Research Of The Automotive Non-resonant Type Knock Sensor’s Design

Knock sensor is one of the critical auto electronic components that assist the carto fulfill the high standard requirements of good engine body protection, great energyconservation and emissions reduction, optimal fuel economy and reliable dynamicperformance. With the rapid increase of Chinese vehicle amount, engine knock sensorin high quality has great market demand. In this paper, choosing the non-resonantknock sensor as research object, knock sensor’s parameter design, componentselection and production of packaging technology were discussed and analyzed by theway of simulation and test, which laid a firm theoretical basis for the manufacturingof knock sensor.Based on the classical mathematical model of non resonance knock sensor, bymeans of MATLAB software, the structure parameters and output parameters of theknock sensor is comprehensively analyzed, results show that reducing the equivalentmass and increasing the equivalent stiffness can obviously improve the naturalfrequency of the sensor; increasing the equivalent mass, equivalent stiffness andreducing damping coefficient can depress the relative damping coefficient of thesensor; there is a positive linear relationship between the amplitude of chargesensitivity and the longitudinal piezoelectric coefficient, increasing the equivalentstiffness and equivalent at the same ratio mass can more effectively improve thecharge sensitivity amplitude of the sensor; the equivalent stiffness and equivalentmass can more effectively improve the amplitude of charge sensitivity; increasing thephase equivalent mass and damping coefficient will increase the degree of phase lagof the charge sensitivity, but increasing the equivalent stiffness can improved it.In the analysis of the core components in the sensor, piezoelectric ceramic ring,based on the non-resonant knock sensor’s equivalent mechanical model, the methodthat combine ANSYS static piezoelectric simulation and vibration test was applied,the effects that piezoelectric ceramic’s material properties and geometrical size haveon the output voltage of the piezoelectric ceramic ring have been systematic analyzed,also the influences that time, temperature and even distribution have on thepiezoelectric ceramic ring’s properties stability were study in depth, research resultsshow that the output voltage of the piezoelectric ceramic ring will decrease with theincreases of material stiffness and the dielectric coefficient; piezoelectric coefficient d33, d31, d15all affect the output voltage; only geometry thickness that has great effecton the output voltage of piezoelectric ceramics; the properties of piezoelectricceramics will degrade when time passes, tend to be stable finally, but damping withincreases of temperature, deteriorate with increase of heterogeneity.Based on the force analysis and vibration test, the effects that the packagepreload force of knock sensor has on the sensitivity have been researched, resultsshow that non-resonant knock sensor needs a proper preload force to work normally,and the suitable packaging tightening torque value is10N/m.