The study of vibration in internal combustion engines

In vehicle engines with pistons, the minimization of vibrations has importance for both the quality, practicability and durability of the vehicle and, comfort and safety of passengers or drivers. In this study by preparing the dynamics model of a single cylinder diesel engine, the behaviours of the engine in speeding up, the block vibration of the engine, the fluctuations of the crankshaft speed, dynamic forces occurring on mounts, effects of frictional forces to angular speed variations, effects of piston masses to the speed variation of crankshaft and the translational vibrations of the engine block were examined. The dynamic models consist of the motion equations of the piston, piston connecting rod, crankshaft and engine block. The model involves the forces and moments caused by inertial effects, hydrodynamics and dry frictions, working gas pressure, mount deformation, external load and start-up moment. The motions of the engine block and the other moving elements were described on a plane perpendicular to the crankshaft axis. The engine block has three degree of freedom; two of them are translational motions on the direction of vertical and horizontal, and the other is angular vibration around the crank axis. Numerical solution was performed on the time domain by means of using initial conditions. The working gas pressure exerting on the piston was experimentally obtained from a four-stroke single cylinder diesel engine.It is observed that the vertical and rotational vibrations of the engine block were caused by piston inertia and variation of working gas pressure respectively. Ones a half of the piston connecting rod mass was included to the mass of crankshaft and other half was included to the piston mass in the analysis, for the minimization of vertical vibrations, a counterweight mass equal to the half of piston mass becomes appropriate. In this case, however, horizontal vibrations of the engine block may increase. Frictional forces found to have effects on rotational vibrations of the engine block. While the inertia moment of rotating components increases, the fluctuation of crankshaft speed decreases. However, it is observed that the cyclic variations of crankshaft speed does not linearly decrease with the flywheel mass-inertia-moment. Below a value of the crankshaft cyclic fluctuation, rather increase of the flywheel mass does not provide a significant improvement. The examinations conducted with different mount stiffness and damping constants indicated that the transmissibility forces occurring on the mounts become larger within the range of natural frequency.