Abstract: The tractor mounts a passive damping constraint system and a fifth wheel brake between the fifth wheel and tractor frame. The fifth wheel is secured to the trailer for rotation therewith relative to the tractor. The constraint system passively resists rotary movement of the trailer and tractor about the kingpin. Upon reaching a predetermined angular relation indicative of a jackknife condition, the fifth wheel brake system is actuated and the driver alerted. Upon manual braking, the fifth wheel brake and passive damping constraint systems are deactuated. Where hard braking is required, the fifth wheel braking system is again activated to assist the driver to prevent the jackknife condition. The fifth wheel braking and passive damping constraint systems are deactivated upon actuation of the turn signals.

Abstract: A releasable coupling for an articulated vehicle of the type having a tractor and a trailer comprises a brake system and locating members for preventing or inhibiting jack-knifing of the articulated vehicle, the locating members comprising two or more pairs of members one of each pair adapted to being mounted on the tractor and the other of each pair adapted to being mounted on the trailer and arranged so that they mate when the tractor is connected to the trailer, each pair being arranged a sufficient distance on each side of the longitudinal center line of the articulated vehicle so as to result in reactive moments of force about the direction of travel that will resist any tendency of the trailer to overturn when cornering or traveling on uneven roads at operating speeds.