抄録
As the diesel engine used for the forklift and construction machineries is operated in 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 the engine noise is increased at the pulley side. Modal synthesis method is applied to reveal this phenomenon and to lead to a low noise design of the gear casing. This method employs the vibratory characteristics of engine block and gear casing and its static deflection induced by engine block vibration. In this paper, the combination of vibration mode of each structure to enlarge the gear casing vibration is discussed. This method reveals that similarity of static deflection and eigen mode shape of the gear casing is the major factor of the large vibration response of the gear casing and the separation of the these two natural frequencies is essential to reduce the radiated noise from the gear casing.
