The Study On Measurement Errors And Correction Of Torsional Vibration Of Rotational Machinery’s Shafting

Rotating parts such as crankshaft, transmission shaft and power transmission shaft are important in vehicle’s driveline, and the torsional vibration exists extensively in these parts when a vehicle is running. Due to its harmful effects, it’s really important to measure the torsional vibration accurately. The frequency modulation demodulation method is a kind of the torsional vibration analytical method, whose extraction accuracy of the torsional vibration is directly affected by the parameters setting of the extraction procedure. It’s necessary to analyze the matters that need to pay attentions in the whole testing process to improve the accuracy of this method. Another testing method is the instantaneous speed filtering method. During the measurement of instantaneous rotational speed, the eccentricity of encoder or the asymmetrical of the code line in the glue joint of the code strip would bring great errors to the result of the torsional vibration. It is extremely important to study the cause of the error and find the error correction method for improving the measure accuracy of torsional vibration. The main contents of the paper are as follows:(1) The principle that the eccentricity of encoder will bring error to the testing result are studied. The relationship between the actual speed and the measured speed from eccentric encoder is theoretical deduced. The effectiveness of the theoretical derivation are verified by the simulation and experimental result. In the simulation result, the biggest relative error between the directly calculated value and the value that without regard to the term of high eccentricity ratio orders is 2.83%, experimental results shows that the biggest error is 5.6%. Based on the duduced relationship, a correction method which using several sensors to measure the torsional vibration in the same time is proposed, and the effectiveness of this method are also verified by simulation. The simulation result indicate that the error between the corrected value and the theoretical value is less than 1% when using 3 sensors at the same time. The result can meet the engineering requirement.(2) The error causing by the asymmetrical of the new code line in the glue joint of the code strip is studied, and a correction method called twice correct to improve the accuracy of the testing result is figured out. The effectiveness of this method is verified by the simulation and experimental result. In the simulation, the biggest errors between the theoretical value and calculated value that without correction, with once correction and with twice correction are 69.11%, 9% and 5.63%, respectively. experimental results shows that the biggest errors between the theoretical value and calculated value that without correction, with once correction and with twice correction are 530%,151% and 4.83%, respectively. Both the simulation results and experimental results indicate that the measure precision of torsional vibration after twice correction is improved obviously. This method can meet the need in engineering applications.