# A Study on a New Independent Metering Valve for Hydraulic Boom Excavator
## 1 Introduction  
Hydraulic systems are usually applied to construction machinery and are widely used in industry, such as for excavation, construction, and agriculture systems. Due to their high power-to-size ratio and robustness, hydraulic systems are considered to be the perfect alternative to electrical actuators that require high power. Among these, hydraulic excavators are the most generally used [1; 2; 3]; however, conventional excavators consume a great deal of fossil fuel, which are gradually being depleted. Moreover, the emissions from conventional excavators emit harmful gases into the environment, which cause problems related to air pollution and global warming [4]. Hence, reducing energy consumption is presently an urgent issue for excavators [5; 6; 7; 8; 9; 10; 11; 12]. Regarding energy consumption problems, a conventional excavator is controlled by electro-hydroraulically directional spool valves, in which four-way proportional directional control valves are the most popular. However, these directional valves cause a high energy loss of approximately 30% through many factors, such as high-pressure margin, throttling loss, and load differential. In addition, the leakage and friction in the pumps and pipelines are also elements that motive energy loss in conventional excavators [13; 14; 15; 16], leading to increasing costs during system operation. Hence, to achieve the desired performance in terms of cost- and energy-saving, an independent metering valve system (IMV) has been developed [17; 18; 19; 20]. A conventional independent metering valve (CIMV) configuration uses four proportional valves (2/2-way-proportional valve) or an electro-hydraulic poppet valve (EHPV)and a check valve. In detail, two valves are connected to the inlet and the other two valves are located at the outlet of the cylinder. A check valve is placed on the tank return line (as shown in Figure 1). The valves are independently controlled according to different working modes, which represent flexible operations and energy-consumption optimization in the system. In addition, a regeneration mode in the CIMV system operates without a flow from the pump. Thus, the energy consumption of the CIMV system is lower than that of the conventional excavator, which has been proven by numerous research projects and patents [21; 22; 23; 24; 25; 26]. However, controlling four proportional valves is not simple when they depend on a pressure difference between the inlet and outlet of the valves, which leads to poor performance in valve control. To overcome this problem, [PERSON] developed a mathematical model of a hydraulic system using four independent metering valves with an optimal valve coefficient ratio. The experiment results indicated that the velocity errors of the valves could be reduced [27]. Nevertheless, using an equivalent valve coefficient equation is a complicated approach because it causes difficulties in terms of programming and control. Moreover, another significant disadvantage of this system is that the regenerative and pumped flows are combined directly, resulting in a difficult conservation of regenerative energy. Using a different approach, [PERSON] proposed a valve conductance method, which was computed using the desired flow and pressure difference across the valve. After that, it is combined with the characteristic curves of EHPV to exactly determine the control valve signal [28]. This approach ensures that the cylinder operates at its design speed in the experimental environment; in reality, however, valves always leak due to pressure changes during operation. Therefore, closed-loop control methods to compensate for leakage are widely used for controlling proportional valves [29; 30; 31; 32]. The CIMV system has great benefits in terms of energy-savings for hydraulic excavators and provides more flexibility in designing a control strategy, but using four EHPV circuits to control one actuator is an expensive approach.