Synthesis and analysis of the steering system of an adjustable tread-width four-wheel tractor

In this paper the problem of synthesizing the Ackermann linkage and the steering control mechanism of an adjustable tread-width tractor is presented. Several conflicting requirements were simultaneously considered as follows: ensuring minimum wheel-slip and symmetric steering control for left and right turns, ensuring minimum cross-coupling between steering and axle oscillation, maintaining favorable pressure angles in the joints, and avoiding interference between the moving parts of the mechanism and between these and the body of the vehicle. This difficult multi-criteria optimization problem was solved in a simplified manner by sizing the Ackermann linkage first, followed by an optimum synthesis of the steering control mechanism, assuming it has the drag link removed. The removal of the drag link induced the extra degree of freedom which allowed the steering arm and the pitman arm to be exactly coordinated over the whole working range of the mechanism. An objective function based on the variation of the distance between the centers of the drag-link joints in several essential configurations of the steering control mechanism, was defined and further minimized in the presence of interference avoidance and pressure angle constrains.