Note: Descriptions are shown in the official language in which they were submitted.
2140~8~
HAND OPERATED HOI~T
BACKGROUND OF THE INVENTION
In compact, light duty, hand operated chain hoists
it is known to provide a hand operated drive wheel and
a load lift wheel interconnected by a drive train
including a drive pinion coupled to the drive wheel, a
pair of first driven wheels arranged to mesh with the
drive pinion, a pair of driven pinions rotatable with
the first driven wheels, and a second driven wheel
coupled to the lift wheel and arranged to mesh with the
driven pinions.
In all known hand hoists of the type described, the
pinions and the driven wheels are spur gears with each
of the pinions typically having four teeth in order to
provide a mechanical advantage within the range required
for this type of hoist. These prior hoists have contact
ratios of less than one, which means that the pinions
are not disposed in continuous drive engagement or
connection with their associated driven wheels. When a
disengagement or uncoupling of the pinions and driven
wheels occurs, a hoist supported load is permitted to
momentarily accelerate with the result that a hoist
operator observes an abrupt change in hand chain pull
loading.
Hoists of the type described generally have load
ratings of up to ten tons. Hand operated chain hoists
having larger load ratings typically employ different
types of drive trains developed for heavy duty opera-
tion, such as that afforded by planetary gearing, whose
use does not produce abrupt changes in hand chain pull
loadings.
It is theoretically possible to achieve a contact
ratio of one for constructions employing pinions formed
with five teeth. Further, hoists employing pinions
formed with more than five teeth may of course be
constructed to provide contact ratios greater than one.
However, this leads to the need to provide pinions and
2140~86
-
driven wheels of greater diameter, determined by the
requirement that a certain tooth size be maintained to
accommodate tooth loading conditions, and results in an
unacceptable increase in the overall size and weight of
the hoist.
Accordingly, with a view towards minimizing overall
size and weight of light duty hoists of the type
described, manufacturers of such hoists have for at
least ten years offered hoists having the undesirable
feature of exposing an operator to abrupt changes in
hand chain pull loads.
SUMMARY OF THE INVENTION
The present invention relates to an improvement in
compact, light duty hand operated chain hoists, which
avoids the problem of abrupt changes in hand chain pull
loadings without resort to the use of pinion gears
having more than four teeth.
In accordance with a preferred form of the present
invention, a compact, light duty hand operated chain
hoist of the type having a drive train including a drive
pinion coupled to a chain operated drive wheel, a pair
of first driven wheels arranged to mesh with the drive
pinion, a pair of driven pinions rotatable with the
first driven wheels, and a second driven wheel arranged
to mesh with the driven pinions and to be coupled to a
load lift wheel, is modified to provide the pinions and
the driven wheels with helical teeth, wherein the
helical teeth of the pinions are from one through four
in number and the teeth have axial lengths sufficient to
ensure creation of a contact ratio of at least one.
BRIEF DESCRIPTION OF THE DRAWINGS
The nature and mode of operation of the present
invention will now be more fully described in the
following detailed description taken with the
accompanying drawings wherein:
214~086
Fig. 1 is a perspective view of a compact hand
operated hoist incorporating the present invention;
Fig. 2 is a sectional view taken generally along
the line 2-2 in Fig. l;
Fig. 3 is a sectional view taken generally along
the line 3-3 in Fig. 2; and
Fig. 4 is a sectional view taken generally along
the line 4-4 in Fig. 2.
DETAILED DESCRIPTION
A compact, light duty, hand operated chain hoist
incorporating the present invention is generally desig-
nated as 10 in Fig. 1. Hoist 10 is conventional from
the standpoint that it includes a casing 12, which is
adapted for suspension from a suitable support, not
shown, by a hook 14, and serves in turn to support a
drive wheel 16, a load lift wheel 18, and a drive train
shown in part in Figs. 2-4 and generally designated as
20. Typically, rotation is imparted to drive wheel 16
by a manually operable link chain and lift wheel is
coupled to a suitable load via a link chain, neither
link chain being shown.
Drive train 20 typically includes a drive shaft 22,
which is coupled to drive wheel 16 via a clutch, not
shown, and is supported to extend transversely within
casing 12 for rotation about an axis 22a disposed
concentrically inwardly of lift wheel 18; a drive pinion
24 carried by and keyed for rotation with drive shaft
22; a pair of stub shafts 26 and 28 which are supported
by bearings for rotation about a pair of axes 26a and
28a disposed parallel to drive shaft axis 22a and which
carry a pair of first driven wheels 26b and 28b each
arranged to mesh with drive pinion 24, respectively.
Stub shafts 26 and 28 also include driven pinions 26c
and 28c, respectively, which are each arranged to mesh
with a second driven wheel 30 fixedly coupled to lift
wheel 18 by a tubular shaft 32 concentrically and
slidably mounted about drive shaft 22. Pinions 24, 26c,
2140~86
and 28c and driven wheels 26b, 28b, and 30 are mounted
within casing 12 in a manner which prevents relative
movement therebetween in an axial direction.
In accordance with the present invention, pinions
24, 26c, and 28c and driven wheels 26b, 28b and 30 are
provided with helical gear teeth 34. In a preferred
form of the invention, drive pinion 24 has four gear
teeth 34, a normal diametral pitch of ten teeth-per-
inch, a pressure angle of 14.5 degrees, and a right-hand
helix angle of 15 degrees; first driven wheels 26b and
28b each have sixteen gear teeth 34, a normal diametral
pitch of ten teeth-per-inch, a pressure angle of 14.5
degrees, and a left-hand helix angle of 15 degrees;
driven pinions 26c and 28c each have four gear teeth 34,
a normal diametral pitch of ten teeth-per-inch, a
pressure angle of 14.5 degrees, and a left-hand helix
angle of 15 degrees; and second driven wheel 30 has
sixteen teeth, a normal diametral pitch of ten teeth-
per-inch, a pressure angle of 14.5 degrees, and a right-
hand helix angle of 15 degrees.
In order to avoid the problem of abrupt change in
hand chain pull loading encountered in prior art light
duty hoists, gear teeth 34 are of sufficient length in
the axial direction (face width) to provide a total
contact ratio of approximately one or more for both the
input mesh between drive pinion 24 and first driven
wheels 26b and 28b, and the output mesh between driven
pinions 26c and 28c and second driven wheel 30. Where
a face width of 3/8" is provided for the input mesh of
the preferred gear train described above, gear analysis
indicates that a total contact ratio of 1.16 is
achieved. Where a face width of 1-1/8" is provided for
the output mesh of the preferred gear train, a total
contact ratio of 1.78 is achieved.
As may be appreciated from the above description,
the gear train of the preferred embodiment provides a
hoist which is of acceptable overall size and weight,
yet which also provides the necessary mechanical advan-
21 41~08~
tage without undesirable abrupt changes in hand chain
pull loading.
While the preferred embodiment described above employs
pinions 24, 26c, and 28c each having four gear teeth 34,
S it is contemplated to provide fewer than four gear teeth
on each pinion while maintaining a total contact ratio
of approximately one or more for the input and output
meshes. Also, use of a single first driven wheel and
single driven pinion is considered to be within the
scope of the present invention, as defined by the claims
below.
