A piston assembly friction model has been developed to predict the individual performance of compression rings, the oil control ring and the piston skirt. Validation of this model has been undertaken by comparing the predicted results with the experimental measurements of piston assembly friction in a gasoline engine under fired conditions using the IMEP (indicated mean effective pressure) method. The experimental results for an SAE 0W20 without friction modifier were compared with the predictions. The predicted results correlate very well with the measurements, especially at higher lubricant inlet temperatures. Piston skirt friction was predicted using both a simple concentric / cylinder model and a more realistic but computationally intensive method incorporating piston secondary motion. The results clearly indicate than the latter more realistic method is required to achieve satisfactory correlation with the measured data.

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