The Four-cylinder Diesel Engine Crankshaft Torsional Vibration Testing And Analysis

With the improvement of cylinder detection technology based on high pressure common rail diesel engine, and also the pursuit of perfect cylinder detection technology, Torsional vibration has become the main factor which affect the accuracy of cylinder detection of the diesel engine. To study the influence of crankshaft torsional vibration to the accuracy of cylinder detection, torsional vibration measurement and analysis has become indispensable in this study. With the development of society and economy, People's request on automotive NVH has become strict and serious. The effects of torsional vibration to the engine cannot be ignored. Considering the influence of crankshaft torsional vibration to the performance of engine and the security threat to the engine, The past torsional vibration measuring device has been insufficient.With the non-contact measurement method, take the instrument of high precision photoelectric encoder as the crankshaft speed signal generator, Use high frequency sampling method for time measurement of rotating speed signal, resort to LabVIEW software programming for data processing and analysis, Combine with the existing NI hardware platform to design a set of crankshaft torsional vibration measurement and analysis system, meanwhile, a four cylinder high pressure common rail diesel engine were tested.Test procedure consists of data acquisition, data processing, data analysis, and data storage module. Considering the influence of transient speed fluctuation on the torsional vibration measurement results, This procedure is also provided with instantaneous speed monitoring module to Judge whether the torsional vibration waveform is available according to the instantaneous speed waveform. The data acquisition module is based on the combination of hardware and software to realize,Data processing and analysis is based on software programming and mathematical algorithm to realize.Engine test has been done on zero load and full load conditions. After obtaining the time signal, various mathematical transformation, processing, is carried out on the time sequence for instantaneous speed measurement and waveform display on the front end of the crankshaft, Calculation of torsional angle and the mapping of torsional vibration waveform in time domain under various speed, Extraction of each harmonic amplitude and graphics rendering. Analyze the torsional vibration waveform in time domain on full load under different rotating speeds, Results show that the torsional vibration amplitude is mostly within0.4degrees. The spectrum shows that torsional vibration peak value of the engine tested happened at the speed of1780r/min and2400r/min, the peak value is0.17degrees and0.15degrees. Compare the torsional vibration waveform in time domain on zero load and full load condition, Zero load amplitude decreases obviously.Torsional vibration simulation calculation is carried out on the engine researched in this paper by using AVL Designer software. And then, the measured results and the simulation results are compared, the natural frequency of simulation calculation is very close to that of experiment, The test results and Simulation results of torsional vibration in time domain is in the overall trend consistent.