Research Of Portable Engine Speed Measurement System Based On Vibration Signal

Accurate measurement of engine speed is an important link in vehicle inspection and maintenance,and provides key data support for vehicle fault diagnosis and analysis.The engine speed measurement method based on vibration analysis has the advantages of convenient measurement and non-intrusion.It is an ideal solution to replace the traditional intrusive speed measurement method.However,existing speed measurement instruments based on vibration analysis have inaccurate main frequency recognition and poor anti-noise performance.And other issues.To this end,this paper conducts research on vibration signal fundamental frequency extraction and correction algorithms,software and hardware system design,etc.,designs a portable engine speed measurement system based on vibration analysis,builds a portable engine speed measurement instrument prototype and completes the experimental test,the main work as follows:1、Designed an engine speed measurement scheme based on vibration analysis.Based on the requirements of the portable engine speed measurement system for high accuracy,non-intrusion,small portability,and independent / networked work,the common engine speed measurement methods were analyzed and compared.Based on the principle of vibration analysis engine speed measurement method,an overall implementation scheme of a portable engine speed measurement system based on vibration analysis is proposed.2 、 A vibration signal fundamental frequency extraction algorithm combining energy centroid method and Non-Harmonic Fourier Analysis(NHFA)is proposed.First,the energy centroid method is used to roughly estimate the fundamental frequency of the signal,and then NHFA is used at the fundamental frequency sweeping around with fixed steps to achieve accurate estimation of the fundamental frequency of the signal.The performance of the energy centroid method,chirp Z-transform method,AR spectrum estimation method and the algorithm proposed in this paper is analyzed through algorithm simulation.The results show that the accuracy of the proposed algorithm is superior to the rest of the algorithms,and the error value is within 0.15% in the range of 20 Hz to 100 Hz,Measurement error is within 0.5% in 5d B noise environment.3、A portable engine speed measurement system based on vibration analysis was built,a low-noise signal acquisition and conditioning circuit was designed,and a signal fundamental frequency extraction algorithm and program based on a digital signal processor(DSP)were designed and implemented.The functions such as accurate measurement of engine speed and wireless data transmission have designed the fault diagnosis and analysis software based on LabVIEW,and realized the functions of engine working state judgment and misfire diagnosis.4、Complete the engine speed measurement experiment and preliminary fault diagnosis analysis experiment.The experimental results show that the developed engine speed measuring instrument has a speed measurement error of less than 2%under uniform speed and variable operating conditions,and completes the calculation of external engine characteristic parameters and Measurement experiments such as curve drawing and fault diagnosis of missing cylinder and misfire.