Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to tractor transmissions,
and in particular to a transmission comprising a main change-
speed mechanism, an auxiliary change-speed mechanism, and
a gear type backward-forward drive switching mechanism for
transrnitting powr from an engine to a propelling system.
2. Description of the Prior Art
In conventional tractor transmissions comprising a
main change-speed mechanism, an auxiliary change-speed
mechanism, and a gear type backward-forward drive switching
mechanism as described above, the gear type backward-forward
drive switching mechanism is provided in one of the three
fashions, namely combined into the main change-speed mechanism,
disposed ~orwardly of the main change-speed mechanism, or
disposed rearwardly of the auxiliary change-speed mechanism.
The case of the gear type backward-forward ~rive switch-
ing mechanism being combined into the rnain change-speed
mechanism is a mere remnant of the times when plural backward
speeds were unnecessary to tractors as still are to ordinary
motor vehicles. Such a construction cannot meet the require-
ment of tractors to perform varied functions by utilizing
plural backward speeds.
In order to meet this requirement, plural backward
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speeds are now provided. A backward-forward drive switching
mechanism to provide plural backward speeds without necessi-
tating extensive rnodifications to the main change-speed,
mechanism is in many instances disposed forwardly of the
main change-speed mechanism to reverse the rotation of a
transmission shaft prior to power input to the main change-
speed mechanism. ~owever, this arrangement involves a
change gear operation prior to reduction of the engine speed
by the main change-speed mcchanism, and therefore has the
disadvantage of having to effect gear meshing under high
speed ro-tation which lacks in smoothness.
It has also been practised to dispose the backward-
forward drive switching mechanism rearwardly of the main
and auxiliary change-speed mechanisms. In this instance,
a hand lever for operating the switch mechanism is provided
close to a hand lever for operating the main change-speed
rnechanisrn adjacent the driver's seat. It has the disadvan-
tage of re~uiring a long interlocking rnechanism operatively
connecting the backward-forward drive swi-tching mechanism
to its hand lever.
Summary of the Inven-tion
The object of this invention is to eliminate the draw-
backs of the prior ar-t constructions described above and
to arrange the gear type backward-forward drive switching
mechanism in a rational manner which is operable by a sirnple
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interlocking mechanism and e~fects a smooth backward-forward
drive switching.
In order to achieve the above object, a transmission
for a tractor according to the present invention comprises
a main change-speed mechanism9 an auxiliary change-speed
mechanism, and a gear type backward-forward drive switching
mechanism for transmitting power from an engine to a propel-
ling system, wherein the main change-speed mechanism, the
gear type backward-forward drive switching mechanism, and
the auxiliary change-speed mechanism are arranged in a trans-
mission case in the mentioned order in the forward to rearwarddirection of the tractor.
More particularly, the construction according to the
present invention in which the main change speed mechanism,
the gear type backward-forward drive switching mechanism,
and the auxiliary change-speed mechanism are arranged in
a transmission case in the mentioned order in the forward
to rearward direction of the tractor, results in the following
advantages over prior art constructions. Since the backward-
forward drive switching mechanism is disposed rearwardly
of the main change-speed mechanism, gear shifting is carried
out under a low speed condition provided by the main change-
speed mechanism thereby realizing a smoother backward-forward
drive swi-tching than where the two mechanisms are arranged
in the opposite order. Furthe.rmore, a hand lever for
operating the backwar~-forward drive swi.tc~ing mechanism
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is generally disposed adjacent a lever for operating the
main change-speed mechanism since backward-for~ard switching
operations are often carried out along with main change-
speed operations. The construction of the present invention
in which the backward-forward drive swi-tching mechanism
is disposed forwardly of the auxili.ary change-speed mechanism
permits the backward-forward drive switching mechanism to
be located closer to the hand lever therefor than where
the backward-forward drive switching mechanism is disposed
rearward]y of the auxiliary change-speed mechanism, thereby
simplifying the interlocking between the backward-forward
drive switching mechanism and the hand lever there~or and
also simplifying the structure for its operation.
Other objects and advantages of the presen~ invention
will be apparent from the following description.
Brief Description of the Dra~ings
: The drawings illustrate a tra:nsmission for a tractor
according to the present invention, in which;
; Fig. 1 is a side elevation of a tractorl
Fig. 2 is a vertical section of the transmission,
Fig. 3 is a vertical section showing a backward-forward
drive switchihng mechanism and an i.nterlocking system there-
for,
Fig. 4 is a plan view of hand levers,
Fig. 5 is a vertical section of a modified transmission,
and
Fig. 6 and 7 are views showing different backward-
forward drive swithcing mechanism for the purpose of
comparison.
Description of the Preferred Embodiment
Figo 1 shows a four wheel drive tractor comprising
a tractor body mounted on a propelling system A or front
and rear drive wheels 1 and 2. The tractor has an engine E
at the front and a lift arm 3 and a power -takeoff shaft 4
at the rear for coupling various kinds of working implement
such as a rotary cultivator and a mower to the tractor.
Power is transmitted from the engine E to -the drive wheels 1
and 2 through a main clutch 5, a main change-speed mechanism
~, a gear type backward-forward drive switching mechanism 7,
an auxiliary change-speed mechanism 3 and a differential
mechanism 9, and to the power takeoff shaft 4 -through the
main clutch 5 and a further change-speed mechanism 10.
Thus the tractor is adap-ted to carry our varied functions
by trailing and driving a working implement.
this transmission s-tructure for transmitting the power
of the engine E to the front and rear wheels 1 and 2 and
to the power takeoff shaft 4 is particularly described with
reference to Fig. 2. The power of engine E is transrnitted
to an input shaft 13 of the transmission through the maln
clutch 5 disposed in a clutch housing 11~ From -the input
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shaft 13 the power is transmitted to a first lay shaft 15
of the propelling system through the gear type main change-
speed mechanism 6 adapted to provide four speeds and disposed
in a first case 14 removably attached to the clutch housing
11, and to the power takeoff shaft 4 through the gear -type
change-speed mechanism 10 also disposed in the first case
14 and adapted to provide two speeds. From the first lay
shaft 15 the power is giYen to the gear type backward-forward
drive switching mechanism 7 housed in a spacer case 16
removably attached to the first case 14, and then to a second
lay shaft 17 which is an output shaft of the backward-forward
switching mechanism 7. From the second lay shaft 17 the
power is given to the gear type auxiliary change-speed mecha-
nism 8 housed in a second case 18 removably attached to
15 the spacer case 16, the auxiliary change-speed mechanism
8 being adapted to provide two speeds, and then to a pinion
shaft 19. From the pinion shaft 19 the power is transmitted
to the rear wheels 2 through the dif~erential mechanism 9
and to the front wheels through a gear type transmission
mechanism 20 and a transmission shaft 21.
The first and second cases 14 and 18 and the spacer
case 16 together constitute a transmission case.
The main change-speed mechanism comprises four gears 22a,
22b, 22c and 22d having different diameters from one another
and fixed to the input shaft 13, and four shift gears 23a,
23b, 23c and 23d axially slidably mounted on the first lay
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shaft 15 which is parallel to the input shaft 13. The
shift gears 23a and 23b form a pair and the shift gears
23c and 23d form another pair to be engageable with the
gears 22a...., respec-tively. Two shift forks 24a and 24b
5 to shift the two pairs of shift gears 23a, respec-tively,
are rigidly attached to a rod 26 slidably supported by a
first casing member 25 which is removably attached to the
first case 14. ~ hand lever 28 oscillatable crossways
for operating the main change~speed mechanism is provided
on a second casing member 27 removably attached to the first
case 25, the hand lever 28 being selectively engageable
with the two shift forks 24a and 24b.
Referring to Fig. 3, the backward-forward drive switching
mechanism,7 comprises an inpu-t shaft, which is tne first
la~ shaf t 15, supported by a partition wall 16a and carrying
a first gear 29 and a second gear 30 opposed to each other
across the partition wall 16a, the first gear 29 being
rotatable together with the first lay shaft 15 and the second
gear 30 being freely ro-tatable relative to the first lay
shaft 15, the partition wall 16a being an extension of the
spacer case 16. There is provided a further lay shaft
31 extending parallel to the first lay shaft 15 between
the partition wall 16a and a partition member 16b opposed
to the wall 16a. The lay shaft 31 carries a third gear 32
and a fourth gear 33 rotatable together with the lay shaft 31.
The third gear 32 is in mesh with the first gear 29, and
the fourth gear 33 is in operative connection with the second
gear 30 through a reversing gear 34, whereby the first and
second gears 29 and 30 are constan-tl~v rotating in opposite
¦ directions. The first lay shaft 15 carries a ~i~th gear
35 at the rear end thereof which is rotatable with the first
lay shaft 15, and the second lay shaft 17 which is in abutting
relationship wi-th the first lay shaft 15 carries a two step
gear 36 at the forward end thereof rotatable together with
the second lay shaf-t 17. An internally threaded shift
gear 37 straddles between and axially sliclably along the
first and second lay shafts 15 and 17 and, together with
the fifth gear 35 and the two step gear 36, constitutes
a clutch mechanism 38. ~he shift gear 37 is slidable between
a position to interlock the fifth gear 35 and the two step
gear 36 wherehy the tractor travels forward and a position
to interlock the second gear 30 and the two step gear 36
through a toothed portion 3g integral with the second gear 30
whereby the tractor travels backward.
A hand lever 40 for backward-forward drive switching
operations is provided on the second casing member 27 ne~t
to and on the lefthand side of the hand lever 28 for operating
the main change-speed mechanism 6, the hand lever 40 being
oscillatable in longitudinal directions of the tractor body.
The lever 40 engages an element 41 attachecl to a first shift
rod 42 slidably mounted in the first casing member 25.
A second shift rod 43 is disposed below the rear end of
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the first shift rod 42 and is slidably supported by a first
and a second parti.tion walls 14a and 14b opposed to each
other in the longitudinal direction of the tractor body.
The second shift rod 43 is rigidly connected at the forward
end thereof to a rearward portion of the fi.rst shift rod
42 by an interlocking arm 45, and carries a fork member
~4 at the rearward end thereof to engage the shift gear 37.
The described construction facilitates the change-speed
operations and the backward and forward drive switching
operations when -the tractor is subjected to a frequent repeti-
tion of backward and forward movements during mowing work,for example.
In the drawings, particularly in Figo 3, numeral 50
indicates a ball stopper structure provided in the second
partition wall 14b to maintain the hand lever 40 for operating
the backward-forward drive swi-tching mechanism 7 in a forward
drive position, a neutral position or a backward drive posi-
tion~
A third casing member 46 is removably attached to -the
first casing member 25 rearwardly of the second casing member
27, and a hand lever ~7 is provided on the third casing
member 46 oscillatably in sidewise directions on a vertical
axis to effect change speed on the power takeo~f shaft ~
The hand lever 47 is operatively connected to a shift rod
(not shown) supported by the first casing member 25 slidably
in the longitudinal direction of the tractor body. The shift
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rod carries a shift fork 48 rigidly attached -thereto and
operatively connected to a shift gear 49 adapted to transmit
power from the input shaft 13 of the transmission -to the
power takeoff shaft 4 in two alternative speeds.
Referring to Fig. 5 showing a modified transmission,
the main clutch 5 comprises what is known as the double
clutch type which breaks power transmission to the power
takeoff shaft 4 by a first step operation and breaks power
transmission to the propelling system A as well by a second
step operation. Furthermore, in the backward-forward drive
switching mechanism 7, the firs-t to four-th gears 29, 30, 32
and 33 and the reversing gear have such transmission ratios
that the backward traveling speeds are greater than the
forward traveling speeds.
As described, the spacer case 16 housing the backward-
forward drive switching mechanism 7 is removably attached
to the first case 14 housing the main-change speed mechanism
6 and the second case 18 housing the auxiliary change--speed
mechanisM 8. This arrangement has the following advantages.
There is a case where a tractor desirably has greater backward
-traveling speeds than forward traveling speeds, and there
is a case opposite thereto. So the backward-forward drive
switching mechanism must be provided with gears having trans-
mission ratios suited to the functions of the tractor.
It has heretofore been necessary to change all of the main
change-speed mechanism, the auxiliary change-speed mechanism
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and the bac~ward forward drive switching mechanism to
obtain transmissions of different designs, which has
resulted in the high manufacturing costs. According
to the present invention, the main change-speed mechanism 6,
the first case 1~ housing the main change-speed mechanism 6,
the auxiliary change-speed mechanism 8 and the second
case 18 housing the auxiliary change-speed mec~anism
need not be Ghanged and only the backward~forward drive
switching mechanism 7 is interchangeable with its like
having gears of different transmission ratios. A different
transmission may be obtained simply by operatively connecting
the different type of backward-forward drive switching
mechanism to -the main change-speed mechanism 6 and the
auxiliary change-speed mechanism 8 and by assembling
~15 the spacer case 16 to the first and second cases 1~ and 18.
The transmission may also be adjusted to tractors having
different distances between the engine E and the rear wheels
! 2, by employing the spacer case 16 and the shafts of the
baclcward-forward drive switching mechanism 7 having suitable
lengths, thereby adjusting the wheelbase. Thus the present
invention realizes a tractor transmission whose backward-
forward drive switching mechanism 7 may have varied gear
transmission ratios, which is on the whole simple to assemble
and inexpensive to manufacture.
In the described embodiments, the interloclcing structure
for operating the backward-forward drive switching mechanism
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is made si~ple and has compact constituent elements~ and
yet is capable of smooth and reliable switching operation.
More particularly, the hand levers 28 and 40 for operating
the main change-speed mechanism 6 and the gear type backward-
forward drive switching mechanism 7, respectively, areprovided on the transmission case above the main change-
speed mechanism 6. The first shift rod 42 engaged by the
hand lever 40 for backward-forward drive switching operation
is mounted slidably in the transmission case. The second
shift rod 43 is disposed below and substantially parallel
to the first shift rod 42 and is slidably supported by a
pair of partition walls 14a and l~b opposed to each other
in the transmission case. The second shift rod 43 is rigidly
connected at the forward end thereof to the first shift
rod 42 by the interlocking arm 45 and carries the fork member
~ 44 at the rearward end thereof to engage the gear type
backward-forward drive switching mechanism 7.
Since the main change-speed mechanism 6, the gear type
backward-forward drive switching mechanism 7 and the auxiliary
change-speed mechanism 8 are arranged in the mentioned order
in the transmission case, the backward-forward drive switching
is effected under a low speed condition provided by the
main change-speed mechanism and therefore more smoothly
than where the gear type backward-forward drive switching
mechanism 7 is disposed forwardly of the main change-speed
mechanism 6. MoreoverJ since the backward-forward drive
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switching lever 40 as well as the mai~ change-speed ~ever
28 are provided above the main change-speed mechanism 6,
the operator can change his grip to and fro between the
hand levers 28 and 40 easily and quiclsly when carrying out
a mowing operation or the like which requires a frequent
repetition o~ the main change-speed and backward-forward
switching operations.
According to the present invention, the backward-forward
drive switching mechanism 7 is disposed forwardly of the
auxiliary change-speed mechanism 8 as described. This
arrangement has the advantage over the opposite order in
that the hand lever 40 and the backward-for~ard drive switch-
ing mechanism 7 are a short distance apart which helps
simplify the interlocking mechanism therebetween. Moreover,
the hand lever 40 and the backward-forward drive switching
mechanism 7 are interlocked the first shift rod 42, the
second shift rod 43 disposed therebelow and carrying the
fork member 44, and the inter~ocking arm 45 extending between
the two shift rods 42 and 43, in other words, the fork member
44 is interlocked with the backward-forward drive switching
lever 40 provided above the main change-speed mechanism
6 through a single continuous rod. Therefore, it is un-
necessary to change the construction of the transrnission
case or form it in a bending shape. Besides, since the
second shift rod 43 extends through the opposed partition
walls 14a and 14b within the transmission case to obtain
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a strong support therefrom, the second shift rod 43 may
comprise a thin piece and the interlocking arm ~5 need not
be very strong, wherefore these interlocking elements 42,
43 and 45 are all made simple and compact.
In the forgoing embodiments~ the gear type backward-
forward drive switching mechanism is constructed to be compact
by rationall~ arranging the gears. ~ore particularly9
the clutch mechanism 38 is provided between the input shaft
15 of the gear type backward-forward drive switching mechanism
7 to receive power *rom the main change-speed mechanism
6 and the output shaft 17 of the drive switching mechanism '7
to give power to the auxiliary change-speed mechanism 8, and
this clutch mechanism 38 is switchable between a position
to coup]e -the input shaft 15 and the output shaft 17 directly
15- and position to operatively connect the two shafts 15 and
17 through the reversing gear 38. The input shaft 15 carries
the first and second gears 29 and 30 across the partition
wall 16a supporting the input shaft 15, the first gear 29
being rotatable together with the input shaft 15 and the
second gear 30 being rotatable relative to the input shaft 15.
The partition wall 16a further supports the lay shaft 31
to be parallel to the input shaft 15, the lay shaft 31 carry~
ing the third and fourth gears 32 and 33 across the partition
wall 16a, both gears being rotatable together with the lay
shaft 31. The third gear 32 is in mesh with the first
gear 23 and the fourth gear 33 is in mesh with the second
gear 30 through the reversing gear 34.
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In the above-described construction of the gear type
backward-forward drive switching mechanism 7, the pair of
first and second gears 29 and 30 and -the pairof third and
forth gears 32 and 33 respectively mounted on the input
shaft 15 and the lay shaft 31 which are necessary for revers~
ing the drive transmitting state are divided across the
partition wall 16 as described. By virtue of this arrange-
ment, the reaction forces act on these gears during power
transmission such that the bending forces act on the input
shaft 15 and -the lay shaf-t 31, respectively, in directions
to cancel one another. Therefore~ the inpue shaft 15 and
the lay shaft 31 may each comprise a thin piece having a
relatively small strength, and the input shaft may project
from the partition ~all 16a only slightly, which together
contribute toward the compact construction of the gear type
backward-forward drive switching mechanism 7.
For a better understanding of the advantages of the
above construction, it is to be compared with the construction
shown in Fig. 6, for example. The input shaft 15 here
carries on a portion pro~ecting from -the partition wall
16a a first gear 29 rotatable together with the input shaft
15 and a second gear rotatable relative to -the input shaft
15, while the output shaft 17 carries a clutch member 51
axially slidably and rotatably together with the output
shaft 17 and extending onto the input shaft.15. This clutch
member 51 is slidable to switch between a position to mesh
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wi-th a toothed portion ~2 of the input shaft 15 to cause
the tractor to drive forward and a position to mesh with
a toothed portion 53 integral with the second gear 30 to
cause the tractor to drive backwardO The input shaft 15
in this example must have a longer portion thereof` pro~ecting
frorn the partition wall 16a than in the present invention
in order to carry both the first and second gears 2g and
30 on the pro~ecting portion. Moreover, the reaction forces
that act on the first to fourth gears 29, 30, 32 and 33
dur:ing power transmission all result in forces to bend the
input shaft 15 and the lay shaft 31 away from each other.
To withstand the bending forces this construction therefore
requires the input shaft 15 and the lay shaft 31 to be thick
and strong.
Figu 7 shows another conceivable construction in which,
instead of mounting the first-and second gears 29 and 30
on the input shaft 15 to reduce the length o~ the portion
of the input shaft 15 projecting from the partition wall 16a,
, only the first gear 29 is mounted on the input shaft 15
1 20 to be rota-table therewith and the second gear 30 is mounted
on the output shaft 17 to be rotatable relative thereto.
However, the reaction forces that act on the first and second
gears 29 and 30 will result in forces to bend the respective
ends of the input and output shafts 15 and 17 away from
the lay shaft 31. This brings about displacement bet~een
the clutch member 51 and a toothed portion 54 of the input
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shaft 15 which is detrimental to a smooth backward-forward
drive switching. It is therefore again necessary for the
input shaft 15 and the lay shaft 31 to be thick and strong.
The described embodiments of the present inventlon solve
these problem in a rational manner.
Furthermore, since the main change-speed mechanism
6, the gear type backward-forward drive switching mechanism 7
and the auxiliary change-speed mechanism 8 are arranged
in the mentioned order in the transmission case, the backward-
forward drive switching is effected smoothy under a lowspeed condition provided by the main change-speed mechanism.
By providing the backward-forward drive switching mechanism 7
closer to the main change-speed mechanism 6 than is the
auxiliary change-speed mechanism 8 9 the backward--forward
drive switching rnechanism 7 is now disposed closer to the
backward-forward drive switching lever 40 which is generally
located near the operating device for the main change-speed
mechanism 6 since -the backward-forward drive switching is
often carried out together with the main change-speed opera-
tion. The shortened distance between the backward-forward
drive switching mechanism 7 and the hand lever 40 therefor
has the advantage of simplifying the interlocking mechanism
therebetween.
, ~ . . .