Study On Semi-Active Air Suspension With Stiffness And Damping AD Justable And Its Control System

The semi-active air suspension with adjustable stiffness and adjustable damping has many advantages. Regulating suspension stiffness can avoid system resonance frequency to avoid resonance effectively, and then adjusting damping can damped vibration further. Not only for the road vehicles, but for the off-road vehicles such as agriculture vehicles, military vehicles, the application of semi-active air suspension would help to improve their ability to adapt running road condition, thus improve the damping effect.Based on the design and manufacture of semi-active suspension with stiffness and damping continuous adjustable, the Magnetorheological damper have been developed, and then taking firestone1T15M-2type air spring as elastic element, the semi-active suspension with adjustable stiffness and adjustable damping have been established. According to related studies at home and abroad in present, the dynamic characteristics of Magnetorheological damper was systematically researched using the methods of theoretical analysis combining with experiments. The semi-active suspension system vibration characteristics were experimentally studied, and the semi-active suspension control theory and strategy were put forward. Finally the design of semi-active control system was completed. The completed work and achieved results are generalized as follows:1. The suspension model with adjustable stiffness and adjustable damping and the standard deviation analytic expression of vibration response were established, then the optimum matching between stiffness and damping under different working conditions was analyzed, and the matching scheme of air spring and magnetorheological damper was determined. The control dynamics model and a quarter-vehicle suspension model were established, then the influences of suspension parameters to steering stability were analyzed and the suspension performance was evaluated. The results showed that, air spring and magnetorheological damper matching scheme is reasonable.2. The flow mode magnetorheological damper was puts forward, then the magnetic circuit simulation model was established. The magnetic field distribution and structure parameters’effects on magnetic field characteristics were analyzed, and then the magnetorheological damper structure design was completed. Experiments were conducted to study the impact of input current and the excitation rate on the magnetorheological damper’s damping force. The results showed that, the magnetic circuit design method is reasonable, and choosing appropriate parameters can make the magnetic function better. The output damping force can change by adjusting the applied current. The saturated working current is between1.6and1.8and the damping force controllable ratio reaches5.9. Perceived results justify the validity of the design and provide evidence to damping adjustable semi-active air suspension control research.3. In order to obtain the mechanical properties of the magnetorheological damper, the fluid dynamic analysis including the magnetorheological fluid flow characteristic and the establishment of a flow continuity equation was done based on fluid dynamics theory. The mathematical model was established combined with magnetic field analysis. The model coefficients were identified so as to establish the damping force simplified model, and then the precision verification was done.4. The experimental system of semi-active air suspension with adjustable stiffness and adjustable damping was established. Suspension stiffness and damping were respectively adjusted by position control valve input voltage and damper excitation current. The effects of position control valve input voltage, damper excitation current and actuating frequency on the suspension vibration characteristics were experimentally studied. Experiments showed that, the resonance frequency is reduced with the increase of the positioning control valve input voltage, and at the same time, displacement transmissibility, response acceleration root-mean-square value and maximum dynamic load are reduced quickly. The three indexes all drop to the minimum when the voltage increases to4.6V. In the case of that the position control valve input voltage is less than3V, vibration can be greatly attenuated when the damper excitation current is increased from0to0.6A. However, when position control valve voltage is greater than3V, excitation current has less effect to damped vibration.5. A frequency adjust based control strategy was presented in order to real-time control stiffness and damping, so as to improve the suspension performance. Using labview for software development platform, the PCI6024E DAQ as the core, the control system was established. Based on the bench sine excitation vibration test, comfort performance index of semi-active and passive suspension were compared and the control strategy and control system hardware design were verified. Experiments showed that, the control system is stable and reliable, the control method is feasible, the designed semi-active control strategy can effectively suppress sprung mass vertical vibration.Through the research in this project, the dynamics characteristics of air suspension system based on the magnetorheological damper can be systematically attained, and the semi-active control theory system will be further improved, so as to realize the semi-active suspension design and production. This research is of important theoretical significance and practical value to promote the application of semi-active air suspension system to vehicle and to improve the performance of vehicle suspension system.