Abstract
This Paper shows that NVH Optimization process of newly developed 12.9-litre Heavy-Duty diesel engine(HDDE) using Electronically-controlled Unit Injector(EUI). EUI is shown to be very effective device for high pressure injection and has been recently employed to emission and fuel consumption are greatly improved by EUI in HDDE, compared to conventional injection systems. However there was little considered on engine noise caused by the highly pressurized injection device, EUI. Although firstly noise level of our EUI engine was so high, we improved by noise reduction treatments. After analyzing of noise radiation characteristics using sound intensity, we improved the parts step by step as a high noise contribution. However in low idle and low load engine operating conditions, the hammering noise has dominated. So we precisely investigate the source and transfer paths and mainly improved the sound quality by structure modification.