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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.

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.