Measurement devices for piston assembly friction and oil film thickness

Abstract

A technique for estimating the instantaneous frictional force between the piston assembly and the cylinder wall has been developed by improving the moveable bore technique. The technique can be easily applied to small multi-cylinder engines since its structure is simple and stable so that the measuring range could be extended. The reliability of the friction data can be improved by a newly proposed compensation method. The technique was applied to a four cylinder SI engine under various engine speeds. engine loads. and oil viscosity. An instrument for measuring the oil film thickness on the piston rings was also developed by using the commercially available gap sensors. It as possible to measure the oil film thickness,, on thin oil ring rails as well as on the compression rings. The frictional characteristics were established as a relationship between frictional mean effective pressure and a parameter which is the product of the piston mean speed and the oil viscosity.