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An engine configuration has a significant influence on the sound quality from the powertrain. Whilst the fundamental order content can be readily apparent from the firing order over the engine, or bank of a V engine, some characteristics and how the engine design can influence them requires some more specific investigation. Understanding, on a fundamental level, the aspects of the engine design which influence these characteristics is critical to allow more detailed analysis and development work to be focused appropriately. The configuration of a Boxer engine gives a distinctive sound characteristic producing a unique sound compared to an In-Line configuration. Depending on the application it may be desirable to enhance or subdue some of these characteristics.

Requirements for reducing powertrain NVH drives the selection of low piston skirt to liner clearances contradicting the requirement to maintain larger skirt clearances for minimizing engine friction. Whilst this clearance trade-off between low friction and low NVH is fundamental, piston design features have a significant effect on where the trade-off curve sits on the friction/NVH map. Design features can therefore be viewed not by either friction or NVH improvement measures but a shift in the friction-NVH trade off curve. Specifically, some piston design features which may be targeted at reducing friction can be viewed as either a friction benefit for similar NVH or an NVH improvement for similar friction levels. The ability to realistically quantify the effect of the design changes on NVH is therefore critical to determining what design changes to recommend, the direction of the piston design being highly sensitive to the process by which the impact on NVH is assessed.

A robust analytical process for evaluating the effects of engine component design on the powertrain NVH has been developed. The work presented focuses on design modifications for refinement of the NVH levels and sound quality of a 4 cylinder Boxer engine with automatic transmission. Assessment focuses on the powertrain structure, cranktrain, torque converter and valvetrain. Comparison of predicted mount vibrations with measurements on a fired engine are made. Through detailed post-processing of the analysis results, looking at modal contributions, modal excitations and loading contributions, the causes and contributions to the NVH are understood and used to direct potential modifications to the powertrain and component design. The models are used to quantify the relative benefit of these modifications in terms of both overall vibration levels and sound quality through implementation of a rumble metric.

The design of the spring pack providing torsional compliance within motorcycle clutch assemblies is often determined from the mean torque and a factor to allow for torque fluctuations. While this approach may work for many applications the selected spring rates can sometimes cause a driveline resonance within the operating speed range with major implications for NVH. For motorcycle engines it is also often impossible to select a spring rate low enough to shift the resonance below the operating speed range due to the requirement to transmit torques under steady load and transient events within tight spring package constraints. This paper demonstrates the approach of using a linear frequency domain analysis to model the entire driveline, from the crankshaft to the bike mass, to provide a relatively quick assessment of the driveline torsional vibration and assess potential design solutions.

When designing a sump system for a high performance engine the choice of the size of the inter-bay breathing passages is critical. The passages should be chosen to minimize the crankcase pumping loss and oil aeration while still maintaining adequate removal of blow-by gases and a good block structure. This paper presents an approach to the modeling of engine crankcase gas flow using Ricardo WAVE software. The model was developed during the design of a dry sump version of a racing engine and was validated using pressure and blow-by data. The model was used to quantify gas velocities, pressure fluctuations and power loss due to the pumping of crankcase gas. The effects of changes to a series of parameters such as breather hole size, sump volume, engine size and crankcase compression ratio were quantified. This approach provides useful guidance in the design of dry sump systems at the concept design stage.