The Research On Miniaturized Charge Amplifier Applied To Engine Cylinder Pressure Measurement

The development and progress of modern technology are inseparable from accurate measurement methods.First of all,we need to obtain accurate data,so that we can take corresponding measures.For the pressure signal in the engine cylinder,we need to use piezoelectric materials or other sensitive components as the main measurement tool.When measuring,the piezoelectric sensor will generate a charge proportional to the cylinder pressure,however,this charge signal is very weak,and it needs to be converted by a secondary instrument such as a charge amplifier.Due to the research needs of my research group on the combustion analysis system,this article has designed a small charge amplifier with high measurement accuracy,the maximum measurement range can reach 240 bar.At the same time,this charge amplifier has intelligent control and communication functions,besides it is not high cost.This charge amplifier can be used inside the vehiclecan or use it with a combustion analysis system in the laboratory,monitoring the pressure in the engine cylinder for real-time analysis of the combustion process.The research contents and main conclusions of this article are as follows:(1)The piezoelectric effect and the properties of various types of piezoelectric materials are introduced.Based on the characteristics of the engine cylinder pressure signal,the formation principle and calculation method of the cylinder pressure curve are analyzed;(2)Design of miniaturized charge amplifier,including pre-charge conversion circuit,normalization circuit,low-pass filter circuit,overload indication circuit,and MC9S12XEP100 microcontroller as the control chip,using microcontroller interruption,serial communication and host computer software Etc.,so that the charge amplifier has an intelligent control function,leaving an RS232 interface to facilitate the establishment of communication with other embedded systems or computers;(3)Draw the schematic diagram,PCB layout and wiring according to the circuit specifications,avoid circuit violations,reduce the stray capacitance of the circuit board,and finally complete the physical production;(4)Build an engine test bench,measure the cylinder pressure data on a four-cylinder gasoline engine,compare the actual effects of different feedback capacitor and feedback resistor combinations,and finally analyze and test the measured data of the AVL charge amplifier as the performance evaluation standard.The results show that the designed charge amplifier has good accuracy,meets the design requirements,and reduces the size of the charge amplifier while measuring the engine cylinder pressure accurately.