This paper focuses on a systematic revelation of the driving principle andmechanical properties of
this special variable center distance gear type. On the basis of screw theory, this paper first establishes
its mathematical model, including kinematic relations, instantaneous screw axis, “nonconjugated”
pitch curves, generator, envelope surfaces and generated surfaces. And then, the
mechanical properties, forms as well as advantages of applicable variable center distance gear
train are all discussed.