Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a drive assembly for an
agricultural tractor, comprising a drive case supporting
a right and left pair of wheels, the drive case housing a
differential mechanism in an intermediate position between
a right hand end and a left hand end thereof and reduction
mechanisms in the right hand end and -the left hand end, rest
pectively, to transmit power from the differential mechanism
to the wheels.
With the above tractor, the smaller the outside
diameter of a portion of the drive case housing the dip-
feren-tial mechanism and a pair of transmission shafts opera-
lively connecting the differential mechanism to the two
reduction mechanisms, respectively, the higher is that port
lion of the drive case from the ground and the less likely
is the drive case to come into contact with ridges or crops
when the tractor engages in work while straddling the ridges
in a field. Furthermore, since the differential mechanism
has a larger outside diameter than the transmission shafts
extending from the differential mechanism to the reduction
mechanisms, i-t has been conventional for the portion of the
drive case housing the differential mechanism and the trays-
mission shafts to comprise a combination of individual parts,
namely a part for housing the differential mechanism and
two other parts having a smaller diameter than the mentioned
part and housing the transmission shafts, respectively.
Therefore, that portion of the drive case, and hence the
entire drive case, is expensive to manufacture.
I
A primary object of the invention is to provide a drive
case whose portion housing the differential mechanism and trays-
mission shafts has a maximum height above the ground and which
may be manufactured at low cost.
' According to the present invention there is provided a wheel drive structure for an agricultural tractor comprising:
drive case means extended transversely of said tractor for sup-
porting right and left wheels, said drive case means comprising a
first case member and a pair of second case members connected to
opposite ends of said first case member; said first case member
being formed of a length of structural steel pipe and housing a
differential means in an intermediate portion thereof and a pair
of differential output shafts extending in opposite directions
from said differential means; said differential means including a
driving gear operatively connected to a differential input shaft
and a differential gear case fixedly secured to said driving
gear, said driving gear and said differential gear case having a
substantially same outer diameter; said second case members each
housing reduction means, said reduction means operatively con-
netted to one of said differential output shafts from said dip-
ferential means for driving one of said wheels, said reduction
means having a greater reduction ratio than an average reduction
ratio of said differential means.
A described above, the first case portion comprises
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one continuous unit extending from one of the second case
portions to the other, with a small diameter gear provided
to mesh with a pinion gear. The first case portion now
has a maximum height above the ground away from ridges and
crop and permits the tractor to operate desirably.
Moreover, the first case portion may be manufactured at low
cost utilizing an existing structural steel pipe; the
manufacture involves minor shaping work only such as per-
foraying it to receive the pinion gear and constricting
certain of its parts. This results in low cost of the drive
case taken as a whole.
A secondary object of this invention is to fully come
sensate for inability to provide a large reduction ratio
resulting from the differential mechanism being housed in
the steel pipe having a substantially equal diameter, as
described above.
In order to achieve the secondary object, the invention
provides, in addition to the foregoing construction, reduce
lion mechanisms each having a greater reduction ratio than
an average reduction ratio provided for the right and left
wheels by the differential mechanism.
Even though torque input to the differential mechanism
is insufficiently reduced by the small diameter gear in
mesh with the input pinion gear, the small diameter gear
being provided to decree the outside diameter of the differ-
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entail mechanism, it is compensated for by the reduction
mechanisms each having a greater reduction ratio -that an
average reduction ratio provided for the right and left
wheels by the differential mechanism. In order that the
wheels receive a predetermined value of torque transmission,
the rotary power -transmitted to -the differential mechanism
is reduced to predetermined slow rotations for transmission
to the wheels. Thus, this arrangement has the advantage of
effecting sufficient reduction while permitting the first
case portion to be formed of an inexpensive, continuous steel
pipe extending from one of the second case portions to the
other.
The invention will now be described in more detail,
by way of example only, with reference to the accompanying
drawings, in which:-
Fig. 1 is a side elevation of an agricultural
tractor;
Fig. 2 is a partly developed and partly broken
away rear view of a front wheel mounting assembly;
Fig. 3 is a partly developed front view of the
front wheel mounting assembly; and
Fig. 4 is a sectional view taken on line IV-IV of
Fig. 3
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AL
Referring to Fig. 1, an agricultural tractor come
proses a four wheel drive vehicle having a right and left
pelf of steerable front wheels 1 and a right and left pair
of non steerable 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 at the rear end thereof for driving
the attached working implement.
us 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 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 Verdi-
gaily oscillatable in opposed relationship with each other
about the axis Pi, whereby the tractor body maintains a sub-
staunchly horizontal altitude regardless of an incline of
the ground transversely of the tractor.
A front wheel drive assembly will now be described.
The drive case 6 comprises a first case portion 12
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formed owe a length of structural steel pipe-and two second,
cast case portions 11, the first case portion 12 constituting
an intermediate portion and the second case portions 11
constituting the right and left ends of the drive case 6,
respectively. The first case portion 12 houses a differ-
entail mechanism 13 at an intermediate position thereof and
a right and left pair of transversely extending transmission
shafts I operatively connected to a right and left pair of
side gears or output gears aye of the differential mechanism
13, respectively. Each of the second case portions 11
houses a vertically extending transmission shaft 16 opera-
lively connected to one of the transverse transmission shafts
14 through a bevel gear mechanism 15 acting as reduction
means, and a bevel gear reduction mechanism 19 comprising a
small drive gear 17 formed integrally with a lower end of the
vertical transmission shaft 16 and a large driven gear 18 in
mesh with the small gear 17 and splinted to the axle 5.
The bevel gear reduction mechanism 19 has a greater reduction
ratio than an average 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 shalt i3b, reduces its
speed and divides the output to right and left. The divided
output is transmitted to each axle 5 after being reduced by.
25 the bevel gear mechanisms 15 and 19. Number eye in Fig. 2
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denotes a drive pinion gear, and number doughnuts a pair
of pinion gears.
A shown in tug 2, the firs-t case portion 12 contains
two position setting tubes 12' to retain bearings 13' of the
differential mechanism 13 in position axially of the trays-
verse transmission shafts I These tubes 12' are removably
inserted into the first case portion 12 and retain thy bear-
ins 13' in position by abutting against the bearings 13'
and against case portions 21 to be described hereinbelow.
A construction Jo render the front wheels 1 steerable;-
will be described next. Each of -the second case portions
11 comprises a stationary case portion 21 housing the Verdi-
eel transmission shaft 16 and fixed to a flange aye of the
first case portion 12 7 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.
The first case portion 12 defines a bore 24, as seen in
Fig. 2, to permit lubricating oil in the first case portion
12 to flow into the boss 9 as lubricant between the boss 9
, and the tubular support 7.
The bevel gear reduction mechanism 19 may-be replaced
by a planetary reduction mechanism, and they are generally
US
referred to as a reduction mechanism in this specification.
Figs. 3 and 4 show a modified embodiment in which
only one position setting tube 12' is provided on one side
Or the differential mechanism 13. This embodiment will
S particularly be described hereinafter using like reference
number for like components in the preceding embodiment.
was shown in Fig. 3, a drive case 6 is provided bearing
the front wheels 1 at right and left ends thereof by means
of axles 5. The drive case 6 includes a tubular support 7
and an input shaft case 8 welded to an intermediate position
between right and left ends thereof. The drive case 6 is
attached through the tubular support 7 and the input shaft
case to a pair of front and rear bosses 9 and 10 provided
on a tractor body, to be 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 first case portion 12
formed of a length of structural steel pipe and two second,
cast case portions 11, the first case portion 12 constituting
an intermediate portion and the second case portions 11
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constituting the right and left ends of the drive case 6,
respectively. The first case portion 12 houses a differ-
entail mechanism 13 and a right and left pair of transversely
extending transmission shafts 14 operatively connected to a
right and left pair of snide gears of the differential mocha-
noisome 13, respectively. Each of the second case portions 11
houses a vertically extending transmission shaft 16 opera-
lively connected to one of the transverse transmission shafts
14 through a bevel gear mechanism 15 acting as reduction
means, and a bevel gear reduction mechanism 19 comprising a
small drive gear 17 formed integral with a lower end of the
vertical transmission shaft 16 and a large driven gear 18
in mesh with the small gear 17 splinted to the axle 5.
The differential mechanism 13 receives an output torque of
a transmission 20 through an input shaft 13b, reduces its
speed and divides the output to right and left. The divided
output is transmitted. to each axle 5 after being reduced by
the bevel gear mechanism 15 and 19.
A construction to render the front wheels 1 steerable _:
will be described next. Each of the second case portions.ll
comprises a stationary case portion 21 housing the vertical
transmission shaft 16 and fixed to a flange aye of the first
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
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vertical transmission shaft 16. The oscillatable case
portion 22 is oscillated by means of a knuckle arm 23.
The differential mechanism 13 comprises a drive pinion
gear eye, a driving gear 13c, and a differential portion 28.
The differential portion 28 includes a differential gear
case 26 fixed to the driving gear 13c by four bolts 25
extending through a space between bearings 13' of the differ-
entail gear cave 26 through a support pin 27, and the pair
of side gears aye attached to the differential gear case 26
and the driving gear 13c, respectively. As seen in Fig. 3,
the differential portion 28 and the drive pinion gear eye are
opposed to each other transversely of the tractor across
the driving gear 13c. Further, the driving gear 13c and
the differential gear case 26 have similar outside diameters
to render the differential mechanism 13 compact.
Reference number 12' denotes a position setting tube
abutting at one end thereof against one of the bearings 13'
of the differential mechanism 13 and at the other end against
the flange aye, the other bearing 13' being held in position
by a snap ring fitted to the first case portion 12, whereby
the differential mechanism 13 is fixed in position in the
first case portion 12. This construction involving only
one position setting tube has the advantage of low menu-
lecturing cost over the preceding embodiment in which two
position setting tubes are used.
