Abstract

Articulated vehicles are known to exhibit appreciable yaw oscillations during high-speed directional maneuvers. Excessive vehicle off-tracking of multiple axle semitrailers causes rapid tire wear and poor maneuverability at low speeds. The concepts in articulation damping and forced-steering of the semitrailer axles are investigated to achieve improved low speed maneuverability as well as high speed directional control performance of the vehicle. The concept of a damped articulation mechanism is introduced and its potential benefits in limiting the yaw and lateral oscillations of semi-trailer are investigated. Different force-steering algorithms are formulated to achieve both improved low- and medium-speed maneuvrability and high-speed directional control performance. A nonlinear yaw plane model of an articulated vehicle with a multiple axles semitrailer comprising two articulation dampers and forced-steering of a semitrailer axle is formulated. The cornering forces and aligning moments of a radial truck tire are characterized by a nonlinear function in normal load, side-slip angle and pneumatic trail. The damping forces and moments acting on the sprung masses due to the articulation dampers are derived from the kinematic and dynamic analysis of the articulation mechanism. The equations of motion of the vehicle are solved for typical low-speed cornering and high-speed lane-change and evasive maneuvers. A parametric study is performed to establish the influence of articulation damping coefficients on the magnitude of lateral and yaw oscillations of the semitrailer. The results of the study show that the yaw and lateral oscillations encountered during high speed directional maneuvers can be significantly reduced by the articulation dampers. The low- and medium-speed maneuvrability and high-speed directional dynamics of the vehicle are further investigated using forced-steering of a semitrailer axle, assuming proportional control and negligible generator dynamics. The results are discussed to highlight the influence of the location of the forced-steering axle, feedback variables and control gains. The study showed that a forced-steering algorithm based on articulation angle and speed sensitive articulation angle offers considerable potentials in realizing both the improved low speed maneuvrability and high-speed directional control performance.