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.
Modern agricultural tractors are complex systems, in which multiple physical (and technological) domains interact to reach a wide set of competing goals, including work operational performance and energy efficiency. This complexity translates to the dynamic, multi‐domain simulation models implemented to serve as digital twins, for rapid prototyping and effective pre‐tuning, prior to bench and on‐field testing. Consequently, a suitable simulation framework should have the capability to focus both on the vehicle as a whole and on individual subsystems. For each of the latter, multiple options should be available, with different levels of detail, to properly address the relevant phenomena, depending on the specific focus, for an optimal balance between accuracy and computation time. The methodology proposed here by the authors is based on the lumped parameter approach and integrates the models for the following subsystems in a modular context: internal combustion engine, hydromechanical transmission, vehicle body, and tyre–soil interaction. The model is completed by a load cycle module that generates stimulus time histories to reproduce the work load under real operating conditions. Traction capability is affected by vertical load on the wheels, which is even more relevant if the vehicle is travelling on an uncompacted soil and subject to a variable drawbar pull force as it is when ploughing. The vertical load is, in turn, heavily affected by vehicle dynamics, which can be accurately modelled via a full multibody implementation. The presented lumped parameter model is intended as a powerful simulation tool to evaluate tractor performance, both in terms of fuel consumption and traction dynamics, by considering the cascade phenomena from the wheel–ground interaction to the engine, passing through the dynamics of vehicle bodies and their mass transfer. Its capabilities and numerical results are presented for the simulation of a realistic ploughing operation.
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