of the automatic transmission mechanism of a road vehicle are connected to a common transistor through which current must flow to energize the electromagnets, the conduction of the transistor being controlled by the accelerator pedal and by means responsive to the propeller shaft speed. In Fig. 2 the pneumatic operation of the gears is controlled by the reverse gear electromagnet SR and by the electromagnets S1, S2, S3, S4 for the three forward gears respectively. Reverse and the three forward gears 1, 2 and 3 may be selected manually by the reversing switch GR and the respective forward gear switches G1, G2 and G3, the circuit being completed by a common transistor T1 responsive to circuits depending upon the accelertaor position and the speed of the engine. Automatic engagement of second, third and fourth gears is effected by operating switch GA and is controlled by the common transistor T1 and transistor circuits T12, T21 and T29, again controlled by the accelerator position and a propeller shaft speed sensitive circuit. The detailed circuit is shown in Fig. 1, where like references to those of Fig. 1 are used. The arrangement comprises an alternator A the output of which is rectified to produce a control voltage on lines 8 and 9 dependent upon the propeller shaft speed. Change speed control signals for automatic control and also a " low speed " control voltage are obtained from the control voltage at lines 8 and 9 through a potentiometer R45, R46 the mid-point of which is connected to a trigger circuit comprising two transistors T13 and T14 which are cross-coupled and which, when the speed is above 240 r.p.m., provides a control voltage at the collector of T14 which is fed through transistor T15 to the control transistor T2 for the main gate transistor T1 so that the gate is opened whenever the engine speed exceeds 240 r.p.m. and has not dropped below 145 r.p.m. Manual control.-The reverse gear is selected by operating switch GR and by depressing the accelerator to open contact A1 and thus energize transistors T2 and T1 whereby the circuit of the selector electromagnet SR is energized. This energization operates a transistor T3 which holds the transistor T1 conducting irrespective of subsequent position of the accelerator pedal so that the gear remains engaged until switch GR is opened. First gear is selected by operating switch G1 and depressing the accelerator pedal to open contact A1 and thus rendering transistors T2 and T1 conducting to complete the circuit for the corresponding selector electromagnet S1. In this case the gear is disengaged when the accelerator is released. Second and third gears are similarly controlled by operation of the corresponding switches G2 and G3 and operating the accelerator pedal but low speed engagement of third gear, which is controlled by transistor T22, is prevented by applying the low speed control voltage, referred to above, to a transistor T23 which prevents T22 becoming conductive if the speed is below 145 r.p.m. Automatic control.-Automatic control of second, third and fourth gears is selected by closing selector switch GA, and is in part controlled by accelerator switches A1-A4, contact A1 being open whenever the accelerator pedal is depressed, A2 and A3 when it is depressed to normal or beyond and A4 on full throttle. The control transistor T12 for the second gear electromagnet is controlled by a transistor T11 which is normally biased to be conducting so that this gear, except as otherwise described later, will" normally be engaged providing transistor T1 is conducting. For normal accelerator positions third gear is engaged when the engine speed rises above 735 r.p.m. as a result of the speed control voltage at the junction of R51 and R50 rising to a value such that a trigger circuit comprising cross-coupled transistors T16 and T18 is operated. Such operation causes transistor T11 to be rendered non-conducting so that second gear is disengaged and causes transistor T19 to render transistors T20 and T21 to be conductive so that solenoid S3 is energized and third gear engaged. Reversal of this process takes place when the speed falls below 545 r.p.m. Fourth gear is automatically engaged in a similar manner at an engine speed of 1165 r.p.m. as a result of the speed control potential from the junction of R76 and R77. The resulting conduction of transistor T26 causes transistor T20 to ensure that third gear is disengaged and to prevent re-engagement until fourth gear is disengaged. Accelerator controlled modifications of automatic third and fourth gear selection.-The trigger circuit T16, T18 for controlling third gear selection also includes a further transistor T17. The base electrode of this transistor is connected to contact A2 so that when the accelerator pedal is pressed to its mid-position or beyond third gear is held even if the engine speed falls below 545 r.p.m. If, however, it falls below 145 r.p.m. a signal derived from the low speed control voltage via transistors T14 and T18 causes third gear to be disengaged and the engine to return to neutral mixing out second gear. A third control voltage to T17 prevents a hold on condition before third gear is engaged. Automatic fourth gear is similarly controlled by transistor T25 but in this case, return to neutral missing second and third gears occurs when the engine speed is between 145 and 545 r.p.m. unless the accelerator pedal is depressed, when the engine will change to second gear. A further accelerator-controlled switch A3 which is opened when the accelerator is pressed beyond normal raises the speed at which change from second to third or from third to fourth occurs, while a fourth switch A4 operated on full accelerated depression, raises still further the speed at which the change occurs. If, during full throttle acceleration the accelerator pedal is momentarily eased, change down into second or third gear is prevented by a timing circuit comprising cross-coupled transistors T30 and T31 together with a capacitor C6 brought into operation by the resulting momentarily closure of contact A3. Protection circuits.-The engagement of two gears simultaneously is prevented by the fact that if two control signals are simultaneously applied to the main gate T1 the voltage across resistor R4 rises to such a value that transistor T4 is cut-off to trigger a bi-stable circuit T5, T6 which turns off the main gate circuit. To prevent engagement of second gear at high speeds as a result of a fault, an unrectified speed dependent voltage from terminal 7 of the alternator is applied to a " diode pump integrator " C4, D26, D9, C3 which will provide a rising voltage to the base of transistor T7, while a voltage dependent upon engine speed is applied to the shunt connected transistor T8 from line 9 so that T8 is switched off until the engine speed reaches 600 r.p.m. If failure occurs, transistor T7 will be switched off and a cross-coupled bi-stable circuit T9, T10 will be changed in state, causing the engine to be returned to neutral. In addition, the circuit biases transistor T23 to allow third gear to be engaged manually, even though a signal is produced corresponding to an engine speed below 145 r.p.m.