Xian-Xu Bai

Magnetorheological Damper Utilizing an Inner Bypass for Ground Vehicle Suspensions

This study presents the design, fabrication, and test of a magnetorheological (MR) damper utilizing an inner bypass that can simultaneously produce large dynamic range (i.e., ratio of field-on to field-off stroking load) and low field-off stroking load at high piston velocity. These two damper properties, large dynamic range and low field-off stroking load, are critical to achieving high performance in ground vehicle suspensions. The MR damper is comprised of a pair of concentric tubes, a movable piston-shaft arrangement, and an annular MR fluid flow gap between the concentric tubes. The inner tube serves as the piston guide, the inner surface of the annular flow gap, and the bobbin for the five electromagnetic coils used in this design. The outer tube serves as the flux return and the outer surface of the annular flow gap. The annular flow gap is an inner bypass annular valve where the rheology of the MR fluids, and hence the stroking load of the damper, is controlled. The MR damper is analyzed using a Bingham-plastic nonlinear fluid mechanics model. To experimentally validate the analysis of the MR damper with the inner bypass, and to illustrate its advantages over the MR damper with the conventional annular orifice, the prototype damper is tested in terms of controllable damping force or stroking load, dynamic range, and equivalent damping as a function of shaft/piston velocity.

An integrated relative displacement self-sensing magnetorheological damper: prototyping and testing

In this paper, an integrated relative displacement self-sensing magnetorheological damper (IRDSMRD) and the corresponding electronic system to realize the integrated relative displacement sensing and controllable damping, including the relative displacement modulator/demodulator, circuit for superposing the carrier signal for the integrated relative displacement sensor (IRDS) on the exciting current from the controllable current driver for the controllable damping and controllable current driver are developed and tested. In the developed IRDSMRD, the exciting coil is energized by the current from the controllable current driver, on which the carrier signal for the IRDS is superposed by the superposition circuit. The amplitude modulation of the carrier signal for the IRDS by the relative displacement between the piston and cylinder of the IRDSMRD and the magnetization of the MR fluid are realized through the frequency division multiplexing of the exciting coil for both the IRDS and the MR damper and the relative displacement is accessed by demodulating the induced harmonic voltage from the induction coil of the IRDSMRD by the demodulator. The characteristics of the developed IRDSMRD, including the linearity, sensitivity and hysteresis error of the IRDS and the controllable damping force are tested on the established experimental setup based on the MTS 849 shock absorber test system and the real time simulation system. The testing results indicate that the developed IRDSMRD can not only achieve the integration of the relative displacement sensing capability but also possesses good performance of the relative displacement sensing of the IRDS and the large controllable damping force range. In addition, the performance of the IRDS will not be affected by the exciting current within a certain range and the damping force will not be degraded by the carrier signal for the IRDS. The realized principle and technology of the IRDSMRD lay a foundation for reducing the commercializing cost of MR dampers.

A magnetorheological damper with an integrated self-powered displacement sensor

In this paper, aiming at self-powering the integrated relative displacement sensor (IRDS) and the corresponding electronic system of an integrated relative displacement self-sensing magnetorheological (MR) damper (IRDSMRD) based semi-active system, the principle of an MR damper with an integrated self-powered displacement sensor is proposed and realized. The prototype of the MR damper with an integrated self-powered displacement sensor is designed and fabricated. In this MR damper, a coil evenly wound on the piston simultaneously acts as the exciting coil for the MR fluid and the IRDS, while a coil evenly wound on the cylinder simultaneously acts as the induction coil (i.e., pick-up coil) for the IRDS and the pick-up coil for the energy harvesting device. On one hand, both the MR fluid and the IRDS are simultaneously magnetized by a mixed signal, in which the carrier signal for the IRDS and the current for the MR fluid with different frequencies are superposed by a superposition circuit. That is, the exciting coil is frequency division multiplexed. On the other hand, when the exciting coil of the MR damper is energized by the carrier signal for the IRDS and the current for the MR fluid, the induced voltage in the pick-up coil not only can be harvested by the energy harvesting circuit to power the IRDS and the corresponding electronic system of the IRDSMRD, but also can be demodulated to obtain the relative displacement of the piston relative to the cylinder. That is, the induction coil for the IRDS and the pick-up coil for the energy harvesting device are functionally multiplexed. The characteristics of the fabricated MR damper with an integrated self-powered displacement sensor, including the energy harvested by the pick-up coil, the relative displacement sensed by the IRDS, and the controllable damping force, are modeled, analyzed, and tested. The feasibility and capability of the proposed principle are validated theoretically and experimentally.

Pareto Optimization-Based Tradeoff Between the Damping Force and the Sensed Relative Displacement of a Self-sensing Magnetorheological Damper

In order to make the best compromise between the damping force and the linearity of the integrated relative displacement sensor (IRDS) of an integrated relative displacement self-sensing magnetorheological damper (IRDSMRD), a Pareto optimization-based method, which optimizes the key structural parameters by taking the damping force and the linearity of the IRDS of the IRDSMRD as the objective functions, is proposed and realized in this article. The Pareto front, representing the best tradeoff between the damping force and the linearity of the IRDS of the IRDSMRD, is obtained by considering that the maximum magnetomotive force applied to the exciting coil of the IRDSMRD is constant. Three IRDSMRDs with different piston modules, which are determined according to the Pareto optimal solutions, are developed and tested. The research results indicate that every point on the Pareto front is an optimal solution that compromises the damping force and the linearity of the IRDS of the IRDSMRD and the optimal damping force of the IRDSMRD with a certain linearity of the IRDS as well as the optimal linearity of the IRDS with a certain damping force can be determined according to the Pareto front for a specific application.

A fail-safe magnetorheological energy absorber for shock and vibration isolation

Magnetorheological (MR) energy absorbers (EAs) are an effective adaptive EA technology with which to maximize shock and vibration isolation. However, to realize maximum performance of the semi-active control system, the off-state (i.e., field off) stroking load of the MREA must be minimized at all speeds, and the dynamic range of the MREA must be maximized at high speed. This study presents a fail-safe MREA (MREA-FS) concept that, can produce a greater dynamic range at all piston speeds. A bias damping force is generated in the MREA-FS using permanent magnetic fields, which enables fail-safe behavior in the case of power failure. To investigate the feasibility and capability of the MREA-FS in the context of the semi-active control systems, a single-degree-of-freedom base excited rigid payload is mathematically constructed and simulated with skyhook control.

Maximizing semi-active vibration isolation utilizing a magnetorheological damper with an inner bypass configuration

A single-degree-of-freedom (SDOF) semi-active vibration control system based on a magnetorheological (MR) damper with an inner bypass is investigated in this paper. The MR damper employing a pair of concentric tubes, between which the key structure, i.e., the inner bypass, is formed and MR fluids are energized, is designed to provide large dynamic range (i.e., ratio of field-on damping force to field-off damping force) and damping force range. The damping force performance of the MR damper is modeled using phenomenological model and verified by the experimental tests. In order to assess its feasibility and capability in vibration control systems, the mathematical model of a SDOF semi-active vibration control system based on the MR damper and skyhook control strategy is established. Using an MTS 244 hydraulic vibration exciter system and a dSPACE DS1103 real-time simulation system, experimental study for the SDOF semi-active vibration control system is also conducted. Simulation results are compared to experimental measurements.

Integrated semi-active seat suspension for both longitudinal and vertical vibration isolation

“Functional integration” is to integrate two or multiple systems or mechanisms that are independent with each other and to realize the two or multiple functions using only one actuation system. Maximization of engineering applications of actuation systems could be achieved through the use of the “functional integration” concept-based structural design. In this article, an integrated semi-active seat suspension, mainly composed of a switching mechanism, a transmission amplification mechanism, and a damping force- or torque-controllable rotary magnetorheological (MR) damper working in pure shear mode, for both longitudinal and vertical vibration attenuation, is proposed, designed, and fabricated. The switching mechanism employs the parallelogram frames as a motion guide which keeps the seat moving longitudinally and vertically. Both longitudinal and vertical motions are transformed into a reciprocating rotary motion that is transmitted to the rotary MR damper after an amplification by a gear mechanism. The torque generated by the MR damper can be tuned by adapting the applied current in real time, and hence, effective two-dimensional vibration control of the seat could be realized. The mathematical model of the semi-active seat suspension system is established, and vibration isolation performance of the system is simulated and analyzed. Based on the established experimental test rig, the prototype of the semi-active seat suspension system is tested, and the results of the mathematical model and the experimental test are compared.

A magneto-rheological fluid mount featuring squeeze mode: analysis and testing

This paper presents a mathematical model for a new semi-active vehicle engine mount utilizing magneto-rheological (MR) fluids in squeeze mode (MR mount in short) and validates the model by comparing analysis results with experimental tests. The proposed MR mount is mainly comprised of a frame for installation, a main rubber, a squeeze plate and a bobbin for coil winding. When the magnetic fields on, MR effect occurs in the upper gap between the squeeze plate and the bobbin, and the dynamic stiffness can be controlled by tuning the applied currents. Employing Bingham model and flow properties between parallel plates of MR fluids, a mathematical model for the squeeze type of MR mount is formulated with consideration of the fluid inertia, MR effect and hysteresis property. The field-dependent dynamic stiffness of the MR mount is then analyzed using the established mathematical model. Subsequently, in order to validate the mathematical model, an appropriate size of MR mount is fabricated and tested. The field-dependent force and dynamic stiffness of the proposed MR mount are evaluated and compared between the model and experimental tests in both time and frequency domains to verify the model efficiency. In addition, it is shown that both the damping property and the stiffness property of the proposed MR mount can be simultaneously controlled.

Magnetorheological fluid behavior in high-frequency oscillatory squeeze mode: Experimental tests and modelling

This paper presents an experimental investigation on the behavior of magnetorheological (MR)fluids in high-frequency oscillatory squeeze mode and proposes a mathematical model to reveal the MR mechanism. A specific MR squeeze structure avoiding the cavitationeffect is designed for the experimental tests. The magnetic field- and gap distance-dependent damping force of the MR squeeze structure is presented and compared with the dramatically large damping force under quasi-static excitations, a moderate damping force is observed at high frequencies. Subsequently, in order to interpret the behavior of MR fluids at high frequencies, employing the continuum media theory, a mathematical model is established with consideration of the fluid inertia and hysteresis property. The damping force comparison between the model and experimental tests indicates that in high-frequency oscillatory squeeze mode, the squeeze-strengthen effect does not work and the shear yield stress can be applied well to characterize the flow property of MR fluids. In addition, the hysteresis property has a significant influence on the damping performance.

Principle, modeling, and control of a magnetorheological elastomer dynamic vibration absorber for powertrain mount systems of automobiles

This article proposes and validates the principle of a new magnetorheological elastomer (MRE) dynamic vibration absorber (DVA) for powertrain mount systems of automobiles. The MRE DVA consists of a vibration absorption unit and a passive vibration isolation unit. The vibration absorption unit composed of a magnetic conductor, a shearing sleeve, a bobbin core, an electromagnetic coil, and a circular cylindrical MRE is utilized to absorb the vibration energy, and the passive vibration isolation unit is used to support the powertrain. The finite element method is employed to validate the electromagnetic circuit of the MRE DVA and obtain the electromagnetic characteristics. The theoretical frequency-shift principle is analyzed via the established constitutive equations of the circular cylindrical MRE In order to demonstrate how the parameters of the MRE influence the vibration attenuation performance, the MRE DVA is applied to a powertrain mount system to replace the conventional passive mount. The frequency-shift property of the vibration absorption unit and the vibration attenuation performance of the MRE DVA on the powertrain mount system are experimentally tested. To validate and improve the vibration attenuation performance for the semi-active powertrain mount systems, an optimal variable step algorithm is proposed for the MRE DVA and numerical experiments are carried out.