Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 2 Indirect Power Transfer Devices 91
Figure 2-16 Oil would be
injected at high pressure to
reduce friction in critical areas of
contact
faces. Each of the separating forces in the several meshes would contribute
to the torque on the gear and to an axial force on the worm. To
counteract this axial force and to reduce the friction that it would otherwise
cause, oil would also be pumped under pressure into a counterforce
hydrostatic bearing at one end of the worm shaft.
This type of worm-gear transmission was conceived for use in the
drive train between the gas-turbine engine and the rotor of a helicopter
and might be useful in other applications in which weight is critical.
Worm gear is attractive for such weight-critical applications because (1)
it can transmit torque from a horizontal engine (or other input) shaft to a
vertical rotor (or other perpendicular output) shaft, reducing the speed by
the desired ratio in one stage, and (2) in principle, a one-stage design can
be implemented in a gearbox that weighs less than does a conventional
helicopter gearbox.
Heretofore, the high sliding friction between the worm coils and the
gear teeth of worm-gear transmissions has reduced efficiency so much