Vibrations have become an increasingly important attribute for determining the quality of automotive products. Particularly, this becomes more acute in the case of tactile vibrations of powered two-wheelers - motorcycles and scooters. This paper deals with vibrations of a scooter vehicle. Scooters are normally a two-wheeler with a four stroke single cylinder spark ignited engine. Vibrations of a scooter are mainly caused by the inertial imbalance forces of the engine, combustion forces and road undulations. Vibrations due to road undulations are mostly reduced by toggle link mechanism, resilient mounts of the engine and the shock absorbing suspension of the frame. The power train assembly is designed in such a way that the inertial imbalance forces in the power train assembly are distributed at a required angle called the ellipse angle. This configuration ensures that the engine forces which are spread unequally in different directions are made to align and contribute only to the vertical and pitch modes of the engine. In spite of the achieving the above mentioned configuration, there are vibrations due to force transfer through the toggle link mechanism to the vehicle frame. This paper explains ways of reducing of tactile vibration of a scooter by addressing these issues by using the theory of center of percussion. It also explains ways of determining the optimum mounting position of a scooter engine based on engine layout, engine geometry, inertial balancing of engine forces, isolation and the center of percussion for reduced vibration. Theoretical analysis with calculations about the angle of engine mounting, length of the swing arm, aligning engine forces by distributing the imbalance mass are discussed. Analytical models are then validated using experiments on design optimized configuration resulting in increased vibration comfort of the vehicle.
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