Modeling and Prediction of Engine-Radiated Noise of a Motorcycle

Study of noise radiating from an internal combustion engine is of great interest and challenge to automobile engineers. Design of low-noise engines is becoming increasingly important because of progressively stringent regulatory requirements. Further, customers are demanding products that have pleasing sound quality. As any improvement in this area will have significant impact on image of the product, addressing these concerns will prove highly beneficial. Most of the critical engine performance parameters - power, fuel economy, and emissions - impact engine noise and sound quality. Therefore, to avoid intractable engine noise and sound quality problems later, it is very imperative to deal with them upfront in the development process.

This work presents the work done to reduce the noise generated by a 4-stroke motorcycle engine by redesigning the crankcase using state-of-the-art topology optimization tools in conjunction with boundary element-based acoustic sound level prediction tools. The baseline design of these crankcases lacked sufficient rigidity at frequencies at which the engine noise levels were high. The crankcases were analyzed for static stiffness followed by dynamic analysis. Normal mode analysis was done to identify problematic frequencies that contribute to high sound pressure levels. Topology optimization tools were used to increase the static stiffness and dynamic stiffness in the problem frequency range. The impact of stiffness improvements on engine-radiated noise is predicted using white noise excitation at the crank bearing. These are further validated by actual operational measurements on the vehicle.