Study on the Friction Characteristics of Double Reciprocating Elements and Micro Surface Textures

Abstract

A new test device has been designed and manufactured on trial in order to investigate into reducing total friction in the system where double mechanical elements, like a piston ring-package, slide simultaneously. The test device has much simpler structure than others because of having shear force sensors to measure friction and coil springs to load the double elements. Using the test device, the effects of the micro surface textures of mated materials, oil supply flow and position to the sliding parts and others on the total friction have been examined in detail. Under oil fully flooded condition, the total friction of double elements was smaller in case of transverse texture which is perpendicular to the sliding direction than the ones in cases of longitudinal and cross textures. Under oil starved condition, that was smaller in case of longitudinal texture due to easy oil transportation than the other two textures. Oil supply position on the outer side far from the crankshaft gave larger friction than the one on the inner side. This seemed to be caused by the difference of element velocity around both dead centers. Double elements gave larger friction than the sum of friction of each single element. The phenomenon is mainly attributed to the sliding area and the small oil flow with the upstream element. These experimental results were simply analyzed with a theoretical model of mixed lubrication with consideration of surface roughness and oil starvation.