Layout Optimization of Input Coupled CVT Transmission for Agricultural Tractors Through Real-World Data

The general trend of improving the fuel consumption efficiency of agricultural tractors goes hand in hand with the progressive increase in drivetrain design complexity. In this regard, the need to ensure low consumption, high performance, and operator comfort has widely recognized continuously variable transmissions (CVTs) as an optimal design solution. As part of the development of continuously variable transmissions for high-power tractors, several solutions have been proposed, showing an always strong interest in the type of hydromechanical CVT drivetrains. Given the intrinsic complexity of CVTs, the development of parametric-based drivetrain models is essential to accomplish predictive performance analysis and design development matching users’ and manufacturers’ requirements. This paper first presents a parametric modeling process of input-coupled multi-staged hydromechanical continuously variable transmissions (IHMCVT) for agricultural tractors. The procedure was designed to guarantee flexibility in terms of modeled numbers of transmission working stages, moreover, using an iterated model evaluation, it was possible to generate the output mesh for every operating point of the ICE and for each transmission ratio. A model validation activity was then carried out by applying the algorithm to a real-world IHMCVT architecture of a tractor already on the market. The tractor was properly instrumented so that real output data were available to be collected, while input data were extracted from the vehicle CAN-bus network. Validation was performed on both on-field and on-road tractor tasks. Finally, a constrained optimization algorithm was structured to define a possible objective procedure for the selection of optimal parameters in a generic considered IHMCVT transmission. This resulted in the identification of the best-suited design parameters for the given objective function and the number of requested working stages.