A Study on Friction of Journal Bearing under Dynamic Load

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1. Objective: Journal bearings are usually used in multi-cylinder internal combustion engines. They are operating under very heavy dynamic load. On the other hand, their frictional loss should be low. Few studies have been presented which had dealt with pressure distribution, that is most important quantity for discussing all of bearing characteristics, under dynamic loading. Patrick had only measured simultaneously the frictional force in them. On this background, this study was carried out in order to make clear the dynamic characteristics of journal bearings.2. Approach: The test rig was designed and constructed so that all of basic and important quantity of journal bearing, namely pressure distribution, load of bearing, journal center orbit, oil temperature, frictional torque and oil flow rate, are simultaneously detectable. Data processing was carried out by on-line mini-computer system.Experimentally negative pressure was always measured. The maximum value is -0.35MPag. The liquid-gas two phase hydrodynamic lubrication theory was used to expound those negative pressure. Comparison was made between theoretical results and experimental one on pressure distribution, frictional torque and pil flow rate.3. Conclusings: (1) The shape of negative pressure distribution depends upon the loading pattern. The level of flat pressure region corresponding to oil film ruptured region is about absolute vacuum under high frequency of load. (2) The two-phase theory can explain negative pressure measured experimentally. However, it over-estimates value on the frictional torque. So, the theory should be improved from this point of view. (3) Measured values of frictional loss agreed qualitatively with theoretical results under static loading, whereas no reliable results were obtained under dynamic conditions by means of an imperfection of the measuring system. (4) Good agreement was obtained between the theoretical and the experimental results for oil flow.