Tractor traction performance simulation on differently textured soils and validation: A basic study to make traction and energy requirements accessible to the practice

Several models exist to simulate traction performance of a tractor, however, for most of them a proper experimental validation is missing. Moreover, their possible application for a practical use in a wide range of vehicles, equipment and soil configurations has never been further developed. This study examines a semi-empirical model of soil-tyre interaction, adapted to simulate the traction performance of mechanical front wheel drive tractors, taking into account not only mechanical soil and tyre parameters and static vehicle load but also the multi-pass effect, the load transfer effect, and the theoretical speed ratio between front and rear axles. This model simulates drawbar pull, traction coefficient, traction efficiency, and motion resistance as a function of slip, wheel load, tyre size and pressure. Several traction tests were performed on four Swiss agricultural soils of different type (clay, clay loam, silty loam, and loamy sand) in order to validate the model experimentally. Three tractors of widely ranging power (from 40 to 132 kW) and weight (from 24 to 68 kN) were used. Tractor configurations were varied by changing tyre pressure and tractor weight. Slip normally ranged between 5 and 30%. In most of the cases the model simulated drawbar pull as well as its variations due to changes in tyre pressure, wheel load, and soil strength reliably for practical purposes. Only when high wheel load was combined with low inflation pressure the model did not give suitable results due to an overestimation of the rolling radius. Based on the presented model, a convenient Excel-application called TASCV3.0 was developed for the practice. Such a practical computer-tool supports farmers in decision making concerning the tractor configuration, oriented to save fuel during agricultural operations.