Development of controllers for vehicle suspension system with enhanced ride comfort

Abstract

Control of an automotive active suspension to enhance the vehicle ride comfort is the focus of this research. Active suspension systems have been widely studied over the last three decades. The basic idea of an active suspension system is to use an active element to apply a desired force between the vehicle body and wheel axle. Optimal control has been most widely used for active suspension systems. The dependence of the optimal control on the state variables led to the development of an observer design in the present work. Since conventional observer cannot guarantee global asymptotic stability, robustness or convergence in the presence of plant uncertainties, Sliding Mode Observer (SMO) is developed to provide state estimation. To overcome the limitation of an optimal controller and observer, a model free Fuzzy Logic Controller (FLC) is designed and its parameters (scaling factors and membership functions) are optimized with Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithm. To handle the chattering problem of SMC, fuzzy sliding mode control is designed based on signed distance approach and this led to the development of Distance based Fuzzy Sliding Mode Controller (DFSMC). Rules are designed based on Lyapunov stability theorem. Simulation results and the Power Spectral Density (PSD) analysis of sprung mass acceleration confirm the superiority of the PSO based DFSMC method. Active Force Control (AFC) loop is used so that the system remains stable and robust in the presence of known/unknown disturbances and uncertainties. AFC loop is integrated with force tracking loop and outer loop for target force computation. Finally, Active Vibration Isolator (AVI) test rig is developed in real time and control of vibrations using the PID, FLC, PSOFLC and SMC strategies are experimented. PSOFLC control scheme gives the best performance in compensating the disturbances introduced into the suspension system. newline