Design of a Compensating Fifth Wheel for Improving the Roll Dynamic Behavior of the Tractors Semi-Trailers 2002-01-3058

This work describes a 3 dimensional modeling technique for investigating the random response of tractor semitrailer systems considering different types of fifth wheels and their kinematic constraints. The inputs to the vehicle model are the power spectral density (PSD) of the vertical road irregularities considering different road types. In addition to the time delay axle correlation, the cross correlation between the left and right tracks is modeled using the coherence function. The masses of the driver/seat assembly, tractor, semi-trailer and wheel/axle assemblies as well as their suspension elements are considered in the vehicle model. The possibility of reducing the roll accelerations of both tractor and semi-trailer by using a compensating fifth wheel (articulation) has been studied. The designed fifth wheel is a fully oscillating unit. Using this fifth wheel, the tractor and semi-trailer could oscillate relatively in the pitch and roll directions. Torsional spring and dampers are fitted in the fifth wheel to suspend it against the roll excitation.

Three dimensional random responses are presented for a 3 axles tractor semi-trailer, showing power spectral densities (PSDs) and root mean square values (RMS) of the linear and angular accelerations and displacements. The results showed that the direct connection between the tractor and semi-trailer using conventional semi-oscillating fifth wheels has lead to increase the coupling between the tractor and semi-trailer units and increase their roll acceleration responses. Moreover, the proposed fully oscillating fifth wheel offers significant improvements in the roll responses of both tractor and semi-trailer due to compensation of its torsional spring and damper that reduce the torque and twist transfer. Additional improvement in the tractor roll response is achieved by increasing the torsional flexibility of the tractor frame. The final results are compared with results obtained using an unsuspended fully oscillating fifth wheel (off road fifth wheel). The comparisonshowed that the compensating fifth wheel exhibits the better responses.