Due to the large number of motion pairs on the diesel engine, there are many mechanical excitation forces, including noise generated by piston and cylinder knocking, timing gear noise, fuel injection system noise, and gas distribution mechanism noise.
In the engine, any one of the rotating parts such as the crankshaft, the flywheel, and the pulley will form a vibration force. Since this vibration force is proportional to the unbalance amount of the component, it is proportional to the square of the rotational speed per minute. Therefore, when the rotational speed increases, the vibration It is also amplified abruptly, so the balance between the rotating parts is preferably smaller. Other mechanical noise comes from engine pistons, valve trains, etc., which form part of the engine noise, such as piston knocking, tappet noise, noise generated by valve opening and closing, noise generated by valve and valve spring vibration, and timing chain and The noise generated when the sprocket is engaged.
The piston knocking cylinder is the noise generated by the side of the piston striking the cylinder wall. When the compression pressure applied to the piston is converted into the combustion pressure, a knocking cylinder is generated. The piston knocking cylinder differs depending on the piston clearance. When the piston clearance is large, the knocking sound is most likely to occur. The characteristic of the piston knocking cylinder is that the engine is very loud when it is cold, so the piston clearance is large, and the sound becomes smaller as the engine temperature rises. To reduce the piston knocking, the main side pressure must be reduced, so some engines can reduce the knocking sound by cutting the center of the piston pin away from the piston centerline by a certain distance. Another way to reduce the piston knocking cylinder is to install a steel frame on the piston skirt to reduce the thermal deformation of the piston skirt, so that a slightly larger piston can be used to reduce the piston clearance and make the piston knocking sound smaller.