# Numerical Performance Investigation of a Hybrid eCVT Specialized Agricultural Tractor
## 4 Numerical Investigation
### Work Cycles--Fuel Consumption  
In this section, the fuel consumption of the conventional and HeCVT powertrain is compared. Numerical simulations were performed to evaluate the overall energy efficiency of the powertrains during work activities, in particular while pulling trailers and using attached implements powered by the PTO. In particular, the following aspects were investigated:  
* Fuel and energy consumptions per hour in CD mode. * Fuel consumption per hour in CS mode. * Fuel consumption in proposed working cycles of 8 h. \begin{table}
\begin{tabular}{l c c} \hline \hline  & **HeCVT** & **Conventional** \\ \hline
40 km/h, no trailer & 25\% & 22\% \\
5 km/h, 10,000 kg trailer & 18\% * & 40\% \\
15 km/h, 5000 kg trailer & 20\% & 15\% \\ Max speed 45\% slope, no trailer & 19.4 km/h & 20.3 km/h \\ \hline \hline \end{tabular}
\end{table} 
Table 6: HeCVT performance in different slope tests. * Boost function activation required. Figure 9: HeCVT 0-15 km/h acceleration test with 5000 kg trailer and 20% slope. The main parameters of PTO work activities are described in Table 2. Regarding CD mode, Table 7 shows the energy consumption, defined as the sum of the fuel equivalent energy content and the electric energy used from the battery pack. This value was compared in relative terms to the equivalent energy consumption of the conventional powertrain during the same tasks. For a fair comparison between the conventional and hybrid architecture, the equivalent energy approach was chosen to take into account the use of electric energy in the hybrid powertrain. Given the same mechanical work for the two case studies, the fuel consumption of the diesel engine alone would not be sufficient to demonstrate efficiency improvement because part of the requested energy would be satisfied by the electric reservoir. In this way, both sources were considered together in comparison with the only internal combustion engine of the conventional tractor. The HeCVT architecture recorded great energy saving during the trailer handling thanks to the possibility of optimizing the ICE working point, since the thermal unit was kinematically free from the wheels. Regarding CS mode, Table 7 shows the fuel consumption of the HeCVT architecture compared to the fuel consumption of the conventional powertrain of reference while performing the same tasks. Lastly, two different types of work cycles were considered: PTO cycles and trailer handling. PTO cycles consisted of an 8 h work day: 90% of the time using the PTO powered implements and 10% of idling for accessory activities, where the tractor is left on to maintain the machine ready to be used. The trailer handling cycle consisted of an 8 h work day: for 45% of the time, handling was performed at 40 km/h pulling the full payload of the trailer (10,000 kg); for 45% of the time, handling was performed at 40 km/h with an empty trailer (1400 kg); for the remaining 10% of the time, the tractor was left idling. During tractor idling, the powertrain was controlled to recharge the batteries if necessary. Table 8 shows the results of these tests. In this case, daily fuel consumption was considered, comparing the HeCVT fuel consumption with that of the conventional tractor in the same test. Results of these tests showed good improvement in energy and fuel consumption for the HeCVT architecture compared to that of the conventional powertrain. In particular, the hybrid powertrain achieved more than 20% of fuel saving in the handling trailer cycle, and an average of 10% of fuel saving in the PTO cycles. Figure 10 shows the results of \begin{table}
\begin{tabular}{l c c} \hline \hline  & **CD Mode** & **CS Mode** \\  & **[\%]** & **[\%]** \\ \hline Shredder & 14 & 13 \\ Atomizer & 10 & 9 \\ Rotary harmony & 10 & 8 \\ Handling at 40 km/h a 1400 kg trailer & 30 & 25 \\ Handling at 40 km/h a 6000 kg trailer & 21 & 16 \\ Handling at 40 km/h a 10,000 kg trailer & 19 & 14 \\ \hline \hline \end{tabular}
\end{table}