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Abstract
Most machinery failures are attributed to wear of components. Experimental investigation of wear is highly demanding, especially for internal combustion (IC) engines, due to the complex reciprocating mechanism.
This thesis presents a simulation based approach to investigate the wear related faults in IC engine bearings, through the integration of two approaches i.e. wear and vibration based analysis, for timely fault detection and prediction of remaining lifetime of the bearings.
An engine dynamics model is established to provide the connecting rod bearing with actual service environment. The inherent engine inertia and the combustion force determine the magnitude of load on the bearing. To balance this load, a hybrid force model is developed to cover a range of lubrication regimes and provide real time information on bearing dynamics.
The simulated information is robust to predict wear depths and generate corresponding vibration signals for a range of operating conditions. For wear calculation, a variable wear coefficient is simulated as a function of asperity contact area during transition from the mixed to boundary lubrication regime, thus signifying the severity of impending wear with growing contact. The effect of speed, external load and bearing clearance on vibration signals and wear severity is studied and validated through experiments. Envelope analysis successfully revealed the wear critical locations and wear severity for all operating conditions tested.
From simulated data, appropriate vibration and wear based indicators are identified for correlation analysis. A relation is developed which can enable the prediction of bearing wear situation directly based on the selected vibration based indicator (I-Kaz coefficient) without having to actually inspect the bearing for wear. A framework for predicting the remaining lifetime of the bearings through instantaneous wear rates obtained from simulation is also presented. The application of the developed method is demonstrated on a Toyota 3SFE engine, but the application is equally valid for any similar engine, provided the engine parameters are updated.
Being vested with the combined benefits of wear and vibration based analysis techniques; the developed simulation is capable to detect bearing faults with good accuracy, with minimal dependence on real engine testing, for validation purpose only.