Electric motor control by shifting brushes

Claim 1

A CONTINUOUSLY VARIABLE-SPEED, REVERSIBLE, A.C. MOTOR HAVING A COMMUTATOR AND A WOUND ROTOR CONNECTED THERETO AND HAVING A WOUND FIELD CONNECTED IN SERIES WITH SAID ROTOR, MEANS MOUNTING A PAIR OF BRUSHES FOR COOPERATING WITH SAID COMMUTATOR, AND SPEED RESPONSIVE MEANS FOR SHIFTING THE MOUNTING MEANS TO ALTER THE POSITION OF THE BRUSHES WITH RESPECT TO THE FIELD FOR MAINTAINING A PREDETERMINED SPEED AND DIRECTION OF ROTATION OF SAID MOTOR, THE FIELD AND EFFECTIVE ROTOR WINDINGS FORMING A MUTUAL INDUCTOR IN WHICH THE TOTAL INDUCTANCE IN THE MOTOR IN STALLED CONDITION AND THE BRUSHES IN AN OPERATIVE NULL POSITION IS A MAXIMUM CAUSING A LOW CURRENT VALUE IN THE MOTOR AND IN THE OTHER INACTIVE NULL POSITION OF THE BRUSHES IS A MINIMUM CAUSING A HIGH CURRENT VALUE IN THE MOTOR; AND MEANS FOR LIMITING THE ROTATION OF THE BRUSH MOUNTING MEANS ON EITHER SIDE OF SAID OPERATIVE NULL POSITION IN FULL SPEED FORWARD OR REVERSE POSITION WHEREBY SAID BRUSHES ARE PREVENTED FROM PASSING THROUGH THE INACTIVE NULL POSITION AND THE CURRENT VALUE IS LIMITED TO A SAFE CURRENT VALUE FOR THE MOTOR, SAID SPEED RESPONSIVE MEANS COMPRISING A METALLIC DISK-LIKE MEMBER CONNECTED TO THE CARRIER, A PLATE ROTATABLE WITH THE ROTOR AND HAVING A PLURALITY OF MAGNETS FACING THE PLATE AND FORMING A SLIP DRIVE THEREFOR ADAPTED TO ROTATE SAID METALLIC DISK IN THE DIRECTION TO MOVE THE BRUSHES TO NULL POSITION, AN ADJUSTABLE MEMBER CONNECTED TO SAID DISK-LIKE MEMBER BY A SPRING MEANS, ADJUSTMENT OF THE MEMBER FROM A ZERO SPEED POSITION TENSIONING SAID SPRING TO COUNTERBALANCE THE DRAWING FORCE OF SAID MAGNETS WHEREBY THE BRUSHES ARE MAINTAINED IN THE DESIRED POSITION TO PRODUCE A CONSTANT SPEED.