Research On SAW Torque Sensor For EPS

In recent years,the automotive industry has gradually developed towards the direction of safety,intelligence and emission reduction.Electric Power Steering(EPS)has become the preferred steering system for automobiles because of its simple structure,good driving feel,high space efficiency and environmental protection.In electric power steering system,steering torque is a very important parameter,so the better the performance of sensors used to measure steering torque,the better the response speed and safety performance of EPS.Surface Acoustic Wave(SAW)products have the characteristics of wireless passivity,good perception,small package and strong anti-environmental interference.In this paper,a wireless passive SAW torque sensor is proposed,which combines the advantages of EPS system and SAW products.Firstly,the formula is deduced based on SAW torque sensor detection theory and rotation axis measurement theory,and the corresponding relationship between the resonant frequency of SAW devices and the change of the torque of EPS system is established to determine the feasibility of measuring the torque.The spindle of EPS system is a very important part.Firstly,the structure and material of the spindle are determined,and the stress and strain of the spindle are simulated by COMSOL software to verify the reliability of the spindle.Resonator is the core component of SAW torque sensor.When designing the resonator,it is necessary to calculate the central frequency,IDT interdigital logarithm and acoustic aperture of the resonator,determine the final parameters of the two resonators.Then,according to the modal coupling theory,the matrix models of each part of the SAW resonator are established,and the frequency response of the resonator is verified by MATLAB simulation.The performance of antenna affects the accuracy of wireless measurement.Firstly,the structure size of antenna is calculated theoretically.Then,the 437MHz microstrip antenna model is established and optimized by HFSS antenna simulation software,and the final size of microstrip antenna is determined.Aiming at the problem of frequency offset and error of traditional M-Rife frequency estimation algorithm in frequency estimation of echo signal,a new algorithm based on Welch and Iterative interpolation based(IIN)algorithm is proposed to optimize M-Rife algorithm,and the new algorithm is simulated and validated in frequency estimation and residual by using MATLAB.Finally,the feasibility test of SAW torque sensor is carried out,and the specific sensor structure is designed,and the actual production is carried out.Feasibility test is divided into two parts.The first part is wire test and the second part is wireless test.Through feasibility test and analysis of output data,the feasibility of wireless passive SAW torque sensor in EPS application is proved.