Unit Rig & Equipment Co.

Sabern D Buchanan

Stephen L Faulkner

An improved drive system for large mining trucks employing combined diesel/electric propulsion or the like wherein AC current generated by the alternator is rectified before powering wheel motors and wherein the wheel motors are used as generators to produce a retarding current that is directed to a resistive grid with plurality of shunting circuits thus extending the retard torque during dynamic braking and deceleration of the vehicle wherein the improvement comprises the use of silicon controlled rectifiers (SCR's) rather than contactors to achieve the desired electric circuit arrangement and in particular wherein four SCR's are used in the resistive grid to achieve a seven stage extension of the retarding torque and wherein the SCR's in the DC circuit are deactivated (opened) by back biasing with an SCR circuit that delivers AC current from the alternator to the cathode of a switching SCR in the retarding circuit.

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Tulsa, OK, United States of America

Sabern D Buchanan