Engine bearing analysis and design
The work described in this thesis, Engine Bearing Analysis and Design, is directed towards the prediction of the performance characteristics of full central circumferentially grooved journal bearings. Due to the complexities of a full solution of such bearings, several simplifications have been made, including the assumptions of rigid circular journal and bearing and that a thin isoviscous Newtonian lubricant exists between the bounding solids. The work presented can be split into three main areas of research. These are theoretical predictions in relation to the performance predictions of steadily and dynamically loaded cases, and the subsequent verification of the transient solution techniques developed by carrying out an extensive experimental investigation. The tests were carried out on the front main bearing of a single cylinder engine; the Ricardo Hydra. For the research into the performance of steadily loaded journal bearings, extensive design charts have been generated for the dimensionless load and shear power loss variation with eccentricity ratio at a range of dimensionless oil supply pressures. The total oil flow rate data, considering coupled surface velocities and oil supply pressure, was found to be represented accurately by a single curve. There was only a 4% difference between this and the pressure flow equation. The cavitation algorithm of Elrod and Adams (1974) was used for this part of the research work, with a view to its extension to transient cases. However, the excessive time required for a solution point meant that it would be impractical for transient situation where it would be solved several hundred times for a complete journal orbit. Subsequent to the analysis of steadily loaded bearings, attention was focused on the solution of dynamically loaded cases. A simplified oil film history solution was developed which reduced the computer run time for a converged journal centre orbit considerably. In addition, simple preditive techniques have been developed based on the pressure flow equation and a fully flooded bearing for purposes of shear power loss predictions. This approach for the full central circumferentially grooved bearings considered gave excellent agreement with the more rigorous analysis. The transient analyses developed have been verified by comparison with a significonE amount of experimental data which was collected for the front main bearing of a single cylinder gasoline engine. It was found that simple expressions for the oil flow rate and power loss provided a good prediction of the experimental data. There was found to be no justification in carrying out a rigorous film history solution, and from a design point of view the range of tolerances on the journal and bearing could give a diametral bearing clearance which could vary by a factor of 2.4. This has a more significant effect on the bearing side leakage than any uncertainties involved in the performance predictions themselves.