Challenges in Muffler Mounting Design for Resilient Mounted Scooter Engine

In recent times gearless scooters are becoming popular means of transport in ASIA because of their ease of handling in crowded traffic and superior comfort over motorcycles. Major difference, which is contributing for least vibrations incase of scooters is mechanism of engine mounting on the frame. In most of the cases motorcycle engines are rigidly fixed to the frame where as in case of scooters engine will be swinging with respect to frame. It is easy to design muffler mounting for fixed engines. Since there is no relative motion between engine and frame for motorcycle both can be fixed to frame. Swinging scooter engine demands muffler mounting directly on engine. These direct mounts may include bosses, brackets, and bolts. While useful for their intended purpose, it is possible that vibrational energy can pass between the exhaust components and the engine through this direct mounting. This occurs due to directly coupling a large radiating surface (the exhaust component) to an active vibrating structure engine. There is also the possibility that the exhaust mounting bolts get loose because of vibration and in turn leads to shear failure of bolts and structural failure of muffler and engine parts.

This paper is aimed at simulating complex behavior of muffler mounting system for scooter engines in design level itself. Critical locations for structural failure are identified through first level simulation and these critical areas are used for measuring the strain experimentally. Simulation model for the existing design was refined through experimental measurement of natural frequencies and strain values. On validated simulation model Design of Experiments (DOE) was done for minimizing stress at critical locations and optimize design. The concept of robust design was used for optimizing the design for manufacturing and assembly variations. Optimized design through this process helped us in reducing product development cycle by minimizing number of physical prototype testing.