Note: Descriptions are shown in the official language in which they were submitted.
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Description
Countershaft Transmission
Technical Field
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This invention relates generally to a
countershaft transmission for a vehicle or the like,
and more particularly to a countershaft transmission
having a plurality of forward and reverse speeds usiny
constant mesh gearing and a plurality of fluid
actuated, rotating clutches of the interleaved multiple
plate and disc type.
Background Art
Countershaft transmissions having a plurality
of speed ratios in each direction of operation are
particularly useful in the drive line of vehicles such
as wheel loaders, rubber tired log skidders, and other
heavy duty vehicles. Such transmissions are
advantageous in that a plurality of rotating clutches
and associated continually meshing gears can be so
positioned on the usual parallel shafts as to allow
considerable structural compactness and an adaptability
to the elevational drop requirement between the input
and output axes.
One powershaft transmission offered by
Kabushiki Kaisha Komatsu Seisakusho, of Japan, is a
countershaft unit driven by a longitudinally aligned
englne and torque converter and employing a pair of
directional clutches, three speed clutches, five shafts
and eleven gears. Since the last shaft and two of the
gears are merely used for transfer purposesl that
transmission can basically provide three forward and
three reverse speeds using four shafts and nine gears.
While it is axially compact, and can provide the
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elevational drop between the input and output axes, it
is more complex and costly than is desired. This is
mainly due to the incorporation of an undesirable idler
gear and associated shaEt.
Clark Equipment Company also produces several
countershaft transmission families and reference is
made to U.S. Patent No. 3,465,609 issued September 9,
1969 to J.F. Fisher, et al, showiny a reversible unit
providing two, three or four speed options. However,
that family has the disadvantage that the third speed
clutch and its associated gears are located on the far
side of the wall containing the remainder of the unit
so that another housing wall is required and the unit
is extended axially.
Further illustrating the prior art are the
following United States Patent Nos : 2,958,231 issued
November 1, 1960 to C. Gerst; 2,97~,901 issued February
28, 1961 to C. Gerst; 3,254,541 issued June 7, 1966 to
C.E. Schou; 3,540,556 issued November 17, 1970 to
J.B. Snoy, et al 3,65~,819 issued April 11, 1972 to
Fl, Link; 3,913,616 issued October 21, 1975 to
J. Horsch; 4,275,607 issued June 30, 1981 to J.B. Snoy;
and 4,333,358 issued June 8, 1982 to G.P.
Grattapaglia. For the most part these transmissions
have too many shafts and gears for the number of speeds
provided and are therefor more complex than i5
necessary.
Accordingly, what is needed is a structurally
simple and compact countershaft transmission providing
at least two forward speeds and at least two reverse
speeds using a maximum of three shafts and a minimum
number of gears. For example, if three forward speeds
and three reverse speeds are needed then the number of
gears required in conjunction with the three shafts
should preferably be limited to eight. These
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limitations are noted with respect to the primary speed
shifting and directional functions, `and should be
considered independent of any subsequent transfer gear
train that might be required in a particular vehicular
environment.
Moreover, the desired countershaft
transmission should preerably maximize parts
commonality by using similarly sized rotating clutch
elements, and have a long service life by designing the
elements and their connections such that undesirably
high operating speeds or clutch plate engagement speeds
are avoided. And, the shafts, gears and rotating
clutches should be radially internested and be of
relatively short axial length so as to fit into the
limited space in a vehicle and between the front and
rear walls of a separable housing.
Disclosure of the Invention
The present invention is directed to
overcoming one or more of the above problems.
In one aspect of the invention there is
provided a countershaft transmission including an input
shaft having first and second gears freely rotatable
thereon and first and second clutch assemblies for
selectively connecting one of them to the input shaft
for joint rotation, an output shaft having a third gear
freely rotatable thereon and a fourth gear connected
thereto and third clutch assembly for selectively
connecting the third gear to the output shaft, and a
third shaft having a fifth gear freely rotatable
thereon, a sixth and a seventh gear connected to the
third shalt and a fourth clutch assembly for
selectively connecting the fifth gear to the third
shaft, and with the first and third gears being
connected, the second and seventh gears being
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connected, the third and sixth gears being connected,
and the fourth and fifth gears being connected. This
is effective to provide two forward and two reverse
speeds.
Advantageously, an eighth gear can be mounted
for free rotation on the output shaft and be
intermeshed with the seventh gear, and a fifth clutch
assembly can be provided to couple the eighth gear to
the output shaft so as to provide three forward and
three reverse speeds without the necessity for another
shaft or use of an idler gear.
grief Description of the Drawings
Fig. 1 is a diagrammatic, developed, but
substantially side e;evational sectionalized view of a
three-speed forward and three-speed reverse
countershaft transmission constructed in accordance
with the present invention; and
Fig. 2 is a diagrammatic, front end
elevational view oE the countershaft transmission of
Fig. 1 talcen along line II-II thereof and showing the
relationship of the various shaft axes and th
constantly meshing gearing associated therewith, and
the cutting plane of developed Fig. 1
Best Mode for Carrying Out the Invention
Referring to the developed sectional view oE
Fig. 1, there is shown a countershaft transmission 10
having an upper input shaft 12, a lower output shaft
14, and a third or intermediate shaft 16 rotatably
supported in a housing or drop box 18. The shafts 12,
14 and 16 are rotatably mounted within the housing
respectively along parallel axes 20, 22 and 24 and have
an elevational end view relatlonship as shown in Fig.
2. The input and output axes 20 and 22 reside in a
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vertical plane 26, and the third axis 24 is located to
one side thereof at an elevational level between the
levels of the other two axes.
The housing 18 is generally constructed of two
major pieces; namely, a front main case portion 28
disposed at the central portion and at the left when
viewing Fig. 1, and a rear cover portion 30 located at
the right. A Eront wall 32 of the main case portion
integrally defines a stepped cylindrical bore 34 on the
input axis 20, and blind cylindrically shaped stepped
pockets 36 and 38 on the output axis 22 and on the
third axes 24 respectively. Similarly, a rear wall 40
of the cover portion integrally defines blind
cylindrically shaped stepped pockets 42 and 44 on the
input axis 20 and on the third axis 24. A cylindrical
bore 46 is also defined in the rear wall along the
output axis 22 which is adapted to releasably receive
an annular flange member 48 having an inner bearing
seat 50 and an outer seal seat 52. An output yoke 54
is releasably secured to the rear part of the output
shaft l by a spline joint 56, and an annular seal 58
extends between the seat 52 and the yoke. An
encircling peripheral wall 60 extends rearwardly from
the front wall and is releasably secured to a
peripheral wall 62 of the rear cover portion 30 at a
coupling joint 64 disposed on a transversely oriented
vertical plane. A plurality of threaded fasteners 66
secure the case and cover portions positively together
and serve to define a sealed internal chamber 68.
Input shaft 12 is driven by a hydrodynamic
torque converter as is schematically indicated at 70 in
the instant embodiment, with the torque converter being
serially connected to an engine in the usual manner,
although not illustrated. A torque converter output
shaft 72 is releasably connected to the transmission
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input shaft 12 at a spline joint 74, and another torque
converter member 76 drives a pump drive gear 78
rotatably disposed within an annular forwardly facing
pocket 80 defined in the main case portion 28.
The Eront end of the input shaft 12 is
rotatably supported in the bore 34 by a needle or
roller bearing assembly 82, and the rear end is
rotatably supported in the stepped pocket 42 by a
similar needle or roller bearing assembly 84. An
annular web 86 is integrally connected to the input
shaft centrally thereof, and an internally splined
front drum 88 and an internally splined rear drum 90
are integrally connected to the web. The drums 88 and
90 respectively form the driven members of a reverse
clutch assembly 92 and a forward clutch assembly 94 of
the usual interleaved multiple plate and disc type.
For example, the front or reverse rotating clutch
assembly 92 includes an annular actuating piston 96
selectively movable to the left under fluid pressure in
a normal manner when viewing Fig. 1 to clamp a
plurality of interleaved annular plates and friction
discs 98 against a reaction plate 100. This connects a
first gear 102 and associated hub assembly 104 for
conjoint rotation with the input shaft. The reverse
rotating clutch assembly is positively disengaged by
movement of the actuating piston back to the right by a
plurality of compression springs 106 when pressure is
reduced to the actuating piston. This allows the first
gear 102 and hub assembly 104 to freely rotate together
on the input shaft through an intermediate needle or
roller bearing assembly 108.
A second gear 110 and a hub assembly 112
splined thereto are also freely rotatably mounted on
the input shaft 12 by a needle or roller bearing
assembly 114. Movement of another actuating piston 116
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of the forward clutch assembly 94 to the right when
viewing the drawing will similarly couple the second
gear 110 and the hub assembly 112 to the input shaft.
Thus, actuation of directional clutch assemblies 92 and
94 are efEective to provide drive to either of the
gears 102 and 110~ with it being understood that the
designation of clutch assemblies 92 and 94 as being
reverse and forward respectively is arbitrary and could
be as easily considered as forward and reverse
respectively.
Turning now to output shaft 14, it can be
noted to be supported in the stepped pocket 36 of the
front wall 32 by a tapered roller bearing assembly 118,
and in the rear wall 40 by an oppositely cooperating
tapered roller bearing assembly 120 mounted in the seat
5n of the flange member 48. Actually, the bearing
assembly 120 indirectly supports the rear of the output
shaft through a fourth gear 122 mounted for joint
rotation with the output shaft as by a spline joint
124. A third gear 126 and associated hub assembly 128
are mounted for free rotation on the front of the
output shaft and are selectively coupled for joint
rotation therewith by a second speed clutch assembly
130. An eighth gear 132 and associated hub assembly
134 are Ereely rotatably mounted on the rear of the
output shaft and are selectively coupled thereto by a
third speed clutch assembly 136. The third gear 126 is
disposed in continually intermeshing engagement with
the first gear 102.
A fifth gear 138 and associated hub assembly
140 are freely rotatably mounted on the third shaft 16
via a flanged bearing 141 having considerable capacity,
and are selectively engaged thereto by a first speed
clutch assembly 142 having a rearwardly extending drum
143 secured to the third shaft. Also, a sixth gear 144
is mounted for joint rotation with the third shaft by a
spline joint 145, and a seventh gear 146 is connected
to the drum 143 via a spline joint 147 and thus is
indirectly connected to the third shaft. The sixth
gear 144 is continually intermeshed with the third gear
126, the seventh gear 146 is continually intermeshed
with both the second gear 110 and the eighth gear 132,
and the fifth gear 138 is continually intermeshed with
the fourth gear 122. Like the input shaft, the third
shaft 16 is rotatably supported in the front pocket 38
by a needle or roller bearing assembly 148, and in the
rear pocket 44 by a needle or roller bearing assembly
150~
The first, second and third speed clutch
assemblies 142, 130 and 136 are similar in construction
to the directional clutch assemblies 92 and 94 and
therefor need not be described in detail. However, the
size oE the plates and discs, the actuating pistons,
and several other members are advantageously the same
or improved parts commonality.
Industrial Applicability
In operation, the input shaft 12 of the
countershaft transmission 10 is driven by the torque
converter output shaft 72 and this drives the front and
rear drums 88 and 90 of the directional clutch
assemblies 92 and 94 respectively in, for example, a
clockwise direction when vlewing along the input axis
20 from the front of the transmission. Assuming that a
first forward speed condition is desired, the operator
so controls the vehicle as to cause the forward clutch
; assembly g4 and the first speed clutch assembly 142 to
be hydraulically actuated so as to engage or clamp the
interleaved plates and disGs thereof together. This
respectively connects the second gear 110 to the input
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shaft 12 and the fifth gear 138 to the third shaft 16.
Accordingly, the output shaft 14 is driven at a
relatively low speed ratio by way of gear pairs 110-146
and 138-122. As shown by the broken line arrows
indicated by the letter A in Fig. 2 the output shaft is
driven in a clockwise direction or in the same
rotational direction as the input shaft.
It is only necessary to disengage the first
speed clutch assembly 142 and to engage the second
speed clutch assembly 130 in order to shift the
transmission 10 from first to second forward speed. In
this mode the speed reduction ratio is reduced and the
output shaft 14 is driven at a higher speed by way of
gear pairs 110-146 and 144-126.
Second speed clutch assembly 130 is disengaged
and third speed clutch assembly 136 is engaged to shift
Erom the second forward to the third forward speed
condition. This further reduces the speed reduction
ratio and drives the output shaft 14 at a maximum speed
via gear pairs 110-146 and 146-132.
In the first reverse speed condition only the
reverse clutch assembly 92 and the first speed clutch
assembly 142 are engaged. Torque is thereby
transmitted to the output shaft 14 via the three gear
chain 102-126-144 and the gear pair 138-122. In this
instance the freewheeling third gear 126 advantageously
serves as the idler so that the output shaft is driven
in a rotational direction opposite to the input shaft
12 and this may be visualized by reference to the
directional arrows identified by the letter B in Fig. 2.
The number of gear teeth and corresponding
speed reduction ratios obtained with one embodiment of
the countershaft transmission 10 are shown by the
charts immediately below:
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Number of Gear Teeth
Gear 102 : 33 teeth
Lear 110 : 47 teeth
Gear 126 : 57 teeth
Gear 122 : 69 teeth
Gear 138 : 27 teeth
Gear 144 : 41 teeth
Gear 146 : 58 teeth
Gear 132 : 39 teeth
Gear Reduction Ratio
Forward Reverse
Low 3.15 3.18
Intermediate 1.72 1.73
High0.33 0.84
A feature of the countershaft transmission 10
is that the physical location of the first speed clutch
assembly 142 on the third shaEt 16 is such as to
minimize the overall size thereof because additional
speed reduction is provided downstream thereof via the
gears 138-122.
Another feature oE the countershaft
transmission 10 resides in the use oE back-to-back
directional clutch assemblies 92 and 94 which are
laterally in longitudinal alignment with the
back-to-back second and third speed clutch assemblies
130 and 136 respectively. Also, the first speed clutch
assembly 142 is laterally in longitudinal alignment
with the forward and third speed clutch assemblies 94
and 136. This closely spaced radial relationship of
the`clutch assemblies with the various gears being
axially spaced outside thereof, but within the front
and rear walls 32 and 40, provides maximum radial
compactness of the transmission as can be visualized by
reference to Fig. 2 and the overall width and height
delineators identified by the letters We and "H"
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respectively. A relatively short length of the
transmission is also obtained in the longitudinal
direction of the shafts as can be noted by reference to
Fig. 1 and to the overall length delineation thereof by
the letter "L". A portion of the overall length is due
to the construction of the stepped pockets 36, 38, 42
and 44 which advantageously provide a plurality of
pressurized fluid operating passages and lubrication
passages thereat. Moreover, the two-piece housing 18
and its bores 34,46 and pockets 36, 38, 42 and 44 allow
convenient assembly and disassembly of the transmission.
In view of the foregoing, it is apparent that
the countershaft transmission 10 is simple and rugged
in its construction, and is of light weight. Two
forward and two reverse speeds are achievable through
use of only four clutch assemblies 92, 94, 142 and 130,
seven gears 102, 110, 126, 122, 138, 144 and 146, and
three shafts 12,14 and 16. Moreover, only one
additional clutch assembly 136 and one additional gear
132 are required to provide three forward speeds and
three reverse speeds.
Other aspects, objects and advantages of this
invention can be obtained from a study of the drawings,
the disclosure and the appended claims.
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