# A Study on a New Independent Metering Valve for Hydraulic Boom Excavator
## 1 Introduction
In recent years, some studies have focused on reducing the number of proportional valves and simplifying the control process of the system, as well as on developing new control strategies. Different strategies using pump/valve coordinate controls with two 4/3-way proportional directional valves for the IMV system, one for meter-in control and another for the meter-out control have been developed [33; 34; 35; 36]. These studies take advantage of combining the pump control into the IMV system to smoothen system operation and save energy. Although the number of proportional valves is decreased, the use of proportional directional valves is still an  
Figure 1: The conventional independent metering valve system. expensive solution compared to EHPV though their functions are almost the same. In another study, a new configuration of a single metering edge was presented [13], where only one proportional valve (2/2-way-proportional valve) was used with a function of a meter-out valve. Moreover, the combined control algorithm for the meter-out valve and pump was developed with improved energy-savings and auxiliary functions, such as anti-flow overload and overload protection. Hence, this system can achieve low operational costs and an energy-consumption reduction. However, the control method of this system is highly complex with many levels of control for the pump and valves; this could cause instability and difficulty for the operator. Considering the high cost of the IMV system, [PERSON] et al. proposed a new IMV (NIMV) circuit that replaced the expensive proportional directional valve with a cheaper directional valve [37]. This study explained the working principle of the NIMV system under the different load conditions. Moreover, an equivalent valve coefficient equation was developed for this system. Based on the simulation results by the AMESim software, the energy savings of this system were higher than those of the CIMV system by 16.43% in the high-side regeneration extension mode and 63.63% in the low-side regeneration retraction mode. However, the equivalent valve coefficient equation is still complex and difficult to exactly control the flow rate through the valve. Simulation results are not sufficiently qualified to accurately evaluate the effectiveness of the NIMV system. Intensive experiments are required to have a more accurate view. Based on the above reasons, in this paper, a coordinated pump-valve control strategy is proposed to improve energy-saving and displacement tracking precision. In detail, the velocity feed-forward and position feedback signals were used to control the valves. In addition, the pump speed command was calculated from the tracking error through a proportional integral derivative (PID) controller. To prove the effectiveness of the new IMV system with the proposed control strategy, a real test bench was built based on the proposed hydraulic circuit under laboratory conditions. Then, the proposed control strategy was verified in real-time. The experiment results of each metering mode were compared with equivalent modes using the CIMV system. The result shows that the NIMV can save energy by approximately 4% in the power extension mode, by 22% in the power retraction mode and by 6.5% in the high side regeneration extension mode. Moreover, the displacement tracking precision of the proposed IMV is higher than that of the CIMV. The rest of this paper is organized as follows: Section 2 introduces the NIMV system and the working principle of the metering modes. The control strategy of the system is presented in Section 3. The experimental results are discussed in Section 4, and finally, conclusions are given in Section 5.