Abstract
There often occurs an abnormal torsional vibration influenced by the excessive external torque, the gear backlash and the characteristics of the bearing oil film in such light gearing load for the propulsive shafting with the reduction gear. In order to clarify the conditions and the mechanism of this abnormal vibration, the differential equations of the torsional vibration considering self exciting vibration of the bearing oil film is proposed and analyzed by the characteristic equations and also the computer simulation. As the result, it is concluded that the abnormal vibration is caused by the instability of the torsional vibration coupled with self-exciting vibration of the bearing oil film and the existence of the gear backlash makes the stable area changed. And the design criteria to prevent the abnormal vibration can be obtained by the assumption of the constant whirling of the journal. And authors indicate that this abnormal vibration may generally occur referring to such a diesel engine plant as has the reduction gear.
