Friction Characteristics of Piston and Piston Rings

In internal combustion engines, one of the most important issues is to clarify the complicated friction characteristics of piston and piston rings because of the demand for improved fuel economy through the reduction in friction loss. In the present study, the floating liner method, in which the cylinder liner was supported by means of hydrostatic bearings, was developed to measure the friction force of piston and piston rings in an operating diesel engine. The decreases in either the number or the width of piston rings, the piston skirt area, and the lubricating oil viscosity were effective in reducing total friction loss, but these increased the boundary friction at the beginning of the power stroke. The boundary friction could be reduced by either a surface treatment on the piston and the piston ring or a friction modifier in the lubricating oil. The reduction in total friction loss was more significant when decreasing the total piston ring tension rather than changing the piston specification.