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This paper shows some discussions regarding an experimental consideration of booming noise level when a vehicle drives over a small protruding object on a road. Booming noise level is subjected to vehicle speed and is not proportional to the speed. Generally, it is known as the maximal noise level is being created with vehicle speed of around 40 km/h, however, the obvious cause of the phenomena have not been completely determined so far. In this paper, at first, it shows an experimental data that was being observed in detail with variable vehicle speed. Based on our detailed observation of the experimental data, reversed-phase two inputs by existence of a protruding object, was confirmed. By considering correlation between time difference of two inputs and vehicle speed, it is demonstrated that those two inputs around 40km/h induce a tire resonance which leads to a booming noise in a cabin. We define it as ‘harsh booming noise’ here.

Knock noise induced by automotive shock absorbers has serious influence on driving comfort and vehicle quality. Some research focusing on knock noise had been introduced in the past. However there is the unidentified phenomenon that has been unnoticed. This paper describes the new theory to clarify one of the unidentified phenomenon and proposes the equation for stability assessment which is useful on designing stage of development. First of all, the characteristics of the unidentified rod vibration of shock absorbers are investigated experimentally. Second, the new theory is established on the basis of the non-linear physical model with friction forces between piston and cylinder. This theory shows that the unstable vibration, so called the Self Excited Vibration, can be induced by not only friction property but also structure of rod and piston. Third, the equation for stability assessment, which is useful on designing stage of development, is proposed on the basis of new theory.