Research on the Novel Electro-Hydraulic Flow and Direction Control Principle and Its Applications
|School||Taiyuan University of Technology|
|Course||Mechanical and Electronic Engineering|
|Keywords||proportional direction valve flow feedback principle dynamicand steady state characteristics electronic closed-loop control|
Proportional directional valve of high performance with servo function is the key element of electro-hydraulic control technology. Because of the long-term gap in these key components, the technology of equipment manufacturing industry in our country falls behind that of developed countries, and the development of many important technical equipments for national demands is restricted. Therefore, developing the proportional control elements of low cost, high performance and high reliability is of great significance for promoting the international competitiveness of proportional valve products in China and driving the technological progress of the hydraulic industry and related host industry in our country. As a part of the research content of National Natural Science Foundation "Theories and Methods of Electro-hydraulic Flow Rate Control With Active, Flow Closed-loop and Pilot-Operated"(51175362), this thesis focuses on the comprehensive discussion, analysis and simulation research of the novel electro-hydraulic proportional direction valve based on displacement-flow feedback control principle.First of all, it is stated the work principle of the new kind of three-position four-way proportional direction valve by adopting the hydraulic transistor technology theory. According to the proposal of the innovative structure scheme by the research group, the structure of the core components is designed and the geometric parameters of the key parts are calculated. With the detailed establishment of the valve’s2D engineering drawings and3D entity models by using AutoCAD and Pro/E software, the rationality of the structure parameters is verified, laying a foundation for the subsequent simulation optimization design、performance analysis and physical prototype production.The mathematic model is set up based on the structure and working principle of the novel proportional direction valve. The theoretical calculation and analysis on the static properties and dynamic properties of the new valve are conducted with the help of linearization theory. Main geometric parameters that affect the steady state control characteristics and neutral position valve coefficients are discussed. Based on reasonable hypothesis, the nonlinear state space model of the valve is simplified further, and the systematic block diagram and transfer function are derived. Then with analysis of the system stability, the stability criterion of the new type of proportional direction valve is obtained. The research shows that the dynamic characteristics of the valve is of a first-order lag link whose break frequency increases with the throttle slot area gradient and decreases with the spool area ratio. To guarantee the stability of the valve, the throttle slot always has to maintain a certain underlap.By importing the CAD entities of the valve into simulation platform ——SimulationX, the multi-domain model of new type of proportional direction valve is created. Thus the simulation research on the valve’s steady state and dynamic performances is carried out separately in time domain and frequency domain. This thesis also includes a further discussion about the influence on valve’s dynamic characteristics by sending the pilot flow directly to the tank, or changing the throttle slot area gradient. The results show that the new type of proportional direction valve is of good steady state control characteristics and equal displacement characteristics. The linearity of the control curve of the main spool displacement is well. However, there exists a certain neutral position control dead zone. The dynamic step response time of the valve is comparatively long. The response speed of the spool displacement is related to the system pressure and given signals. The valve’s working bandwidth is about7Hz, and its frequency response curve doesn’t appear resonance peak and has the feature of a typical first-order lag link. The simulation results prove the validity of the theoretical analysis.In order to improve the valve’s control accuracy and dynamic property, the thesis presents three control schemes:main spool displacement-electronic closed-loop control, pilot spool displacement-electronic closed-loop control and double electronic closed-loop control. The structure features and working principles of the three valves are introduced and the multi-domain modeling and simulation research are included respectively at last. Results show that the valve under the main spool displacement-electronic closed-loop control can effectively restrain the interference of the flow force and viscous force. Accordingly it can improve both the steady state control accuracy and dynamic response speed of the valve with broadening the bandwidth of the valve to18Hz. As a result, the overall performance of the valve is promoted by a large margin. The adoption of pilot spool displacement-electronic closed-loop control cannot remove the interference from the power stage because the system closed-loop range is too limited. Therefore there is little influence on the valve’s performance. Relatively, the valve under double electronic closed-loop control can combine the advantages of the former two valves, and by adjusting the control parameter reasonably, the valve will obtain optimal working characteristics. In addition, after introducing the electronic closed-loop control strategy, it can not only improve the dynamic and static properties of the valve but also make the valve possess the ability of fault tolerance by means of working in open-loop control once the closed-loop channel is in trouble.