Oil Film Thickness in a Bearing of a Fired Engine Part II: The Bearing as a Capacitor

A new technique has been developed to measure the actual oil film thickness in a fired engine bearing over the complete engine cycle. It involves isolating the bearing electrically from the rest of the engine, imposing a high-frequency AC voltage, and measuring the capacitance of the entire bearing. From this, the oil film thickness can be determined as a continuous function of time.

The precision of the new technique is excellent and is sensitive enough to detect cycle-to-cycle variations in peak pressure, as well as such conditions as engine knock and misfire. The effect of engine load and speed and of oil viscosity is clearly noted.

The overall conclusion from this work is that this technique is probably the best method currently available for determining the load carrying ability of engine oils in fired engines.