Engine Lubrication System Analysis by Considering Aeration and Cavitation within the Rotating Oil Supply Passage

Abstract

The connecting rod big-end bearing is one of the most heavily loaded components of the lubrication circuit system of modern combustion engines. The bearing's oil supply has to be designed accordingly in order to ensure its sustainable operating reliability. As can be seen, the oil supply has to pass the main bearing and the rotating crankshaft before entering the connecting rod bearing. It is common knowledge that the centrifugal forces due to the crankshaft rotation affect the oil flow through the rotating supply passage into the rod bearing. The oil pump has to maintain a certain pressure level in the main oil gallery to overcome these centrifugal forces. In the early eighties, the second oil pressure limitation to the rod bearing operation was identified, which is lower than the centrifugal pressure limit. As a result of this, the dissolved air will be released in the rotating oil passage due to the pressure decrease caused by the centrifugal forces. Aeration or cavitation within the rotating oil supply passage occurs at much lower oil pressure. The detrimental effects of aeration or cavitation are loss of lubrication, overheating, metal erosion, mechanical shocking, and even system component failures. In this paper, a novel approach of identifying the second pressure limit is introduced by applying the CFD method. The three-dimensional, transient, multiphase flow in the transfer passage has been solved by considering its dynamic attributes. The characteristics of the aeration and cavitation flows and their effects on rod bearing oil supply have been investigated. The mechanisms underlying the interrupted oil supply to the rod bearing have been discussed in detail by studying the dynamics of aeration and cavitation. Finally, a map of the operational range has been established as an exemplary guideline for the design of engine lubrication systems and the key operating conditions including rotational speed and main bearing inlet pressure. Review led by Yuan-Ren Jeng