09-05-2012, 10:37 AM
SPEED-REDUCTION GEAR-BOXES
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This invention relates to speed-reduction gear-boxes of
the type providing for direct application via an output
sleeve to a shaft to be driven, and having an input shaft
parallel to the output sleeve and in geared connection with
it. Such a gear-box, providing a predetermined ratio of
speed-reduction (or a selection of predetermined ratios
by varying the ratio of any one or more of the pairs of
intermeshing gears making up the total reduction sequence)
is commonly used as a unit for application to
and support by a shaft to be driven, to be driven itself
from a parallel shaft, usually that of a driving motor, by
belt or chain connection to the input shaft, with the gearbox
capable of being anchored against the tendency to rotation
about the axis of the shaft to be driven. Adjustability
of the anchoring means permits the tension of the
driving connection to the input shaft to be regulated.
Thus, the gear-box may be anchored by a torque-arm of
adjustable length and operating under tension.
However, the usual construction of such a gear-box
consists essentially of a two-part metal housing, which not
only serves to enclose all the gears but contains the housings
for the bearings of all the shafts to which the gears
are secured. The two parts of the housing must therefore
be of substantial, rigid character, and accordingly they
are usually castings. Because they are also large enough to
enclose the gears, they are bulky and relatively heavy.
Moreover, they are directly subjected to the vibrations
arising from the gear-box when in use. As a consequence,
the advantage that the input can be provided by a highspeed
low-torque source of power is accompanied by the
considerable disadvantage that the high-pitched noise generated
by the use of parts operating at high speed is
transmitted directly by the housing to the surrounding
space.