Study on the noise and vibration of engine block coupled with the rotating crankshaft and gear train (Effect of the torsional vibration of crankshaft)

As the small-sized high speed diesel engine used for construction machinery and generator is operated under continuous heavy load condition, a gear train is employed to drive the fuel injection pump and valve train. When a loading torque acting on the crankshaft and gear train is small at the idling condition, the gear tooth separation and impact are caused by the fluctuating torque and they increase the engine noise level. Particularly when the torsional vibration of the crankshaft occurs and its rotational amplitude is magnified at a specified rotational speed, the gear impact is intensified and it leads to increase of the engine noise. Author has developed the theoretical procedure using modal analysis technique to predict the vibratory response and radiated noise of the engine block coupled with the rotating crankshaft and gear train shafts which drives the fuel injection pump and valve system. The exciting forces acting on the engine block and shaft system are combustion pressure, inertia forces of the moving parts, piston slap force, fuel injection pressure and valve driving force and torque. This method is applied to reveal the effect of the torsional vibration of crankshaft on the gear impact force and engine noise of the four-stroke four-cylinder engine. The gear train is equipped at the pulley side of the crankshaft and the torsional vibration mode of the crankshaft is enlarged at the pulley side than flywheel side. Countermeasure to reduce vibration and noise by changing the location of the gear train from the pulley side to the flywheel side is evaluated and its result indicates the prospects which can reduce the radiated noise from the engine block.