Analysis and Strategy for Superharmonics With Semiactive Suspension Control Systems

This paper focuses on an experimental implementation of a semiactive seat suspension using magnetorheological (MR) dampers. We first introduce the nonlinear dynamics phenomena induced by skyhook control. Skyhook control has been widely applied to applications ranging from structural vibration suppression to commercialized vehicle suspensions. Unfortunately, skyhook control generates superharmonic dynamics; yet, this issue has not been clearly addressed in such vibration control systems. This paper will attempt to explain how superharmonics are created with skyhook controls through analysis of test data. Furthermore, a nonlinear model-based adaptive control algorithm is developed and evaluated for reducing the negative impact of the superharmonics. Based on an empirical MR damper model, the adaptive algorithm is expanded mathematically, and the system stability is discussed. Then in the following sections, this paper describes implementation procedures such as modeling simplification and validation, and testing results. Through the laboratory testing, the adaptive suspension is compared to two passive suspensions: hard-damping (stiff) suspension with a maximum current of 1A to the MR damper and low-damping (soft) suspension with a low current of 0A, while broadband random excitations are applied with respect to the seat suspension resonant frequency in order to test the adaptability of the adaptive control. In two separate studies, both mass and spring rate are assumed known and unknown in order to investigate the capability of the adaptive algorithm with the simplified model. Finally, the comparison of test results is presented to show the effectiveness and feasibility of the proposed adaptive algorithm to eliminate the superharmonics from the MR seat suspension response.