Research On SAW Torque Sensor For EPS System

As the automotive field is evolving toward a more environmentally friendly and safer trend in recent years,auto parts which is purely mechanical structure have also gradually transformed to mechatronics.More and more functional units have started to use electronic control devices to work.Among the functional units,as an important function module and a direct operation unit in a car system,the steering module has a direct impact on the driving feeling of a car.Compared with the traditional mechanical hydraulic steering assist mode,the EPS system has great controllability and environmental protection,includes the light control with low speed,weight with high speed,simpler structure and higher space utilization,fuel savings and etc.In the electric power steering system,as an important functional component,the performance of torque sensor is directly related to the working status and safety of the EPS system.Based on the EPS system and the Surface Acoustic Wave(SAW)technology,a surface acoustic wave torque sensor suitable for EPS system is studied in this paper.The paper introduces the working principle of the SAW torque sensor in EPS system in detail,and analyzes the working principle,advantages,disadvantages of the existing torque sensor in the EPS field.The technical principle and development trend of SAW torque sensor are expounded.Starting from the most basic theory of positive and negative piezoelectric effect,the structure and function of interdigital transducer and working principle of resonator,the whole surface acoustic wave resonance measurement system is designed SAW resonator(SAW resonator,SAWR)structure and materials.specified the theoretical feasibility of torque measurement.By analyzing the theory of solid mechanics and measuring principle of shaft torque,the paste form of piezoelectric crystal of SAW torque sensor is studied,and the design of torsion bar and the selection of torsion bar material are also carried out.Using COMSOL Multiphysics finite element simulation software,the torsion bar was subjected to a separate stress analysis.The whole system mathematical model of torsion bar and piezoelectric crystal was established according to the design of the piezoelectric crystal paste form,and then subjected to force simulation and fatigue analysis Finally,according to the simulation results to determine the piezoelectric crystal paste form.Papers on descripts the theoretical of the wireless and passive characteristics of SAW sensor,achieve the main echo of the signal frequency estimation algorithm.Based on the Welch algorithm and the M-Rife algorithm,an improved M-Rife algorithm based on Quinn algorithm is proposed.The feasibility of the algorithm is analyzed by using Matlab simulation software to improve the signal processing accuracy and reduce the design difficulty of the hardware circuit.The conversion circuit module was completed by using Multisim circuit simulation software,including the oscillation circuit,low-pass filter circuit,band-pass filter circuit,mixer circuit and plastic circuit design and simulation.Altium Designer software was used to draw the PCB of the designed circuit and make the physical circuit board of the conversion circuit.The function of the conversion circuit was verified by using the signal generator and the oscilloscope.Using Altera DE2 development board to achieve the final detection of the signal frequency.This paper applies the SAW torque sensor to the EPS system for the first time,which provides a theoretical basis for the application of SAW torque sensor in the field of small-range torque and fast signal acquisition.At the same time,it provides a new method for the torque collection method of the EPS system,which plays a key role in improving the performance of the EPS,and promotes its development toward a more stable and safer direction.