A drive axle with a gear ring meshing with a drive pinion is designed with silent running properties, in that an intermediate member is secured to the differential carrier and is connected to the gear ring by an elastic coupling. Between the contacting faces of the gear ring and the intermediate member there are annular grooves and a cylindrical space is formed between an inner face of the gear ring and an outer cylindrical face of the intermediate member. The cylindrical space and the annular rings are filled with a viscous substance.

A counter gear mechanism having a large gear coaxially engaged to a small gear. The large gear comprises a disk-like portion and a circumferentially extending portion continuously extending on a peripheral portion of the disk-like portion. The circumferentially extending portion has a circumferential outer surface on which first gear teeth are provided. The small gear comprises a disk-like plate and a body being cylindrically shaped to have a circumferential outer surface on which second gear teeth are provided. A tubular member, provided at a center of the disk-like portion, defines a hole and extends along a rotational axis around which the large gear rotates. At least one recessed portion, formed in the disk-like portion, extends in a circumferential direction relative to the rotational axis. At least one projection is fixed to the disk-like plate of the small gear on an opposite side to the side on which the body is provided. The projection inserts into the recessed portion to move along the circumferential direction relative to the rotational axis. First and second spring members are provided within the recessed portion at opposite sides of the projection.

A radially compliant gear is provided to reduce transmitted shock loads and/or resist jamming as a result of debris entering its mesh with another gear. The radially compliant gear includes a hub adapted to rotate about an axis, and a compliant rim. The hub includes a first surface that faces radially inwardly. The rim includes external gear teeth and a second surface that faces radially outwardly. The rim is mounted to the hub through the first and second surfaces to allow localized radial deflections of the rim relative to the hub. The first and second surfaces are configured to provide a predetermined minimum radial preload between the rim and the hub.

The main rotor of a helicopter is driven by an epicyclic gearbox comprising a rotor sun gear coaxial and co-rotational with the rotor, a stationary sun gear coaxial with the rotor sun gear, at least one planet having an axis parallel to and rotating about the sun gear axis, and making contact with both sun gears. The planet comprises first and second planetary coaxial gears mechanically constrained to rotate together. The first planetary gear is in meshing engagement with the stationary sun gear and the second planetary gear is in meshing engagement with the rotor sun gear. The first planetary gear is also in meshing engagement with the internal teeth of a first ring gear and the second planetary gear is also in meshing engagement with the internal teeth of a second ring gear. The first and second ring gears are separately driven, and torque is combined by the planets.

A worm 1 is composed of an annular tooth body 11 having a tooth 10 on the outer surface thereof, a core body 12 inserted inside the annular tooth body 11; and an elastic coupler 13, which can be transformed in the radial direction, for coupling the core body 12 with the annular tooth body 11. The worm 1 is engaged with the worm wheel with the elastic coupler 13 being transformed in the radial direction in such a manner that a negative amount of backlash is generated at the engagement portion. This can be also employed for the worm wheel. With a reduction gear combination having this structure, the backlash amount at the engagement portion can be adjusted to a proper amount without selecting elements such as the worm and the worm wheel to be assembled.