Dynamic Analysis of Hydrodynamic Bearing Performance in IC Engines

Lot of work has already been carried out on the hydrodynamic bearings under the static loads but very few literature is available on the investigation under dynamic loads and its effects on inertia forces of engine parts like piston, connecting rod, crank shaft and flywheel. An attempt is made in this paper to analyze the effect of frictional force and variations in oil film thickness on power loss by fluctuations in pressure gradient stiffness and damping effect during dynamic loading conditions. The frictional force is measured under various conditions of fluctuating /steady load ratio, journal frequency and load frequency, geometrical accuracy and also for different material properties. The oil film thickness for the above-mentioned conditions is measured (by Eddy-current gap sensors) to deduce the shaft trajectories. When the oil film thickness becomes lower than a critical value, then there is a series of electrical discharges. The amplitude of these discharges determines the minimum film thickness. The vibration of the crankshaft and the unbalances between the crankshafts have also large influence on the minimum film thickness and variation of vibration force is measured by Vibrometer. Power is lost due to frictional force, which is caused by variable load acting on the crankshaft and fluctuations of inertia forces in the engine parts at various crank angles. Change in forces cause change in pressure gradient which will create delay in time response in pressure gradient. This makes physical contact between journal and bearing and causes the power loss.