Elsevier

Mechatronics

Volume 12, Issue 7, September 2002, Pages 963-973
Mechatronics

Technical Note
MR damper and its application for semi-active control of vehicle suspension system

https://doi.org/10.1016/S0957-4158(01)00032-0Get rights and content

Abstract

In this paper, a semi-active control of vehicle suspension system with magnetorheological (MR) damper is presented. At first a MR damper working in flow mode is designed. Performance testing is done for this damper with INSTRON machine. Then a mathematical model, Bouc–Wen model, is adopted to characterize the performance of the MR damper. With optimization method in MATLAB® and experimental results of MR damper, the coefficients of the model are determined. Finally, a scaled quarter car model is set up including the model of the MR damper and a semi-active control strategy is adopted to control the vibration of suspension system. Simulation results show that with the semi-active control the vibration of suspension system is well controlled.

Introduction

Vibration control of vehicle suspension systems has been a very active subject of research, since it can provide a very good performance for drivers and passengers. For a long time, efforts were done to make the suspension system works in an optimal condition by optimizing the parameters of the suspension system, but for intrinsic limitation of passive suspension system the improvement is effective only in a certain frequency range. Compared with passive suspensions, active suspensions can improve the performance of the suspension system over a wide range of frequency. Semi-active suspensions were proposed in the early 1970s [1], which can be nearly as effective as fully active suspensions in improving ride quality. When the control system fails, the semi-active suspension can still work in passive condition. Compared with active and passive suspension systems, the semi-active suspension system combines the advantages of both active and passive suspensions; i.e. it provides good performance compared with passive suspensions and is economical, safe and does not require either higher-power actuators or a large power supply [2].

In early semi-active suspension, the regulating of the damping force can be achieved by adjusting the orifice area in the oil-filled damper, thus changing the resistance to fluid flow, but the changing of speed is much slow for using of mechanical motion. More recently, the possible applications of electrorheological (ER) and magnetorheological (MR) fluids in the controllable dampers were investigated by many researchers [3], [4]. ER and MR fluids are two kinds of smart materials, which made by mixing fine particles into a liquid with low viscosity. The particles will be formed into chain-like fibrous structures in the presence of a high electric field or a magnetic field. When the electric field strength or the magnetic field strength reaches a certain value, the suspension will be solidified and has high yield stress; conversely, the suspension can be liquiefied once more by removal of the electric field or the magnetic field. The process of change is very quick, less than a few milliseconds, and can be easily controlled. The energy consumption is also very small, only several watts. Both ER and MR fluids were initially developed independently in the 1940s [5], [6]. Initially it was ER fluids that received the most attention, but were eventually found to be not as well suited to most applications as the MR fluids. In their non-activated or “off” state, both MR and ER fluids typically have similar viscosity, but MR fluids exhibit a much greater increase in viscosity, and therefore yield strength, than their electrical counterparts. For ER fluid, the maximum yield stress is about 10 kPa; but for MR fluid, the maximum yield stress can reach about 100 kPa.

The application of ER damper in vibration control of vehicle suspension system was investigated by many researchers [7], [8], [9], [10]. As for MR damper, a research group at Virginia Tech [11] evaluated the response of a MR vehicle suspension under different control schemes of sky-hook, ground-hook, and hybrid semi-active control. They evaluated the performance of semi-active MR suspension for a quarter car model test facility, as well as for a heavy truck on road.

In order to characterize the performance of the MR damper, several models were proposed by many investigators [12], [13], [14]. Spencer et al. [12] proposed a modified Bouc–Wen model to describe the MR damper behavior. This model can accurately capture both the force–displacement and the force–velocity hysteresis loops, which involves as many as 14 parameters. Kamath and Wereley [13] developed an augmented six-parameter model to accurately describe both the force–displacement and the force–velocity hysteresis cycles, which is constructed using a nonlinear combination of linear mechanisms. Li et al. [14] also proposed a nonlinear viscoelastic–plastic model to describe the dynamic behaviors of the MR damper, however this model cannot accurately capture the smooth transition from pre-yield to post-yield region.

In this paper, a MR damper is designed and fabricated first, and then a non-parametric model for the damper is constructed and parameter estimation is done for the MR damper based on the experimental results. The model results are compared with those of experimental results. A half-scale quarter car model is established with the model of the MR damper and the governing equation is obtained for the suspension system. Finally a semi-active control strategy, sky-hook control is adopted to control the vibration of suspension system over random road excitation. Simulation is carried out and results are compared with those of passive suspension. The potential application of MR damper in vehicle suspension system is proved.

Section snippets

Design of MR damper and experimental setup

The prototype MR damper works in flow mode as shown in Fig. 1. The damper is 218 mm long in its extended position, and has ±25 mm stroke. The main cylinder houses a piston, a magnetic circuit, an accumulator and MR fluid. MR 132 LD, which was obtained from Lord Corporation, is used in the damper [15]. The MR fluid valve is contained within the piston and consists of an annular flow channel with 1.5 mm gap. The magnetic field is applied radially across the gap, perpendicular to the direction of

Vehicle suspension model

In this analysis a simple quarter car model with a MR damper being installed in suspension system will be used as shown in Fig. 6. This is a two-degrees-of-freedom system, mass m2 represents the sprung mass while mass m1 means the unsprung mass; k2 represents the stiffness of suspension system and k1 means the stiffness of tire. The property of the MR damper is determined by Eq. (1), Bouc–Wen model. x0 is road excitation. In this study, the road excitation is a stationary random process with

Conclusions

From the experiment investigation for the MR damper, it has been shown that the MR damper has a very broad changeable damping force range under magnetic field and the damping coefficient increases with the electric current, but decreases with excitation amplitude. The MR damper will become saturated as the applied electric current reaches a certain value. Under electric current, the MR damper cannot be treated as a viscous damper, but the property of the MR damper can be described with the

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