According to the transmission ratio:
Fixed transmission ratio -- circular gear mechanism (cylinder, cone)
Variable transmission ratio -- non-circular gear turbine (elliptic gear)
According to the relative position of the axle
Plane gear mechanism, spur gear drive, outer meshing gear drive, inner meshing gear drive, gear and rack drive, helical gear drive, character gear drive, space gear mechanism, bevel gear drive, interlace shafts helical gear drive, worm gear and worm gearing
According to the process
Conical gear, blank semi-finished gear, spiral gear, internal gear, spur gear, worm wheel and worm gear.