Low noise structural design for internal combustion engine

(Model test of gear casing damping treatment)

Abstract

As the diesel engine used for the forklift and construction machineries is operated at the continuous heavy duty condition, it employs the gear train to drive the fuel injection pump and valve train. When the driving torque acting on the rotating shaft is decreased in the idling condition, separation of gear tooth and rattle noise are induced. Moreover, torsional vibration of crankshaft increases the impact vibration between the gear train. This gear train is commonly installed at the pulley side of the crankshaft and the gear casing is attached to an engine block to cover the gear train. Vibration level of this gear casing is often magnified due to the engine block vibration and consequently the engine noise is increased at the pulley side. The effects of changing the structure of gear casing and noise radiation from the gear casing are evaluated by use of the modal synthesis method which employs the vibratory characteristics of each structure and static deformation caused by the displacement of the connecting points. The rubber pasting on the gear casing is carried out to reduce engine noise. A modal damping ratio of coupled system after pasting rubber on the gear casing evaluated by use of modal analysis technique and its validity is confirmed by vibration experiment of a box model which imitates engine block and gear casing. Change of actual engine noise level by rubber pasting on gear casing is also discussed in detail.