## 3 Results and Discussion
### Fuel Consumption and Electric Driving Shares  
Figure 4 presents a comparison of the real-world fuel consumption of the PHEV under investigation for the hybrid driving mode (Figure 4a) and for the sport driving mode (Figure 4b). The boundary conditions such as ambient temperatures between the tests conducted in hybrid driving mode and the sport driving mode tests are similar and both test series are performed within 2 weeks. It should be noted that here the actual fuel consumption related to the ICE is shown, which is measured by a fuel mass flow sensor (cf. Figure 2). The energy consumption of the electric machine is not included. Figure 3: Overview of the main measured values for an exemplary real-world test drive in the Stuttgart metropolitan area. Table 4 summarizes the electric driving shares of the studied PHEV for each real-world driving test, considering the different vehicle speed categories. The electric driving shares are calculated as the relative distance share at which the ICE is inactivated, and no fuel consumption is measured. The comparison indicates an average fuel consumption of 4.6 L/100 km for the hybrid driving mode and 6.2 L/100 km for the Sport driving mode concerning the total test route (Figure 4). The fuel consumption values for the respective vehicle speed ranges are also about 20-25% lower for the hybrid driving mode compared to the sport driving mode. This can be explained due to the fact that when the sport driving mode is activated, the PHEV activates the ICE more frequently and follows a more dynamic operating strategy than in case of the hybrid mode. Regarding the influence of the vehicle speed on fuel consumption, for both the hybrid and the sport driving mode, the values for urban and rural vehicle speed ranges are on a similar level, while the fuel consumption for motorway driving is considerably higher. Especially for the urban driving parts, the vehicle indicates high electric driving shares (Table 4) and therefore low ICE driving shares, which leads to low fuel consumption values. For rural vehicle speed ranges, the ICE is activated more often, but fuel consumption values are relatively low due to more constant (or less dynamic) driving patterns and low driving resistances. At motorway vehicle speeds, the air resistance and hence the fuel consumption rise disproportionately to the vehicle speed increase [18]. As the ICE needs to be activated most of the time to reach the high power demand, the electric driving shares of the PHEV are low. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test No.** & **Driving Mode** & \begin{tabular}{c} **Electric Driving** \\ **Share, Urban [\%]** \\ \end{tabular} & \begin{tabular}{c} **Electric Driving** \\ **Share, Rural [\%]** \\ \end{tabular} & \
\begin{tabular}{c} **Electric Driving** \\ **Share, Motorway [\%]** \\ \end{tabular} &
\begin{tabular}{c} **Electric Driving** \\ **Share, Total [\%]** \\ \end{tabular} \\ \hline
1 & Hybrid & 72 & 32 & 3 & 57 \\
2 & Hybrid & 71 & 35 & 37 & 59 \\
3 & Hybrid & 69 & 38 & 14 & 55 \\
4 & Hybrid & 69 & 54 & 8 & 58 \\
5 & Hybrid & 77 & 39 & 7 & 64 \\
6 & Sport & 63 & 11 & 0.4 & 44 \\
7 & Sport & 60 & 21 & 13 & 47 \\
8 & Sport & 64 & 12 & 0 & 44 \\
9 & Hybrid & 66 & 42 & 6 & 54 \\
10 & Hybrid & 71 & 19 & 27 & 60 \\
11 & Hybrid & 64 & 34 & 16 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Overview of the PHEVs electric diving shares in the real-world driving tests. Figure 4: Influence of driving mode on the real-world fuel consumption of the studied plug-in hybrid electric vehicle (PHEV) during summer time. (**a**) Hybrid driving mode; (**b**) Sport driving mode. Figure 5 shows a comparison of the real-world fuel consumption of the studied PHEV for driving in the hybrid mode in summer (Figure 5a) and driving the same mode in autumn (Figure 5b). Besides of the ambient temperature differences, the driving tests in autumn are conducted with winter tires, while summer tires are used for the tests during the warm season (Table 3).