This study is to measure the friction between the piston-ring assembly and cylinder wall for various engine operating conditions including motoring and firing. The assembly friction force was indirectly measured by the thrust force applied on connecting rod. The strain gage signals detecting the thrust force were led out of the engine by a grasshopper linkage system.
At cranking the assembly lubrication is apparently in boundary and mixed lubrication range, however, at idle speed of 800 rpm already significant part of friction was shifted to hydrodynamic mode. At higher speed of 1500 - 2500 rpm the assembly fmep (friction mean effective pressure) was found to be influenced mostly by hydrodynamic lubrication.
Above 1500 rpm considerable noise input apparently originating from crankshaft caused a serious distortion in the friction signal. Appropriate test procedures filtering out those noises were deemed to be necessary to improve the credibility of friction data.
