A Comprehensive Lumped Parameter Approach for the Dynamic Simulation of Agricultural Tractors in Real Operating Conditions

Vehicle dynamics is of primary importance for the determination of the vertical load on wheels and consequently on their traction capability. This is even more true if the vehicle is travelling on an uncompacted soil and influenced by a variable load applied to the hitch, as it is for a ploughing tractor. In this framework, the authors present a comprehensive lumped parameter approach for performance assessment of agricultural tractors in real operating conditions. The proposed methodology integrates in a modular context different numerical models related to the main subsystems of a modern tractor, i.e. diesel engine, hydro-mechanical transmission, full multibody frame and tire mechanics. In particular, the engine and transmission modules reproduce powertrain characteristics and control strategy, the multibody module characterizes the dynamic behaviour of the vehicle detailing the interaction between the tractor rigid bodies, and the tire model predicts tractive capability and resistance to motion on soft soil. It also provides the possibility to properly reproduce real load cycles and their influence on the vehicle setup. The presented lumped parameter model is intended as a powerful simulation tool, capable of considering a large number of phenomena affecting tractor performance, both in terms of fuel consumption and longitudinal response due to load distribution. The predictive capabilities of the proposed modelling approach are presented by simulating a realistic ploughing operation, focusing on tire-soil interaction. Considering the cascade phenomena from the wheel-ground interaction to the engine, passing through the dynamic of vehicle bodies and their mass transfer, numerical results are presented in terms of tractive capability and its effect on fuel consumption.