# A Study on a New Independent Metering Valve for Hydraulic Boom Excavator
## 4 Experiments and Results
### Comparison with CIMV  
We conducted an experiment to compare the energy consumption of the NIMV system to that of the CIMV system in order to assess its effectiveness. Two cycles were chosen, with Cycle 1 including two modes: PE and PR (see Figure 7a) and the other including the HSRE and LSRR modes (see Figure 7b). The energy consumption and energy savings of each mode are recorded and shown in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mode** & **NIMV** & **CIMV** & **Energy-Saving** \\ \hline PE & 1.69 kJ & 1.76 kJ & \(\sim\)4\% \\ PR & 0.42 kJ & 0.54 kJ & \(\sim\)22\% \\ HSRE & 2.59 kJ & 2.77 kJ & \(\sim\)6.5\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: The energy consumption of the experiment model.  
Figure 7: Comparison of the operation between the NIMV and CIMV systems in both cycles. (**a**) Cycle 1; (**b**) Cycle 2.  
Figure 7a describes the energy consumption between the NIMV and CIMV in cycle 1. The energy consumption of the NIMV was lower than that of the CIMV, i.e., the energy-saving on the PE mode was 4% and that of PR was 22%. The reason is that the returned oil to the tank of the CIMV system needed to maintain a higher pressure than the setting pressure in the check valve. This leads to more energy being required from the pump. Therefore, from 1 to 2 s, the speed and torque of the CIMV system were higher because during this time the pump needed to supply a greater flow rate to reduce the delay response of the cylinder. Similarly, from 11 to 12 s in the PR mode, the cylinder moved down unimpeded in the NIMV system (does not have a check valve), so the torque from the motor was very low. Thus, this system has better energy savings than the CIMV system. However, with more used energy, the CIMV system can achieve a better tracking performance in the early stage. The comparison is evaluated based on the displacement tracking error, as shown in Figure 8a. Although the displacement error of the NIMV is higher in the early stage (from 1 to 5.5 s), it is closer to the target position after that (similar to the PR mode).  
The results of Cycle 2 are displayed in Figure 7b, with the LSRR mode consuming nearly no energy on both systems. The energy is consumed mainly in the HSRE mode, which is better in the NIMV system because, in this mode, losses mainly occur at the EHPV. In the NIMV system, the oil from the pump flows through the \(K_{sa}\) valve combining with the returned oil from the rod chamber and flows to the bore chamber. In contrast, in the CIMV system, the oil from the pump combines with the returned oil from the rod chamber and flows through the \(K_{sa}\) valve after that. Therefore, losses at the \(K_{sa}\) valve of the CIMV system are higher than those of the NIMV system. In addition, in the LSRR mode, the check valve of the CIMV system causes the delayed response time of the cylinder, thus it takes a long time to move the cylinder in the starting cycle. From the cylinder displacement results, Figure 7b shows that the cylinder in the NIMV system has a better tracking performance and a faster response time. In addition, the displacement tracking error from the NIMV system is lower than that of the CIMV system, as shown in Figure 8b. Therefore, this proves that the proposed system, not only focuses on minimizing the factors that cause losses in the IMV system, but also achieves a good working performance.  
Figure 8: Comparison of the displacement errors in the NIMV and CIMV systems. (**a**) Cycle 1; (**b**) Cycle 2.