Noise Reduction and Sound Quality Improvement of Valve Train in V6 Gasoline Engine

This paper presents an advanced technique for noise reduction and sound quality analysis in direct-acting type of valve train system. Mechanical Lash Adjust (MLA) system has lower friction loss and simpler and lighter structure in comparison with Hydraulic Lash Adjust (HLA). Despite of such advantages, MLA system has a weak point which generates harsh impulsive noise whenever cam comes into contact or detaches suddenly from tappet during the valve operation in the ramp area. A sound quality analysis technique was used to analyze the detail noise and vibration characteristics during valve opening and closing operation respectively. This paper describes a procedure and advanced technique to identify noise sources and its generation mechanism by analyzing measured data taken from direct-acting valve train system. Subsequently, an optimum cam profile was redesigned and used in new Hyundai-motor V6 engine. The results show 1) Sound quality analysis and transfer path analysis were done for noise source identification and generation mechanism was accomplished. 2) Noise sources and noise effect factors are classified according to the results of measurements and analysis. 3) From the result of improvement of cam profile based on optimized factors (velocity, acceleration and jerk) in the ramp area, cam profile and clearances were optimized and chatter vibration of tappet bore was improved. 4) Not only noise level was reduced significantly but also sound quality was improved without great loss of engine performance. 5) Sound quality values were calculated, taking advantage of the quantitative analysis.