Friction Reduction of an All-aluminum Cylinder for Motorcycles by a Mirror Finished Bore with Dimples 2019-32-0530

In recent years, the demand for fuel economy of small engines has been increasing for further improvement of product competitiveness. As a solution for this issue, a lot of developments on reduction of friction losses of engine components have been actively performed by engine manufacturers, especially the friction loss between the cylinder bores and pistons or piston rings is main issue to solve because these frictions highly contribute to the fuel economy for the small engines. In this study, focusing on the effect of the texture of the all-aluminum cylinder bore on friction loss, we verified the friction loss of all-aluminum cylinders having several kinds of surface textures by a floating liner method. For the evaluation, we prepared cylinders which have the texture of the following three types, 1) plateau type (having conventional cross-hatches), 2) mirror finished type (having no cross-hatches and no irregular surface characteristics), 3) dimple type (most of part is mirror finished but small dimples are given at a limited part). As a result of the evaluation, it was confirmed that FMEP of mirror type was 14.1% lower and dimple type (optimized for low friction) was 19.5% lower than plateau type. In addition, when comparing FMEP for each crank angle, it was revealed that mirror type was effective evenly in all strokes of intake, compression, expansion, and exhaust, and the dimple showed a large effect particularly on the expansion stroke.