Research On Structure Optimization Of Magnetorheological Damper And The Semi-active Suspension Control Strategy

The suspension syatem is a key component to ensure vehicles operation stability and ride comfort. In recent years, magnetorheological technology application becomes a hot point in research of intellectualized suspension. Dominated by this technology, the semi-active suspension structure is simple, energy consumption is low and reaction mechanism is sensitive. However, whether this technology can make breakthroughs depends upon two bottleneck problems: developing magnetorheological damper and designing of semi-active control strategy. Compared with other adjustable shock absorber, the magnetorheological damper has the merits of large adjustable range, high speed of reaction and low energy consumption, which draws attention from scholars. But there exists many unknown factors in magnetorheological semi-active suspension and lots of problems in nonlinearity dynamics, the design of control strategy is very difficult. In view of magnetorheological damper showing obvious features of fractional order dynamics, fractional calculus can have a better description of semi-active suspension characteristic. Revolving around structure optimization of magnetorheological damper and the semi-active suspension control strategy, this paper finishes the following work:(1)Structural design and optimization of magnetorheological damper. First, principles and theories of the design of magnetorheological damper are analyzed, which lays a good theoretical basis for the design of magnetorheological damper, then vehicle model is established, which is by the reference of operation stability and ride comfort, and under various conditions simulation, the ideal damping force value is got. We optimize the damping force as a shock absorber design aim, carries on the design of related structural parameters of shock absorber, establishing mathematical model based on structural parameters of magnetorheological damper, and then make sensitivity analysis of structural parameters and get the effect of channel clearance, effective length and shear yield stress on damping force and adjustable range. Finally, genetic algorithm is applied to optimize the parameters of magnetorheological damper and parameters of damper design are got.(2)Test verification and semi-active suspension simulation. According to the result of simulation and optimization, we design magnetorheological damper, and have indicator test. Results show that damping force of magnetorheological damper increases with the increase of speed and current, indicator test curves is relatively plump, performance of damper meets the actual requirements, hysteretic characteristic of damper is related with speed or frequency and the higher speed or frequency is, the more obvious is the hysteretic characteristic. At the same time, we get the comparing result of the optimized results and test results under circumstances of 4A of current and 0.52 m/s of maximum speed, which shows that restoration damping force is smaller than the optimization aim of 49 N, adjustable damping range is smaller by 0.3, Inaccuracy is in the reasonable scope and verifies the accuracy of simulation optimization results.(3)The dynamic model of magnetorheological damper was established by using BP neural network model. The results of model output and experimental results are fitting well, which shows that this method can adapt to the actual frequency, amplitude and current variation of the shock absorber and can simply and accurately predict actual damper force of magnetorheological damper.(4)Put forward a kind of semi-active suspension fractional order PID control strategy. In view of the traditional PID control is insufficient, fractional order PID controller is proposed to control and two-degree-of-freedom model is built to analyze.Compared with traditional PID control, fractional order PID control offers two more degrees of freedom. They are differential and integral orders which makes more of the controlled dimension of the whole system. The completion of whole controlled strategy goes through two steps: to use PI controller to input vertical acceleration of car body; to use PD controller to input suspension dynamic torsion action and we have simulation calculation of the sum of two steps as output result. Results show that when vehicles are driven on road of class B with the speed of 12.5m/s, compared with negative suspension, the acceleration RMS values of the integer order and fractional PID semi-active suspensions are reduced by 20.9% and 36.3% respectively. PID control strategy of calculation based on fractional order can restrain car body resonance more effectively and improve comfort.(5)An improved immune algorithm is proposed to optimize the fractional PID control parameters. Aiming at the difficult problem of fractional order PID control parameter tuning, differential and integral parameter order of fractional order PID control are optimized. Based on immune concentration inhibition mechanism, a strategy for global optimization is proposed, algorithm evaluation function is established, and gives a concrete optimization process. Based on the idea of immune injection, a fast method of combining expert experience and evolutionary computation is studied, and a more excellent fractional PID controller is obtained. The results shows that after 20 times the evolution algebra, compared with integer order PID semi-active suspension, for the fractional order PID semi-active suspension, the acceleration RMS values of acceleration are reduced by 43.4% and 55.9% respectively. The algorithm is more suitable for solving the fractional PID control parameters, and can improve the efficiency of the parameters optimization, and has the faster response speed and higher accuracy.