Development of a Piston Ring-Cylinder Bore Wear Model

In an internal combustion engine, the wear in the piston ring/cylinder bore contact initially increases rapidly due to run-in and then attains a steady state during which the engine spends most of its useful life. This paper describes the development of an abrasive wear model for both cylinder bore and piston rings for the steady state period. The model took into account shear thinning of the lubricant, but it did not consider the effects of transient operations, geometry changes due to bore distortions, ring twist, ring motion, and corrosion. The model predicted the bore wear depth distribution from the top dead center (TDC) to the bottom dead center (BDC) and ring wear depth under different operating conditions. The maximum bore wear depth was predicted to occur at about 20 degrees after TDC where the combustion gas pressure reached its peak value. The model predicted an increase in bore and ring wear depth with increasing engine speed. Doubling the ring tension increased wear depth of both the cylinder bore and the ring. The ring face curvature influenced ring wear depth more significantly than bore wear depth. The model was validated by measuring bore wear near TDC on 3.0L Taurus and 4.6L Crown Victoria obtained from customers with 50 - 150 K miles and 3.0 L Windstar from Las Vegas Taxi Fleet. A reasonable correlation was observed between the predicted and the measured bore wear.