| With many advantages, such as reliable performance, low cost, high precision and fast dynamic response, Electro-hydraulic proportional technology can control the position, speed and force of the load, and replace electric-hydraulic servo system in many fields, especially in mobile hydraulic systems. Among all of the proportional hydraulic elements, electro-hydraulic proportional directional valve represents the development direction of the electro-hydraulic proportional technology.There are two types of electro-hydraulic proportional directional valve(EPDV), direct-acting and pilot-operated EPDVs. The former has limitations of small flow and low pressure due to the limited thrust of proportional solenoid; and the later has complex structure, needs pilot oil and cannot work under zero-pressure condition though achieving high-pressure and large-flow control. Therefore, based on the current situation of EPDVs, aiming at the limitations of large-stroke proportional solenoid, such as difficult to manufacture and low frequency response, a novel design of roller thrust torsion coupling is put forth in this paper, 2D EPDV combined with roller thrust torsion coupling can amplify not only the thrust of proportional solenoid and also the displacement of spool, with improved static and dynamic characteristics, it has the advantages of direct-acting and pilot-operated valves. Its key technology had been studied in this thesis. The main study content and achievement of this thesis are as follows:1. Based on the systematic review of the current EPDVS, aiming at the limitations of the current 2D EPDVs, their spool displacement are limited to the working stroke of proportional solenoid, a novel design of roller thrust torsion coupling is put forth in this paper, after combining it with 2D valve, the proportional solenoid for 2D valve is easy to process, high pressure and large flow proportional control is achieved in 2D EPDV with improved static and dynamic characteristics.2. Aiming at the non-linear effects caused by the backlash in the thrust torsion coupling with displacement enlarging, dither compensation technology which uses high frequency dither signal to superimpose on input signal is proposed in order to diminish and even eliminate hysteresis, and improve its input-output characteristic; its mathematical model is established, and the backlash characteristic is analyzed by using phase plane method, which lay theoretical foundation for the applying in 2D EPDVs; Then experimental study on prototyping coupling is carried out and the hysteresis curves under different dither amplitude and frequency are gotten, its hysteresis is down to about 1%, experimental results show that the effectiveness of dither compensation technology is proved by experimental results.3. The mathematical model of solenoid for 2D valve is established, bi-directional proportional solenoid and switching solenoid are simulated by software Maxwell, contrast experimental study on prototyping solenoid are carried out. Studies show that the longer linear stroke of solenoid, the more difficult to manufacture. But 2D EPDV with displacement enlarging can solve the problem.4. Based on the analysis of clamping malfunction of traditional spool, computational formula of 2D valve clamping force is deduced, then the calculation method of resistance torque for thrust torsion coupling is gotten, the research on resistance torque for 2D spool lay foundation for structure parameter determining and static characteristic of the valve. Applicating the theory of gap flow the radial force of 2D valve under eccentric and non-eccentric situation are systematically analyzed by using software MATLAB, then the relationship between 2D valve clamping force and the eccentricity with the angle between the high pressure and low pressure hole is deduced. Based on the 2D valve’s property, the improvement measure of solving spool clamping malfunction is put forward. The flow field of the spool surface is CFD simulated and analyzed by using Fluent software. Based on the velocity vector and pressure distribution of the spool, the improvement measure of solving spool clamping malfunction is proved correct. Clamping phenomenon is effectively reduced in high pressure experiment after the improvement of 2D EPDV.5. Based on the mathematical model of 2D valve and its thrust torsion coupling, the stability with backlash characteristic is analyzed by using describing function method, which shows that the system of 2D valve though with backlash is stable after dither compensation, its stability condition is gotten; the influence between key parameter of 2D valve and its dynamic characteristic is simulated by software MATLAB, simulation results show that 2D valve has better dynamic characteristic.6. The experimental project are respectively designed and hydraulic test rig is built, the experiments of null position leakage of pilot stage, flow characteristics, repeatability and dynamic characteristics of the two kinds of 2D valves are performed, the experimental results are comparative analyzed, which show that under the condition of same system pressure and output flow, the multiple of displacement enlarging is 2.5. The maximum flow is approximately 190L/min when system pressure is 27 MPa; the leakage of pilot stage is about 0.2L/min; frequency width is improved to about 12 Hz at-3d B and-90°and rising time of step response is about 0.45 s before displacement enlarging, but frequency width is about 38 Hz at-3d B and-90°and rising time of step response is about 0.20 s after displacement enlarging, its dynamic performance is improved greatly. |
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