Improved Criterion for Ring Conformability Under Realistic Bore Deformation

Increased engine loads, coupled with low friction rings, renew the attention for predicting the maximum bore deformation which a given ring design can conform to before losing contact. The MIT developed “Software of Ring Design Tools” (RDT) code was used to verify the different published ring conformability criteria by progressively increasing the bore deformation until the model predicted lack of contact. For simple order deformations, the semi-empirical Tomanik criterion was found to correlate with the model predictions. However, as expected, more realistic deformations combining different harmonic orders were able to cause lack of conformability, even with the individual order amplitudes being lower than the criterion limit.

In search of a more comprehensive criterion, an automated model ran hundreds of thousands of deformation cases in combination with relative ring angular positions looking at conformability. The results suggest that ring conformability can be seen as a potential that is consumed by the individual distortions at each harmonic order. An improved, but still simple conformability criterion is proposed to account for realistic bore deformations. Other operating condition influences such as thermal and gas loading, ring ovality, etc. are also briefly discussed.