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In this paper, the vibration and noise reduction technology for diesel common rail injection system is studied. The NV problems of the injection system come typically from mechanical contacts (injector needle, pump) or fluid pulsations. They are exciting the injection system, which translates the excitations to the engine through the connection points. But it's not easy to identify the characteristic of internal excitation force exactly, so the simulation model based measurement test is considered at here. In order to predict the vibrations due to excitation related with the injection system of the diesel engine, the 1D/3D simulation models are used and the necessary dynamic tests, which are needed to create and validate the models, are done in the test bench.

A comprehensive investigation was carried out in order to develop the idle sound quality for diesel V6 engine when the engine development process is applied to power-train system, which included new 8-speed automatic transmission for breaking down the noise contribution between the mechanical excitation and the combustion excitation. First of all, the improvement of dynamic characteristic can be achieved during the early stages of the engine development process using experimental modal analysis (EMA) & the robust design of each engine functional system. In addition, the engine structural attenuation (SA) is enhanced such that the radiated combustion noise of the engine can be maintained at a target level even with an increased combustion excitation. It was found that the engine system has better parts and worse parts in frequency range throughout the SA analysis. It is important that weak points in the system should be optimized.

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.

Hyundai has developed a brand new 3.0L V6 diesel engine for luxury vehicle with electronic VGT, piezo injector and bedplate block structure. In addition to challenging targets for fuel consumption and emission levels, engine specifications were focused on performance and NVH. This paper presents the detailed process of reinforcing engine components such as block, cylinder head and oil pan in view of low sound pressure and high quality. Generally, the fast reaction speed of piezo injector can improve the emission, but it usually causes injector noise. We reduced this noise through developing new ECU logic and isolating this part with noise reduction foam. In addition to that, we could reduce the combustion noise using DoE method for the optimization of injection parameters considering the emission and fuel economy. As a result of these attempts, 3∼4dBA of overall sound pressure level from engine itself could be reduced without any loss of fuel economy and power characteristics.

This paper presents practical work on the reduction of gear whine noise. In order to identify the source of the gear whine noise, transfer paths are searched and analyzed by operational deflection shape analysis and experimental modal analysis. It was found that gear whine noise has an air-borne noise path instead of structure-borne noise path. The main sources of air- borne noise were the two global modes caused by the resonance of an axle system. These modes created a vibro-acoustic noise problem. Vibro-acoustic noise can be reduced by controlling the vibration of the noise source. The vibration of noise source is controlled by the modification of structure to avoid the resonance or to reduce the excitation force. In the study, the excitation force of the axle system is attenuated by changing the tooth profile of the hypoid gear. The modification of the tooth profile yields a reduction of transmission error, which is correlated to the gear whine noise.

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.

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.

This paper presents NVH optimization procedure for the 2.5L I4 common rail diesel engine. Distinctive design feature is the low noise timing chain system which realized by chain case modification and meshing noise improvement. The former was effective for reduction of sound level and the later was for sound quality. Combustion excitation force, vibration transmission in engine structure were also improved and countermeasured to achieve powerful and comfortable Sports Utility Vehicle.

This paper reflects an efficient and comprehensive approach for vehicle sound optimization integrated into the entire development process. It shows the benefits of early consideration of typical vehicle NVH features and of intensive interaction of P/T and vehicle responsibilities. The process presented here considers the typical restriction that acoustically representative prototypes of engines and vehicles are not available simultaneously at the early development phase. For process optimization at this stage, a method for vehicle interior noise estimation is developed, which bases on measurements from the P/T test bench only, while the vehicle transfer behavior for airborne and structure-borne noise is assumed to be similar to a favorable existing vehicle. This method enables to start with the pre- optimization of the pure P/T and its components by focusing on such approaches which are mainly relevant for the vehicle interior noise.

In an automotive engine impulsive sounds and vibration are induced by faults or design constraints which degrade the sound quality of the engine. Thus it is important for an NVH engineer to detect and analyse impulsive sound and vibration signals for both fault diagnosis and also for sound quality assessment. However it is often difficult to detect and identify impulsive signals because of interfering signals such as those due to engine firing, harmonics of crankshaft speed and broadband noise components. These interferences hinder the early detection of faults and improvement of sound quality. In order to overcome this difficulty we present a two-stage ALE (Adaptive Line Enhancer) which is capable of enhancing impulsive signals embedded in background noise. This method is used to pre-process signals prior to time-frequency analysis via a bilinear methods such as the Wigner-Ville distribution and the Choi-Williams distribution.

Identification of structure borne sound sources induced by the structural vibration of an automotive powertrain has been studied. Based on the principal component analysis which uses singular value decomposition of a matrix consisting of the auto- and cross-spectra, the operating vibrational analysis is performed. The quantitative description of the output power due to intrinsic incoherent source is addressed. The applicability of the technique is tested both numerically and experimentally. First, the coherence analysis is numerically carried out with a simple structure which is modeled as multi-input and single output to identify the structure borne noise generation process. Second, the actual vibrational behavior of a powertrain structure and the interior noise analysis of a car under the running condition are carried out. The technique is shown to be very effective in the identification of the structure borne noise sources.

It has been recently reported that the crankshaft vibration provides the main exciting source in the power train vibration. This paper presents the analytical method for the vibration of crankshaft by using the finite element method. The optimization process is employed so that the beam model of the crankshaft can have the same natural frequencies as those of solid model on the free-free condition. The mode analysis of the crankshaft whirling is made in the consideration of the gyroscopic effect and the changes of the natural frequencies are also studied with the increase of the engine speed. Finally, the forced vibration of the crankshaft is solved on the time domain and the results are compared with those of the experimental measurements of bending moment by using the strain gage. This crankshft system model can be used to analyze the forced vibration of the full power train as well.

The weight reduction and noise refinement of powertrain has been major concern in automotive industry although they are known as self trade-off. This paper presents various methods to deal with those problems for new Hyundai 1.5 liter powertrain. It was possible to reduce the weight of powertrain by using plastic for both headcover and intake manifold, aluminum for crankshaft damper pulley and stainless steel for exhaust manifold and by reducing the general thickness of cylinder block On the other hand, the noise refinement of vibration in the powertrain was made by optimizing the engine structure and by adapting the hydraulic lash adjuster valve train system, which was proved to be effective in mechanical noise of engine.

This paper shows the cause and the solution to the uncommon noise which happens ½ order component of engine rpm when a vehicle with automatic transmission has an air conditioning load and “drive” range load on the engine. By measuring cylinder pressure, main bearing cap vibration, engine mount vibration, and interior noise simultaneously, the cause of the noise can be proved by analyzing and comparing the data. The cause of the uncommon noise is bending vibration of the crank shaft. To solve the problem, one can change the crank shaft dynamics by reducing the mass of the damper pulley.

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.