Effects of bearing clearance and atmospheric temperature on performance of pinion bearings of railway vehicles

In Japan, most of the gear units for transmitting driving force in railway vehicles employ one-stage speed reducers. The gear unit is composed of a pinion connected to a traction motor via a coupling mechanism, a gear installed on an axle, and a gear case that covers them. In their rotating parts, tapered roller bearings are mainly used, and are lubricated by gear oil splashed by the rotating gear. In order to prevent seizure of the bearings and to improve the reliability of the gear units, it is important to appropriately adjust the bearing clearance. The bearing clearance can change from its initial value during the travel of the vehicles due to an atmospheric temperature and its initial value when assembling the gear unit, and can affect the performance of bearings. In this research, an actual gear unit was subjected to bench rotation tests under various bearing clearances and various atmospheric temperatures. The bearing temperature and torque were measured, and changes in bearing clearance were estimated. As a result, it is found that the bearing clearance decreases immediately after the rotation starts, and this tendency becomes more remarkable as the initial bearing clearance is smaller and as the atmospheric temperature is lower.