Study On An Ultra-High-Speed Electro-Hydraulic Proportional Valve

The electro-hydraulic proportional valves, based on the conventional industry hydraulic control valves, are key components of electro-hydraulic proportional control techniques. Using analog electro-mechanical conversion devices, they can convert electric signals into displacement signals, and control the parameters such as pressure, flow and direction of hydraulic systems continuously and proportionally according to the electronic input reference signals. The electro-hydraulic proportional valves offer prominent advantages of strong anti-contamination abilities compared to electro-hydraulic servovalves of servo control systems, in spite of certain poor characteristics in some perspectives. They are more suitable for industrial environments because they are less prone to malfunction due to fluid contamination and can improve the stability and reliability of hydraulic systems. In addition, proportional valves are much less expensive, since proportional valves do not contain sensitive, precision components, they are easier to handle and maintain, and are becoming increaingly popular in fluid power control applications. However, the conventional electro-hydraulic proportional valves are the electro-hydraulic signals conversion components by way of the proportional solenoid which offers as the driving device. Due to the limitation of proportional valves' natural characteristics, the response time and response speed of electro-hydraulic proportional valves are not very swift, the response speed is slightly faster while the flow is smaller.Towards this end, in this paper, an ultra-high-speed electro-hydraulic proportional valve is proposed, which can control the flow and direction of hydraulic control systems, and can satisfy the synthetical requirements of high response, high accuracy, high flow, low cost and anti-contamination characteristics of electro-hydraulic proportional control systems. The moving coil electromechanical converter is used as the electro-mechanical conversion component of the driving device for an ultra-high-speed electro-hydraulic proportional valve. Ultra-high-speed electro-hydraulic proportional valve enjoys advantages of control performance, and some performance indexes are achieved and even exceeded those of electro-hydraulic servovalve.Above all, in order to improve the characteristics of conventional moving coil electro-mechanical converter, such as weak points on electro-magnetic force, response time, response speed, studied from permanent magnet structure that is key component of moving coil electro-mechanical converter, different magnetization techniques of single permanent magnet and different magnetization array structures of multiple permanent magnets are compared in this paper. A novel moving coil electro-mechanical converter using eight-pieces tegular Halbach magnet array with air gap magnetized along the external field force lines is proposed as well. The analyses on magnetostatic field, parametric field, transient field, thermal field, eddy current field, power loss and shin effect of moving coil electro-mechanical converter demonstrate that the redesigned moving coil electro-mechanical converter possesses the good dynamic and static performance, electro-magnetic force, the response time and response speed are improved enormously than those of conventional structures.Subsequently, this paper studies from the hydraulic parts of electro-hydraulic proportional valve, and analyzes the dynamic and static characteristics of electro-hydraulic proportional direct operated pilot valve, stacked unidirectional throttle valve and main control valve in terms of the structure and principle, with the combination of power bond graph and computational fluid dynamics. The mechanism of high frequency and rapid response is put forward as well.Afterwards, aiming at overcoming the limitation of the generic electro-hydraulic proportional valves modeling, the paper first develops an orifice flow equation that involves various nonlinear effects and then proposes the unified nonlinear equations for an ultra-high-speed electro-hydraulic proportional valve model. These equations relate the spool geometric properties and physical model parameters to the flow rate through the proportional valve ports. The development focuses on obtaining the flow rate equations applicable to overlapped, underlapped and critical center proportional valves. Here, the flow rates are expressed as a continuous but nonlinear function of lapping parameters, as well as other conventional parameters. Meanwhile, a non-dimensional analysis of the unified model for an ultra-high-speed electro-hydraulic proportional valve confirms that the accuracy of the model is independent of the choice of model parameters, unified model errors depend on the value of the hydraulic damping coefficient alone.To ensure reliable performance of ultra-high-speed electro-hydraulic proportional valves, it is important to be able to monitor certain critical parameters of proportional valves in order to determine whether a fault is occurring. However, direct measurement of these parameters during proportional valves operation may be exceedingly difficult. In this paper, three well-known parameter estimation techniques, the ordinary least squares, the maximum likelihood and fuzzy RBF neural network, are used to estimate the spring constant of an ultra-high-speed electro-hydraulic proportional direct operated pilot valve. The results agree well with the real values, providing a promising indication of their potential.Eventually, the experimental investigations of an ultra-high-speed electro-hydraulic proportional direct operated pilot valve present that the experimental results are fairly good agreement with the simulation results. The results show that the developed electro-hydraulic proportional valve offers extremely high frequency and rapid response characteristics, and can satisfy the requirements of high speed electro-hydraulic proportional control techniques.