| Vehicle suspension system is an important component of the running gear due to itsimportant role in ride comfort and steering stability. For now, passive suspension is usedmost widely as a vehicle suspension system. Although passive suspension improvesvehicle ride comfort and steering stability in a certain extent, its structure parameterscan not change automatically with external ride conditions and different vehicle states,which restricts its application greatly. The semi-active suspension is main researchaspect of automobile suspension engineering, because its performance is close to activesuspension, the manufacture and use costs are far lower than active suspension.At present, there are two problems which are difficult to solve for the control ofautomotive semi-active suspension system. One is the research of the variable dampingshock absorber which is reliable and convenient adjustable, because the shock absorberis one of the key components of semi-active suspension, and its performance influencesthe semi-active suspension performance directly. The other one is the control algorithmof semi-active suspension system, the scientific research personnel used some controlmethod to semi-active suspension system, but have not achieve ideal result. So, thepractical application for the semi-active suspension system is still in its infancy.The semi-active suspension system based on the variable damping shock absorberis an intelligent structural system which is constituted by many discipline, such asmachinery, fluid, information, control and system theory, there are many problems to besolved for semi-active suspension system. This paper takes a car as research object anddoes some systematic research about variable damping shock absorber and semi-activesuspension control methods, which is supported by Key Natural Fund Projects forTechnology Plan Projects of Chongqing Science and Technology Commission,Specialized Research Fund for the Doctoral Program of Higher Education(20100191110004) and2010Annual Open Fund of State Key Laboratory of VehicleNVH and Safety Technology (NVHSKL-201010).1) Basing on the working principle, internal configuration and valve systembehavior of the shock absorber, the equation for annular laminar deformation under auniform load is deduced by using a deflection differential equation for throttle slice andboundary condition. The detailed mathematical model of double-tube hydraulic shockabsorber is established according to hydrodynamics gap flow, nozzle flow and small orifice throttle theory. The model is simulated by MATLAB/Simulink, and the outercharacteristic of the shock absorber is compared with the test result, the consistencybetween simulation result and test result verifies the correctness and creditability of themathematical model. In addition, the influence law and sensitiveness of damping forceaffected by structure parameters of the shock absorber are analyzed using the model, thegeneral controlling rule of shock absorber damping force is got, and the results obtainedcan provide technical support to the design and performance prediction of shockabsorber to a certain degree.2) A stroke-sensitive shock absorber was developed by improving the ordinarydouble tube hydraulic shock absorber. Basing on the theory of hydraulics and elasticity,the function expression of the embranchment flow rate and throttle pressure of the valvesystem for stroke-sensitive shock absorber is deduced by proposing and usingpolynomial fitting method series and parallel complex pipeline flow rate, themathematical model of the stroke-sensitive shock absorber is established with theequation for annular laminar deformation under a uniform load. The detailed model issimulated by MATLAB/Simulink, the calculated results agree well with the test results.In particular, the influence rule of the by-pass groove diameter on the shock absorberdamping is analyzed using the model.3) A variable damping shock absorber of high cost performance for semi-activesuspension is developed; the structure and operation principle of the shock absorber isillustrated. Based on the theory of hydraulics and elasticity, the ways of calculating thethrottle pressure on the parallel pipe line and the embranchment flow rate on theseries-parallel complex pipe line are deduced and employed, and the detailedmathematical model of the variable shock absorber is established by using the equationfor annular laminar deformation under a uniform load. The MATLAB software is usedto simulate the detailed model, and the calculated results agree well with the test results.Using the variable damping shock absorber test results, the relationship curve betweenthe damping force of shock absorber and the angle of the adjusting mechanism in avibration frequency is obtained. In addition, the influence rule of the structure parameteron the circumfluence pipeline to damping force of the shock absorber is analyzed usingthe model.4) Body acceleration, suspension dynamic deflection and tire dynamic load areregarded as the evaluation indexes of vehicle suspension performance. The roadincentives formula of suspension system is introduced, and the time domain models of the random road and arc road are obtained. According to Lagrange equation, the vehiclevibration differential equation of the suspension system is established, and the systemstate space model is established for the vehicle vibration system of7DOF. TheMatlab/Simulink software is used to simulate the vehicle model. In order to evaluatevehicle vibration system comprehensive performance conveniently, the comprehensiveperformance evaluation index is established including sprung mass acceleration,suspension deflection and tire dynamic deflection.5) Combining with the characteristics of vehicle control system, the method of“three parallel controller damping control” is proposed by taking vertical vibration,pitch vibration and roll vibration as inputs of controller. Basing on the semi-activesuspension system model with the variable damping shock absorber, the PID control,fuzzy control and fuzzy-PID control are designed. The three control strategies arecompared by simulating the semi-active suspension under the random excitation and arcbarriers road condition. To improve system comprehensive performance, the simulationresults show that the semi-active suspension is obviously superior to passive suspension,and fuzzy-PID control is better than the fuzzy control and PID control. The controleffect of the three kinds of control mode such as front suspension control, rearsuspension control, and full vehicle control is completed by using the fuzzy-PID control.It is demonstrated that the control effect of full vehicle control is much better than frontsuspension control and rear suspension control, and the control effect of rear suspensionis better than front suspension. |
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