Pressure Sensor Module for High Temperature,High Pressure, and Quick Response 2018-01-0759
According to the advance of engine control development, demands for direct sensing of physical quantity have been growing. Regarding pressure sensing, key properties for direct sensing are robustness against high temperature and pressure, and response time in addition to accuracy. In this work, a pressure sensor module with these key properties was developed. First of all, a piezoelectric device was selected as a suitable sensing principle for the required properties because of its thermally stable piezoelectric effect and potential for simple installation structure. Regarding robustness against temperature, the sensor module was designed to form thermal isolation layer with outer housing which is optimized according to its application. Regarding robustness against pressure and response time, breakage of the piezoelectric element is the main technical issue. Based on FEM analysis, a bounce of piezoelectric element in the sensor structure was proven to be the main cause of the element breakage. To prevent piezoelectric element bounce, a pre-load design method was developed as a countermeasure. Regarding high accuracy, the piezoelectric sensor module was modeled as an equivalent spring model. Based on this model, a degradation mechanism of the sensor accuracy was established by converting the sensor component degradation to spring constant changes. Then the contact state between each component was proven to be the important factor for sensor accuracy. Finally, a cylinder pressure sensor was designed as an application example of this pressure sensor module. As a result of engine bench tests, the potential of the module to measure high frequency pressure under high temperature was confirmed.