# A Study on a New Independent Metering Valve for Hydraulic Boom Excavator
## 2 New Independent Metering Configuration  
To overcome the shortcomings of the CIMV circuit, a new NIMV configuration is shown in Figure 2a, in which three EHPVs (\(K_{\text{sa}}\), \(K_{\text{sb}}\), \(K_{\text{th}}\)) and one directional valve (\(K_{\text{d}}\)) are logically linked together to control the cylinder. In this configuration, the NIMV can reduce the number of EHPVs, but still guarantees the same working modes as the CIMV configuration. Moreover, the NIMV does not have check valves for pressure maintenance in the low side regenerative modes, thus the power loss in these operating modes is minimized. The NIMV system has five metering modes, like the CIMV system; however, only four metering modes are used in this study. The load force in this study has the same direction as gravity. The CIMV system has a low side regeneration extension mode (LSRE) that requires the load force be in a different direction from gravity; therefore, the LSRE mode is neglected in this research. The four modes of the NIMV are shown in Figure 2b and the EHPV operation in each mode is shown in Table 1.  
The power extension mode (PE) is described in Figure 2(b-I). In the PE mode, the bore chamber of the cylinder is supplied with the flow rate from the pump through the \(K_{8t}\) valve. The oil from the rod chamber goes to the tank through the \(K_{8t}\) valve. Directional valve \(K_{d}\) changes the position of the spool to adjust the direction of the flow to the cylinder. With the PE mode, the directional valve operates at the left position. Like the PE mode, the power retraction mode (PR) has the same working valve as the PE mode (shown in Figure 2(b-II)). The cylinder retracts when directional \(K_{d}\) valve operates at the right position, and the oil from the pump goes into the rod chamber through the \(K_{8t}\) valve. The oil from the bore chamber returns to the tank through the \(K_{8t}\) valve.  
Operations of the high side regeneration extension mode (HSRE) is described in Figure 2(b-III). Different from the PE mode, the HSRE drives the cylinder with a high velocity. In these modes, returning oil from the rod chamber through the \(K_{8t}\) valve combines with the supplied oil from the pump through the \(K_{8t}\) valve, and goes into the bore chamber. Therefore, a lager flow is supplied to the cylinder in the HSRE mode than in the PE mode, resulting in higher speeds during operation.  
The low-side regeneration retraction mode (LSRR in Figure 2(b-IV)) allows the boom cylinder to move without using the flow rate from the pump. In the LSRR mode, the cylinder retracts under the effect of load and the gravitational force. The output flow rate from the bore chamber is reused through the \(K_{8t}\) valve and pumped into the rod chamber during piston retraction. The excess flow rate due to differences in chamber volumes goes to the tank through the \(K_{8t}\) valve.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Metering Mode** & \(K_{8t}\) & \(K_{8t}\) & \(K_{8t}\) & \(K_{8t}\) \\ \hline PE & Open & Closed & Open & Left \\ PR & Open & Closed & Open & Right \\ HSRE & Open & Open & Closed & Left \\ LSRR & Closed & Open & Open & Left \\ \hline \hline \end{tabular}
\end{table}
Table 1: Valve operation in each mode.  
Figure 2: (**a**) Configuration of an actuator using the new IMV circuit. (**b**) Four metering modes of the NIMV; (I) PE mode; (II) PR mode; (III) HSRE mode; (IV) LSRR mode.