Speed control system of traction motor for electric vehicles

Claim 1

A speed control system for a traction motor for an electric vehicle comprisin: a D.C. supply source for supplying a D.C. voltage to the traction motor; a chopper for chopping the voltage to be fed to the traction motor; and, a chopper control circuit for controlling the duty factor of the voltage which is fed through the chopper, said chopper control circuit including: a pulse generator circuit for generating pulses periodically, a signal generator circuit comprising means for producing a D.C. signal which is varied in response to an adjusting operation for running speed of the electric vehicle, and an amplifier for amplifying the D.C. signal to produce an output which prolongs the pulse generation period at the pulse generator circuit in accordance with an operation for decreasing the running speed, and a monostable multivibrator which is set to a semi-stable state by the pulse generator circuit to produce a rectangular wave signal whose semi-stable duration is controlled by the D.C. signal fed from the signal generator circuit, said chopper being controllable by the rectangular wave signal from the monostable multivibrator, said monostable multivibrator including a saw-tooth wave signal generator circuit for generating a saw-tooth wave signal which is returned to an initial value by the pulse from the pulse generator circuit, and a comparator which compares the saw-tooth wave signal from the saw-tooth wave generator circuit with the D.C. signal generator circuit to produce a rectangular wave signal which is set when the saw-tooth wave signal is returned to the initial value and reset when the saw-tooth wave signal coincides with the D.C. signal during ramping of the saw-tooth wave signal.