Three-ring internal and external gear type slewing bearing

A disclosed three-ring internal and external gear type slewing bearing is divided into an underslung internal gear type slewing bearing and an underslung external gear type slewing bearing. The underslung internal gear type slewing bearing comprises an inner ring, a middle ring and an outer ring; a first roller path is arranged at the slightly upper position on the combination face of the inner ring and the middle ring, a second roller path is arranged at the slightly lower position on the combination face of the middle ring and the outer ring, and the first roller path and the second roller path are in the shape of an annular circular tube or square tube; rollers are a steel balls or short circular columns; an internal gear is arranged at the lower half of the inner lateral side of the inner ring, and the external gear is arranged at the outer lateral side of the external ring; a first filling hole is communicated with the first roller path from the slightly upper position on the inner lateral side of the internal ring, and a second filling hole is communicated with the second roller path from the slightly lower position on the inner lateral side of the middle ring; and the underslung gear types of the underslung internal gear type slewing bearing and the underslung external gear type slewing bearing are opposite. The slewing bearing is reasonable in structure design and is applicable to main machines needing to perform double rotation and double force transferring.