Determination of Critical Operating Point of Short Journal Bearings during Variable Load and Angular Speed Condition

Determination of Critical Operating Point of Short Journal Bearings during Variable Load and Angular Speed Condition

There are very large fields of short bearing application in which the load is not stationary or constant in value; it varies in both magnitude and direction, usually going through a more or less repetitive cycle. Bearings subjected to this kind of loading can be found in internal combustion engines, steam engines, reciprocating compressors and poorly balanced high-speed rotors. In this situation the critical operating point cannot be found easily, because shaft, bearing and load vector have angular speed and the magnitude of load changes instantaneously. In this study authors introduced a new method for determination of this point. In the first step load vector diagram of bearing is plotted and effective speed is computed for each position. In the next step the effective speed-to-load ratio as a function of shaft angle is drawn, and the global minimum of this diagram is determined. This point is the critical operating point and the journal bearing must be designed for this condition. For this purpose a code is developed. Also with this method the location of the oil inlet-hole in the bearing and shaft is designated according to load vector diagrams. Finally an example, crankpin bearing of an internal combustion engine, is solved by this method and the results are compared with the available literature.