Study On Damper-in-the-Loop System And Its Application

Adapting to the demands on improving vehicle handling stability, safety and ridecomfort, the structure and function of vehicle damping components are increasingly complexand diverse. To speed up the development of new damping products, especially for dampingadjustable dampers, it is imperative that engineers need new technical means by which thereal damping characteristics of new type dampers can be analyzed, moreover, the matchingexperiment between damping characteristics and vehicle dynamic performance, the controlstrategy for semi-active suspensions can be carried out conveniently.According to the demands above, the Damper-in-the-Loop (DIL) system is constructedin this dissertation, theoretical analysis and experimental research of its key technologies arecarried out. To study the damping characteristics of dampers (e.g. double tube damper,displacement sensitive damper and damping adjustable damper) and the influences ofdamping characteristics on vehicle dynamic performance, application technology research ofthe DIL system is also processed in this article. To summarize, the main contributions of thisdissertation are listed as follows:Firstly, real time platform of the DIL system is constructed based on xPC-Target, thereal time vehicle dynamic model and real time communication between physical subsystemand numerical subsystem of DIL system are developed on this platform. The dynamiccharacteristics of servo actuator, servo valve, servo controller, etc. of the hydraulic servo testrig and testing specimen are analyzed systematically in this dissertation. A coupled dynamicsystem which takes the interrelation of hydraulic test rig and testing specimen intoconsideration is established. Parameter identification and model validation of this coupleddynamic system are processed using suspension deflation of which the vehicle driving onB-level random road at70km/h as actuating signal. The influences of these parameters onfrequency response characteristics and stability of the coupled dynamic system are alsodiscussed.Secondly, in consideration of significant phase delay characteristics of the coupleddynamic system, moreover, the coupled dynamic system can be simplified as a pure transferdelay in low frequency band. Based on analysis mentioned above, a delay dynamic system of quarter car model is built in which a delay damping force, delay spring force and delaydamper-spring force are embedded respectively. The delay dynamic system mentioned issolved by using Páde approximation. The influences of time delay on dynamics, stability andthe critical delay time of the delay dynamic system are also analyzed and solved. Finally, theinfluence mechanisms of time delay on the delay dynamic systems above are studiedtheoretically by using energy dissipation theory.Furthermore, because dynamics of the coupled dynamic system has extremelyimportant influences on tracking accuracy and stability of the DIL system, the time-invarianttracking compensator is developed based on extrapolation and the frequency responsecharacteristics in which the coupled system can be simplified as a constant transfer delay.The simulation analysis of this tracking controller is conducted under open loop and closedloop condition in the low frequency band. An extrapolation based adaptive trackingcompensator (EATC) is also developed based on time delay identification online algorithm.The simulation analysis of EATC is also studied under open loop and closed loop conditionto make a compensation of variant time delay. For the purpose of further improving thetracking accuracy of the coupled dynamic system and implement compensation on thevariant time delay and amplitude attenuation in frequency spectrum of interest, model basedfeed-forward tracking compensator (MFTC) is developed by using the information of thecoupled dynamic system, and its tracking accuracy is also validated under open loop andclosed loop condition. In order to reduce the influence of model parameter perturbation andsensor measurement noise on displacement tracking accuracy, model based compoundtracking compensator (MCTC) is developed on the basis of MFTC and stochastic optimalcontrol theory. MCTC in which the weighted matrix of the feedback compensator isoptimized using Genetic Algorithm off-line and MFTC are analyzed under open loop andclosed loop condition with/without noise interference. Finally, compensators developedabove are validated in the experiment by using various command signals, the results ofexperiments demonstrate that MCTC has better capacity of resisting disturbance andtracking ability than EATC and MFTC.At last, the DIL system is constructed using MCTC controller, the differentiate-trackingalgorithm is also implemented in the DIL system which can improve the signal quality ofLVDT sensor and the accuracy of differential operation of displacement signal.1) Completing the construction of the DIL system of normal double tube damper, acomparative analysis is processed between MVP (Multi-Velocity Peak force, MVP) dampermodel and the real damping characteristics, and the effectiveness of the DIL system has beenverified. The influences of damping characteristics on vehicle dynamic performance areanalyzed by means of the entire damping force scaling DIL experiment, the stretchingdamping force scaling DIL experiment and the compression damping force scaling DILexperiment.2) Completing construction of the DIL system of displacement sensitive damper,a comparative analysis is carried out between MVP damping characteristics of differentdamping areas (soft damping area, hard damping area and soft-hard damping area) and thereal damping characteristics. The influences of different damping area on vehicle dynamicperformance are analyzed by means of DIL experiment.3) Completing construction of theDIL system of damping adjustable damper using MCTC compensation and bump-lesstransfer logic by which the displacement tracking accuracy has been improved when thedamping force of CDC (Continuous Damping Control) damper is varying during the DILexperiment. This DIL system not only include CDC damper but also the drivers of solenoidvalve and semi-active controller. Dynamic damping, damping force tracking and semi-activecontrol of the CDC damper are studied by means of this DIL experiment. The driver powerand performance have been enhanced from DIL experiment, at the same time, the referenceMVP model of CDC damper also has been revised, which has improved the force trackingaccuracy of CDC damper.Major Innovations of the Dissertation:(1) The dynamic model coupled with the dynamics of the servo-hydraulic test rig andtest samples is established. The influence mechanism of physical parameters ofservo-hydraulic test rig and experimental specimen on frequency response characteristicsand stability of this coupled dynamic system is revealed.(2) The DIL delay dynamic model is constructed and the critical delay time is solved.Moreover, the intrinsic influence of time delay on the dynamical characteristics and stabilityof this DIL system are analyzed based on energy dissipation theory.(3) An extrapolation based adaptive tracking compensator (EATC) and model basedcompound tracking compensator (MCTC) are developed, compensation on the variant time delay and amplitude attenuation of the coupled dynamic system in frequency spectrum ofinterest are implemented successfully base on compensators developed above.(4) The first DIL experimental system is developed in China, and the dampingcharacteristics of double tube damper, displacement sensitive damper and dampingadjustable damper of vehicle are studied using the DIL system.