# Numerical Performance Investigation of a Hybrid eCVT Specialized Agricultural Tractor
###### Abstract
This is very typical for agricultural tractors, which can be considered to be mobile propulsion systems to propel externally attached implements and tools [15]. Full electric tractors (FETs) are explored in the literature for small-medium sized machines. [PERSON] et al. [16] proposed an FET powered by a low-voltage battery pack for small-arm low-power applications. [PERSON] et al. [17] proposed optimizing a dual-motor FET architecture to improve overall efficiency. In this case, the authors also considered a small-medium sized power tractor as reference for their analysis. The main reason was related to the objective difficulty in the design of a proper battery pack in heavy work-vehicle applications in terms of the trade-off in performance [18] and costs [19]. As shown in [6; 20], hybrid electric tractors (HETs) represent the most feasible solution for medium-high size machines in the upcoming decade. [PERSON] et al. [21] proposed an HET with parallel architecture powered by a downsized diesel engine and a 25 kWh battery pack. The authors numerically investigated the architecture against several field working scenarios with a charge-sustaining energy management strategy showing promising fuel savings. A similar parallel architecture was investigated by [PERSON] et al. [22; 23], testing the HET model against test cases derived from field measurements on a traditional diesel-powered orchard tractor. The authors demonstrated that the proposed architecture was able to perform as well as the traditional tractor in terms of peak performance despite the downsized diesel engine, and to achieve 18% fuel saving in daily working cycles on average thanks to the proposed load observer strategy. [PERSON] et al. [24] proposed a HET with series configuration with four dedicated wheel motors receiving power from both the battery pack and the four gasoline engine-based commercial generators. However, the range extender configuration of the architecture, a limited range of 2.5 h, was estimated for heavy plough tillage and 6 h for low-speed drive. [PERSON] et al. [25; 26] proposed a numerical investigation to optimize the use of a series architecture for agricultural tractors. Using dynamic programming to approach optimal control, the authors were able to improve fuel efficiency by about 5% with respect to results of the same architecture managed with rule-based strategies. Parallel and series configurations have advantages and disadvantages. Parallel HETs are the most promising configurations because of their relatively easy implementation on existing vehicles. However, 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. This is the reason why the combined power-split configuration was recently investigated in the literature for agricultural tractors. [PERSON] et al. [27] explored a hybrid eCVT (HeCVT)-based tractor architecture for performance evaluation. The proposed layout consisted of an eCVT transmission inspired by the Toyota Prius layout for the driveline [28] and a direct connection of the sun gear/ICE to the PTO allowing for direct power path from ICE to attached implement. The authors defined three different operating modes for this powertrain architecture: full hybrid mode to approach full speed and heavy load; parallel hybrid mode for heavy load at low-medium speed; and EV mode for low-power application. 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.