Abstract
The need for highly efficient agricultural machineries is increasing the interest of the research community and of industrial manufacturers towards the use of integrated electric systems in combination with traditional powertrain elements. In this work, a hybrid electric tractor with electric continuously variable transmission (eCVT) capabilities was studied to investigate their performance in comparison with that of traditional diesel-powered tractor designs. This hybrid electric configuration can be classified as a power-split architecture that aims to combine the best characteristics of both the simpler parallel and the series hybrid layout while minimizing their main drawbacks. An eCVT configuration can allow for optimizing the diesel operating point with respect to the current working conditions, and achieving peak power performance and energy saving with relatively small electric machines. The proposed hybrid eCVT (HeCVT) tractor architecture was studied using a numerical model that allowed for developing two different control strategies: a charge depleting mode enabling the driver to use full power for the most power-intensive scenarios and a charge sustaining mode developed to optimize efficiency and battery use along an entire work day. To test the proposed architecture, several tasks derived from experimental field measurements on a specialized agricultural tractor were used. HeCVT results were compared with a numerical model of the traditional tractor validated by these experimental data. The HeCVT tractor showed good performance in terms of peak power capabilities using a downsized diesel engine, and consistent fuel savings were obtained according to typical daily working scenarios.
Highlights
The growing need for food to sustain population growth requires a high level of productivity from the agricultural field, which is responsible for raw material supply
A hybrid eCVT (HeCVT) tractor architecture was studied to investigate its performance in terms of peak power capabilities in field-derived work tasks and fuel saving in daily work cycles against a traditional orchard tractor taken as the case study
The HeCVT was equipped with a downsized diesel engine of 56 kW and two electric motors of 30 kW, whose capabilities were mechanically combined with a two-stage planetary gear
Summary
The growing need for food to sustain population growth requires a high level of productivity from the agricultural field, which is responsible for raw material supply. The main limitation of parallel configuration is the mechanical coupling between ICE and mechanical load (wheels and power take off (PTO)), which prevents it from achieving the best results in terms of efficiency and emissions optimization These problems would be solved in a series HET configuration that would instead require large electric machines to have full power on both PTO and drivetrain. Despite the higher complexity of the architecture and its control algorithm, the power-split configuration allowed for the engine to work at the optimal rotational speed for a given instantaneous load but at the same time gave the possibility of a joint cooperation in parallel with the electric system when needed This is crucial to keep electric motors small and in compliance with space requirements for agricultural tractors. Capability for full electric operations decoupling the ICE and using the two electric machines in a dual-input-motor configuration using the energy stored in the battery pack
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