Effect of Oil Rheology on Journal Bearing Performance: Part 2 - Oil Film Thickness in the Big-End Bearing of an Operating Engine

The instrumentation of the big-end bearing of a 2.8 litre V-6 gasoline engine to measure bearing oil film thickness during engine operation is described. The electrically insulated bearing and the journal form a capacitor with the oil film as the dielectric. Synchronous measurement of the capacitance enables the determination of the minimum oil film thickness, h_m, as a function of crankangle. The minimum value of h_mfor a complete 720° crankshaft rotation can be measured to a precision of about 5%; it is little affected by chemistry of the engine oil performance package or by engine torque but decreases significantly with increasing oil temperature and increasing crankshaft speed.