# Development of a Hybrid Electric Motorcycle that
## 2 Materials and Methods
### Power Mode Switching Control Strategy in the Hybrid Electric Motorcycle  
Based on the energy management strategy, the HEM has three modes: motor drive mode, ICE drive/generator mode, and dual power drive mode, with different power requirements. The motor drive mode runs at low power, in which the motor alone is used to drive and provide power, which is converted into torque output in two-fold by the inverse differential gear power splitter. The ICE drive/generator mode is used when the driving load exceeds the motor power, in which the ICE is used to drive and optimum performance is maintained by adjusting the generator output according to the driving load. The dual power drive mode is used at high speed or heavy load driving, in which the motor power is added to compensate for the insufficient power output from the ICE, which ran at its best performance. The energy management strategy is depicted in Figure 3. Table 4 lists the abbreviations used in the figure. On the other hand, the brake kinetic energy recycling mode is specific for periods without power requirements. In this mode, the brake's kinetic energy can be recycled to recharge the battery, thus increasing the driving distance. \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Specification** \\ \hline Displacement & 149.5 cc \\ Ignition type & Capacitor discharge ignition \\ Compression ratio & 10.6:1 \\ Maximum output & 8.8 kW at 7500 rpm \\ Maximum torque/ & 11.76 N-m at 6000 rpm \\ Cooling type & Water cooling \\ \hline \hline \end{tabular}
\end{table} 
Table 3: ICE specifications. The efficiency of ICEs is poor when the vehicle just starts and is at low-speed cruise. Thus, the proper control strategy was to use electricity for the motor drive mode under the speed of 25 km/h. Such a strategy avoids the low-efficiency range of ICEs, achieves the idle-stop objective, and reduces fuel consumption and exhaust emission. However, when the power requirement is higher than the maximum power output of the motor (6000 rpm) and the SOC of the battery is under the lowest limitation (250 mAh), the ICE takes over the power output. After the ICE acted, the increasing rotation speed of ICE gradually approaches stabilization at 6000 rpm, coinciding with the motor rotation speed decreasing. \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Description** \\ \hline \(\mathrm{P_{D}}\) & Vehicle demand total power \\ \(\mathrm{Pe}\) & Output power of ICE \\ \(\mathrm{Pe1}\) & The optimal operating zone \\ \(\mathrm{Pe2}\) & The 2 nd optimal operating zone \\ \(\mathrm{P_{m}}\) & Output power of motor \\ \(\mathrm{P_{m-max}}\) & Maximum output power of motor \\ \(\mathrm{SOC}\) & State of charge \\ \(\mathrm{SOC_{B}}\) & Base value of SOC \\ \(\mathrm{SOC_{L}}\) & Preset minimum residual capacity \\ \(\mathrm{SOC_{H}}\) & Preset maximum residual capacity \\ \(\mathrm{V_{B}}\) & Battery voltage \\ \(\mathrm{V_{G}}\) & Generator output voltage \\ \(\mathrm{V_{B0}}\) & Initial battery voltage \\ \(\mathrm{\Delta V}\) & \(\mathrm{V_{G}-V_{B}}\) \\ \(\mathrm{X}\) & Value for power switch \\ \(\mathrm{A}\) & Input of starting value \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Definition of abbreviations in the energy management; SOC: state of charge. Figure 3: Energy management strategy flow. As the rotation speed of the motor approaches 0 rpm, the motor may switch to the generator mode. The switch can adjust the torque loading so that the ICE can be maintained at the optimal operating range. The ICE drive/generator mode is required while the SOC is under the lowest limitation. The ICE provides power for driving, as well as when the motor runs as a generator and reverses excess kinetic energy to electrical power to batteries. In contrast, when the ICE cannot satisfy the driver's power needs (11.76 N-m) and the SOC is higher than the lowest limitation, the motor can switch to drive, and the vehicle can enter to the dual power mode. In an extremely high-power requirement, the maximum power output of ICE is insufficient.