GB1480054A - Control circuits for electrically driven vehicles - Google Patents

Abstract

1480054 Control of D.C. motors LUCAS INDUSTRIES Ltd 11 June 1974 [30 June 1973 (2)] 31306/73 and 31307/73 Heading H2J The motor control system described with reference to Figs. 1 to 4 of Specification 1,480,064 is provided with means to switch on the power supply to the control circuit for the forward, reverse and brake contactor devices and the accelerator and brake potentiometers, when forward or reverse drive is selected, and to switch off the power supply after a time delay following return of the selector switch to its OFF position. As shown in Fig. 5, movement of the switch 35 to its forward drive (resistors 36, 64 connected) or its reverse drive (resistors 37, 65 connected) position causes transistors 38, 44 to switch on, capacitor 41 to charge and winding 33 to be energized, the latter closing contacts 33a to connect battery 40 to the contactor devices F, B, R and the accelerator and brake potentiometers 70, 71. The control circuit includes contacts 52 which open when the vehicle speed exceeds a predetermined low value, contacts 53 which close when the accelerator pedal is released, contacts 54, 55 respectively closed by pression of the accelerator and brake pedals, contacts 62 which close when the accelerator pedal is depressed and before contacts 53 open (the latter feature also being possessed by the contacts 54), contacts 63 which close when the motor current is above a predtermined value, contacts 73, 76 respectively closed by depression of the brake and accelerator pedals, and auxiliary self-hold contacts F2, B2, R2 of the devices F, B, R. With switch 35 in its forward position, transistor 48 is turned on and thyristor 49 is fired through contacts 52, 53, so that depression of the accelerator pedal closes contacts 54 to energize device F. Thyristor 49 remains on after switches 52, 53 open and the subsequent increase of the command signal from potentiometer 70 to unit 26 will close contacts 63 if the current exceeds the predetermined value, thereby closing the self-hold circuit F2, 63. If switch 35 is moved to its OFF position transistor 38 immediately turns off, but transistor 44 is held on for a predetermined time corresponding to the discharge of capacitor 41, after which contacts 33a open. This time is selected so that the motor current falls below the predetermined value before contacts 33a open, since movement of switch 35 to its OFF position also turns off a transistor 66 to turn on transistor 68 and so remove the signal from potentiometer 70 to unit 26. Hence device F will be de-energized before contacts 33a open, either by opening of contacts 63 or members 48, 49. Similar operations occur when the brake pedal is depressed to energize device B or when the switch 35 is moved to its reverse position to energize device R, the latter action involving members 58, 59, 62. The time delay after movement of switch 35 to its OFF position may be provided by using a slow-acting relay in place of relay 33, 33a, and the switch 35 may be replaced by the combination of an on/off and a selector switch.