## 5 Conclusions  
Influencing factors for energy recovery rate of regenerative braking system in hydraulic hybrid vehicles were investigated in this study. Through the theoretical analysis, analog simulation, and the experimental validation, the following conclusions were obtained. (1) The adjustable influencing factors for energy recovery rate of the regenerative braking system in the hydraulic hybrid vehicle, which included braking intensity, initial pressure of the accumulator, and initial braking speed, were theoretical analyzed, analog simulated, and experimental validated in this research. The best energy recovery rate achieved in the constructed experimental bench was 83.33%, and the corresponding optimal parameters of the braking intensity, initial pressure of the accumulator, and the initial braking speed were 0.4, 19 MPa, and 300 rpm, respectively, which was exactly consistent with the simulation results. The obtained best energy recovery rate was favorable to develop novel regenerative braking system for the next generation hydraulic hybrid vehicle. (2) Effects of three influencing factors to energy recovery rate of the regenerative braking system were studied by simulation and experiment respectively, and the research results were summarized as follows, which were favorable to select appropriate parameters for the various conditions. (i) The simulation and experimental validation with different braking intensity indicated that effect of the braking intensity was not linear, and the energy recovery rate reached its peak with the optimal braking intensity of 0.4, because the maximum regenerative braking torque supplied by the accumulator was limited. (ii) It could be concluded from the analog simulation and experimental validation with different initial pressure of the accumulator that the energy recovery rate was gradually decreased along with the increase of initial pressure of the accumulator, because the difficulty degree of the energy recovery was increased along with increase of the initial pressure owing to performance characteristics of the hydraulic accumulator. (iii) Judging from the simulation and experimental validation with different initial braking speed, it could be concluded that improvement of the energy recovery rate was almost linear along with the increase of initial braking speed, because performance characteristics of the hydraulic accumulator showed that its efficiencies of energy absorption and desorption were higher when the corresponding energy input was larger. (3) The feasibility of energy recovery by the regenerative braking system was simulated by the model and validated by the experiment. Consistence between the simulation result and experimental result proved effectiveness of the constructed simulation model and that of the built experimental bench, which provided a helpful method to improve energy recovery rate of the regenerative braking \begin{table}
\begin{tabular}{c l c c c c} \hline \hline \multirow{2}{*}{Parameters} & Braking intensity & 0.40 & 0.40 & 0.40 & 0.40 & 0.40 \\  & Initial pressure of the accumulator (MPa) & 19 & 19 & 19 & 19 & 19 \\  & Initial braking speed (rpm) & 100 & 150 & 200 & 250 & 300 \\ \hline \multirow{3}{*}{Results} & Braking time (s) & 2.21 & 3.89 & 4.81 & 6.18 & 7.45 \\  & Kinetic energy change (J) & 6035 & 13,579 & 25,222 & 37,719 & 56,750 \\  & The recycled energy by the accumulator (J) & 4449 & 10,359 & 20,501 & 31,310 & 46,722 \\  & Energy recovery rate (\%) & 73.72 & 76.29 & 81.28 & 83.01 & 83.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The experimental results in the operating mode with different initial braking speed. system and promote its practical application in the hydraulic hybrid vehicle. Meanwhile, it supplied a meaningful reference for the further development of other hybrid vehicles.