Friction and wear bench tests of different engine liner surface finishes

Abstract

Six different bore finishes of combustion engines were bench-tested against PVD-coated rings. Ring and liner specimens were removed from actual Heavy-Duty Diesel engine. The test was conducted in a CETR UMT-2 reciprocating tester. Current bore honings, e.g. slide honing, as well as recently developed structured laser were tested. For friction bench tests, the specimens were tested at different reciprocating speeds and loads. When lubricant condition approached the boundary regime (speed/load tending to zero), most of the finishes showed the usual boundary friction coefficient ∼0.11. When the conditions tended to the hydrodynamic regime, the specimen removed from the non-laser region of the laser-structured finish showed a remarkably low friction coefficient, followed by the laser-structured ones. For wear bench tests, the lubricant was doped with hard particles, and higher load and speed were used to accelerate the wear rate. Wear tests ran for 4 h and, as expected, friction coefficient reduced during the wear test due to break-in. In general, friction during the wear test followed the friction test ranking. The remarkable exception was the UV laser finish, which initially presented one of the highest coefficient and after 0.5 h of testing turned to be one of the lowest. Liner and ring wear was measured post-test by profilemeter. In general, the smoother surfaces presented lower ring and bore wear. Greenwood asperity parameters and Patir and Cheng flow factors were calculated from two measured surfaces. A computer model was applied to calculate the oil film thickness and friction for the different speed and load conditions. The calculated friction results showed good adherence to the measured data.