| Due to the characteristics of high power density and large output force,hydraulic transmission system is widely used in various kinds of engineering machineries.In existing hydraulic system of engineering machineries,each actuator is controlled by a four-side linkage proportional direction valve.In this way,the inlet and outlet throttling exist at the same time,resulting in large throttling loss,especially in overrunning load working condition.The solution is to use two or more valves to separately control the two chambers of hydraulic actuator,which is known as independent metering valve control(IMV)system.The existing research work on IMV system mainly focus on the velocity,pressure and energy-saving characteristics.However,with the development direction of intelligent mobile machinery and improvement of work quality requirement,each actuator should not only meet the requirement of velocity control and low energy consumption,but also achieve higher positioning accuracy.For the above problems,under the support of the NSFC-Shanxi coal-based low-carbon coalition fund "basic research on energy-efficient operation of large-scale excavation equipment for open-pit coal mines"(U1510206)and the National Natural Science Foundation of China,"The theory and methods of energy-efficient conversion and utilization of separate chamber volume direct-drive electrohydraulic control systems"(51575374),this paper proposes a velocity and position compound control strategy based on pump/valve compound control and independent metering valve controlled system,in order to further improve the operational characteristics and accuracy of the system on the basis of energy-saving features of independent metering valve controlled system.And related theoretical,Simulation and experimental research are studied.Furthermore,a novel separate chamber variable speed volume control system is proposed,which is called independent volume direct drive system.Thus the throttling losses in the system are completely eliminated and the energy efficiency is greatly improved.Then related control strategies and control characteristics are carried out.The specific research content is as follows.The paper first establishes the mathematical model of the independent metering valve controlled system,and summarizes and analyzes its static characteristics,control methods,and energy consumption characteristics,in order to provide theoretical basis and guidance for the design of control strategies.Then,corresponding velocity and position compound control strategies are separately designed for the typical two quadrant actuator and four quadrant actuators in the construction machinery.Taking the hydraulic excavator boom and arm as research objects,a co-Simulation model is established and related Simulation analysis are performed.Further,a test rig is built on an excavator and the test researches of operating characteristics are carried out.The research results show that with the proposed control strategy,the actuators can operate along the desired trajectory smoothly and achieve high accuracy positioning with low energy consumption.Based on the principle of independent metering valve controlled system and the principle of variable speed pumps controlled system,an separate chamber variable speed volume control system called independent volume direct drive system is further proposed in this paper.The throttling losses are completely eliminated in the new system and the energy efficiency is greatly improved.According to the analysis of its static and dynamic characteristics,the corresponding control strategies are designed.Then the simulation model is established and its pressure,position,velocity and position compound characteristics are simulated and analyzed.The results show that the system can achieve the same dynamic characteristics as the valve controlled system with the designed sum pressure control strategy.And the velocity and position compound control strategy can improve the operating characteristics and accuracy of the system.Further research work can pay more attention to its application on hydraulic excavators or other construction machinery. |
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