The paper deals with the modelling of the dynamics of farm tractors in order to simulate their motion on smooth or rough surface, on road or off road and in different loading situations. The aim is to develop reliable models to speed-up the design and development activities. The derived farm tractor models can simulate the working conditions of the farm tractor while hauling a plough or running at relatively high speed on a rough soil, or steering on a sloped, soft surface. Two models of farm tractors have been developed and experimentally validated. The first model is based on a proprietary software, able to quickly simulate the motion of a vehicle on smooth or rough soil. The second model has been developed with the software ADAMS/Car~(~R) which allows to model complicated transmission and suspension systems. In both of the models, the tires, the transmission system, the suspension system, the steering system, the engine and the body inertia are carefully described mathematically. Particular attention has been devoted to the measurements of the tire characteristic and of the inertia parameters of the farm tractor body. Both of the models are defined in a parametric way. Parameters sensitivity analysis shows a strong influence of the transmission system on the tractor dynamic response in all of the considered working conditions. Experimental tests have been realized to validate the two models.
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