Before attempting to reduce the vibration levels in a machines or structure of the
vehicles by increasing its damping, every effort should be made to reduce the vibration
excitation at its source. Motor engine should be considered as one of the vibration generators.
Rotating machinery such as motors can generate disturbing forces at several different
frequencies such as the rotating velocity and blade passing frequency. Reciprocating
machinery such as compressors and engines can rarely be perfectly balanced, and an exciting
force is produced at the rotating velocity and at harmonics. There are two basic types of
structural vibration: steady-state vibration caused by continually running machines such as
engines, air-conditioning plants and generators either within the structure or situated in a
neighboring structure, and transient vibration caused by a short-duration disturbance such as a
lorry or train passing over an expansion joint in a road or over a bridge