Study On Piston Slap And Induced Noise Of Internal Combustion Engine

The piston slap is the major source of the engine vibration, and induced noise is the biggest mechanical noise that is only smaller than combustion noise. With the development of the high-speed and lightweight engine, the mechanical noise of internal combustion engine is therefore consequently more prominent. Meantime, the measures for controlling combustion noise come into conflicting with improving power of internal combustion engine. So the mechanical noise is the key point of engine noise control. The induced noise of piston slap, as the biggest mechanical noise of the internal combustion engine,is the focus of noise control. Therefore, deeply understanding of the mechanism of piston slap, precisely describing the induced noise of piston slap, and clearly analyzing the influence factor of piston slap noise, are of great significance to acquire the kernel technology of mechanical noise control, suppress the traffic noise and reduce the environment noise.Based on the force analysis of piston in working condition, a dynamic model of piston slap was established with consideration of possible contact status between pistons and cylinder wall. And the accuracy of this model is improved by considering the heat expand and oil film. And then the validity of the dynamic model was proved by the transfer function between the piston slap force and the acceleration of engine block surface.The dynamic model of piston slap was solved by the 4th order variety step size Rung-Kutta method. And then the mechanism of piston slap was acquired through analysis of the pistons'horizontal movement, the rotational angle, side force and slap force. All research results indicate that in explosion stroke the pressure of gas is the main reason of piston slap, and during intake, compression and exhaust stroke the inertia force of piston is the main reason of piston slap.According to piston slap dynamic model, an acoustic model basing dilating sphere source of piston slap noise was established. Consequently the induced noise by piston slap was precisely described through the acoustic model. Finally, the validity of acoustic model was proved by measuring the sound power of internal combustion engine.According to the acoustic model of piston slap noise, how the parameters affect the piston slap noise at different rotate speed was discussed. And those parameters were piston clearance, piston pin offset, connect rod ratio, piston skirt stiffness, crank shaft offset, height of piston's gravity center, total length of piston skirt, vertical position of piston-pin axis and under part length of piston skirt. Finally the principle of design and improvement for decreasing the piston slap noise was summarized.According to the principle of design and improvement for decreasing the piston slap noise, the piston was modified for decreasing slap noise considering the actual situation. The sound power of piston slap noise was averagely reduced by 1-1.5dB (A) at different rotate speed of internal combustion engine.