Tomanik, E. and Bruno, R., "Calculation of Piston Ring Radial Pressure Distribution from its Measured Free Shape," SAE Technical Paper 2012-01-1322, 2012, doi:10.4271/2012-01-1322.
Piston ring radial pressure effects both the manufacturability of the ring as well as its performance in the engine. While lack of radial contact can cause increased blow-by and lubricant oil consumption, high local contact pressure can cause excessive wear and even scuffing. Current methods to evaluate ring radial pressure fail to identify subtle, local pressure changes. To overcome such limitation, a new method to evaluate ring radial pressure at each peripheral angle was developed. In this experimental procedure, the ring free shape is recorded by an optical device and then this free shape is used as input to code that calculates its radial pressure distribution. In order to validate this method, six different sample variants of ring pressure distribution, (i.e. free shape), have their radial pressure evaluated by two different methods: 1,) the new procedure and 2,) a mechanical jig with 11 circumferentially spaced radial load sensors. By contrast, the usual ovality plot, frequently used for production and design control, was unable to distinguish between variants with same ovality but different radial pressure near the ring tips. To validate the proposed new method, both theoretical and the measured ring free shapes were analyzed. Correlation and resolution of the new method against both the theory and the mechanical measurements was very good.