Converter dolly for permitting backing up of tandem trailers

Claim 1

A tandem trailer assembly comprising; a first wheeled vehicle, hitch means carried by a rearmost portion of said first vehicle, a second wheeled trailer vehicle positioned in tandem behind said first vehicle and including a coupling member comprising a kingpin projecting from an underside of said second trailer vehicle and a converter dolly positioned between and interconnecting said first and second vehicles, said converter dolly comprising a frame including a base portion and a tongue portion extending forwardly from the base portion, hitch means carried by said tongue portion and connected to said hitch means on said first vehicle to permit pivotal movement of the dolly relative to said first vehicle about a first substantially vertical axis, ground engaging wheels carried by said frame, a fifth wheel fixed on said base portion of said frame and having a front end defining opposing front corner portions, and comprising a longitudinal slot formed therein and adjacent to its front end and receiving the second trailer vehicle kingpin to interconnect the converter dolly to said second trailer vehicle to permit pivotal movement of the second trailer vehicle relative to said dolly about a second substantially vertical axis, and locking means cooperating with said fifth wheel and with said second wheeled trailer vehicle, said locking means including a spaced pin housing secured at each front corner portion of the fifth wheel so that when the fifth wheel pivots up or down, the housings move as units with the fifth wheel, a pin positioned in each housing and movable therein from a retracted to an extended position, and motor means operatively connected to said housing and cooperating with said pins to move them between retracted, inactive positions for permitting free pivotal movement of said second trailer vehicle relative to said dolly about said second substantially vertical axis during normal driving operations and extended, active positions in engagement with said second trailer vehicle during backing up of the tandem trailer assembly to restrain said second trailer vehicle against pivotal movement relative to the dolly whereby said dolly and said second trailer vehicle operate as a non-articulated unit and pivoting is only permitted about said first substantially vertical axis to thereby permit backing up the tandem trailer assembly without the need for disconnecting the first and second vehicles.