Research On The Key Theory For A Semi-active Damper Based On Pilot Relief Valve

Supported by China FAW Group Corporation and KH Automotive Technologies(Changchun) Co., Ltd, the crucial theories of a semi-active damper governed by a pilot relief valve are studied so that the structure, technology and theory can be revealed, which are helpful to designing similar dampers.The essential problems of the damper mainly focus on the external pilot relief valve and control strategy. The pilot relief valve shows numerous advantages such as the outstanding performance, less number of components, compact structure and rapidly dynamic response. However, the external valve is made up of pilot valve, relief valve and shim valve. The pilot valve is driven by a proportional solenoid. The relief valve and shim valve are governed by thin annular plates. Therefore, combining the materials, electromagnetism, fluid mechanics, elastic mechanics, kinematics and many other aspects, the pilot relief valve is a complex coupling system. In addition to the complexity, there are not the literatures to deeply reveal the structure, performance, mechanism and other crucial issues, which will bring great difficulty in designing, modelling and analyzing. In order to obtain the crucial technology of the valve, the current research focuses on two essential issues, one for the flow characteristics of the law of diminishing and the other for the ability of dynamic response. According to the modular concept, the difficulties of each part of the valve can be solved out, such as the structure, technology, basic theory and so on. Finally, the experiments of damper as well as vehicle are carried out. All the work is helpful to forming a relatively complete analysis method and development process.The main contents and research results of this paper are as follows:(1) In view of the overall structure and mechanism of the damper, this paper analyzes how the main components of the damper itself and the external pilot relief valve achieve the damping characteristics of diminishing and the ability of dynamic response.(2) According to various forces of the pilot valve, the modelling and analysis are performed, thus obtaining the behaviors of displacement and flow rate. Combining the nonlinear mathematics model, metallographic analysis and experiments, a composite method is used to deeply reveal the behavior of constant forces achieved by the structure, materials and other aspects of the proportional electromagnet. Using CFD method gets the static flow force, viscous force and transient flow force, which are helpful to analyzing the static and transient behavior of the complex pilot valve. The displacement of the pilot valve can be determined by the electromagnetic force, flow force and spring force, and the constants of the springs will be reversely chosen by the behavior of the displacement. According to the novel method for calculating the flow area and flow coefficient as well as the behavior of the displacement, the theoretical flow rates work very well with experimental results, which can reveal the necessary conditions for obtaining the great ability of keeping static positions and rapidly dynamic responses, such as small flow rate of the pilot valve and relatively large stiffness of the spring. The dynamic response time of the pilot valve, about 4-6 milliseconds, provides a rapid foundation for adjusting and controlling the pilot valve itself as well as the whole valve.(3) In order to analyze the opening of the relief valve governed by the thin annular plates, the basic research of theory is carried out, thus obtaining the geometrically nonlinear static and transient models of the relief valve. Presenting the static deflection of thin annular plates, non-linear equations have been developed. And then, according to the concentrated load, locally uniform load and globally uniform load, more equation groups are also determined. In order to solve the control equations and convert the groups to one group, our team has successfully found equivalent methods that the concentrated load can be converted to a locally uniform load by hyperbolic tangent function and the locally uniform load can be followed the hyperbolic tangent or power function. A method of unconstrained nonlinear optimization is introduced to solve the large deflection equation. The results drawn from the new method are proved by those of the well-known method of perturbation and finite element method(FEM), which shows the simplicity, higher accuracy and additional ability of dealing with more complex boundary conditions and loads. Using the equivalent methods and unconstrained nonlinear optimization, the static deflection of the thin annular plate and the opening of the relief valve are successfully solved out. Also, a FE model is not only used to evaluate the reliability of the new method but also reveals the details in solving the opening of the relief valve. The nonlinear mathematical model of vibration of the relief valve controlled by thin annular plate is developed, and the development of harmonic differential quadrature(HDQ) is used to obtain the transient solutions. With very complex features such as fourth-order, strong nonlinearity and coupling, the partial differential system in cylindrical coordinate system is successfully solved out using the equivalent method and HDQ. The transient deflection of the thin annular plate and the opening of relief valve extracted from HDQ are verified by those of FE model. Finally, reflected through the static and transient analysis, the unique characteristics of the relief valve are as follows: The great difficulty in opening the relief valve, smaller opening and shorter response time will be achieved when the pressure is larger; “large pressure versus small opening or small pressure versus large opening” is the necessary condition for obtaining the appropriately degressive behavior once the relief valve is opened; The dynamic response time, less than 1 millisecond, is one of the important conditions for assuring rapid switch between soft and hard damping force.(4) According to the theoretical analysis, simulated results and locally experimental conclusions, a calculating model of the whole valve is developed. The comparisons between the theoretical flow rates and experimental values show that the theoretical analysis, modelling and the new numerical method are reliable. Finally, the experiments of damping characteristics, vehicle’s handling stability as well as ride comfort are successfully carried out. Compared with the experimental results, the theoretical analysis is consistent with the damping behavior. According to experiments of vehicle, the performances of vehicle have been greatly improved.