Research On Noise Source Identification And Vibration Characteristics Of Timing Chain System For Diesel Engine

As an important component of engine, the noise and vibration characteristics of timing chain system directly affect the reliability and service life of engine. As a result the noise and vibration characteristics of timing chain system have become concerns for carmakers. A noise and vibration problem of4D20type diesel engine was listed in this paper to explain how to establish a perfect vibration and noise source identification and noise value prediction system, which contains test methods, dynamic analysis and noise value prediction. This work was supported by Science and Technology Major Planning Project of Jilin Province, China (No.20126003), and was also supported Natural Science Foundation of Jilin Province, China (No.20140101085JC). The research results have important theoretical value and engineering significance for noise and vibration problems of timing chain system.The noise and vibration research status of engine and timing chain system at home and abroad were summarized in this paper. And the generation mechanism of timing chain noise and vibration were introduced. Noise and vibration problems of4D20type diesel engine were listed as an example to explain noise and vibration identification methods. Firstly, One meter noise test had been done to point out engine front end was the main source of noise. Then near-field sound intensity method and near-field acoustic holography technique were employed to identify that chain drive system was the noise and vibration source, especially in2kHz frequency at low rotational velocity. In addition, vibration testing methods were used to verify the timing chain cover was the noise and vibration source of diesel engine.According to the theory of multibody dynamics, a3D dynamic analysis model was established by RecurDyn software. Consider the timing chain system dynamic response of crankshaft speed fluctuations and camshaft torque fluctuations, dynamic analysis of timing chain system at1000rpm and2000rpm were done respectively. Analysis results show hydraulic tensioner did not agree well with the bush roller chain timing drive system was the main reason caused huge noise and vibration, especially in2000Hz frequency. With the enhancement of damping characteristic for hydraulic tensioner, the displacement fluctuation of plunger has decrease and the excitation magnitude around2000Hz reduced either, the vibration of timing cover should be cut down.Dynamic analysis data were used as boundary condition to study the vibration characteristics of timing chain system, according to chain tension force rule, the nonlinear statics analysis, prestressed modal analysis and harmonic response analysis were investigated to discussing the modal frequency and modal shapes, studying vibration characteristic of timing chain system, explaining reasons of severe vibration. Vibration response characteristics of the system were compared before and after tensioner optimization to evaluate tensioner’s influence on the system vibration characteristics.A complete prediction system of timing chain radiated noise was established. Radiated sound power curve was calculated, radiated noise value and radiated noise contours at2000Hz-2400Hz frequency were investigated in detail, the calculate data show that radiated noise value reduced5dBA after the tensioner optimization, infer damping characteristics of tensioner has huge influence on noise and vibration characteristics of timing chain system.The reach results of this paper help improving vibration noise source identification, noise value prediction and evaluation system of timing chain system. Accelerates noise and vibration technology development, enhance the performance quality of domestic timing chain system.