Research on mechanism diagnosis of an idling abnormal noise of automobile engine

Abstract When a vehicle is under the idle condition, the direct engine noise and structure-radiated noise caused by engine vibration are perceived by passengers more easily than the vehicle is in moving due to the absence of road and wind noises. These abnormal noises have become the most annoying sound of passenger vehicles. However, there are very few researches on the mechanism of how such noises were generated. In this paper, a passenger vehicle equipped with an inline four-cylinder turbocharged gasoline engine was used to diagnose the abnormal noise under idle condition. The experimental studies with replacement of some engine parts and adjustment of electric control parameters of the valve train showed that the influence of variable camshaft timing (VCT) system on the idling abnormal noise was significant, and increasing the angle of the VCT system of the intake camshaft can greatly reduce the abnormal noise. In order to reveal the mechanism of idling abnormal noise, the oil pressure inside the camshaft phaser of the VCT system was further measured with the vibration and noise signals being simultaneously acquired. The vibration signal characterizing abnormal noise was extracted by the algorithm of dichotomy-based variational mode decomposition. Based on the comprehensive angle domain analyses of the oil pressure of the VCT system, the vibration of the cylinder head and the rotating speed of camshaft and crankshaft, and verification with the experimental data, it was finally concluded that the idling abnormal noise was caused by the impact of the rotor and stator inside the camshaft phaser of the VCT system. The result of this research can also be applied as guideline for diagnosis of other abnormal noises of vehicles.