Patent ID: 7536930

Claim:
A reduction gear unit, comprising: a pinion shaft and a main gear shaft that are disposed in parallel to each other; a pinion mounted on the pinion shaft and a main gear mounted on the main gear shaft that are arranged to mesh with each other, so as to transmit a rotation of the pinion shaft to the main gear shaft; a housing that encloses the pinion and the main gear, comprising: an inner surface whose width, in a cross section perpendicular to an axial direction of the pinion shaft and the main gear shaft, perpendicular to an imaginary line that connects centers of the pinion shaft and the main gear shaft evenly increases from a pinion side toward a main gear side between ends of arcuate regions respectively enclosing the main gear and the pinion a first housing region enclosing the pinion; and a second housing region enclosing the main gear; wherein the housing is oriented such that the main gear shaft is inclined with respect to a horizontal surface and such that the first housing region is disposed lower than the second housing region; and wherein an oil and fat lubricant is contained in a lower part of the first housing region, and wherein the first housing region is partially filled with the oil and fat lubricant to a predetermined fill level and a part of a meshing portion of the pinion and the main gear is immersed in the resin lubricant located below the predetermined fill level.