High Temperature Hydraulic Flow Control System Based On Frequency Conversion Technology

Considering the viscosity of the hydraulic oil and the flexibility of sealing materials, the working temperature of the common hydraulic system is usually under 80℃. But in some extreme environments, such as in the military vehicles, air crafts or space crafts, the need of power density is so high that the biggest power transmitting with the lightest weight is wanted. With the inevitable power loss, the temperature of the whole system will increase strenuously. So the high temperature hydraulic system has to be designed for those mechanical equipments which can endure much more high temperature than common hydraulic systems. For example, the working temperature of the tank hydraulic system nearly 130℃, and some spacecraft hydraulic system, the working temperature is more than 150℃All of these hydraulic systems are very expensive because their extreme materials and precious components are used.Because of the low cost and simple structure, the gear pump is chosen as the key component to design a high temperature oil supply system used for the power unit of tank vehicle in this thesis, which supply flow rate 200L/min, pressure at 15MPa, and working temperature is 125℃. The system can supply 3 paths of oil simultaneously, and the working pressure and the flow can be realtimely controlled. In the system, the working pressures were controlled by the proportional valves, and the output flow was controlled through frequency conversion technology. All of the measuring and control components were revised for using under high temperature.In this thesis, the high temperature gear pump hydraulic system controlled by the frequency conversion was researched. The mathematical model of each part of the system was established, the Simulink toolbox has been used for characteristics simulation of each part. The effect of temperature and other main structure parameters was analyzed. In order to compensate the flow leakage caused by temperature changing, a closed loop PID controller is designed. The flow rate control accurate of the frequency conversion control system is under 4%, and the setting time is about 18s.Basis on the theoretical modeling and simulation, the local operating and the remote PC controlling was implemented. Real modeling was used in the interface design of the touch screen and PC. The oil liquid level in the tank, the temperature of oil, the status of each filters and valves can be seen clearly on the interface. It is easy to operate and the reliability of the system has been improved. Flow and pressure adjustment can be done on the remote PC or local touch screen, which will be executed through the PLC. This avoids the danger and trouble of the direct operation of the hot handle in the hydraulic system.The research of the gear pump controlled by frequency conversion provided a new way to establish of a high temperature hydraulic system economically, the technology may use in many fields. Right now the high temperature hydraulic oil supply station is successfully used in the scientific experiments.