A Study on the Feature of Several Types of Floating Liner Devices for Piston Friction Measurement
To be published on April 2, 2019 by SAE International in United States
Engines are still required fuel economy for reducing CO2 emission, because they will be adopted as power sources for mobility till it is achieved that electric power is generated carbon-free. It is well known that the friction reduction of a piston/piston-ring assembly is effective for fuel economy of an engine. Friction measurement method, therefore, is also required for developing low friction pistons, piston-rings and additives for lubricants. Most suitable method for friction measurement for piston assemblies is “floating liner method”, which measurement principle is developed by Furuhama. It has load sensors between a floating cylinder liner and cylinder block, and the sensors can detect friction force acting on the cylinder liner. Nowadays, a lot of apparatuses using floating liner method are developed for piston friction measurement. They are roughly divided to two categories. In one of them, floating liner is supported by load washers which axis is set parallel to the center line of the cylinder liner. In another type, floating liner is supported by three-component sensors installed on the side face of the cylinder liner. In this paper, five types of floating liner devices including three-component type were compared, and feature of each device was shown. The natural frequency of such devices is an important design factor because it affects measurement accuracy and the highest engine speed for friction measurement. Then, the natural frequency was investigated for each device in this study. It was found that natural frequency was strongly affected by sensor type and its mounting condition. Further a simple calculation model was shown for estimating the frequency of floating liner device. Those results showed that setting appropriate natural frequency of a floating liner device which meets the purpose is essential for ensuring measurement accuracy.