Novel power hop model for an agricultural tractor with coupling bouncing, stick-slip, and free-play dynamics

Abstract

Self-excited pitch and bounce oscillation occasionally occurs when a tractor pulls a high-draft load on dry soil. This dynamic instability is referred to as the power hop phenomenon. Power hop drastically degrades tractor performance and ride quality and can result in damage to the tractor, operator injury, and soil compaction. Power hop dynamics are characterised by three typical nonlinear elements; i.e., vertical jumping or bouncing, longitudinal stick-slip dynamics, and free-play in the joint between the tractor and implement. This paper couples these nonlinear elements and develops a novel power hop model for time-domain simulation. The occurrence process of power hop was demonstrated using the developed model using numerical experiments. Parametric investigations were conducted varying the drawbar pull, soil, and tyre conditions. The original draft load, joint clearance, static friction coefficient, ratio of coefficients of dynamic and static friction, front tyre stiffness, and rear tyre stiffness were taken as control parameters. The developed model predicted appropriately the occurrence of power hop for a higher draft load, drier soil, and “front stiff and rear soft” tyre stiffness conditions. The results agree obtained with conventional knowledge concerning power hops accumulated by previous experimental research. Thus, the developed model provides a strong platform adopting measures to control and suppress power hops. • A novel power hop model was developed for time-domain simulation. • Bouncing, stick–slip, and free-play dynamics coupled in a developed model. • Occurrence of power hop was demonstrated in a numerical simulation. • Parametric investigation into various drawbar pull, soil, and tyre conditions. • The developed model predicted power hop appropriately.