An experimental study of temperature effect on material parameters of PZT ceramic ring used in knock sensors

This article describes the experimental research of a ring of PZT ceramics used in knock sensors. The main aim of the paper is to investigate the temperature effects related to the parameters of piezoelectric materials and to characterize the influence and changes exerted by these parameters on the properties of knock sensors. The purpose of the research is to facilitate the fault diagnosis of an active piezoelectric element, thus enabling the self-diagnostics of a sensor in normal engine operation. Such self-diagnostics is necessary to prevent engine damage and can be performed via online health monitoring of knock sensors. The properties of the material forming the active element based on PZT ceramics are significantly affected by temperature changes. In the paper, the temperature deviations are compared with the impedance and phase characteristics in the working temperature range of the engine and also related to different types of sensor damage. Based on the material defects (cracks, fissures, fractures) and changes in the material coefficients connected with the frequency characteristics, we can assess the degree of the damage in the examined sensors and evaluate the quality of the inside piezoelement. The results of the realized experimental comparison are shown within the paper. A series of experiments was conducted on a knock sensor, in which we used piezoelectric elements with a differing number of cracks. The experiments demonstrate that the proposed methods can be used for the above-mentioned purpose and are applicable to eliminate any possible damage of an automotive engine caused by vibrations.