Xubin Song

Editors’ perspectives: road vehicle suspension design, dynamics, and control

This paper provides an overview of the latest advances in road vehicle suspension design, dynamics, and control, together with the authors’ perspectives, in the context of vehicle ride, handling, and stability. The general aspects of road vehicle suspension dynamics and design are discussed, followed by descriptions of road-roughness excitations with a particular emphasis on road potholes. Passive suspension system designs and their effects on road vehicle dynamics and stability are presented in terms of in-plane and full-vehicle arrangements. Controlled suspensions are also reviewed and discussed. The paper concludes with some potential research topics, in particular those associated with the development of hybrid and electric vehicles.

An Adaptive Semiactive Control Algorithm for Magnetorheological Suspension Systems

In this paper, we will present a nonlinear-model-based adaptive semiactive control algorithm developed for magnetorheological (MR) suspension systems exposed to broadband nonstationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and/or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include on-line system identification such as a recursive least-squares method. Based on a nonparametric MR damper model, the adaptive system stability is proved by converting the hysteresis inherent with MR dampers to a memoryless nonlinearity with sector conditions. The convergence of the adaptive system, however, is investigated through a linearization approach including further numerical illustration of specific cases. Finally the simulation results for a magnetorheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, and such comparison further shows the effectiveness of the proposed nonlinear model-based adaptive control algorithm for damping tuning.

No-Jerk Skyhook Control Methods for Semiactive Suspensions

This paper presents two alternative implementations of skyhook control, named ‘‘skyhook function’’ and ‘‘no-jerk skyhook,’’ for reducing the dynamic jerk that is often experienced with conventional skyhook control in semiactive suspension systems. An analysis of the relationship between the absolute velocity of the sprung mass and the relative velocity across the suspension are used to show the damping-force discontinuities that result from the conventional implementation of skyhook control. This analysis shows that at zero crossings of the relative velocity, conventional skyhook introduces a sharp increase (jump) in damping force, which, in turn, causes a jump in sprung-mass acceleration. This acceleration jump, or jerk, causes a significant reduction in isolation benefits that can be offered by skyhook suspensions. The alternative implementations of skyhook control included in this study offer modifications to the formulation of conventional skyhook control such that the damping force jumps are eliminated. The alternative policies are compared to the conventional skyhook control in the laboratory, using a base-excited semiactive system that includes a heavy-truck seat suspension. An evaluation of the damping force, seat acceleration, and the electrical currents supplied to a magnetorheological damper, which is used for this study, shows that the alternative implementations of skyhook control can entirely eliminate the damping-force discontinuities and the resulting dynamic jerks caused by conventional skyhook control. @DOI: 10.1115/1.1805001#

Modeling Magnetorheological Dampers with Application of Nonparametric Approach

This article studies the application of nonparametric modeling approach to model magnetorheological (MR) dampers. For comparison purposes, another typical parametric modeling method for electrorheological (ER) and MR dampers is reviewed. The existing parametric MR damper model includes a stiff Bouc-Wen model that is not friendly for simulation study and real time implementation of model-based advanced control algorithms. In order to avoid the difficulties by using the existing parametric model, the test data from a commercialized MR damper is employed to develop nonparametric models, which can consist of a series of numerically efficient mathematic functions. In addition, the selected functions are required to be continuous and differentiable for potential model-based control algorithms. The results of the nonparametric models show that such different models are comparable. Furthermore, one nonparametric model is selected to be compared with a parametric model and the test data to illustrate the accuracy of the model. The comparison shows that the proposed nonparametric models are able to accurately predict the damper force characteristics, damper bilinear behavior, hysteresis, and electromagnetic saturation. It is further shown that the nonparametric models can be numerically solved with an integration step size of the order of 10 2 s, much faster than the parametric models of the order of 10 5 s, which clearly shows that the proposed nonparametric models are feasible even for real time model-based control algorithms.

System non-linearities induced by skyhook dampers

The nonlinearities induced by skyhook dampers are studied experimentally and analytically using a single degree of freedom base-excited system that is representative of the systems that such dampers are often used in. The experimental results are used to show that the nonlinearities introduced by skyhook dampers manifest themselves as high frequency peaks in the frequency spectrum of the system response. More precisely, using a pure tone input with a known frequency, it is shown that these peaks occur at odd multiples of the system input (or driving) frequency. Using a Fourier series analysis, it is proven that the nonlinearities are caused by the switching policy of skyhook dampers, in which the damper force is changed according to the relative sign of the sprung mass absolute velocity and the relative velocity across the damper. The analysis shows that the skyhook damper force always contains a frequency component that is equal to the frequency of the system input (as is expected for a linear system), in addition to other frequencies that are odd multiples of the input frequency. The damping force peak that occurs at the input frequency is necessary for controlling the forced response of the system. The peaks at higher frequencies, however, are not desirable – although always present – because they introduce corresponding peaks in the system response that can cause ancillary vibration problems. For most systems, the high frequency peaks can significantly diminish any isolation benefits that are gained by the skyhook damper. When using skyhook dampers, such effects must be considered and their impact on the system dynamics studied carefully.

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 1 A to the MR damper and low-damping (soft) suspension with a low current of 0 A, 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.

An Adaptive Semiactive Control Algorithm for Vehicle Suspension Systems

In general, a vehicle suspension system can be characterized as a nonlinear dynamic system that is subjected to unknown vibration sources, dependent on road roughness and vehicle speed. In this paper, we will present a nonlinear-model-based adaptive semiactive control algorithm developed for nonlinear systems exposed to broadband non-stationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and/or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include a recursive least square (RLS) method for on-line system identification. Since the adaptive algorithm is developed for semiactive systems, stability is guaranteed based on the fact that the system is energy conservative. The convergence of the adaptive system, however is not guaranteed, and is investigated through a numerical approach for a specific case. The simulation results for a magneto-rheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, as well ae other configurations of skyhook control, in order to show the extent of the procurement that can be expected with the suggested adaptive skyhook control provides a better broadbandk performance for the suspension, as compared to the other damping configurations that are included here.Copyright

Wheelbase Filtering and Characterization of Road Profiles for Vehicle Dynamics

Random road profiles and wheelbase filtering, both of which strongly affect vehicle dynamic performance characteristics, have been explored in many studies. These studies invariably focused on either characterizing road roughness or vehicle dynamics considering wheelbase filtering effect. No effort, however, has been attempted to characterize road roughness profiles upon considering vehicle wheelbase filtering effect, and then to investigate their combined roles on vehicle dynamic responses. In this study, characteristics of different random road profiles are investigated upon considering wheelbase filtering effect. Two vehicle models, including quarter-car and pitch-plane models, are then employed to analyze the combined influence of random road roughness and wheelbase filtering on vehicle dynamics. The simulation results reveal the significant difference between the characteristics of random road profiles with and without wheelbase filtering effect. The results further demonstrate that wheelbase filtering has a positive effect on vehicle vertical ride, with a negligible or small compromise on suspension travel and dynamic tire deflection.Copyright

Designing an adaptive semiactive magneto-rheological seat suspension for heavy truck applications

The primary purpose of this paper is to present the theories leading to the development of a semiactive adaptive controller for nonlinear systems. The adaptive algorithm developed in this paper is applied to one class of nonlinear vibration systems, namely semiactive base-excited vibration isolation systems. The algorithm includes the on-line system identification and the adaptation of the control signal. Finally, the stability of the semiactive adaptive system is presented.

Modelling generalisation and power dissipation of flexible-wheel suspension concept for planetary surface vehicles

Flexible-wheel (FW) suspension concept has been regarded to be one of the novel technologies for future planetary surface vehicles (PSVs). This study develops generalised models for fundamental stiffness and damping properties and power consumption characteristics of the FW suspension with and without considering wheel-hub dimensions. Compliance rolling resistance (CRR) coefficient is also defined and derived for the FW suspension. Based on the generalised models and two dimensionless measures, suspension properties are analysed for two FW suspension configurations. The sensitivity analysis is performed to investigate the effects of the design parameters and operating conditions on the CRR and power consumption characteristic of the FW suspension. The modelling generalisation permits analyses of fundamental properties and power consumption characteristics of different FW suspension designs in a uniform and very convenient manner, which would serve as a theoretical foundation for the design of FW suspensions for future PSVs.