Speed control system for an AC locomotive

A speed control system for an alternating current (AC) electric locomotive, the locomotive including a plurality of wheel-axle sets with each wheel-axle set being coupled to an independently controllable AC electric traction motor, each traction motor having a corresponding speed sensor and each speed sensor providing a pair of signals which are resolvable to determine the speed and direction of rotation of the associated motor rotor, the speed sensor signals being coupled to process control means which controls power to the motors, said system comprising:

• means for detecting the presence of each of the pair of signals from each speed sensor;
• means responsive to detection of only one of the pair of signals from one of the speed sensors for setting motor speed in response to the detected one of the signals;
• and
• means for using signals from another of the speed sensors for establishing motor rotational direction for the motor coupled to said one of the speed sensors.