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Powerplant NVH decisions are sometimes made looking only at how the change impacts either the source radiated noise level or the source vibration. Depending on the engine configuration, those can be good approximations, but they can also be very misleading. By combining both noise sources into a vehicle equivalent noise level a much better analysis can be made of the impact of any proposed design change on the customer perceived loudness. This paper will investigate several different scenarios and identify how the airborne and the structureborne paths combine for I4, V6 and V8 engine configurations. Similar relationships will be shown for path as well as the source contributions.

Piston slap is a problem that plagues many engines. One of the most difficult aspects of designing to eliminate piston slap is that slight differences in operating conditions and in part geometries from build to build can create large differences in the magnitude of piston slap. In this paper we will describe a design for robustness CAE approach to eliminating piston slap. This approach considers the variations of the significant control factors in the design, e.g. piston pin offset, piston skirt design, etc. as well as the variation in the noise factors the system is subjected to, e.g. assembly clearance, skirt collapse, peak cylinder pressure, cylinder pressure rise rate, and location of peak cylinder pressure. Using analytical knowledge about how these various factors impact the generation of piston slap, a piston design for low levels of piston slap can be determined that is robust to the various noise factors.

Powertrain radiated noise is an important design factor that must be evaluated during the concept phase of the design process. Unfortunately, the tools currently available to evaluate radiated noise, empirically derived relationships, detailed CAE models, or experimental data, are not useful during this critical phase of the design when many of the fundamental design aspects are determined. Empirical models are too general to capture the impact of many typical design decisions, and detailed CAE models or hardware tests are not practical due to the level of design detail necessary, the cost involved, and the timing. This paper lays out a simplified approach for the prediction of powertrain radiated noise that is useful for both quantitative and qualitative evaluation of design alternatives.