Drive mechanism for track-laying tractor

Claim 1

DRIVE MECHANISM FOR USE WITH A TRACTOR HAVING A PAIR OF TRACKS FOR SUPPORTING THE TRACTOR FOR MOVEMENT OVER THE GROUND, SAID DRIVE MECHANISM COMPRISING A SUPPORT MEMBER ADAPTED TO BE AFFIXED ON FRAME STRUCTURE ON SAID TRACTOR AND EXTENDING TRANSVERSE TO THE NORMAL LINE OF MOVEMENT OF THE TRACTOR, FIRST AXLE MEANS SECURED TO SAID FRAME STRUCTURE FOR DRIVING ONE OF SAID TRACKS, SAID FIRST AXLE MEANS HAIVNG FIRST AND SECOND DRIVEN MEANS THEREON, SECOND AXLE MEANS SECURED TO SAID FRAME STRUCTURE FOR DRIVING THE OTHER OF SAID TRACKS, SAID SECOND AXLE MEANS HAVING THIRD AND FOURTH DRIVEN MEANS THEREON, A ROTATABLE SHAFT HAVING FIRST, SECOND, THIRD, AND FOURTH DRIVE MEANS THEREON, MEANS MOVABLE WITH RESPECT TO SAID SUPPORT MEMBER FOR ROTATABLY SUPPORTING SAID ROTATABLE SHAFT, SAID FIRST AND FOURTH DRIVE AND DRIVEN MEANS, RESPECTIVELY, BEING OPERATIVELY ENGAGED BY FLEXIBLE BELT MEANS FOR MOVING THE TRACTOR IN ONE DIRECTION, SAID SECOND AND THRID DRIVE AND DRIVEN MEANS BEING ADAPTED TO BE MOVED INTO FRICTIONAL ENGAGEMENT TO MOVE THE TRACTOR IN A REVERSE DIRCTION, AND CONTROL MEANS FOR MOVING SAID MOVABLE MEANS SELECTIVELY FROM A NEUTRAL POSITION, WHEREIN NONE OF THE DRIVE AND DRIVEN MEANS ARE OPERATIVELY ENGAGED TO SELECTIVELY OPERATIVE POSITIONS WHEREIN EITHER ONE OR BOTH OF THE FIRST AND FOURTH DRIVE AND DRIVEN MEANS ARE OPERATIVELY ENGAGED OR, WHEREIN EITHER ONE OR BOTH OF THE SECOND AND THIRD DRIVE MEANS ARE OPERATIVELY ENGAGED.