Truck with steerable rear wheels

Claim 1

An automatic steering system for use upon a vehicle having a driving position and a unitary frame supported by two or more sets of selectively steerable wheels longitudinally spaced along the frame which may simultaneously be given a complementary orientation by a single control device or alternatively oriented individually, comprising: a first set of steering wheels functionally interconnected with a control device at the driving position, a turntable, movable through an arc substantially greater than 2°, to which a second set of wheels are mounted, said wheels being driving wheels and having an orientation entirely controlled by a self-centering hydraulic spool valve movably mounted to the framework and interconnected with the control device at the driving position, said valve means including an intermediate or neutral position and opposing extreme position selectively directing fluid to one of a pair of opposing hydraulic rams interconnected with and controlling the position of the turntable and attached second set of wheels such that when the valve is in the intermediate position, no additional fluid is directed to the rams and when it is in a position other than the intermediate position, additional fluid is directed to one of the rams, selectively urging the rear wheels to turn until the valve is in the intermediate position, means interconnecting the valve body to one set of wheels and means interconnecting the spool to the other set of wheels such that the condition of the valve depends upon the relative orientation of the two sets of wheels and when the two sets of wheels are properly tracking the valve is in the intermediate position holding the wheels in that orientation until the relative position of the spool is changed, and means to override the control device such that the operator may control the orientation of the second set of wheels independently from the first set.