## 4 Experimental Validation  
Based on the established theoretical model of the regenerative braking system, an experimental bench was constructed, and its schematic diagram was shown in Figure 8. Its operating principle was as follows, which corresponded to the marks Figure 8.  
\begin{table}
\begin{tabular}{l l c c c c} \hline \hline Parameters & \begin{tabular}{c} Braking intensity \\ Initial pressure of the accumulator (MPa) \\ Initial braking speed (rpm) \\ \end{tabular} & 0.40 & 0.40 & 0.40 & 0.40 \\ \hline \multirow{3}{*}{Results} & \begin{tabular}{c} Braking time (s) \\ Kinetic energy change (J) \\ The recycled energy by the accumulator (J) \\ Energy recovery rate (\%) \\ \end{tabular} & 7.54 & 7.54 & 7.54 \\ \cline{1-1}  & \begin{tabular}{c} Kinetic energy change (J) \\ The recycled energy by the accumulator (J) \\ Energy recovery rate (\%) \\ \end{tabular} & 56,750 & 56,750 & 56,750 \\ \cline{1-1}  & \
\begin{tabular}{c} The recycled energy by the accumulator (J) \\ Energy recovery rate (\%) \\ \end{tabular} & 49,719 & 49,663 & 49,608 & 49,553 \\ \cline{1-1}  &
\begin{tabular}{c} Energy recovery rate (\%) \\ \end{tabular} & 87.61 & 87.51 & 87.41 & 87.32 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The simulation results in operating mode with different initial pressure of the accumulator.  
\begin{table}
\begin{tabular}{l l c c c c} \hline \hline Parameters & \begin{tabular}{c} Braking intensity \\ Initial pressure of the accumulator (MPa) \\ Initial braking speed (rpm) \\ \end{tabular} & 0.40 & 0.40 & 0.40 & 0.40 \\ \hline \multirow{3}{*}{Results} & \begin{tabular}{c} Braking time (s) \\ Kinetic energy change (J) \\ The recycled energy by the accumulator (J) \\ Energy recovery rate (\%) \\ \end{tabular} & 7.54 & 7.54 & 7.54 \\ \cline{1-1}  & \begin{tabular}{c} Kinetic energy change (J) \\ The recycled energy by the accumulator (J) \\ Energy recovery rate (\%) \\ \end{tabular} & 56,750 & 56,750 & 56,750 \\ \cline{1-1}  & \
\begin{tabular}{c} The recycled energy by the accumulator (J) \\ Energy recovery rate (\%) \\ \end{tabular} & 49,719 & 49,663 & 49,608 & 49,553 \\ \cline{1-1}  &
\begin{tabular}{c} Energy recovery rate (\%) \\ \end{tabular} & 87.61 & 87.51 & 87.41 & 87.32 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The simulation results in the operating mode with different initial braking speed.  
Figure 7: Simulation results with different initial braking speed: (**a**) Evolution of speed of the flywheel, (**b**) Evolution of pressure of the accumulator.  
(1) The motor was utilized to realize the function of internal-combustion engine of the selected vehicle, and it drove the connected pump as the major power source.  
(2) The accumulator could work as accumulation component during the braking time and as auxiliary power source during the driving time, and switch of the working mode could be adjusted through the electro-hydraulic proportional directional valve.  
(3) The maximum working pressure of the system was set by the electromagnetic relief valve, and the real-time working pressure could be adjusted through the relief valve.  
(4) The moment of inertia of the selected vehicle was equivalent to a flywheel, and it could be considered as a power component to drive the hydraulic pump/motor during the braking time.  
(5) There were many sensors used in the constructed experimental bench, which consisted of pressure sensor, temperature sensor, flow sensor, torque-speed transducer, and so on, which aimed to constantly test and monitor status of the system.  
Besides these components, the integrated control system was designed and developed by the digital signal processor of TMS320F2812 and the corresponding data acquisition module, which could realize accurate control of the experimental bench and rapid collection of the experimental data. Meanwhile, the validated experiments were also conducted in three series of operating modes, which was consistent with the simulation process.