Design of a Modal Controller With Simple Models for an Active Suspension System

This paper presents a method to design a modal controller with simple 1-DOF models for an active suspension system. Full-state feedback controller, especially, linear quadratic regulator (LQR) and H-infinity controller, designed with 7-DOF full-car model is hard to implement in actual vehicles because there are so many state variables and gain elements needed to be precisely measured and finely tuned, respectively. To overcome the problem, it is required to design a simple controller with a smaller number of gain elements and sensor signals. For the purpose, a modal controller is designed from controllers designed with three 1-DOF models describing heave, roll and pitch motions of a sprung mass. With these 1-DOF models, discrete-time LQR and sliding mode control (SMC) are adopted to design three feedback controllers which generate vertical force, roll and pitch moments for controlling the heave, roll and pitch motions of a sprung mass, respectively. In the modal controller, three control inputs are converted into active forces at four corners with input decoupling transformation. The modal controller is a type of static output feedback (SOF) one. By LQ SOF control methodology, the modal controller itself is designed with a heuristic optimization method. A frequency domain analysis and a simulation on vehicle simulation software, CarMaker (R), show that the proposed modal controllers are effective in controlling the active suspension system for ride comfort.