エンジン要素の熱的な摩擦特性に関する研究

- 粗面接触ロジスティック曲線の適用：リング・ライナ混合・境界潤滑

抄録

To clarify tribological characteristics of engine components, an analytical method is proposed for investigating how the surface temperature T involves the friction and scuffing using temperature and friction data measured with a rotary-disk typed reciprocative sliding friction tester, which can set the same contact pressure and sliding velocity as those of piston rings in actual engines. The relationship among shear stresses s_i and surface coverage ratios θ_i is determined for four contact areas in a mixed/boundary lubrication model: hydrodynamically lubricated oil film, adsorbed oil molecules film, tribo-chemically reacted oil additives and true metal-metal contact, because a logistic curve is applied to relate the film thickness ratio with the solid contact ratio for rough interfaces as in the previous study. The shear stress and temperature rise of oil-film area and metal contact area are iteratively calculated, where the oil-film thickness depends on conditions of prediction and the shear stress of metal contact follows the change of Vickers hardness with temperature and elastic-plastic contact parameter. The product of shear stress s_ar and surface coverage ratio θ_ar for the tribofilm consisting of adsorbed oil molecules and tribo-chemically reacted oil additives is larger than those for the other areas, so that the tribofilm is a dominant factor in friction. The surface temperature coefficient C_ar is estimated under the exponential relationship between s_ar and T_ar similarly to the Arrhenius equation for chemical reaction rate. The C_ar values become smaller indicating higher involvement of T_ar in reducing s_ar to improve the scuffing resistance.