Design Of A New Damp Element And Investigation On Control Algorithm Of Reducing Vibration In Vehicle Suspension System

Nowadays, investigations on vibration of vehicle suspension system mainly concentrate in two aspects: (1) new spring elements and damp elements; (2) new vibration control algorithms. According to the idea, the dissertation proposes some original works in the two aspects: (1) according to analyzing actual vehicle chassis layout, a new damp element (torsion damp shock absorber) is presented and investigated; (2) controllable suspension is regarded as control object to investigate some suspension vibration control algorithms. Its investigations are followed as:1. Investigation on torsion damp shock absorberIn the process of designing practicable vehicle chassis, designers usually hope that the vehicle chassis is very compactly designed. According to the principle, analysing the installment method of the shock absorber with the spring and the guide mechanism in current suspension structure, a torsion damp shock absorber is originally proposed to practise compact installment with torsion bar spring and successfully applied into the seventh diamond vehicle. Therefore, the dissertation will investigate the torsion damp shock absorber in some fields in order to make it popular in present vehicle with torsion spring.It is firstly discussed that a damp element and a spring element matchs with the diamond vehicle middle suspension. The function of suspension performance index and vehicle parameters was established according to the 1/4 suspension model. Analyzing the effect of the vehicle parameters to the suspension index, it was detemined that damp coefficient was regarded as an optimization variable in the 1/4 suspension system multi-objective optimization. The multi-objective optimization problem was sovled by micro multi-objective genetic algrothim. The effect of the damp coefficient to the suspension index was discussed in frequency range and the rule of the damp coefficient matching with the suspension system was obtained. The rule is that the resonance range of the vehicle body and unspring weight need heavy damp and the body sensitive range need soft damp. Because the damp force in resonance range of the vehicle body corresponds to the opening valve damp force and the damp force in resonance range of the unspring weight corresponds to the max opening valve damp force, the velocity characteristic curve of the shock absorber can be controlled with three stage damp force. The method is implemented that using optimization design damp coefficient in linear suspension system constructs nonlinear velocity characteristic curve. According to suspension index requirements, choosing ten groups typical non-dominated solution and calculating their probability was to obtain average opening valve damp coefficient and average max opening damp coefficient. Choosing bidirection damp ratio, the opening valve damp coefficient and the max opening valve damp coefficient in promotion and compress process of the shock absorber were calculated. After the opening valve velocity and the max opening valve velocity was obtained according to the shock absorber in suspension structure arrangement, the nonlinear velocity curve of the shock absorber matching with the suspension structure can be obtained. The piston and piston stick diameters of the equivalent tube shock absorber matching the diamond vehicle middle suspension system can be calculated with the opening valve damp force in the promotion process. After the damp element is determined, the spring element is easy to be obtained by torsion bar spring design method in the vehicle design theory.According to fluid mechanics and hydraulic theory, the basic equation to calculate the damp moment of the torsion damp shock absorber was established. The diameter of the normal open orifice and the basic parameter of the promotion valve and compress valve were calculated. Its physics parameter mechanics model was built up. The velocity characteristic curve obtained by simulating in a computer was similar with the equivalent damp force curve controlled by three stage damp force. The gap effect to the torsion damp shock absorber was analysed.Afterwords, in order to demonstrate that the theoretical calculation to the above-mentioned torsion damp shock absorber was correct, a torsion damp shock absorber was designed and manufactured in order to be investigated in experimental rig. Through comparing the experimental results with theoretical model, it was indicated that the above theory calculation was reasonable. To be convenient vibration analysis in the next chapter, the mathematical model of it was proposed by experimental results. The parameters of the model was inversely solved by genetic algorithm.Finally, the nonlinear ride equality of the torsion bar spring double wishbone suspension based on torsion damp shock absorber was simulated in the disstertation. The kinematics and dynamics equations of the torsion spring double wishbone suspension was concluded according to space kinematics and dynamics. It was proved that space movement of the double wishbone suspension can not affect the equivalent damp force produced by torsion damp shock absorber above the tire vertical direction. The function of the nonlinear suspension stiffness with tire skipping distance was obtained by virtual displacement theory. At last, the nonlinear ride equality was simulated according to the national standard requirements to vehicle ride equality stimulated by pulse stimulation and random sitmulation. The simulation results presented that the ride equality of the torsion bar spring double wishbone suspension based on torsion damp shock absorber was reasonable.2. investigation on controllable suspension control algrithmsThere are two forms of the controllable suspension in the dissertation: (1) magnetorheological damper semi-active suspension; (2) active suspension. Above-mentioned two suspensions were respectively regarged as controllable object to investigate their vibarion control algorithms.(1) magnetorheological damper semi-active suspension optimal control investigationMagnetorheogical damper is a semi-active damper based on intelligent materials. The damp force adjustable scope produced by it is more than traditional damper. Because the MR damper can quickly react and be easily controlled, it can be applied into vehicle suspension damp systems. In the paper, the quarter vehicle system based on magnetorheological damper is investigated by the optimal control. The improved Bouc-Wen model is used to describe the mechanical model of MR damper. The weight values in the optimal control are found by the micro-genetic algorithm. Numerical results demonstrate that the optimal control strategy for the performance improvement of the semi-active suspension based on MR damper is very effective.(2) the investigation on the mixed H₂/H_∞multi-objective control on the active suspension based on multi-objective mirco genetic algorithmsThe paper presents to use micro multi-objective genetic algorithm (μMOGA) to deal with the conservation problem about the active suspension multi-objective control while solving the mixed H₂/H_∞multi-objective robust control with linear matrix inequality (LMI) method. A quarter-vehicle model with active suspension system is considered. The acceleration of the vertical vehicle body is defined in the H₂ performance specification. The max suspension workspace and the tyre deflection are defined in the H_∞performance specification. After the control gain has randomly been sought byμMOGA, the H₂ and H_∞norm of the close-loop system are calculated by LMI toolbox. The comparison between H₂ and H_∞norm calculated byμMOGA/LMI and the multi-objective control toolbox in Matlab shows clearly in simulation the advantages of theμMOGA/LMI method. The conservation problem is obviously reduced by uMOGA/LMI method. In the framework ofμMOGA/LMI optimization, the mixed H₂/H_∞multi-objective robust control active suspensions are designed on a quarter-vehicle model. The comparison of the simulation results between passive and active suspension shows that ride comfort performance is clearly improved while assuring suspension deflection within bounds and convincing a firm contact of wheels to road.