*4.2. HEV Optimization Model with ECMS*

The ECMS was applied as optimization strategy for fuel economy simulation. The result is shown in Table 5. With ECMS, the fuel economy of urban and highways driving cycles had improvements around 8%, while the efficiencies of MG1 and MG2 were tracked as well, as shown in Table 6. The average of urban and highway efficiency values of MG1 were 0.83 and 0.85, and those of MG2 were 0.85 and 0.83, respectively. The difference between the baseline and ECMS was the MG2 highway efficiency, 84% vs. 83%, which was around 1.2% different. Under two different control strategies, the motor/generator efficiencies were very much the same. That indicates the improvement of fuel economy using ECMS was mainly due to the selection of the engine operating points.

**Table 5.** Comparison of fuel consumption between the baseline and equivalent combustion minimization strategy (ECMS).


**Table 6.** Motor/generator efficiency in ECMS.


Figure 11 to Figure 12 show the engine operating points of baseline and ECMS models. With ECMS optimization, the distribution of the engine operating points in urban and highway driving cycles was significantly smaller than that of the rule-based control strategy. With less engine power during the driving cycles, the ECMS model had less fuel consumption, as shown in Figures 13 and 14.

**Figure 11.** Comparison of engine operating points when driving in urban areas.

**Figure 12.** Comparison of engine operating points when driving on expressway.

**Figure 13.** Comparison of fuel consumption rate in urban cycle.

**Figure 14.** Comparison of fuel consumption rate of highway cycle.

Figures 15 and 16 show the accumulation time of engine operation points in urban driving cycle. The engine load with the rule-based control strategy had up to 42% of the engine running time when operating in the less efficiency range, while the engine load with ECMS had 27% of the engine running time in less efficiency range.

**Figure 15.** Engine operating time in urban driving cycle with baseline model.

**Figure 16.** Engine operating time in urban driving cycle with ECMS optimization.

In highway driving cycle, as shown in Figures 17 and 18, the engine load with the rule-based control strategy had a significant operating time ratio in the less working efficiency range, accounting for about 22% of the engine operating time, while ECMS did not operate at all in the less efficiency range. With respect to overall operating time, ECMS optimization had a longer running time when operating in the better efficiency range, so HEV model with ECMS optimization could obtain better fuel economy.

**Figure 17.** Engine operating time in highway driving cycle with baseline model.

**Figure 18.** Engine operating time in highway driving cycle with ECMS optimization.
