Estimation of Dynamic Forces for Agricultural Tractor Soil-Tyre Interaction Mechanics

The dynamic forces generated between the tractors' tyres and soil are very difficult to carry out experimentally. These dynamic forces have an important role in the analysis of the tractor stability moving over the soil surface. The main aim of this article is to predict the three directions of dynamic forces between the lugged tyre and the soil. A theoretical study of tractor stability based upon the non-linear equations mathematical model of the whole tractor subject to road surface input in the time domain is presented. Pull, lift, and lateral forces between the tyres and soil are predicted. The investigation includes a study of the effect of lug height, lug angle, and slip ratio to improve tractor stability. Also, three types of common soil namely; sand, silt, and clay are used to evaluate their effect on lug dynamic forces in three directions. Most of the parameters of each soil are measured in the soil laboratory and fed to the mathematical model. The results showed that the lug tyre characteristics have a good influence on tractor stability. The sand soil has a larger effect on the dynamic forces than the clay soil. Box-Behnken design (BBD) is used to estimate the effectiveness of lug height, lug angle, slip ratio, and types of soil on the lift force. The results show the lift force decreases with the increase both of the lug height and lug angle. Furthermore, the estimated regression equation is obtained to evaluate the influence of different factors on lug dynamic forces.