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For optimizing the performance of SI engine such as engine torque, fuel consumption, and emissions, various types of system for variable valve timing were developed by many automotive researchers. In this paper, we investigated the relationship between valve timing and intake orifice noise, and suggested how to improve NVH (Noise, Vibration and Harshness) performance as well as engine torque. Some experiments using the engine dynamometer were carried over about 150 different operating conditions. BEM analysis was also conducted in order to calculate acoustic modes of intake system. The results show that the valve timing and overlap of breathing systems have influence on NVH behavior, especially intake orifice noise over whole range of operating conditions. Valve timing and overlap of intake and exhaust valve were optimized in the view of sound quality as well as overall noise level.

Gear rattle is generated basically due to the impacts of unloaded gear pairs in transmission. The rattle noise level is determined by two main factors, excitation level at transmission input shaft and rattle sensitivity of the transmission at that excitation level. In this work, (1) the transmission rattle sensitivity was measured and investigated (2) torsional vibration model of driveline system was developed to estimate the speed fluctuation at the transmission input shaft and to find some rattle improvement potential by tuning driveline components so that the speed fluctuation be minimized.

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 crankshaft torsional vibration angle is measured from a running engine, using a toothed wheel attached to the front of crankshaft. The torsional vibration stress near the node of torsional vibration is also measured by using strain gages mounted on the journal of crankshaft in a running engine. A theoretical analysis of torsional vibration of crankshaft is performed with a simplified model subject to the excitation torque. The comparison between the theoretical and experimental results shows that the idealized approach is applicable to predict the torsional vibration of crankshaft. It is found that the torsional vibration of crankshaft is mainly dependent upon the characteristics of rubber damper, i.e., the stiffness and damping coefficient of rubber, and the inertia of damper ring. It is recognized that the rubber damper should be carefully selected considering the variation in the dynamic characteristics of rubber.