201480667 engine bearing tribology doc
DESCRIPTION
engine tribologyTRANSCRIPT
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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 crankslider 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.
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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.
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Flowchart Representing Analysis Methodology
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Flowchart Representing Operation of Matlab Code
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Experimental Bearing Model
Results
Experimental Bearing Model OFT Iteration 2 (Load = 3.11 kN)
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Pressure Variation for the Elastic Case Bearing Load = 17 kN (Pressure in MPa)
Pressure Distribution along length of bearing Pressure distribution along width of bearing
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Pressure Force, Inertia Force and Total Force 1250 rpm and 3 Nm
Polar Plots of Bearing Loading 1250 rpm and 3 Nm
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Results Oil Film Thickness vs CAD 1250 rpm and 3 Nm
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Results Oil Film Thickness vs CAD 1250 rpm and 3 Nm
Results - Journal Orbit 1250 rpm and 3 Nm
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Indicated Elastic Deformation = 9 m
Results - Displacement Indicated by Finite Element Model 1250 rpm and 3 Nm
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Results Comparison of Journal Orbit determined by Mobility Method with
Experimental Result 1250 rpm and 3 Nm
Mobility Method Experimental Result