GB1480064A - Electrically driven vehicles - Google Patents

Abstract

1480064 Control of D.C. motors LUCAS INDUSTRIES Ltd 3 June 1974 [30 June 1973] 31300/73 Heading H2J A series D.C. motor driving an electric vehicle is supplied with a desired current by a conventional thyristor chopper and commutating circuit, Fig. 1 (not shown), controlled by a unit 26 responsive to the setting of either an accelerator potentiometer 61 during a forward drive mode of the motor or a brake potentiometer 65 during a regenerative braking mode of the motor, mode selection means being provided to ensure that the forward drive mode is selected in the event of the accelerator and brake pedals being simultaneously depressed. Forward or reverse motor drive is produced by movement of a changeover switch 33 to energize relay coils 34 or 35, whose contacts 34a, 35a respectively control contactor operating devices F, R for contacts (F1, R1) in the motor circuit, Fig. 4 (not shown). When in the forward drive mode, selection between energization of the device F and a device B, which opens contacts (B1) in the motor circuit to produce the regenerative braking mode, is controlled by contacts 46a of a relay whose coil 46 is controlled by a transistor 45, in turn controlled by a circuit consisting of resistors 41, 42, 43, capacitor 44, contacts 36 which open when the accelerator pedal is depressed, contacts 37 which close when the brake pedal is depressed, contacts 38 which close when the vehicle speed is above a predetermined low value, and contacts B2 which close when the device B is energized. When only the accelerator pedal is depressed, transistor 45 is not switched on, coil 46 is not energized and its contact 46a energizes device F which also opens contacts F2 to isolate device B. AND gate 52 receives two inputs to energize a coil 53 and so cause contacts 54 to open and unit 26 to receive a signal from potentiometer 61. With forward travel of the vehicle and the accelerator pedal not depressed, depression of the brake pedal causes transistor 45 to switch on (if the vehicle speed is above the predetermined value) and energize coil 46, whose contact 46a changes over to energize device B which also opens contacts B3 to isolate device F. AND gate 55 now receives two inputs to energize coil 56, open contacts 57 and cause the unit 26 to receive a signal from potentiometer 65. Closure of contacts B2 ensures that braking (if permitted by contacts 38) continues down to zero vehicle speed, augmented by an hydraulic braking system operated when the brake pedal is depressed. If both pedals are depressed, transistor 45 cannot be turned on and only device F can be energized. Capacitor 44 provides a time delay when transistor 45 changes state, to allow the motor current to fall to a safe value before devices F, B are energized or de-energized. Instead of using a capacitor, this protective function may be provided by connecting the emitter of transistor 45 to a changeover makebefore-break switch (71) and its collector to a further normally-open contact (46b) of relay 46, the switch (71) being in one position when the motor current is above a predetermined value and in the other position when the current is below this value, Fig. 6 (not shown). The motor of the vehicle may be of shunt or compound field type instead of series.