Safety device for tractor-trailers to prevent jackknifing

In a tractor-trailer rig which comprises a tractor having a fifth-wheel coupler and a semi-trailer having a complementary coupler comprising a wear plate and a coupling pin projecting downwardly from said wear plate and providing, when the rig is coupled, an axis about which the rig is articulated with the angle of articulation being sufficiently large to permit maneuvering of the semi-trailer as needed, with the undesirable consequence that jackknifing can occur under certain circumstances, and adjustable means adjustable from an inoperative position to an operative position, said adjustable means in the operative postion limiting the angle of articulation sufficiently to eliminate or to minimize the danger of jackknifing, the combination therewith in which said adjustable means comprises a pressure fluid cylinder which has its top affixed to the undersurface of said fifth-wheel coupler and which is adapted to project a pin up through a bore in said fifth-wheel coupler and then through an enlarged aperture in said wear plate, said pressure fluid cylinder having a collar integral with the top of said cylinder which surrounds said pin and projects up into said bore in a close complementary fit to a point near but not above the upper surface of said fifth-wheel coupler, said enlarged aperture having stops circumferentially displaced from said pin, so that the rotation of said tractor relative to said trailer is limited by said stops when said pin is in the projected position, whereby the thrust on said pin, resulting from it engaging one of said stops, is transferred to said fifth-wheel coupler through said collar.