| In order to satisfy the requirements of ride comfort and handling stability of vehicles, controllable suspension systems are required in modern vehicle industry. Aiming at the special requirement of off-road vehicle for the suspension systems, the key techniques of hydro-pneumatic suspension are studied in this thesis combined with the research project. Based on the mathematical model of hydro-pneumatic suspension, the damping and spring characteristics of the suspension system are obtained by the simulation analysis. The prototype of designed hydro-pneumatic was tested on the bench tester. Combined with the test results, the mathematical model of the suspension has been further improved. In order to have a good coordination between the ride comfort and handling stability, the suspension state observer and continuous damping control algorithm were designed, respectively. The hardware-in-loop tests are also carried out to validate the effects of the control unit. The main research contents and highlights are as follows,(1) Based on the theory of Inverse Fast Fourier Transform(IFFT), the method of the time domain excitation model of the four wheels was presented. This road excitation model considers the coherence of left track and right track as well as the time delay of front and rear wheel. The statistical properties of the four wheels excitation have good match with the recommended standard. The quarter-car suspension model and full-vehicle dynamic model were built, respectively. And the spring and damping characteristics of hydro-pneumatic suspension was validated according to results of the bench test. The full-vehicle dynamic model was validated by Matlab/CarSim co-simulation environment. These works laid the foundation for the design of suspension state observer and damping control algorithms.(2) The design scheme of the damping adjustable suspension is proposed. The damping continuous adjustable suspension is realized by paralleling the ring shim oil-way with the solenoid oil-way. The mathematical model of suspension rebound and compression were built respectively. The effect laws of key parameters of solenoid were studied; this will provide design and theoretical suggestions. Combined with the suspension bench test, the polynomial function for damping forces were obtained, so that the control current can be easily calculated.(3) In the design of suspension control logic, the road excitation is difficult to be measured. So the suspension state estimation algorithm has been designed by measuring the easy-detected state information. And the soft and hard mode of damper is decided by these states information. The state observer was designed based on unscented Kalman filter for the quarter-car model and full vehicle model. Numerical simulation results clearly indicated that compared with the extended Kalman filter, the estimation precision of Unscented Kalman filter is high, but the computation load is similar.(4) The load transfer will increase during the sharp turning or acceleration and brake; this will deteriorate vehicle handling stability. In order to have a good coordination between ride comfort and handling stability, a hybrid reference model is proposed. The hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the vehicle stability especially in high speed condition. A sliding mode controller is developed to track the states of the reference model. The performance of controller is demonstrated under four typical working conditions. The simulation results indicated that, compared with the traditional passive suspension, the proposed control algorithm can offer a better coordination between vehicle ride comfort and handling stability. This approach provides a viable alternative to costlier active suspension control systems for commercial vehicles. Based on the TTC200, the hardware-in-loop bench tests are carried out to validate the effectiveness and real feature of the designed controller. |
PDF Full Text Request