Note: Descriptions are shown in the official language in which they were submitted.
I
A Wheel Drive Apparatus for an Agricultural Tractor
Background of the Invention
This invention relates to a wheel drive apparatus for
an agricultural tractor which comprises a vertical trays-
mission shaft provided between a differential mechanism and wheel axles respectively and a drive bevel gear in
mesh with a reduction driven gear operatively connected to
the wheel axles respectively and integrally formed with
a lower end of the transmission shaft respectively, said
bevel gears being tapered to the upper portion thereof.
It is considered that the above agricultural tractor
increases the height of a differential mechanism case from
the ground by providing a vertical transmission shaft bet-
wren a wheel axle and the differential mechanism respectively
so that operation or working may be carried out while evading
contact between ridges or crop and the differential mechanism
case to the utmost even if the ridges locate between the
right and left wheels.
However, in the prior art, the drive bevel gear is
formed in integral with whole the transmission shaft and as
the result, the height of the differential mechanism from
the ground does not become sufficiently high! Because,
the following is the reasons: In the case of the bevel
gear such constructed, when cutting the teeth of the bevel
gear, it necessitates notate contact a cutting tool, which
ISSUES
is moved in the longitudinal direction of the teeth, with
the transmission shaft. The transmission shaft per so
cannot be one having small diameter since it has to provide
a predetermined strength for transmission of power.
When the diameter of the reduction driven gear is made
small in order to make sufficiently great reduction ratio
between the drive bevel gear and the reduction driven gear,
the construction for reduction becomes large and projects
greatly over the wheels, so that it becomes easy to contact
the crop or ridges. Therefore, the reduction driven gear
cannot be made with large diameter and the reduction ratio
between the drive bevel gear and the reduction driven gear
can be small and as the result it necessitates to increase
an average ratio of reduction of the differential mechanism
to the right and left wheels so as to reduce rotation power
for the differential mechanism into a predetermined low
rotation and then transmit same to the right and left wheels.
Because, it is necessary to enlarge the diameter of the
reduction driven gear which engages with an input pinion
gear of the differential mechanism in spite of small reduce
lion ratio.
Summary of the Invention
An object of this invention is to compactly construct
a reduction mechanism which comprises a drive bevel gear
and a reduction driven gear and further to obtain the
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sufficient height of a differential mechanism from the
ground without raising the center of gravity of a tractor
body.
In order to achieve the above-mentioned object, a
wheel drive apparatus for an agricultural tractor according
to this invention comprises an axle, a reduction driven
gear operatively connected to the axle, a differential
mechanism, a vertical transmission shaft interposed between
the axle and the differential mechanism, a bevel gear formed
integral with a lower end of the vertical transmission shaft
and tapered to the upper portion thereof, said bevel gear
being engaged with the reduction driven gear wherein the
vertical transmission shaft comprises a lower shaft portion
having the bevel gear and an upper shaft portion located
there above and these portions are welded to each other at
a portion thereof located adjacent an upper portion of the
bevel gear.
Namely, the lower shaft portion of the transmission
shaft having the drive bevel gear and the upper shaft portion
are manufactured independently to each other and finishing
process is given to the drive bevel gear and thereafter both
of the upper and lower shaft portions of the transmission
shaft are welded to a single one.'' Therefore, even if the
bevel gear is made with the irreducible minimum diameter of
a demand, there occurs an inconvenience of contacting a cut-
tying tool with the transmission shaft when cutting the teeth
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of the drive gavel gear.
Accordingly, the input rotation power to the different
trial mechanism can be reduced to a predetermined low rota-
lion and transmitted to the right and left wheels without
increasing a reduction ratio in the reduction construction
or mechanism between the reduction driven gear and the
vertical transmission shaft by enlarging the diameter of
the driven gear or increasing the reduction ratio of -the
differential mechanism by enlarging the diameter of a gear
in mesh with the input pinion gear to the differential
mechanism. Thus, it becomes possible to make the differ-
entail mechanism compact while minimizing a reduction mocha-
noisome which comprises the drive bevel gear and the reduction
driven gear and as the result, it enables to raise the
height of the differential mechanism case sufficiently from
the ground without raising the center of gravity of the
tractor body as in the case of extension of a vertical trays-
mission shaft, so that even if ridges are located between
the right and left wheels, it may be possible to carry out
operation or working favorably while satisfactorily evading
contact between the ridges or crop and the differential
mechanism or other transmission mechanisms and then traveling
safely by positioning the center of gravity of the tractor
body low.
Other objects and advantages will be apparent from the
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following description with reference to the drawings.
Brief Description of the Drawings
The drawings show an embodiment of a wheel drive Papa-
fetus for an agricultural tractor according to this invent
lion in which:-
Fig. 1 is a side view of the agricultural tractor,
Fig. 2 is a rear view of mounting portions of frontals partly broken away and partly developed,
Fig. 3 is a front view of a vertical transmission shaft,
and
Fig. 4 is an enlarged side view of a lower end portion
of the vertical transmission shaft having a spiral bevel
gear.
Description of the Preferred Embodiment
Referring to Fig. 1, an agricultural tractor comprises
a four wheel drive vehicle having a right and left pair of
dirigible front wheels 1 and a right and left pair of non-
dirigible rear wheels 2. The tractor includes a lift arm
3 at the rear end thereof for vertically movably attaching
a rotary plow or other working implements, and a power
takeoff shaft 4 at the rear end thereof for driving the
attached working implement. I
As shown in Fig. 2, the tractor further includes a drive
case 6 bearing the front wheels 1 at right and left ends
thereof by means of axles 5. The drive case 6 includes a
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pair of front and rear -tubular supports 7 and 8 welded to
an intermediate position between the right and left ends
thereof. By means of these supports 7 and 8 and a pair of
front and rear bosses 9 and 10 provided on a tractor body
the drive case 6 is vertically oscillatable about an axis
Pi extending longitudinally of the tractor body. Thus,
the front wheels 1 are attached to the tractor body to be
vertically oscillatable in opposed relationship with each
other about the axis Pi, whereby the tractor body maintains
a substantially horizontal posture regardless of an incline
of the ground transversely of the tractor.
A front wheel drive structure will be described herein-
after. The drive case 6 comprises a case portion 12 formed
of a length of structural steel pipe and two cast case port
lions 11, the case portion 11 constituting an intermediate portion and the case portions 11 constituting the right and
left ends of the drive case 6, respectively. The case
portion 12 houses a differential mechanism 13 at an inter-
mediate position thereof and a right and left pair of trays- ,
tersely extending transmission shafts 14 operatively
connected to a right and left pair of output gears aye and
13b of the differential mechanism 13, respectively. Each
of the case portions 11 houses a vertically extending trays-
mission shaft 16 operatively connected to one of the trays-
verse transmission shafts 14 through a bevel gear mechanism
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15 acting as reduction means, and a bevel gear reduction mechanism 19 comprising a spiral bevel gear lo formed
integral with a lower end of the vertical transmission
shaft 16 and tapered to the upper portion thereof and a
reduction driven gear 18 in mesh with the spiral bevel
gear 17 and splinted to the axle 5. The bevel gear reduce
-lion mechanism 19 has a greater reduction ratio than an
verge reduction ratio provided for the right and left front
wheels 1 by the differential mechanism 13. The differential
mechanism 13 receives an output torque of a transmission 20
through an input shaft 13c, reduces its speed and divides
the output to right and left. The divided output is trays-
milted to each axle 5 after being reduced by the bevel gear
mechanism 15 and 19.
A construction to render the front wheels 1 dirigible
will be described next. Each of the case portions 11
comprises a stationary case portion 21 housing the vertical
transmission shaft 16 and fixed to a flange aye of the case
portion 12, and an oscillatable case portion 22 having the
axle 5 and connected to the stationary case portion 21 to
be oscillatable about a vertical axis Pi coaxial with the
vertical transmission shaft 16. The oscillatable case
portion 22 is oscillatable by means of a knuckle arm 23.
Bores aye and 24b, as seen in Fig. 2, are openings for
lubricating oil.
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As shown in Fig. 3, the vertical transmission shaft
16 comprises a lower shaft portion aye having the spiral
bevel gear 17 and an upper shaft portion 16b located
there above and these portions aye and 16b are welded by
friction welding to each other at a portion 25 located
adjacent an upper portion of the spiral bevel gear 17.
Namely, the vertical transmission shaft 16 is divided into
the lower shaft portion aye and the upper shaft portion 16b
at the portion 25 which is not contacted with a cutting
tool moving in the longitudinal direction of the teeth of
the spiral bevel gear 17; in other words the portion 25
being located on the side of the spiral bevel gear 17 to
a cross point of an elongated line 26 of the bottoms of the
teeth of the spiral bevel gear 17 and an outer periphery
of -the vertical transmission shaft 16, and thus manufactured
independently and then finishing process is given to the
spiral bevel gear 17. Thereafter, these portions aye and
; 16b are welded to each other into a single shaft.
Weld of the lower shaft portion aye and the upper port
lion 16b may be practiced by arc welding, gas welding or
resistance welding. Further, the reduction driven gear 18
may be operatively connected to the axle 5 via a reduction
mechanism such as a planetary gear.
The above-mentioned embodiment utilizing the spiral
bevel gear 17 provides the following advantages.
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Namely, since -the spiral bevel gear is adopted as a
transmission gear, the characteristic of a spiral bevel
gear which may transmit a high torque by engagement of -
a number of teeth thereof greater than those of a normal
bevel gear. As a predetermined torque can be transmitted
even if the diameter of the bevel gear is made small,
rotation to the differential mechanism can be reduced to
a predetermined low rotation and transmitted to the wheels
without increasing a reduction ratio of a reduction mocha-
noisome between the reduction driven gear and the vertical transmission shaft by enlarging the diameter of the reduce
lion driven gear or without increasing a reduction ratio of
the differential mechanism by enlarging the diameter of
a gear in mesh with the input pinion gear of the differential
mechanism. Therefore, the differential mechanism can be
compact while compacting the reduction mechanism comprising
the drive gear and the reduction driven gear, so that the
height of the differential mechanism case from the ground
may be increased without raising the center of gravity of
the tractor body as in the case of making a vertical trays-
mission shaft long. As the result, even if ridges are
located between the right and left wheels, it may be possible
to carry out operation or working favorably while satisfact-
rile evading contact between the ridges or crop and the
differential mechanism case or other transmission mechanisms
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and -then traveling safely by positioning the center of
gravity of the tractor body low.
