# Overflow Energy Loss Recovery System Based on Hydraulic Motor-Electric Generator
## 5 Simulation Research  
To study the influence of the energy regeneration system on the relief valve, simulation research is carried out. The system schematic diagram is given in Figure 13. The system consists of a hydraulic pump source, safety valve, proportional relief valve and energy regeneration system. The safety valve is used to limit the maximum working pressure of the system. The electric energy regeneration system is composed of the hydraulic motor  
Figure 11: The control flow chart of energy regeneration system for the relief valve. Figure 12: Control framework of energy regeneration system for the relief valve. and electric generator. The 2-3 direction valve is used to realize the switching between traditional overflow and energy regeneration. The simulation model based on AMESim is built and given in Figure 14. The parameters of the system are given in Table 1.  
The feasibility of system differential pressure control is given in Figure 15. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Displacement of pump & 50 mL/r \\ Speed of electric motor & 0–2000 rpm \\ Displacement of motor & 100 m/r \\ Maximum torque of motor & 300 Nm \\ Opening pressure of relief valve & 0.5 MPa \\ Maximum displacement of main valve core & 4.6 mm \\ Main spool area & 226 mm\({}^{2}\) \\ Spring factor & 6 N/mm \\ Flow coefficient & 0.7 \\ Maximum flow & 100 L/min \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of components in the system. Figure 14: The simulation model. Figure 13: The system schematic diagram. At the beginning, the set pressure of the proportional relief valve is 15 MPa. At 3 s, the set pressure of this relief valve is adjusted to 18 MPa, and at 6 s, the set pressure of the relief valve is set to 15 MPa. By controlling the electric generator torque, the inlet pressure of the hydraulic motor can be controlled. At the beginning, the inlet pressure of the hydraulic motor is 12 MPa, and at 1.5, 3, 4.5 s, the inlet pressure of the hydraulic motor is adjusted 13, 16, 12, and 8 MPa, respectively. As can be seen, the pressure differences of the relief valve can be controlled through the energy regeneration system. In order to study the control characteristics of the system, the pressure response of the system is simulated. Under the condition of the overflow pressure of the proportional relief valve of 20 MPa and the flow of 100 L/min, the constant pressure control simulation of the outlet pressure is carried out. The pressure step response curve is given in Figure 16. As can be seen, for different target pressures of the relief valve outlet, the actual pressure can be realized within 80 ms.  
To analyze the influence of system flow rate on system pressure control, the influence of system flow change on pressure is simulated. The pressure change curve when the flow rate changes is given in Figure 17. As can be seen, when the flow rate changes through the proportional relief valve, the inlet pressure and outlet pressure of the relief valve fluctuate slightly, but maintain stability quickly. The change curve of spool displacement, hydraulic motor speed and torque  
Figure 16: The pressure step response curve. Figure 15: Pressure difference control simulation curve. when the flow rate changes is given in Figure 18. As can be found, when the flow rate changes, the hydraulic motor speed also changes correspondingly to adapt to the change of flow rate. Since the target pressure does not change, the torque of the hydraulic motor remains unchanged. Pressure, flow rate and main spool displacement curves of relief valve under traditional working mode and with energy regeneration are given in Figure 19. The outlet pressure of the proportional relief valve is 0 MPa from 0-0.5 s, and the relief valve works in the traditional overflow mode. At 0.5 s, the system performs energy recovery, and the outlet pressure of the relief valve is 15 MPa.