DYNAMIC BEHAVIORS OF A TWO-CYLINDER FOUR-STROKE
In this study the vibrational aspects of a two-cylinder four-stroke internal combustion engine were studied. A dynamic model has been prepared with four degrees of freedom which are: the translational vibrations of the engine block in vertical and horizontal directions, the rotational vibration of the engine block around the crankshaft center and the fluctuation of crankshaft angular speed. The model comprises forces and moments caused by inertial effects, hydrodynamic and dry frictions, startup moment, external load, gas pressures and mount forces. Vibrations of the engine block and fluctuation of crankshaft speed were optimized by using practical values. The inertia moment of the flywheel was found to be the dominant factor to minimize the angular speed fluctuation of the crankshaft. The gas force and the mass of the pistons were found to be the prevalent parameters contributing to the rotational and translational vibrations of the block respectively. It is observed that the vertical vibration of the block could be adequately minimized by means of exposing counterweights to the crankshaft, however, the counterweight induces a horizontal vibration while diminishing the vertical vibration. Therefore, in minimization of the translational vibrations of engine block, in addition to exposing counterweights, the piston mass should be very well minimized.