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NVH refinement of passenger vehicles is crucial to customer acceptance of contemporary vehicles. This paper describes the vehicle NVH development process, with specific examples from a Diesel sedan application that was derived from gasoline engine-based vehicle architecture. Using an early prototype Diesel vehicle as a starting point, this paper examines the application of a Vehicle Interior Noise Simulation (VINS) technique in the development process. Accordingly, structureborne and airborne noise shares are analyzed in the time-domain under both steady-state and transient test conditions. The results are used to drive countermeasure development to address structureborne and airborne noise refinement. Examples are provided to highlight the refinement process for “Diesel knocking” under idle as well as transient test conditions. Specifically, the application of VINS to understanding the influence of high frequency dynamic stiffness of hydro-mounts on Diesel clatter noise is examined.

Internal combustion engine noise is primarily composed of combustion and mechanical noise shares. Mechanical noise contributions in engines have increased relevance at low load conditions when combustion related noise is not significant. Current literature on mechanical noise in engines includes: piston pin ticking, piston secondary motion, and valvetrain impacts. A mechanical noise source from excitation of piston tertiary motion is described here in the form of a case study on an engine exhibiting a cold start “clatter” noise. Targeted experimental measurements were initially used to rule out potential mechanisms such as impacts resulting from piston pin ticking and piston secondary motion. Experimental modification studies and piston load and kinematics modeling led to discovery of instability of the piston which is understood to excite tertiary motion of the piston and result in impulsive “clatter” noise under certain low load/speed conditions.