Abstract : This paper introduces an energy-saving valve-controlled electro-hydraulic servo system and analyzes the application research of the main components in the hydraulic system. Experiments show that the proposed technical implementation scheme is feasible. Keywords : Energy saving; Valve control; Electro-hydraulic servo system 1 Introduction With the development of engineering applications and science and technology, some fast-response, high-precision electro-hydraulic servo control technologies have begun to be applied in many military and civilian mobile machinery. This requires hydraulic systems to have miniaturization, energy saving and pollution resistance capabilities. Therefore, the engineering design of hydraulic systems has become more difficult. Due to the low efficiency and large hydraulic power loss of valve-controlled electro-hydraulic servo systems, it is very difficult for oil tank and cooling technologies to meet the above requirements. This paper, based on the overall system optimization and to meet the technical requirements of engineering applications, briefly describes the application research results of the energy-saving hydraulic source, dual-channel air-cooled cooler, low-pressure sealed oil tank, fast-response electro-hydraulic servo motor, and other main components of the valve-controlled electro-hydraulic servo system, as well as the application of position closed-loop control. The schematic diagram of the hydraulic system is shown in Figure 1. Energy saving is mainly evaluated by reducing the ineffective power loss of the hydraulic system and the rated power of the prime mover. For valve-controlled electro-hydraulic servo systems with inertial loads, a feasible technical measure to achieve energy saving is to improve the matching efficiency between the hydraulic source and the load characteristics, that is, to minimize excess pressure while ensuring the valve pressure drop Pv necessary to achieve the control function. Figure 2 shows the flow rate Qs and pressure ps characteristic curves of the energy-saving hydraulic source. [align=center] Figure 1 Schematic diagram of the hydraulic system[/align] 2 Energy-saving hydraulic source Research results show that compared with the constant pressure variable pump hydraulic source (vertical dashed line in Figure 2), the energy-saving hydraulic source can make the valve pressure drop pv change very little under different load conditions, reducing the valve power loss Ar (area of ​​the triangle in Figure 2). Generally, it can reach 25% to 35%, and at the same time, since the maximum power is also reduced, the rated power of the motor can be reduced by 30% to 40%. In this design, the prime mover is reduced from 30kW to 18.5kW, saving about 38% energy. The characteristic curve in Figure 2 is achieved using a Rexroth A1OVSO45DFLR variable pump. It shows that the hydraulic source achieves energy saving while minimizing flow gain variation, thus reducing the nonlinearity of the electro-hydraulic servo control system. [align=center] Figure 2 Matching of Energy-Saving Hydraulic Source and Load Characteristics[/align] 3 Dual-Channel Air-Cooled Cooler Since the valve-controlled electro-hydraulic servo system regulates flow based on throttling, i.e., pressure loss, the power loss is large, and the oil temperature rises rapidly. To ensure the performance requirements of the electro-hydraulic servo system, forced cooling of the oil is necessary. Based on the working environment of the mobile machinery, a high-efficiency plate-fin air-cooled cooler is used to cool the oil. Considering that when the dual-channel position closed-loop electro-hydraulic servo system is operating at zero speed, the system has virtually no working return oil flow, only the pump and motor's drain oil flow. Experimental studies show that if the pump operates continuously at zero speed for an extended period with only the main return oil cooled, the pump body temperature can reach 90℃ within 25 minutes and will continue to rise, thus deteriorating the working conditions of the hydraulic system. To ensure the oil temperature at zero speed does not exceed the upper limit of the allowable operating range and guarantee the reliable operation of the electro-hydraulic servo system, a dual-channel air-cooled cooler is used to simultaneously cool both the main return oil flow and the drain oil flow. 4. Low-Pressure Sealed Oil Tank To achieve a small size and resistance to contamination, the hydraulic system uses a low-pressure, fully sealed small oil tank. Since all mobile machinery has a pneumatic braking system, it has an air source of 0.5–0.7 MPa. A high-precision low-pressure reducing valve maintains an air pressure of 0.02–0.025 MPa inside the tank. This ensures sufficient oil supply to the pump in various outdoor environments while preventing dust from entering the tank, improving its contamination resistance. The tank capacity is determined according to the engineering design of the hydraulic system of the mobile equipment, generally based on the pump's flow rate per minute. The rated flow rate of the pump source in this system is 68 L/min. The oil tank volume is only 16L, and the oil capacity is 12L, accounting for only 18% of the general design requirements, thus achieving miniaturization of the oil tank volume and weight reduction. 5. High-frequency response electro-hydraulic servo motors: The design of two high-frequency response electro-hydraulic servo motors is based on two hydraulic motors, A2F16 and A2F28, with modifications to the motor's rear cover to make it also serve as a connecting plate for the electro-hydraulic servo motor. The criterion for improving the open-loop bandwidth of the valve-controlled motor is to make the volume from the servo valve to the motor plunger cavity in the connecting plate very small. Experiments have shown that the bandwidth of the electro-hydraulic servo valve-controlled motor with inertial load can reach 13-20 Hz. 6. Experimental verification : After verifying the feasibility of the above overall design and developing its main components and assembling the electro-hydraulic servo system, comprehensive experiments were conducted on the hydraulic system and the electro-hydraulic servo control system. Experimental results show that after adopting energy-saving hydraulic power source and cooling technology, the average temperature of the pump body and motor body is 30℃ higher than the ambient temperature; the average temperature of the oil tank is 20℃ higher than the ambient temperature under normal working conditions. Therefore, the system can work normally when the ambient temperature is below 45℃. Figure 3 shows the experimental curve of the electro-hydraulic servo control system using a feedforward self-adjusting control strategy for tracking control. During the tracking process, the hydraulic system is energy-saving, the electro-hydraulic servo system works stably and reliably, and the tracking accuracy reaches 0.21%. [align=center] Figure 3 Feedforward self-adjusting tracking control test curve[/align] 7 Conclusion This paper studies the engineering application of valve-controlled electro-hydraulic servo system. The results show that: the energy-saving hydraulic power source can both guarantee and improve performance and achieve high efficiency and energy saving; the dual-channel air-cooled cooler ensures the oil temperature requirements when the electro-hydraulic servo system is working normally under various working conditions; the low-pressure sealed oil tank technology ensures sufficient oil supply to the pump in various outdoor environments and prevents dust from entering the oil tank, improving the system's anti-pollution ability; the energy-saving hydraulic power source is highly efficient and energy-saving. Not only does it reduce the burden of system cooling, but it also makes the hydraulic system smaller and lighter. For mobile machinery with strict requirements in terms of space and weight, this creates conditions for the overall optimization design of the host: the system works stably and saves energy. It also meets the requirements of high-precision closed-loop tracking control. 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