Control Strategies And Simulation Study For Vehicle Active Suspension Based On Fuzzy Theory

The suspension system, an important part of vehicle, directly affects the performance of vehicle like ride comfort and handling stability. Nowadays, the widely used suspension is passive suspension composed of spring and absorber. With fixed system parameters, the design of passive suspension system must compromise the conflicting requirements of ride comfort and handling stability. Therefore, to the vehicle working in various conditions, the traditional passive suspension has become incapacity in meeting expected demands of vehicle. In order to overcome the limitations of passive suspension, active suspension comes out. The active suspension is able to adjust or produce controlling force between wheel and vehicle body according to road conditions. So it can restrict vehicle vibration and improve the performance of suspension and achieve the purpose of improving ride comfort and handling stability simultaneously.Control strategy which plays an important role in the performance of active suspension, is the core of active suspension control technology. There are many control strategies for active suspension. PID control regarded as a classical and practical control method has some advantages such as little work of computing and easy realization. So PID control has been applied firstly as a basic control strategy. Fuzzy logic control has been chosen as the second control strategy because it features insensitive to variant and independence on exact mathematical model of the system. Fuzzy-PID control combines the two control strategies of fuzzy control and PID control. It can eliminate the disadvantages of each single control strategy and provide more stable and reliable control effects compared to the single control strategy of PID or Fuzzy.In this dissertation, a dynamic model of active suspension is created, which is based on the vehicle dynamics theory. The mathematical and simulating model of road surface irregularity is also established, which is the model of integral white noise. According to the different control theories, the dissertation individually designs active suspension PID controller,Fuzzy controller and Fuzzy-PID controller based on fuzzy theory, the computer simulations are individually built with Matlab6.5/Simulink to verify the robust of the control system. Then to run it can get the control simulation for different disturbance inputs. By analyzing the simulation results, we find that the active suspension control based on fuzzy theory control strategy is more reasonable and feasible than any other control strategies. When being compared with PID control and fuzzy control, this new control strategy can considerably depress severe vibration of the system in the vicinity of resonant frequencies, reduce the variety of the acceleration and better the control performance.The new strategy combining the fuzzy control theory and PID control theory is employed for the first time to control the active suspension system. It has been shown by simulation analysis that the active suspension Fuzzy-PID control based on fuzzy theory is applicable and remarkably effective. It also offers a new idea to the field of research on suspension control strategies.Some theoretic and numerical reference can be given in experimental research and development of vehicle active suspension in this thesis.