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In accordance with the characteristics of the engine structure and of combustion excitation, diesel engines have distinctive noise characteristics in comparison to gasoline engines. In particular, the combustion excitation of the diesel engine produces significant excitation of high frequency noise. This paper describes the influence of the piston pin clearance, bed-plate design, and transmission bell housing structure, using a variety of experimental methods. Design solutions to improve the high frequency noise of diesel engines are also provided, beginning with identification of the root cause for noise generation, through the design modification of the engine structure, to the control of combustion excitation forces.

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.

Key on/off vibration on the vehicles comes from many characteristics of powertrain (P/T) system. It is the combination of source and transfer system. So, vibration can be refined by either source reduction or transfer system redesign. In this study, critical factors affecting the key on/off vibration have been identified. An improved example case will be presented from the source and transfer viewpoint. Engine mounting stiffness has been changed by simulation and experiment. The simulation method has been used to assist in the identification of the key design factors of engine mounting system. By determining the rotation angle of an engine mount that is critical factors to powertrain mode and movement, we have reduced key on/off vibration level. The experiment has been performed using an engine mount sample to build the confidence of simulation model. The test results have shown significant improvement of vehicle vibration in key on/off situation.

This paper presents a series of experimental and analytical works to improve driving surge in a vehicle with CVVT (Continuous Variable Valve Timing) engine. To fully understand the surge mechanism, comprehensive vehicle tests were performed in relations to engine pressure variations, rotational dynamics of driveline, and rigid body dynamics of powertrain. Base on such experimental results, a simple yet reliable model was developed and simulated to optimize driveline. This study found that parameters, such as characteristics of the clutch in a torque converter, roll mode of powertrain, and timing of CVVT, were shown to have noticeable influence on performance of driving surge. A significant improvement in surge vibration was possible by optimizing each of these parameters both through simulations and experiments.

Driveline clunk is perceived as disturbing metallic noise due to severe impact at driveline components such as gear pairs when the engine torque is suddenly applied and transmitted to the driveline system. In this work, experimental method detecting the most contributive gear pair to the clunk generation was investigated and applied to mini van vehicle of front-engine and rear-wheel-drive. Another experimental method, TPA (Transfer Path Analysis), was employed to identify transfer path of the clunk. And then, driveline clunk model was developed using commercial multi-body-dynamics program, ADAMS, in order to further investigate the critical clunk mechanism and potential clunk reduction solutions by performing parameter study.