Piston ring and cylinder bore friction simulation in mixed-lubrication regime

A new bench friction testing system, which has high stroke length and large contact width has been designed and built to measure piston ring and cylinder bore friction under simulated actual engine conditions. This test system controls the running speed, contact temperature and lubricant amount and records the friction force, loading force, crank angle signal and contact temperature data simultaneously. Developed test system has wider range of testing capabilities than previous bench testing systems. This system provides reliable and repeatable data for piston ring and cylinder bore friction simulations.; A computational scheme for simulating frictional performance of piston ring and cylinder bore contact in mixed lubrication regime based on Patir and Cheng's modified averaged Reynolds equation and Greenwood and Tripp's asperity contact model has been developed. The friction force between piston ring and cylinder bore is predicted considering cavitation, surface flow factors, surface roughness, surface roughness orientation and metal to metal contact load. Fully flooded inlet boundary condition and Reynolds boundary conditions for cavitation outlet zone are assumed. Reynolds boundary conditions have been modified for non-cavitation zones. Pressure distribution along the ring thickness and lubricant film thickness are recorded for each crank angle degree.; The effects of running speed, contact load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores using developed computational scheme and bench test data. Friction coefficient predictions are presented as a function of crank angle position. Numerical predictions correlated well with bench test results.; Low cost and solid lubricant containing plasma spray coated cylinder liners have been investigated for their frictional performance under simulated engine conditions. Results are compared with conventional cast-iron samples. Cylinder bore samples were examined using optical photo-microscopic and surface profiler techniques. Results showed that plasma spray coated cylinder liners enables the use of bore surfaces with low surface roughness which result in higher hydrodynamic lubrication compared to conventional cast-iron cylinder bores.