# A Study on a New Independent Metering Valve for Hydraulic Boom Excavator
## 4 Experiments and Results
### Verification with Mode Control  
From the working principle of the metering modes and the control strategy, two test cases for the boom system were conducted based on two main evaluation criteria: the working performance and energy-saving potential. The first case includes the experimental results from the NIMV system with four metering modes over one cycle to evaluate the proposed system's performance. Meanwhile, the second test case was a comparison of energy-saving between the NIMV system and the CIMV system based on the same working conditions to prove the effectiveness of the proposed system. The NIMV system's experimental results are depicted in Figure 6, and show the working parameters of each mode, including the EHPV control signal, system pressure, and cylinder displacement. The PE mode begins from 1 to 9 s with a target velocity of 62.5 mm/s (the target velocity can be obtained by the derivative of the target position). In the initial state from 0 to 1 s, all valves are closed, only the pump runs to maintain the P\({}_{\mathrm{s}}\) pressure to protect the pump from returned pressure at the cylinder (in some cases, the initial position of the cylinder is not zero, so the system still maintains the P\({}_{\mathrm{a}}\) pressure before the pump opens). Under the coordinated control of the PBC and the VFPB, the actual displacement of the cylinder is stability controlled and reaches the target trajectory. The \(K_{\mathrm{sa}}\) valve is fully open while the signal control of the K\({}_{\mathrm{bt}}\) valve increases quickly from 0 to 10 V at 2.5 s and drops gradually after that. The pump must deliver the necessary flow for the cylinder to move in the required trajectory when the PE mode is activated. Thus, the position feedback in the VFPB method increases the valve control signal, enabling the valve to open faster. Therefore, the loss at the valve is minimal, helping the cylinder reach the target speed faster. The cylinder moves to its maximum stroke length after 9 s, at that point the pump and all valves are closed to save energy and the position of the cylinder is maintained. \begin{table}
\begin{tabular}{c c c} \hline
**Parameters** & **Specification** & **Value** \\ \hline Cylinder (D140H-LA40B-N500) & Piston diameter \(\times\) rod diameter \(\times\) length & 40 mm \(\times\) 20 mm\(\times\) 500 mm \\  & of stroke & \\ \hline \multirow{3}{*}{Gear pump (SAP20-8.0)} & Pump displacement & 8.3 cc/rev \\  & Max. speed & 3500 rev/min \\  & Max. speed control & 1500 rev/min \\ \hline Relief valve (VPN1-06-MP-32S) & Cracking pressure & 100 bar \\ \hline \multirow{3}{*}{EHPV (SP10-24)} & Max. flow rate & 26.5 L/min \\  & Max. operating pressure & 207 bar \\ \hline Check valve (VJ3-10-005-G1) & Cracking pressure & 0.5 bar \\ \hline \multirow{3}{*}{Directional valve (SP10-21)} & Max. flow rate & 60 L/min \\  & Max. operating pressure & 250 bar \\ \hline \end{tabular}
\end{table} 
Table 2: Experimental parameters for boom–excavator model. From 10 to 17 s, the PR mode is used for the cylinder to retract at a high speed (100 mm/s) because this mode is affected by both flow rate in the pump and the gravitational potential energy. Therefore, the \(K_{bl}\) valve plays a major role in adjusting the speed of the cylinder. However, a high speed can cause damage to the dampers and endanger the operator. In addition, when the cylinder moves down at a high speed, the flow rate from the pump goes to the rod chamber, which cannot keep up with the speed of the cylinder. Because the valve and pump are opened at the same time and the cylinder moves down as soon as the valve opens, the pump cannot provide the correct flow rate to the cylinder at that time; thus, the cylinder will draw oil from the pump. This is also the reason why pressure P\({}_{\rm s}\) is zero when the valve is open (shown in Figure 6). After that, the flow rate from the pump increases gradually and responds to the speed of the cylinder, so that the P\({}_{\rm s}\) pressure increases gradually until the position is zero.