Stability Assessment of an Agricultural Tractor with a Front-End Loader Using Multibody Dynamics

This study develops a multibody dynamics model of a tractor equipped with a front-end loader and a rear three-point hitch (TPH), comprising 20 degrees of freedom. The front axle comprises independently suspended double-wishbone semi-axles with hydropneumatic suspension, connected to a centrally pivoted central axle body. The model represents tyre dynamics using the PAC2002 model and applies a PI controller to distribute torque based on slip. The model was validated statically by checking the centre of gravity, and then quasi-statically and dynamically. The study then analyses stability during braking and during forward and backwards 180° U-turns, testing each manoeuvre on level ground and on a 5° slope. A preliminary rear TPH analysis identified its optimal position and showed that the counterweight is essential for stability during braking and backward U-turns. Sensitivity analyses then vary loader height and deceleration during braking, and initial speed during the U-turns; these analyses map the critical states and identify the backward U-turn as the most critical manoeuvre. The stability was evaluated using wheel normal forces and the Load Transfer Ratio (LTR). Based on the stability insights obtained, this study proposes an innovative feature to effectively enhance stability and operational safety for the investigated front-axle concept.