Research On Piezoresistive Accelerometers Applied To Magnetorheological Damper

Magneto-rheological(MR) dampers are semi- active devices that have many advantages with continuously adjustable damping, fast response, wide dynamic range and low power consumption. So far, MR dampers have been applied in many application fields, such as civil structure, vehicle, healthcare etc. However, there may exit some defects for MR dampers, such as the MR fluid deposition, hardening and leakage or other mechanical and electrical fault. All these can lead to the attenuation performance or even the failure of MR dampers. Therefore, the health of MR damper in operation needs to be monitored. Besides, the semi-active system needs the feedback of the state to realize the control; the premise is to use sensors to obtain real- time dynamic information of the application objects. The real-time dynamic information of the damping system, including damping force, temperature, displacement, velocity and acceleration is needed. Apart from damping force, temperature; the other parameters can be induced to each other by differentiation or integration, so we only need to obtain one parameter. Compared with sensor of velocity and displacement, accelerometer is smaller and has a higher reliability. Generally, RMS of acceleration is regarded as an evaluation to system's safety and comfort and it can largely reflect the health status of the operation of the MR damper. So it is very necessary for MR dampers to develop an output acceleration- monitoring system online.Aiming at the existing shortcomings of semi-active suspension system separated with MR dampers, such as complex wire, high cost and low reliability. A piezoresistive MR damper accelerometer integrated with the piston rod of the MR damper is proposed in this study. Study on working principle and structural design principles of piezoresistive accelerometer. Have an analysis of the performance and the manufacture and the package of it. To test with the MR damper integrated with piezoresistive accelerometers.The main work of this paper is summarized as follows:(1)A comprehensive review of background and significance of the study, research and development of magnetorheological fluid and MR damper, research status of magnetorheological damper sensing technology and piezoresistive accelerometers at domestic and abroad are given in this paper.(2)According to the operating characteristics of the magnetorheological dampers for automobile and the design principle of piezoresistive accelerometer, we design the overall structure and the chip of the piezoresistive accelerometer. The sensor is designed in order to measure dynamic reciprocating stroke of the MR damper which need to achieve the design range, obtain larger sensitivity and natural frequency. According the best damping ratio, the gap between the Cantilever beam and the cover is determined. The size of the sensor chip is determined by the combined method of theory calculation and finite element simulation. The type of the sensor chip, the measuring circuit and the fabrication materials are determined through analytic demonstration. For the design of the chip layout, the crystal orientation, the doping concentration and temperature are critical factors influencing the piezoresistive coefficient. The doping concentration, the arrangement direction, the position, the size, and the bending number of the resistance are acquired according to theoretical analysis and FEM.(3)The analysis of process and package of the MR damper accelerometer based on piezoresistive principle is carried out. The key process and the mask used during production process of MR damping force sensor are designed. Besides, the thermal stress generated by adhesive with different parameters are simulated when the sensor is packaged. All this work lay the foundation for the further processing.(4)The static and dynamic performance index of the MR damping accelerometer based on piezoresistive principle is ana lyzed. By test, Sensitivity, linearity, zero drift, Thermal sensitivity drift, repeatability, hysteresis and the accuracy can be measured. We simplify the magnetorheological damper force sensor for single degree freedom linear system of two order, and derive the calculation of air damping coefficient of the sensor system, then obtain the transfer function of the sensor. At last, we analyze the dynamic performance of the sensor with Matlab. The characteristics of the sensor in time domain and frequency domain are obtained by exerting different excitation.(5)A sensor of new type which can measure the acceleration and the temperature at the same time is proposed. The effect of the temperature is decoupled from the output, as a result, the Thermal sensitivity drift can be compensated. By exploring the theory, the theoretical model is established.(6)To integrate damper with the piezoresistive accelerometer, test it on MTS and suspension of single degree and compare the signal with the standard pizeoelectric accelerometer to ensure its effective for measuring the performance of the system.