ENGINE BEARING TRIBOLOGY Overview The design of journal bearings is important for the development of internal combustion engines. They experience load that varies both in magnitude and direction, the load being caused by the pressure forces and inertial forces of the crank–slider mechanism. It has been found that the most common causes of premature failure in internal combustion engine bearings are fatigue, sliding surface wear, erosion due to cavitation phenomena and all these effects are directly or indirectly related to the shape of the oil pressure field in shaft-bearing interface. An accurate estimation of oil pressure distribution characteristics and measurement of oil film thickness in the shaft-bearing interface would allow better prediction of the bearing performance and reliability. The goal of this work is to develop a method for calculating the oil film thickness (OFT), oil film pressure (OFP) in the shaft-bearing interface and its validation by experimental results. The detailed analysis of the lubrication condition around the position of minimum oil film thickness conditions is based on finite difference method of integration of the Reynolds equation coupled to the elastic deformations determined by a detailed finite element model. Four non contact eddy current gap sensors mounted on the main bearing of a single cylinder engine are used to measure the oil film thickness and the journal orbit for variable speed and variable loading conditions.
Approach To arrive at the OFT, the instantaneous eccentricity was used as a starting point along with the operating and physical parameters. OFP distribution corresponding to these conditions was calculated by a numerical solution of the Reynolds equation. The loading information thus obtained was applied to a FEM model of the bearing shell in Hypermesh environment coupled to Nastran solver, to determine its elastic deformation. This was fed back to the instantaneous eccentricity and an iterative technique leading to the OFT under elastohydrodynamic conditions was developed by matching the Load Carrying Capacity at every step. The benefit of this model is that is somewhat accurately predicts OFT and the corresponding OFP for the real case of an elastic bearing shell. The journal orbit was plotted using Mobility method, and compared with the experimentally measured orbit. A correlation was established between the two, leading to a validation of the elastohydrodynamic lubrication model developed.
Flowchart Representing Analysis Methodology
Flowchart Representing Operation of Matlab Code
Experimental Bearing Model
Results Experimental Bearing Model – OFT Iteration 2 (Load = 3.11 kN)
Pressure Variation for the Elastic Case Bearing Load = 17 kN
Pressure Distribution along length of bearing
(Pressure in MPa)
Pressure distribution along width of bearing
Pressure Force, Inertia Force and Total Force 1250 rpm and 3 Nm
Polar Plots of Bearing Loading 1250 rpm and 3 Nm
Results – Oil Film Thickness vs CAD 1250 rpm and 3 Nm
Results – Oil Film Thickness vs CAD 1250 rpm and 3 Nm
Results - Journal Orbit 1250 rpm and 3 Nm
Indicated Elastic Deformation = 9 μm
Results - Displacement Indicated by Finite Element Model
1250 rpm and 3 Nm
Results – Comparison of Journal Orbit determined by Mobility Method with Experimental Result 1250 rpm and 3 Nm
