# Numerical Performance Investigation of a Hybrid eCVT Specialized Agricultural Tractor
###### Abstract  
The need for highly efficient agricultural machieries 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. a +
Footnote †: journal: Applied sciences  
those limit values would prevent their customers from sell their machines. However, those systems require increasingly more dedicated space with the increasing level of restrictions. Aftertreatment systems both do not solve the emissions problem due to side products they produce, and have introduced an increasing level of complexity when it comes to vehicle integration of such devices. Agricultural, in particular specialized, tractors, are well-known for the compactness of their powertrain, which helps in improving stability, visibility, and manoeuvrability. This is the reason why researchers and manufacturers involved in the agricultural field are investing time and money to explore new technologies to reduce emissions production, improving the overall machine efficiency for a given working task. Thanks to the achievements in the transportation field, electrification is now one of the most promising strategy to improve machine efficiency in agricultural applications [6; 7; 8]. Electrification of an agricultural powertrain can take place at different levels depending on the specific use. [PERSON] et al. [9] proposed a Hybridization Factor (HF) for NRMMs with the aim of defining the correct weight between the thermal engine and the electric machines in the powertrain. The authors suggest that the HF should derive from the knowledge of the work cycles the machines are expected to accomplish [10]. Although several attempts from different associations and companies [11], today the lack of standard work cycles forces researchers and manufacturers to the adoption of an experience-based design approach related to statistical features of historical and experimental data [12]. For some machines, a good understanding of the daily work cycle can bring to full electric (FE) architectures [13] where the internal combustion engine can be totally replaced by a battery-pack-based storage system, achieving an HF = 1. This, with the use of green technology for clean electricity [14], would achieve zero emissions at least in the use phase of agricultural machines' life cycle. However, in most cases, knowledge of the work cycle is not so straightforward because of the multi-purpose nature of agricultural machinery.