SIMULATION OF CYLINDER BORE SURFACE FINISH PARAMETERS TO IMPROVE LABORATORY-SCALE FRICTION TESTS IN NEW AND USED DIESEL OIL

摘要

The development of alloys, coatings, surface treatments, and lubricants for improved cylinder liners and rings has historically included friction and wear testing. The correlation of results from motored engines or laboratory-scale tribotests with those from full-scale, fired engines remains a subject of contention. Attempts to develop valid engine wear simulators have met with varying degrees of success. Complexities in understanding and duplicating the relevant contact conditions in fired engines have challenged the designers of sub-scale, simulative laboratory tests. The current paper describes one aspect of this problem; namely, simulating the cylinder bore surface finish for use in bench tests. A rapid method to prepare cast iron test specimens that have similar surface roughness parameters to a production cast iron cylinder liner has been developed. To compare the sliding response of simulated liners with actual liners, cast iron specimens were friction-tested in both new and used 15W40 commercial diesel engine oil, in mineral oil, and without liquid lubrication. A reciprocating, ball-on-flat testing machine was used with test lengths that ranged from 100 to 20,000 cycles. Kinetic friction coefficient data compared favorably between the simulated cylinder liner specimens and actual cylinder liner segments. The friction coefficients obtained in tests with different lubricants on the simulated surfaces were related through a second-degree polynomial to the change in arithmetic average roughness that occurred during running-in. Additional elements of the fired engine environment will be added in the next stages of this research to determine the degree of complexity that is needed to obtain increasingly better simulations.