Research On A Valve-controlled Semi-active Damper And Its Application In A Vehicle

A suspension is the most important assembly of a vehicle, which is a general term forall force transfer between the body and the tire. Its main functions are as follows.1)transfer the force and torque acting on the tire to the body, including vertical force,longitudinal force and lateral force;2) relax the impact loads passed from the uneven road,damping the vibration caused by the impact loads;3) guiding the movement of the body andthe wheels, decided wheel alignment;4) control the body posture when the car roll or pitch.Hence, the design of the suspension must match the requirements for ride and handlingcharacteristics of full vehicle. However, the ride and handling of the vehicle need differentsuspension performance. To have good ride, the suspension must be soft, but to have goodhandling, the suspension must be hard. Contemporary automotive design philosophy issafety, comfort, energy saving and environment protection. And the pursuit of comfort andthe overall quality of the car is rising. Smart suspension can considering both ride andhandling, and can adapt to different driving conditions and different roads, is the currentfocus of attention. A semi-active suspension can make a good tradeoff during performance,energy consumption and manufacture cost. Hence, this dissertation expores thecharacteristics of a semi-active suspension with adjustable valve in order to improve thevehicle ride comfort, handling and stability. The main research contents are as follows:1) The study of valve-controlled semi-active damper’s characteristics. First, theprinciple of the passive damper and a passive damper theory model considering thestructural parameters is presented and then, the structure and working principle of thevalve-controlled semi-active damper is presented and the structure and working principle ofthe actuator is also presented. Secondly, the external characteristics of valve-controlledsemi-active dampers was tested in the damper dynamometer machine, and the current andspeed showed their influences on the valve-controlled semi-active damper externalcharacteristic. The valve-controlled semi-active damper use inversely proportionalcontrol, at the same speed, the larger the current, the damping force is smaller, so we have a failsafe function, when the current is a constant, the greater the speed, the greater thedamping force. Finally, based on the results of the bench test, a neural network model isproposed to approximate the external characteristics of the valve-controlled semi-activedamper, the damper piston speed, piston displacement off the equilibrium position and thecurrent strength of the solenoid valve are the input of the neural network, numericalsimulation results show that the consistency of the non-parametric model match theexperimental results very well, so it can express the external characteristics valve-controlledsemi-active damper and can be used for dynamic analysis.2) A comprehensive evaluation index for the performance of the7DOF (degrees offreedom) vehicle is proposed. Firstly, this dissertation expounds and analyzes theevaluation methods of the suspension characteristics systematically. Secondly, it builds afour-wheel incentive model for the stochastic road which considers the coherent of bothsides of wheel/road. Then, it establishes a7DOF vehicle model for the vehicle ride comfort,from which it derives the generalized acceleration of the whole vehicle model, the transferfunctions for the dynamic load and dynamic deflection; finally, builds the evaluation indexof7DOF vehicle model for the dynamic control using dimensionless and general weightedmethods.3) The development of hybrid control algorithm of7DOF vehicle. This dissertationuses Matlab/Simulink to set up seven degree of freedom vehicle dynamics model. Themodel takes the vertical vibration of the vehicle into consideration, and at the same time itcan also express the pitching movement vehicle caused by different road excitation ofvehicle front-rear axle and the roll movement caused by different road excitation of right-leftvehicle wheels, and gets the derivation of the algorithm based on the Skyhook hybrid controlalgorithm, and puts the semi-active algorithm into the vehicle model. Then, it optimizesfeedback matrix in random road input and use numerical simulation method to study theoptimized semi-active model and the characteristics of optimal passive suspension. Acomparesion is presented between a passive vehicle and a vehicle with an adjustable vavleruns over a bump while the speed is36km/h, the peak value of vertical acceleration, rollacceleration and pitching acceleration all can be reduced more than30%. In other word,the semi-acive damper with adjustable valve can improve the vehicle performance significantly, but the effect will be decreased as speed increases. As a result, the correlationbetween control algorithm and the excitation frequency need to be explored in the further.4) An advanced hybrid control algorithm for27DOF vehicle was developed andvalidated, considering the roll and pitch movement aroused by lateral movement andlongitudinal motion. With a27DOF vehicle model based on Carsim, an advanced controlalgorithm of pitch and roll for handling and stability conditions was established via theco-simulation between Matlab and Carsim. The effectiveness of the control algorithm wasverified by simulations of double lane change and emergency braking, and the optimal gaincoefficient K and Kp was obtained by co-simulation method. After then, a valve-controlledsemi-active damper and the controller were integrated and assembled on the test vehicle andthe advanced hybrid control algorithm were validated via the real road test, whichdemonstrated that the handling and ride comfort has significant improved.Major Innovations of the Dissertation:1) The external characteristic of valve-controlled semi-active damper was obtained, thisdissertation clarifies its mechanism of external characteristics and establishes the externalcharacteristics non-parametric model of the valve controled semi-active damper which canbe used for dynamic analysis;2) An evaluation index of seven degree of freedom of vehicle model for dynamicscontrol was proposed based on nondimensional and comprehensive weighted method;3) A hybrid control algorithm of7DOF (degree of freedom) vehicle and a hybridcontrol algorithm for a27DOF vehicle considering the roll and pitch motions weredeveloped. And then, a valve-controlled semi-active damper and the controller wereintergrated and the advanced hybrid control algorithm is validated via the real road test.