| The electro-hydraulic servo system is often used to realize the displacement or force load in test apparatus, however, the rated flow and resolution of servo valve limit the wide-ranging loading static and dynamic precision. For instance, in order to test the strength and deformation characteristics of the soil, the triaxial test instrument is needed to load displacement or force of different amplitude through the electro-hydraulic servo system for observing the relationship between stress and strain. Different samples need servo valves with different rated flow so as to ensure the control accuracy to get the ideal test data. But frequent change process makes servo valves vulnerable to dust to result in servo valve failure. Even if several servo valves with different rated flow are linked in parallel and are switched among them, the larger size, switch trival, high cost cannot enable this mode in many occasions. To solve this problem, this paper mainly studied from the following aspects:Firstly, based on relevant rotary valve research at home and abroad reviewed in this paper, a new rotary valve whose spool can move radially and axially to change the valve port area in order to achieve two dimensional flow control is put forward and the single valve can get different rated flow to meet the precision requirements of all kinds of test apparatus. And, three different schemes are designed, one of them is chosen and the structure of a novel variable area gradient direct drive rotary valve is established in detail.Then, operating principle of the servo valve is expounded in this paper, the parameters of key components are determined, curves of different rated flow are drawn and the spool of the rotary valve is checked. According to the determined parameters of rotary valve, the3D model is built by Pro/E and the processing technical requirements of valve parts are proposed.Besides, all the force on the rotating valve’s spool is also analyzed, their mathematical models are established, the causes of valve clamping force are analyzed and optimization measures are put forward. The mathematical model for the steady-state flow torque and the flow is established in detail and the simulation of steady-state flow torque and flow characteristics are carried out by Fluent. Then it is concluded that valve sleeve and spool structure have adverse effects on steady-state flow torque and flow, thus three kinds of optimized scheme are put forward and analyzed through simulation. Simulation results also show that the steady-state flow torque has a non-linear relationship with spool rotation angle and the actual value is much smaller than the theoretical value, which makes driving torque reduce greatly. Finally, static and dynamic characteristics of rotary valve are analyzed in this paper. According to the rotary valve drive torque demand, the appropriate servo motor is selected and its mathematical model is built and then simulated. According to the existing laboratory dynamic triaxial apparatus test platform, the parameters of the system are determined. Then the rotary valve is applied to the apparatus to establish the model of axial loading system. The further research about effects of rotary valve area gradient change on the dynamic performance of the system is conducted through simulation by Matlab. The simulation results show that the frequency width of the system can reach10Hz, which meets the test requirement. |
PDF Full Text Request