To accurately measure piston ring radial-force, we constructed an instrument arraying 12 measuring assemblies, spaced 30o apart around the ring circumference, each comprising a roller, a slider, a load cell in a holder, and a micrometer head. Using this measuring device, we investigated the radial-force distribution in several compression rings with various ovalities. For each ring, we first measured the radial force at 30o intervals around the ring circumference, avoiding the ring gap, and then we displaced the ring 15o in the circumferential direction, and set a custom jig between the ring gap and the measuring assembly. Thus we were able to measure the radial-force at 15o intervals around the entire circumference, including the ring gap position. Results indicated that the plots of radial-force distribution indeed resembled the ring ovality contours- except in rings with negative ovality or a lower tangential force, where the plot of radial-force distribution differed from the ring ovality contour on the ring gap side.
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