Measurement of friction and noise from piston assembly of a single-cylinder motorbike engine at realistic speeds

Abstract

This paper presents a thorough experimental study of piston assembly friction and noise in a single-cylinder motorbike engine operating at low speeds. The friction of the piston ring pack is evaluated using a foil strain gauge with minimal cylinder modification on the thrust side. The technique involves transmitting deformations through the cylinder bore and recording reflections from the lubricated interface as the piston assembly passes. Under these conditions, the piston side forces and the thermal deformations on the output side of the strain gauge sensor are critical. Therefore, the proposed methodology is designed under controlled operating conditions. The overall deformation of the piston assembly is analysed to measure the primary reflection due to friction between the piston assembly and the cylinder wall. Simultaneously, the piston assembly noise is recorded on the thrust side of the engine block using a microphone. Taking measured noise data into account, possible piston slap events resulting from varied engine speeds are taken into account using continuous wavelet signal analysis. The calibration procedure for both tests is also illustrated. The measured friction results show that the strain gauge technique is a challenging work in providing realistic results to enhance current technology. For low engine speeds, a higher contribution is noted by boundary friction at the top dead centre reversal, extending to the position of maximum combustion pressure in the power stroke. Furthermore, the main contribution of the piston slap is estimated at the thrust side when the piston assembly passes at the beginning of the combustion stroke. These results can also be attributed as data to validate piston ring models in terms of friction and piston slap.