epitrochoid

a epicycloyd. a roulette traced by a point attached to a circle of radius r rolling around the outside of a fixed circle of radius R, where the point is at a distance d from the center of the exterior circle (from Google);or, in short: a roulette rolling with a R radius in a fixed outer circle, with the roulette itself being a "r" one, rolling freely inside a fixed last one. Like in a Mazdarotary engine

Mazda has a epitrochoid engine. You know it as a rotary engine