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This paper investigated an abnormal noise under idle condition and analyzed the mechanism of the noise based on the results of experiments and dynamics simulations. It is confirmed that knocking inside variable valve timing phaser is the source of the abnormal noise. The results of experiments show that half-order rhythm of the vibration and noise components around 1000 and 2100 Hz are different from the other dominant components, which is possible to involve the abnormal noise. Numerical analyses are conducted to simulate the process of the abnormal noise. It is found that the thickness of the blades of the variable valve timing rotor has significant influence on the abnormal noise. The simulation implies that increasing the thickness of the rotor blades will decrease the abnormal noise. When the thickness increases to 3.0 mm, the acoustic frequencies within 1000–1200 Hz have an average drop of 3.7 dB(A), and the acoustic frequencies within 2000–2200 Hz have an average drop of 12.5 dB(A). The results of verification experiments show that the amplitudes of the abnormal noise have obvious reduction, and the abnormal noise is basically eliminated under subjective evaluation.

Investigation and optimization of valve train abnormal noise under idle condition