Traction motor control system

Claim 1

In a control system for an electric motor coupled to a mechanical load; A. first current controller means operable to respective ON and OFF states when respective ON and OFF signals are received by the first current controller means; B. resistor means; C. respective first, second, third and fourth switch means each being operable to mutually exclusive ON and OFF states; D. means including said first switch means when in the ON state for connecting the motor and the current controller means in a motoring circuit arrangement wherein the first current controller means controls motoring current; E. means including said second switch means when in the ON state for connecting the motor, the resistor means and the first current controller means in a dynamic braking circuit arrangement wherein the current controller means controls braking current; F. an ON signal circuit which is rendered effective to provide ON signals to the first current controller means in response to an enabling signal; G. circuit means including the third switch means for supplying an enabling signal to said ON signal circuit when said third switch means is ON; H. circuit means including the fourth switch means for supplying an enabling signal to said ON signal circuit when said fourth switch means is ON; I. second controller means to which all said switch means are responsive, the second controller means being operable in first and second modes; and J. control means responsive to transition of the second controller means from mode to mode for a. in response to transition of the second controller means from its first mode to its second mode, operating the first and fourth switch means from ON to OFF and the second and third switch means from OFF to ON, in such order that the enabling signal is cut off before the first switch means opens, and is reapplied after the second switch means closes, and b. in response to transition of the second controller means from its second mode to its first mode, operating the first and fourth switch means from OFF to ON, and the second and third switch means from ON to OFF; in such order that the enabling signal is cut off before the second switch means opens, and is reapplied after the first switch means closes.