A Study of the Excitation Mechanism of Half-Order Vibrations in an In-Line 4-Cylinder Internal Combustion Engine.

Abstract

One of main causes of poor sound quality in a passenger car is the high contribution of relatively low-frequency half-order multiple components of the in-line 4-cylinder power-train vibration, principally 2.5 and 3.5 order of engine rotation. In order to identify the excitation mechanism for the half-order power-train vibration, the excitation forces raised by inertial force and torque fluctuation were investigated. The results can be summarized as follows. Since half-order multiple rolling moments caused by the torque fluctuation have a different working point and a different phase angle in each cylinder, the combined torsional moment acts on the cylinder block around the crankshaft axis as an internal force, and hence the torsional vibration shape is excited as half-order multiples of engine rotation. This theory has been proven by the experimental operating deflection shape analysis.