| Both experimental and analytical methods were used to study the friction produced by the piston and rings of a spark ignition engine. A friction measurement technique, the improved Fixed-Sleeve method, was set up to measure the total friction produced by the piston rings and the piston skirt (piston/ring assembly). The Fixed-Sleeve method was greatly improved by rearranging the lateral support wiring and the calibration method. The measured data were later used to guide the development of a piston/ring assembly friction model. This model uses basic engine design and operating data as inputs to predict the total friction of piston and rings using the concept of the Stribeck diagram and similarity principles. Finally, with the knowledge gained from the engine friction test and the piston/ring assembly friction modeling, an additional analytical friction and lubrication model for the piston skirt was developed. In this model, a simplified piston skirt structure was introduced which considered the effect of skirt elastic deformation and thermal expansion. Asperity contact was included also.; The results predicted by the models were compared with available experimental friction data. Good agreement was obtained. It was concluded that similarity modeling produces a good estimate of piston/ring assembly friction for designs, lubricants and operating conditions which are modest extensions of those for which experimental data are available. |
