A Holistic Approach to Develop a Modern High Power Density Diesel Engine to Meet Best-in-class NVH levels.

The ever-increasing customer expectations put a lot of pressure on car manufacturers to constantly reduce the noise, vibration and harshness (NVH) levels. This papers presents the holistic approach used to achieve best-in-class NVH levels in a modern high-power density 1.5 lit 4 cylinder diesel engine. The base engine architecture was designed with NVH reduction features such as crank-offset, cast iron crankcase, stiffened ladder frame, structural oil pan and front cover. Piston skirt profile was optimized to reduce the slapping noise by carefully studying the secondary motion and skirt contact pressure. The plastic parts such as cylinder head cover and intake manifold were designed with closely spaced ribs and high wall thickness. Natural frequency targets for different parts were set for the entire engine at component level and system level and confirmed through simulations. High frequency acoustic simulation was carried out to identify and improve the areas of high surface velocity. "Acoustic holography" technology was extensively used to identify the areas of high noise radiation in the running engine. Based on the measurements, it was identified that the timing gear drive (intake camshaft to exhaust camshaft) is a major source of noise due to the heavy rattle noise. The resultant broadband frequency air-borne noise was found to be acting as a major contributor for the 1m engine noise measured in a semi-anechoic engine dynamometer. The timing gear noise could be significantly reduced by introducing a spring-loaded scissor gear assembly. Moreover, the measurements revealed that the crank pulley and fuel injection pump (FIP) are the next big contributors for the overall engine noise. Hence, an acoustic damper cover with isolated mounting scheme and a close-field acoustic FIP cover were introduced to improve the NVH. As a result, the average (left, right, front and top) 1m engine noise of the engine was measured to be 64 dB(A) could be achieved. The results are considered to be the best-in-class based on the extensive benchmark data collected. The paper gives an overall insight about the design, simulation, measurement and development approach followed to achieve extremely low NVH levels.