GB1381856A - Electric motor driven vehicles - Google Patents

Abstract

1381856 Control of electric motors CABLEFORM Ltd 6 March 1972 [8 Dec 1970] 58177/70 Heading H2J To dynamically brake a motor for a vehicle when the motor is de-energized, one of the motor field windings is energized, from a permanent magnet generator coupled to the motor. Dynamic braking may also be applied when the motor is energized and exceeds a preset speed, as selected at the generator output. In a motor control of a fork lift truck, having an armature 2 and a series winding 3 fed from a battery 1 through a reversing switch 7 and D.C. switch 5 which is pulse controlled to vary the mean power to the motor, the output of a permanent magnet generator 8, mechanically coupled to the motor, is detected by relay 9. which is energized at a predetermined generator output i.e. motor speed, to close contacts 10. This allows current to flow to an additional motor winding 4 from the generator 8 through resistor 11, which determines the amount of dynamic braking current through diode 6. The braking is stopped when relay 9 is de-energized i.e. at a preset lower speed, which may be zero. When the motor is at a halt and the motor is de-energized, relay 13 closes contact 12 across resistor 11, so that if the vehicle moves due to faulty mechanical braking, current from the generator is applied to the motor to limit the vehicle to a low creep speed. The system may be used with a compound wound motor, see Fig. 2 (not shown).