Gears 1 and 2 rotate about fixed axes A and B. Double-rim gear 1 is composed of circular gears a and b. The geometric centre of gear a coincides with axis A. The geometric centre 0 of gear b has the eccentricity e. Gear 2 is composed of half of noncircular gear c and half of circular gear d. Gear 2 makes one revolution to two revolutions of gear 1, and the average transmission ratio in a full cycle is i₁₂=2. When portions a and d of gears 1 and 2 are in mesh, the transmission ratio is constant and equals i₁₂=2. When portions b and c of gears 1 and 2 are in mesh, the transmission ratio varies within the limits from i_min=(1-ε)/(m-(1-ε)) • to i_max=(1+ε)/(m-(1+ε)) where ε=e/r₁, m=l/r₁, r₁ is the pitch radius of gear b and l is the centre-to-centre distance.
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