An Improved Approach to the Instantaneous IMEP Method for Piston-Ring Assembly Friction Force Measurement

The instantaneous IMEP method is advantageous in that it is feasible for piston friction measurement with minor engine modification, while its weakness is the low accuracy achievable in the end result. Because of error accumulation from various input data measurements and ensuing data processing, its result is bound to have a low confidence level. For minimization of the error, the frequency response function was determined for each measuring system, and the relative time delays among the measured signals were obtained by the application of the cross-correlation function. In order to further increase the accuracy, an accelerometer was installed at the piston skirt for direct inertia force measurement of the piston assembly. In addition, the crank case pressure was measured. Relatively reliable friction data were obtained up to 2000rpm motoring and 1500rpm firing conditions after taking these appropriate measures.